# Quarter Scale Merlin V-12



## mayhugh1

The Rolls Royce V-12 Merlin, was one of the best known, if not most influential, WWII aero engines. It was deployed in the British Spitfire and later replaced the Allison in the American P-51 Mustang. I recently purchased a set of quarter scale castings from a small San Diego start-up that originally planned to build and sell completed quarter scale Merlins nearly a decade ago. 
http://www.quarterscalemerlin.com 
The parts I received were investment cast and can be best described as large pieces of (expensive) jewelry. They share most of the realistic features and intricate detail with the equivalent parts on the full-size engine. Photos of the castings are available here:
http://www.quarterscalemerlin.com/castings/
I've no experience in working with castings, and was a little taken back by the notes accompanying them. The notes warned, in several places, that being long, complex, and thin-walled, they will likely require straightening and, in some cases, heat treating.
The set I purchased includes castings for a functional supercharger, but it's not clear whether its scaled development was ever fully completed and just how much of it became a part of the prototype that was produced. The original designers opted for a glow plug engine, and so the magneto development may not have been completed. Finally, the notes mentioned fuel distribution issues with the Merlin's scaled-down intake manifold. The developers eventually designed an alternate configuration with multiple carburetors in order to get a running prototype, but the drawings didn't include information on its design. Over-heating issues were also mentioned, and a prop didn't show up in the published video of their running engine. Working these issues will add some interesting challenge to the project, but I'd rather additional development work wasn't going to involve very expensive and perhaps irreplaceable castings.
I've been able to find online evidence of three other builders who have tackled this project using these particular castings. One posted his crankshaft build on 'the other' forum but he never returned after creating his own piece of art.
My plan is to spend the first few weeks evaluating the castings I have so I can better understand the issues involved with getting them ready to machine. My first goal will be to see if I can get the major crankcase components straightened and fitted together with minimal machining. -Terry


----------



## ///

I've been dreaming about these castings for a very long time but I just know it is well beyond my capabilities!
Really looking forward to following your build.


----------



## Herbiev

WOW!! That's some project. Will be following along for sure


----------



## mayhugh1

I'm going to try to justify some of the craziness that I'm about to apply to these very expensive parts with some background theory. Precipitation hardening is a common way of strengthening 356 aluminum which is a popular casting alloy. To promote this process, certain impurities such as magnesium and silicon must also be present in the aluminum melt. As the castings cool these impurities form simple compounds which gradually, over time, come out of solution (precipitate) and they end up distributed throughout the casting. These precipitates harden the casting by preventing its plastic deformation (bending or stretching) when it is put under stress. These precipitates strengthen the casting, but they also make it brittle. This hardening process is kicked off just after the castings solidify, and it continues for hours to days or even weeks later depending upon the casting's storage temperature. Because of this process's dependency upon time, it is also commonly referred to as age hardening.
A casting that has been age-hardened has little tolerance to bending, twisting, or stretching. If a 356 casting warped during its solidification, and if it requires straightening before it can be finish machined, then it must be annealed. This can be done by heating the casting to about 700F and then allowing it to air-cool. The common shop technique of using an acetylene torch to create a soot coating for use as an annealing temperature indicator also works for 356. If, after straightening, the part is left in its annealed state, significant strength will be lost. For 356 the tensile strength loss can be as great as 10,000 psi. Unfortunately, a 700F annealing is not high enough to kick off another age hardening cycle.
The casting can be re-hardened, though, back to its maximum strength by heating it to 1000F for a dozen or so hours and then quickly quenching it. What makes this difficult to do in a home shop is the fact that aluminum melts at 1035F, and so careful temperature control is required. There is also a chance that the casting will deform under its own weight if it isn't properly supported. In addition, air-cooling needs to be minimized which means the quench tank needs be located within seconds of the furnace. 
Unlike the more familiar hardening process associated with steel, precipitation hardening does not occur immediately after the quench. The metal may remain soft enough to be straightened for up to a full day after the quench. 
Production castings should normally be straightened by the foundry before age hardening has progressed to any significant extent. An even better solution, of course, is to design the part so warpage is a minor concern, and the casting can be corrected by finish machining. The Merlin castings were not straightened by the foundry, and their thin-wall and complex cross sections make them very susceptible to warping that may not be correctable solely by machining. Straightening, after the castings have been allowed to harden, was therefore left to the end-user.
Since this is a totally new experience for me, I felt it would be best to practice on some scrap cast parts I picked up long ago from my favorite scrapyard. My practice pieces, which are louvered vents, were sand cast from 356 and allowed to age-hardened for many years.
I decided to immediately answer a question that was in the back of my mind, and that was just how much could I permanently deform one of these castings without annealing. After breaking two practice parts, I realized the answer was 'pretty much nothing at all.' The rest of my practice was done using only annealed parts.
I eventually developed a process, after cracking a few annealed practice parts, for controlling the pressures I used to bend the castings. I learned to clamp the parts down firmly and to use positive calibrated stops to quantitatively limit the distance that an edge was being pushed. Rather than using a press I typically used my own strength and body weight in combination with fulcrums, levers, and clamps so I could maintain a hands-on feel for what I was doing. I found it was important to proceed in small deformation steps of .005" at a time and continually return to the surface plate to check my progress. I also decided it was best to not aim for perfection but to stop at the point where measurements showed I could machine the remaining defects away without negatively impacting the part's appearance. Since I had decided to not even attempt age-hardening in my shop, I tried to minimize the areas that I annealed. Before attempting any straightening, I located the major axis of the warpage using a surface plate, and I tried to anneal only a narrow region along that axis. I then applied my straightening efforts across this axis. After a full day of experimenting I had gained enough confidence to start on the Merlin parts.
I first selected the three crankcase-related castings. I was able to machine flat the bottom surface of the main casting with respect to the crankshaft bores in order to obtain a reference surface. The front gear case turned out to be the major problem area on this part. It was out of perpendicular by almost .050" over its 5" height. I annealed a line across the gear case just above the top deck of the crankcase. After clamping the crankcase with its reference surface down to my drill press table, I clamped a long piece of wood to the gear case to which I applied the straightening force. With a pencil mark on the wood as a moving pointer I carefully monitored the distance the part was being pushed. After a half dozen tries which included returning to the surface plate to check my progress after each push, I had finally bent the gear case to within .015" of perfection. At this point I was able to machine its cover mounting surface flat and perfectly perpendicular to the reference surface in order to meet the drawing dimensions with no noticeable impact on appearance. I then machined the rear of the crankcase to its finished dimension. The decks for the cylinder heads will be done later, since they can be cleaned up with just finish machining.
The gear case cover was relatively simple to correct because its major warp was also about a single axis. The documentation warned that this rather rigid part might have to be widened, and the drawings included the design of a complex 'stretcher' to attempt this. I'm thankful that my particular cover, which is a fairly rigid part, didn't require this really scary correction.
The oil pan was considerably more complex and problematic. Being rather flimsy by design, it was warped across two separate axes. In addition, it's width had to be spread to match the crankcase. When checked on the surface plate, one corner of this part was initially almost 1/8" higher the other three. This part required almost a full day to correct, and I ended up annealing practically the whole casting. Fortunately, the oil pan is not a structural part, and the loss in strength that it likely suffered is not important. In the set-up for its final flange machining, the pan had to be packed with plastic modeling clay in order to dampen the chatter created by the mounting flange machining. I used high relief aluminum-cutting Korloy carbide inserts for all the machining operations and was able to obtain excellent surface finishes on both the annealed and un-annealed areas of all three castings. - Terry


----------



## kvom

Quite an interesting process.  If I understand properly you only needed to apply the torch to anneal along the axis of warping, while the rest of the casting was not heated.


----------



## Scott_M

Nice work Terry, those really are some good looking castings.

Scott


----------



## michael-au

This is a big project, I know someone that has completed the same engine, I have seen it run 
It is an amazing project

Here is a picture of his engine

View attachment ImageUploadedByModel Engines1424169717.048976.jpg


----------



## Ethan D

This is going to be amazing! the detail is crazy! Can't wait to see updates


----------



## gus

Mind boggling and only a true-blue blood HMEM Forum Member will attempt to build this engine. 1,000,0001 parts to machine. This engine will take at least 2 years to complete and run.


----------



## Ripcrow

Following along. Can't wait to hear it run. The most famous engine in the world. To me anyway


----------



## mayhugh1

Commercial parts recommended for purchase by the documentation include 25 ball bearings and 24 gears. That's a lot of shafts. I decided, for now, to purchase only the bearings associated with the crankcase group since I'm going to need them shortly, and the rest are commonly available. Gear cutters, though, are a different matter. My own experience is that actual in-stock gear cutters are becoming hard to find, and they now seem to be manufactured only in Poland and China. I've never had a problem with the Polish cutters, but out of several Chinese cutters I've purchased, two were so poorly made that they were unusable. I've previously purchased the Polish cutters from McMaster-Carr, but back-order times have sometimes stretched out as long as six months. As luck would have it, I have on hand only four of the seven cutters that I'll eventually need. I placed an order for the remainder, but only one was in current stock. The engine's documentation spec'd the gears only as part numbers from a specific U.K. gear manufacturer, and so I used their online catalog to extract the cutter requirements. Purchasing the gears from them outright would have cost nearly $700 compared with less than half that amount for all the necessary cutters. If the back-ordered cutters don't arrive before I need them I'll make my own as I did for the CAM drive gears on my radial engines. Most of the gears in this engine are cut from steel; and so I'd rather start out with quality commercial cutters, if possible.
The next step in this build is to mate the crankcase to the gear case cover and oil pan which, in Merlin parlance, is the lower crankcase. I decided to do this with 2-56 SHCS's even though the plans suggest an elegant but much more complex 'to scale' option. There's very little excess screw boss material on either part; and so cover needs to be precisely located over the gear case, and the spindle needs to be carefully centered over each boss before drilling. The bosses in the cover have cast-in dimples to help locate a drill, but not all of them are actually centered; and so I decided to re-spot them all with a 2-flute carbide v-drill. My eyes continued to trick me into positioning the spotting drill over the off-center dimples instead of the true centers of the bosses. So, I put a small length of close-fitting brass tubing over the spot drill in order to hide them. With this combination I was able to easily position the spindle over the center of each boss so I could re-spot its center (after removing the tube, of course).
In order to locate and temporarily secure the cover on the gear case I turned close-fitting Delrin alignment plugs for the as-cast openings in the prop and drive shaft bores in both the gear case and gear case cover. These openings were amazingly round - and indicated to within a few thousandths. I drilled four .070" holes through the pair which is the tap drill size for 2-56. After removing the cover I reamed the cover holes to .087" to clear the screws and then I tapped the four holes in the gear case. After bolting the cover back into place on the gear case using these four holes, I drilled and tapped the remainder of the holes similarly. Match drilling the holes in this way eliminated transfer errors and allowed minimum clearances around the cover holes. A simple shop-made alignment tool was used to hand-tap the 2-56 holes. The 45 holes securing the oil pan to the crankcase were drilled and tapped similarly.
The crankcase was then mounted vertically on the mill table against an angle plate with the gear case facing upward in order to bore the openings for the drive shaft and the prop shaft bearings. (Drive shaft is Merlin-speak for the front end of the crankshaft.) The center of the drive shaft opening was indicated and used as the reference datum for the next four boring operations. It will also be used later when the crankcase is line-bored. 
With the cover bolted in place, the opening for the driveshaft bearing retainer was bored. The spindle was then moved into position to bore the front prop shaft bearing opening. The distance between the prop shaft and drive shaft is critical for proper mesh of the gear pair that will eventually connect them. I had to rely on the print for this distance as I don't yet have the cutters needed to make these particular gears. 
The cover was then removed and, without moving the spindle, the blind recess for the rear prop shaft bearing was bored. Leaving the spindle in place for both boring operations insured alignment of both prop shaft bearings. A shop-made bearing puller was needed to check the fit of the rear prop shaft bearing in its blind recess. Finally, the spindle was moved back to the driveshaft reference point where the lower gear case opening for the driveshaft retainer was bored.
Being overly cautious about cracking one of these castings I opted for an interference fit of .0002"-.0003" instead of the .001" fit I would have normally used for these bearings in aluminum. The result is a snug fit using my upper body weight as a press. All four bearings will eventually be held in position with retainers. The circular hole patterns for the retainers' mounting screws were finally drilled in the cover. The prop shaft retainer uses 2-56 but the drive shaft retainer requires 1-72.
There are a lot of tiny tapped holes in this engine. I've barely scratched the surface of this build, and I've already drilled/tapped ninety-two 2-56 /1-72 holes. And, there's a lot more 1-72's and 0-80's ahead. - Terry


----------



## wirralcnc

Terry great progress.  I will be following with great interest,and following your techniques for when I machine mine. I actually purchased the full set of gears from hpc gears.  Great quality and good delivery time.


----------



## mayhugh1

Wirralcnc,
One thing I haven't mentioned is that you'll need to spend several hours with dental picks carefully going through the castings to remove all remaining traces of investment stuck in the numerous hidden interior corners. Digging around in there will give you even more appreciation for the effort someone put into their design. On mine, the water passages in both cylinder blocks were totally blocked. I discovered this while trying to understand how the liners were actually cooled.  You don't want this stuff circulating in the oil or coolant loops. - Terry


----------



## petertha

Wow Terry, you don't mess around. Impressive start to a complex project.

Newbie question: I've noticed variants of your tapping method for small, finicky size threads - freehand locating a tapping block jig over the pilot hole & some sort of knurl wheel handle affixed to tap. I've got the same job in front of me.
- is the tapping block hole a close sliding fit to tap OD or also partially threaded to assist engagement in the part? 
- do you use the block just to the point where tap is nicely established, then remove bock? Or better to keep block positioned the whole operation?
- any words of wisdom on threading blind holes in aluminum (tap type, cutting fluid, swarf ejection etc)


----------



## digiex-chris

I've got a thing for the Merlin engines after working on a full size Lancaster bomber at the Nanton air museum as a kid. Recently got to hear them run. Can't wait to hear this one run!


----------



## digiex-chris

petertha said:


> Wow Terry, you don't mess around. Impressive start to a complex project.
> 
> Newbie question: I've noticed variants of your tapping method for small, finicky size threads - freehand locating a tapping block jig over the pilot hole & some sort of knurl wheel handle affixed to tap. I've got the same job in front of me.
> - is the tapping block hole a close sliding fit to tap OD or also partially threaded to assist engagement in the part?
> - do you use the block just to the point where tap is nicely established, then remove bock? Or better to keep block positioned the whole operation?
> - any words of wisdom on threading blind holes in aluminum (tap type, cutting fluid, swarf ejection etc)



I use a tapping block like that all the time. A close fit to the tap thread major diameter seems to be fine. If the hole I need to thread is so deep and the material so hard that I'm concerned, I'm locating the tap with a spring center on the mill. Especially in aluminium, I almost always spend the extra cost on spiral flute taps. Also interested with the huge experts here suggest.


----------



## mayhugh1

petertha said:


> Wow Terry, you don't mess around. Impressive start to a complex project.
> 
> Newbie question: I've noticed variants of your tapping method for small, finicky size threads - freehand locating a tapping block jig over the pilot hole & some sort of knurl wheel handle affixed to tap. I've got the same job in front of me.
> - is the tapping block hole a close sliding fit to tap OD or also partially threaded to assist engagement in the part?
> - do you use the block just to the point where tap is nicely established, then remove bock? Or better to keep block positioned the whole operation?
> - any words of wisdom on threading blind holes in aluminum (tap type, cutting fluid, swarf ejection etc)



Peter,
The block isn't threaded but is a close fit to the body of the tap. I used it to go full depth with WD-40 for a lubricant. The depths of many of these holes were about the same as the total length of the threaded portion of the tap. I typically tapped them in two steps of about half depth each. I cleared the chips and re-lubed the tap for each cycle, and I use compressed air to clear the chips from the hole. For these holes I just used a hand plug tap. - Terry


----------



## XD351

It takes a truly special machinist to take on building that big daddy and i'm really looking forward to watching the build progress !
It inspired me enough to hunt around on you tube to find anything i could on a Merlin engines and surprisingly enough there is some fabulous footage of the full size engine being made .
It amazes me that men worked in factories wearing ties ,vests ,suites and the ladies wearing floral dresses !
Some of the machinery just blew my mind and much of it was designed specifically for this engine.
I never knew Packard made them also or a version of them anyway .

Ian.


----------



## gus

digiex-chris said:


> I use a tapping block like that all the time. A close fit to the tap thread major diameter seems to be fine. If the hole I need to thread is so deep and the material so hard that I'm concerned, I'm locating the tap with a spring center on the mill. Especially in aluminium, I almost always spend the extra cost on spiral flute taps. Also interested with the huge experts here suggest.




Hi Chris,

 Good and wise decision to invest in quality spiral taps that gives good thread and chips are brought up and not pushed down into tapped hole and causing obstruction. Gus invested in Japanese Taps and Dies. Why save pennies and risk breaking a tap and lose the job piece at the very last tapped hole??  ( I have yet to see any M.I.C. Spiral Taps in the market)


----------



## Cogsy

gus said:


> ( I have yet to see any M.I.C. Spiral Taps in the market)


 
Just had a look on ebay Australia and there are plenty of Chinese spiral taps in metric at least - looks like they've caught on.

Terry - Another excellent build for me to follow. I love the Merlin and I once got to fly 'hands on stick' in a very rare twin seat trainer P51D. Cost $2000 for a 20 minute ride. Over 4G in the loops, 500+ KPH flyover the family with me at the controls and that beautiful noise. Love it.


----------



## XD351

Cogsy said:


> Just had a look on ebay Australia and there are plenty of Chinese spiral taps in metric at least - looks like they've caught on.
> 
> Terry - Another excellent build for me to follow. I love the Merlin and I once got to fly 'hands on stick' in a very rare twin seat trainer P51D. Cost $2000 for a 20 minute ride. Over 4G in the loops, 500+ KPH flyover the family with me at the controls and that beautiful noise. Love it.




I purchased a set of metric spiral taps from an Ebay seller here in Sydney the set has 3-4-5-6& 8 mm in it are TiN coated and cost $15 ! 
I thought for certain they would be junk but for that amount I thought i would buy1set and suck it and see, at least i could use them to clean out tapped holes if worse came to worse.
When they arrived they seemed to be of ok quality , made in japan (yamasomething brand) nice and sharp with no apparent faults i could see , i even took to them with a magnifying glass and could find no faults .
I used the 3mm one yesterday and was happy with its performance in cast iron and 6061 aluminium.
I went back to that site today and bought another 2 sets !  

Ian


----------



## gus

XD351 said:


> I purchased a set of metric spiral taps from an Ebay seller here in Sydney the set has 3-4-5-6& 8 mm in it are TiN coated and cost $15 !
> I thought for certain they would be junk but for that amount I thought i would buy1set and suck it and see, at least i could use them to clean out tapped holes if worse came to worse.
> When they arrived they seemed to be of ok quality , made in japan (yamasomething brand) nice and sharp with no apparent faults i could see , i even took to them with a magnifying glass and could find no faults .
> I used the 3mm one yesterday and was happy with its performance in cast iron and 6061 aluminium.
> I went back to that site today and bought another 2 sets !
> 
> Ian




Hi Ian,

Thats a good buy.Please advise website address. For last ten years been buying from the M.I.J. "Linc'' Spiral Taps from neigbourhood hardware shop.Its not cheap.


----------



## Mattsta

This is going to be 2 years of fascinating reading!


----------



## kvom

Mattsta said:


> This is going to be 2 years of fascinating reading!



At the rate Terry works it will be running well before 2 years from now.


----------



## XD351

gus said:


> Hi Ian,
> 
> 
> 
> Thats a good buy.Please advise website address. For last ten years been buying from the M.I.J. "Linc'' Spiral Taps from neigbourhood hardware shop.Its not cheap.




Hi Gus,
They don't have a website address of their own as it was from EBay Australia  , the seller is called themoove (one word ) but they won't ship to south east Asia and quite a few other places .
I'm not sure if ctc tools sell them (out of china) i will have a look around for you , i have purchased a fair few reamers from suppliers in Hong Kong and have found these to be ok also .
Shipping will probably be a killer from Australia but from HK it is usually free .

Ian


----------



## XD351

gus said:


> Hi Ian,
> 
> 
> 
> Thats a good buy.Please advise website address. For last ten years been buying from the M.I.J. "Linc'' Spiral Taps from neigbourhood hardware shop.Its not cheap.




Gus, 
I just had a quick look around on the CTC website and they do sell spiral flute taps ( the 8mm one is around $14 au +postage ) i can't vouch for the quality but everything else i have bought from them has been really good.
I had a look at Ebay and searched worldwide for spiral flute taps and there are a couple of sellers (out of Hk)  that have the exact same set and brand as what i purchased  around $10 au with free postage.
Hope this helps!

Ian


----------



## mayhugh1

Milling the crankshaft channel through the crankcase, fitting the main bearing caps, and line boring the assembly are important foundational operations for this engine. For these operations the crankcase needs to be rigidly supported with its bottom (reference) surface facing up. Although I was able to hold the crankcase in the mill vise earlier for light surfacing of the pan mounting surface, I didn't feel comfortable using the same set-up for these operations. The complex shape of the crankcase makes it difficult to safely support in a vise, and accurately aligning it to all three axes while being supported that way would be very difficult.
I decided to begin using the crankcase motor mounts for work-holding, and so I machined their (top) surfaces parallel to the bottom (reference) surface of the crankcase. Their narrow widths and unequal heights added some complexity, but they gave me full machining access to the bottom of the crankcase.
I've been waiting for an excuse to build a milling table for the cross slide on my Enco lathe, and it looks like the line boring operation that's coming up is a good excuse. I had a half inch ground steel plate in my scrap collection that was just wide enough to hold the Merlin, and so I spent a few days machining it into a universal fixture for my lathe. I attached the crankcase to this plate so it could be mounted on either my lathe or mill table. I set the height of the crankcase so the center of the crank bore was slightly below the center of my lathe's spindle. Later, when it's moved to the lathe, the height will be tweaked with shims.
After another day's effort the crankcase was finally under the mill's spindle and indicated along all three axes. One of Delrin plugs that was used earlier to help position the gear case cover was re-machined to snugly fit the bored opening in the lower gear case where it was used to indicate the crankshaft's centerline.
After milling the channel for the bearing caps, I machined the crankshaft thrust bearing surfaces on either side of the center bearing. Since the Merlin uses an offset prop shaft, the crankshaft doesn't bear a significant thrust component of the prop load. The midpoint of this bearing is the engine's forward/aft zero reference, and so it was used to surface the rear of the crankcase and oil pan to their finished lengths.
In addition to a pair of conventional cap bolts the Merlin also uses a pair of cross-bolts to tie each bearing cap to the sides of the crankcase. These were probably necessary in the 2500 hp version of this engine, but they greatly complicate the machining of the bearing caps in this scale model. The cross-bolts are made of 3-3/4" lengths of .098" diameter drill rod threaded 3-48 on each end. Fourteen .102" holes must be drilled completely through the 3-1/2" wide crankcase where they will actually intersect the cap bolts. The cross-bolt holes can't be moved without offsetting them in their external cast bosses since this would spoil the engine's appearance. The 8-32 cap bolts must be necked down where the cross-bolts would otherwise contact them. The total interference ultimately depends upon how well the trajectory of the cross hole bit is controlled, but it will be a minimum .010" if all goes perfectly.
This interference might be a consequence of the incompatibility of the scaling in this particular area of the engine with the use of standard size model fasteners. I've looked ahead in the drawing package, and I'm afraid this may be a continually repeated story. There's another nasty scale-related issue coming up involving the heads and cylinder liners.
The fixture'd crankcase was reoriented on the mill with one of its sides facing up for the cross-bolt drilling. A Guhring parabolic bit was used to drill the cross-bolt holes without the bearing caps in place. Drilling the holes with the caps in place may seem like a better idea, but I couldn't come up with a way of clamping them securely in place. I didn't want to drill the cross-bolt holes with the caps already bolted in place because even with necked down bolts the drill would have wandered after breaking into the cap bolt holes. Plenty of WD-40 was used as a lubricant since any aluminum stuck to the bit would also cause the bit to wander off course.
The major issue I ran into was indicating the starting positions for the cross-drilled holes. The bosses for the cross-bolts cast into the sides of the crankcase are dimpled to help locate the drill since there are no drawings referencing their positions. I used them for the first set of holes in the rear bearing, but they ended up offset .010" from its center. The starting locations for the rest of the holes were determined by indicating the centers of the cast bearing webs, but these still ended up with errors as large as .005". The errors that accumulate during the drilling of the cross-bolt holes will increase the amount of material that has to be machined from the cap bolts for clearance, and this may weaken them.
The bearing caps, themselves, plus a few spares were CNC machined +.002"/-.000 in 'cookie sheet' fashion. They were engraved with numbers indicating their bearing positions, and they were individually fitted.
With the snugly-fitted caps temporarily in place, the locations of the cross-bolt holes were marked on each side using the Guhring drill held in a pin vise. The caps were then moved to the mill vise where each hole location was indicated using a spindle microscope. The holes were spotted and drilled to half depth from either side which resulted in 12 operations per cap. A .102" reamer was finally run through both holes to smooth any discontinuities at the intersections.
The crankcase was repositioned on the mill with the bottom of the crankcase facing up. Each cap was temporarily held in place with four .100" diameter drill bits inserted in the cross-bolt holes. The cap bolt holes were drilled through to the crankcase using an 8-32 tap drill with the four drill bits being moved as required. After removing the caps the crankcase was threaded for the bolts, and a reamer was run through the cap bolt holes to provide clearances for the bolts.
The diameters of the cap bolts were smoothly necked down to .125" around the point of contact with the cross-bolts. This was sufficient to clear the worst-case cross-bolt, and since it matches the minor diameter of the 8-32 thread there should minimum impact on the bolt's strength. I'm currently using stainless SHCS's for the cap bolts since I had them on hand, but I'll likely replace them with stronger steel versions later. I had only 3-48 lock nuts on hand for the cross-bolts, but since I don't like their looks I plan to replace them with plain hex nuts. The other three holes machined into the tops of the caps will eventually be used to mount injectors that will supply pressurized oil to the bearings.- Terry


----------



## Scott_M

Hi Terry

looking good !

Would it be possible in your next post to include a six inch scale for reference  ? I think I have the scale , but a reference  would be nice.

Man that really is a bunch of holes so far 

Scott


----------



## gus

Hi Terry,
Gus watching the Grand Master at work. Now dreaming of building this engine. I know my limits------machine tool ,space,skill and space. Just dreaming. Meanwhile still bashing the V-2. After the V-2 ,maybe the V-4 2016.


----------



## Mattsta

This is better than any TV show!


----------



## makila

Hi Terry,
The methods of assembly, machining and design is captivating. The cross drilling with the Guhring would have had a breath holding journey across the crankcase hoping that no miss-alignment would be amplified on its arrival on the other side.
I wonder why that method of main bearing cap retaining was employed, my thoughts are that the engine would have had to be manufactured with serious weight contingencies in mind (it has to fly). The bearing caps would have to be as small and light as possible therefore a means of reinforcing this primary load bearing area makes an interesting view of the ideas, technology and materials available during those times. Its actually good to see this stuff is being replicated in a scale build when it would be easy to avoid this complication.
Great stuff Terry, I think I would have thrown the towel in at stage one, straightening distorted crankcases!
Steve.


----------



## mayhugh1

My next step was to line bore the seven main bearings in the crankcase. I've never done an actual line boring operation before since the engines I've made up to this point have all used built-up crankshafts, and their crankcases were short enough for a simple boring bar or reamer. The Merlin's crankcase is almost 12" long with a target bore of .938". My original plan was to support a 27" shop-made boring bar between centers on my lathe, and with the crankcase bolted to the carriage I hoped to take advantage of my lathe's power feed. My 36" Enco lathe was theoretically capable of the job, but I ran into a couple of problems.
The first issue involved the new shop-made lathe milling table that I had put so much effort into just a few weeks ago. I designed it to replace the cross slide on my lathe's carriage so it swivels and can be locked down in exactly the same way as the cross slide. Because of clearance limitations I mounted the crankcase directly to it instead of using a sub-plate. This put the mounting screws that I needed to get access to for shimming in difficult-to-reach locations. After wasting a lot of time moving the mounted crankcase on and off the lathe in order to shim it, I realized I had yet another problem. 
Line boring the Merlin crankcase requires most of the usable length of my lathe. All the wear on its 20 year-old ways is up close to the spindle since I seldom turn workpieces longer than 7 or 8 inches. I found what appeared to be a slight three dimensional bow in the ways when measured over the distance I was now planning to use. While I was trying to figure out if I could live with these errors, reality began to set in about just how flexible a 27" length of 5/8" drill rod supported between centers really is.
In order to eliminate the uncertainties of the lathe errors and to stiffen the boring bar I made a pair of temporary bearing plates that I mounted to each end of the crankcase. These were placed on the crankshaft centerline and bored to exactly the diameter of the drill rod. These end-plates isolated the line boring operation from any errors outside the crankcase; and, in fact, the whole operation could now be done using an electric drill with the crankcase laying in my lap. I still wanted to use my lathe's power feed, though, since it could produce a superior surface finish. With the crankcase back on the lathe's carriage, I inserted a double U-joint between the boring bar and lathe chuck to absorb any misalignment between the lathe's spindle and the centerline of the crankshaft. As an alternative, I probably could have just hung the crankcase from the boring bar, but I already had a machinable U-joint left over from a custom car steering linkage from a previous life. Testing showed this combination ran with negligible vibration and essentially no run-out where it mattered.
I made a cutter for the boring bar from a broken carbide end mill. I ground a left-hand profile to cut on the boring bar's centerline with lots of rake. A flat ground on its top allowed it to be secured in the drill rod with a set-screw. A second axial set-screw against the rear of the cutter also acted as a crude vernier to adjust the depth of cut.
Because of the lack of a real vernier, I wasn't expecting to obtain an exact bore diameter with this set-up. An exact diameter isn't really important because the diameters of the bearing inserts and even the crankshaft journals can be adjusted later to fit. But luck was with me, and I was able to come within a thousandth of the finished value. 
I calculated the expected bore diameter before each pass by measuring the cutter height. This was done using a depth gage referenced to the oil pan surface and the formula: Bore Diameter = Boring Bar Diameter + 2 (Height of Cutter Above Boring Bar). The surface finish was monitored during a few of the initial passes as well as the next-to-the-last pass by temporarily removing the bearing plate on the head-stock end and pulling the bar. Final measurements showed all bearing bores to be within a tenth or so and no measurable circularity errors. - Terry


----------



## Davewild

Hi Terry

Very very impressive, it's a pleasure to watch

Dave


----------



## camm-1

Hi Terry
When I see your setup I remember I have see it before.
Here is a Swedish guy, Tryggve , who  have built an Merlin but I dont think it is from a casting.
Anyhow it could be fun to look at hes site.
Ove
http://www.orkenrud.com/apps/photos/album?albumid=1502432


----------



## Scott_M

Very nice indeed !
And thanks for the scale in the photos.  

Scott


----------



## mayhugh1

A couple of the photos shows the set-up on my mill that I used to machine the crankcase decks. It's important that these final steps in the crankcase machining are carefully referenced to the centerline of the crankshaft.
I left the end plates used for the line boring operation in place on the crankcase through which I inserted another length of 5/8" drill rod so I could indicate the crankshaft centerline. In addition, I bolted a flat plate to the oil pan mounting surface to give me a reference plane for setting the 30 degree deck angle since the Merlin is a 60 degree V engine.
One end of the rod was supported in a 5C collet chuck, and the other end was clamped in a V-block. It was aligned to the mill's axes within .001" along its entire length in both the x-z and x-y planes. For convenience an initial alignment was done before the crankcase was slipped onto the rod. Keeping the cylinders normal to the crankshaft will prevent rod bind, and care taken now will also minimize fitting issues later between the intake manifold and the very tall cylinder blocks and heads that are coming later.
A sine plate was locked to exactly 30 degrees on a surface plate before being brought into the set-up on the mill. It was slid into position below the crankcase, and the crankcase was then rotated on the rod until the full length of its bottom reference plate fit perfectly up against the sine plate. These two were bolted together, and then the sine plate was bolted down to where it happened to be sitting on the mill table. The result was a rigid and precise fixture for machining the right-side deck. For the left-side deck machining, the sine plate was simply turned around and similarly repositioned.
The spindle was zero'd to the center of the drill rod along the y and z axes, and it was zero'd to the center of the number four main bearing along the x axis. After the deck was surfaced, the bores for the skirts of the cylinder liners were machined, and stud mounting holes were drilled, tapped, and counterbored with respect to the center of each cylinder bore. In this engine, cylinder liners will be installed in cylinder blocks which, in turn, will be sandwiched in an unusual manner between the heads and the crankcase decks. I'll describe the details of this rather unique arrangement in my next post. The skirts of the liners extend below the cylinder blocks where they will protrude into the crankcase. A pair of oil drain holes still need to be drilled through the bottoms of the outside stud counterbores. The reasons for these will also become apparent later.
The drawings specify the distances between the cylinder bores, but accompanying notes warn about issues with some batches of castings requiring a different spacing. My castings fell into this latter category, and so here I began to deviate from the drawing package in a very critical portion of the design. For the crankcase, this deviation isn't important because it matches a deviation I've already dealt with while machining the main bearings. It will become more important, though, when the cylinder blocks and heads are machined. 
Notice the raised surfaces left on the decks for mounting the cylinder blocks. Very few gaskets were used in the original engine, maybe to facilitate wartime maintenance. These surfaces need to be smooth with minimum machining marks since they will seal the blocks to the crankcase.
These steps complete the major crankcase machining operations. The biggest reason for the extra care taken in the above set-up was actually because of its impact upon the next machining operations on the cylinder blocks and heads. These operations require the machining of some 28 fluid tube connections between the head and cylinder block on each deck in addition to the matched holes required for the 38 fasteners that hold them together. These operations would be challenging enough in billet parts, but they will made even more difficult by fabrication details of the head and block castings. I plan to diagram this portion of the design in my next post before doing any machining so I can draw on the experience of others about potentially better approaches. At this point I'm not feeling real confident about my ability to successfully machine the cylinder blocks and heads per the original drawings especially since the notes warn about unresolved issues with the design. - Terry


----------



## Scott_M

Hi Terry
Looking good. Nice setup.

How much deviation was there along the length of the cyl. bores ? The screw holes still look to be centered in their bosses.

Scott


----------



## gbritnell

Impeccable work Terry! I really enjoy looking at the setups you make. It takes a lot of ingenuity at times to figure out how to machine parts. Sometimes the setup take longer than the actual cuts. 
gbritnell


----------



## Mattsta

Mindblowing!


----------



## mayhugh1

Scott_M said:


> Hi Terry
> Looking good. Nice setup.
> 
> How much deviation was there along the length of the cyl. bores ? The screw holes still look to be centered in their bosses.
> 
> Scott



Scott,
The distances between bore centers were amazingly uniform at about .005" to .007", and I think part of that was measurement error due to slight imperfections in the bore circularities. It was the whole length of the crankcase that was too short including the relative spacings of the stud bosses, and so I think that's why everything looked centered at the end. - Terry


----------



## mayhugh1

The notes accompanying the castings devote more text to discussing issues with the Merlin's cylinder/head construction than with any other single aspect of the build except, possibly, for its unresolved carburetion. The bottom line of the discussion is that the quarter-scale head/cylinder design is very similar to the full-size version, but scaling leaves some unresolved fabrication issues for the builder. In defense of the design the authors mentioned that the full-scale design had suffered a rather rocky evolution.
For illustration I made some not-to-scale sketches showing the installation of a single liner in a portion of the cylinder block. These sketches also show coolant transfer tubes and stud tubes on the same sectional view even though they are really not on the same plane. The studs and head mounting bolts were left out for clarity.
The liner is inserted down through the top of the cylinder block, and a shoulder on the flange that protrudes above the block seals the compression chamber against the face of the head. Both the coolant jacket and the compression chamber are sealed by metal-to-metal contact as there is no head gasket. The bottom end of the coolant jacket is sealed by an o-ring compressed between two metal collars sandwiched between the crankcase and a machined shoulder on the circumference of the liner. 
An implementation concern with this design is that the heights of the shoulders on all six liner flanges in a particular bank must be precisely machined to identical heights. These shoulders, though, will be individually machined when the liners are turned; and they must also be free of machining marks. These combustion chamber seals are reminiscent of valve seals and will likely share similar issues. If it weren't for the raised liners the block could be simply machined flat for a conventional head gasket, but it appears there wouldn't be enough material left above the water jacket in order to sink them after the block castings are cleaned up. Anyway, as will be obvious later, the gasket would likely be unwieldy with 70% of its area removed to accommodate some 58 penetrations.
A subtle detail on the cylinder liner drawing, though, may actually be an important but unmentioned part of the design. A fillet is called out for the inside corner of the liner shoulder instead of leaving it sharp. The sharp rim on the aluminum combustion chamber will be deformed against this fillet when the head is torqued down to the block and may be the key to an effective seal. Unfortunately, though, only the first-time assembly will give the very best result. High temperature bearing retainer can probably be used to seal the water jacket at the top of the cylinder.
Assuming the combustion chambers can be effectively sealed, I still have three concerns about the cylinder design. Using the stock bore diameters and their center-to-center distances there will be less than .024" between the edges of the block bores. Although doable, this sounds a little thin to me. More importantly, though, the liners have a wall thickness of only .035". During my Howell V-4 build, I discovered the piston ring sealing was limited by circularity errors in the liners due to their thin wall construction, and the Merlin liners have half the wall thickness of the Howell liners. The Howell liners were made from cast iron which I know from experience can be dimensionally unstable when machined in thin cross-sections. The Merlin liners are intended to be made from 4130 steel; and, admittedly, I have no similar experience with that material. My third concern is with the narrow .040" wide water jackets around the cylinders. This is less than 3/4 teaspoon of coolant surrounding each cylinder, and so the coolant flow rate will be important. I looked ahead in the drawings, and the water pump looks awfully small - only about 30% larger than the pump on the Howell V-4. Overheating was, in fact, a problem with the quarter scale prototype. 
The next section will describe the numerous coolant and oil passages that must be provided between the block and the head. - Terry


----------



## mayhugh1

When a fully machined head is assembled to a fully machined cylinder block, not only must two halves of six combustion chambers come precisely together, but 14 stud tubes and 14 coolant transfer tubes between them must also align. In addition, the two mating parts must also be drilled and tapped for an additional 24 head bolts.
The stud tubes serve a couple functions in addition to acting as conduits for the studs that secure the head and cylinder block to the crankcase. The seven outside tubes double as oil returns for the top-end of the engine. Machined Delrin seals installed between the block and crankcase are compressed to prevent oil leaks when the assembly is bolted together. The outside central stud hole on each block also penetrates the water jacket, and so it must also be sealed with an additional piece of tubing.
The stud tubes are flanged at their tops, and they extend through the head and into a shallow reamed recess in the block. An o-ring around each tube is compressed between the block and head to control oil leaks. The flanges are set in counterbores on the top of the head. Special slotted washers between these flanges and the stud nuts allow top-end oil to drain down along the studs and into the sump under the crankcase.
A significant fabrication issue is that the stud tube holes have already been cast into the heads since they were necessary for core supports. The construction notes warn these cast holes are not likely to be in the correct locations for the stud tubes, and so they will probably have to be slightly moved. Because my particular crankcase casting was undersize, my holes may have to be moved a bit further. Hopefully the cast holes are undersized by more than the distance they will have to be moved.
Because the head and cylinder block are two separate pieces, provisions must be made for coolant to flow between the two. In the Merlin this is accomplished with fourteen sleeved transfer passages. The transfer tubes are short lengths of aluminum tubing 'snugly fitted' into matched reamed recesses in both the head and block. O-rings around each tube are compressed when the assembly is bolted together in order to seal the gaps. Locating all these holes for these 'snug fits' seems unreasonable since the holes on both parts are blind, and there is no way to match drill them. Excess clearance will likely have to be provided for these tubes on at least one side of the interface, and hopefully the o-rings will still be able to handle the sealing. A coolant leak is much more serious than an oil return leak. According to the design notes, early Merlins were sometimes damaged at start-up due to hydrolocked cylinders created by coolant leaks during engine cool-down.
Drilling the rather deep stud holes through the cylinder block so both ends end up in the exactly correct positions for mating with the crankcase seals and the head transfer tubes is going to be difficult. Identical drilling patterns are used on both cylinder blocks, and so time spent developing fixturing will at least apply to two parts. A single casting pattern was used for both blocks, and in the Merlin the left side block is just a right side block turned 180 degrees.
Not shown on the simplified cross-section are the holes for another 24 head bolts used to assemble each head to its block before the paired assembly is bolted to the crankcase. However, since they are only 3-48 SHCS's they may be more cosmetic than functional. - Terry


----------



## gbritnell

Hi Terry,
The issues you are explaining are engineering problems when scaling everything, especially I.C. engines. For the last couple of decades I have been designing and building my own engines. While doing the extensive drawing layouts I try to resolve some of the worst conditions in regard to building and operation. Sometimes concessions have to be made to the design to allow somewhat reasonable operation. These small engines make a lot of heat when running. That being said the only way to run coolant through the head is generally by longitudinal channels drilled through the head and plugged at one end. I have done this on my 302 and inline 6 engines. The flathead that I'm currently working on has it's own unique constraints. 
From what you're showing it looks like the author designed the engine to be built and operated mostly in theory and not practicality. It would certainly be a shame to put in mega-hours of building only to find out that you have a beautiful paperweight. 
After following your radial build I am confident that you of all people are more than capable of solving some of these issues but my only question is "were any of these casting sets built into running engines?"
gbritnell


----------



## mayhugh1

George,
There's only two examples of running engines using these actual castings that I know of. The first is by the original authors; and the second is by Gunnar Sorensen, a Danish master craftsman:

http://translate.google.com/transla...meside.dk/gunnarsorensen/30857372&sl=da&tl=en

In both cases, though, the running demos were pretty short. The designers of the castings, to the best of my knowledge, have never published any construction photos of their build. The description of the original prototype is so vague that even with the notes accompanying the castings I purchased, I've never been able to figure out just how much of the total design is really functional. The change notices on the drawings span more than ten years, and so a lot of effort was put into the project. Gunnar published some photos of his build and, as far as I can tell, they show him following the stock head design. 
I got involved with this project with my eyes wide open, and I have no complaints or regrets. I assumed the supercharger was probably never made truly functional, and I would likely spend a lot of work only to end up with a cool looking diffuser. I also assumed the magneto design was never completed, and I would have to come up with something on my own. It seems that Gunnar did just that. I also assumed I could somehow adapt an RC carb to this engine as I did with my radials. The carb discussion in the notes accompanying the castings propose solutions that do seem to be products of someone's limited experience with actual running models.
I spent a lot of time composing the two previous posts because I think I was using them to clarify in my own mind the thinking behind both designs - the full-scale and quarter scale - and to convince myself I could do the machining needed for the quarter scale. I'm beginning to realize that I really don't like working with castings because options for modifications and improvements are really limited.
My gut tells me the machining is going to be very difficult but not impossible. After all, Gunnar did it. It also tells me the cooling system is most likely inadequate. At this point my plan is to continue with the stock design but to not do any liner construction until I finish the critical head and block machining. If I get through that, I plan to modify the liner design for a thicker wall and wider coolant jacket. This may not entirely solve the overheating problem if one exists, but it should extend the running time a bit. This will mean that the cylinder and piston diameters will have to be reduced, but I can live with that. I should have an option later to design a larger coolant pump since, on the surface, it appears to be a bolt-on. In addition I may have the option to run additional coolant lines since much of the oil and coolant systems on this engine are externally plumbed anyway. - Terry


----------



## mayhugh1

I decided to do some of the 'easy' machining on the blocks and heads so I could make some progress while thinking more about how I'm going to handle the fixturing for the more demanding drilling and boring operations. Having as many machined surfaces as possible on these parts can only help, and these 'baby steps' should help me get a feel for the kind of precision I can hope to maintain while working with these castings.
The machining of the cylinder block began with facing it's top surface. It turned out that my particular blocks were warped well beyond the limits for which straightening was recommended, but I decided to correct them solely by machining, anyway. There were no cosmetics to be impacted, and with all the deep drilling that's coming up later, I didn't want to deal with hardness variations created by annealing.
I made a fixture to support the blocks by the inside diameters of their two outside cylinders. The complex sides of the blocks made them too difficult to hold with any precision in a vise. This fixture also avoids toe clamps which might disturb the warp I'm trying to remove. It also gave me a reasonable chance of an already cast through-hole coming out normal to the top and bottom machined surfaces. This hole was probably used for a core support, and its location corresponds to that of the outside center stud hole. My naive plan was to use it later as a datum on both surfaces for referencing those drilling and boring operations. Since I'll later be machining features on both the top and bottom surfaces of the blocks it would be really nice if this hole ends up normal to both finished surfaces. A design note mentioned cleaning up this hole up with a 5/32" reamer so a piece of standard size tubing could be used to seal the coolant jacket it penetrates. My holes were quite a bit oversize, and I had to use 7/32" tubing. 
The 1/2" thick aluminum baseplate for the fixture was carefully surfaced and squared. Its geometry will become even more important when it's reused later for the drilling and boring operations. I machined this base plate to be as perfect as I possibly could, but after an evening of chasing my tail, the best I could achieve was .0005" flatness over the plate's 12"x4" area, and even that involved some luck. I'm not one to blame my tools, but I think my 20 year old Enco mill was at least part of the problem. Using a less stressed material than 6061-T6 might have also helped. I thought about annealing it, but I was afraid the resulting surface finish might create other problems.
The warped block was installed on the fixture, and its ends were shimmed to equalize the amount of material removed from each end. The two portions of the fixture that actually grasp the block are shop-made expandable Delrin collets. I took light cuts and continually monitored the tightness of the shims on either end to make sure the block didn't shift during machining. After machining the top and bottom surfaces of the first block, surface plate measurements showed a whopping corner-to-corner parallelism error of about .002" between the two surfaces. After an afternoon of experiments and head-scratching I realized the problem was being created by my fixture. The unfinished bores in which the collets were grasping the part were not parallel to each other because of the warped casting. Tightening the Delrin collets bowed the base plate a few thousandths and pulled the block with it - unbelievable! The final solution was a thicker, one inch, baseplate. 
After all the effort I put into the first baseplate, I thought the second one would be easier. It was, but I still ended up with the same .0005" flatness over its same area. Re-machining one of the surfaces of the bad block reduced its error to .0005" which is what I'm learning to live with.
After the block surfaces were machined, I drilled the clearance holes for the twenty-four 3-48 head studs. This was as good a time as any since they were located on the centers of now-machined bosses distributed around the top perimeter of the block and were easy to do. Their drilled locations will be later transferred to the heads so the matching threaded holes can be drilled and tapped. A similar technique was used for spotting their locations, i.e. aligning a tube-covered V-drill in the center of the boss, as was done earlier with the oil pan mounting holes. 
Final measurements on the reamed hole showed nearly perfect perpendicularity with respect to the long axis of the block and a relatively small, but unacceptable, error along its short axis. The measurement of the hole's offset error was very difficult and inconsistent, and so it became clear it wouldn't be suitable as a reference for the block's top surface machining. When I machined the second block I tried to fixture it so I would machine its first surface normal to this hole, but that became an exercise in futility, and the second one came out with an even larger error than the first.
Setting the blocks down on the crankcase to see how the bores roughly line up around the central stud tubes was a little worrisome. The finished bores in my 'short' crankcase are significantly misaligned with the unfinished block bores which, themselves, seem to be on slightly wider centers than the drawings assume. Hopefully, there's enough excess block material to allow them to be moved over into alignment.
Beginning the head machining required a bit more thought because of the slope of the valve cover mounting surface. For me it was important, for cosmetic reasons, that its thin flange be kept uniform. I decided to clean up the block-mating surface first by removing the minimum amount of material to get it flat. The head was supported in a vise with leather packing against the movable jaw and a machinist jack at one end to adjust for the valve cover slope. After machining, this reference surface was placed against the stationary jaw of the vise so the intake and exhaust flanges could be machined flat. In both cases only the minimum amount of material was removed from the head. The exhaust flange heights are not at all critical, and will be left as machined. The intake flange, though, will be brought to its finished height after the head's face is finish machined and a full trial assembly is made with the intake manifold.
Finally, the valve cover mounting surface was machined. The exact angle of its slope was not important and so it was adjusted to keep its mounting flange uniform in thickness. 
So, I'm off to an OK but not a really great start. I'm now confident, after some experimenting though, that mating the stud tubes in the heads with their corresponding holes in the block isn't going to require the precision fits called out in the drawings since the o-rings are capable of absorbing the machining differences I can probably maintain in the non-pressurized oil returns. The pressurized coolant passages are still an lopen question, though. - Terry


----------



## makila

Terry,
This is a fantastic build.
I think that your solution of reducing the bore to rectify the thin cylinder wall and increasing the water capacity adjacent to the cylinder is a excellent idea. Not knowing what the dimension of the cylinder bore is, if it was reduced by .100" for example, this could be used to increase cylinder strength and have a outside waisted portion at the water jacket to allow more cooling water to surround the cylinder. The cylinder external dimensions at the top and bottom would be the same as the drawings so as not to have any affect on the castings, but you would have a .025" increase in water capacity/flow each side and .025" increase in wall thickness at the mid point of the cylinder giving a bit more structural stability to the component. 
Of course, I do not know if this modification would have an impact on valve clearance at the top of the cylinder, hopefully not. There may be a need to provide cut outs for connecting rod clearance at the base of the cylinders. Also, I am not sure how this modification would affect performance, but at least the whole modification would be reversible (with x 12 new cylinders) and may solve possible over heating and cylinder integrity at elevated temperatures.
As George mentions, concessions are sometimes needed.
Steve.


----------



## mayhugh1

Makila,
Yep, that's just what I was thinking, er... hoping. - Terry


----------



## petertha

Terry I was Amazon surfing & happened to see this. Its dated Mar-15-2015, not sure if that means its a new release or reprint date. Anyway just a FYI.

http://www.amazon.ca/dp/0857337580/?tag=skimlinks_replacement-20


----------



## Charles Lamont

mayhugh1 said:


> I machined this base plate to be as perfect as I possibly could, but after an evening of chasing my tail, the best I could achieve was .0005" flatness over the plate's 12"x4" area, and even that involved some luck.



I would say that was pretty good going. To get any better I would expect
to have to scrape it, (something I don't think I have tried with light alloy).


----------



## mayhugh1

Thanks, Peter. I just ordered a copy. - Terry


----------



## mayhugh1

I started the more demanding machining on the blocks by mounting the first one upside down on the heavy baseplate I made earlier. It was secured to the baseplate with Delrin disks screwed down inside the two outside cylinder bores. These disks clamp the top lips of the two bores against the baseplate so the long axis of the block can be held securely in alignment with mill's x-axis. A gage plug fitted in the single reamed stud tube hole was used as a reference to ensure alignment of it and the bottom-side block machining with the already-machined crankcase. 
Because of the hold-down disks inside the outer cylinders, only the four central cylinders were initially bored. Once these bores were completed, a second pair of disks were screwed down inside the inner cylinders before the outer disks were removed. An inconspicuous dimple spotted on the far end of the block before machining began was targeted with a spindle microscope to verify the block hadn't shifted during boring or the disk change-out. A high rake triangular carbide insert fitted to a boring bar and driven by a boring head was used to bore the cylinders.
The boring was done in four passes: three passes of .010" radial doc and a finish pass of .005". Just after the first pass of the first cylinder in the second block I noticed a dark spot on the interior wall of the cylinder. The cast i.d. of this particular cylinder had always looked a little suspicious compared with the others because of a slightly sunken-in pea-size area. At first I thought I was looking at was a shadow, but when I touched it with my finger I felt a sickening pang in my stomach. This pea-size area was now a thin layer of foil covering what was evidently a void just below the surface. Succeeding passes peeled the foil away to reveal a small cavity. After boring the adjacent cylinder I was left with an irregularly shaped hole between the two cylinders. Although it'll eventually be hidden by the liners, and it isn't fatal since it basically connects the water jackets of two adjacent cylinders, it's the only thing I see when looking over the last several weeks of work. If it were a bar stock part I'd scrap it without a second thought. I eventually filed the hole into a rectangular shape so it wouldn't look like so much like a defect. 
Curiously, the block is the only casting for which drawings were supplied for a bar stock equivalent. The reason for their existence isn't mentioned anywhere in the documentation which leads me to wonder if there were yield problems with the block castings, and billet replacements were plan B. The issue with using them, however, is that they contain no provision for coolant flow which makes them impractical for use in a functional multi-cylinder engine. 
The holes for the studs were referenced to each bore before being spotted, drilled, and counterbored. Because of concern about the holes not coming out in the exact same locations on the other side of the 2" thick block, they were drilled to only half depth using a slightly undersized Guhring drill. Once the holes are similarly drilled from the top side they will be reamed to their finished diameters. The counterbores on the bottom surface of the block match those previously machined in the top surface of the crankcase. The counterbores were drilled using a very long 4-flute end mill extended out from a 'special' collet with a known TIR problem so i could get the over-size diameter I needed. Oil seals will eventually be inserted into these counterbores to contain the drain-back oil from the engine's top end.
As mentioned in an earlier post, my particular crankcase was cast slightly undersize which necessitated altering its machined bore spacing from that of the drawings. Because the blocks which were properly cast on-size, the machined cylinder bores and stud holes in them had to be relocated to match those in the crankcase. If you look closely at the block photos you may notice the stud holes are not in the exact centers of their bosses. Since all machining was referenced to the center of the block, the resulting errors progressively increase toward the two ends. The cylinder wall thicknesses around the machined bores are reasonably uniform, though not identical, due to a slight lateral warp in the castings.
Other than my little gas bubble, the undersize crankcase, and all the warped parts, I still remain impressed with the castings. Next up is to flip the heads over for the top side machining and to decide how to deal with the center stud tube holes which were not cast vertically through the block. - Terry


----------



## digiex-chris

Is that an optical alignment tool held in your mill spindle?


----------



## mayhugh1

Yes, it is. I calibrated it by drilling a tiny spot on a piece of metal and then replacing the spotting tool with the scope. There is an adjustment on the scope to zero the spot under its cross hairs. It works especially well on my Tormach because it can be re-inserted into same position in the spindle due to the spindle lock in their mill. Once calibrated it doesn't have to be messed with. I believe I bought it from Enco. It's one of those items that often goes on sale. - Terry


----------



## petertha

mayhugh1 said:


> I was left with an irregularly shaped hole between the two cylinders. Although it'll eventually be hidden by the liners, and it isn't fatal since it basically connects the water jackets of two adjacent cylinders, it's the only thing I see when looking over the last several weeks of work.


 
Dang. If it doesn't adversely affect cooling or performance, I guess the biggest challenge is just mentally forgetting its there once its all buttoned up. Tough for a perfectionist, but maybe the best solution of few available options. I don't know what to suggest for fear of making matters worse.

I can visualize a patch made from HT aluminum filled epoxy or urethane casting putties using a male release plug in the opposing cylinder, but would that even hold up under service?  Any kind of braze like those zinc? alloy wonder sticks is asking for trouble. I've seen pictures where people Loctite a plug & re-machine, but the cavity is such a thin, irregular feature as an add-on & only 'grip area' is the small periphery of the open window. 

Don't let my armchair ramblings influence you. I'd feel real bad if a repair attempt went sideways. Trying to be helpful, but way out of my league.


----------



## mayhugh1

Peter,
I gave some thought to repairing it, but in every case the repair had more long term uncertainty associated with it than the hole itself. The section is just too thin for a cold patch, and the heat required for a hot patch is too risky for a number of reasons. It stings now, but my long term memory isn't what it used to be, and I'm sure I'll have a lot of more serious issues to deal with before this project is over. - Terry


----------



## Scott_M

Hi Terry
Bummer about the gas hole. But like you said, any repair will likely introduce more issues than the hole itself. And If you have to have a void somewhere, that is not a bad place.
Awesome work, following along closely 

Scott


----------



## digiex-chris

You could cut a hole through all cylinders like that, and call it a little extra coolant flow...


----------



## mayhugh1

Next, the blocks were flipped over on the baseplate for their top-side machining. Since the necks of the bores are no longer against the baseplate the bores couldn't be clamped down with disks, and so I made another pair of expandable Delrin collets to grip the i.d.'s of the newly finished bores. As before, these collets were used in the two outside cylinders to hold the blocks down against the baseplate. It was important to keep the heads tightly against the baseplate and to align the axes of their already finished bores with the mill. These next operations will impact the seals of the combustion chambers as well as the seals of some 28 oil and coolant transfer tubes between each block and head. I was prepared to spend a lot of time shimming the baseplate-mounted block into alignment with the mill but was pleasantly surprised to find both block centerlines were aligned to within .003" before shimming.
The first operation was to bore the cylinder necks to their finished i.d. The shoulders of the liners will be lightly pressed into these bores in order to seal the water jackets at the tops of the blocks. Each liner will be supported at top of the block by its shoulder and at the bottom by a sealing ring that forms a joint with the crankcase, and so the neck bores need to be accurately centered over the cylinder bores. Both should have been machined in the same set-up, but I couldn't come up with a fixture that would have allowed me to measure both i.d.'s during machining.
I used a DTI in the mill spindle to find the center of each bore. Each of these indicated centers were used for the corresponding neck boring operation as well as the second half drilling and counterboring operations on their associated stud holes. Because the two cast central stud tube holes were too far off vertical to be corrected during the previous facing operations, they were not where they were supposed to be on the top surfaces. In fact, the hole in the right-side block was off by a whopping .020". These holes will have to be specially treated later when the matching operations are performed on the heads. As far as I could tell, the topside half-depth stud holes appeared to match up with the bottom-side half-depth holes previously drilled. I could feel no detectable intersections when they were reamed through.
I machined the diameters of the 14 stud hole counterbores .005" larger than the diameters of the head stud tubes that will be inserted into them. I used a long stick-out end mill in a spindle chuck with a poor TIR to get the counterbore diameter I wanted. These tubes will have to be pressed into the heads since they penetrate the head coolant jackets. The holes for these tubes are those holes mentioned earlier that were pre-cast in the heads in the wrong locations, and so they will all have to be 'moved.' The .005" clearance assumes I can match the hole placements in the blocks and heads to better than .0025" each which doesn't seem reasonable, but it's twice the clearance called out in the drawings. I really wonder what the placement accuracy was for all these holes in the full-size engine back in the 40's. O-rings will be inserted on these stud tubes and compressed between the head and block to help seal the intersections against oil leaks. I won't be surprised, though, if I have to come back later and manually increase these clearances in order to be able to assemble the heads to the blocks.
The last top surface operation was drilling and counterboring the 14 holes for the coolant transfer tubes that carry pressurized coolant from the blocks to the heads. The same .005" over-size counterbores were applied to these holes. I haven't yet decided if the coolant tubes will be a tight fit in the heads or whether the heads will also receive the same counterbore clearances. I need to do some assembly experiments on some dummy parts before I decide. Compressed o-rings will also be used around these tubes.
The depths of the stud tube counterbores are slightly deeper than the depths of the coolant tube counterbores. This was done so the pressed-in stud tubes that will extend down from the head can be made a bit longer than the coolant transfer tubes. When the head is assembled to the block the hope is that the 14 stud tubes will engage the head first and act as guides for the 14 coolant tubes and five liner spigots following closely behind. I really have trouble describing this critical assembly step without laughing hysterically.
A confusing, at least to me, issue involved determining the asymmetrically placed locations for the coolant tubes. They, too, had to modified from the locations called out for them in the drawings in order to accommodate the changes created by the short crankcase. For simplicity, the same drilling pattern is specified for both the left and right blocks since both are machined from the same casting. The left block is just the right block turned 180 degrees, but since the hole patterns are not symmetrical across the long axis centerline of the block, some algebra and a lot of mental gymnastics were needed to calculate their new locations. If I were starting over, I would just allow the rods to run a bit offset in their pistons rather than correct for the crankcase casting error which seems to be propagating with no end in sight throughout the engine.
The final block operation included surfacing the coolant tube flanges on the outboard side of each block. A pair of external coolant feed tubes are affixed to the outside of each block using three small, but highly detailed, cast tube fittings. I believe these tubes are the coolant inputs for the engine. There's no explanation of the cooling system in any of the documentation I received, and so I'll need to do some research on the full-size engine when I get to that point. I was disappointed to discover there was no casting supplied for the coolant reservoir which is a prominent component on the top front of the engine. It's shape is very complex, and it will have to be hammer-formed from sheet metal or CNC'd from billet.
I decided to machine the cast tube fittings at this time, as well, so each block could be match-drilled for them while still on its baseplate. It was very difficult to fixture these parts for machining, and after a few unsuccessful attempts that left their flanges considerably thinner than intended, I decided to hand file them. It's important that the flanges on these tube fittings be flat and normal to their mounting surfaces on the block since they connect a pair of tightly-fit rigid tubes between them, and provide at least seven opportunities for coolant leaks. A couple long, small diameter bosses that had to be through-drilled for mounting screws kept the filing even more interesting. I think the intention was to use 2-56 SHCS to mount them, but I settled on 1-72's because of a lack of excess stock. I Loctited short, thin-wall tubes into the block flanges to help locate the fittings for transfer drilling their mounting holes to the block. These tubes will also make it a bit easier to seal the flanges.
I received the Haynes 'Workshop' manual for the Merlin. It'll be interesting reading, but it's mostly an historical accounting of the engine's development with very little workshop content. I did find a warning about about the necessity of monitoring the oil level in the Merlin as it was known to leak quite a bit of oil, probably from the numerous seals I've been encountering. It reminded me of a joke that I heard long ago from a mechanic friend who incessantly teased a Jaguar owner whose car spent more time in his repair shop than it did on the street: "Why is it that the British don't manufacture televisions?" Answer: "They've never figured out how to make them leak oil." - Terry


----------



## petertha

Impressive positioning & finicky machining operations. 
Can you elaborate on your Delrin ID clamping collets. I see the slits & assume a tightening nut on top? So is there a steel cone under the nut that yields the radial expansion? How is the shaft fixed in the base plate? What is a typical collet OD vs Bore ID dimension?


----------



## mayhugh1

Peter,
The collets are threaded for shoulder bolts that are inserted up through the bottom of the baseplate. I turned the collets for .003" smaller diameter than the bores. There is a 60 degree counter sink bore in the end of the collet and a 60 degree conical piece that is forced down into the countersink to spread the collet. I tightened the nuts that forced the conical sections into the countersinks while the the center of the assembly was lightly clamped in a vise. When done, I tried to pull the block up from the baseplate while checking with a .001" piece of shimstock as well as for any light between the block and the baseplate. During machining, I also watched for any hydrodynamic pumping of the coolant that collected around the bottom periphery of the intersection of the block and baseplate. I saw none and assumed all went well. - Terry


----------



## mayhugh1

My next step was to match-machine the heads to the blocks. Earlier, when I surfaced the heads I left them tall so I could finish their surfaces in the same set-up where all the critical drilling and boring will be done. I also thought it best to calculate the static compression ratio before surfacing the heads. The c.r. came out to 7.8 compared with 6 for the full-size engine, which may be a bit high if the supercharger turns out to be functional. Since most of the foundational machining will be finished by the time I get to the supercharger, I should be able to lower the compression by shaving the pistons. 
I'll also model a complete operational cylinder soon since I'm planning to increase the size of the water jackets as well as the wall thicknesses of the liners by reducing the diameter of their bores. Although this seems like an inconsequential change, it provides opportunities for valve and connecting rod interferences.
The faces of the heads were mapped to determine the best centerlines for the bores before doing any of the head machining. The cast features in the heads must be machined to match those features already completed on the blocks. For appearance sake I also wanted the outer perimeters of the assembled heads and blocks to align as closely as possible. 
The mapping showed I could easily achieve near perfect alignment between the left-side head and block, but there would be a compromise misalignment of .007" on the right head because the cast central stud tube hole in the right block was just too far out of place on its top surface. This small misalignment won't be noticeable because the heads don't actually mount against the blocks. Even though all the cast holes in the heads had to be relocated as mentioned earlier, I was not able to align the already cast central stud hole in the right head to the one in the block without shifting the head .007".
The heads were surfaced to produce an average combustion chamber depth equal to that called out in the drawings before the sealing shoulders on the combustion chambers were bored. It was important to simultaneously keep the intake mounting flanges parallel to these surfaces and also to match their heights on both heads to reduce difficulties later when fitting the intakes. The rest of the interiors of the combustion chambers were left as cast since the valve guide machining will be done later. The Merlin heads are designed for separate valve seats and guides, but I hope to come up with an integral valve cage design. It looks to me like the multi-angle and multi-level contours cast into the heads behind the valves will make it difficult to end up with separate seats and guides which are concentric.
Since the stud tubes penetrate the coolant jackets in both the head and block they must be sealed. I ended up with a slight mismatch, after all, on the troublesome center stud tube hole in the right head; but I believe it can be sealed with gap-filling Loctite.
In order to relocate the pre-cast stud tube holes in the head I fabricated a flat-end drill from a slightly undersize 4-flute carbide end mill. Starting a quarter inch behind the end of the cutter I ground the flutes down slightly in order to clear the hole left behind by the cutting portion of the tool. In the past I've plunged deep holes using unmodified 4-flute end mills, and the results were usually inconsistent. I don't know for sure if my modification helped, but 23 of the 24 relocated holes came out on size and where they were supposed to be. The reamer I used to bring the holes to their finished diameters was dulled rather quickly by investment packed in the coolant passages under the surface of the head. After some research I learned the investment typically used in aluminum casting can be dissolved in water. I soaked the heads in warm water for several minutes, but it didn't seem to have much effect. After the next machining operations on the head I'll try boiling them in water.
I turned partial dummy liners out of Delrin for use as fixtures to assemble the head/block pairs for match drilling and tapping the 24 auxiliary head bolt holes in each head. These liners were turned for press fits in the blocks, and the sealing spigot diameters were turned undersize by .002" just as will be done on the actual liners. The blocks, with their press-in plastic liners, assembled onto the heads perfectly with no alignment issues; but, of course, I'm not yet dealing with the interconnecting tubes. 
These plastic liners will protect the sharp sealing edges on the combustion chambers in the heads later while checking the alignments of the 28 fluid tubes running between them. Note how the heads do not sit down against the blocks when assembled but are, instead, clamped against the elevated liner spigots. This gap is what creates the need for all these crazy fluid tubes. My guess is that with the level of horsepower generated by the full-size engine, Rolls-Royce engineers didn't feel that the head gaskets available at the time would be reliable. The high clamping pressures in the sealing corners of the narrow liner spigots may also be the reason that an alloy steel rather than brittle cast iron was specified for the liners. - Terry


----------



## Joe90

The sound of a full size Merlin in a Spitfire at an air show is something else. And to build a working model of one is just as exciting I think.

This is an absolutely superb project, thanks for sharing progress with us. I would like to try this at some time but I'll watch and learn first.

Joe.


----------



## Mattsta

Awesome stuff Terry

Only 2 valves per cylinder on the scale model then? Well! It'll save you machining an extra 24 valves and associated components!


----------



## mayhugh1

Mattsta,
Yeah, I've been studying the top end, and it is pretty complicated with only two valves. I'm still trying to wrap my head around the dramatic differences between the left and right camshafts. I'm going to have to enter the top-end into SolidWorks in order to be able to even begin to visualize it. While between planes during the past few days I've been reading up on the history of the Merlin's development. It's a remarkable story with its mechanical complexity, wartime schedule pressures, and company politics. It's mind-blowing that over 160,000 of these engines with their 11,000 parts were built on two continents in such a short period of time with such great reliability and no modern high tech tools. It makes my machining challenges on this model seem whiny and insignificant. It's a shame that when the war ended nearly all of them were destroyed and its story allowed to fade into obscurity for most of us. - Terry


----------



## M130

Hi, my name is Morten and i'm from Norway. I have followed your 18 cyl. Build and now this one. I just want to say that I enjoy reading about your work very much. 17 years ago I visited Norwegian aviation museum in Bodø and they had a fullsize Merlin cutaway model. I was very impressed of that engine. It had technology that was not used in automotive engines before in the 80th ( 4 valves/cylinder). A complex engine constructed with pencil and paper, made with manual machines and handwork.

Morten


----------



## kvom

I met Terry at NAMES this weekend.  He said that this build is "frustrating" since he's spending so much time tapping holes and not making any parts.


----------



## Mattsta

mayhugh1 said:


> Mattsta,
> Yeah, I've been studying the top end, and it is pretty complicated with only two valves. I'm still trying to wrap my head around the dramatic differences between the left and right camshafts. I'm going to have to enter the top-end into SolidWorks in order to be able to even begin to visualize it. While between planes during the past few days I've been reading up on the history of the Merlin's development. It's a remarkable story with its mechanical complexity, wartime schedule pressures, and company politics. It's mind-blowing that over 160,000 of these engines with their 11,000 parts were built on two continents in such a short period of time with such great reliability and no modern high tech tools. It makes my machining challenges on this model seem whiny and insignificant. It's a shame that when the war ended nearly all of them were destroyed and its story allowed to fade into obscurity for most of us. - Terry



I recently found a thread on an engine building forum posted by a someone in the US who rebuilds Merlin engines and he posted some very interesting photos and accounts of how exacting and precise the tolerances are in these engines. He detailed the procedures for reconditioning the fork and blade connecting rod assemblies and their respective bearings and I was amazed at how precise the tolerances specified for correct manufacture and assembly are. As luck would have it, my hard drive self destructed and I lost the link to this forum. I'll try to find it for you.

Indeed! How on earth did the British and Americans mass produce these engines under wartime conditions with slide rules and pencils? This applies equally to Bristol, Napier and the American manufacturers, Curtis and P&W and Packard.

It's mindblowing

I've visited the Science Museum in London where they have a cutaway Bristol Centaurus and a Napier Sabre engine in addition to a Merlin and a Griffon engine and wondered in awe..............how the hell did they design and mass produce these things in the mid 1940s???

Makes you realise how ingenious human beings are when their backs are against a wall and their creativity and enterprise is not strangled by government.............but encouraged.


PS. If you need any CAD skills in this enterprise, I'll gladly help you out


----------



## mayhugh1

It's my understanding that the Merlins bulit by Rolls-Royce were actually built up completely by small teams using craftsman techniques common to coach building at the time. The parts from one engine were 'filed to fit' and didn't necessarily fit into another engine. When Packard started their production in the U.S., their engineers spent the first year converting Rolls drawings over to their drawing and production standards which included producing the engines using assembly line techniques and, for the first time, interchangeable parts. Considering these engines were typically rebuilt after 100 hours service, their repair and overhaul was another unbelievable feat. -  Terry


----------



## mayhugh1

When I first started this build I thought it would be wise to work top-down and verify the assembly of the castings before starting on any of the bar-stock components. Thanks to the large number of castings and an engine that seems to have been hermetically sealed with bolts, I've been drilling and tapping holes for nearly three months. It's been a tedious process because the precise location of each fastener usually has to be individually found, nearly all the holes require match-drilling, and I seem to be able to only do a half dozen or so per hour. In addition, 3-48's have become the 'large' bolts in my shop.
The next hundred fasteners, though, will complete an important milestone for this project which is the fitting of the intake manifold and a trial assembly of the major castings forward of the wheel case.
I first had to make some Delrin liner collars for insertion between the blocks and the crankcase. These collars are temporary replacements for the metal ones which will be machined later. Their purpose is to precisely locate the blocks on the crankcase and set the proper heights of the heads so the intake manifold can be properly fitted. Notice in the photos that the blocks are separated from the crankcase by the thickness of these liners. The gap they introduce creates the need for oil seals between the blocks and crankcase to contain the top-end drain-back oil.
The crankcase and blocks in the early Merlins were actually a single casting, but performance testing uncovered a tendency for the blocks to crack during full-power runs. The engineers felt that a redesign of such a complex casting would have seriously delayed production, and so it was decided to separate the blocks from the crankcase. This decision complicated the engine's assembly and added a number of additional parts; but it solved the reliability problem and, with war looming, minimized the impact on production.
The Merlin's intake manifold is made up of three separate castings: a center 'log' section and two side sections. These three pieces will be combined into a single assembly which fits in the 60 degree valley between the heads. Measurements on the temporarily assembled heads showed the included angle between their flanges was exactly 60 degrees and, within the limits of my measuring capability, they were parallel.
Machining the center log section was fairly straightforward and required only a simple facing operation and 30 transfer-drilled tapped holes. The critical side sections, though, were another story. Both were badly warped, and each had a spiral twist along its major axis. I couldn't come up with a coherent plan for straightening them, and so I just did the annealing and then spent hours randomly pushing, pulling, and twisting them until they looked acceptable. The process wasn't at all satisfying, but it seemed to work.
The side castings, even after straightening, were extremely difficult to fixture for machining. Each had a pair of mounting flanges that needed to be machined at 30 degrees to each other; and, upon assembly, the flanges facing the heads must end up parallel. The head mounting flanges on both side sections were hand-lapped after straightening to provide a starting point for the machining. The only fixture I could come up with to support them while machining their second surfaces, though, was a kluge; and I held my breath during every .002" pass.
I tried to adjust the height of the assembled manifold in the valley between the blocks by only milling flange material from the heads since it was a straight forward fixturing and machining operation. After removing as much as I possibly could, the manifold still set high by about .030". Some simple trig showed that .013" still needed to come off each side of the manifold. Since this was too much material to lap away, another fixture was created to support each manifold side section so its head flange could be milled.
Another important requirement in the fitting process is that the intake must also end up exactly centered between the blocks. A 1-1/8" diameter rigid fuel tube will eventually connect the manifold's center section to the supercharger at the rear of the engine, and there will be no way to later adjust for an off-center error.
Eventually, I had the assembled manifold resting between the heads. The angles matched perfectly, the log section was centered, and there were no measurable gaps which showed the flanges were indeed parallel. Twelve of the bolts that hold the three castings together actually pass through the thin wall manifold, and they will be joined by several more after being secured to the heads. The issue is that the internal supports for these bolts were left out of the designs of these castings even though they were a part of the full-size castings. Since they're very fragile, the slightest over-tightening causes the side sections to flex, and as a result a slight gap is opened between them and the heads.
I was hoping that the 70 bolts that I will be installing to secure the manifold to the heads would also seal them so I could avoid intake gaskets. However, it now appears that nearly a third of them will be counterproductive during final assembly, and so I will have to use intake gaskets after all.
I measured the thickness of some 1/64" gasket material samples I had on hand because the exact gasket thickness will have to be removed from each side of the manifold before the mounting holes are match-drilled. I measured as much as .005" thickness variation between my samples. In practically any other application this would have little effect, but for an angled manifold installation it raises a red flag. The .004" hole clearances I've been using for the recommended 3-48 manifold screws is limited by the small diameters of the cast bosses. Because of the manifold angle, a .005" change in gasket thickness will move the mounting hole locations about .011" along the manifold, and this is much greater than the hole clearance. This means that the holes must be drilled for the exact batch of gasket material that will eventually be used, and I need to plan for spares. I decided to delay the mounting hole drilling until I have time to think about this some more. I'm dealing with the flu right now, and I don't want to make any irrevocable decisions with my currently unclear head. - Terry


----------



## kvom

Holey castings, Batman!! 

Looking good.


----------



## ozzie46

Astounding work!!

 As far as the gasket material, how about using a curing gasket material like high temp silicon or something along that line?

  Ron


----------



## aonemarine

not a project for the faint of heart thats for sure....


----------



## JLeatherman

aonemarine said:


> not a project for the faint of heart thats for sure....


 
Or the faint of talent...


----------



## wirralcnc

Terry
Can you not find some uniformly thick gasket material.
Get enough to make a few gaskets and a piece to go between mating faces for match drilling.
Robbie


----------



## mayhugh1

Robbie,
So far, that's my plan. Right now, I'm trying to decide if it would be best to do the match-drilling and then mill away the flanges for the gasket or, as you say, mill the flanges and then insert the gasket while match-drilling. It would be easier to do the drilling without involving the gaskets, but then I would get only one chance to mill away the correct amount for the gasket. Terry


----------



## wirralcnc

Terry
I would mill flanges first. Any miss calculation can be rectified with thicker gasket, and the match drilling will still be perfect. I wouldn't make gaskets till all drilling is complete. Only require a piece of gasket material between mating faces. Maybe a spot of oil to hold in place.
Robbie


----------



## mayhugh1

Robbie,
I think you're right. That's probably what I'll do. - Terry


----------



## Metal_slicer

Wow!

Can I say "Master"

To get to your level for me is... un-achievable. ;D

Fantastic work.


----------



## barnesrickw

Impressed with the workmanship and the huge intake manifold on that engine.


----------



## bigrigbri

I would have loved to shake the mans hand who made the patterns for these amazing castings.
Love the patience for straightening those casings. Great work.


----------



## mayhugh1

While procrastinating over the intake manifold drilling I tried to keep the project moving along by working on the valve covers. This project has taught me to spot a problematic casting even from a distance, and my experience tells me the valve covers will be the last ones to require straightening. Besides having a twist along their major axis, their thin half-shell shape had to be spread to fit completely across the heads. Compared with the intake castings they weren't difficult to correct, but they were also about 3/32" too short for my heads which wasn't correctable. I couldn't figure out a way to safely stretch them, and so I settled for an alignment of their fronts with the fronts of the heads since this was the most prominent area of the engine. This decision left a gap at the rear of each head; but, even worse, the threaded holes for the cover's rear mounting bolts almost completely missed the rear mounting flange on the head. This was disappointing, but the defective threads will eventually end up hidden under the valve covers. The increasing front-to-rear mismatch of the cover's mounting hole bosses with those in the heads tells me that maybe the valve cover shrinkage wasn't fully compensated. The surfaces of the valve cover flanges were lapped instead of milled because the castings were too flexible to be safely supported for machining.
I've noticed my head castings seem to be different from those in the photos on Gunnar Sorenson's website as well as those on the Quarter Scale Merlin website. There is a series of holes in the top surfaces of my heads that were probably used for core supports. I hope my heads aren't an early obsolete version, because measurements I made show the required surfacing operations for the camshaft support blocks will leave the top surfaces dangerously thin. I guess it's possible that the mismatch that I encountered between the valve covers and the heads was actually the fault of my heads and not the valve covers.
The valve covers were match-drilled to the heads using 2-56's, and I decided to also use these smaller bolts for the intake manifold instead of continuing with the 3-48's. This gave me a opportunity to experiment with bolt hole clearances, but I eventually ended up again with a .004" diametral clearance which meant that the head mounting holes needed to be drilled and tapped with a positional accuracy of +/-.002". This was one of the reasons I'd been putting off the manifold drilling.
After finishing the valve covers, I finally began the tedious process of drilling the mounting holes for the intake manifold. I match-drilled the side flanges of the assembled intake manifold to the heads using strips of gasket material sandwiched between the two to account for the thicknesses of the intake manifold gaskets. There will eventually be a total of eight manifold gaskets. Six of them will used in the assembly of the manifold itself, and one will be used between each head and the manifold. I purchased a sheet of 1/64" fiber gasket material with an actual measured thickness of .013" to use for the temporary spacers and then, later, for the gaskets themselves. After drilling and tapping all the mounting holes in the 60 degree valley, any other gasket material that deviates more than .002" from this value may no longer work.
Eighteen of the seventy manifold mounting bolts went through the manifold's plenum, and they had to be carefully drilled from both sides of the manifold before being reamed to their final diameters in three steps for the 1-1/4" 2-56 mounting bolts. The reaming was complicated by the rounded interior surfaces of the plenum that continually pushed the reamers off trajectory. All these new long bolts were slightly bent, which isn't at all unusual, and this took up most of the their clearance allowance. After match-drilling and tapping all the manifold mounting holes in the heads, I performed a test to see how critical my hole alignments really were. I increased the effective gasket thickness by .004" by adding a sheet of paper to the strips of temporary gasket material between the manifold and heads. Sure enough, the additional .004" material shifted the manifold holes with respect to the threaded holes in the heads so that only a few of the bolts could be inserted. When the actual cylinder liners and liner collars are machined later, their dimensions will have to closely match the temporary Delrin parts used to fit the manifold. 
In total, 180 hole pairs were match-drilled and tapped in order to install the manifold and valve covers onto the heads. I ceremoniously retired the single 2-56 tap that did all the work by grinding its end off so it can someday takes its place as a piece of shafting or a cutting tool in another project. - Terry


----------



## ozzie46

Amazing!! Your ability to overcome obstacles and press on with this project is truly inspiring.

  The finished product will be a testament to your tenacity and skill. Roll On!!!

Ron


----------



## napoleonb

I seldom post on this forum but you are the main reason of my precense the last years. Your projects are truly inspiring and well documented! 
The engine castings for this project are absolutely beautifull and your solutions and plan of operations mindboggling.


----------



## mayhugh1

I drilled and tapped yet another 60 hole pairs in the heads for the exhaust tips as well as a pair of coolant outlets at the top front of the engine. Installing the exhaust tips was more interesting than working on the intake manifold or the valve covers since I got to add a new part to the assembly for every four new hole pairs I created. The exhaust tips are beautiful castings and needed only light facing and drilling. They add realistic detail to the engine that would be very difficult to duplicate even with CNC capability. 
Only one pair of castings was supplied for the coolant outlet tubes. In the full-size engine, coolant flows between the heads and a header tank located at the front of the engine. The drawings and notes accompanying the castings don't provide any design detail about the tank, nor anything else about the coolant system for that matter, but a riveted sheet metal tank is shown installed on the quarter scale prototype in the original designers' video. A photo on their website shows the outlets installed on the front-end of the heads' manifold flanges, and another photo shows the rears of the manifold flanges drilled and tapped for second set connections to the coolant jacket. Castings for these connections were not supplied, but I also drilled and tapped these holes even though I haven't yet figured out how they'll be used.
The exhaust tips complete my trial assembly of the 30 machined castings forward of the wheel case. My original goal was to get the castings assembled before investing any time or material into the bar-stock components since I had some misgivings about actually getting the castings assembled. I would continue with the foundational machining on the remaining 18 castings and complete the entire exoskeleton of the engine, but the wheel case castings need to be match-machined to bar stock components that I'll have complete first.
A third of the castings and half of the engine's complexity will end up at the rear of the engine behind the wheel case. This is where my understanding becomes a little fuzzy about just how much of the model's development was actually completed. This is also where the notes accompanying the drawings begin to thin out, and comments containing the words 'proposed', 'try', and 'somehow' show up with more frequency.
I included photos of the assembled castings for which nearly all of the machining has been completed. The very last photo shows the 18 un-machined castings that will eventually take their place at the rear of the engine. Although these photos may imply that much of the build is behind me, I've really only scratched its surface as there are probably a thousand parts yet to be machined. (The full-size engine had over 11,000 parts.)
My current plan is to start working on the crankshaft and the bar stock components associated with the overhead cam drive housing. The cam housing is needed so machining on the rest of the castings can continue. I'm including the crankshaft so I can work on a component that doesn't require a bunch of tapped holes.
The Merlin crankshaft is a thing of real beauty, and I'm looking forward to holding it in my hands. It'll be my first attempt at machining a complex multi-throw crank from a single billet. A chunk of 1144 stress proof steel is on its way, and I'm currently studying George Britnell's excellent tutorial on crankshaft fabrication. - Terry


----------



## Swifty

Every time I see those castings, I'm amazed at the quality. 

Paul.


----------



## Davewild

Beautiful work terry, man that looks cool


----------



## gbritnell

My goodness that is one impressive looking engine! I don't think I would have a problem with the machining aspect of the project but I probably would have quit after finding so many mismatches and warpage. I applaud your tenacity.
gbritnell


----------



## kvom

If you had drawings of everything then in theory a bad casting could be drawn and then 3D printed; no warpage and the holes would match up.


----------



## wirralcnc

Terry
I might send you my set of castings for you to put all them tapped holes in.


----------



## sbdtasos

Hi terry
as always extremely perfect ..
i know that project like yours need so much time that you can not imagine
thanks for that you offer
exelent job

ps: all the money that you spend to buy this kit you will spend to buy the bolts for it lol: P: P


----------



## gus

We are getting excited and quietly waiting to see the video of this engine roaring away.

You are  SuperMachinist/EngineBuilder.


----------



## barnesrickw

The size of the blower is amazing. Full scale must be a powerful engine.


----------



## mayhugh1

I came across two online references to help me with machining the Merlin crankshaft. The first is a thread by a Belgium builder 'Zapjack' who fabricated this exact part with some 200 hours of work over a period of two months nearly three years ago. It's located at
http://www.homemodelenginemachinist.com/showthread.php?t=18747
He first published his build on a French forum and then cross-posted its highlights on HMEM in 2012. The original non-English forum where he posted his realtime build as well as an additional two year's work on his Merlin is located at:
http://www.usinages.com/threads/rolls-royce-merlin-v12-echelle-1-4.42350/
Unfortunately, his posts faded away in 2014 after completing the crankshaft, prop shaft, and cylinder liners as well as the crankcase and some of the cylinder block machining.
The second reference is George Brittnel's crankshaft tutorial inside his V-8 flathead build thread starting at:
http://www.modelenginemaker.com/index.php?topic=3846.210
Since I have some limited four axis CNC capability, my hope is to combine the information in the two threads and take advantage of my Tormach's fourth axis. I don't if my particular CAM software can be convinced to continuously machine the offset throws from billet, but it's worth several days of experimenting to see just what it can do. Hopefully, I can at least come up with g-code for some of the tedious roughing.
Work started on the crankshaft by sawing off a 10-1/2" length of 2-3/4" diameter 1144 steel. I've not used this particular alloy before, but it comes highly recommended for crankshafts by George. I bought a piece long enough for two parts just in case my learning curve takes an ugly turn. I purchased the metal from an online supplier who advertises it as 1144 Stressproof or 'equivalent'. The 'equivalent' sounded ominous, but their price was nearly half that of the other online supplier that I've used used in the past for material not available in my scrap collection. Since Stressproof is a brand name, I'm not sure it's legal to use it to advertise a generic equivalent.
Anyway, after facing and center drilling one end, I turned the o.d. down to 2-1/2" over as much of the length as I could before flipping it around, facing and center-drilling the opposite end and then turning the rest of the o.d. After cutting through the black outside layer I was relieved to find the material turns pretty similarly to mild steel. The chips resemble those from free machining steel, and the surface finish is similar. An amazing thing I noticed was the material's consistent o.d.. The run-out at the end of the 10.5" long un-machined round was only .002" after being chucked in my lathe's 3-jaw without tailstock support. The material I purchased was their low-end cold-roll, but it is also available as precision ground and polished.
After studying the crankshaft drawing I realized just how complex this part is. The webs are not identical, and there are many machining features associated with them. Another wrinkle is that each bearing and crank pin is bored-through in order to reduce weight. In addition, both ends of each of these bores must be counterbored for end plugs since internal oil passages supply pressurized oil from the mains to the crank pins. The workpiece I'm starting with weighs 18 pounds, and the weight of the finished part will be only 1-1/2 pounds. A lot of metal has to be removed from some very difficult to reach locations. 
The first and probably most important decision to make is how the workpiece will be held for offset turning. George's offset end blocks looked good to me as they positively grip both ends of the heavy eccentrically rotating load. When I tried to adapt his technique to my crank I realized the four-sided headstock block he used for his 90 degree throws would not work with my crank and its 120 degree throws. I looked at using a hexagonal end block but I wasn't happy with two of the four jaws gripping on the corners of the block. A 12-sided polygon would work, but it wouldn't have long enough sides to handle the crank's 1-1/2" stroke in my 4-jaw.
Zapjack center-drilled the ends of his workpiece for center-turning on each of the three offset axes. I don't have much experience with center-turning, but supporting the weight of this workpiece between two centers concerned me. None of Zapjack's photos showed his headstock drive, but I can't imagine it was merely a conventional drive dog. 
I decided to both center-drill and mill reference flats on both ends of the workpiece. Currently my plan is to use the center-spots to locate the workpiece between centers while finish turning the crankshaft. However, I will also add a head support block similar to George's to secure the crankshaft to my lathe's faceplate. The tailstock end will just be supported in an offset center-drilled spot by either a live or dead center. Most of the material will be initially roughed out on the mill and probably with the workpiece held horizontally in a vise. If I run into problems and have to come up with a plan B, at least I'll still have the flats and center-drill references to work with.
A first pair of reference flats was milled into each end of the workpiece while it was held horizontally in a vise. The workpiece was then stood vertically in the mill and clamped against an indicated reference plate using a ground block between the flat and the plate. I was relieved that this rather dicey set-up was actually able to hold the workpiece truly vertical and was rigid enough to mill the additional flats. Zapjack actually removed the table from his mill so he could perform a similar operation. The 120 degree center-drills were then drilled, and the remaining two flats were milled on the perimeter. Both ends of the workpiece were similarly machined but an additional nine holes were added to the front-end. These will eventually be tapped and used to secure a driveshaft to the front of the finished crankshaft. 
Because of its complexity and the need to modify its dimensions to fit my 'short' crankcase, I modeled the crankshaft in SolidWorks so I could better understand what I will be up against. This crankshaft looks like a part that can be easily ruined by lapse of attention. It also looks like it will be the most complex part I've ever attempted to machine. It wasn't too long ago, when I was intimidated by what now looks like a pretty simple crankshaft in my 18 cylinder radial. - Terry


----------



## Scott_M

Wow Terry, that is gonna be a lot of work. And as you said a little distraction could ruin a bunch of work. Best of luck, I'll be watching.

Scott


----------



## petertha

mayhugh1 said:


> None of Zapjack's photos showed his headstock drive, but I can't imagine it was merely a conventional drive dog.  Terry


 
I might be way off base but between the pics & posts it almost looks like the jig plate he used on the milling operation somehow served double duty in the lathe setup? I see some sort of thickish pin, but not sure if that's what's engaged to a faceplate slot?

I know this is a few miles down the road, but what are your thoughts on the journals final sizing/finishing - compound mounted grinding attachment or...?


----------



## Mattsta

You're a very brave man Terry! LOL!

It's going to be a treat to see how you manage this insane challenge!


----------



## gbritnell

Hi Terry,
Another suggestion I could make which would help in the crank pin turning operation is this but it depends on the tooling you have available. When starting out in this hobby I had limited tools, a lathe with a milling attachment, so it took some creativeness to machine certain parts. The one thing that I did have was a face plate for the lathe. I don't mean a driving face plate but a true face plate. Depending on the size of the lathe a face plate can have holes or slots in it, or both. I don't have one for my Logan lathe and have been looking for quite some time. It's not that it would get used a lot but they sure are handy for jobs such as this. 
If you do have one I would make the fixture block and securely mount it to the face plate with the required offset. Another nice feature of a face plate is you can bolt opposing weight to the plate to somewhat counterbalance the working weight. For the tailstock end you could still use the center drilled holes in the stock.


----------



## mayhugh1

George,
Thanks for the advice. I do have a facplate for my lathe and will likely follow your advice when I get to the crankpins. I'm currently experimenting with cutters for the various operations I expect to have to do. The one I'm having trouble with (no surprise) is the deep grooving cutter for the crankpin turning. I admit I haven't yet tried to duplicate your 1/2" bifircated HSS cutter. I've been trying to use carbide grooving inserts that I have on hand. I have one in particular that will do a nice job, but the deep blade holder I need doesn't commercially exist, and it looks like a useable shop-made equivalent may not be practical. I may be gravitating to something similar to your cutter. If it isn't too much trouble could you post some profile photos showing the rake and relief angles? I've been wondering why you didn't start with a 1/2" HSS blade in a toolholder instead of grinding your tool from a full 1/2" square blank? I'm seeing a lot of side flex on the 1.7" long 3/32" wide 1/2" HSS blade cutter that I've been running some quick and dirty tests with. And that is just with plunge cutting. I'm not sure the toolholder is causing this, but I might be wrong and thought I would ask for your opinion in case you had already been down this road. -Terry


----------



## gbritnell

Hi Terry,
I have in the past used high speed cutoff blades. The problem I had was not with the plunging but rather when moving from side to side to clean up the journal the tool would flex. On a crank with no counterweights the tool can be shorter and therefore is more rigid. 
This is why I ground my own. I will admit it was a tedious job but once finished it did a wonderful job. The width of the tip is a little less than half the journal width so that when moved from cheek to cheek it will overlap at the center with the radius on the corner. It has no top clearance. It's just flat like a cutoff tool. The sides and front have about 2 degrees on them. Once I had the blade ground parallel I went back and removed about .020 from each side leaving about .200 of full width at the tip. This would allow me quite a few sharpenings if needed. To split the tip I used a thin abrasive disc to rough it and then used a tapered diamond burr to give some clearance to the inside edges. I will take some pictures tomorrow morning and post them for you. 
gbritnell


----------



## Charles Lamont

A potential problem, especially with a broad faced tool, will be chatter.
For the far less complicated Seagull crankshaft I finished the pins in bottom back-gear. That is 25 rpm.


----------



## Blogwitch

Terry,
I have to disagree with you in that commercial ones are not available. Have a look at this video from Mircona, start at 1 minute and it shows the type I bought from off ebay for about £25 each, I bought a left and right hand one, plus a load of different tips, including half round ones for giving the stress reducing corners in deep cuts. The advantage of these tools is that they can cut in all directions, not just in and out, but side to side as well (within logical reason). The ones I bought will give a depth of cut of around 1.5".

[ame]https://www.youtube.com/watch?v=ZUwJXZEyctI[/ame]

I am not trying to persuade you into buying any, but maybe to have a look at how they are made, to give you that long range support. I know of a couple of people who I sent the link to and have copied this design and fitted their own tips to it, and they have worked very well indeed.

This is mine at work doing a bit of deep parting.

[ame]https://www.youtube.com/watch?v=BG4qEw3eMcQ[/ame]

Great work and best of luck with the rest of your build.


John


----------



## digiex-chris

I was able to make an 1/8" HSS parting blade into a bifurcated tool for this purpose and make it perform cutting sideways by making a toolholder for it instead of using a standard parting blade holder. Rather than clamping down like most parting blade tool holders do, I cut a slot in the side of my tool holder the depth of the parting blade, then made a clamp to clamp the blade sideways, giving it more side-to-side support. I also used a T shaped blade, so that it was easy to round the edges and make some relief on the sides. I broke the tip with the edge of my grinding wheel. I also added a few degrees of top rake to ease the cutting somewhat. I used it mostly for light finishing cuts and cleaning up the corners. I'd done the roughing on the milling machine using my dividing head to turn it.


----------



## DICKEYBIRD

Can you set up a faceplate on the 4th axis & a tailstock in the mill and make the roughing cuts with an endmill?  A rougher in your Tormach would move metal quickly.

Some of the videos of "real" crankshaft manufacturing show it being done that way.  I think they were mounted on center and the Z-axis traveled up & down in sync.  'Tis somewhat beyond hobby CAM though!

Just a thought.


----------



## mayhugh1

John,
Thanks for the heads-up. The Mircona tools look like an optimum solution. I checked Ebay but only found some inserts currently available. I wish they had a US distributor since overseas purchases directly from the manufacturer don't typically seem to go well for me, and they nearly always end up with my credit card being suspended even when I warn my credit card supplier.
What I was referring to in my post was the lack of a deep blade holder for my Iscar GIP inserts. These inserts cut steel very nicely, have a usable corner radius; and I was even able to do limited side-to-side cutting with them. The holder I have for them is a similar style to the Mircona holder but nowhere deep enough (I need 1.7" depth), and since the insert shape is different, the method of gripping it is different. 
I also have a number of no-name GTN inserts and a usable deep blade holder for them. Although, on a good day, I can usually use the combination with aluminum, these particular inserts work poorly with steel, and there is no side-to-side cutting with them. There is a bewildering selection of inserts available, and it's expensive to buy and test especially when the name brands can cost more than $20 each; and a minimum buy of ten is often required. I may use what I have for the interrupted clean-up of the mill-roughed bearings, but so far George's cutter looks like the best solution for finishing without investing a bunch of money. - Terry


----------



## mayhugh1

DICKEYBIRD said:


> Can you set up a faceplate on the 4th axis & a tailstock in the mill and make the roughing cuts with an endmill?  A rougher in your Tormach would move metal quickly.
> 
> Some of the videos of "real" crankshaft manufacturing show it being done that way.  I think they were mounted on center and the Z-axis traveled up & down in sync.  'Tis somewhat beyond hobby CAM though!
> 
> Just a thought.



I'm going to rough the mains out on the mill but with the workpiece held in a vise and manually indexed. I'll probably use the fourth axis for the crankpins. I just found out I can remove material a lot faster if I put the cutter directly in an R-8 collet rather than use a TTS toolholder, but this causes clearance problems between the fourth axis and spindle. The vise also gives me a more rigid set-up for roughing. - Terry


----------



## mayhugh1

I decided to tackle the main bearings first. My hope is to completely finish them before starting on the crankpins so I'll have all the needed cutting tools in hand and some experience with them before dealing with the more complicated offset turning. Finishing the main bearings first will also make them available for extra workpiece support during the offset operations. 
After some playing around with my CAM software I found I could easily generate the g-code needed to rough out both the main and crank pin bearings. I could have used my fourth axis to automatically index the workpiece, but I was concerned about the rigidity of the relatively long workpiece during the heavy roughing operations even with tailstock support. I chose, instead, to support the workpiece horizontally in my mill vise and to manually rotate it in 60 degree increments for the main bearing roughing. For roughing, precise indexing isn't really required; and an electronic protractor on the end flats of the workpiece provided more than enough accuracy. This setup will be more troublesome for the crankpins with their deeper roughing depths because of interference with the vise. The fourth axis becomes more attractive for roughing the crankpins since I'll be able to support the center of the crank with a bearing block under the center bearing.
Because I have no experience with machining Stressproof, I ran some experiments on my Tormach to find a set of usable feeds and speeds. My tests were with a 4 flute 3/8" carbide end-mill using a 1.7" stick-out since I'll need this later for the crankpin machining. With the cutter mounted in the spindle in an R-8 collet (no TTS toolholder) I eventually arrived at a .150" DOC running at a 20 ipm and 2500 rpm. I tested a portion of the g-code by roughing out a full bearing in a piece of scrap. There was little to no chatter, the chips came off with a light straw color, and the load meter showed my mill was running at only about .6 hp. With this removal rate the roughing operation for all seven main bearings required about 70 minutes of actual machining time. After it was completed I saw no visible wear on cutter, and so I'll be able to re-use it on the crankpins.
The workpiece was then moved to my lathe's 3-jaw plus tailstock for the next roughing operation. This time the hexagonally shaped main bearings were turned to get them circular. I used an NGTN-3-PV52 carbide insert in a blade holder extended 1.7" beyond the tool post with the lathe running at 120 rpm for this interrupted cutting operation. This particular 1/8" wide blade and a companion box of equally wide no-name inserts was one of my first Ebay tooling purchases many years ago. It taught me that my lathe didn't like cheap 1/8" imported inserts, and so the parts had been languishing in one of my drawers. I decided to try them on this interrupted cutting operation since I was worried about chipping my more useful ($) inserts. I won't say the cutting went smoothly, but it was fairly quick, and plunge cutting accomplished what I needed. Once the bearings were turned fully circular and the insert was cutting continuously, though, the chatter was too excessive to continue especially on the bearings downstream from the chuck.
I was left with nearly .100" excess diametral stock that I needed to remove from each of the seven bearings before moving on to the finishing operations. I used a Dremel diamond abrasive disk to cut a Britnell notch in the center of the cutting edge of the insert to reduce its contact area with the workpiece. This totally eliminated the chatter and produced a beautiful surface finish. This particular insert had enough side clearance for limited side-to-side turning. Even though I ground relief on the inside of the notch, my side-to-side d.o.c. was limited to about .005" due to the side flex of the 1/8" wide blade holder.
The last roughing, or semi-finishing, step on the main bearings was to clean up the faces of the webs on each side of the bearings. During the mill roughing operation I ran the cutter down the right side of the slot while it was cutting 100% of its width, but on the return pass it was engaged by only a fraction of its width. Tool deflection during the full width pass caused the cutter to remove excess material on the right side of each slot. Indexing left a pattern of deep machining marks. I included excess stock in the g-code to account for this, and so the purpose of this last roughing operation was to remove just enough material to clean up the web faces so their locations can be consistently measured. The widths of the bearings will be brought to their final dimensions later during finishing. 
To face these walls I used a small boring bar mounted as a conventional radial turning tool. This set-up nicely handled the left web faces, but I had to invert the cutter and run the lathe in reverse in order to face the right-sides.
The final step on the main bearings will be to complete their finishing operations. In order to do this I plan to grind one of George's HSS bifurcated tools. I thought about just continuing with my notched insert, but a HSS blank will allow me to increase the effective blade width nearly 50% for improved rigidity and elimintate the holder for the blade. I also need .020" fillets on the corners of the tool, and these will be easier to grind on a HSS blank than on a carbide insert. In addition, I'll likely also construct the fixture needed to support the driven end of the workpiece against my lathe's faceplate so I'll have the option of finishing the main bearings between centers. - Terry


----------



## Charles Lamont

I strongly recommend against taking the mains to finished diameter before getting the pins rough milled and turned to the same stage as you now have the mains. You just don't know what built in stesses there may be in the bar, nor how these may cause distortion when you take metal away asymmetrically. I would suggest you rough the whole thing, *everything*, including webs, weights, and holes, leaving the bearings  +10 to 15 thou on diameter, before going for finished dimensions on* anything*.


----------



## mayhugh1

Charles,
That's probably good advice that I think I'm going to follow. The only legitimate reason I had for finishing the mains first was that I was hoping to get to run the lathe at a higher rpm for their finishing operation before I unbalanced the heavy workpiece. But, as I've since learned, my cutters are limiting me to 120 rpm anyway.
My understanding of Stressproof is that it shouldn't create the warping issues that Zapjack ran into with his crankshaft using SAE 4140. George Britnell mentioned in his flat head build that he has seen no evidence of warping in his cranks since he started using 1144. In any event, I can see no downside to roughing most the feature before beginning any of the finishing operations, and so I'm revising my plan. I'll still have to leave the boring operations that hollow out the bearings until after finishing, though, because those operations remove all my machining references on both ends of the finished crankshaft. Thanks. - Terry


----------



## mayhugh1

I decided to take Charles' advice and hold off finishing the main bearings until after I complete more of the roughing. Since a lot of what I'm doing right now is in new territory for me it's also best I gain my experience during the more forgiving roughing phase. As a precaution and before doing additional cutting on the workpiece I measured and logged the current locations of the roughed-in main bearings to verify I actually had the excess web stock that I had planned. 
For the crankpin roughing I used my mill's fourth axis to support and index the workpiece instead of manually repositioning it in the mill vise as I did for the main bearings. The deeper cuts needed for the crankpins would have required many error-prone repositioning and re-referencing steps in order to work around the vise. The downside of roughing between centers on the fourth axis, though, is a considerable loss of rigidity compared with using a mill vise. A 4-jaw chuck added to the fourth axis to support the front end of the workpiece would have blocked my spindle's access to a significant portion of it since I'm not using a toolholder for the cutter.
I machined a fixture for a close slip fit over the crankshaft's front spigot which was previously machined with three peripheral flats and the four axial center-drilled holes that define the four axes of the crankshaft's bearings. The crankshaft is secured in the fixture by cup setscrews bearing against the three flats, and the whole assembly is bolted to the fourth axis face plate. I machined the mounting slots in the fixture so it can also be used with my lathe's faceplate while turning between centers on any of the crankshaft's four axes.
In use, after positioning the desired axis of the crankshaft between centers, the setscrews are tightened against the flats, while the assembly is rotated to align the fixture's mounting slots with those on the machine's faceplate. Once this is initially done for one offset axis, the setscrews may be loosened and, with the tailstock withdrawn, the workpiece can be simply pulled out of the fixture and rotated to an alternate offset axis without touching the fixture's mounting bolts. The axial alignment is controlled entirely by the machines' centers. This fixture allows me to move the crankshaft between either of my lathes or mills' fourth axes without worrying about losing axial alignment. The fixture merely adds the rigid support needed at the front of the workpiece. The rear of the crankshaft is supported by the centers in the machines' tailstocks. The fourth axis can be zero referenced by indicating the appropriate flat on the tailstock end of the crankshaft.
In order to handle the heavy crankpin roughing I felt additional support was needed at the center of the workpiece. Since I planned to rough the crankpins with the fourth axis aligned with the axis of the main bearings, my vision was to anchor to the mill table a bearing block having a close slip fit to the center main bearing. This would allow the fourth axis to freely rotate, but it would limit any flex or vibration at the center of the workpiece. After a few machining attempts I realized I probably wasn't going to easily get the fit I wanted to my roughed-in bearing. I settled, instead, for a tight fitting block that provided the support I wanted, but one that would have to be loosened to allow rotation of the workpiece. As a result I divided my roughing program into six smaller programs that required me to manually index the fourth axis before running each one. Actually, I've learned from experience that my equipment and its operator are usually much happier if long untested grueling programs are broken into a number of smaller programs. A lot of things can go wrong, and when they do it can be difficult to recover a valuable workpiece.
I had to increase the stick-out of my 3/8" cutter by an additional .2" for a total of 1.9" in order to clear the fixture while machining the front of the workpiece. This left only about 1/2" of the cutter's shank inside the R-8 collet during the 18 ipm, .150" d.o.c. roughing operation. I monitored the slip, but it amounted to only .004" over the entire two hour machining time.
Since I really didn't like interrupted lathe cutting operation that previously turned the hexagonal mains into circular bearings I decided to clean up the crankpins in the mill while the crankshaft was in the fourth axis setup. Since typical mill cutters do not have flat bottoms due to the relief ground into them, the roughed-in crankpins did not end up with perfectly uniform diameters across their widths. I couldn't use my center support for this operation, and the chatter while machining the two central crankpins was severe enough that it affected the surface finish.
I moved the crankshaft and its fixture over to my lathe to verify my work-holding scheme actually worked there and also to clean up the crankpins. Even though their roughed-in states were just fine as they were, I'm going to be looking at them for quite some time; and their surface finishes bothered me. I also faced the webs to remove the spoke-patterned grooves left by my mill's roughing operation. These grooves were significantly more shallow than those left on the main bearings. I suspect part of the problem with the main bearings' webs was created by an inconsistent manual repositioning on my part. These re-facings allowed me to make and log consistent measurements to determine the actual locations of the crankpin bearings and the excess stock that will eventually be removed. 
For these operations I initially ran the lathe at 100 rpm, and all the carbide cutting ran fine with no chatter and excellent surface finishes. I eventually speeded the operation up to 300 rpm, and this was the point where chatter just began to set in. However, it wasn't severe enough to affect the surface finish. The oscillating assembly, though, while running at 100 rpm was just too hypnotic; and my focus seemed to be continually and dangerously drawn into it. 
I added a counterweight to the faceplate to balance the rotating assembly at 300 rpm. I also changed my tailstock's dead center to a live center when it dawned on me how much time this workpiece is going to be spending in the lathe. 
My next step will probably be the roughing-in of the web counterweights. I'm currently planning to use my CAM software to try to coax my Tormach into doing most of the work for me on its fourth axis. - Terry


----------



## petertha

That's quite the setup. Looking good!

- on the end-milling operation, have you noticed any advantage or disadvantage to types of end mills? By that I mean those notched, toothy roughing end mills vs. more conventional spirals. Only reason I mention is I tried one for the first time the other day & was pleasantly surprised. Aside from nice short curly shavings, seemed like less load when ploughing through material & interrupted cuts.

- I've seen CS build pics where some guys epoxy in supporting wedge blocks progressively between the webs when the centers are in off-center positions - I assume to prevent 'accordion distortion'. But maybe that's more related to lathe-mode cutting vs your milling + support post. Have you found a need for anything like this so far? (I'm not really sure how one would measure its actually bowing anyway unless it was returned to neutral axis).


----------



## mayhugh1

Peter,
I've tried those HSS corncob roughing cutters in aluminum, and they do work really well. I have no experience with them in steel, though, and since the ones I have are relatively low end I wasn't confident enough in them to try them in this new (to me) steel. The cutter I used for these roughing operations was a 4 flute variable helix cutter that I purchased with no other information on it at a show two years ago. It has a dark purple coating on it that still shows no sign of wear. I used tbis same cutter on 304 stainless during my 18 cylinder radial build. I wish I knew more about it but it has no markings on it.
I've seen those wedges also, and my own questions about them was one of the reasons for the center support that I used for the heavy cutting. The only roughing that is left is on the webs, and I hope to use some kind of support while milling them also - maybe even the wedges. Since I now have nice clean turned faces on all of the webs I should be able to tell by indicating them if the crankshaft does warp either from relieved internal stresses or from the forces of heavy cutting. Finishing all the heavy cutting before starting the finishing, as Charles pointed out, might let me recover from any induced distortion. - Terry


----------



## mayhugh1

We got to spend the past week with our grandkids, and so my shop time was limited to only a handful of late night hours. The break did give me an opportunity, though, to re-think my order of the crankshaft machining operations. I've not been looking forward to the through-drilling and associated counterboring specified for the Merlin's main and crankpin bearings. My next step was going to be to rough machine the webs. The original plan was to delay the through-drilling until after all the finish machining was completed since this drilling will remove the four center-drilled holes on each end of the workpiece. These center-drilled holes are required for all the remaining machining operations, and they will have to be replaced with machined buttons if the drilling is moved forward in the process.
Early on, it was obvious that the crankshaft would be very difficult to fixture for drilling on the mill after the webs were machined. Therefore, I had been planning to do it on my lathe using a custom made steady rest. After thinking about the design of this steady rest, though, I realized that it was going be a very significant project all by itself. I also began thinking about the forces generated by the offset drilling and how they might bend a completely finished crankshaft. There was also Charles' warning to leave ALL the finishing to the very end.
So, I decided to through-drill the bearings on the mill and to do it now before the web machining. With the workpiece vertically supported under my mill's spindle, the headspace was barely enough for the long drill I needed to use. Since there was no room for a drill chuck, I modified the diameters of the though-holes specified on the Merlin drawings so I could use an R8 compatible drill size. The drawings actually specify a slightly smaller hole size for the crankpin bearings than for the main bearings. Since I'll later have to make a special inserted counterboring tool to machine the counterbores, I elected to make both holes the same diameter. I selected the R-8 compatible drill size to be very close to the hole specified for the crankpins so I wouldn't significantly affect the crankshaft balance. I also had to shorten the shank of a very expensive long parabolic drill that was specially purchased for this operation.
The hole centers were accurately located using a spindle microscope, and the holes were reamed after being drilled so I could get an accurate fit to the buttons. The finished diameter was selected so I could use a piece of standard size drill rod later when I make the piloted counterboring tool. The buttons, themselves, were machined from steel although a softer metal could probably have been used since, with the live tailstock center, there's little relative motion between the machines' centers and the workpiece. I made several spare buttons with various degrees of light interfering fits so I could maintain a close fit in case the reamed holes open up later during use. (Actually, these 'spares' were my failed attempts to machine a pair with just the right fit.) The hope was that even if the new button centers did not precisely correspond to the original centers, the remaining machining would correct the crankshaft's axes to them.
There are some important recesses that must eventually be bored on each end of the crankshaft. These recesses locate power take off shafts at each end of the engine, and they must be concentric to the main bearings. I considered also boring these while I had the workpiece fixture'd on the mill, but adding them at that time would have complicated the button design. A reasonably simple steady rest will be needed to bore these on the lathe after the remainder of the machining is completed.
After all the drilling was completed, I installed my best fitting pair of center-drilled buttons into the ends of the workpiece on the main bearing axis. I installed the workpiece on my Tormach's fourth axis to prepare for the web roughing operation and also so I could check the resulting runout of the main bearings. I was pleasantly surprised (shocked, actually) to find it measured less than .001"
The next step will finally be the rough machining of the webs. - Terry


----------



## gbritnell

Hi Terry,
In my experiences of using 1144 steel I have been very satisfied with the accuracy when machining. When roughing the main journals and throws I took some fairly aggressive cuts with a 4 flute end mill and like you ended up with minimal distortion. 
The only crank I ever ground was the one in my 302 engine. At that time I had a 9 inch South Bend lathe and made a tool post grinder for it. The biggest problem I had was finding a grinding wheel narrow enough to traverse the journals to get about .020 overlap at the center. I purchased a wheel .250 wide and then while spinning it I used a single point diamond dresser to thin the wheel to about .180. 
This was back in the days when I was just starting out making multi-cylinder I.C. engines and the only steel I knew of was 1018 or tool steels and really didn't want to tackle anything like 4130 or 4140. I had machine some 8620 for a fellow who wanted to make a full sized camshaft for a diesel engine fuel pump but I only had to rough turn it. It was then case hardened and ground. 
Some fellows use 12L14 steel and while I do make miscellaneous parts from it I haven't made a crankshaft. 
Your vertical drilling/reaming setup looks a lot like what I do. When working in the pattern shop we had some large, very accurate V-blocks and they worked great for doing vertical machining operations on both rectangular and round stock. I have always wanted to buy one but the cost for something like an accurate 8 or 10 inch V-block was more than I wanted to spend. 
I'm following along to see the further operations. 
Even though this is your first foray with this type of crank and seeing your other work I have no doubt that it will be a thing of beauty. 
gbritnell


----------



## mayhugh1

George,
Thanks for the comments. The 'long' vee-block in the photo is actually two short ones separated by a 2-3-4 block. The clamp on the top of the stack is holding the sandwich together and keeping it from tilting when when it is drawn up toward the vertical reference plate. I also have a ground bar between the vertical plate and the reference flat on the bottom end of the workpiece for good measure. 
Might I ask what is the minimum d.o.c. you are able to take off with your HSS bifurcated tool? I'm still trying to make a carbide grooving insert work, but I don't seem to have control over the d.o.c. to better than .002-.003" (diameter). - Terry


----------



## gbritnell

Hi Terry,
As I recall I didn't take much more than .02 per cut (dia). The biggest reason being that as the the bifurcated tool was moved into the material once it got to the depth of the groove it would start to chatter so I didn't press it. The one thing I did do was to move the tool left and right as I was plunging in. This allowed me to take a slightly deeper cut.


----------



## mayhugh1

My next step in the crankshaft construction was to rough machine the webs. The webs on this crankshaft are pretty complex, and a lot of metal has to be removed from the workpiece in order to form them. Since I had good success with the crankpin roughing on my four axis Tormach, I decided to rough machine the webs similarly. I chose to manually index the crankshaft around the axis of the main bearings so I could again use my shop-made center bearing support since I was expecting chatter from the deep passes on the relatively thin webs. I also limited the maximum cutting depth at each indexed position to half the diameter of the workpiece so I could use a minimum stick-out for the cutter. I configured my CAM software to create g-code that would allow me to manually index the workpiece in 90 degree steps for two complete revolutions. I removed most of the excess stock during the four 90 degree increments of the first revolution using a d.o.c. of .15" and a feedrate of 18 ipm. This coarse waterline operation left .15" tall steps on the machined surfaces in addition to a .015" base layer of excess safety stock. This coarse stepped surface would have been OK if I had known for sure that I will be able to later run a continuous four axis finishing pass. Right now, though, that's not 100% certain. Continuous four axis machining was the holy grail for my particular CAM package (Sprutcam) during its past several years development. This feature, with a number of restrictions, was first made available in the version of the software that I upgraded to some four years ago. But, with only the modest effort I've put into it so far, I've never been able to actually machine a real part using this new operation. To make things a little more interesting there also seems to be issues with inverse time feed-rate in my particular version of Mach3. This G93 mode is used by my CAM's postprocessor for this particular operation, and it tells Mach3 the time to be used for each incremental blended move rather than specifying an actual feedrate. (This is done because mixed units of inches and degrees are being blended.)
Because of these uncertainties, another roughing pass was run during the second revolution, but this time with a d.o.c. of .015". This second pass reduced the size of the surface steps just in case I have to manually finish the webs' radial surfaces.
Since I already had a lot of time accumulated in this workpiece I did something that I rarely intentionally do. I created a short dummy workpiece from a piece of scrap steel so I could test a portion of my web roughing code on a single pair of webs. The test ran pretty much as expected except the feeds and speeds I had been using for Stressproof seemed much too high for the cold rolled I was using for the test. I had to drop the 3/8" cutter speed from 2500 rpm to 2100 rpm and the feed rate from 18 ipm to 10 ipm in order to bring the chip color back down from deep purple to light straw. This really surprised me because I was expecting the machinability of my cold rolled blank to be somewhat better than that of 1144. But, since I don't know where it actually came from, it's possible that my test blank is just a chunk of garbage steel. I found the uniquely rolled shapes of the Stressproof chips interesting enough to include a close-up photo. Maybe I've not worked very much with quality steels, but I'm learning to really like this material.
The three hour web roughing operation nearly doubled the amount of metal removed from the workpiece so far, and it is finally starting to look like a crankshaft. Except for the end spigots, the rough machining is now completed.
My next step will be to put some more effort into working with my CAM software to generate the toolpaths needed to finish machine the radial surfaces of the webs. If I can generate the tool paths I'll have my test part with its pair of roughed webs to use for testing. If I'm not successful, then I'll likely run some additional finer roughing passes in order to further reduce the amount of manual finishing. - Terry


----------



## Scott_M

Hi Terry
Looking good !
If you can find an long end mill like you are using with a corner radius of about .015" your waterline steps will blend really nice. A finish step of about .005" to .007" with a .015" corner radius would be really smooth and require little blending.

Just a thought, but I bet you already knew that 

Scott


----------



## mayhugh1

Scott,
Thanks for the suggestion, and no that didn't occur to me. If I can't get Sprutcam 7's rotary machining operation working for me on this I'll run another roughing pass just as you suggest. - Terry


----------



## mayhugh1

My ancient version of Sprutcam (7) software contains the first version of what the vendor called a 'Rotary Machining' operation. There are some restrictions, but this particular operation was designed to produce g-code with blended moves of three linear and one rotary axis to produce a continuous tool path for machining camshafts and crankshafts. I have respect for any software that can generate 3-D tool paths, but when a rotary axis is included I'm truly humbled. I've been playing with this particular operation on and off for the past several weeks and hoping I could apply it to the complex web peripheries of my Merlin's crankshaft. Most of my problems with this particular operation have been related to the fact that being a first release, it wasn't hardened against a newbie's attempts to use it. The manual for this software has never been one of its strong points, and so I typically learn new features by trial and error. Once I learned where the dark corners were, I stayed out of them, and eventually I was able to get some useable simulation results.
Even though this operation is categorized as a finishing operation, and unlike the other finishing operations in this package, a workpiece can be included in the simulation. In fact, I was able to import the simulation results of my roughing operation into this finishing program for use as a starting workpiece. 
The software is capable of working with a variety of end mill types, but this particular operation seems to prefer a ball mill. Because the webs have relatively wide flat surfaces, I spent a lot of time trying to make a 3/8" cylindrical end mill with .060" radius'd corners work. The radius'd corners were helpful in reducing the machining marks left on my test part during some of the complex reverse rotary moves.
Unfortunately, and this may be a common issue with other four-axis packages, a truly flat bottom is assumed for a cylindrical cutter even though nearly all endmills have bottom relief ground into them. I tried using a flat bottom counterbore on a test part, but the chatter was excessive and the surface finish was poor probably because this tool wasn't designed for side cutting. I've read that Sandvik makes a special cutter for this application, but I was unable to locate it. It sure would be useful when I start working on the camshafts.
The cutter relief in a stepped-over rotary operation will create a series of ridges around the machined part instead of a nice flat surface. The simulator isn't much help in tuning out these imperfections since it doesn't understand the cutter relief.
The software allows two choices for orienting the cutter: 1) normal to the cutting surface or (2) through the axis of rotation. My best cylindrical cutter results with acceptable machining times were obtained using a normal orientation and a spiraling .025" step-over. These parameters were finally determined by cutting actual profiles on a test part. The ridges left behind were high enough, though, that they would have to be manually ground or filed away.
I eventually migrated to a 1/2" ball cutter normally oriented to the part's surface with a lead angle of 10 degrees. This lead angle moved the zero SFM center point of the ball cutter off the tool path for a better surface finish. I was initially surprised to discover the ball cutter produced a nicer finish than the radius'd cylindrical cutter for the same step-over. The simulator also properly handled the material removed from the workpiece with the ball cutter. According to my calculations the theoretical scallop size was only .0002", and the machining marks easily polished out with a Scotchbrite pad.
I originally intended to machine the webs in pairs instead of trying to do all of them in a single operation. I ended up, though, machining them one at a time because of the way in which the software handles the rotary roll-over. Each rotary machining operation starts out assuming the rotary is positioned at the part's zero reference position. When the first operation is completed, the rotary has to unwind its accumulated revolutions and return to zero before the second operation can begin. I found it quicker to re-indicate the rotary's starting position myself rather than wait for it to return to its starting point. This also gave me an opportunity to vary some of the operation's parameters so I could learn more about fine tuning it.
The three hour rotary machining went extremely well considering it was my first serious attempt at using it, but I've learned to leave a maximum stock of only .010" or so in the future for it to finish. The operation makes some quick and unexpected moves off its spiral trajectory whenever it sees certain types of nearby cutting opportunities. It will try to clean out deep lateral ditches in a single pass using the feed/speed parameters that were originally selected for a more modest .025" step-over, and the result can be unnerving.
I manually polished out the web machining marks, and then I returned the crankshaft to the lathe where I measured the run-outs of the bearings to get an idea of any mis-alignments created by my new button axes. The run-outs of the main bearings were less than .002" while the run-outs of the bearings on the three crankpin axes ranged from .003" to .004". I was happy with these results given the trauma I had put the workpiece through when I replaced all my original center-drilled end references. I next turned all the bearings to semi-finished dimensions since I was still experimenting with bifurcated turning tools.
Before starting to grind a version of George's HSS tool for turning the bearings, I thought I would give carbide inserts one last try. The insert I previously used with some success was a low-rake no-name import intended for heavy cutting in a big lathe. Since I had just received a 40% off coupon from MSC I went through their catalog looking for an insert designed for 'light finishing' since it would likely have more rake and have less tendency to chatter in my lathe. Because of the long stick-out required to turn the crankpin bearings, I also needed a wide blade holder to minimize flex during side-to-side cutting.

I found a .199" wide Kennametal KC5025 A2 insert (MSC #80757750) and a matching A2 blade (MSC #03266133) that seemed like my best option. I also had to purchase a blade holder (MSC #51018497) for the blade. The blade holder and one of my Aloris-type tool-holders had to be heavily modified to get the insert at the correct height for my lathe. I cut a raked Britnell notch into the insert with a Dremel diamond cut-off wheel. The stock insert came with .010" radius corners which was half what I really wanted, but I decided to live with them rather than try to modify the insert any further. For the bifurcated cutter to work properly, its cutting edge must be perfectly parallel to the lathe's axis. I tried using the broadside of the blade as an indicating surface but found it wasn't sufficiently accurate because of a very slight tilt in the toolholder. Instead, I used George's method of indicating the tips of the insert itself.
I was thrilled with the results. This combination cut with no chatter, and the surface finish appeared polished. This insert cut smoother with hand-applied moly-based cutting oil rather than the synthetic coolant I normally spray from my Micro-drop dispenser. The only issue is with the minimum depth of cut that I can take. I can easily take .010" (dia.) cuts, but the minimum depth of cut is somewhere around .001"-.002" which is limited by the insert's rake. As a result, when I finally finish the bearings I will likely have to polish more material that I had hoped in order to get them all to identical diameters.

The next step is to bring the web thicknesses to their final dimensions so the bearing counterbores can be completed. These two operations must be completed before turning the chamfers on the counterweights. - Terry[ame]https://www.youtube.com/watch?v=8vc_jYkt2eg[/ame]


----------



## gbritnell

Terry,
That's a thing of beauty!
gbritnell


----------



## ozzie46

WOW!! It's a shame you have to hide it in the crankcase.


Ron


----------



## Scott_M

Outstanding !
Working with SprutCam can sometimes be maddening, especially with such a complex operation, my hat is off to you for getting it to do what YOU want !
It is looking really good Terry.  

Scott


----------



## Davewild

You sir are a master, beautiful


----------



## Charles Lamont

Most impressive. I think a sharp HSS tool would get you closer than 1 to 2 thou.


----------



## bigrigbri

Very skillful indeed. Well done.


----------



## mayhugh1

With the crankshaft fully roughed-in the 'easy' part is over, and now it's all about discovering and dealing with all the tiny details that affect its final accuracy. As I get closer to the final finishing operations there's less and less stock available to protect me from my mistakes.
The rear of the crankshaft on the full-scale Merlin is internally splined for a rear driveshaft. Rather than risk the crankshaft with a difficult splining operation, the quarter scale model uses a separate internally splined coupler that's Loctite'd into a half inch bore in the rear of the crankshaft. The drawings show this coupler having a circular array of mounting holes, but the crankshaft drawing doesn't show a corresponding array of tapped holes. The recommended Loctite can probably handle the torque requirements of the magnetos and maybe even the supercharger, but I'm not sure it will be adequate for the starting torque requirements of an electric starter. So, I decided to drill/tap an array of holes in the rear end of the crankshaft for six 3-48 mounting screws. These holes should have been drilled much earlier in the workflow, but I've had my head down in the crankshaft drawing which I had been assuming was complete. I wasn't happy with the setup that I had to use at this late date to support the crankshaft for drilling, but it was adequate for the forces needed to drill the tiny holes.
I left excess stock on all the crankshaft webs, and now it must be removed before machining the counterbores at the ends of the bearings. These counterbores will eventually be plugged in order to seal up the pressurized oil passages between the main and crankpin journals. Since I can't trial fit the crankshaft into the crankcase, I built partial CAD models of my crankcase and the crankshaft workpiece in its current state using measurements of the actual bearing locations. This allowed me to overlay the two and determine the best way to distribute the removal of the excess web material. The center bearing establishes the forward/aft position of the crankshaft in the crankcase, and so I provided a .0015" clearance for it. I followed the drawing for the remaining six bearings which calls for .040" clearances. I used a radially mounted right-hand boring bar to finish the left sides of the webs. Rather than invert it and run my lathe in reverse as I did previously, I made a left-hand tool to finish the right sides. It started out as a boring bar for a triangular insert, but due to a measurement error I ended up using a trigon insert, instead. I also ground a form tool to machine a radius on the neck of the crankshaft just behind the front flange.
Now the real fun begins...
I had .070" excess material on the main bearings, and so I decided to experiment some more with my bifurcated cutter. Since I wasn't 100% happy even with my new insert, I honed its front edge on a diamond hone and added more rake to the insides of the Britnell notch. I think its edge is now as keen as anything I could have done using HSS. My results using the improved insert was a slightly smoother cutting action and an improved d.o.c. resolution to less than .001" while cutting near the supported ends of the crankshaft. This depth control will be important later when I try to finish all the bearings to a common diameter. 
I still had some serious workpiece deflection while turning the three center bearings, however. Initially, I wasn't aware of it because the edge of the tool was hidden deep inside the webs and under a thick layer of the moly-based cutting oil I've been using. The symptom that alarmed me was a ridiculously high TIR of two to three thousandths on a freshly turned bearing. The deflection was created by the compromised rigidity of the workpiece which is a result of the now fully machined webs particularly around the offset crankpins. The real problem for a crankshaft is that this deflection can't be compensated by taking a heavier cut. The offset crankpins cause the workpiece's reaction to the cutting tool to be a function of the angle of rotation of the workpiece. This can be measured using a dial indicator on an adjacent bearing while cutting. The actual amount of deflection continuously changes as the workpiece rotated. At high rpm the symptom would have been a squeal as the cutter chattered against the workpiece. At my 50 rpm turning speed, though, it showed up as a non-circular turned bearing. Because of the limited space between the deep bearing webs it's very difficult to get accurate measurements, but I'm reasonably certain that I measured a couple thousandths difference between two almost orthogonal measurements taken on the diameter of the center bearing. This closely correspond to the unreasonable TIRs I measured just after turning the bearing. The bearing breathes instead of wobbling as it spins, and it's hard to notice a problem with the naked eye.
Some quick and dirty things I did to understand the problem included wood shims forced between the crankpin webs as well as a length of close fitting drill rod inserted through the hole in the center of the crankshaft. I was able to significantly affect the results but not cure the problem since I'm sure even the oak was reacting to the high cutting forces. 
In any event, I completed the web machining, and this produced identical final finished spaces between the webs. By this time I had removed .020" of my .070" safety margin from the main bearings. 
After re-turning the main bearings with the wood shims in place, I removed the workpiece from the lathe and then re-installed it to check the repeatability of the TIR measurements. I found the runout to be similar for all the bearings, but it had nearly doubled to an unbelievably value of .010". This result led me to believe I may have yet another problem with my headstock fixture and, in particular, the newly machined buttons. I suspected the center-drilled holes weren't deep enough and that my setscrews that bear against the spigot flats might be pushing the workpiece around slightly. I made new buttons with deeper center-drilled holes, and I re-turned the bearings with the wood shims in place and then repeated the test. Again, I measured almost the same ridiculously high run-out, and now I have only .030" safety stock remaining.
After spending a couple days doing various experiments but no additional cutting I concluded the issue related to the fixture was probably due to my method of tightening the setscrews. When I previously checked the consistency of the fixture I wasn't paying close attention to any particular tightening sequence. I had been just tightening the screws against the flats, but my workpiece at that time was a heavy chunk of rigid steel. Now the workpiece is much more flexible, and the setscrews need to be iteratively tightened so the workpiece is allowed to find its center with little or no net stress.
To check out these theories I machined a set of aluminum cervical collars which fit between the crankpin webs. These are not jammed into place but were lapped for a close sliding fit. I think it's important to not fixture the workpiece under any stress that can affect dimensions because after machining and when the part is removed from the fixture these dimensions will change. I Ty-Wrapped these collars in place, and for good measure I also inserted a length of close-fitting drill rod through the previously drilled hole through the center of the workpiece. (I could really use a steady rest behind the center of the crankshaft, but my lathe carriage is in the way, and there is no room for a follow rest.) I carefully tightened the setscrews to allow the workpiece to find its own position on the headstock center, and then I turned just enough material off the center bearing to clean up its TIR. I then removed the workpiece from the lathe so I could re-fixture it and re-check the TIR. Thankfully it now repeated. 
And so, to answer Peter's earlier question about whether stiffening spacers are needed while turning a crankshaft, my answer is a resounding 'yes'. And thanks to Charles who warned me about being too quick to finish the most important surfaces on the part.
It's now obvious to me that there is a major advantage, besides surface finish, to grinding crankshaft journals rather than turning them. The grinding forces against the workpiece will be much less than a cutter's turning forces, and the resulting deflection even on a 10-1/2" long crankshaft would be nearly insignificant.
Now, I plan to finish up the last few semi-finishing operations before returning to the bearings. Hopefully, I've paid my dues and the problems are understood well enough to successfully finish up. - Terry


----------



## gbritnell

Terry,
This is a wonderful presentation of the amount of work and fixturing it sometimes takes to make a part. By the time a project is finished you have a whole box full of plates, pins bushings and what-have-you parts that were required to complete a part. 
I don't know how stress proof this 1144 material is. By that I mean when I made the crank for my inline 6 cylinder engine I left the shaping of the counterweights till last. That way I could use hose clamps in conjunction with bushings to clamp the round counterweights together for added stiffness. I then made up a fixture with support blocks mimicking the main journals to clamp the crank into to remove the remaining stock from the counterweights. When I got finished I had a total runout of .0012 on the whole crank. It's not like you're going to make 2 of these to try out different approaches but sometimes a different process works a little better. I'm sure grinding is the best way to go but that involves another whole process and heaven knows we have enough specialized tools laying around. 
http://www.modelenginemaker.com/index.php/topic,2295.0.html
gbritnell


----------



## makila

Hi Terry,

That crankshaft is a work of art, as mentioned on an earlier post, too good to hide in the engine!
Great presentation as always, you should write a book!

Steve


----------



## mayhugh1

I have only blind access to the journals that need to be counterbored since their ends are blocked by the workpiece spigots as well one or more adjacent journals. My counterboring tool will have to pass through the bores of the adjacent journals in order to reach the ones to be machined. What's required is a toolholder with a removable insert that can be assembled and disassembled while the tool is between bearings. It also has to be long enough to pass through the entire crankshaft from either end in order to reach all 23 journal ends.
The tool I made was a single-insert manual piloted counterbore. I had some tiny triangular carbide inserts on hand that seemed to be perfect for the job. A simple toolholder was milled from a piece of drill rod that was .004" under the reamed diameter of the bearing bores. I pressed a bronze pilot bearing onto the nose of the tool that was just a thousandth under the journal hole diameter. I relaxed the clearance to the tool's main body so it could be easily rotated while passing through the entire crankshaft on any of its four axes. 
In use, the tool is inserted through the crankshaft until the pilot reaches the journal to be counterbored. The insert is then screwed into position on the tool and coated with cutting oil. A tap handle attached to the rear of the tool is then smoothly rotated while applying light pressure until the depth gage bottoms out. Since the insert's cutting edge has a tiny radius, it's easy to overpower the tool and end up with a spiral groove in the wall instead of a nice smooth finish. I made this mistake a couple times but was able to repair the finish, with some difficulty, by adding several additional passes. The insert must, of course, be removed before the tool can be withdrawn.
Two counterboring depths were used: .060" for the main journals and .090" for the crankpin journals. The difference between the two is because a portion of the crankpins' counterbores will be removed later when the windage chamfers are turned. The counterbores are only .030" over the bore diameters, and each was checked with a shop-made gage to make sure they all ended up with a smooth, common diameter. Although the process took several hours, the tool worked surprisingly well. The next time, though, I'll use an insert with a larger cutting radius.
With counterboring completed the webs could be finish machined. The last operation was an 11 degree windage chamfer turned on the counterweights and crankpin throws. I desperately tried to use the cross slide on my Enco lathe to cut these chamfers, but I ran into multiple interference issues between the carriage and tailstock and the narrow cutting window I had to work with. Reluctantly, I moved the workpiece over to my 9x20 lathe where I compiled g-code to cut the chamfers. The workpiece was simply held in the lathe's 3-jaw with tailstock support since, for this operation, there's really no great center precision required. The support collars couldn't be used, but I was able to install the central support rod. Although the program was fairly simple, the approach and retract moves for the cutter had to be carefully considered. There was barely enough room between the webs even for the tool that I had to radically modify, and so my pucker factor was off the charts the first several times the program was run. For simplicity and ease of testing I created a small program to cut only a single chamfer. This meant the cutter had to be re-referenced and the program run twelve times giving me ample opportunity to set up a crash. Once I had turned the six left side chamfers, I reversed the workpiece in the lathe and re-ran it six more times to turn the right side chamfers.
The next step will be to drill the oil passages between the main bearings and the crankpin throws. I may have a major fixture coming up just to drill these six holes. - Terry


----------



## petertha

Your tool is ingenious! Is the insert just flush mounted or does it sit within a pocket/edge that's not quite visible?


----------



## DICKEYBIRD

Absolutely mind-boggling.  Having recently done a bit of Mach3 close-quarters CNC  lathe work, I can truly understand what the pucker factor must've been when you pressed Cycle Start with so much time & effort invested in that crankshaft.  Your mental clarity & focus is astounding.


----------



## mayhugh1

Peter,
There's no pocket, but the insert is a snug fit inside the slot cut into the tool.
Terry


----------



## mayhugh1

The Merlin's crankshaft oiling system is a little different from those I've encountered on other engines. Instead of a pressurized oil channel daisy-chained through the main and crankpin bearings, all seven of the Merlin's main bearings are parallel plumbed to an external oil pressure regulator. Each main bearing, except for the rearmost, provides oil to an adjacent crankpin bearing through an internal drilled passage that connects the two. So, in addition to drilling seven entry holes in the main journals, six 60 degree oil holes must also be drilled through the crankpin journals to connect them to the main journals. 
Although I've never intentionally rotated the head of my Bridgeport clone off vertical, it can be set at the required angle and save me the construction of yet another single-use fixture. I set up an indexing head with its tailstock support under the spindle, indicated everything true, and then chucked up a test piece of drill rod to practice on. I tried to use a 60 degree carbide v-bit to spot the holes since it would have produced a nice transition between the angled holes and the journals' surfaces, but I chipped it on the first practice spot. I eventually used the cutting tip of a HSS center-drill to spot the holes. This worked OK, but it didn't produce quite as nice of a result. Because the angle-drilled holes pass through the bores of the crankpin journals, the journals had to be plugged with a filler rod so the drill could properly re-enter the crankshaft on the other side of the bore. For nearly all the journals I used the body of the counterboring tool I made earlier as the filler.
The diameter of these holes wasn't specified, and so I drilled them .087" which was the diameter of the Guhring drill bit I used on the crankshafts of my two radials. I really like these bits because unlike my 300 piece import set these drills are straight, cut smoothly, and handle deep holes really well. The main journals were drilled with a conventional .070" diameter twist drill.
After the drilling was completed, I de-burred the edges and polished all the machined surfaces with a medium grit Scotchbrite pad. I'm not as good with a file as George, and so I elected to not try filing fillets around the counterweights.
The crankshaft was then moved back into its fixture on the lathe so the journals could be brought to their final diameters. I really wasn't looking forward to these next finishing operations because of all the TIR issues I ran into during the roughing steps. Since this was my first one-piece crankshaft, I was worried that I didn't yet understand all the problems that had been causing the runout, and now they might show up with the finish line in sight.
I started the finishing operations with the crankpin journals which still had some .025" excess stock left on them. I used the support collars on every crankpin except for the one being turned, and this time I was especially careful about sequentially tightening the setscrews in the headstock fixture. I managed to turn all the crankpin journals to the same diameter within a half thousandth except for number three which came in a full thousandth under. All but the two middle journals had beautiful surface finishes straight off the bifurcated cutter. 
The final TIR of the 1&6 crank journals measured .0005". These are the journals which are nearest the supported ends of the crankshaft. The final TIR of the 2&5 journals measured .0007". The final TIR of the 2&3 journals, the poorest supported center pair, measured .0007" and .001". The runout of the lathe spindle measured at about a tenth, and the TIR of the live center in the tailstock measured three tenths. I suspected the crankpin run-outs in excess of a half thousandth, or so, were most likely due to circularity errors left behind by the rotational flex created by the cumulative slop in my six support collars. And, as expected, the higher numbers were measured on the two center crankpins. 
I tackled the main journals next. After re-installing the workpiece in the headstock fixture with all the crankpin support collars in place, I was relieved to find that the central bearing TIR measurement closely matched the one made several days ago using the support collars. After a couple passes through all seven journals with the bifurcated cutter, they were all at the same average diameter +/-.00025". I say 'average diameter' because I still had significant runout in the center bearings. Six of the TIRs ranged from .0005" to .001", but the center journal ended up with .0018" no matter what I did. Maybe my sliding fits to the support collars could have been a bit tighter. I was eventually able to verify that the bearing TIRs were definitely due to circularity errors after I found my long lost narrow body micrometer at the bottom of one of my toolboxes. A multi-lobe TIR pattern was also obvious in the oscillating needle movement on the dial indicator as the crankshaft was rotated through a full revolution. The main journal diameters ended up .015" below the values called out on the drawing, but this was OK since I had been planning to make the bearing sleeves somewhat thicker than specified. 
While taking .001"-.002" diameter passes I found that my thick moly-base cutting oil was a detriment even though it seemed to perform well on deeper cuts. I found WD-40 worked best while taking very light cuts.
After turning, I polished all the journals with 400g paper to remove the minor machining scratches and then followed this with 600g. I doubt that I polished off even a tenth, and so I wasn't concerned with changing the profiles of the journals.
The steps remaining are to remove the spigots and complete the machining on both ends of the crankshaft. It looks like I'm definitely going to need a steady rest for these operations, and my best candidate seems to be a modification to the one on my 9x20 lathe. The stock support arms are too wide to fit between the webs, and so it looks like I will need to make a set of new ones.
Six weeks ago I would have considered a runout of .0018" to be a failure and almost enough reason to start over. After my experience with this project, though, it's not clear what I could do differently to improve the results. I think the only way to get better numbers is to grind the journals so the flex on a very flexible workpiece is reduced. - Terry


----------



## stevehuckss396

Holy Freakin Smokes!


----------



## gbritnell

Terry,
I think what we fail to realize when working on these small parts is just that, they are small parts. The tolerances that we are trying to achieve using 'shop tools' is generally extremely accurate, even if they are out by .0012. The complexity of this crankshaft makes the task even that much harder. I would venture to say that there is no other process, pressing or silver soldering, or material that could have given you the results that you have achieved. 
I have mentioned in other threads and postings that there are extremely talented machinists and miniature builders out there but they aren't contributors to forums such as these and with that being said the ability to learn from their experiences is lost. 
I personally am delighted and impressed with your work and documentation. Even garnering one or two bits of knowledge from your postings is a great learning experience for me. 
There's no doubt that this will be a magnificent engine when finished. 
gbritnell


----------



## ozzie46

("I personally am delighted and impressed with your work and  documentation. Even garnering one or two bits of knowledge from your  postings is a great learning experience for me. 
There's no doubt that this will be a magnificent engine when finished. 
gbritnell")

 I fully agree. Well said George.
I know personally that I couldn't come anywhere near to what you have accomplished.  Keep up the good work.

Ron


----------



## RiekieRhino

All I can say is awesome work.


----------



## jschoenly

Really fun to watch this build and learn!


----------



## mayhugh1

Thanks everyone for your kind comments...
.
While waiting on some special ball bearings that I need to modify my lathe's steady rest, I started thinking about the shell bearings that I'll soon need to install the crankshaft. Although I have some experience with replacing these bearings on full-size engines, I've never actually made any from scratch. I searched the forums to see how other model builders are making them, and I was especially interested in the two-piece soldered-blank technique. After thinking about my journal TIRs and wondering what I was going to use for a diameter to bore them, it occurred to me that I needed a shell that would easily adjust to the effective diameter of my non-circular journals after they had been allowed to rotate for a while. Instead of all the soldering, turning, boring, and unsoldering I wondered if I could press-form the bearing halves from a soft metal. 
I thought I'd perform a quick experiment. When I was much younger I collected coins, and like a few others at the time I purchased a number of 'collectible' silver bars at a premium price back when the price of silver was less than $6/oz. Since the silver in these bars is very pure I figured it should be very malleable and perform well as bearing material. I rolled one of my bars into a flat sheet having roughly the thickness needed, and then I cut off a narrow strip to make a test bearing shell. I annealed the silver using the same torch technique used earlier to anneal the aluminum castings. Using just my hands and a wood dowel that closely matched the diameter of my crankshaft's main journals I pressed the silver strip into one of the finished bearing caps. Sure enough, it conformed perfectly to the bearing cap with no spring-back.
Unless someone talks me out of it, I think I'm going to try to make my Merlin bearings this way. My plan is to machine a simple two-piece die that I can use to press-form the bearing halves. Since the main bearings require an internal oil groove I'll try to include that feature in the die. I believe that some of the older racing engines used silver bearings, but I don't know why it isn't common practice today. - Terry


----------



## gbritnell

Terry,
That's what Ron Colonna uses for his Offy engine bearings. He bought sheet silver material from a jewelry supply house.
gbritnell


----------



## petertha

You beat me to it George, good memory. I thought I also saw it used in an SIC engine build too, something smallish, but same implementation.

Just wondering, what is it about silver sheet that yields desirable properties in this application? Lubricity or wear? On some build I thought I saw the stock extend over the journal web edge & figured silver would be good in that regard, but this is a half-circle? Anyway, possibly bronze sheet can also be had, but would need to confirm alloy spec.

http://www.whimsie.com/brass%20sheet.html


----------



## jschoenly

I was just going to say I thought Ron's Offy had silver bearings.  Great minds (George, Terry, Ron, Etc - Not me) think alike.  Good stuff!


----------



## mayhugh1

Both ends of the crankshaft have to be machined for power take-off shafts, and their locating recesses need to be concentric with the end journals. The lathe set-up to properly do this requires a steady rest, but the rests on both of my lathes are too wide to fit into the journals behind the spigots on either end of the crankshaft. The steady rest on my 9x20 is almost useable, but the ball bearing support arms are about an eighth inch too wide. I ordered some slightly narrower ball bearings, but I also had to machine a new set of thinner arms. The new arms aren't as beefy as the originals, but they are plenty adequate for the machining I need to do.
After chucking up the front end of the crankshaft in my lathe's three-jaw, I adjusted the steady rest for less than a half thousandth runout at the rear bearing. Since the steady rest ball bearings ride on the finished bearings of the crankshaft, I made up a simple cardboard shield to keep chips from finding their way in between them where they could mar the crankshaft's newly finished surfaces. As an extra precaution I also used the crankpin support collars for these final turning operations. The machining on the rear end consisted of facing off the spigot and bringing the end main bearing to its final length. A parting tool would have speeded up the process; but there wasn't room for one, and so the quarter inch wide spigot was slowly faced away at .008" per pass. The rear main bore was also opened up to later accept a splined coupler.
The crankshaft was then flipped around in the lathe so the front spigot could be transformed into the crankshaft's front flange. The finished rear bearing was now supported in a 5-C collet chuck while the front main bearing was indicated in the steady rest. Another cardboard shield was made, and then the half inch thick front spigot was turned down and faced to a .075" wide flange. The flange was then bored for a locating recess for the front drive shaft as well as a second smaller and deeper bore for an oil sealing plug.
When the machining was completed I was finally able to sanity check the fit of the crankshaft in the crankcase. Although I haven't yet made the shell bearings, the crankshaft seemed to fit as hoped between the webs with no measurable forward/aft play. I had to modify many of the dimensions of the crankshaft from those given in the drawings in order to match my 'short' crankcase; and I've been a bit anxious since I haven't been able to do any trial fitting until now, after the spigots were removed.
The last step will be to cap the ends of the journals and seal up the internal oil passages. - Terry


----------



## Swifty

That crankshaft is a real work of art, it's a shame it won't be seen in the end.

Paul.


----------



## Mattsta

total awesomeness!


----------



## jimjam66

Man, that last shot of the crank inside the upside-down engine casing should hang in the Tate Gallery - way better than most of the so-called art in there!


----------



## mayhugh1

The final step in the Merlin's crankshaft construction was to cap the ends of the journals. This required twelve pairs of turned aluminum end-caps that fit into the end recesses cut earlier. These caps seal the pressurized oil paths between the main and crankpin journals. Each pair of end-caps is drawn into the ends of the journals with a 2-56 tie-bolt between them. Later I'll add Loctite to the caps and tie-bolt threads to ensure everything is oil tight under pressure, but for now they're just temporarily assembled. The quarter scale drawing show these caps having plain flat ends, but I dished their faces to look more like the end-caps in the full-scale engine. It was nice for a change to make a few (dozen) simple parts that could be scrapped if necessary without creating a catastrophe.
I've been wondering why the Rolls engineers decided to bore the journals in the first place since it created extra machining and a lot of additional engine parts. Their decision might have been made to save weight - a factor in performance aircraft engine design. Reducing the crankpin weight has the additional benefit of reducing the mass of the counterweights required to balance them. I've read that the engines in some fighter aircraft of the period weren't fully balanced in order to save weight, but I don't know if this was the case for the Merlin. Another reason for the bores might be the oil reserve they hold that's available to the bearings during start-up as well as during combat maneuvers when even a dry sump's oil pressure might fluctuate. I've also been curious about the Merlin's counterweight design because although it looks cool, it's functionality isn't all that clear to me.
I included a photo that I found online of a full-scale Merlin crankshaft. The front flange of the full-size crankshaft doesn't have the three scallops that are a part of my and Zapjack's quarter scale versions. These scallops are a deviation from the quarter scale crankshaft drawing; and they were a compromise that I, and probably Zapjack, made to simplify the tooling required to bore the journal recesses. The scallops will eventually be hidden by the driveshaft flange; but I thought they were cool looking standalone features of the crankshaft, and so I chose the simpler tooling.
The next step is to fabricate the shell bearings so I can finish testing the fit in the crankcase. I've been working on a process to press out the silver shell bearings, and although I'm still refining it, I've managed to create my first usable first pair. - Terry


----------



## Scott_M

My that really is beautiful. As others have said, it is a shame that it will be hidden. 

This shot deserves to be blown up and framed for your office/shop wall !

Scott


----------



## petertha

I keep thinking the journals are finished because they shine like chrome. And then a few days later some new holes & features appear! So I haven't seen anything resembling tool post grinder or even lapping tool. Is the procedure basically turn these to within 'real-real-close' & then hand finishing to final dimension with abrasive backed sticks or...?

How have you found that stress proof for teeny skim cuts? (it doesn't have work hardening tendencies?)

Have you been able to get in there to measure journals with standard mic ok, or does that require some jiggery (mic frame hanging up on neighboring counterweights etc.)

What is a typical +/- you figure you need to be within across all bearing journals?


----------



## aonemarine

Man im telling you, watching that 4th axis machining of the counterweights makes me so so so jealous!


----------



## mayhugh1

Peter,
I can't reliably check the uniformity of the diameter across the width of the journal because there just isn't enough space due to interferences with the corner radii and the counterweights. I'll know more when the shell bearings are completed and installed as then I'll be able to use Plastigauge to measure the bearing clearance across the entire journal. With seven main bearings and this being a model engine that will be run for display and not for any kind of competition, I imagine I could get away with a lot of clearance and never even know it. The crank journals are as cut with the bifurcated insert, and with about 30 seconds polishing with 400g and 600g strip paper. The cutter was carefully indicated in, and after watching it cut I would not be surprised if the uniformity was unmeasurable. With my modified insert and while cutting near the headstock or tailstock I was able to take a thousandth (diameter) cut. The 1144 showed no tendency to work-harden and was really nice to work with except for boring. I've just used it to make some dies for my shell bearings, and so far I've not found the secret to getting as nice a bore finish as I can get with 12L14. I was planning to use it for my cylinder liners due to its great stability, but I'll first have to improve my bore finishes. - Terry


----------



## mayhugh1

After reading some of the responses to my question about using silver bearings, I checked out Ron Colonna's 270 Offy and, indeed, he used .010" thick silver sheet liners for the crankshaft's three main bearings. He was able to manually form the thin silver sheet into the bearing webs and caps using a piece of drill rod as a planishing tool. The thin metal was easily worked and provided a bearing surface. I didn't get deep enough into his design to understand the oil system, but there doesn't appear to be any conventional oil grooves in the liners. 
Had I originally planned on using silver, and knowing what I now know, I would have also planned for thinner bearings than the .053" ones I now need. During construction I had two opportunities to choose the bearing thickness, but since I was planning to use SAE 660 bearing bronze, I selected a convenient machining thickness for that alloy on my lathe.
I thought about using silver after realizing that I had not been able to turn the crankshaft's main journals perfectly round by cutting them on a lathe. A softer bearing material would allow me to plan for an initially tight fit that would quickly open up just enough to conform to the journals' imperfections. Babbitt came to mind, but it likely wouldn't stand up to the pounding it would receive in a model IC engine. Pure silver has less than half the hardness of bearing bronze, and since I already had some hidden away in a closet I decided to give it a try.
I learned a lot from my failed attempt to press out a first bearing from a chunk of silver inserted between the halves of a steel die set that I had machined. My 20 ton press deformed the dies as much as it formed the silver. I spent the next few days playing with the remains of my dies as well as my re-melted scrap silver in order to get some some hands-on experience in working with the two.
The first and most disappointing lesson learned was that in order for me to have any hope of forming the bearings using dies, the silver blanks would have to start out much closer to their final thickness than I had hoped. The shop roll that I was using to roll out my one ounce ingots exerted enough force, but its control was very coarse. The rolling had to be done in multiple passes, and so the final thickness was a crapshoot. A miniature jeweler's rolling mill is probably better suited for this type of work, but lacking one I ended up re-melting and re-rolling my ingots several times. My empirical and very lofty goal for the starting blank thickness eventually evolved to .053" +.003"/-.000".
The second lesson learned was that it was much better to finesse the silver into its final shape by beating on the dies with a wooden mallet instead of brutalizing them in a hydraulic press.
Using my new-found knowledge I re-purposed a few of the original dies and created some new ones to manually form the silver with much less trauma to the dies. The dies are very simple, but since my crankcase has two different web widths, I (needlessly) duplicated a couple of the dies to accommodate two different bearing widths. I included a feature on the Final ID Die to press-form a .055" wide x .020" deep oil groove. All the dies except for the large ones were heat treated. The large dies were machined from Stressproof since I didn't have any large diameter harden-able steel.
The forming process starts out with an annealed silver blank having the target thickness and its dimensions closely trimmed to the bearing's final length and width. The blank is inserted between the ID Starting Die and the OD Starting Die, and a mallet is used on the ID Starting Die to rough form the bearing half shell.
The rough formed shell is then inserted on the Width Die, and the two sides of the blank are sanded against 220g/400g paper on a hard flat surface to bring the shell to its final width.
The shell is then inserted on the Height Die, and the two ends are simultaneously sanded until the shell has been brought to its finished height. The Height Die has an additional thousandth crush height built into its design.
The shell is returned to the Starting OD Die, and this time the mallet is used to pound the Final ID Die into the shell blank in order to start the formation of the oil groove. The goal of this step is to get the Final ID die deep enough into the blank so the combination can be inserted into the Final OD Die which is where the groove will actually be formed. It turned out that centering the ID Starting Die during this step was the most critical part of the entire forming process. All my scrapped parts originated from poor centering of the oil groove during this step. 
The bearing shell, which is now sandwiched between the Final OD Die and the Final ID Die, is set on a pair of sturdy metal support blocks so a large wood mallet can be used to complete the forming process. The combination is rotated on the support blocks while the periphery of the Final OD Die is pounded with the mallet over the top (only) 180 degree portion of the die resting on the bearing. The Centering Guides help keep the blank centered in the die, and they are designed to provide visibility to the bearing as it's being formed. As the oil groove is deepened, excess metal is displaced and the shell grows a bit in width. There's no positive stop in this die set to halt the forming process when the the final shell thickness is reached except for an increase in forming resistance. It's difficult but not impossible to go too far. The Height and Width Dies are used once more to finish the final edge dimensions.
The bearing is finally inserted between the Height Die and the Starting OD die to verify the final bearing dimensions. The mallet is used against the combination resting on a hard flat surface to set the final bearing dimensions without damaging the oil groove.
The process sounds more complicated than it really is. The most difficult step is creating the starting blanks; and, frankly, I don't recommend my method for creating them. I've done some research and silver sheet is available in a wide range of gauges from online jewelry supply houses. I plan to design the rod bearings around commercially available silver sheet instead of rolling any more ingots. After making the first two bearing halves, the fabrication time dropped to less than five minutes per shell. 
For my particular bearing design I was able to get six half shells out of a single one-ounce ingot. At the current price of silver the cost of each bearing pair worked out to about $5.00. My bearings were thicker than they needed to be, and this ran up their cost as well as the effort to make them. I hope to do better planning for the rod bearings.
I sanity checked my first pair of bearings using Plastigauge on the best-behaved number seven journal. Due to the max .0018" TIR that I previously measured on the three center journals, my planned target clearance for all the bearings was .003"; and this is very close to what I measured on the number seven journal. The next step is to drill the holes in the top shells for the oil injectors which will also serve as anti-rotation stops. The rest of the bearings will then be installed and measured. - Terry


----------



## mayhugh1

The final step in the bearing construction was fitting them to the crankshaft. Since I wasn't able to turn all the journals to the exact same diameter, the bearings required individual fitting. The goal I set for myself was to end up with a freely rotating crankshaft with a maximum .003" clearance at each journal.
I installed the seven lower bearing halves in the crankcase before laying in the crankshaft. I was relieved to see the crankshaft spin freely with no sign of binding, and I took this as an indication that it wasn't noticeably bent or warped. My plan for the fitting process was to install the bearings one-by-one while continually checking the crankshaft for drag.
I installed the first upper bearing on the #7 journal and torqued its cap down while rotating the crankshaft. The bearing added no noticeable drag, and Plastigauge showed a .003" clearance. This process was repeated on the #1 journal with essentially the same results. Thanks to a bit of luck and the fact that the two outside journals were well supported by the lathe headstock and tailstock while being turned, their dimensions were right on target. 
The journals toward the center of the crankshaft, though, were another matter. They were victims of the workpiece flex, and previous TIR measurements showed they didn't end up perfectly round. The installed bearings on three of the five inner journals nearly seized the crankshaft, and so their i.d.'s had to be opened up. Plastigauge measurements showed these particular journals were oversize by as much as .0015". Measurements taken while turning the journals had led me to believe they were more consistent, but those measurements weren't entirely reliable due to the TIR errors and the limited micrometer access. 
In order to free up the crankshaft, the bearings for the three over-size journals were hand-fitted one-at-time using a shop-made lap. The lap was simply a single layer of 600g paper wrapped around a mandrel that had been turned, to match the target i.d. of the bearing. I used the lap on both the upper and lower bearing halves for these three journals, and so the fitting process took a while with the crankshaft coming into and going out of the crankcase several times.
An unexpected issue that I ran into while fitting the bearings to these three journals seemed to be related to the two thousandths crush height that I had built into the bearing height gage. This additional bearing height somehow created a problem that required more material than should have been necessary to be removed from the bearing i.d. to obtain a satisfactory fit. I didn't understand what was going on here, but I ended up removing the crush height.
Plastigauge measures the diametral bearing clearance by measuring the space between the crankshaft journal and the upper bearing while the cap is torqued down, and the crankshaft is resting at the bottom of the lower bearing. Bearing clearance is primarily important for oil control. With too much clearance there will be excessive oil leakage from the bearings resulting in increased windage losses and possibly increased oil consumption. Also of concern is the effect that excessive leakage can have on oil pressure. In a full-size automobile engine the general rule of thumb is .001" clearance for each inch of journal diameter. In a typical street engine this translates to .0020"-.0025" clearance. I've personally measured .004" bearing clearances in an engine that was running fine before disassembly. In my Merlin's case, due to the measured .0018" journal imperfections that I can't correct as well as its nearly one inch diameter journals, I set the target bearing clearance to .003".
At this point the anti-rotation stops for the bearings weren't yet installed. The bearing caps were previously drilled for oil injector flanges, but the injector tubes had not yet been installed. These tubes double as anti-rotation stops once the upper bearing halves are drilled for them. After all the bearings were fitted, the caps were removed and the upper shells were drilled for the injector tubes. A simple drilling fixture was created so the bearing shells could be accurately drilled for these tubes. Small brass injector tubes were Loctited into the bearing caps, and the tops of these tubes will eventually mate to the flanges of the oil supply lines. After verifying the fit with the installed injector tubes, the bearings were marked with their location so they can always be returned to the journal to which they were fitted.
With all the bearings fitted, the crankshaft seems to turn as freely as it does when resting on the just the lower bearing halves. Its difficult to quantify, but when one of the counterweights is 'thumb flicked' the crankshaft will spin 1 to 1-1/2 revolutions before coming to rest. This isn't quite as freely-turning as the crankshaft in my last radial, but that engine had only three bronze and two ball bearings compared with the seven sleeve bearings in this engine. The final measured clearances ranged from .003" to .0035".
I guess I'll need to let the kids know about the salvage value of the silver that will be inside this particular engine so they don't price it too low in the big garage sale, someday. - Terry


----------



## ddmckee54

You ARE going to leave instructions to let the rest of us know about the date of that garage sale aren't you?  Tell them that when they have that garage sale they'd better have an auctioneer on standby because they'll probably have bidding wars over all those beautiful toys that you've got.  Ah well, that's a couple of decades away yet because I know you've got a lot more engines you want to build.

Don


----------



## mayhugh1

With the crankshaft completed I was anxious to start machining some of the less involved crankcase parts. The first of these are components of the gear reducer assembly. This assembly is located inside the gear case at the front of the engine, and its purpose is to transfer power from the crankshaft to the prop-shaft. It includes a number of interesting components, and after several months of drilling and tapping holes it was nice to start adding scratch-made parts to the engine.
I felt it was also a good time to get the crankcase on an assembly stand so it will be easier to work on. Before doing that, though, I had some crankcase (hole drilling) operations that needed to be finished up. The most difficult of these were ten pairs of oil drain-back holes that I'd been putting off completing because of their importance and my uncertainty about how to drill them. They need to pass through the corners of the counterbores that were earlier machined atop the threaded holes for the cylinder block studs. They also need to be drilled at compound angles with respect to the cylinder block decks in order to avoid the structural ribs below them. I fixture'd the crankcase on a 5 degree sine plate under the spindle of my mill whose head was rotated 33 degrees, and luckily the holes came out where they needed to be.
The final crankcase drilling involved the mounting and feed-thru holes for an oil valve relief housing that will later be constructed and mounted on the exterior right side of the crankcase. The engine will eventually receive its lubrication from rigid oil lines coming from this housing. A mounting surface for it, not shown on any of the drawings, had been cast into my particular crankcase, but the cast bosses don't match the mounting holes shown on either the crankcase or valve drawings. I drilled the holes according to the bosses on the crankcase, and so the relief valve will be redesigned later on.
For the assembly stand I reused a portion of the one that I built for my 18 cylinder radial, but I had to make a new adapter plate to match the Merlin's mounting points. I tried to make a compatible adapter that would give open access to either end of the engine, but its asymmetrical mounts made this impractical. I'll have to make a second adapter plate later when I start working on the wheel case components at the rear of the engine.
The first component in the gear reduction assembly is a short driveshaft centered in a locating recess on the front of the crankshaft and bolted to it with nine SHCS. The driveshaft was turned from 12L14, and the locating boss on its rear was the final turning operation on that part. I managed to screw it up, and its o.d. ended up two thousandths undersize. I was ready to toss it into my scrap box when I remembered reading somewhere about fixing mistakes like this by displacing metal with a punch. Using a spring-loaded center punch, I made some prick marks in a circular pattern near the edge of the boss. The included photo shows a couple circular patterns that I tested, but only the pattern near the outer diameter of the boss had any effect. The displaced metal from these punch marks reduced the centering error from .002" to .0005" and saved the part. 
The driveshaft is keyed to a 21 tooth drive gear. This gear will eventually drive a 49 tooth prop gear to produce a 2.33 rpm reduction which is very close to the ratio used in the full-scale engine. When the original engine was running at a maximum 3600 rpm, its huge three or four blade adjustable-pitch propeller was turning at only 1575 rpm. 
The drive gear was made from a piece of 1144 that I purchased to use for the cylinder liners. I normally cut gears on my Tormach using its fourth axis, but I had another job set up on that machine that I couldn't disturb. I had to re-acquaint myself with using a manual indexer on my Bridgeport clone. In the process I managed to make a another piece of scrap, but this one I couldn't save. With the drive gear and driveshaft mounted to the crankshaft the runout measured on the teeth at the end if the drive gear was only .0015". I added witness marks to the flanges on the crankshaft and driveshaft so they can be reassembled in their same relative positions.
I've included an ancient but interesting historical video on the Merlin's development and manufacturing. -Terry
[ame="https://m.youtube.com/watch?v=-fo7SmNuUU4"]https://m.youtube.com/watch?v=-fo7SmNuUU4[/ame]


----------



## mayhugh1

Continuing with the components of the gear reduction assembly, I next machined the retainer for the drive gear. A boss on the rear of this retainer locates it in the center of the bore of the drive gear, and after a light press fit it's secured with a SHCS. The nose of this retainer rides in the inner race of a ball bearing. The outer race of this bearing will be supported in a driveshaft cover which, in turn, is bolted to the gear case cover. The combination of these parts nicely supports the front end of the driveshaft under its load.
The prop gear has been one of the parts that I've been looking forward to making. With a 3/4 inch width and a 3-1/8 inch diameter, this is the largest gear I've ever made. Because of its large diameter, it's especially important that its mounting face be machined perfectly normal to its bore. The final center cross section will be fairly thin, and so I prepared the blank by boring its center hole and turning the critical mounting face in the same lathe set-up leaving the back face un machined. The blank was inserted on a tapered mandrel, and the OD was finished on the mill in the same four axis setup used to cut the teeth. After the teeth were cut, the gear was pressed onto a short dummy prop shaft and assembled with the prop shaft bearings in the gear case so clearances could be checked. A temporary collar was also machined to simulate the driveshaft cover so the fit with the gear case cover could be verified with both gears and all bearings installed. Since I didn't have the gears available for measurement when I bored the gear case and its cover several months ago, I used the theoretical diametral pitch for the gear separation. I was a bit anxious, but the initial test showed no binding nor noticeable backlash; and the crankshaft still turned freely while driving the gear set. After testing, the rest of the gear machining was completed, including its non-critical rear face. The mounting face was engraved for identification during assembly.
The two piece driveshaft cover appears to be an overly elaborate design when it's viewed as only a cover. While machining it, though, I realized that it's designed to absorb some machining error in the front cover. I was a bit surprised because nearly everything else in this engine, so far, has required spot-on machining. It's a clever design that allows the the driveshaft bearing to find its own running position before its cover is secured into position on the front cover. I didn't appreciate the purpose of the small inspection cover on its front end, though, until during trial assembly it became invaluable for removing the driveshaft bearing. The final fitting will be verified when actual prop shaft is completed. 
Two of the three bearings in the gear case are open. I don't like using unshielded bearings in my engines because debris created during engine break-in can find its way into the bearings and damage them. My own experience with this occurred during my Howell V-4 build. I had a lot of trouble with ring sealing on that engine because the extremely thin wall cast iron cylinder liners used in that design were not holding their circularity over time. I still have a small box of reject liners whose dimensions changed days after being perfectly machined. In the process of 'motoring-in' the engine to troubleshoot the problem, and despite the use of a magnetic drain plug, I destroyed the crankshaft bearings in the process. Open bearings show up all through the quarter scale Merlin design, and they were probably used to maintain the scaling since smaller shielded bearings are usually slightly wider than their open equivalents. I couldn't find shielded replacements that would fit inside the gear case, and so I reluctantly used the specified open bearings. In addition to the magnets that I plan to add to the bottom of the oil pan, the notes accompanying the castings also recommend an oil filter.
The last component of this assembly, and one that I haven't been looking forward to, is the prop shaft. A drawing was supplied for a scaled splined shaft that looks good and shouldn't be difficult to make. But, I'm going to want to add a propeller to the engine, and that means I'll also have to make an internally splined adapter for it. I can easily cut the prop shaft splines with a Woodruff cutter and worry about the prop later, but I think it's probably best to deal with them both up front. I've no experience with cutting splines, and so I'm curious about how this will all come out. - Terry


----------



## petertha

mayhugh1 said:


> The prop gear has been one of the parts that I've been looking forward to making. With a 3/4 inch width and a 3-1/8 inch diameter..


 
Wow, nice. What material did you select & will it need to be hardened?




mayhugh1 said:


> ..trouble with ring sealing on that engine because the extremely thin wall cast iron cylinder liners used in that design were not holding their circularity over time.  Terry


 
Similar thought crossed my mind on my project, liner seemed thin relative to similar bore RC engines. Do recall your numbers by chance?


----------



## mayhugh1

petertha said:


> Wow, nice. What material did you select & will it need to be hardened?
> 
> 
> 
> 
> Similar thought crossed my mind on my project, liner seemed thin relative to similar bore RC engines. Do recall your numbers by chance?


Peter,
The large gear is 4130, or at least that's how it was marked. There wasn't any thought process in its selection. It was the only piece of material that I had that was large enough to make the gear. It happened to be a piece of machine shop scrap that was almost the exact size I needed.
The wall thickness of the liners was .063". I had several lots of cast iron to choose from, but one didn't seem any better than another. I believe there is some art and science to working with liners that thin; and it involves the material, the machining sequence, and maybe even some stess relieving and aging. The Merlin's liners are only .030" thick, and so I'm not even going to attempt to make them to the drawings. Not sure yet exactly what I'll do, but mine are going to be a lot thicker. I translated Zapjack's posts on the French website where he posted his build, and noticed he had a lot of trouble with his liners as well. - Terry


----------



## Charles Lamont

mayhugh1 said:


> The Merlin's liners are only .030" thick, and so I'm not even going to attempt to make them to the drawings. Not sure yet exactly what I'll do, but mine are going to be a lot thicker.Terry


Last year I had no trouble at all with the 1/32 thick liners for the Seagull. If I can do it you certainly can: http://www.charleslamont.me.uk/Seagull/cylinder_liner.html


----------



## mayhugh1

Charles Lamont said:


> Last year I had no trouble at all with the 1/32 thick liners for the Seagull. If I can do it you certainly can: http://www.charleslamont.me.uk/Seagull/cylinder_liner.html


Your technique seems very thorough and methodical. I especially appreciated your two year aging period between roughing and finishing.  Terry


----------



## mayhugh1

The quarter scale Merlin's prop shaft is a scaled version of a design that's still in use today on full-size aircraft. It's externally splined, and its end is threaded for a castellated prop nut. In order to fit a propeller to this shaft I designed a splined hub that will become an integral part of a four blade prop. Its front also includes a threaded section for a spinner.
I've cut key slots before, but never splines - neither internal nor external. Cutting external splines looks fairly easy and is pretty similar to cutting gear teeth. Initially, the internal splines seemed more intimidating, and so I decided to start with the hub.
One of the options on the Merlin's prop shaft drawing is a variation of an SAE 16 straight tooth spline. I designed the hub for sixteen 3/4" long splines spaced 22-1/2 degrees apart. The splines in this hub can be cut using an ordinary 3/32" keyway broach. Since I had a .875" diameter broach bushing, this became the i.d. of the hub as well as the minor diameter of the shaft. Actually, I reduced the shaft diameter .010" to obtain a tooth end clearance of .005". I pulled this number out of the air with no experience or reference material to justify it. Broaching this i.d. creates sixteen teeth having a 22-1/2 degree included angle and a height of a .050". The prop splines must be cut using a form tool that matches the shape of these teeth.
My initial thought was to use a rotary to index the hub under a broach held in the locked spindle of my mill. I did a few experiments and realized the force required to drive the broach through a one inch piece of 12L14 was more abuse than I was willing to apply to the bearings in either my spindle or rotary. Instead, I manually indexed the hub, and I used a manual press to drive the broach. I CNC-engraved the top of the hub's blank with the 22-1/2 degree alignment marks and I scribed a corresponding reference mark on the broach bushing. Accurately aligning the broach for each cut was easy, and the whole splining operation took less than half an hour. After finishing the splines, the remaining machining on the hub was completed.
Instead of spending fifteen minutes grinding a single tooth form tool for the shaft splines, I spent most of an afternoon modifying a 3/16" HSS Woodruff cutter. The sides of the teeth were ground as close as possible to the theoretical 11-1/4 degree side angles, and the width of the flat end came out to .078". Normally, I would have turned a four tooth cutter from scratch as I did for the crankshaft gear for my two radial builds. In this case, however, I had a lot more material to remove, and I wasn't sure how well drill rod, even heat treated, would hold up against the Stressproof shaft especially if I had to make more than one shaft. The most difficult part of the Woodruff cutter modification was relieving the sides of the teeth. During testing I found this relief helped to reduce the height of some very tough burrs that tended to rise up on either side of the spline. These burrs interfere with the test fitting of the hub to the shaft while it's still fixture'd for splining.
I first tested the cutter by splining an aluminum test shaft. The splines looked great, and the shaft slipped into the hub with a close sliding fit. The clearances of the splines on the rear of the hub where the broach had entered looked nearly perfect, indicating that the spline cutter was accurate. However, the clearances between the shaft's teeth and the hub's slots on the front of the hub where the broach had exited were much greater. I checked the broach bushing and the perpendicularity of the press, and all was as it should be. I purchased a new duMONT broach since the one I had been using was part of an inexpensive import set. I made a new blank and reduced some clearances, but the results were essentially the same. Even with 3-4 teeth cutting at a time, the bottom of the broach drifted to the outside of the blank during every cut causing the splines at the bottom end of the hub to be deeper than those at the top end of the hub. Turning the set-up around on the table of the press had no effect. I examined several parts on other projects that I had key-broached, but none of them showed the drift I was seeing on these hubs. The only solution seems to be a rigid set-up to keep the bottom of the broach tight against its bushing, but since it wasn't obvious how to do that, I decided to save it for the next splining project. 
Although not desirable, the tapered splines really don't create a significant problem in this particular application. Both hubs fit the test shaft snugly since the hub teeth fit into the shaft splines with their proper clearances along the entire length of the hub. It's only the shaft teeth that end up with excessive clearances to the hub slots. The two-piece propeller hub that I plan to make will sandwich the prop and should insure its perpendicularity to the prop shaft independent of the splines. I was concerned about possible run-out issues with the hub that would cause the spinner to wobble. But, with sixteen mating possibilities, it wasn't difficult to find one with near zero run-out.
I turned an 1144 prop shaft blank and adjusted the parameters of the splining program for the new material. When the part was completed it was immediately obvious that the splines weren't uniform. I had evidently over-tightened tailstock of the the fourth axis (again), and this caused the rotary to loose steps. My second attempt was more successful. Its fit inside either hub was smooth and very snug with no backlash.
The rest of the machining on the shaft was completed including a pair of shoulders for two ball bearings and a 7/8-20 thread for the prop nut. The bearing shoulders were turned concentric with the splines in a 4-jaw set-up. The center of the shaft was also drilled out in order to lighten it, and a mating position for the hub was found that produced a TIR of only .001". Punch marks were added to the hub and shaft for use during assembly. Finally, a bearing retainer was machined for the front of the gear case to limit the forward thrust of the shaft.
Manually rotating the shaft of the completed gear reduction assembly smoothly spun the crankshaft at nearly twice speed with no binding or rough-felt areas. Now there's even a flywheel effect due to the large prop gear. The next step, while I'm working at the front if the engine, will be to finish up the rest of the prop components. - Terry


----------



## jimjam66

That is just awesome machining Terry!  Can't wait for more progress.


----------



## Mattsta

An absolute work of art


----------



## petertha

> _sixteen teeth having a 22-1/2 degree included angle and a height of a .050".... Instead, I manually indexed the hub, and I used a manual press to drive the broach._

I don't know much about presses or broaches. Just out of interest, what kind of force/capacity is required on an operation like this? is it a once-through type deal, or a progressive sequence of cutters or shims to get to 0.050" depth? Very nice!


----------



## mayhugh1

Peter,
I was using an Enco one ton arbor press, and it took nearly every thing I had to push the broach through the hub. The broach was a progressive type with a number of teeth and about five inches long. It didn't require any shims and it was designed to cut a .050" deep keyway in a single pass. - Terry


----------



## ddmckee54

So you think maybe pushing/exceeding the limits of the press is what caused the broach to drift in the bore?  I realize that you've got a work-around for the parts you've already made, but maybe for future reference?

Don


----------



## ICEpeter

Considering the direction the teeth of the broach are facing when broaching, it seems likely that the teeth and broach pull in the direction where the cutting force bites into the material. That would in my opinion cause the depth of the cut to be deeper at the bottom versus the top. A sort of reverse guide for the broach below the bottom of the piece that keeps the broach in line and counteracts the broaches teeth attempting to dig in deeper than wanted may do the job but is difficult to implement. Another way may be to make the bushing longer and part the excess off after broaching.

Peter J.


----------



## ICEpeter

The effect of the broach wandering to the outside maybe reduced if a multi step broaching process is used by using maybe two or three stepped broach bushings and taking lighter cuts and not one full depth cut with the broach.

Peter J.


----------



## mayhugh1

All good comments. The specs for the Dumont broach are a maximum length of cut of 1-1/8" and a required pressure of 780 pounds. I suspect the one ton press being max'd  out was probably related to the broach drifting and taking a bigger byte than it was supposed to. It's probably also true that the press isn't really capable of its own rating.
The broach was rated to take the cut in one pass, but creating some additional bushings for a couple lighter passes might have helped. I thought about trying that at the time but cutting deep 3/32" square slots in steel bushings looked like another set of problems to deal with.
If you study the teeth on the broach you'll probably agree with PeterJ that the broach is just waiting for an excuse to drift out and take too big of a byte. Probably even an imprecise sharpening job would make the problem even worse very quickly.
After thinking about it for a few days, I'm beginning to think the problem was in my technique. I had only a quarter inch clearance in my press to start the broach; and I'm pretty sure that due to a lack if experience I wasn't paying enough attention to getting the broach started truly vertical with its spine totally against the bushing. This is a bit trickier than you might think since at the start of the operation the broach isn't yet sticking out the bottom of the workpiece, and at the top there are one or two teeth already down inside the bushing. So you need to pay attention to the angle of the broach with respect to the top of the workpiece which I was probably not doing. - Terry


----------



## bigrigbri

Bloody marvelous


----------



## mayhugh1

After finishing the prop shaft it seemed reasonable to complete the rest of the parts needed to mount a propeller even though I'm a very long way from needing them. The Merlin drawings don't include a prop, but it wasn't difficult to adapt a large scale model propeller to its prop shaft. During my last radial build I was given a 26"x10" four blade prop that I never used. It'll be a negligible load for the Merlin even at its highest rpm, but it happens to be a semi-scale prop for a P-51 Mustang, and so the Merlin will be a fitting home for it.
The center of the propeller was drilled out with a 1-1/8" Forstner bit to accept the splined hub I machined earlier. A second hub without splines was turned and bored for a close slip fit over the prop shaft. The propeller will be sandwiched between these two hubs, and the assembly held together with six 6-32 SHCS. The ends of the hubs bottom against each other inside the prop to avoid compressing the prop when the screws are tightened. Because of the clearances involved, the bolts need to be tightened while the assembly is aligned and on the prop shaft. I made this step difficult when I designed the assembly with the bolt heads facing to the rear of the prop. Fortunately, the splined aluminum test shaft I made earlier turned out to be a perfect tool for performing the assembly off the engine.
I machined a castellated prop nut to keep the prop assembly on the shaft. Its 7/8"-20 thread was cut for a very close, but smooth fit to the shaft. The prop assembly is captured between this nut and the inner race of the large gear case bearing. The rear side of this race is backed up by a machined shoulder on the prop shaft. An actual full-size prop assembly would have also included a pair of centering cones.
The front hub was previously threaded for a spinner to complement the P-51 prop. My decision to attach the spinner in this way wasn't well thought out, and it greatly complicated the spinner design after I decided to extend it between the prop blades. This required a two piece spinner with a rather complex rear half.
The spinner halves were designed around a pair of short 4" diameter 6061 drops that I had in my scrap collection. After truing them up, the machining on the rear end of the front half was completed while it was still easy to fixture. This included a 1-1/2"-18 thread carefully matched to the one on the front hub to minimize any run-out of the spinner. This hub was also used as a mandrel for turning the spinner's profile. A small radial through-hole was also drilled and reamed for a tommy bar. The profile was drawn in SolidWorks and turned on my 9x20 lathe using g-code generated by Sprutcam. I really wanted to make the front spinner slightly longer, but I continued with the material I had on hand.
The rear half was machined from the second drop. It turned out to be a fairly complex part for all that it does. Several boring operations were completed on the lathe before moving it to the mill to machine the prop blade cut-outs and internal contours. The deep and narrow slotted mounting holes were the most difficult features to machine, and I ended up writing scratch code to plunge mill them. Plunge milling is a feature that would be worth the price of an upgrade to my CAM software, if it were ever offered. During assembly, the rear half of the spinner with its four loosely inserted mounting bolts is slipped onto the prop shaft before adding the prop assembly. After tightening the prop nut, a shoulder on the front half of the spinner slides into a recess in the rear half as it's threaded onto the front hub. Finally, the four rear spinner bolts are screwed into threaded holes in the front half of the spinner. Removing the propeller will be a bit like opening a Chinese puzzle box. - Terry


----------



## stevehuckss396

Fan-freakin-tastic


----------



## Swifty

Your attention to detail is amazing, even your clamping down of the prop to bore out the centre is well thought out and executed. 

Paul.


----------



## Scott_M

Holy Crap Terry !!

That is one impressive spinner.  It looks really cool with the 4 blade prop.

That is definitely not  one of those snap on plastic spinners from Tower Hobbies  .

Scott


----------



## Gerhardvienna

Hi Mayhugh1
Who the hell will build the MK24 around it and fly that monster:hDe:
You are a real role-model to me! Thanks for showing, waiting for much more!!!!!!
Regards 
Gerhard


----------



## ddmckee54

OK, I think I'm following how the spinner is mounted.  The front half of the spinner is threaded onto the front of the prop hub, then the back half of the spinner is bolted to the front half, easey-peasey.

My question is how are you going to start this beast?  If you use an electric starter pressed against the spinner isn't that going to loosen the spinner?  I realize that it can't loosen too much, but won't that allow the slots in the back half of the spinner to rattle against the prop blades?  What am I missing?

Don


----------



## wirralcnc

Scale coffman starter???


----------



## mayhugh1

Don,
You're right. I've not provided a way to start this engine using a starter on the front. This engine has a starter shaft that engages a gear on the rear of the crankshaft. It has a one way clutch and can be driven by a drill, but I'll likely adapt an electric motor to it. - Terry


----------



## ddmckee54

Terry:

I knew there had to be something that I wasn't seeing, thanks for showing me the light.

Don


----------



## mayhugh1

I returned to working on the heads and, in particular, the camshaft assemblies. I should start with the valves, but I have some more thinking to do about how I'm going to handle the seats. There will be nearly 300 parts in each top end, and so I'm going to be working on them for a while. 
The Merlin is an overhead cam engine, and each camshaft in the full-scale version is connected to the crankshaft through nearly a dozen gears. Mercifully, the designers of the quarter scale version reduced the cam drive system to a much simpler chain drive, and they converted the model from four valves per cylinder to two. The quarter scale's top-ends are really impressive and probably why I've seen photos of the model displayed without its valve covers.
The camshafts are almost ten inches long. Each has seven 9/32" diameter bearings and will be turned from a single piece of steel. I thought the crankshaft would be the most difficult part of this engine, but making the camshafts will be another growth experience.
The first challenge, though, is to machine the bearing blocks that support the camshaft and rocker arms in each head. There isn't enough height clearance in the heads to properly line bore the bearings, and so great care is needed to individually machine these deceptively simple parts so they can be assembled in proper alignment.
The first step was to machine the mounting surfaces for the bearing blocks in each head. An alignment key slot was milled at each bearing location in addition to a pair of drilled and tapped holes for mounting studs. The key slots are especially critical, and they form the foundation on which the assemblies are built. Matching keys are milled into the lower halves of the bearing blocks, and these fit tightly into the alignment slots.
Each bearing block consists of an upper and a lower section that are dowelled together with two short lengths of #9 gauge hypodermic tubing. The mounting studs pass through these dowels. In order to make the parts as identical as possible the first stud hole in each bearing block pair was reamed for its dowel with a snug fitting gage pin inserted in the opposite side hole pair. The second hole pair was reamed in the same set-up with the first dowel set in place. Even though a floating reamer was used, testing showed the holes had to be reamed .001" over the diameter of the dowels in order to absorb machining errors and facilitate assembly/disassembly of the block pairs.
In addition to alignment keys, the drawing notes recommend machining the mounting studs with essentially zero clearance to the dowel i.d.'s. Following this recommendation locates each bearing block to its position in the head with three zero-clearance anchors. In addition, since the studs penetrate the coolant jackets, and so the drawings warn that the studs must be Loctited in the heads using a fixture to insure the studs are truly vertical when cured. It seemed to me that using the studs in addition to the keys to locate the blocks in the heads would create more problems than they solve. I could visualize ending up with fitments that were too snug to even be assembled, and most likely the bearings would have to be reamed over-size anyway. 
Instead, I decided to mount the bearing blocks using SHCS's whose o.d.'s measured .005" under the dowel i.d.'s. I reamed the blocks a thousandth over the diameter of my camshaft test bar, but as expected the fit of the bar in the seven block assembly was too tight. After reaming the bores another thousandth over, the test bar turned freely. Both head assemblies were checked using the same +.002" bearing bore, and they were assembled/disassembled a few times to verify the alignment repeated. The test bar proved the block alignment was sufficiently precise, and its diameter set the target for the cam bearing diameters. 
Although it wasn't necessary to select blocks for a particular location, I plan to engrave the blocks with their current locations so the same tested assembly can be duplicated.
The next step is to add the rocker arm assemblies. - Terry


----------



## petertha

Wow again
- dumb question, but after you profile mill the block outlines from solid bar stock, now they are little islands but still attached. Do you then flip the bar over & mill the backside to 'release' the parts? If so, what keeps the parts from flying around once the end mill breaks through?

- Is the center hole for oil lubrication? If so, where does the waste oil get picked up?

- just curious (sorry if you already mentioned), what did you receive for plans & instructions package? I'm visualizing a volume set of Encyclopedia Britannica... but suspect something less  Are they kind of builders notes with pictures or set of plans only? Are you modelling in SW as needed or just when required?


----------



## mayhugh1

Peter,
The hole you see was drilled for an oil passage and it will be plugged with a screw. The waste oil collects in the head and splash lubricates the cam lobes. When the level gets high enough it drains back into the sump through the cylinder stud tubes.
The documentation I received was about 100 sheets of drawings and some 30 pages of notes. About a third of the notes are 'boiler plate' talking about the need to straighten the castings, etc. There isn't alot of hand holding, which is OK, but it feels like some key basic information has been left out. For instance there are ports that aren't documented, and so I'll probably end up plugging them until I realize what I should have done with them. I'm only modelling portions of the engine that will help me understand and/or visualize some of the more difficult (for me) workings. For instance, I'm really struggling with the two camshafts which are not identical and not at all intuitive due to the crazy rocker assemblies. 
These particular cookie sheet parts were cut apart on a bandsaw after being milled, and a secondary milling operation brought them to their finished height. Terry


----------



## Scott_M

Hi Terry
Looking fantastic !
I can recall working on some automotive cylinder heads ( aluminum ) that had different torque values for the head bolts. The reason was the head was structurally weaker in some places and would distort. Just a thought, you may want to try bolting the head to the block and see if the cam still spins. It would be one of those things that would be nice to know before final assembly. 

Scott


----------



## mayhugh1

Well, Scott, that didn't occur to me. I can't test it in any meaningful way, though, until I make the liners since the heads sit down on them and not the blocks. In my previous mock-up I used some delrin spacers to simulate the portion of the liners above the blocks, but the delrin would compress in a torque test, and the result wouldn't be meaningful. Something else to worry about, I guess. - Terry


----------



## Scott_M

Oh man,I didn't mean to add anything to your worry list. :-[ 
And I'll bet you can deal with it at that time. Just sneak up on your target torque values while testing for cam rotation. Chances are good that you will be fine. 
I just thought it would be worth mentioning.

It really is looking fantastic.

Scott


----------



## mayhugh1

The bearing blocks support not only the camshafts but also the rocker arms above them. After gaining confidence in their keyed alignment, I drilled and reamed the blocks for the rocker shafts. Again, I reamed the blocks .002" over the diameter of the shafts. Although the drawings specify the shafts with zero clearance to the blocks, I didn't want to risk the possibility of them affecting the alignment I had already achieved. I later realized that this clearance is also needed during assembly because in order to install the rockers the shafts must be slid in from the rear of the head through the already installed blocks. The alignment of the rocker shaft bores was verified using a length of the drill rod that was eventually used to make the shafts. 
Each assembly uses six individual rocker shafts rather than a single continuous shaft. This is done so the shafts can be axially drilled for a central oil passage to lubricate the rocker arms and cam bearings. The cam lobes are splash lubricated with waste oil that accumulates in a trough that runs the length of the head. This waste oil is eventually returned to the sump at the bottom of the engine through the stud tubes. Special slotted washers under the stud nuts on the outer (lower) studs provide the return paths.
My castings and bearing blocks are a bit different from those in the photos I've seen of Gunnar's completed engine. Gunnar started construction, in 2006, of one of the first engines sold, and his is the only completed engine for which I've been able to find any construction photos. From what I've been able to tell from translating a copy of a diary he sent me, he also helped debug the Quarter Scale documentation. Evidently, the bearing block design evolved into the version in the drawings that I have. Gunnar's photos show two screws in the top of each block that were likely used to secure the ends of the rocker shafts. A gap is needed between the adjacent tubular shafts so oil can flow out from between them and down through a drilled hole in the center of each bearing block. It's this oil that lubricates the cam bearings. My drawings call for a single screw in the center of the block which I assume is now used as a separator between the shafts to establish the required gap. Since there's no provision other than a recommended close fitment to prevent the rocker shafts from spinning, I drilled and tapped the sides of my blocks for set screws to secure them.
Another major difference is that oil is pumped into the top of the bearing block in the center of the assembly in Gunnar's engine. My drawings show the oil being injected into the side of the rearmost bearing block. This was a peculiar change because most of the oil port in this new location is blocked by the bearing block's mounting studs. Even though I would have thought it best to inject the oil in the center of the assembly, I decided to follow the revised drawings. There was probably a good reason for the change, and it might have been that the original top-ends were being flooded with oil. This would also explain the change to the head castings that included a deeper waste oil trough.
While the blocks were out of the assembly to be drilled for the rocker shaft set-screws I also engraved their sides with their current positions in the assembly. This will insure the blocks always go back into their original tested locations.
The rocker arm design is rather novel and deceptively complex. I was able to do most of the tedious machining on the Tormach, but finishing them to their final width became an issue since there weren't two parallel surfaces to grip in a vise. After ruining all my spares by launching them across the shop, I machined a plastic fixture to orient the rockers so they could be held in a vise while being finished. I also machined a fixture to safely and accurately machine the slots for the cam rollers - four at a time. I substituted standard miniature ball bearings for the shop-machined cam rollers shown in the drawings. Curiously, the rollers in the drawings were an exact match to a standard bearing.
The Merlin has 24 rockers, and the exact same part is used on both the intake and exhaust valves in both heads. Using a common part simplified the construction, but it will also result in two very different profiles for the two camshafts. The effects of my short crankcase continued to bubble up through the top-end of the engine, and the rocker arms and shafts had to be modified to accommodate my shorter cylinder spacing. The camshafts will also have to be modified.
The machined parts needed to complete the cam block assembles included 24 valve rollers, eccentrics, and thrust washers. The number, intricacy, and small size of the aluminum bronze eccentrics would have made their machining very tedious on manual equipment. The valve rollers were hardened after being parted off from drilled-through lengths of drill rod. Care was taken when preparing the workpieces to make sure the holes were drilled through the exact center of the stock. If the shaft holes aren't centered in the valve rollers, the lash will be inconsistent as the rollers spin on the eccentrics. The tiny thrust washers for the valve rollers were turned from phosphor bronze.
I made two full sets of eccentrics having two different offsets. The offset of the eccentric wasn't specified in the drawings, and so I thought it best to have some options available when the camshafts and valves are completed. After thinking about it more, I realized it really wasn't necessary and was a big waste of time. 
Adding the rockers to the cam block assemblies added another 200 parts to the engine. I'm going to take a break from the high volume stuff for a while and begin working next on the camshafts. - Terry


----------



## Scott_M

Again...Wow. Really nice work Terry !

Have you ever used Polycapralactone to hold odd shaped parts ? I works really well and saves a lot of fixture time. Tormach sells it. 
Pretty handy stuff.

http://www.tormach.com/store/index.php?app=ecom&ns=prodshow&ref=31846

and

http://www.tormach.com/blog/super-soft-jaws/

Scott


----------



## mayhugh1

Scott,
I've been meaning to try it and have been planning to include some on my next order with Tormach. It does look really useful. I once used a football mouthpiece that I found in a local Walmart to solve a tricky fixturing problem, and it may have been made from the same stuff. After being heated in water it would conform and hold its shape. I only used it once, and so I don't know if it could be re-used like the Tormach product. - Terry


----------



## Cogsy

I bought some of the same sort of thermoplastic a while back and I have used it a lot, for everything from workholding to repairing items around the house (the button mechanism of the kitchen garbage can entirely relies on this stuff) and even replacing half of the nosepiece on my sunglasses (most people can't tell it's not the original piece). I haven't tried directly machining it yet, although I hold high hopes. 

I can confirm it is a great product, but it is the same stuff sold on ebay under various different names (plastimake, etc) for much cheaper. I paid around $25 USD including postage for 1kg (2.2 pounds) of the stuff. But it goes a long way, my 4 kids have all made toys with it, various friends have created stuff and I have made many things, yet I still have 3 of the 4 250gm packets it came in unopened.

Long story short, grab some cheaply off ebay and have a play with it, everyone should have some on hand.


----------



## mayhugh1

The Quarter Scale Merlin's camshafts seem like perfect candidates for being built up similarly to the cam in Jerry Howell's V-4. The camshafts are almost ten inches long with diameters over most of their lengths on the order of a quarter inch. One of the photos shows a sketch of the cam blank that will be used in both heads. There are clearance grooves on each side of the bearings, and a narrow integral thrust bearing at the rear end limits the shaft's forward/aft movement. The necked down sections between the lobes are required to clear the valve spring assemblies. The rear of each shaft will later be fitted with a sprocket drive adapter, and I added a hex at the front of each shaft per John's suggestion to help with indexing the cams during final assembly.
I originally thought I would machine six spools for each cam with each spool having an intake and exhaust lobe pair separated by a turned bearing. I planned to bore these spools for a close slip fit on a length of known-straight drill rod. Done this way, the cam lobes could be easily machined with the spools set vertically in a simple fixture on a 3-axis mill. A difficulty with this built-up approach, though, is that a scheme is needed to accurately align the spools on the shaft before the Loctite sets up. If the parts are properly prepared this can occur almost immediately. Being roller cams I wouldn't expect the load on the Loctite'd spools to come anywhere near the shear strength of the adhesive. 
I decided, though, to first try my hand at machining a test blank from a single piece of steel, mainly to see if I could do it. I considered more than half the battle being the machining of the cam blanks with the same fit that I had with the drill rods in my cam block assemblies. To machine the actual cam lobes I'll most likely later create a CNC program similar to the one I used to machine the crankshaft counterweights. My concerns with a single workpiece approach included warping as well as my own ability to stay focused throughout the lengthy and unforgiving machining required to complete the entire part. If the test part wasn't reasonably successful, I still had the option of making the cams as built-up assemblies.
I started with a length of ground/polished 5/8" diameter Stressproof that I ordered from Speedy Metals. I bought enough (surprisingly inexpensive) material for two camshafts plus a spare for about $15 plus shipping.
On paper I divided the cam blank design into six 1-1/2" long segments, and I made six worksheets with all dimensions referenced to the same lathe z=0 point at the rear of the camshaft. I kept the pertinent sheet immediately above my lathe at eye level to help keep me focused. My plan was to chuck the workpiece into the 5C collet chuck in my manual lathe and incrementally pull it through the collet just far enough to machine a single section at a time. The run-out of my lathe's chuck and collet combination is pretty lousy at almost four thousandths, and so I used a reference line scribed along the side of the rod to maintain a consistent alignment as the workpiece was pulled through the collet. I was careful to always tighten the chuck using the same key socket, and I used a dial indicator to verify the runout near the far-end of the workpiece after each repositioning. After every other repositioning I also found it necessary to pull the workpiece out of the collet and the collet out of the chuck and clean the chips off everything before reassembling. 
Even though it wasn't initially needed, I started out using a live center in the tailstock to prevent the workpiece from whipping around as more of it was pulled through the collet. The rear end of the cam required some machining for a sprocket drive adapter, and so this was done on the mill before starting the lathe work. Part of this machining included the reaming of a locating recess where the tailstock center would wind up, and so I turned a center-drilled button to insert into this recess. My live center has a run-out of 1-1/2 thousandths, but in this particular set-up the tailstock is used only for stabilizing the far end of the workpiece and, so there's no first order effect on turning accuracy.
As a precaution I decided to turn the bearings a thousandth under the diameter of the test rod that currently fits my cam block assemblies, because I didn't know what to expect for machining-induced warpage. The completed ten inch blank will be somewhat flexible, and with seven bearings supporting it, the assembly itself might tend to gracefully straighten out a slight bow without binding. I also added generous fillets to the blank on each side of every lobe in hopes of reducing the tendency of the workpiece to warp during machining. I had no science to justify this, just gut instinct.
Most of the machining between the lobes was done with a full-radius Iscar grooving insert (GIP 2.39-1.20). This .093" wide cutter has sufficient relief to cut side-to-side chatter-free in steel for a depth of cut up to .010". I used this insert on my 18 cylinder build, but being designed for larger lathes it was necessary to modify its toolholder to fit my 1/2" Aloris clone tool post. Combined with the lathe's power feed, I found this insert capable of mirror finishes in Stressproof. The only polishing I had to do was typically to remove a few tenths with 1000 grit folded paper.
The machining of the blank's numerous features was, as expected, pretty stressful and required a lot of concentration. I spent nearly ten hours bent over the lathe making the test cam blank. I had to spread the machining time over a couple days to accommodate my knees, back, and frequent bouts with brain fog. A real disadvantage of this single workpiece approach is that a momentary lapse of attention can spoil a lot of invested time. To be honest, I'm not sure I can come up a single advantage of this approach over a built-up version.
The TIR of the finished blank, measured at its center between two vee-blocks, was only 1-1/2 thousandths - a very unexpected surprise. The blank fit nicely in my cam block assembly and spun so freely that I was left thinking that the extra thousandth bearing clearance that I had added wasn't necessary after all. 
I ran into an issue, though, when I installed the rocker arms. For purely cosmetic reasons I had increased the width of the cam lobes shown in the drawings. What I hadn't realized was that the cam lobes actually run inside the rocker arm slots for a portion of their rotation. After going back and modeling this section of the assembly I realized that the stock assembly had been designed for only .007" radial clearance between the peak of each cam lobe and a portion of the rocker body inside the slot. When I machined the cam blanks I left an excess radial stock of .010" on the unfinished lobe disks, and this created interference. As I discovered, there's very little leeway in the design of the cam block assemblies, and the tight clearances between its numerous parts needs to be carefully followed. I was able to salvage my test blank by re-machining the widths of the lobe blanks. Since these were facing operations, they didn't affect the TIR of the blank even though I no longer had a reference line and had to use a different collet for the re-work. I left the excess radial stock, though, for the lobe profiling operations later.
With the test cam feeling like a success, I continued on and machined two more cam blanks from the material I had left. For these 'production' blanks, I didn't add the extra thousandth bearing clearance that I had used for the test blank. The TIR of the next two blanks measured .002", and even without the extra thousandth bearing clearance, both blanks turned freely in both assemblies. Except for the bearing clearances of the test part, all three cam blanks are essentially identical, and so I ended with an unexpected spare. The next step is to figure out how to fixture the blanks so the lobes can be machined without screwing them up. - Terry


----------



## wirralcnc

Terry great job on the cam blanks. As a lobe milling fixture can you not machine a vee block up. Keyed to the table of the cnc along the x axis. Then machine a slot 90 degrees to the vee. ( y axis ) for the lobe blank to sit in. Then you can machine each lobe and just move the cam along. A simple indexing plate on the end of the cam to aid indexing each cam lobe. Robbie


----------



## mayhugh1

A curiosity that I encountered with Stressproof but forgot to mention in my last post, is its tendency to become magnetized while being machined. If you look back at the second photo in my last post you'll see the chips standing up along flux lines created by drilling-induced magnetism. The residual magnetism of the final machined blanks was strong enough that they tended to stick to my metal work table without wanting to roll around. I've included a photo of a rocker shaft attracted to an end of one of the finished blanks. Before starting the lobe machining I degaussed the blanks using an ancient bulk tape eraser that I keep around the shop. Residual magnetism can create surface finish problems when chips clinging to the workpiece are re-cut. This issue wasn't noticeable while I was turning the blanks because I was using a drop-type coolant dispenser with the air flow turned up high enough to blast the chips away from the cutting tool. This magnetism may have been the cause of the poor surface finishes that I consistently experienced while trying to bore Stressproof a few months ago while testing its suitability for cylinder liners.
Continuing, though, with the experience I gained earlier while working on the crankshaft I was able to use the 'rotary machining' operation in my Sprutcam software to create the g-code to machine the cam lobes. The profiles of the intake and exhaust lobes on the Quarter Scale cams are identical, and so I compiled a single lobe profiling program and fine tuned it using some scrap material. 
I found a local source for true flat bottom carbide end mills, and I was able to use them to mill rotating fourth axis surfaces flat and without chatter. Since the diameter of the cutter I used was wider than the lobes, the program didn't require any lateral moves. I had to hone a small radius on the tips of the cutter, though, to get rid of a slight gouge that consistently showed up on a portion of the linear ramps of the lobes. After making this modification, the surface finish was very smooth and required only a fine Scotchbrite pad to polish off the machining marks.
A significant issue, of course, was fixturing the long skinny cam blank in the mill. It might have been possible to machine the lobes with the blank supported in the cam block assembly itself. However, the same clearance issues that prevented me from line-boring the assembly also prevented connecting the blank to a rotary. Machining a similar assembly in a new form factor with rotary access seemed like a lot of work with no guarantee that the resulting clearances wouldn't create chatter that would degrade the surface finish.
The solution that I finally settled on was to support the cam blank in a collet chuck installed on my horizontal rotary. And, as with the blank machining, I incrementally pulled it through the collet just far enough to machine one lobe at a time using my already tested code. In order to grip the blank I machined three pairs of split brass collets to fit the finish-machined surfaces on the blanks. 
After the blank has been chucked and referenced, the rotary can accurately keep track of its angular position, but when the chuck is loosened to reposition the blank this reference is lost. In order to get around this, I machined a disk having a snug fit over the tailstock-end of the blank. Once attached, the disk was prevented from slipping on the blank by a pair of setscrews tightened against the flats of the hex that was previously machined on the front end of the blank.
A centerline was scribed across the face of this disk and, with the blank secured in the chuck, the rotary was used to set this line vertical. The profiling code was then used to cut the first, or reference, lobe. The code machines a single lobe with its nose pointing straight up, but it also assumes the rotary is initialized to zero degrees before it is run. Since the lobe disks had already been machined on the blank, it was only necessary to position the correct one just outside the chuck and then approximately center the end mill over it. I color-coded and numbered each disk on both blanks to help me keep track of which lobe I was working on to avoid making stupid mistakes. 
Setting the correct angles for machining the rest of the lobes is certainly simple in theory, but in reality there are a lot of opportunities for screw-ups. After the first lobe was machined the vertical line on the reference disk was used as the workpiece reference to set up the angles for the remaining eleven lobes. A machinist square set against the scribed line on the disk was used to reset the reference lobe each time the blank was repositioned. The angle of next lobe to be machined was computed from this reference. The main difficulty was keeping my brain from going into standby mode while going through the multitude of repetitive motions and remembering to re-zero the rotary before running the code.
Fortunately, both cams were completed without incident; and, as far as I can tell, they are correct. I usually have difficulty interpreting model engine camshaft documentation, but the Merlin drawing seemed well thought out and unambiguous. I decided to not do any further machining on the spare test blank but to save it in case one of the completed cams had to be replaced.
One of the photos shows a comparison between the two very different cam profiles for the port and starboard heads of the engine. The reason for this difference is that both cams turn in the same direction, even though the positions of the intake and exhaust valves are reversed between the two heads. The intake rocker is 90 degrees ahead of the exhaust rocker in the port-side cam, and the reverse is true for starboard-side cam. These rocker arm geometries create the need for a 180 degree difference in the lobe separation angles between the two cams which makes them look very different. The six lobe pairs on each cam are, of course, separated from one another by 360/6 = 60 degrees.
With the excess stock machined away from the lobes I was finally able to test the fit of the rockers with the cams installed. I thought I could feel a slight interference between the cam lobes and the inside corner of the slot where the design clearance mentioned in my previous post is minimal between the two. I disassembled all the rockers and filed a relief fillet on this corner, which probably should have been a part of the original rocker design.
The next step is to continue with some of the less stressful camshaft drive components. - Terry


----------



## cfellows

Terry, the quality of your work never ceases to amaze me.  Now that the cams are finished, I guess it's all down hill from here, right?

Chuck


----------



## mayhugh1

Chuck,
On this engine it seems like everytime I finish the hard part, the next one shows up.
Terry


----------



## DICKEYBIRD

mayhugh1 said:


> "...everytime I finish the hard part, the next one shows up."  Terry


Them's powerful words pardner!;D


----------



## makila

Hi Terry,

Great work as usual, I have a question regarding the appearance of the cam lifting lobes. Even though you explain this in your post above. It still appears an odd timing sequence when you consider the rotation of the cams in any direction.

Looking at the cam lobes, the lifts on the Starboard cam look like they are closer to 180 degrees (I am guessing), whilst the lifts on the Port side look closer to 20 - 30 cam shaft degrees, (not crankshaft rotational degrees), the lifts look odd on the Port cam assembly as both valves appear to open within the same 180 degrees of crankshaft rotation (or 90 degrees of cam shaft rotation) -considering the 720 degrees of rotation (2 x turns) of the crankshaft for a complete cycle.
The Port cam, on the other hand, looks to be too close to 180 degrees, but this may just be an illusion given that I am looking at a picture. Generally, (but not always) a cam has lobe spacing within the same 180 degree quadrant? Hopefully this is part of the design based on the rocker configuration that act on the cams from differing pivoting points.

Just read again your post, the rockers act 90 degrees ahead on one side, 90 degrees behind on the other side, this explains everything, left the post in however as it must take a lot of thinking to create this engine!! 

All the same, a great build that deserves to be followed by us all.

Regards

Steve


----------



## mayhugh1

The designers of the Quarter Scale Merlin greatly simplified the camshaft drive system when they converted it from a gear train of some dozen gears used in the full-scale version to a much simpler chain drive. They designed their system around a 3/16" pitch roller chain which, after an online search, I discovered is a fairly rare and difficult size to find. I contacted Nordex, the supplier recommended in the documentation for this chain, but was told they hadn't sold it for many years and no longer stock it. Fortunately, I received an email a few days later from a sympathetic sales lady who had come across a short length in obsolete inventory. The Quarter Scale documentation does mention that a more common .1475" pitch chain might be made to work with some sprocket changes, but I wasn't sure if its fit had actually been verified, and so I purchased the 3/16" remnant from Nordex.
The Merlin documentation includes drawings for machining the sprockets, but I used http://www.gearseds.com/files/design_draw_sprocket_5.pdf to double-check them. The tooth profile is rather complex; and this being my first experience with sprocket design, I found the Quarter Scale drawings a bit confusing. The reference helped me better understand the drawings but didn't completely agree with them.
I started with the 20 tooth aluminum sprockets that will be attached to the rear of each cam. The proper way to machine these miniature sprockets might be to first make a form tool similar to a gear cutter, but I thought I'd try to profile them with a 5/64" end mill that seemed to fit comfortably in the contours between the teeth. I turned the blanks on the lathe along with a fixture to hold them in a vise on the mill. The blank design includes 20 degree bevels turned on each side of the tooth contact areas. 
I used a 3X speed multiplier (Speeder) for my Tormach, to reduce the machining time while using the tiny end mill. To lighten the load on the cutter I pre-drilled holes between the teeth in order to rough out the workpiece. The idler sprockets are about half the diameter of the cam sprockets, and were similarly machined from 316 stainless. These little sprockets were fun to make and came out looking great, but I haven't yet been able to test their fit with an actual chain.
The drive system uses two drive sprockets and three idler sprockets, and so I made a few spares while I had the equipment set up. The crankshaft sprocket will be machined as an integral part of the rear driveshaft, and that will be made later after I have the chain in my hands.
The cam sprockets are attached to the cams with two-part assemblies that provide for rotating the cams with respect to the sprockets when the engine is timed. A hub is bolted to the rear of each cam, and the sprocket is gripped between it and a retainer which, in turn, is secured to the hub with eight SHCS. The screws are loosened in order to index the cams with respect to the crankshaft. The hex that John recommended be machined on the front of each cam will be used to rotate the cam before the retainer screws are tightened. This arrangement provides a very high resolution timing adjustment compared with the several degrees available from a typical gear driven system. The hub was machined from drill rod and hardened whereas the retainer was machined from 6061 aluminum. - Terry


----------



## dsage

Hi Terry:

I've been watching silently in awe of your workmanship. Wonderful as usual. 
  Have you attempted to measure the lift and duration as well as lobe center angles of your cam lobes? Perhaps the drawings didn't specify actual duration, overlap etc. but sometimes it's interesting to measure and record it.
   I usually set a dial indicator (with a proper sized tappet pad) over a cam lobe on the centerline of the shaft and use the rotary to measure the pertinent points in degrees like open and lose angles. Taking into account a bit of gap for desired valve lash.
  For you, using the indicator with a flat tappet will of course give you different results than you will actually get on the engine since you are using a roller rocker, unless you can arrange a similar sized roller on the end of your dial indicator. Might be interesting to try.

Amazing stuff your doing. Keep it coming. 

Sage


----------



## dsage

Oops. One more question.
 Is it just clamping force that keeps the sprockets from slipping in the clamps / retainers or am I missing some small detail there.

Sage


----------



## mayhugh1

Dave,
I haven't made any actual measurements yet and will probably wait until the valves are installed so I can make them at the valve tips. The specs for the cam are:
intake opens 10 deg BTDC and closes 50 deg ABDC
exhaust opens 50 deg BBDC and closes 10 deg ATDC.
So, the valves are open for 240 deg of crankshaft rotation plus another 10 deg or so on either side for lash take-up.
Yes, it is the clamping force that holds each sprocket in position. If you look closely at the photo of the retainers, there is a small ridge turned on the rear of each retainer near its i.d. for this force to react against.  - Terry


----------



## mayhugh1

I took some time off for travel to visit my youngest son and to attend my newest grandson's first birthday party. With me I took a single Merlin drawing so I'd have something to keep my mind occupied during our quiet time. This drawing contained the design of a three-piece cover for enclosing the timing chain and sprockets. Four aluminum tubes interconnect two upper covers located at the rear of each head with a third cover enclosing the idler sprockets at the top of the wheel case. I spent many hours before and during our trip trying to visualize these upper covers from the flat views in the drawing. These two covers are the most complicated parts in the assembly, and their dimensions are critical. But, most of their design is contained in a sectioned view of a drawing detail taken from a top view of an assembly drawing of an installed cover. All the information was there, but with no photo or isometric view to help me get started, they just didn't want to come into focus for me regardless of how long I stared at them.
After returning from our trip, I began modeling them in my CAD software. After a couple days of trial and error but no 'a-ah' moments, parts slowly took shape that reasonably matched the drawing. To make things a little more interesting the drawing contained the design for only one cover, and it had to be mirrored to get the second one. Some of the dimensions had to be changed to fit my particular castings, and I also made some changes to the mounting screw locations since there appeared to be issues with the ones in the drawing. After compiling my own 3-D assembly it was obvious what the drawing was trying to tell me, and I'm embarrassed to admit how much I had struggled with it. In any event, I've included several photos of the final parts so the next builder will have a better starting point.
This timing cover was not part of the original Quarter Scale design. From what I can tell from translating Gunnar's diary, it came into existence after he complained to the original designers that the engine needed a cover and that he intended to design one. The designers apparently agreed, designed one of their own, and sent him the drawing that I've been working from. This drawing was included as an addendum to the rest of the Quarter Scale documentation, and it's dated without revisions to the time Gunnar was working on this portion of his engine. Notes accompanying the drawing warn that the design is intended only as a suggestion, and modifications and individual fitting may be required. I did find it necessary to make a few changes; but, over all, the design seems pretty well thought out, and it's nicely integrated into the engine's overall design. 
The three machined covers will be connected by four metal tubes in a close-fitting rigid assembly that must clear the chain. I focused only on the two upper covers at this time and will probably make the third one later along with the rest of the wheel case components.
The top covers were every bit as complicated to make as their drawings were for me to understand. Eight different set-ups were required to machine all the features on each cover. Construction began by contouring their outer peripheries from chunks of one inch aluminum. A clearance notch was then milled along one side of each cover in order to clear a flange on its head. It's important for the depths and angles of the holes that are drilled and counterbored for the interconnecting tubes to be spot-on so the three covers can properly mate up without interfering with the chain. I used a sine plate to set the head of my mill for these operations. Although I got the angles correct, I managed to scrap several hours of work when I reversed the two degree angled holes on both parts. These particular holes were a constant source of confusion for me since, to me, they always seemed to be going in the wrong direction.
After re-drilling the holes in a pair of new parts I milled the shallow rectangular pocket in the top of each part which allowed me to compare the drilled hole intersections with those in my CAD drawing. When the intersections didn't match I realized the first two parts were actually correct after all. I exchanged my two new workpieces for the pair I had thrown into my scrap pile and continued on, hoping the brain cobwebs would soon clear.
The next step was to machine the clearance pockets for the cam drive sprockets. These pockets are contoured to fit very closely to the diameter of the sprocket with its chain. My piece of NOS chain had arrived while we were on our trip, and so I was able to use it later to check the clearances. I set the first cover up on my lathe faceplate in order to bore the pockets, but while I was trying to make up a one-off boring bar I decided to CNC the pockets using an ordinary end mill on my Tormach. The pockets came out looking great, but the end mill's diameter reduced the clearance to the chain a little more.
I filleted the rear outside corners of the covers. This wasn't a part of the original design, but I thought it was a nice touch to what had turned out to be a couple of really miserable parts. The final step was to drill and tap the five mounting holes in each cover and head. The drawings called out 1-72's but warned that washers might be required due to break-outs created by the limited drilling space. I dropped down to 0-80 button-head socket screws to avoid this, but I had to carefully match drill each pair of holes. I'm really, really glad these two covers are finally finished. - Terry


----------



## petertha

Very inspiring. Angles, angles, everywhere angles. Initially I wondered if the roller chain could install as a closed loop.. but now other bits enter the picture. Is it threaded through the assembly open ended & then linked together? Is there any tension tweak-ability with the intermediate sprocket? Re the sprockets you made, do those get hardened?


----------



## mayhugh1

Peter,
I think the chain will have to be linked together after the cover assembly is assembled on the engine. The third cover is to be built as two halves so it can be closed up after the chain is linked. The assembly process will be tricky, but hopefully it will have to be done only once. One of the three idler sprockets inside the third cover will have limited tension adjustment, and so the chain will need to start out with the right number of links. 
The cam drive sprockets are aluminum, the idler sprickets are stainless steel, and so only the chain is hardened. - Terry


----------



## jimjam66

The only adjective I can think of is 'extraordinary'!  I can't think of many people who would even take on this task, let alone produce such ... extraordinary ... results.  Respect.


----------



## mayhugh1

While still procrastinating over the valve seats I decided it was probably safe to go ahead and machine the lower timing cover which is the third component in the timing cover assembly. Its drawing was much easier to follow, especially after my experiences with the top covers, but I'm pretty sure it is missing the dimension for its overall length. I had to use an actual measurement of the mating flange on the wheel case casting to complete my model.
The two pairs of interconnecting tubes from the top covers terminate inside this cover. Once its outer perimeter was contoured, the critical machining was basically more of the same angled drilling and counterboring that was performed on the top covers. This part had a slight twist, though, because it had to be split into two halves. Since the chain is completely enclosed by the timing cover assembly, the outside half of this lower cover can't be installed until the rest of the assembly is in place, and the chain is linked and moving freely without interference. The drawing for this cover recommends sawing it into two halves after completing its machining and then RTV'ing it back together during final assembly. I knew I wouldn't be able to live with the gap left by the saw kerf, and so I machined the part as two complete halves. The base of this cover is secured to the top of the wheel case with 14 screws, and there is a pair of additional fasteners pulling the two halves together. 
After machining the two halves, I drilled and tapped them for the 1-72 cross fasteners. To help support the two halves in alignment in the vise while they were being match-drilled for the cross fasteners, I used a short piece of Delrin round whose diameter was turned to closely fit the contour in the center of the part. After drilling, the halves were screwed together so the four tube holes could be machined.
The cover's mounting flange made it difficult to support during the angle drilling, and so I screwed it down to a sacrificial block. This block was machined with the two angles required for the drilling so I didn't have to adjust the angle of the mill's head. 
After the holes and counterbores for the tubes were completed, a shallow cavity was milled into the bottom of the cover to match the opening in the wheel case and to provide clearance for the chain. 
Two pairs of temporary tubes were cut in order to tie the three covers together as a sanity check on the assembly, but its final fit to the engine really can't be verified until the engine itself is closer to its final assembly. - Terry


----------



## Davewild

Beautiful Terry, absolutely outstanding


----------



## dsage

A work of art to be sure. And to have it all fit together AND look good too ! - Amazing.

Sage


----------



## ICEpeter

Terry,
That's a fantastic job. My admiration for those beautiful executed parts!

Peter J.


----------



## mayhugh1

Thanks all for your kind comments.... 
-Terry


----------



## mayhugh1

The last operation that I can do on the heads before I'm out of excuses to start on the valves is to machine the spark plug ports. The plans specify Viper Z2 plugs with their tiny 10-40 tapped holes because there just isn't enough room for anything else. I used much larger CM-6 plugs in my two radials because even though they were a poorer match to the scale that I was working with, they were much more immune to oil and fuel fouling. The Quarter Scale's plugs are located on the bottom outer sides of the heads just below the exhaust tips. They penetrate the sides of the combustion chambers right next to the exhaust valves, and so the hot exhaust gases may help to keep them clean. 
Since the full-scale engine uses two plugs per cylinder, the plans suggest installing a second set of plugs on the inner side of the heads next to the intake valves. Functional spark plugs placed in such a location in a model engine would likely be continually fuel fouled due to the cool fuel/air charge constantly flowing across them. And, so, this suggestion was likely for cosmetic reasons rather than for any improved functionality. At $23 each, I opted for one plug per cylinder especially after I realized the second set of plugs would be buried under the intake manifold, never actually seen, and be impossible to service without disassembling a major portion of the engine. In fact, I'm not even sure there's enough room under the intake assembly to install them. I currently have only two spark plugs for test-fitting, and I plan to wait until much more of the engine is completed before I order the remainder.
The ports for the plugs were drilled into the heads at alternating ten degree angles in order to come up with usable plug depths, and so counterbores were required for sealing surfaces for the scary narrow compression washers. Having learned a lesson about deburring spark plug ports during my T-18 build, I spotted, drilled, threaded, and then counterbored each port in the same set-up; and this time I left the corners of the threaded holes sharp.
As the photos show, the ports had to be carefully placed because of the limited space around them. My measurements predict the clearance between the plug's ground electrode and the stock exhaust valve would be on the order of only five to ten thousandths, and this is with a minimum plug depth that barely un-shrouds the plug gap. I don't plan to use the stock valve configuration, though, for other reasons.
The drilled/counterbored holes between the spark plugs are for 'freeze' plugs that will be installed later. These holes were actually cast into the heads for core supports, and they penetrate the coolant passages. I'll likely press/Loctite the plugs into place after all the valve work is completed just in case the heads need to be heated for the valve guide/seat installation. - Terry


----------



## mayhugh1

The valve guide/seat design supplied in the drawing package is similar to that used in the full-scale version. The full-scale heads were fitted with renewable steel alloy seats, while the intake and exhaust guides were machined from cast iron and phosphor bronze, respectively. The Quarter Scale documentation includes drawings for seats and guides, but the accompanying notes strongly encourage the use of integral seats instead. There's significant risk associated with installing seats in what, at this point, are irreplaceable heads. The floors of the combustion chambers are rather thin and known to be brittle, and I'm concerned about their ability to withstand the forces required for a .002" press-fit. In addition, the surfaces on which the concentric holes for the guides must be started and drilled through are pretty rough, non-parallel with the seat surfaces, and they may not be homogeneous. For good concentricity both the seats and guides should be press fit, although the guides can Loctited with a near zero interference fit. With 48 components to be installed, I'm concerned there's a good chance that at least one will end badly.
On the other hand, the critical machining required for a valve cage, although still no walk in the park, can be done on a lathe in a single set-up, and its accuracy can be verified before installation in the head. The precision of the required head machining can be relaxed some when using valve cages since high temperature Loctite can be used to seal and hold the cages in place. 
I briefly looked at integral seats. I estimated the peak pressure on the stock seats during combustion in this engine to be 16.5 kps, and I compiled a table of what I thought were the pertinent properties of some commonly used seat materials in model engines:
.
Material...............Yield/Rupture.................Brinell
.............................Strength....................Hardness
7075 Al....................73kpsi........................150 
6061 Al....................40kpsi.........................95 
356 Al......................26kpsi......................70-100 
544 Bronze...............57kpsi.........................65 
932 Bronze...............20kpsi.........................65 
954 Bronze...............37kpsi........................180 
Grade 40 C.I.............42kpsi........................220 
. 
The seats need to be durable (hard), but in a model engine we typically like them to conform (yield) to the valves over time for a better seal than we can typically achieve solely with machining. In the above table, 356 cast aluminum does look like a good candidate for valve seats in a model engine.
I've included some photos that I used while studying the intake and exhaust ports in the heads as well as some sectioned CAD assembly drawings I made. I also found an online photo of an actual sectioned Merlin head for comparison. Although the cam and rocker arm assemblies are very different between the full-size and the Quarter Scale versions, the cross sections of the heads are pretty similar.
An issue that the modeling uncovered is that the stock exhaust valve will indeed contact the spark plug if the plug depth is extended, as I have done, to un-shroud the plug's electrode. Since the heads came with large cast-in starter holes for the seats, I'll have to reduce the size of my valves as well as the i.d.'s of the seats compared with the stock versions. Smaller valves are a negligible price to pay to get the plug gaps inside the combustion chambers, though. The stock .560" diameter valves are much larger than necessary for a 3600 rpm engine, and this was also an observation made by the Quarter Scale designers.
The full-scale four-valve heads have vertical dividers in the intake and exhaust ports to isolate the flows between the valve pairs. The Quarter Scale ports have the same dividers even though the heads have only single intake and exhaust valves. I initially thought the dividers might have been present for mechanical support, but they were likely added for esthetics.
I made two cross-sectional CAD assembly drawings: one showing the stock arrangement with individual (or integral) seats and guides and a second one using my valve cage design. I cut away a portion of the intake and exhaust port dividers in the cage version because they blocked the machined openings in the cages. The dead space in the ports behind the cages could be filled with JB Weld to improve flow.
The cage version is a bit complicated because I'm using a valve cage in an existing head that wasn't designed for it. As a result, I'm adding additional risk when the object has been to reduce it. So, I generated a third assembly drawing which shows a modified version of the stock design with smaller valves but slightly larger valve stems.
Before making a final decision I thought it would be wise to get some experience with shrink fitting some test seats into scrap aluminum. I made a seat pocket boring bar from a four flute end mill by grinding down all the flutes but the shortest one on an eBay grab-bag re-sharp. This established the i.d. of my seat pockets at .493". I had some 1/2" o.d. phosphor bronze round stock on hand which, with care, can be finished with an o.d. of .495". This established the o.d. of my seats for an interference fit of .002".
I drilled a number of .427" diameter holes through some 1/4" aluminum stock to simulate the seat starter holes in my heads. I then used the boring bar to open up .100" deep, .493" diameter pockets centered on them. 
The .110" wide phosphor bronze seats were parted off from one inch turned/bored blanks, and a .005" chamfer was placed on their bottom outside edge to help ease installation. I also made an installation tool from a piece of drill rod to closely fit the .388" seat i.d. that I selected to use.
My first test was to tap a seat into place using the installation tool and a mallet in order to get a feel for the force required to seat it without heat. It took three healthy taps to fully seat it. The reason for the mallet is that my press is on the other side of the shop from my oven. Next, I heated the block to 400F and tapped in another seat. The effort required to install it in the heated block felt about the same as it did in the unheated block, and so I increased the temperature to 450F and tried again. The results were about the same with the third seat. Next, I purchased some dry ice to cool the seat and installation tool; and I reheated the block to 450F. With at least a 500F temperature differential the seat should have fallen into place, but again I got essentially the same results. At first I thought the seats might be warming up to the block before I could get them completely driven home. What was more worrisome, though, was that all the seats in my test block were sitting slightly crooked. I tried to section a couple of the installations to get a look at what was going on at the bottom of the pockets, but in both cases the end mill grabbed the seat and pulled it out. However, I found evidence of galling in the pocket wall as well as tell-tale aluminum slivers at the bottom of the pockets that were likely causing the seats to sit crooked.
I installed the next seat using the mill with the installation tool chucked into the spindle, and I pressed it into place immediately after boring its pocket. I didn't have enough leverage with the quill to completely set the seat, and so I had to finish the installation on my press. The seat appeared to be in straight, though I was left concern about the amount of force needed to install it.
Since I was sure the seats were being properly started on the mill, I decided to increase the size of their corner bevels to .010"-.015". This greatly reduced the installation force so I was able to fully seat three practice parts on the mill, and they finally looked straight. I also tried chilling a few seats with dry ice on the installation tool immediately before pressing them in. It was unclear, though, how much difference the dry ice made although I'm sure it likely helped.
These experiments told me that if I decided to use individual seats I would probably be better off installing them on the mill in the same set-up used to bore the pockets rather than trying to do shrink fits using a mallet. Of course a piloted installation tool would probably help. The logistics of adding heat into my mill set-up looked too tricky, but the truth is I never really did like the idea of applying heat and pressure to my already finish-machined heads. I think the dry ice, though, is probably a good idea. I once read a white paper that claimed that only about 30% of the area involved in a typical shrink fit really ends up in intimate contact. So, with the larger bevels I think the use of a bit of high temperature Loctite would be beneficial not only because of its holding strength, but it may act as a lubricant during installation. The dry ice, in addition to providing a bit of clearance, may prevent the Loctite from going off from the heat generated by the pressing operation.
Before making a final decision I need to machine a few cages and valve guides in order to make sure there aren't some surprises with them. If I'd have launched off with my initial idea of shrink-fitting the seats, the heads would now be sitting in my scrap pile.- Terry


----------



## kvom

That use of dry ice for facilitating shrink fits is a great idea.


----------



## petertha

Terry, is 356 aluminum commonly available as round rod, or maybe you will source from tooling plate stock or similar? Do you think the ring style valve seats can somehow lend themselves to a pre-testing apparatus along the lines of your vacuum method ie. pre-validates valve/seat before pressing them home? Ultimately, what would a remove & replace scenario look like?


----------



## mayhugh1

Peter,
The 356 is likely available only in ingot form as it's used for casting. The reason I included it in my table is that I was considering the possibility of cutting integral seats directly into the heads which, I believe, were cast from 356. It might be possible to check the seal integrity of an installed valve and seat by pulling a vacuum on the port, but it will require a complicated silicone plug to fit tightly against and seal to the port opening. As far a removing a worn seat, I guess if I really had to I would try to mill most of it out and then pick at the rest with a dental pic. - Terry


----------



## mayhugh1

The valve springs slip over the upper ends of the valve guides and cages. And, so, before the designs of those parts can be finalized the springs have to be defined. I would like to make the diameters of the valve stems as large as possible so the valves will be easier to machine, and this will require making the upper diameter of the guides as large as practicable. The clearances around the valve train will accommodate a maximum valve spring diameter of .310" at which there is a .010" minimum clearance between the edges of the keepers and the rocker arms. There was no design information provided for the valve springs, and so they will have to be designed from scratch.
The valve springs in a four cycle engine need to be strong enough to keep the closed valves tight on their seats with good gas tight seals. While I was leak-checking the valves during my T-18 build I found that 1 to 1-1/2 pounds of force on the face of the valve under test was sufficient to obtain each valve's best leak-down time. Another required function is that the exhaust valve spring must exert enough force on the exhaust valve to keep it from being sucked off its seat during w.o.t. If the springs meet both these requirements they will likely handle the rest of the valve train needs of a typical model engine. The unseating force on the exhaust valve that needs to be overcome is a result of atmospheric pressure operating on its face. 
For a calculation we can assume this pressure is 15 psi plus some implementation margin for a total of, say, 19 psi. To calculate the resulting force on a valve we need to multiply this pressure by the effective area of the valve using its diameter measured at the i.d. of the seat. My seat diameter is .388", and so the effective valve area is pi*(.388^2)/4 = .120 square inches. The spring force required to overcome atmospheric pressure on this valve is therefore (19 psi)*(.120 sq in) = 2.3 pounds. Since this force is greater than the valve's gas tight seal requirements, the springs will be designed to supply a minimum of 2.3 pounds of force on each closed valve.
This spring force will be created by the difference between the free length of the spring and its installed height multiplied by a parameter of the spring called its spring rate. Spring rate is a complicated function of several physical and metallurgical properties of the wire used to wind the spring. It specifies the force in lbs/inch that must be exerted to compress the spring.
It's easy to calculate the spring rate of a spring using an online calculator such as the one at: http://www.acxesspring.com/spring-calculator.html. The inputs for this calculator include the wire material and its diameter, the o.d. of the spring, and the number of turns in the spring. This particular calculator also asks for the free length of the spring since the vendor sponsoring the calculator needs this piece of information to provide a manufacturing quote. The free length isn't actually used in the spring rate calculation, though. For a given wire material and free length, a stiffer spring can be wound by reducing its diameter, or its number of turns.
I have some .031" diameter 302/304 stainless steel spring wire left over from my Howell V4 build that I would like to use. The Quarter Scale valve train was designed for an installed spring height of .478" and an absolute maximum spring diameter of .310". I used the spring rate calculator to compute the spring rate for two options using my wire and the .310" maximum allowed spring o.d.:
.
Free Length------#turns-------Spring Rate
.650"-----------------5-------------10.7 lb/in
.700"-----------------5-------------10.7 lb/in
.750"-----------------5-------------10.7 lb/in
.650"-----------------6------------- 8.9 lb/in
.700"-----------------6--------------8.9 lb/in
.750"-----------------6--------------8.9 lb/in
.800"-----------------6--------------8.9 lb/in
.
I calculated the resulting force on a closed valve by multiplying the spring rate times the difference between the free length and the installed height of the spring for each case. For example, the 5 turn spring with a .700" free length will produce a force at its installed height equal to (10.7 lb/in)*(.700"-.478") = 2.4 pounds. This particular spring meets my requirements since the force it creates is greater than the 2.3 pounds exerted by the atmosphere. A force much greater than this will unnecessarily increase the stress and wear on the cam and valve train components. When the valve is unseated the valve train will see the 2.3 pounds plus the additional force created by the compression due to the cam lift. For the Quarter Scale cam this peak force will be 3.7 pounds.
The next step is to actually wind the springs. A photo shows a fixture that I made for my manual lathe that I used to feed spring wire onto a mandrel held in a collet chuck. For safety I normally set up the power feed to wind the spring toward the tailstock, but I forgot to reset the direction after interrupting my little production run for another quick project. When I restarted the run, I ran the carriage into the headstock and mangled the helical power feed gear located behind the lathe's apron. The repair was a two day diversion, but I managed make a shop-made replacement gear and get running again. The most difficult part of the repair was actually getting to the gear.
Coming up with the diameter of a mandrel on which to wind a spring of a particular diameter is a matter of trial and error since the spring tends to open up when the winding tension is released. It took me three tries to hit my target using my .031" wire:
.
Mandrel Diameter------OD-------Sliding Fit ID
------.203"-------------.320"-----------.250"
------.197"-------------.305"-----------.240"
------.190"-------------.295"-----------.220"
.
I selected the .197" mandrel, and so my spring's physical parameters are:
.305" Spring OD,
.031" dia. 302/304 Stainless music wire OD,
5 turns,
.700" free length,
.478" installed height, and
.240" sliding fit ID. 
With each spring inserted on a snug fitting drill bit I squared up the ends with pliers, and I also made a simple fixture to grind the ends slightly flat. Even more important, though, I stoned the tips of the wires to prevent them from scratching the valve guides since I'm planning a minimum clearance between the two. The springs were inserted onto a .240" mandrel so their lengths and i.d.'s could be verified. Springs that didn't slide freely on this mandrel were discarded since I planned to machine the upper guides to this exact diameter. The springs were then tumbled in wet ceramic media for several hours to polish them.
A final step in spring fabrication that I routinely perform, but others often ignore, is to heat treat the finally formed springs. This heat treatment (a partial annealing) relieves the internal stresses created by the winding process, and it improves the spring's ability to hold its free length and spring rate with use over time. It makes the metal a little happier with its new shape. For my particular wire I held the springs at 400F for 45 minutes and then allowed them to slowly cool. i spot checked several completed springs by measuring the force required to compress them to what will be their installed height. The last photo shows the first part being checked that happened to come out at 2.3 pounds. The rest of the samples ranged from 1.9-2.4 pounds. The margin built into the original calculation will cover the spread on the low end. - Terry


----------



## kvom

In case you're thinking ahead about the next project, here's one that looks interesting:

http://www.agelessengines.com/sleeve.htm


----------



## stevehuckss396

Nice spring tutorial. I have thought in the past about making them and now it seems easier. Thanks for taking the time to show the math.


----------



## mayhugh1

Steve,
You're very welcome.
Terry


----------



## mayhugh1

My little afternoon project making a few prototype valve guides and cages for leak-down comparisons ended several days later with piles of finished valve-related parts.
I decided to machine the valve guides first, and for those I selected 932 bearing bronze. Its properties aren't specified at elevated temperatures, and so I'm not comfortable with using it inside a combustion chamber. It has excellent lubricity, and it machines beautifully; but I've had issues with keeping small diameter holes centered in bronze rod stock. So, I spent some time coming up with a drilling process.
The lower portion of the guide, the half that will be pressed into the head, is the portion with the concentricity requirements. The top half supports the spring and is not as critical, and so this half can be turned as a secondary operation in a separate set-up. 
After turning the o.d. of the guide's lower half, I spot drilled its lower end using a 90 degree tailstock-mounted mill drill. I then drilled the hole using a 134 degree .142" diameter parabolic drill. These drills are designed for deep drilling, and they nearly eliminated the need to peck drill my .7" deep blind hole. (To make these parts in quantity I pulled a single workpiece through the chuck and parted them off as they were finished.) Next, I bored the hole out to about .150". The exact diameter wasn't important since the purpose of boring was to straighten out any drift created by the drill. I then reamed the hole to its final .157" i.d. The theory was that the reamer would follow the hopefully straight hole through the center of the guide and give me a perfectly concentric fit to the valve stem. I could have bored the hole to its final .i.d., but reaming was quicker and more repeatable than having to deal with tool changes and offset variations.
After parting off each half-finished guide I measured its TIR with a dial indicator while rotating the guide on a close-fitting gage pin. Care was taken to not allow the clearance between the two to influence the measurement. Allowing a few tenths for spindle bearings, the results were more inconsistent than I had expected. While trying to track down its source I ended up making some 37 parts that I separated into three bins:
-
# parts ------------ TIR
---10 -------- .0005" to .001"
---16 -------- .00025" to .0005"
---11 -------- less than .00025"
-
After parting off each half-machined valve guide, I found it important to cleanly reface the workpiece for the next part. It seemed that all traces of the center hole remaining from the previous part had to be removed, or the TIR of the next part could be affected. I think I also got more consistent results if I was careful to blow out the chips from the hole just before both the boring and reaming operations. Unfortunately, luck, or maybe the homogeneity of the bronze, seemed to have the last word on the results.
I scrapped the ten parts with the worst errors and then finished the upper half machining on the remaining 27 guides. At this point I had enough seats and guides for both Merlin heads plus a few test parts. All the guides were machined for a zero interference fit in the heads; and, if I use them, they'll be Loctite'd in place.
I also needed a few valve spring retainers and clips for my tests, but once I got set up and running I ended up making all that I will need for the engine. The retainers were turned from 12L14, and the clips were machined from A-2 tool steel. I made the clips by milling their profile into a short length of drill rod, and then individually parting them off in the lathe. I made plenty of extras since these seem to be the parts that go missing during assembly.
I'll also need a few valves for my tests, and so my next step will be to machine those. Since I now have a common valve design that should work with either the seats and or the cages I'll likely machine enough for the entire engine over the next week once I get running. I plan to review my notes from my T-18 build since I spent a long time coming up with a process for making the valves for that engine, and I'll likely re-use it.
I'm still curious about the performance of the double angled seats in my current cage design, but I'll be able to leak-check those just after they're machined. My plan is still to leak-check a couple practice guides and seats pressed into a scrap aluminum block before doing anything with the actual heads. - Terry


----------



## petertha

mayhugh1 said:


> ... machine the valve guides first, and for those I selected 932 bearing bronze. ... and it machines beautifully; but I've had issues with keeping small diameter holes centered in bronze rod stock. So, I spent some time coming up with a drilling process....


 
Hi Terry. Thus far I've been using 12L14 for my valve cage sizing/prototyping but 932 is the target material. I've also got some concentric drilling requirements, the larger port (8mm) on one side & the valve stem hole (3mm) on the other. Do you think its advisable to modify some dedicated drills for this operation like what they recommend for brass (reducing rake angle if I interpret correctly). Also any differences to note for reaming? I've heard varied opinions from no change to spiral work better on bronze for some reason.


----------



## mayhugh1

Peter,
Your questions are certainly relevant, but I'm afraid I don't have enough experience to answer them. Maybe someone else could? I'm not aware of what the effect of rake angle is on free machining bronze, but any modifications would have to be done carefully in order to keep the tip symmetrical. Most of my reamers came from surplus outlets, and they are a mix of both straight and spiral. I've not seen much difference between the two types in the holes I've reamed, although if I were reaming a cross-drilled hole my preference would be a spiral reamer. On the cages I've done I've used a ball mill to ream the large opening for the seat since it gives a nice transitional region between the port and the valve. The exact diameter you end up with depends on how precisely it is aligned with the axis of the lathe, and so it should be gripped in a tapered collet holder for consistency. Grinding down all but one cutting edge will reduce chatter and give a nice surface finish. I would then normally design the valves around the seat i.d. that results. - Terry


----------



## mayhugh1

I took a final look at my valve cage design just before setting up to machine them. After some more thought I don't believe it's safe to use them in these heads after all, especially after I increased the valve stem diameters. Once the head castings are machined for the cages there may not be enough material left to reliably support them. The cages would also be very close to an internal coolant passage that runs the length of each head, and my modeling of this portion of the casting isn't accurate enough to insure they won't break through.
So, I'm going to focus on using the seats and guides that the heads were designed to use. Instead of the wide 30 degree seats against 45 degree valves as shown in the drawings, though, I'm using 45 degree valves against narrow 45 degree seats as I've done in my other engines. The seats and guides have already been machined, but I went through each seat one last time and turned a steeper bevel on its bottom outside corner. My original shallower bevels created a lot of difficulties earlier when I tried pressing some practice seats into a test block. 
I also machined a back-up block to support the heads while they will be upside down in a vise having their seats pressed in. The castings' thin walls behind the combustion chambers seem a bit fragile for the pressure they may have to sustain during the seat installation. I also made a tool for installing the guides. The guides must be pressed in from the tops of the heads after counterbores for the spring perches are machined into the heads' top surfaces. I also made new pilots for my seat cutters to fit the Merlin's guides. These cutters are the same 45 degree Brownell's counterbores that I used on my T-18 valve cages:
http://www.brownells.com/gunsmith-tools-supplies/barrel-tools/barrel-chamfering-cutters/45-chamfer-cutters-prod41716.aspx
The valves, themselves, are the last valve train parts to be machined. I made only two pairs for now to debug and verify my valve-making process. Since machining two dozen valves will be a big deal for me, I want to test fit a couple of them in the actual valve train before spending a week making the rest.
I slotted the stem of one of the valves so it can be used as a test valve for checking the seals. A Mity-Vac can be used to pull a vacuum on the rear of each installed guide with this test valve temporarily installed. With the test valve closed against an installed seat the leak-down time can be measured and compared with results obtained from similar measurements in previous builds. I should be able to apply this technique to the Merlin's heads once I figure a way to reduce and seal their humongous ports. The remaining three valves will be used as piloted laps that will be used to remove the machining marks left by the seat cutters.
It's been my experience that nearly all valve sealing issues are related to the seats. I've been able to machine valves with enough consistency so that practically any valve will seal against a good seat. It's not difficult, on a lathe, to turn the correct geometry and a sealing surface that is free of tooling marks. I don't lap my valves to their seats since this can damage the finished surfaces of the valves. I also don't try to correct geometry problems with lapping. I use manual piloted seat cutters to cut the seat and to establish the proper geometry for the sealing surface. The pilot ensures the contact patch will remain circular even if the seat and guide are not perfectly concentric. A 360 degree circular contact patch is a fundamental requirement for a seal. The seat cutter will leave behind microscopic machining marks, though, that will limit the integrity of the seal. During my T-18 build I found that using two seat cutters on each seat leaves behind a smoother surface than using either one alone. I use lapping to remove these marks, and I use a separate spare valve to lap all the seats. Automotive valve lapping compounds are designed for hard seats and valves, and they will typically embed in softer metals like the bronze I use for seats. I use TimeSaver lapping compound which breaks down during use and does not embed. I can usually lap ten or more valves with a single lap. I lap for only 30 seconds or so, and if I'm not happy with the leak-down results, I'll lap a second time. Finally, I manually polish the seat using a felt bob and a dab of metal polish. This last step brings the seat to a brilliant shine without removing metal, and it usually improves the leak-down time a bit. Generally, narrow seats have fewer machining marks to deal with, and so I like to use .005" as a seat width. If the seat and guide are not concentric then the width of the seat will not be uniform. The seat may have to be cut deeper than desired in order to obtain a complete 360 degree contact patch. If the concentricity is poor enough one side of the seat can end up very wide and require a lot of work to clean up.
My leak-down criteria are my own numbers on my own set-up derived after lots of late night hours experimenting with seat making on my two radial builds. These times are dependent on the volume over which the vacuum is pulled and are most meaningful to my set-up. Using my Mity-Vac on a freshly cut .005" wide seat I expect a 10 second leak-down time from 25 inches Hg to 15 inches Hg. Lapping and polishing can extend this time up to a minute or even more. My criteria is over-kill, but I like to squeeze out all the performance I can get so that compression doubts aren't on the table later. In order to get an engine started the leak-down time needs to be short compared with the time the cylinder is under compression during cranking. With a 120 rpm cranking speed, a four-stroke cylinder will be under compression for something just under a second. Loss of cylinder pressure during this time (from two leaking valves) reduces the effective compression and steals torque during the power stroke. 
If the engine can be started, the seals in a model engine will improve over time as the seat material yields to the extreme pressures created by combustion, and the pristine valve surfaces pound the remaining machining marks out of the softer seat faces.
While waiting on an odd size reamer that I need to properly install the guides (I should have checked my reamer inventory before finishing the diameter of the guides) I decided to assemble a few reject guides and seats into a scrap block of aluminum just to see what results I could get. The TIR of the guides was .001", and with the reamer I had on hand the hole they went into was .002" oversize. By this time, though, I had forgotten the reasons for scrapping the particular seats I was about to use. For these practice parts I wasn't expecting much, and so I didn't bother to purchase any dry ice; but I did use the high temperature Loctite. The two seats I pressed into my test block appeared to go in smoothly with moderate effort, but the guides ended up with sloppy fits as expected. I accelerated the guide's Loctite cures with heat so I could get some quick measurements.
Unfortunately, the seat cutter initially left chatter marks on the very first seat I tried. It may have dug into a burr that I neglected to remove on this rejected part, or it may have been caused by my rusty technique. The pilot was .001" under the i.d. of the guide which is what I normally use, but I swabbed the pilot with some thick grease to reduce the clearance. By the time I had cleaned up the seat its width had grown to some .050" - much too wide for my taste. Its measured leak-down time was 3 seconds. The result for the second seat was a little better at about 5 secs, but it was obvious that this particular seat and guide were not concentric. The seat face width varied from .030" to .010". The guide's TIR and its sloppy fit couldn't fully account for the error, and so there was probably also a drilling problem.
Thirty seconds with TimeSaver extended the leak-down times to 15 seconds for the first pair and to 30 seconds for the second pair. The metal polish extended the time to 20 seconds and 45 seconds, respectively. I stopped at this point and declared them 'good enough' and was very surprised that these seats cleaned up as well as they did. When I start out with similar problems on a valve cage I normally just discard it rather than put any effort into saving it. I won't have that luxury, though, with pressed-in seats on these heads. - Terry


----------



## gbritnell

Terry,
For the life of me I don't understand why they would stipulate 30 degree seats and 45 degree valves. (seats) Common practice is to have the seats and valves at the same angle to insure that there is a good seal. Just as a point of information, if the seat was 30 degrees and the valve 45 degrees where were they expecting the valve to sit on the seat, at the top of the valve angle, the bottom or where. I just can't picture this working. 
gbritnell


----------



## mayhugh1

George,
When I first saw what they were recommending I envisioned the valves sitting deep down in the seats. When I sarted working on this portion of the engine I modeled what they were doing and saw they actually had the valves sitting high up on their seats. I guess the reasoning was that the mismatch in angles would provide a thin contact patch. But they also suggested lapping the valves to the seats, and in this scheme the seat width could grow pretty quickly. I was tempted to try their recommendation, but I'd have had to come up with a 60 degree piloted seat cutter that I'd probably never use again. - Terry


----------



## kvom

There's a set of castings on eBay if you want to make a pair.


----------



## mayhugh1

Kvom,
I just saw those on Ebay! It looks like the seller changed his mind or else found a local buyer for them since the auction was cancelled. 
The interesting thing I learned from his description was that the castings dribbled out from Dynamotive, their source, over a period of some five years from 1994 to 2000 as they were designed and manufactured. It took a lot of faith on the part of the early buyers to purchase them as they became available since there was probably no guarantee that the project would actually be completed. The pressure on the Dynamotive to finish the project was obviously great also - it had to have been a labor of love on the part of the owner. There was evidently a newsletter published to alert buyers to the progress of the project and the availability of castings. I'd love to get access to them. Mention was also made that Dynamotive had also commissioned the CNC manufacturing of some of the other high volume parts including the rocker arms which are the only parts still available. I read on another forum that they early in the project they were trying to cast a crankshaft which evidently was offered in very small quantities. - Terry


----------



## kvom

I wonder if in the very near future direct 3D printing of metal parts would work to replace the castings for this engine (or any other similar).


----------



## mayhugh1

The reamer that I was waiting for arrived, and so I bought some more dry ice and assembled one last pair of practice parts in a piece of scrap 6061. Interference fits are a hit-and-often-miss operation in my shop. I usually err on the loose side and end up augmenting the fit with Loctite. In this case, though, I had 24 of them that had to be tight and straight in a pair of irreplaceable heads, and so I don't feel guilty about being too cautious about this portion of the build.
Everything on the last practice part went as expected, and so I set-up to start installing seats in the starboard-side head. With the head in the vise and the back-up block in place, I used a .236" carbide mill-drill to drill through the pre-cast seat opening, followed it with a .240" reamer for the guide bore, and then bored a .1" deep pocket using my .493" end-mill-converted-to-a-boring bar. The pocket was lightly coated with high temperature Loctite, and then the chilled .495" diameter seat was pressed in place using the mill's quill.
I immediately noticed the force required to install the seat in the head was much higher than needed with the 6061 practice scrap. The press factors for 356 and 6061 are probably similar, and so the extra force was probably due to a bit of additional interference. The force required to press one part into another is directly proportional to the amount of interference and the contact area between the two parts. So, if the actual seat and bore diameters varied such that the amount of interference increased from .002" to .0025" the required force would increase by 25%.
I set up my press as a back-up and continued with the next four seats which went in very much like the first. As best as I could measure, the seat i.d.'s were being shrunk by nearly .002" which was close to what I had measured on my practice scrap.
When I got to the number three exhaust seat it went in very easy which, initially, I attributed to a more thorough chill. The next couple seats returned to being difficult, but then the pocket on the number two intake seat ended up so much oversize that it would not even grip the seat. The same thing happened on the next seat for the number two exhaust valve. I turned two oversize seats to press into these locations and then went looking to see what had happened to my boring tool.
In order to quickly handle tool changes I had put the three tools I was using into Tormach TTS tool-holders for use on my Enco mill. In the middle of a process that I had carefully practiced and which had been working, I decided to make a change and start blowing chips away with compressed air. A sizable chip ended up wedged between the R-8 collet and my spindle bore, and this slightly tilted the tool holders. I seldom use compressed air around my machines, and in this case the spindle of my mill was sitting just above the workpiece when it was hit with a shower of chips. 
After clearing this, the bore diameters went back to where they were supposed to be, but to be safe I started measuring each bore just before installing its seat. I was left feeling really uneasy about that number three exhaust seat, though.
After finishing the seats I installed the guides. They were Loctite'd with no interference; but a few did go in a little hard, most likely because the bore hadn't been completely deburred. These guides had to have their valve stem bores re-reamed. 
After the Loctite had cured, I used my seat cutter to cut very minimal seats just to see how well the drilling had gone. Under a jeweler's loupe it was obvious that the oversize seats had a 2-3 thousandths width variation, and so the drilling at these locations had also been affected by the chip. The rest of the seats looked nearly perfect. The port side head was then completed, and the widths of a couple of those seats varied by 1-2 thousandths for some inexplicable reason. None of these variations are a major concern, but I'll likely not be able to use my favorite .005" seat width on the starboard head's oversized seats.
I trial fitted one of the test valves to a portion of the installed valve train so I could get a final measurement on the valve stem length and the spring retainer location. I also verified the valve's clearance to the spark plug. These measurements completed the valve design so the rest can be machined.
During my modeling I discovered that the channel running lengthwise through the center of my heads is actually a coolant passage and not a waste oil collection trough as I originally thought. The twelve holes penetrating this channel in the topside of each head that I thought were for oil collection were likely used to support the core for this internal passage. I don't believe this trough existed in the early heads because the photos I've seen of Gunnar's engine don't show these holes. It doesn't seem the documentation was ever updated because my drawings don't show them either. This casting change was likely done as an attempt to improve the engine's cooling issues rather than help with waste oil control.
There were a total of twenty core support holes in each head including these that needed to be plugged, and so each was reamed and counterbored for a pressed-in plug. All these holes penetrate coolant passages, but their quarter inch diameters should never see more than a pound or so of force. I installed plugs with .003" interference fits plus high temperature Loctite since there wasn't enough material for a threaded plug. I cured the Loctite overnight with the heads in my 120F welding rod oven. I've learned that curing Loctite 620 in this way will also harden any excess that was squeezed out and left inside the head by the pressing operation. I originally ran across this tip from another builder's unfortunate experience: 
http://homepage2.nifty.com/modelicengine/h9120302.htm
At room temperature and with exposure to air, Loctite 620 will essentially never cure. However, overnight exposure to 120F will turn an air-exposed meniscus sitting on metal into a tenacious rock-hard solid. I was able to view the cured adhesive on the rear of the plugs with a borescope, but I didn't have any means to take a photo. There are still another 14 coolant passage penetrations in each head required for the cylinder studs. These will be sealed with yet-to-be-machined two-piece stud guide tubes.
The borescope also uncovered a large amount of residual investment hidden in the coolant passages. I removed another teaspoon full from each head with a dental pick, but there's still more that I can't get to. This has been a on-going problem with several of these castings. Some of their intricate interiors are coated with investment that wasn't fully removed by the foundry. This particular investment isn't water soluble, and is surprisingly unaffected by acetic acid. So far, scraping it out with dental instruments has been my only way to remove it. This stuff is going to be problematic in the coolant loops and maybe deadly in the oil loop, and so filters will have to be used in both. - Terry


----------



## petertha

mayhugh1 said:


> With the head in the vise and the back-up block in place, I used a .236" carbide mill-drill to drill through the pre-cast seat opening, followed it with a .240" reamer for the guide bore, and then bored a .1" deep pocket using my .493" end-mill-converted-to-a-boring bar.  - Terry


 
As usual, I feel obligated to precede my trivial questions with WOW! Can you elaborate on the end mills.

- the .236" carbide EM preceding 0.240" reamer. Is the EM required because they delivers straight holes or more because irregular entry surface? I always thought plunging like this was not preferred with EMs, but maybe I'm using the wrong ones. What kind of flute geometry works best for this? Is carbide vs HSS for tool rigidity?

- 0.493"  EM converted to boring bar... I don't quite get what's going on.
Also does your pocket need to be flat bottomed? I struggled with this on my head preparing for square valve cage profile to sit down on. The tapered flutes cut well but left a crowned bottom. The flat bottom had a slightly different diameter. Do you have this issue & if so how did you deal with it?


----------



## mayhugh1

Peter,
The end mill I used for the initial drilling was a mill-drill. It wasn't flat bottomed but was pointed like a spotting tool, and so it is capable of both spotting and drilling in the same operation. It's shown in the first photo. I thought it would give me my best chance of drilling straight through an irregular surface.
The 'boring bar' was actually a resharpened four flute end mill I purchased on Ebay. It was grossly undersize for a 1/2" cutter and never got much use. For this operation I ground three of the four flutes down to make a single flute cutter as this tends to reduce chatter when making plunge cuts.
A flat bottom pocket is desirable, but these heads were cast with much of the seat pocket material already removed. My 'boring bar' just had to remove a bit more material. In fact, the i.d. of my seats slightly overhang the floor of the pocket. Although the cutter really didn't have a flat bottom, the bottom of the pocket it left behind was almost flat. The third photo shows just how much seat pocket material I actually removed.
The carbide was for rigidity. - Terry


----------



## Ethan D

This build is unreal! Beautiful work!!


----------



## gbritnell

Terry,
I'm following along enjoying the trip. At the start of a build like this all the superlatives get used so much that they seem superfluous after awhile which by no means diminishes the extreme quality of your work. 
My deepest admiration!
gbritnell


----------



## mayhugh1

After completing the Merlin's valves I will have made a total of 92 valves, including spares, for three different model engines during the past four years. That's a lot of valves for someone who used to hate to make more than one of anything. Even though they were all made using essentially the same technique, it seems I always learn something new from each batch that helps me with the next.
I started by cutting a number of short lengths of half inch diameter 303 stainless rod so I could machine a valve on each end and waste only one spigot between them. I've used my 9x20 CNC lathe to make all my valves, and I machine them in a single batch in four steps.
The first (roughing) step is my favorite because with .020" excess stock left behind for finishing, each part can be run relatively unattended without the hand-holding required for a precision part. This step includes my screwy technique of using a greased leather pad between the end of the valve stem and the tailstock to dampen chatter. My live center is the only center I have that will give the tool holder and inserts that I use for this operation access to the end of the stem, but its run-out produces a larger taper than I can typically get with my leather pad kludge. With all the valves that I've made I probably should have created a custom center by now, but the leather actually seems to work pretty well. The blanks were all rough-machined over a couple days using a Seco DCMT21.51 MF2 TP250 insert. Each end of the blank required about ten minutes machining time, and a single edge of the insert showed negligible wear after roughing out all 28 valves.
However, I had to interrupt the build and devote some time to my lathe. During the T-18 build my 9x20 Mach3-based CNC lathe began acting up, and the spindle motor would sometimes take an inordinate amount of time to start up, or it would not start up at all. This occasionally caused the tool to crash into a non-rotating workpiece. At that time I replaced a couple relays on the break-out board that I thought might be sticking, but that didn't solve the problem. I then made a bus monitor to display the various control signals between the very expensive and poorly supported German-made Hamming motor and the Lathe's breakout board. The problem showed up only intermittently over the past year and, it seemed, only after the lathe had been powered up for a few hours. However, while turning the Merlin's valve spring retainers and clips the problem became much more frequent. According to my monitor the problem appears to be within the motor, and maybe it is heat related.
The motor inside the lathe's enclosure has a powerful fan mounted on one of its ends. Air is blown over a heat sink wrapped around the motor to which the VFD circuitry is likely internally attached. Warm air, chips, and coolant from inside the enclosure is blown through the heatsink and must occasionally be cleaned out. 
In the middle of the spring retainer machining I stopped and cut a five inch vent in the rear of the enclosure and after fabricating a bezel and adapter for a large plastic plumbing elbow I had cool uncontaminated outside air flowing over the motor. This seemed to help, but while machining the valves the problem became even worse and, finishing the valves became difficult. The west coast distributer for the lathe informed me the motor is repairable only in Germany and will likely require several months, and so I've decided to order a replacement. 
The next step used a Kenametal DCMT21.51UF finishing insert, and because of my lathe issues I decided to leave .002" stock instead of my normal .001" stock for later polishing. This higher precision step required more of my involvement. The lathe is typically consistent enough to hold a thousandth if I measure and readjust the work offset between each part. The tailstock wasn't used at all in this step, and I backed up the valve stem with a leather pad in my fingers. This really isn't as dumb as it probably sounds. I usually finish machine all the valves in one sitting, and after the first few parts I can usually maintain just the right amount of pressure on the workpiece to obtain final valve stem diameters that are consistent to within a half thousandth. Because the lathe now forced me to run much smaller batches there were a lot more 'first few' parts, and these diameters ended up all over the place. Typical finishing time was about four minutes.
The machining marks left by the last machining pass were polished out in a third step using 400g and 600g papers followed by metal polish. The valves' rear sealing surfaces were polished with 600g and 1000g before using the metal polish. The sealing surfaces, after close inspection, may be polished one last time later during the fourth operation when the valves are brought to their finished length and the retainer grooves are cut. The polishing time was typically eight minutes.
Before actually finishing the valve stem diameters I had to decide on a target clearance to their guides. I used .0005" +.00025"/-.0000" on both of my radials, but these engines are air cooled, use valve cages, and don't have well-defined top-end lubrication systems. A small clearance seemed appropriate for them in order to prevent un-metered air from being drawn past the intake valve stem. The Merlin's top-end will likely be well-oiled, and some of this oil will end up on the valve stem to help to seal it. If the clearance is too great, oil can be sucked into the combustion chambers during the intake stroke, and the engine will smoke. 
I'm expecting the Merlin heads with their valve-cover'd heads and suspect liquid cooling system to run much hotter than the finned radial heads which sit well up in the prop wash. Since the exhaust valves will likely run much hotter, temperature expansion of the stem diameters is a concern. This, coupled with the use of individual seats and guides rather than valve cages, may result in larger temperature differentials between the stems and their guides so that binding could become an issue. As a result I chose a target clearance of .001" +.0005/-.0000" for the Merlin valve guide clearance Because of my lathe distractions, several ended up closer to .002", and they were marked with a red Sharpie so I could keep track of them during the fitting process.
Leak checking the valves in the Merlin heads is complicated by the individual seats and guides as well as the engine's giant ports. I was tempted to skip this step but finally decided it would be interesting to give it a try.
I purchased a two-part silicone molding kit from a local craft store. After shoving temporary hard rubber plugs through the valve seats and up against the valve guides to create an air space inside the silicone behind the valves, I poured the silicone into the ports. After it cured, the hard rubber plugs were (easily) removed, and I was left with silicone molded plugs that perfectly filled the ports. Just behind each valve was an open space with a volume that very closely matched the volume I would normally leak-check in a valve cage. These equivalent volumes will allow me to compare my leak down times with past results from other builds.
With the silicone mold plugs inserted into the ports, the leak-down times can be measured either of two ways. A vacuum can be drawn through the rear of the guides with the slotted test valve in place. Or, the vacuum can be pulled through a metal tube inserted through the silicone and into the air space behind the cylinder's actual valve while it is held in place. I decided to test a seat and valve pair to see just how well this second check might work.
After some measurements to verify the final valve length I realized my CAD model was accurate enough to use, and so I determined the final length through trial and error with the valve in place in the actual valve train. The lash-setting eccentrics are difficult to use and don't provide much adjustment range, and so the finished valve length needs to be fairly precise. Fortunately the valve train components seem to be consistent enough that the valves won't need to be fitted to their locations. 
The total machining time per valve averaged just over 30 minutes which is probably even more than what a real machinist would need using all manual equipment.
The seat was cut to a .005" width using the manual seat cutter, lapped with TimeSaver against a dedicated steel lap, and then polished using a felt bob and a dab of metal polish. I found that greasing the cutter's pilot to reduce its clearance in the valve guide produced a better finish than I could get without using it. 
To reduce the measurement to a two-handed operation the silicone plug was held in position with a pair of miniature clamps, and its integrity was verified before the measurement by pulling a vacuum against my thumb on the seat. The rear of the guide must be capped even with a valve in place. Even though any leak past the valve stem would become a part of this leak-down measurement it is not a component of a combustion chamber leak which is the leak I'm ultimately interested in. 
My first leak-down test resulted in a twenty second time which seems like a reasonable goal I'll likely set for the rest of the valves. The volume being checked behind the valve is only .05 c.i. which is a small fraction of the total involved volume. The volume of the interconnecting hose between the port and the MityVac is .20 c.i. - Terry


----------



## kvom

That toss off about how fast a real machinist  could make a valve made me smile.  If you're  not a real one nobody is.


----------



## ICEpeter

Hello Terry,
Sorry to hear about your Hanning motor problem. I have a Hanning Varicon motor on the German made mill I have been using for the past 8 - 9 years and it runs fine so far (it's out of the way of swarf and coolant)

One thing I want to bring to your attention is that you may need to program your new Hanning motor by entering the operating parameters (speed for example). Don't know whether the new motor comes pre-programmed from your supplier but it may be worthwhile to check.

FYI, here is a link to the Hanning Varicon short guide. Their website is in English. http://www.hanning-hew.de/wEnglisch/download/Prospekte/AT/BA_65158_VARICON_Part_B_Short_Guide_E.pdf

Peter J.


----------



## mayhugh1

Peter,
Thanks for the link. My motor uses a potentiometer to set the speed, and so I think I can do the comissioning per the right-hand side diagram without Hanning's digital interface. My older version of the motor has a controller board that is different from the one in the photos in your link, but I expect the replacement will match. I hope you don't have problems with yours as the price for a replacement is $2K U.S. -Terry


----------



## ICEpeter

Hello Terry,
The Hanning motor on my machine ( Type CCD-864-122 / 1.1 KW) has the electronics board, i.e. the frequency drive and controller board, incorporated into the motor junction box, similar to the link picture I sent you. It is in fact an electric motor with an incorporated VFD all in one. I assume your motors electronic controller board (VFD) is separate, stand alone, and not incorporated into the motor junction box?

In my case, I had to use what they call a set up unit to program the operating parameters (about a dozen parameters) for the VFD into the motor based on the information in the Varicon manual that came with the machine / motor prior to using the motor. Although the motor, when in use, is controlled either via manual potentiometer when used in manual mode or remotely by the CNC program.

I attached a photo of the programming / set up unit that I received with the Varicon.

I realized in the past that these motors are good quality high priced and cost more than a pretty penny, but $ 2,000.- is inflicting severe pain onto anyone. I know that Hanning has a strange sales policy whereby they only sell direct to OEM manufacturers and force retail customers to buy spares through the OEM. That and customs duty jacks up the price considerably since there are too many hands that reach into ones pocket, deeply I might add.

I keep my fingers crossed for my motor to hold up for another 8 - 9 years and put some money into savings for a future replacement.

Peter J.


----------



## mayhugh1

Peter,
Here's a photo of the inside of the controller box of my 2 hp motor. I'm told it is an older version of the one I'll be receiving as a drop-in replacement. I'm pretty sure yours is a later version that came out just after I received mine and should match my replacement. The lathe's distributer sent me screen shot of the new controller with some instructions on how to map my cable wiring over to the new controller, and it matched the pdf you sent me perfectly. I asked about the need to commision the motor with Varicon programmer and was told that will have already been done on the motor I will be receiving. I've been wondering where the VFD electronics is, myself, as there doesn't seem to be any 1.5kW components on the controller's topside pcb. Maybe they are on the rear of the board. The motor is still in the lathe, and so I haven't wanted to do much disassembly until the new one arrives since it is still intermittently working. - Terry


----------



## mayhugh1

The past week was spent finish-machining and leak-checking the remaining 23 valve/seat pairs in both heads. At about half an hour each, most of the work was pretty routine and tedious; but with all the holiday-related distractions that popped up, it took much longer to finish than expected. 
Strangely, the leak-down times seem to fall within one of two groups: either 15 to 20 seconds or about a minute. With more effort I probably could have gotten them all into the one minute group, but some of the seats grew a little wider than I was used to or comfortable with, and so I settled.
The silicone plug molds worked really well, and I wouldn't hesitate doing something similar on another project. The seats and valves in each head were all finished and tested before finally installing them with the springs in order to prevent debris from the seat cutter from getting between their finished surfaces and damaging them.
I thought I was using a reliable reference on the heads for finish-machining the valve stem lengths last week when I referenced the heights of a couple trial valves to the tops of the installed guides. When I counterbored the castings for the shoulders of the valve guides I wasn't concerned with consistency, and so I counterbored just deep enough to get a clean flat surface. The few guides that I happened to check matched one another, but they were actually sitting lower in the head than most of the rest. When I began installing the rockers over the finished valves I discovered that a majority of the valves were actually too long with no clearance for lash. 
The stock lash adjusters have only .016" adjustment range, but the tolerance stack-up of the valve train components appears to be eating up about three thousandths of this range. Variations in the seat depth were taking up to another seven thousandths due to the wider seats I had to cut on some of the cylinders to compensate for concentricity errors. There were actually more of these than I had originally thought. Since the seat angles are 45 degrees, 70% of the seat width variation turns into a valve height variation.
With .130" valve lift, my plan is to set the lash at .005". Ideally, this clearance should wind up in the center of the eccentric's adjustment range so the adjusters can be used to compensate for bidirectional wear. In order to avoid fitting custom rocker rollers, I decided to re-machine the length of each valve to correspond to its seat. I had already temporarily linked each valve to its tested seat location with a Sharpie, and so I went over my marks with an engraving tool as I re-cut the stems.
I made a gage to reference the valve heights to the machined cam block mounting surfaces on the heads which is the reference I should have been using. I then re-machined the length of each valve.
After correcting the port-side stem lengths I began assembling the head. Just as I was about three quarters finished I spotted a bit more investment in one of the coolant ports that I could reach with a dental pic. Picking at this stuff is like picking at a scab - its hard to quit once you get started. When I finished, I'd scraped out another teaspoonful. One of the photos shows some of the big chunks that I was still finding at this late date. I then thought I could feel grit in some of the moving parts of the valve train, and so I took everything back apart for a thorough cleaning. I went through the stripped-down head once more and re-scraped the coolant passages until I again couldn't feel anything else in them. 
This whole exercise was actually fortunate because it reminded me that I needed to seal the fourteen cam block bolts that penetrate into the coolant area. This time I cleaned the tapped holes and bolt threads with acetone before reassembling the heads. When I'm finally convinced that they won't have to come apart again I'll remove each cam block bolt one at a time, coat the ends of the bolts with purple thread-locker/sealant, and then re-heat the assemblies in my rod oven. This low strength anaerobic thread locker should seal the threads against coolant leaks but allow a relatively hassle-free unplanned disassembly later.
Once the heads were assembled, it was really great to be able to rotate the cam sprockets and watch the 350 parts made during the last three months finally all working together. The feel, though, was totally unexpected. All the 'smooth as butter' motions that I had been working to achieve with the individual parts was now replaced by a stiff 'cogging' action. Having no experience with overhead cam engines, I'd never before rotated the cam in one of them, and it took a while to convince myself that what I was feeling was normal. The 'cogging' occurs between the intake and exhaust valves in each cylinder during the overlap time when one valve is closing and the other is opening. This happens at the start of each intake cycle which, in this engine, is every 60 degrees of cam revolution.
The last check was to estimate the worst-case piston-to-valve clearance in order to verify the engine will be free-wheeling with the stock pistons and rods. The remaining head-related parts are the stud tubes, intake gaskets, and the cam blocks' oil feed lines. At the rate I seem to be going they will likely require the rest of the year. - Terry


----------



## 10K Pete

I've been watch the progress on this amazing engine. I'm blown away
by the level of detail and workmanship shown. Did I say amazing??

And those rocker assemblies are h**l for stout!!  

Pete


----------



## bigrigbri

May I say the cogging action is the sticksion of the valve stems when tying to open and being acted upon at an angle overcoming the initial valve spring load. Try a small smear of motor oil on the stems before assembly.
Running in carefully will loosen things up with adequate lube.
Heavenly work though.


----------



## mayhugh1

I was planning to machine the stud tubes next, but after thinking about it for a while I didn't feel like screwing around with the lathe motor just yet. So, I decided to tackle the long flimsy intake gaskets that I hadn't been looking forward to dealing with either.
If I were were building a billet engine I'd already have a CAD model for the intake ports. Both heads would be identical, and I'd be able to create a CAM program for the drag knife on my Tormach to make multiple copies of the gasket from a common design. 
The intake flanges on the Merlin's port and starboard castings are essentially identical although not quite parallel to the heads' axes. However, I match-drilled their mounting holes to the bosses on the intake manifold halves which have some variations of their own. As a result, most of the holes did not end up perfectly centered in the mounting bosses on the heads, and the port and starboard hole arrays are not quite identical. They're different enough that two slightly different gaskets had to be created. 
Each 10" long gasket requires 46 holes clearance'd for 2-56 mounting screws. I was concerned that cutting so many tiny holes with a drag knife might develop into a hassle, and so I decided to drill them using a metal template.
I started by clamping each head in the mill vise, and with an optical microscope in the spindle I used the DRO's to manually record the center of each mounting hole. I also recorded the locations of some key dimensional features of the ports so I could build simple shape models of them in SolidWorks. Software is available for Mach-based cameras to automate a process like this; and, in fact, Tormach used to sell such a package. My personal experience with the raster-to-vector conversion software that I've tried to use on my plasma table has been disappointing, though.
I then created a pair of gasket models and a CAM program to machine a matching pair of drilling templates from 1/8" aluminum plate. Using the drag knife, I cut out three copies of each gasket from the same automotive gasket material that I used months ago when I match-drilled the intake manifolds to the heads. It was important to use the same gasket thickness that was used during the match-drilling in order to maintain the original fit of the manifold between the 60 degree heads.
The two sets of three gaskets were then stacked under the metal templates which were screwed tightly down to a piece of MDF. The holes were drilled through the gasket stacks using a drill press, and they came out looking as though they had been punched. At this point, these are the only gaskets I currently have planned for this engine, but that may change as the build progresses. - Terry


----------



## kvom

Some good ideas here for the future.  I need to remake some gaskets for my loco and will use this technique.


----------



## mayhugh1

Pressurized oil will eventually be supplied to the valve train components through flanged fittings located at the outside rear of each head. Internal 90 degree flanged elbows are needed to connect these external fittings to the rear-most cam block in each head. From here the oil will be injected into the collinear arrays of hollow rocker arm shafts for distribution to the rocker arms and cam bearings. The waste oil will be collected in a trough running the length of each head and eventually be returned to the crankcase through the stud tubes.
The elbow needed in each head is rather small, and the space around it is very limited. In addition, each will cross over the top of one of the studs; and so the fittings must be easily removable so the stud nuts can be accessed. 
The flanges were machined from brass plate, and soft 3/32" o.d. copper tubing was used to form the elbows. I've found that most small diameter tubing can be easily formed around simple wood mandrels. I usually chuck a wood dowel in the lathe and use a grooving tool to turn a tight fitting slot for the diameter of the bend that I need. The slot helps to prevent the walls from deforming. I've used this technique for copper and stainless tubing less than 3/16" diameter, but I've not had much success in applying it to full tight radius bends in thin wall brass tubing. The 3/32" tubing turns out to be too small even for my miniature tubing cutter, and so I trimmed the elbows to length with an abrasive cut-off disk in a hand-held Dremel-type tool. A few hundred rpm is sufficient to cleanly cut the soft tubing and helps limit the shrapnel field if (when) the disk fractures. The disk will try grab the tubing, and so it needs to be contained in a slotted cutting block. The tubing also gets really hot during cutting and should be sandwiched between the cutting block and a top cover block.
These two fittings are the first of many that will have to eventually be made since most of the Merlin's oil distribution system is plumbed externally. Some time was spent now experimenting with construction techniques for use later.
The real difficulty in making these fittings is coming up with a soldering fixture to hold the components in exact alignment so the completed assemblies will slide into place in the heads with no gaps and with all the mounting holes aligned. With no CAD model or dimensioned drawings to work from, careful measurements were taken of the actual hole locations while each head was resting on a surface plate. Fortunately, both heads' measurements agreed to within a couple thousandths, and so only one fixture had to be made.
The assembly was soldered using low temperature 60/40 solder plus an activated rosin flux. 'Activated' means the flux also contains an organic acid which makes it a better, although more corrosive, cleaner. Since it was only available in gallon containers when I purchased it several years ago, most of it will be around long after I'm gone. The flux was sparingly applied with a toothpick to only the ends of the copper tubes in order to keep the solder from spreading across the flange surfaces. I formed small solder ringlets around the tube ends and pressed them flat against the flanges so I wouldn't have to feed the solder by hand and make a mess of things. The assemblies were allowed to air cool and then were pickled in dilute sulphuric acid (drain cleaner) for a few minutes to remove the flux. Pickling was followed by a neutralization bath of baking soda dissolved in water and then followed by a water rinse. A Scotch Brite pad finally brightened up the surfaces. 
The cam block mounting screws in the heads were removed one at a time and re-installed with low-strength threadlocker to seal the coolant passages they penetrate. After an elevated temperature cure of the threadlocker, a temporary flanged injector was cobbled up and screwed to the rear of each head so a syringe could be used to inject oil. The plug in the front cam block was temporarily removed to verify that oil had traveled through all the rocker shafts to the front of each head. Ample tell-tale seepage between the rocker arms and the cam block ends indicated the rocker arms and cam bearings were likely being well lubricated. - Terry


----------



## ddmckee54

When are we voting to elect the Grand Poobah of engine makers?  When we do, you've got my vote.

On final assembly are you going to put a little high temperature silicone on the mating surfaces to ensure the oil only leaks out where you want it to leak?  It doesn't look they don't have gaskets so I'd think that you'd want to goop up the connections on the outside of the engine at the very least.

Don


----------



## mayhugh1

Don,
Thanks for your kind words. I'll likely make some tiny paper gaskets for the flanges on the fittings external to the engine and just leave metal against metal for the internal fittings. The flanges on these engine fittings are usually small enough that it isn't difficult to get nice flat machined surfaces that leak minimally with oil which isn't a big problem inside the engine. In the oil test I did above there wasn't any significant leakage, fortunately. Coolant is another issue, though. Metal-to-metal flange seals usually don't work with coolant, and so all those will probably be gasketed. - Terry


----------



## 10K Pete

I've been watching this build with great interest and am fascinated by the
work you are doing. I have had nothing to contribute until now.

Have you ever used Permatex #2 Aviation Form-A-Gasket? It is made for
metal to metal seals in fuel and oil systems. Isn't washed away by them,
doesn't harden very much, easy to disassemble and does clean up with
alcohol. I've used it for 50 years and my Dad for a long time before I came
along. 

It was used on the Packard V-12s in PT boats (Dad was a MotorMac)
and Merlins and Allisons.

I suspect it would work perfectly for your application. If the metal to 
metal fit is even close you won't need a separate gasket!

Pete


----------



## mayhugh1

Pete,
Thanks for the tip. I just looked it up, and decided to order a tube. I'm going to need something like that to seal the stud tubes if I can't figure out a way to do it with o-rings. I've used regular Permatex #2 on automotive gaskets, but it wasn't the aviation version you recommend. I'll run some tests on it when it comes in. - Terry


----------



## 10K Pete

mayhugh1 said:


> Pete,
> Thanks for the tip. I just looked it up, and decided to order a tube. I'm going to need something like that to seal the stud tubes if I can't figure out a way to do it with o-rings. I've used regular Permatex #2 on automotive gaskets, but it wasn't the aviation version you recommend. I'll run some tests on it when it comes in. - Terry



You should be able to find it at the local auto parts store. Most all of them
carry the stuff.

Pete


----------



## Davewild

https://www.facebook.com/BattlefieldsPast/posts/827987097324228

This may be of interest to you Terry.

Dave


----------



## golfpin

got to admire you sir stay with it hope  I will see u finish it...all the best to all on the sight for Christmas and new year golfpin


----------



## mayhugh1

I received and bench tested the replacement motor for my lathe, and it seems to run as it should right out of the box. The cooling fan on my older motor comes on immediately when the unit is energized, but on this newer version it evidently switches on only when the motor reaches an elevated operating temperature. This might be one of the 'improvements' made by Wabeco to reduce the amount of swarf blown through the fan to accumulate over the motor. With my new cabinet ventilation system, I'd rather have the improved electronic component reliability expected with a continuously running fan. A rule of thumb I used during my real working days was that electronic component lifetime generally doubles for every 10C that its operating temperature is reduced. Of course, fans have their own reliability issues; but they're typically cheaper and easier to replace. My current plan is to limp along with the old motor for a little while longer - at least until after the holidays. I guess I'm still hoping to stumble upon a fix before completely giving up on it.
The next step in the build was machining the 56 stud and coolant transfer tubes that run between the cylinder blocks and heads. The coolant tubes were trivial - just 28 short lengths of metal tubing that connect the coolant passages around the cylinder liners to the main passage in the head. These .160" long 5/32" o.d. tubes were parted off in the lathe from a length of thin wall aluminum tubing. 
The 28 stud tubes, on the other hand, are a bit more complicated. The long studs that will tie the heads and cylinder blocks to the crankcase pass through the head coolant passages, and so the head stud holes are sealed by flanged metal sleeves. These stud tubes double as conduits for top-end waste oil to return to the crankcase. Openings in the tops of the tubes above the coolant seals allow waste oil to enter and trickle down and around the studs to the crankcase. These openings are really only required on the outside seven stud tubes in each head since the lower sides of the heads are where oil will tend to accumulate.
The first photo shows two possible designs for these tubes. The Quarter Scale documentation provides the design on the left which is made from a length of 7/32" o.d. thin wall aluminum tubing with one end spun to form the flange. The notes call for the bottom of this flange to be coated with a 'suitable' sealant. A steel slotted washer provides a durable surface for tightening the stud nut as well as an entry slot for the oil.
I tried my hand at lathe-spinning this flange on some test parts and was surprised at how easy it was to do using a hand-held sharpened wooden dowel. An issue I ran into, though, was an inevitable radius left in the corner underneath the flange that prevented it from sitting down flat over the sharp corners that I'd left on the reamed stud holes in the heads. I experimented with deforming the radius using a press and a scrap block, but even with re-annealing I could see tiny cracks in the stretched metal. Since I didn't want to radius the corners on the already completed heads I decided to re-design the stud tubes. 
I machined my single-piece design shown on the right side of the photo from stainless steel. The tube's o.d. was turned for a close slip fit in the head, but a slight taper on its bottom end provides a couple thousandths clearance to aid assembly with the cylinder block. A .020" wide groove, machined in the bottom surface of the flange, will be filled with the Permatex sealant recommended earlier by Pete10K to form the upper seal. The tube's wall thickness ended up at just over .020".
The Merlin heads were not designed to fit down against the top surfaces of the cylinder blocks. Instead, shoulders inside the combustion chambers will be sealed to pressed-in liners which protrude slightly above the decks of the cylinder blocks. These liners create a .050" gap between the top surface of the cylinder block and the bottom surface of the head. All 28 tubes must also be sealed inside this space between the block and the head. Although the full-size engine used custom pocketed seals, the Quarter Scale uses simple o-rings placed around the metal tubes bridging this gap. There are no machined pockets for these o-rings in either of the two surfaces, and so the .070" thick o-rings will be compressed by about .020" within the gap.
A challenging part of the assembly is to engage all 28 o-ringed tubes in both the head and block while simultaneously engaging the liners with the sealing shoulders in the combustion chambers. Once this is done the head and block pairs are bolted together with an additional 24 head bolts (whose holes must also align) in order to form a standalone subassembly. This subassembly will be much easier to deal with than the individual heads and blocks when it's time to slip them down over the studs and the ringed-pistons.
Back in April when I drilled all these tube holes I realized it wasn't possible to match drill any of them. They all, including the combustion chambers, had to be referenced to a common datum on each pair of castings. Some of the holes even had to be 'moved' because they had been pre-cast in the wrong locations for my 'short' crankcase. To make things even more challenging, the holes for the coolant transfer tubes were reamed for light press fits in the heads and close slip fits in the blocks.
I was thrilled and totally surprised when the long awaited trial assemblies of each head/block pair with its 28 tubes and 6 temporary Delrin separators went together per plan without having to enlarge any of the holes. I wasn't even sure that over the ten inches I had to work the DRO's on my mill were up for the task. For me, this milestone was even more significant than getting the crankshaft laid in. But, of course, I don't yet know the subassemblies are leak-free. 
Inconsistencies in the head counterbore depths, though, came around to bite me while trial fitting the stud tubes just as the inconsistent counterbores for the valve guide flanges affected the valve fitting. I had to re-machine most of the stud tube lengths and create four different groups of parts based on length to accommodate the range of head thicknesses I inadvertently created for myself. It seems that just as with Jerry Howell's IC engines there are very few quick-and-dirty machining steps allowable in the Merlin. - Terry


----------



## 10K Pete

All the superlatives have been used......

So Wow!! Tiny, tiny little parts.

Pete


----------



## petertha

I'm sorry to be the one to inform you Terry, your pic & others like it show FS valves with some funky recessed dish shaped recess. Are you sure you are OK with flat-bottoms? At the rate you crank out complicated parts, a new set could be delivered by Miller time  Kidding of course, its coming together fantastic. BTW why were the FS valves shaped this way?


----------



## ICEpeter

Hello Terry,
Good to hear you got the new lathe motor and it works out of the box. As far as the aux. fan / cooling fan is concerned, it appears that there are two versions of the cooling fan operation. It depends on the version of your motor. I copied two pages out of the manual I received for my Hanning motor and it shows two versions. In the first version, the cooling fan comes on as soon as the motor is powered up. In the second version, the cooling fan is controlled by the motor's CPU and appears to be controlled by a temperature sensor that monitors the CPU operating temperature and presumably controls the cooling fan operation as well. 

The drive motor is also equipped with what appears to be a thermal switch embedded in the winding and connected to the CPU. I presume the thermal switch will shut down the whole system, indicating a drive motor overheating situation.

I could not find a parameter in the parameter set up in my manual that would permit setting a operating temperature range for the cooling fan. It is apparently an internally set parameter that can not be accessed.

Question: Did you receive an operating manual together with your motor that offers more detaisl about the internal set up of your motor? If not, you may be able to find the applicable manual at the Hanning website.

Peter J. 

View attachment Varicon.pdf


----------



## mayhugh1

Petertha,
I'm really not sure why the RR engineers contoured the valves as they did. Maybe they thought the smooth contours would help with pre-ignition. My understanding is that the Merlin's wartime fuel was eventually 100 octane and even though the c.r. was only 6:1, in an emergency the supercharger boost could run as high as 13 psi. - Terry


----------



## mayhugh1

ICPeter,
Thanks for the diagrams. I didn't receive any documentation with the replacement motor except for a sketch with a comparison of the old vs new control wiring changes. Once I get the new motor installed I plan to take the original one apart to see if there is anything obvious that I can repair. If not, I'll likely try to adapt another VFD to it since there may not be an issue with the motor, itself. To me it smells like the pre-check that the processor runs through to measure the motor's parameters is failing for some reason as the motor heats up. If so, it may be a portion of the measurement circuitry failing. - Terry


----------



## mu38&Bg#

petertha said:


> ..... FS valves with some funky recessed dish shaped recess.....



These are called tulip valves. They were common at the time in all engines. I've not found specific details about how the shape was developed. It seems to have started with the idea that a larger radius between the head and stem improved flow, and the head was relieved to reduce weight.

Greg


----------



## mayhugh1

There were a few loose ends on this build that I wanted to tie up before taking a holiday break. The rear-end adapter on the engine stand that I've been using up to this point will soon get in my way as construction moves toward the rear of the engine. I considered building a scaled-down version of the rotisserie used to assemble the full-size engines, but the more I thought about it the more it seemed too awkward for bench-top use. So, instead, I made a new adapter for my existing stand. With the engine's front cover work completed, I should be able to finish the remainder of the engine with it supported in this new front-attached adapter.
After completing the cam chain enclosure several weeks ago, I wanted to do a little work on the wheel case so I could verify the fit of the chain cover. This would have included machining and installing the rear drive adapter on the crankshaft. While planning it out, though, I noticed that I had somehow neglected to finish machining the rear hub on the crankshaft. This hub was supposed to have been bored to accept a beveled adapter that will drive all the engine's accessories including the water and oil pumps, magnetos, camshafts, and supercharger; and it will be driven, in turn, by the starter drive. Back in July, I had to make up a special steady rest for my 9x20 lathe in order to support the crankshaft while its ends were being finish-machined. Evidently I became distracted and didn't finish boring out the rear hub, and so I had to pull the crankshaft back out of the crankcase to complete the machining. I knew this was coming up, and it was something I wanted to complete before tearing down the lathe to replace its motor. While the crankshaft was back out on the bench I also sealed the 24 oil end caps, as well as the threads of the 12 bolts securing them, with a removable thread-locker.
Finally, I needed to do another production run of some tiny parts so I could finally test the fits of the cylinder blocks to the crankcase. Just as the Merlin heads are offset from the cylinder blocks by short gaps, the cylinder blocks are similarly offset from the crankcase decks; and so, the studs must also be sealed across these gaps. Oil return holes previously angle-drilled through the threaded stud holes in the crankcase allow the oil trickling down and around the studs to eventually return to the sump.
These seals are lathe-turned Delrin sleeves that fit snugly in matching counterbores previously machined in the top two surfaces of the crankcase and the bottom surface of each cylinder block. The alignment of these counterbores is important so the cylinder liners in each block can slip into place in the crankcase openings with all 14 oil seals in place. I was able to verify the fit of both blocks using some snug fitting Delrin spacers in the bores for the liners to simulate the gap. 
That's likely all for a while. To everyone on the forum, have a great holiday and my best wishes for the new year. - Terry


----------



## stevehuckss396

Absolutely beautiful work. Been watching from day one. Keep up the great work and I cant wait to see what next year will bring.


----------



## mayhugh1

Thanks, Steve,
Hope to chat with you at Cabin Fever.
Terry


----------



## mayhugh1

After the holidays and when the house went quiet again, I decided it was time to finally replace the motor in my lathe. Replacing it required a couple afternoons that included hashing-up some fixtures to help me maneuver the old motor out and shoehorn the new one into place. The close-fitting enclosure around this lathe helps to keep the shop floor clean, but it really sucks when maintenance or modifications are required on the machine. Most of this is my own doing, though, since the location I chose for it in my shop made the enclosure unremovable.
Even though I was assured the replacement motor would be the same physical size as the original, it isn't. The new motor protrudes outside the rear envelope of the enclosure by a quarter inch or so. This required a large hole to be cut in the rear of the enclosure and a cover plate to hide the 'bump'. The motor is also about an inch longer than the original, and so I had to modify the fresh air intake that I recently plumbed inside the enclosure for the motor's cooling fan. After working through a few errors in the updated wiring diagram supplied with the motor, I finally had the lathe running. 
The new motor has a few new 'features' that took some getting used to. Most obvious is that its integral VFD and controller remain active for some 30 seconds after its power is removed. If the Mach session is terminated before the energy storage devices inside the VFD have time to discharge, the motor will briefly spin up in some random direction before discharging them. Also, if the lathe is used in its manual mode, almost the same amount of time is required for the motor's internal controller to boot up before the motor can be run. This had me running around in circles the first few times I tried to test the new installation.
I disassembled the original motor hoping to find something simple that I could repair. The integral VFD in this motor is an assembly of four complex circuit boards that fit together in Chinese puzzle box fashion inside a cast aluminum finned enclosure. This enclosure is normally hidden by the cooling fan shroud. There is also a large internal potted inductor assembly as well as a shaft encoder, and so this VFD is not a typical sensor-less type. One of the boards contains four 350uF 400V capacitors sitting on the dc bus. The shrink-wrapped tops of three of them appear to be bubbled which isn't a good sign. The power connector to the motor windings was badly overheated (melted), and indicates the motor has drawn some excessive currents. A temperature-related insulation failure would fit the symptoms I've been seeing, but the failed/failing caps could be also be involved. The issue with replacing them, though, is that they are soldered to one side of the same circuit board that contains all the heat-sinked semiconductors on its opposite side. It seems that a heat conductive epoxy was used to permanently attach them to the interior surface of the finned enclosure, and so this board may not have been designed to be repairable. This is disappointing since aluminum electrolytics are known ticking time bombs in any product especially when they're inside a close-fitting enclosure with heated stagnant air. In frustration I boxed up all the pieces for another day.
Getting back to the Merlin, I thought I had completed all the machining on the crankcase so I could logically start on the liners. However, I had forgotten about the tapped mounting holes on the rear of the crankcase used to attach the wheel case. Five of these 20 holes were drilled earlier using coordinates from the wheel case drawing in order to attach a temporary rear fixture for line-boring the crankcase. It's critical that the centerlines of the crankcase and the wheel case are identical, but only a few of the wheel case holes are accessible for match-drilling to the crankcase. So, I decided to drill the crankcase and wheel case holes in two separate operations using the coordinates provided on the wheel case drawing. I had also planned to add a couple dowel pins for good measure, but I couldn't find suitable locations for them. Instead, I reamed the wheel case holes for close (.002") screw clearances and hoped their sheer numbers would be sufficient to register the two assemblies.
I stripped down the crankcase (again) and indicated it along all three axes on the mill in order to verify the coordinates of the previously drilled holes and to drill and tap the remaining holes. I also scraped away some more investment that I found hiding in some of the corners of the casting. 
Before drilling the holes in the wheel case I first had to do some foundational machining on the casting. The wheel case is an overwhelming casting that will eventually require a lot of precise machining since it supports a number of geared take-off shafts and countershafts in addition to the supercharger. The gear spacings associated with some of these shafts will not adjustable, and so there will be some non-forgiving machining ahead.
The first step was to face the front mounting flange to the crankcase. This had to be done iteratively and in small steps with the rear flange to which the supercharger will mount. My particular casting turned out to be significantly warped, and Ihad a lot of difficulty distributing the casting errors between the front and rear flanges so circumferential variations in their thicknesses were not so obvious. The notes warned that this casting might be problematic but cannot be straightened due to its complex shape. The mounting flange for the timing chain cover was then faced just enough to get it flat. This surface defines the horizontal axis of the wheel case and was used as one of the references for the mounting hole coordinate system.
The coordinates are referred to the center-line of the crankcase which, in turn, must correspond to the centerline of the supercharger. Therefore the wheel case was moved to the lathe where its crankcase-side flange was mounted to a faceplate. After compromise-centering the casting, the mounting flanges for the supercharger and its bearing plate as well as the opening for the crankshaft on the front flange were all concentrically bored. These operations established the finished centerline of the wheel case. 
A confusing note in the documentation also called out the machining of a concentric recess on the front flange of the wheel case for use as a register to the crankcase. I did this without understanding why since the rear of my crankcase is flat, and there is nothing for this recess to register. This note may have pertained to an earlier casting version, or it may make more sense later when I better understand some of the remaining operations on the wheel case.
After spotting, drilling, and reaming the wheel case holes I turned a snug-fitting crankshaft plug to locate the wheel case to the crankcase. All 20 screws freely went in as hoped and were snugged down. I then removed the plug and after loosening each screw one full turn I could measure only a few tenths movement of the wheel case with respect to the crankcase. This gave me some confidence in the alignment of the two sections even though I don't like leaving such things up to screws. Four additional holes were transfer-drilled between the wheel case and the oil pan. Finally, with the crankcase/wheel case assembly sitting flat on the mill table, the timing chain cover flange was indicated. It turned out to be horizontal as expected but was also serendipitously at its finished height above the crankshaft centerline. - Terry


----------



## ICEpeter

Hello Terry,
It's me again. The other Varicon guy. When I read your comment about the 30 second delay in the motor speeding up and the 30 second delay when stopping the motor, it looked to me as if your motor has a programmed ramp up and ramp down parameter that was programmed ex factory as extremely long or wrong or your motor might be wired incorrectly.

I looked up my Varicon manual and there are two parameters that govern the ramp up / ramp down speed on start up and after shut down, expressed in either acceleration / deceleration (min-1 / sec)  or HZ per second.

I would suggest to contact your USA Wabeco representative and question him about your situation. Hopefully he can provide you with the answer to your problem. I am not sure whether you already contacted him since you indicated you found mistakes in the wiring diagram that was provided with the new motor. Hope it all will work out, eventually.

Peter J.


----------



## brendanf

First off.. I must say wow.. To all of this..

Secondly, about your old VFD. Those caps don't look that bad actually.. Usually a cap REALLY buldges when it goes bad or it blows up completely..

The burnt connector probably has more to do with the trouble you were experiencing.. It has been my own experience in the past that it isn't excess current that caused the heating, but just a loose connection with perhaps a touch of oxidation thrown in.. With all the vibrations in the lathe over the years that connection has probably been worked loose just enough to cause this.

I have fixed similiar issues just be de-soldering the plug, and then cutting the wires and soldering them directly to the board. But as you mentioned it sounds like the heat sink covers the solder side making this difficult..


----------



## mayhugh1

Peter,
I did emailed him but received no reply. 
It isn't a ramp up or ramp down time that I'm seeing. It is a 'boot up' time required by the controller before it will even accept commands. After waiting that period of time just after power is first applied, the motor responds normally. The wiring discrepancies were related to one of the wires in their diagram being a different color from the one actually used in the wiring harness in my machine. It involved one of the 24volt direction-select wires, and so I felt on safe ground using the wire I thought was correct for my machine. It turned out that the new motor actually ran in reverse to the old one and so I ended up having to reverse the pair of wires in addition. The second discrepancy was a shield ground for the signal cable. The manufacturer originally grounded this shield to the machine at both ends of the cable, and there was a terminal provided for grounding it in the original controller housing. The new controller had no provision for this ground. It isn't good practice to ground a shield at both ends, and so I didn't have a problem just leaving the shield open at the controller end, but I asked my dealer to check with the factory anyway. He often just ignores what he feels are PITA emails. - Terry


----------



## mayhugh1

brendanf said:


> First off.. I must say wow.. To all of this..
> 
> Secondly, about your old VFD. Those caps don't look that bad actually.. Usually a cap REALLY buldges when it goes bad or it blows up completely..
> 
> The burnt connector probably has more to do with the trouble you were experiencing.. It has been my own experience in the past that it isn't excess current that caused the heating, but just a loose connection with perhaps a touch of oxidation thrown in.. With all the vibrations in the lathe over the years that connection has probably been worked loose just enough to cause this.
> 
> I have fixed similiar issues just be de-soldering the plug, and then cutting the wires and soldering them directly to the board. But as you mentioned it sounds like the heat sink covers the solder side making this difficult..



You might be right about the intermittent connector. That could explain my symptoms as well. If you look at the photo I posted, the burned connector is around The rightmost blackened blade inside the white header on the pcb. I think you've inspired me to repair that connection and put it all back together.


----------



## ICEpeter

Terry,
Seems I didn't read your original problem description thoroughly and correctly. I do understand now that your problem is not a ramp up / ramp down matter but a power up / down situation. 

Having a similar Varicon motor of about the same size on my milling machine, I looked and tried to see if this kind of behavior is found on my motor as well but must say that it does not behave as you described. When I power up, the motor is instantly ready for use and on powering down, the motor does not turn in any way. 

If your motor turns briefly on power down, I could imagine that this could lead to an injury if one is somewhat distracted and may get hurt. If the motor behaves as you describe, I would assume there is something wrong with the motor and its internal controls / set up and may need replacement.

I am sure your Wabeco representative (Assuming its MDA Precision out in CA) will resolve this matter to your satisfaction. Them, being of Swiss heritage, do take care of their customers.

Peter J.


----------



## Ken I

I don't know that particular controller but I've had similar problems.

The boot delay being on power up - thereafter the motor is switched using the "run" or "enable" switch points - if you simply switch the controller on and off at the mains you will keep getting the boot up delay.

Those "Hot Joints" are bad news and need to be repaired / bypassed (by soldering directly to the blade if necessary).

I agree with the prior response by brendonf that the caps are probably O.K. - they normally bulge significantly or blow completely (those indents in the can are deliberate weak points to "control" the explosion of a detonating capacitor).

As regards your build, I've been watching in fascinated silence - there aren't enough superlatives (as said by others) this is just fabulous, mythological levels of workmanship.

The amount of effort you put into documenting what you are doing is a great service to all of us following this build and is greatly appreciated.

I can't wait to see this finished.

Being British I have a special place in my heart for the Merlin engine - without which I might have been writing this in German.

Regards,
             Ken


----------



## mayhugh1

Brendanf,
Your comment about the burnt connector being the source of my problem made so much sense that I spent the day repairing the connections and reassembling the motor/controller. I set it up on the bench fully expecting the problem to finally be solved, but after an hour or so it began intermittently acting up again. There is a 'controller ready' led on the controller circuit board that should be ON when the controller is powered up and all is well, and I noticed that this led is OFF when the motor refuses to start. The 10 volt analog voltage that is generated internally so the motor speed can be controlled with an external pot drops to about 6 volts when the controller is acting up. There is so little else that can be done without a schematic that I think the problem is going to be nearly impossible to troubleshoot without a schematic. Probably the best I will be able salvage is the motor, itself, with an external VFD.  Again, thanks all for your insightful comments. - Terry


----------



## Ken I

Intermittent faults are a sod to dope out.

Yours might be temperature related given that it happens after an hour - try a can of electro-freeze (or similar) and try selectively cooling suspect parts - this is a fairly standard bodge for this kind of problem.

The next place to go looking is bad joints or cracks in the circuit board / tracks.

Remove and re-plug anything that has friction connections and examine the connections. Plug in and out several times to clean up. This includes plug in I.C.s etc.

As regards the board / tracks, examine with a high power loupe or magnifying glass - anything suspicious solder a jumper across any two convenient terminals either side the "crack".

It gets worse with multilayer boards where you need to take resistance readings from point to point (make a list - particularly those near zero) check again when the fault recurs. Again solder bridges over the suspect.

I once did this over several weeks before I finally nailed the sucker.

Hope this helps.

Regards,
            Ken


----------



## dsage

Hi Terry:

I agree with everyone else'  analysis of your controller issues. I've been in the electronic maintenance game for 40 years now and I've been through this type of problem many times. The freeze mist is a really good idea and should get you in the area of the problem components. Spray a small area of board and see if the problem goes away. In this respect you are lucky that it is intermittent as you can duplicate the problem. I'm confident you'll find it in this fashion.
 You didn't say what you did to rehabilitate the burned connector. As others have said it is a loose connection that causes it to burn up and it will be difficult to make it tighter once it's damaged. So soldering the wire directly to the board would be a good idea. Or somehow bypass the bad pin(s).
 In addition I have found many times that the solder joints on the back side of the board where the connector pins go through can have hairline cracks. This comes from years of vibration of the wiring of the connectors. This may be why the pin was heating up as much as a bad connection in the connector itself. I think you said you can't get to the back side easily. But if you can, re-solder ALL of the connector pins on the PC board and any high(er) power device leads all over the board. (power resistors and transistors etc.) You can usually see the crack(s) around the pins under high magnifications but it easier to just re-flow and add a bit of solder as it is to look for them.

Oh. And amazing work on the engine too. 

Good luck

Sage


----------



## mayhugh1

Dave,
Thanks for the suggestions. It turned out that the male-side of the burned connector on the power pcb was just four standard terminal blades soldered through a plastic header. I had a number of female crimp terminals that fit snugly on the blades, and so I cut the melted connector off the harness and replaced it with four individual terminals. Without access to the rear of this board I was afraid to do any soldering on it. Before inserting the terminals over the blades, though, I coated the blades with Nyogel. This is a contact grease that I purchased back in the early eighties to solve oxidation and fretting corrosion problems with the tinned Molex connectors that were used in some PC busses at the time. This particular grease not only keeps air away from electrical contacts to eliminate oxidation, but it also enhances conductivity by becoming electrically conductive under the influence of an electric field. In addition, it doesn't harden from heat like some silicone-based dielectric greases. I still have the original jar that I bought and still use it to this day in landscape lighting fixtures and various motorcycle and automotive electrical contacts that I've had to deal with.
Although the Freeze-mist is a good idea for troubleshooting heat sensitive problems, it wouldn't very practical in this particular case. Three of the circuit boards use multi-pin pcb connectors between them for various interconnections. With the power pcb essentially being epoxied to the interior of the enclosure for its semiconductors' heat-sinking, the whole assembly has to be inside the enclosure to be functional. This leaves only a small opening for troubleshooting and pretty much eliminates any directed access for the Freeze-mist nozzle. 
While it was disassembled I should have examined the solder connections on the pcbs that I had access to under a microscope, but I was too focused on the burned connector. I'm including a few photos that I took during reassembly so you might get a better idea of what I'm trying to describe. - Terry


----------



## dsage

After seeing those pictures I'll have to agree that's a tough one to deal with. Certainly designed to be a FRU (field replaceable unit) not something designed to be repaired for sure. I hope you lucked out on replacing the slip on connectors since, as mentioned, the problem could just as easily be a bad solder joint on the back side of the board heating up the pin. I guess you can only do so much with that. A shame they made it that way really.

Oh, BTW.  We used to dig through epoxy coating quite easily with an electrically heated tool sort of like a small knife but a soldering iron with a wide tip would do as well. A bit stinky but epoxy decomposes easily with extreme heat and you can dig down to the board to get at connections. But you'd want to limit that exercise to ones you know are bad because it's a bit of smelly work.

Sorry to digress from your wonderful engine build. 

Sage


----------



## mayhugh1

While the crankcase/wheel case assembly was still set up on the mill, I transfer-drilled and tapped the fourteen 1-72 mounting holes in the timing chain cover flange to match those previously drilled in the cover. In a second set-up, the through-holes for the three idler sprocket shafts were also drilled and reamed. The center hole was slotted since its sprocket will be used as the tensioner for the chain. I placed the tensioner sprocket on the crankshaft centerline even though its boss is a bit off-center.
Flanged ball bearings were then pressed into the three idler sprockets that I machined back in September. Shafts for these bearings were cut from drill rod, and setscrew flats were milled on their ends. I temporarily assembled the cylinder blocks and heads onto the crankcase so I could check the fits and clearances of all the chain cover components. Since I haven't machined the rear driveshaft with its integral cam drive sprocket, the final chain length can't yet be determined. Fortunately, the chain appeared to ride in the center of its housing. This was something that I'd been concerned about since a lot of parts need to line up properly to make that happen. The clearances between the chain and the i.d.'s of the two inside cover tubes, though, will ultimately end up being a function of the position of the tensioner sprocket in its slot. 
I could already tell that final installation of the chain is going to be difficult especially with the cover tubes in place. So, I wanted to make sure that all the cover components fit properly at this point so the chain won't become an even bigger issue later.
I was initially going to let the three sprockets find their own running positions on their shafts since it would simplify their installation. After feeding the chain down through the cover tubes a few times, though, I decided to turn three pairs of centering bushings to insure the sprockets could not move off the tubes' centerlines. 
When I machined the chain cover components a few months ago I could only rough cut some temporary cover tubes and test their fits since I had no overall dimensions to work with. Fabricating the actual tubes turned out to be a bit tricky since the outside ones with their mitered ends required a lot of trial and error fitting that resulted in several scrapped parts. When I finally had a working recipe, though, I made a few spares. The ends were shaped on a sander using a miter gage since the soft thin wall aluminum tubing didn't play nicely with my mill. Using a pull-string I was eventually able to snake the timing chain through all four cover tubes and around the five sprockets and verify it didn't rub anywhere. My hat is off to the designer of that chain cover. I was sure it was going to need help from a Dremel tool.
I'm still trying to decipher the wheel case drawings and understand how the supercharger castings are to be machined and fitted to the wheel case. Details of the diffuser ring seem to be missing, and currently it seems that so much material will have to be removed from the impeller that I'm not at all confident in my understanding of the single and very busy supercharger drawing that was supplied. It seems it was here that Zapjack's build (http://www.usinages.com/threads/rolls-royce-merlin-v12-echelle-1-4.42350/) became stalled a few years ago. The documentation and notes for this portion of the build are very sparse, and so I expect my own progress will slow some as well. I've emailed John (http://www.homemodelenginemachinist.com/showthread.php?t=24717) with some questions since he's successfully navigated his way through all this. My plan is to start working on the (billet) bearing plate for the supercharger which is a less risky part but one that I think I do understand. Hopefully, making it will shed some light on the machining required on the remaining irreplaceable castings. Terry


----------



## P.J

Wow! That is gorgeous!


----------



## brendanf

Terry is there no provision for sealing the 3 shafts to the block that the sprockets ride on? Would there not be oil leaking out? Or do you have something planned?

Your work is absolutely fantastic.. Wish I could do this!


----------



## mayhugh1

Brendan,
I'll probably cover the ends of the shafts with a bit of clear silicone. - Terry


----------



## RonC9876

Terry: It was great talking to you, your wife, and your son at Cabin Fever. I am  in total awe of what you are doing on this build. Your work is something above what I would expect to be possible for us mortal beings. OMG. How have you accomplished all of this in such a short time? I now believe in alien life forms on this planet. I have only touched the surface of what you have written, but I have come away shaking my head. Such in depth coverage and your ability to come up with fixtures and tooling to do such accurate work is mind blowing. You deserve some type of medal or an award for your abilities. I am in awe!
I think i said that before but it needed repeating! Keep your sanity if possible. 

Ron Colonna


----------



## mayhugh1

Ron,
It was great getting to talk with you again also. It's such a shame we grew up in the same town without ever meeting one another, and now that we have these unique and common interests we live half the country away. Thanks much for your very generous compliments. Looks like I'm really going to have to finish this thing now. - Terry


----------



## mayhugh1

While at Cabin Fever I ran across this gem. I wanted so much to meet its 94 year old builder, but the engine was displayed for only a short period of time during the first day by a friend of his. It's a 1/8" scale Merlin with a two stage supercharger, and it has been run. The entire engine was built from scratch (no castings) over a ten year period by, obviously, a master craftsman. Even the scale fasteners were machined. I took a lot of close-up photos of this beauty, and now I finally understand the coolant flow path through the engine. This one sets the bar at a height that's really difficult to see over. - Terry


----------



## wirralcnc

Terry can you post some pics of the 1/8 " scale merlin.
Cabin fever is abit out of my way. Maybe one day I will get over. 
Robbie


----------



## jschoenly

Boy - Running the show, I hardly get around to see and talk with many people sadly.  I had no idea that Dick's Merlin was there!  I have video of this engine running from years ago when we were originally in Lebanon!


----------



## jschoenly

I thought this video was on our Youtube Channel, but I was mistaken.  I've added the full run of the 1/8th Scale Rolls Royce Merlin that I have:

https://youtu.be/8yWFs6hybGs


----------



## dsage

Gotta love that wonderful sound.  What's the clear tube coming from the back of the engine. Shows a lot of air bubbles passing through. If it's fuel would it explain the rough operation.?

Also I'm surprised you ran that without a shield and with so many people close by especially to the side(s) of the engine. You could have killed someone had the prop decided to fly apart (or any other failure for that matter).

At NAMES they smartened up and now make guys run their engines outside in a loading dock door opening and behind a plexi shield.

Very nice just the same.

Thanks

Sage


----------



## jschoenly

i think the bubbles were fuel and part of the rough first running.  This was years ago and people were blocked from the prop line, but yes there should be a shield and a designated area.  In recent years if people are running aircraft engines, we setup a space for it specifically.  Thanks!


----------



## mayhugh1

Robbie,
Here are some more of the photos that I took at Cabin Fever. As you can see I was more interested in the details at the bottom and rear of the engine. I wish I had gotten some better over-all shots. - Terry


----------



## kuhncw

Terry, 

I sent you a PM.

Chuck


----------



## kvom

If superchargers at that scale are ineffective, are you planning to make the internals?


----------



## mayhugh1

Kvom,
Yes, I am. The supercharger in this engine is of a modular design. My plan, once it is finished, is to install it into a test fixture and spin it up to measure any boost it might be capable of producing. At the rpms it will be running at I'll also want to do some stress testing before attaching it to the engine, anyway. - Terry


----------



## mayhugh1

It looks like the wheel case and its components will end up being the most difficult assembly in this build. There are so many shafts, countershafts, and shafts inside other shafts that the interactions among all the various gears make it difficult to come up with a construction sequence. John has patiently answered some of my dumb bunny questions through email, but the documentation could sure use some sub-assembly drawings. I took a couple drawings with me to Cabin Fever so I could study them safely away from the shop and its temptation to start cutting too early.
I eventually decided to continue construction with the supercharger bearing plate. This scratch-machined plate will support the rear bearings for the main rear shaft as well as the countershaft that drives the supercharger. When completed there will be 10 shafts, 15 bearings, and 14 gears packed inside the wheel case in front of this plate, and they will all interact with the two shafts supported by it. So, it's important that its bearings be accurately located with respect to the crankshaft centerline and, eventually, the axes of all the other shafts as well. It didn't seem practical to attempt to match-machine much of this plate to the wheel case since the important features on both parts face one another and are aren't simultaneously accessible.
There are mixtures of spur, bevel, and helical gears inside the wheel case. I had naively planned to make all the gears for this engine. But, after gaining some appreciation for why the wheel case is called what it is, I felt the learning curves for the bevel and crossed-axis helical gears would be best left for another project. Dealing with all the shop-made cutters and the tooth approximations I'd likely have to make while trying to maintain all the interacting center-to-center running distances was just too much to pile on top of what is already ahead. I still plan to machine the spur gears, but I placed an order for the bevel and helical gears from a gear manufacturer in England that was recommended by the documentation. In terms of the distances we travel here in Texas, that gear factory is likely located next door to the original Merlin engine plant.
When I received the involute cutters purchased for this project back in June of last year I spot tested the tooth cutting profiles of four of the cutters by cutting two pairs of test gears and checking their meshes at their theoretical center-to-center running distances. Most gear cutters that I've purchased are imported, and I've found their quality to be very inconsistent. The 32-pitch gears I made were for three of the shafts in the wheel case; but at the time I was only interested in verifying the tooth profiles, and so I didn't complete their machining. The 50/24 tooth gear-pair ran fine with no binding and minimal backlash at its theoretical 1.156" center-to-center distance, and so I put the cutters away for later use. I decided to install the gear-set back into its test fixture to see what kind of errors I'd be willing to accept inside the wheel case. This particular pair ran with noticeable drag but no binding with a spacing of 1.148", and at 1.164" the backlash was too great for my taste. My plan, of course, will be to aim for the theoretical center spacings for the spur gear pairs, but I'll use measured spacings for the bevel and helical gears once I receive and test them. I felt that a +/-.004" error, if necessary, would probably be acceptable on all but the high rpm supercharger gear set. 
I needed a consistent way of supporting the wheel case for the numerous machining operations to come; and so I mounted it, front flange down, to a faced 1/2" flat plate. I then machined two opposite ends of this plate parallel with the top surface of the chain cover and the other two ends were machined perpendicular to it. When completed, I had the wheel case mounted to a support plate that was square and aligned to its reference top edge within a few tenths.
The next operation on the wheel case was to drill and tap the seventeen 2-56 mounting holes for the bearing plate. The mounting holes were individually located in the centers of their cast blind bosses on the wheel case mounting flange, and their coordinates were recorded for use in SolidWorks where the bearing plate was laid out. The locations of the rough-cast front bearing pockets for the same two shafts in the wheel case as well as the parallel starter countershaft were also measured in the same set-up. Circular features in these castings have been remarkably accurate. A dial indicator showed these 'rough cast' bearing pockets, were within a thousandth or so of being perfectly circular. They are, of course, intended to be machined to finished dimensions.
Their measured locations, however, disagreed with those in the drawing by about .020". This would be enough to bind the gears on all three shafts and is roughly the same size error I discovered in the wheel case's centerline when I machined the chain cover. This was a big concern because adjusting their locations will affect the gears on the other shafts, and the whole avalanche of possible consequences was too much for me to follow especially since I don't yet have most of the gears to play with.
At first I thought all of this might have been caused by me when I initially squared up the warped wheel case casting. But, further measurements showed a possible interference problem between a large countershaft gear and the wall of the wheel case. The complex shape of the interior walls put my measurements into question, and so I decided to double-check the fit by cutting a simple gear set and installing it on a pair of temporary snug-fitting Delrin shafts that I pressed into the cast bearing pockets. Sure enough, the gear was not centered between the walls of the wheel case and, in fact, was jammed against one side. 
In the entire lot of castings this was the first casting error that I had run into that hadn't been flagged in the documentation, and so I spent many hours convincing myself that it was real. I spent even more time experimenting with new locations for the bearing pockets that would eliminate the interference, provide the correct center-to-center running distances for the gears on the three parallel shafts and minimally impact the other shafts. Unfortunately my test gear on the starter countershaft had only .007" clearance to the wheel case, and every fix I came up with moved it even further into the wall. In the end, I could only guess about the ripple-down effects on the various cross-shafts and their gears.
Finally, with a best-effort drawing to work from, I began construction on the bearing plate by chucking a slice of 6061 in my lathe's 3-jaw. Since I was starting with a piece of scrap that was only marginally thicker than the finished dimension of the plate, I cut a plexiglass spacer to help accurately support the material in the chuck. I've found that plexiglass works well for fixtures since it cuts easily on a bandsaw, and its thickness is extremely uniform. 
The o.d. and the mating flange of the bearing plate blank were turned for a snug tested-fit to the wheel case bore, and the bearing pocket for the central main shaft was bored. The blank was then flipped around and mounted in a collet chuck where its face was indicated-in before being turned to its finished thickness.
The blank was then secured, rear side up, to a piece of MDF with a close fitting plug pressed into the center bearing pocket so it could be indicated-in on the mill. The clearance holes for the flange mounting bolts were spotted and drilled using the measured wheel case coordinates. Button head screws were added through the flange mounting holes to further secure the perimeter of the blank to the MDF. The blank was shimmed and checked for z-height consistency across its face to insure the bearing pocket for the countershaft was bored perpendicular to the bearing plate. Excess material was then removed from the rear of the plate where a stiffening brace and some inspection holes were machined. The bearing pocket for the countershaft was bored with a boring bar instead of being interpolated. Finally, the 1-72 mounting holes for the two bearing retainers were drilled and tapped. 
It was this last operation that turned around and bit me. A mysterious errant move of my Tormach's spindle gouged the newly machined brace on the plate as it moved into position to start drilling the retainer holes. I was able to modify the design of the brace to clean up the damage and re-reference the workpiece, but the source of the hiccup was never found. Unfortunately, I had also managed to place two of the eight bearing retainer holes in the wrong locations thanks to the overly cluttered model I had been using to investigate the bearing relocations. 
After assembling a pair of newly designed bearing retainers I discovered that one of the gears in front of the bearing plate will end up so close to one of the .060" thick retainers retainers and its 1-72 button head screws that it will likely rub. So, I redesigned the bearing retainers to use .032" thick brass plate and flat head 0-80's. This meant that I had to re-fixture the bearing plate and re-drill and re-tap it for the new retainers.
In the end, the bearing plate fits snugly into the wheel case, and all seventeen mounting holes line up perfectly. The new bearing retainers hide my drilling errors, or I would have started over on a new plate. However, I think I may have gotten only a taste of things to come with this wheel case. There be dragons hidin' in there. - Terry


----------



## Ken I

I liked your gear mesh test - mental note for future use - thanks.

I presume you are using the axis to determine the best running centre to centre distance via the DRO - cute.

Damn it - your machining ability is downright scary - I just love what you are doing.

Ken


----------



## Scott_M

Hi Terry
As usual ,Beautiful work !
All those gears and shafts are sure to make your head spin.
As far as your errant z move, it may be time to switch to Path Pilot. There are a lot of reports that all the flakey Mach3 issues disappear. I am running it on the SBL but I am still running Mach on the 1100.

Scott


----------



## bouch

Just found this pic on facebook.  A little inspiration for you 

Been watching this thread, simply amazing stuff you're doing there.


----------



## maybach_man

Absolutely awesome thread...Don't know if its relevant to this but I have a copy of the 800+ Merlin engine overhaul manual, on cd ?


----------



## mayhugh1

I still find the wheel case overwhelming, but its design is beginning to grow on me as I better understand it. I didn't yet intend to do very much on it other than locate its mounting holes on the crankcase so I could complete the crankcase machining. I had planned to be working on the cylinder liners and connecting rods, but with the wheel case design finally coming into focus it's hard to set it aside. At this point I think I understand the starting system well enough to begin working on it.
The Quarter Scale Merlin design provides two methods for starting the engine. A shaft on the starboard side of the wheel case, intended for an electric drill-type starter, is connected to the crankshaft through a 10:1 reduction gear-set. A second shaft at the bottom of the wheel case provides a 5:1 reduction for use with an integral electric starter. Both starter shafts are eventually coupled to the crankshaft through a common one-way clutch. There are no details provided for the electric starter, and so it's design is left as an exercise for the builder. In the full-size Merlin the lower shaft was used for emergency hand-crank starts. It's hard to imagine starting the full-size engine this way, but in a life-or-death situation adrenalin can bring a lot to the party.
The main shaft as well as the countershaft will have their rear bearings located and retained in the bearing plate that was just completed. The starter countershaft, on the other hand, will have its rear bearing supported in a bulkhead bracket inside the wheel case. The notes accompanying the castings mentioned that it had been too difficult to include this bulkhead as part of the wheel case casting as was done in the full-size engine. So, in the Quarter Scale this rear support was designed to be an add-on. 
A drawing for a bearing support designed to be inserted through and held inside the electric starter bore at the bottom of the engine was included in the documentation. This is a complex shaped part with contours that are intended to follow the surrounding interior walls of the wheel case for additional rigidity. This support turned out to be another difficult part for me to visualize from the flat three-view drawing that was provided. Its visualization was made even more difficult because the drawing didn't contain some of the projected contours that I needed to create a SoldWorks model. A dimension for one of these contours also seemed questionable because it didn't appear to match the part shown in the drawing. I spent several days wrestling with this bracket and, still not sure I had interpreted the drawing correctly, I decided to machine my best guess. 
John lengthened his starter countershaft so a second rear bearing could be included in the bearing plate along with the rear bearings of the other two shafts. I briefly looked at also doing this, but I wasn't clever enough to figure out how to retain the bearing in the available space at the outside edge of the plate.
In order to be able to install and rigidly support the starter countershaft, its front and rear bearings must be located in the wheel case with very close sliding fits. This requires the support bracket to be permanently installed before line-boring the two bearing recesses. In my particular casting the starter countershaft drive gear had to be moved very close (actually into) the starboard interior wall of the wheel case in order to obtain the correct spacing between it and its driven gear on the countershaft. The wheel case's interior wall around this gear had to be machined for clearance before the support bracket could be permanently installed. With a test driven gear installed on a temporary Delrin shaft pressed into the countershaft bearing pocket, the mill dro's were used to position a test drive gear supported on a shaft held in the mill's spindle. A .010" radial clearance was then machined into the interior wall of the wheel case around the drive gear before the support bracket was Loctite'd in place.
Unfortunately, this bracket will complicate the installation of the starter countershaft. As shown in the assembly sketch photo, the drive gear in front of the support bracket is too large to pass through the opening for the bearing. This means the front bearing, the keyed starter gear and shaft, and a pinion depth spacer must all be fed in from the side and built up within the limited space in front this bracket.
After an overnight cure of the Loctite, the line-boring was completed. A bevel was also machined on the rear edge of the bracket bore for clearance to a pinion drive gear that will be installed on the end of the shaft. The final photo shows the completed machining for the starter countershaft. The casting offset which I had been concerned about can also be seen in the photo. I tested the running fits using test gears between the main shaft and countershaft as well as between the countershaft and starter countershaft several times during the machining to make sure the offset actually was a casting error and not my misunderstanding of the drawing. I don't yet have the bevel gears, and so I've only been able to verify the centerline alignments of the two starter shaft bores. - Terry


----------



## mayhugh1

While waiting for the bevel and helical gears to arrive, I continued on with the wheel case machining operations that didn't require knowing any of their spacings. I want to complete all the wheel case machining before starting to make and fit the shafts because most of the bearings inside the wheel case will be open, and I want to avoid getting chips into them. 
The first 'easy' operation was facing the two magneto mounting surfaces on either side of the wheel case. These pinwheel-shaped flats must be parallel to the vertical plane of the wheel case. I face-milled their odd shapes under a magnifying glass using the flat end of a small dovetail cutter. With a bit of care I was able to surface the contours right up to the edges of wheel case. The dovetail cutter provided better edge visibility than I would have had using a cylindrical cutter and helped prevent gouges in the surrounding areas. The notes mentioned that Rolls workers performed this particular operation on the full-size engines using manual routers guided by templates. Since the magnetos will eventually be driven from the main shaft through a pair of non-adjustable cross-helical gears, the bores for the shafts will have to wait until after the gears arrive so their center-to-center spacing can be measured.
The next operation was the machining of the supports for the coolant and oil pump shaft. The depth of this shaft's driven pinion gear will be adjustable, and so its machining could be completed without having the actual gear available. This shaft must end up vertical and centered on the axis of the main or crankshaft. Its top bearing will supported by a machined retainer that is threaded into a bulkhead support that was cast into the wheel case. Its 9/16-32 thread is fairly uncommon and required the purchase of an expensive tap that I'll likely never use again. The retainer was machined from stainless steel because the minimum wall thickness between its bearing recess and the outside threaded portion is only .010", and so care will also be required when installing it. The shaft's bottom bearing is retained in a recess located inside a machined adapter for the coolant pump. This retainer is bolted to a machined flat on the bottom of the wheel case. The coolant pump, for which castings were supplied, will eventually be secured to this adapter with a screw pinch clamp. 
The rough cast bores for both of the pump shaft retainers were offset by about the same amount that I measured for the countershafts. In my particular warped casting it turned out to be very important to use the supercharger mounting flange to locate the center of the wheel case casting. If the center had been located using any of the other wheel case features including the rough cast main shaft opening it's likely the supercharger mounting screws would have broken out the sides of their bosses.
The oil pumps, which will be located inside the oil pan, will also be driven from this shaft through an idler spur gear. The drive and idler gears are identical and happen to be similar to a gear that I machined several years ago for another project. I had enough left-over 12L14 gear blank material still in my scrap box to slice off two more gears, and after measuring their center spacing I machined the three-piece support bracket for the idler gear. The idler gear bracket will be test fitted on the front of the wheel case's mounting flange after all the wheel case machining is completed, and the fixture plate is removed. This bracket has gone through a complete redesign since Gunnar's engine, but I think John's engine has the same version as mine. In a photo he sent me, though, I noticed he turned his bracket around before mounting it on the wheel case. With as far as I've gotten I can't yet tell if there will be an interference problem with it mounted the way I'm (mis?)interpreting its drawing.
While at Cabin Fever last month I purchased a couple keyway broaches from one of the used tool vendors. Since I'd never seen a keyway broach that didn't require a bushing I had to have the seller explain to me what they were and how they were used. It seemed like these cylindrical bushing-less broaches might solve the non-uniform slot depth problem I encountered earlier when I made the splined prop bushing for this engine. The two tiny broaches (1/16" key slots in 3/16" and 1/4" diameter holes) that I bought seemed pretty pricey at $25 each, but they looked to be in like-new condition. I used the 3/16" broach for the first time to cut the key slot in the pump drive gear, and it seemed to work very well. As it turned out I didn't have a broach in my import set that would fit into a 3/16" diameter hole, and so it was fortunate that I came across this one at the show.
The drawings contain a design for a fuel pump mount on the port side of the wheel case, but there are no details included on the pump itself. I plan to use the same electric fuel pump and recirculation loop that I designed and used on my two radials. My pump will be located external to the engine, and so I didn't include this mount as part of my wheel case.
Finally, as suggested in the wheel case drawing, clearances were machined in the casting around the eventual locations of the large main gear and the pump's driven bevel gear. Since I can't yet verify the resulting clearances, additional material may need to be removed later.
The next step will be to machine the supercharger castings and fit them to the wheel case. Drilling the mounting holes for the supercharger should complete the machining on the wheel case. 
I just realized that it's been exactly one year since I began this build. It seems like only yesterday when I was wondering if this project was going to be too much for me. No, wait, ... that really was yesterday. - Terry


----------



## mayhugh1

I've been looking forward to working on the supercharger section since the beginning of this project because of my fond memories of the Paxton superchargers that were Shelby-installed on a few very special first generation Mustangs. When I was younger I owned a '65 fastback with a hi-perf. 289, and I lusted after the bolt-on kit that became available. However, life seemed to always come up with more practical places to spend that kind of money.
The castings associated with the Quarter Scale's similar centrifugal unit include a four-piece housing and an impeller. The impeller will be geared up 10x from the crankshaft for a maximum 36,000 rpm. Whether its design and my machining abilities can produce any useable boost remains to be seen, but it will nevertheless an eye-catching part of the engine. 
My plan at this stage in the build is to machine the supercharger castings and complete the rear wheel case machining so the two can be attached. The supercharger internals will be added later. 
A recess must be machined into the front half of the housing to accept the mating flange previously machined onto the rear of the wheel case. The two will be secured together with a handful of SHCS's. If everything fits the way it should, a drive gear on the wheel case countershaft will perfectly mesh with a driven gear on the supercharger's impeller.
To begin the machining I prepared the front half of the housing so the recess could be turned on the lathe. A surface plate check of the casting showed no significant warpage, and so its clean-up started with a visit to the mill. The half-housing was shimmed with its rear-side down against the mill table so its frontside (the side that will eventually bolt against the wheel case) could be faced. The casting was then flipped over, and a pair of custom sawed wood clamps secured its irregular perimeter to the table while the rear was machined flat. When this operation was completed the casting was moved to the lathe's faceplate.
With the wheel case side of the housing facing toward the tailstock, a tight-fitting plug located the center hole of the casting to the bored center of the faceplate. My hope was that a dial indicator would show that the area to be turned was reasonably concentric with the center hole of the casting. Fortunately it was, and this saved some tedious set-up and more custom clamps. The housing was then secured to the faceplate with a circular array of screws. The locations of the holes for these screws were selected so they could later be used to secure the internal diffuser ring.
The mounting face was skimmed, and the mating recess to the wheel case was turned. The goal was to exactly match the i.d. of this recess to the o.d. of the shoulder on the wheel case. As I approached the final i.d., I trial-fitted the two parts together after each .001" (diameter) pass. After going .004" beyond where I thought the parts should have fit together (the i.d. of the shallow recess was difficult to consistently measure), I discovered the wheel case flange was not perfectly circular. 
By design, this flange is not continuous around the entire rear end of the wheel case but is interrupted just behind the starter countershaft. One of the ends of this flange had moved slightly - probably due to internal stresses relieved by all the machining done earlier in this area of the casting. A small segment of this flange created enough interference to prevent the two parts from fitting together properly. After filing away a bit of material I then had a sloppy fitting housing with about .003" excess clearance. I finished the lathe work by boring the center of the housing for the impeller bearing retainer. After removing the housing from the faceplate I used a sharp pointed scribe to manually upset the metal around the o.d. of the wheel case flange with an array of 20 prick marks. This appeared to remove the slop; and measurements showed that, with the housing resting on the rear of the wheel case, the impeller bore was concentric with the installed wheel case bearing plate to within .002".
The next step was to drill and tap the holes for the 21 fasteners used to secure the front half of the supercharger housing to the rear of the wheel case. There's barely enough room for 1-72 SHCS's, and even then two locations required using a stud because of limited access. The real challenge was to align the drilling of the 21 pairs of holes in the two parts since they could be neither match nor transfer drilled. 
Matching x-y coordinates between the two parts as I did with the bearing plate seemed risky because I didn't have an independent reference to orientate the supercharger housing. The notes provide a design for a single-hole drill jig that uses the outside contour of each boss to locate its center hole on each part. The problems with this approach were the o.d.'s of my castings do not perfectly match each other nor are they truly circular. My solution was to reference the holes to the machined flange or recess on each part with a tiny washer that matched the radii of the bosses. I placed this washer against the machined flange (or recess) to set the distance between the center of the hole and the center of the casting. I made sure it was also concentric with the boss in order to set its radial angle. A spindle microscope was used to position the spindle over the center of the washer for each spotting and drilling operation.
The accuracy of this scheme, as well as the one recommended on the drawing, depends upon the centers of the screw bosses of both parts lying on identical radial lines. This appeared to be a reasonable assumption, but there was a bit of uncertainty near the top of my wheel case where its rough cast o.d. did not exactly match that of the supercharger housing. Using this washer method I drilled and tapped the 21 holes in the front half of the supercharger housing, and I clearance-drilled their mating holes in the wheel case. The screws are threaded-in toward the rear of the engine just to make things a little more difficult.
During trial assembly, I found the radial locations of the bosses on the two parts evidently did not match up as well as I thought over some 60 degrees at the top of the wheel case. The distortion in this casting, that I've been continually dealing with, required the elongation of several of the mounting holes in this area. I was eventually able to get all screws to freely thread-in without any break-outs, but the result wasn't at all pretty. It won't be visible when the two parts are assembled, and the casting mismatch can only be seen from underneath the engine, but it's a crappy result of poor planning. In retrospect, I probably could have done much better by matching x-y coordinates between the two parts. 
With the front-half of the supercharger bolted to the wheel case I checked the flatness of the supercharger's previously machined rear surface, and it was within a few tenths. I then brought it to its finished height while it was still mounted to the wheel case. I also re-checked the concentricity of the center bore of the housing with that of the installed wheel case bearing plate and found them to now be within a thousandth. 
The bevel and helical gears have arrived, but before returning to the wheel case I'm going to continue machining the supercharger castings. The wheel case, mounted to its fixture plate, has proved to be a convenient machining fixture for them, and so it feels best to continue on - Terry


----------



## kvom

I learn something from every one of your posts.  The modeling clay is one such lesson.


----------



## mayhugh1

The machining of the supercharger castings continued on with the rear-half of the housing. This casting was badly warped and had to be annealed and straightened before any machining could be started. After correcting it using the same heat-and-bend technique described much earlier in this build, its front and rear surfaces were cleaned up and made parallel. The part was allowed to rest for a couple days before finally finishing its faces.
With the front half still bolted to the wheel case on its fixture plate, a tight-fitting center plug was turned to help locate the front and rear halves of the housing to each other. The holes for the 37 screws used to secure the two halves together were then match-drilled and tapped. This turned into several hours of mind-numbing work, but this time all the holes ended up exactly in their correct locations. With such a large number of closely-spaced fasteners, there may not be need for a gasket or sealer between the housing halves. A light test showed no sign of leakage between the flanges.
The casting for the rear cover required only a simple facing operation so it could be attached to the rear half of the housing. A little planning helped distribute the material removal between it and the rear half-housing so its bottom flange matched the top flange on the carburetor casting that was supplied.
According to the notes, the carburetor casting was inspired by the Stromberg PD-18 two barrel updraft unit used on the late model Merlins. A design for a functional, but maybe untested, carburetor using this casting was promised in the early documentation. It appears that the project was abandoned before anything actually materialized because no drawings were supplied. The notes mentioned that the designers had also considered using a Honda GX-120 carb on this engine, but at the end of the day the carburetion was left as an exercise for the builder. 
I faced both ends of the carb casting and drilled and tapped the top flange, but I haven't yet decided how or even if it will be used. I did some online research on the GX-120, and it certainly does look interesting for use on a model aero engine. It has a float, a .456" venturi, and a form factor that would look very much at home on the rear of a Hodgson-type radial. New ones are available from Amazon for about $15.
The last casting in the supercharger group, besides than the impeller, is an elbow outlet. It's used to route a length of straight pipe that will carry the air/fuel mixture from the supercharger to the intake manifold log located between the heads. For my particular assembly I determined a flange angle of 19.4 degrees would be required to locate the pipe on the engine's centerline. After machining the supercharger flange to this angle and cleaning up the elbow flange, the mounting holes were drilled and tapped. A length of scrap plastic rod was turned to simulate the pipe and to keep its trajectory on the engine's centerline while the holes were transfer-drilled. The timing chain housing was temporarily installed on the wheel case to help with this centering. A few of the drilling operations were complicated by the fact that some of the holes weren't accessible with the elbow in place. One of the elbow bosses under the pipe, in fact, had to be cut down with a slitting saw in order to make room for a nut and stud. The actual pipe will be o-ringed at both ends so there will be a bit of wiggle room if, during final assembly, it's found that the flange angle should actually have been a more likely 20 degrees. 
With the elbow temporarily but firmly secured to its own fixture plate, its i.d. was skimmed with a boring bar to provide a smooth sealing surface for the o-ring. A similar operation was repeated on the inlet to the intake manifold log.
These last steps concluded the machining of the supercharger housing which, incidentally, has added another hundred 1-72 SHCS's to the engine. Since the cross-helical gear set for the magnetos has finally arrived, I should be able to determine the spacing required for its proper mesh so I can complete the wheel case machining. I'll then be able to start working on the numerous shafts, gears, and bearings inside the wheel case. - Terry


----------



## 10K Pete

Man, that thing has more screws..... !!! Lookin' good!!

Pete


----------



## petertha

Wow. It looks menacing just standing there! 

Re the initial warp & post-anneal/re-bend resting period, I had no idea the material was so dynamic like that. Collectively from your experience with the other parts, is it the thinner shell and/or asymmetric shapes that have the highest warp deviation? 

And for example on the 1/4" gap part, do you think the majority of distortion occurs on day-1 from the casting procedure itself (like say 90% on day-1 & 10% over next year then finally settles).


----------



## mayhugh1

Peter,
My only experience with castings has been with these, but yes I would say that asymmetric parts or long and skinny parts end up with the worst distortion to deal with. Any design feature in the part that promotes uneven cooling of the freshly poured casting is going to cause it to change shape as it unevenly cools and stresses develop within it. With thin wall parts the cooling is rapid and maybe poorly controlled, the part by its nature is flexible, and there isn't enough excess material to permit the distortion from being machine away. So they must be straightened. I think nearly all of the warp occurs when the part first solidifies. There's a 24 hour or so window for the foundry to straighten such castings before they precipitate-harden. But, I expect the developers had enough problems finding a foundry that would even work with their low volume PITA parts so that straightening wasn't an option for them. Anyway, I've learned the process sounds much more difficult than it really is, and I stopped being afraid of it several parts ago.
Because the part has to be annealed (re-heated) in order to be straightened after that 24 hour window, I was always cautious to do the straightening after the part was allowed to completely cool from the annealing heat. As an extra precaution, I usually waited at least a day to finish machine the part after its initial post-straightening rough-in. This was probably not really necessary as I never measured any changes in any of the parts I checked after that resting period. The only part I've seen move around was the wheel case, and since I never attempted to straighten that part, the change was probably caused by casting stresses relieved by its machining. - Terry


----------



## Ken I

Those "hundreds of bolts" typically seen on aero engines generally do not use gaskets - even on large gas turbines.
They do use sealant - typically "Hylomar" - that's the blue stuff that just never goes completely hard and if you read the bumpf on the box is made under licence to Rolls-Royce.
The "hundreds of bolts" design also allow you to get the metal to metal seal via relatively dainty thin walled castings which would otherwise need to be substantially beefed up with thicker sections and webbing between the bolts (think gearbox/engine bellhousing on a car engine) - too heavy.
You probably know all this but thought I would just put it out there.

Regards,
            Ken


----------



## DICKEYBIRD

Ken I said:


> They do use sealant - typically "Hylomar"


The Jag V-12's I used to work on at the local dealer used Hylomar in the tappet block/ cyl.head junction.  It stayed "gummy" & prevented leaks but the parts could be separated later if needed.  Good stuff!


----------



## ICEpeter

There seems to be an equivalent product made by Permatex called Permashield Gasket And Dressing Sealant, good for temperature up to 500 degree F and multiple easy disassembly / re-assembly without destroying the seal. Considerably less expensive compared to Hylomar. They make a reference to Hylomar on the package where they say "Compare to Hylomar Universal Blue"

I intend to give it a try.

Peter J.


----------



## mayhugh1

Good tip ... Thanks - Terry


----------



## DICKEYBIRD

ICEpeter said:


> There seems to be an equivalent product made by Permatex called Permashield Gasket And Dressing Sealant...


Yabbut, being a Merlin and one of Britain's finest it would be positively un-gentlemanly not to use Hylomar!


----------



## maybach_man

FYI Section d4 gives the specs


----------



## 10K Pete

I keep telling folks about Permatex Aviation Form-A-Gasket but no one
seems to listen.

Pete


----------



## Vixen

Use Permatex on a Packard Merlin and use Hylomar on a Rolls Royce Merlin.

Simples

Mike


----------



## Ca-g

A Loctite rep came to a club I was a member of to give a lecture about twenty years ago. His message to us cheapskates was; Permatex is Loctite, they renamed it so they could keep the top end of the market with Loctite but not miss out on the people who would or could not pay so much.


----------



## 10K Pete

When I think, and speak, of "Permatex" I'm referring to a company and a product as I knew them 40 years ago. What the name has morphed in to
since is anyones guess!!  No company, it seems, is what they say they are
anymore.

Pete


----------



## mayhugh1

Before finishing up the wheel case machining, the rear half of the supercharger housing was bored to bring it to its finished diameter and make it truly concentric with the centerline of the wheel case and the completed front half.
The final wheel case machining included the bores and counterbores for the bearing retainers that will support the magnetos' cross shaft. The 'magnetos' will actually be a pair of CDI-fed distributors operating in disguise. They'll be mechanically driven by a crossed helical gear set whose drive gear is on the main shaft inside the wheel case. This gear set was purchased, and since I had no prior experience with these types of gears I made up a fixture so I could play with them and determine the spacing for their proper mesh. I used my mill's DRO to measure the spacing, but the fixture itself wound up being a little more complicated than the ones used earlier to measure the spur gears. These gear teeth operate with a single point of contact instead of a line of contact that's common with spur gears, and so they're typically used only for light loads. They also generate force components along the axes of their shafts that continually tries to separate them. So, not only is the alignment of their crossed shafts important, but the gears must be constrained against this thrust.
The exact location of the main shaft on which the drive gear will be affixed is known within the wheel case and has been used to locate the positions of all the other shafts. This and the gear-set measurement were used to derive the bore coordinate needed to properly space the magneto driven gear from the main shaft drive gear. However, I could not find the second coordinate on the wheel case drawing needed to place the bore directly above the drive gear. So, I began studying the main shaft drawing to determine the distance between the drive gear and the timing chain sprocket on the main shaft since I know where the sprocket will be located within the wheel case. The drawing for the main shaft assembly shows that the stock helical and pump drive gears will have to be heavily modified in order to shoehorn them into the available space inside the wheel case. However, the dimensioned drawings provided for these modifications don't appear to match the modified gears shown in the main shaft assembly drawing. I was able to come up with the second coordinate, but some work is going to be needed later to sort out those gear modifications. 
After completing the machining required for the magnetos, I also drilled and tapped a hole for a future oil fitting that will be used to lubricate the gears and bearings inside the wheel case. The waste oil will drain into the sump where it will be pumped back into the main oil tank. 
Finally, with all the tedious machining completed on the wheel case and supercharger housing I can start working on the much more interesting but demanding internals of the wheel case. - Terry
.
.
p.s. I was recently informed that Dynomotive Design and Development, the supplier of the Quarter Scale castings, is actually a single-person company consisting solely of Richard Maheu. Through-out this build I've certainly appreciated the magnitude of the effort that must have been expended in creating the design, castings, and documentation for this project even when I assumed the work had been done by more than one ambitious individual. But after learning that it's all been the effort of a single individual, I'm truly impressed by the breadth and depth of knowledge that was needed to actually pull it off. His short bio is available here:
http://dynamotive.biz/dynamotive.htm


----------



## deboom_j

Terry,
  The pics of you testing your gear depthing/mesh have turned on a light for me.  I have a set of bevel gears in a gear box (they are the part of the head elevation mechanism for my surface grinder),  and they are not meshing correctly, they are "cogging" if you know what I mean.  I'm thinking I could build a setup like you have and move the pinion relative to the gear, measuring the changes with my DRO, to determine the correct distances/spacing to get smooth running.  I realize the bevel pinion, and bevel gear are essentially cones, and ideally the tips of the cones are supposed to be coincident, but how to measure this on existing gears I'm not totally sure.  I'm going to have to work on this...

Love the thread, I wish all threads were this detailed and thorough.

I knew about Richard Maheu being a one man show, I always wondered if you two were related?  I guess not since the spelling is different.

John


----------



## mayhugh1

Although it would probably be logical to begin the construction of the wheel case components with the main shaft, this part is going to be very involved as it contains a number of risky features. In addition to driving three other shafts inside the wheel case that require precisely located drive gears, the main shaft is internally and externally splined and includes an integrally machined drive sprocket for the timing chain. Whew!
In order to slightly improve my chances of not generating a lot of scrap, I decided to first work on the much simpler driven shafts. When these are finished and in place I'll at least know for sure the drive gear locations on the main shaft. Since I'm also starting out with uncertainties about the stock gear modifications required for the pump and magneto drive gears, I'm going to begin with those two driven shafts.
The cross shaft for the magnetos is supported by ball bearings held in two-piece bearing holders located on either side of the wheel case. The bearings are pressed into the outer halves of these holders, and three SHCS's are used to pull the halves together. When the screws are tightened, the outer half of the bearing holder is pulled into the counterbore previously machined into the pinwheel flange on either side of the wheel case so the flange is captured between it and the inner half.
The holders were fairly challenging to machine because of their small size, delicate features, and the machining precision required on a number of their surfaces. Since I anticipated a number of trial assemblies, I bored the bearing pockets for close slip fits to the bearings. Once all the parts were completely machined and test-fitted, I stippled the walls of the pockets with a scribe before finally pressing the bearings into place. Loctite could have been used instead, but I didn't want to take the chance of having to someday re-make a holder should a defective bearing need to be replaced. One of the reasons for the delicate nature of these parts as well as a preview of things to come due to the tight quarters within the wheel case, are the cutouts in the rear of the holders that are needed to clear the timing chain. Although it seems unreasonable, I spent two full days machining the holders.
After all that work I wanted zero shaft clearance between the bearings. In an attempt to measure the exact distance between the installed bearings, I put a couple temporary spacers over their inner races and then measured the distance between them with a telescoping gauge. This got me pretty close, but I still had to trim the shaft two more times before I got the fit I wanted.
The magnetos themselves will eventually be coupled to the cross shaft using Oldham couplings. This simple coupler was invented in the early 1800's to solve a paddle placement problem in a steamship design. Its main purpose is to join two parallel but non-collinear shafts. (Universal joints are used to join non-parallel shafts.) Oldham couplers can also provide other features such as electrical isolation. I used similar plastic couplers in the electrical fuel pumps for my two radials in order to separate the mechanical fuel pumps from their electric motors. The major advantage offered by them in this particular application is the modularity they can also provide. These couplers allowed the cross shaft subassembly to be completely finished and tested now as part of the wheel case assembly while the magnetos themselves will be finished and independently tested at a later date. I machined the couplers from Delrin although for more demanding applications they may be made from metal. I milled the slots in the couplers for snug fits to the shaft tenons so the couplers would not add backlash of their own. For those who might have their own use for one, I've included a Youtube link that shows a commercial Oldham coupler in service:
[ame]https://m.youtube.com/watch?v=utEKKox2WHA[/ame]
The stock helical driven gear needed only to be bored out and attached to a hub that was machined to fit the cross shaft. The gear is held in place on the centerline of the wheel case with a hub setscrew that seats into a shallow recess drilled in the cross shaft. I measured .002" runout on the teeth of the installed driven gear which was a little more than I had hoped for but entirely reasonable considering the numerous sources that contributed to it. I also installed a temporary shaft on the centerline of the wheel case in order to verify the mesh of the magneto gear set. The gears turned smoothly with just over a degree of backlash which was my goal, and so I hope I can check the magneto shaft off the list. - Terry


----------



## mayhugh1

Well, it turned out that the magneto shaft assembly was far from finished after all. I continued on with its gear testing by installing the wheel case bearing plate and making up a temporary bearing for the rear of the test shaft. When I re-checked the gear mesh with the rear of the test shaft supported in the bearing plate I found a dreaded tight spot.
I use the word 'dreaded' because of my brief experience with the test set I made up to familiarize myself with the gears earlier. A tight spot in a simple spur gear-set having a bit of runout is just that -- because the line of contact between the teeth tends to maintain the axes of the gears parallel to each other even with a bit of clearance provided between the shafts and their freely spinning gears.
Crossed helical gears, on the other hand, have a centered point of contact between their teeth while they are running with their proper spacing. I found that as I adjusted their center-to-center spacing in my test set, the gears quickly bound up with little warning as they were brought too close together. There seemed to be only a thousandth or so separating 'snug' and 'locked up'. I think the thrust driven contact point caused the large diameter drive gear to tilt slightly on its .0005" clearance'd shaft. This, in turn, caused the contact point to move further up the sides of the gear teeth which caused the drive gear to tilt even further until the pair locked up like a sprag clutch.
The test shaft I had been using to support the drive gear was pressed into a Delrin sleeve which, in turn, was pressed into the center bore of the wheel case and its fixture plate. Without any rear support, the shaft happened to be tilted slightly away from the cross shaft. This tilt added three to four thousandths clearance between the gears leading me to believe I had machined the bore for the cross shaft exactly where I had intended. With the bearing plate and no clearance, though, the .002" runout in the driven gear created the tight spot. 
Measurements showed the center bearing in the bearing plate was exactly on the centerline of the wheel case. And so, after reviewing the notes I made while experimenting with the gear test set, I had to conclude that the bore for the cross shaft was actually .005" too close to the centerline of the wheel case. 
A note on the wheel case drawing had warned that this bore needed to be placed correctly since it was critical, and no gear adjustment was possible afterward. I spent several hours preparing for that particular operation; and an error that size was unexpected, not to mention disappointing, considering all the care I had put into it. I still don't know what actually happened. In retrospect, I probably should have planned for an even greater than theoretical separation for all the gears. My concern at the time, though, was that with so many gears inside the wheel case I didn't want the sound of the running engine to be overwhelmed with the whine of a bunch of poorly fitted gears. 
I decided I'd better bolt the wheel case and bearing plate assembly up to the crankcase so I could check the gears with the front of the test shaft inserted into the rear bore of the crankshaft. After all, this would be the test that really matters. I made up a new sleeve so I could fit the front of the test shaft into the crankshaft, and then I rechecked the fit of the gears. The results were one of those good-news/bad-news things. The good news was that the crankshaft centerline was still exactly on the wheel case centerline, and the bad news was that the tight spot was still there. Reducing the runout, although difficult to do, would just barely mask the problem and leave the gears with an improper separation on the verge of binding.
I think miter gears, if a pair exists that will fit into the available space, would have been a better choice from a machining perspective. I was about to go off looking for a set when I decided to re-visit the stock design of the cross shaft assembly.
After studying the drawing for the bearing holders I felt it should be possible to move the cross shaft another .006" away from the wheel case centerline by redesigning the holders and not making any changes to the wheel case. These parts were already near the top of my 'glad they're finally done' list, but re-making them was more attractive than attempting to re-design the wheel case. I spent another couple days making a second pair of even more difficult-to-machine bearing holders, but the additional .006" provided the gear separation I originally wanted.
Since the bearings are pressed into pockets from inside the holders, the fix is barely noticeable from outside the wheel case. The magnetos will attach to the wheel case using the stock mounting holes which means the internal axes of the magnetos will now be offset by .006" from the axis of the cross shaft driving them. This would have been a show-stopper if it hadn't been for the Oldham couplers used to connect them.
One of the photos shows the new bearing holders along side the originals. If one looks closely at the bearing pocket in a new holder it can be seen to be slightly closer to the mounting screw hole at the top of the holder than it is to the bottom hole. I had to rotate the screw hole pattern from its stock location in order to create some of the space needed for the pocket shift. This new screw pattern can now be used as an alignment aid when installing the holders to insure the timing chain notches are properly oriented. It turned out that my original cross shaft now had a sloppy fit between the new bearings, and so I had to re-make it as well. After thoroughly testing the new assembly, it's finally safe to move on to the next 'simple' driven shaft. - Terry


----------



## RonC9876

Terry: I feel your pain. Glad you were able to overcome these glitches. Those kinds of problems can make you want to throw in the towel. Well maybe not you but me for sure. Finally got my Novi running. Can you believe that the only reason I couldn't get reliable starting was because I needed to spin it faster. It runs well now, but leaks oil in places I didn't think oil could come out of. The only solution is a complete tear down and I have decided to wait till after NAMES for that. Not enough time or desire to do all that. At least I have something new to show. Even if it smokes when oil gets all over the hot exhaust pipes. At least now they get hot! Keep up the excellent work. I have complete faith that you can solve anything that this project can throw your way. Ron Colonna


----------



## mayhugh1

Ron,
It's nice to hear from you again. I'd love to see your latest creation, but I don't think we'll be able to make it to NAMES this year. Down here in Texas we seem to be well out of the mainstream when it comes to the shows. And, I like planning long trips about as much as I like doing our taxes. I would liked to have seen the expression on your face when your Novi suddenly fired up after all this time. I'll bet it was priceless. - Terry


----------



## mayhugh1

The pump shaft, located on the vertical centerline of the wheel case, is driven by a large bevel gear on the main shaft. After a 2:1 reduction, the pump shaft drives the coolant pump located at the bottom of the wheel case as well as the oil pumps located inside the lower crankcase. This shaft is supported by open ball bearings inside a pair of retainers that were machined earlier. The top bearing is in a retainer that is threaded into an internal wheel case bulkhead while the bottom bearing is contained inside the housing that will later support the coolant pump. A keyed spur gear and idler bracket, also machined earlier, will drive the oil pumps. Due to space restrictions during assembly, the top retainer can only be threaded into the wheel case after the shaft has been inserted through the bulkhead, and so a special tool was constructed to install it.
The 30-tooth bevel drive gear was purchased, but it had to be heavily modified in order to fit within the space available in front of the magneto drive gear on the main shaft. It was essentially reduced to a thin ring gear that had to be attached to the magneto drive gear. Even after the extensive surgery on the bevel gear, the magneto drive gear was left with only enough space on the main shaft for a 75% engagement with its driven gear. Fortunately the magnetos will present a negligible load to the gear set, and so the partial engagement is of little concern. The threaded bearing retainer also contains a machined spacer that sets the depth of the shaft's driven gear into the ring gear. Thrust created by the gear set will tend to push the shaft downward, but it's effectively constrained by the bearing in the upper retainer.
The latest drawing that I have for the main shaft assembly lacks dimensions, and the dimensioned drawings for the gear modifications appear to pertain to an earlier version of the main shaft. I followed the assembly drawing to avoid any nasty surprises later since I'm still slogging my way through the wheel case design. It was difficult to obtain accurate and consistent measurements down inside the wheel case, and so the dimensions for the gear modifications were derived using trial-and-error machined spacers to trial fit the pump shaft's gear set. This took some time, but the iterative process helped prevent ruining some expensive and long lead-time gears.
Most of the time and effort spent on the pump shaft involved the fixtures and setups for the various gear modifications. Each set-up was indicated-in for a maximum runout of .001" before any machining was performed. In most cases, the lathe operations involved turning a mandrel onto which the gear was pressed using the lathe tailstock. In those operations where a mandrel wasn't appropriate, the part was either shimmed or turned in a 'set true' chuck. 
Even the small driven bevel gear on the pump shaft had be shortened. The pump shaft assembly drawing called for a pressed-in bushing to reduce its stock bore for the 3/16" shaft. Since this would have created the need for two different press operations during the shaft assembly, I turned the bushing as an integral part of the shaft. The oil and coolant pumps will present significant loads to the shaft gear, and so I used a .00075" shrink fit to assemble it to the shaft.
The shaft was also machined for a 1/16" wide key to accommodate the keyed spur gear that will drive the oil pumps. A flat was milled on the opposite side of the shaft for a gear setscrew that backs up the key. The notch in the idler bracket mounted on the lower front flange of the wheel case is for clearance to the pressurized oil line that will eventually feed the rearmost crankshaft bearing cap.
The magneto/pump drive-gear pair will eventually be attached to a shoulder on the main shaft. Since the main shaft hasn't yet been machined, I turned a temporary shouldered spacer from white Delrin to support the drive gears at a proper distance from their driven gears. All six gears turned freely together with just a bit of backlash, and this time I double-checked them all with the rear bearing plate installed. There are still eight gears, seven shafts, and a handful of bearings to be added to the wheel case. - Terry


----------



## mayhugh1

I was looking forward to working on the coolant pump, but after studying its drawing I decided to make a change to the shaft seal. Since I didn't want to start machining the castings until I actually have the seal in my hands, the pump will have to wait until after the seal arrives.
For now, I turned my attention to the starter countershaft. This simple shaft is driven by a cluster gear which, in turn, is driven by either the manual or electrical starter. A spur gear on its lower end will eventually drive the crankshaft through a geared one-way bearing located on yet another countershaft. The starter countershaft will be supported by a pair of ball bearings. The top bearing will be radially constrained in the bulkhead that was earlier machined, installed, and line bored with a lower bearing recess inside the wheel case. This countershaft will have to be assembled in place in a difficult area inside the wheel case. Assembly will include its bearings, a pinion depth spacer, spur gear and key, and a backup setscrew. In the most recent drawing that I have, a 1/16" diameter radial pin is used to secure the bevel gear to its 3/16" diameter shaft.
This tiny pin caught my attention, and so I decided to do some rough calculations to see if it would really hold up while supporting the engine's starting torque. During my 18-cylinder radial build, I found that a torque of some 14 ft-lbs was required to turn over the completed engine. The radial has six more cylinders than the Merlin that contribute additional resistance, but the torque requirement will also increase when the crank is spun up fast enough to start the engine since the cylinder pressures have less time to leak down. I conservatively estimated that the starter countershaft's pinned bevel gear will have to handle some two ft-lbs of torque after accounting for the gear reduction between it and the crankshaft. Upon converting this torque to a pair of shear forces acting across each end of the pin, I came up with a 40 kpsi tensile strength requirement for the pin. Very little margin would be available from common alloys, and so I decided to shrink fit the parts together and use a short length of spring or 'piano' wire for the pin as a back-up. Eventually, I also increased the diameters of the shaft to 1/4" and the pin to .078". The steels used in the tough control rod stock commonly found in RC hobby shops can often provide well over 100kpsi.
I wasn't willing to accept the dimensions in the drawing for the starter countershaft until its mesh with the gears on the manual and electrical starter shafts could be verified in my actual wheel case. And, I couldn't do this without having the cluster gear that is common to these three shafts. No design details were provided for it other than suggested part numbers for two commercial bevel gears that could be assembled to create it. I derived its dimensions using trial-and-error machined spacers and shafts just as I did for the pump shaft. This gear, which will be located on the shaft for the electrical starter, simultaneously meshes with gears on both the manual starter shaft and the starter countershaft. The gears used to make the cluster were individually trial-mated with their drive/driven gears so the required relative distance between their front faces could be determined. Once this distance was known, the larger gear was machined so the smaller gear could be shrink-fitted into it. The larger gear was bored for a .00075" interference shrink-fit with the smaller gear. In order to simplify the pressing operation, the larger gear was also shortened so that after the gears were joined their rear faces would be flush. A radial pin will eventually secure the cluster gear to the electrical starter shaft, and it will back-up the shrink-fit as well. The temporary Delrin shafts for the manual, electrical, and starter counter shafts were then reused to recheck the gears' mesh. 
My method for fitting the gears down inside the wheel case was a bit subjective. I typically blocked one gear of each pair and then tried to rock its mated gear back and forth to check for backlash. No movement indicated the gears were likely too close, while a degree or so of backlash seemed to provide the clearance needed for quiet and silky smooth operation. Setting the bevel gears up for full tooth engagement was made difficult by the limited visibility of the tiny blued gears down inside the wheel case. I used a magnifying glass, flashlight, and, in one case, a borescope to set the engagement.
After the gear fits were verified, the actual components for the electrical starter shaft assembly were designed and machined. No details were provided for either the electrical or manual starter assemblies as these were expected to be customized by the builder. I designed the electrical starter shaft housing to support a 1/4" diameter shaft with a pair of ball bearings. A spacer within the housing sets the position and controls the thrust of the cluster gear in both axial directions. The bottom end of the shaft was machined for an Oldham coupler for flexibility later when the motorized section is developed. For ease of assembly/disassembly the cluster gear was bored for a close slip fit on its shaft and secured with a .075" diameter pin. The pin is a close slip fit in its bore and is held in place with low-strength (purple) Loctite.
With the electrical starter shaft assembly installed and the cluster gear in final position, the components for the manual starter could be designed and machined. Its twin bearing housing is internally similar to that of the electrical starter, but the driven end of its shaft is a 5/16" hex that can be spun with a suitably adapted socket in an electric drill. There's only a minimal flange on the wheel case to support the manual starter, and so the closely fitted nose of its housing was profiled so it could be extended as far as possible into the wheel case. I machined its 1/4" diameter shaft from an appropriated portion of a handle from a hex wrench. The wrench wasn't hardened, but it machined like a tough alloy that should hold up well in this particular application. The bevel gear on this shaft was also secured with a .075" diameter pin, and its depth and axial thrust were limited in both directions with a pair of machined spacers.
Finally, with the starter shaft assemblies completed and installed, the components for the starter countershaft could be safely machined. The required length of the shaft was determined once again using temporary spacers to trial fit its bevel gear to the cluster gear. The spur gear on the front end of the shaft was machined from the blank used earlier to determine the location of the starter countershaft within the wheel case based on its mesh with its driven gear on a second countershaft. The blank required only minor machining to finish it including a 1/16" broached key slot. At the last minute I decided to integrate the mesh-setting spacer into the spur gear since I had determined the bevel gear's exact spacing requirement. In general, this isn't good design practice, but in this particular case I felt it would help simplify a difficult assembly. Assembling the starter countershaft in place wasn't as difficult as I had feared, and when completed, all the gears in the starter cluster were silky smooth when test driven with a drill.
I performed two .00075" interference shrink fits on two quarter inch bores, and I learned a few things along the way. Of course this is an excessive amount of interference on such a small bore, and a low TIR fit would have been difficult to achieve with a cold press. In the past, I've tried heating the female part in an oven for a shrink fit. But, by the time I got it over on to the press and set up, the part had typically cooled so much that the heat was of little benefit. This time, I set the female part up on a stainless steel plate on the press, and then I heated it in place with a propane torch to 400F. With little additional set-up I was able to press the parts together within seconds. I also turned a simple close-fitting flat bottom sleeve to go around the narrow shaft during pressing. This helped to keep the shaft vertically aligned with its bore during those first few critical seconds.
I didn't expect such a simple shaft to require so much additional work, but the starter shaft assemblies were fun to design and satisfying to complete. The shaft seal hasn't yet arrived, and so I'll likely next tackle the second countershaft. This one will be quite a bit more interesting as it will include a couple clutches and an integrally cut spur gear. - Terry


----------



## Blogwitch

I just can't believe how many anal sphincter twitches are involved in machining bits for this engine 

Do you have an attrition rate amongst the parts you are making or are they all made perfect every time ?

If they are all first timers, then my hat is off to you sir, but even if you do screw up occasionally, my hat is still off because of the great progress you have made so far. 
I for one would be pulling what hair I have left out.

John


----------



## Ken I

Looks like a good call on the drive pin.

Just a suggestion - in my other hobby - restoring old jukeboxes - I found they used a lot of taper pins.

They work really well as they cause the shaft to swell slightly giving the same sort of interference fit from a slip fit.

They never come loose or work loose. You can also pein the small end which guarantees it wont come out without grinding it off.

This prompted me to use them in some of my industrial machines and they have never failed me (other than in one instance where a toolmaker "grew a brain" decided I was a cranky old fashioned git and used dowel pins - once the taper pins were installed no problem).

Regards,
            Ken


----------



## dsage

Terry:

All I can say is OMG.
Your workmanship and attention to every detail is above and beyond.

I certainly hope you are keeping this log safe elsewhere and not just here on HMEM. One never knows how long it will be available here. Certainly no longer than some bean counter figures it's worth it. Your detailed logs and pictures are priceless and very much appreciated. I get a lot of good ideas and encouragement to make MY work better each time I read this.

Thanks

Sage


----------



## mayhugh1

John,
I make mistakes and re-make parts. Even triple-checking isn't a 100% guarantee at my age. My wife kids me all the time about all the prep I sometimes go through to make a single cut. Of course she's occasionally ripping the stitches out of her latest sewing creation while doing so.

Ken,
Thanks for the suggestion on the taper pins. I guess I don't make enough use of them.

Dave,
I do keep a copy of this log for myself. I'm hoping it's useful to others who purchased the castings but found the project too daunting to even begin. Richard Maheu put so much time and effort into such an historically important engine that it would be a shame for his beautiful castings to end up languishing in estate sales.
- Terry


----------



## Blogwitch

Terry,

It was so refreshing to read your reply, there is hope for us all then.

I always think that a notebook and pencil are two of the most critical pieces of tooling when coming to machining a part. Plan everything out first, then cut once, hoping all your calculations are correct. 99 times out of 100, they are.

John


----------



## Ken I

Terry,
           But wait there's more......

Another aspect of taper pins is when the angular alignment is critical and for whatever reason you are out by a whisker - you can force the wheel part in the "right" direction whilst reaming the taper - I've fixed up some horrible jukebox cam alignment issues by this brute force method.

Perhaps that's why they used them ?

WTH it works.

Regards,
            Ken


----------



## bazmak

I grew up on taper pins.Very expensive to buy and require skill to fit
Time consuming and if I remember cutting to length with recommended projection small end filed chamfer and big end rounded for ease of removal
The rolls Royce of accurate remove/refit precision fittings.I still have a few taper reamers.I remember the days when costs became more important
and roll pins became more fashionable and cheaper.I remember fitting a large camshaft with varios cams,fixtures and fitting all of which had to be able to be removed and replaced accurately.It was a days work but they always fitted
taper pins


----------



## Blogwitch

If I remember correctly, there were three versions of taper pins, Imperial was 1 in 48, Metric is 1 in 50 (and the type I use nowadays) and the third was one used in precision aircraft fitting, which was 1 in 20, and the type I fitted when I was in the industry. 
They did have one difference though, it came with a recessed cup washer and with a thread on the end. You reamed until the pin (not thread) was level at the small end, then fitted the cup washer and torque loaded the nut, then the thread, through the castellated nut was drilled through and it was then split pinned. The small taper pins were destroyed on removal, and a new pin had to be fitted each time, larger ones got a second chance as they had dedicated extraction systems.
These were used on torque tube control rods, holding on the bearing ends and anywhere on control systems that reqired a very rigid but removeable fitting, such as holding on helicopter rotor blades etc, bolts were not used as they could easily come undone and their hole tolerances weren't good enough.

Sorry to butt in, but a bit of general info that might be of use to someone sometime.

John


----------



## bazmak

I remember a taper pin with threaded end and a flat,on my pushbike pedals
we called it a cotter pin ?? Before my engineering days, I have seen split pins called cotter pins,which I believe is incorrect


----------



## Blogwitch

Baz,

I think it is just the same thing as split pin, depends where in the world you come from.

But I also use 'cotter' when referring to a straight flat headed pin that has a hole drilled through it at the opposite end to the head that takes a split pin to hold it in position.

Your bicycle cotter pin is in fact a straight pin with an angled flat on it that holds against a flat machined on the main crank pin. Same as here in the UK. 
When I was a kid, they were treated like gold dust as everyone seemed to have well worn ones on their bikes, which soon gave you a kerplonk type of motion as the cotter was so worn, it couldn't hold against the crank's flat face.

That is why we have to be careful, someone at the other side of the world just might misunderstand what is going on in a post, purely because of a different phraseology in the same language.


John


----------



## mayhugh1

What I would call the 'main' countershaft in this engine is really just referred to as the 'countershaft' in Merlin parlance. Inside the wheel case, it's located between the main shaft and the starter countershaft. When the engine is running, an integral gear on the countershaft is driven 5X the crankshaft speed by the main gear on the main shaft. A slip-clutch on the rear of the countershaft, behind the bearing plate, will eventually drive the supercharger another 2X the crankshaft. During starting, the starter countershaft drives the countershaft through an over-running clutch.
Since the countershaft will spin some 18k rpm at a maximum engine speed of 3600 rpm, its bearings deserve some consideration. The maximum speed of a ball bearing is limited by several factors including its roller and cage types, the lubricant being used, and its pitch diameter (Dm). Manufacturers empirically spec the maximum speed of their bearings using an NDm factor which is the product of a bearing's pitch diameter and its maximum rpm. The pitch is calculated by averaging the bearing's i.d. and o.d. in millimeters. The single-row, open-cage, oil-lubricated countershaft bearings that I'm using have a typical NDm of 300,000. The pitch diameter of the rear (largest) bearing is roughly 15, and so this corresponds to a maximum speed of 20K rpm. The supercharger itself may rev to 36k rpm, and for it I've ordered a pair of full ceramic bearings.
The recess for the front countershaft bearing in the front flange of the wheel case was bored earlier during the wheel case machining just after the locations of the various shafts were determined. This particular recess left very little supporting material behind the shoulder for its bearing which I wasn't comfortable with. I machined a backup insert and pressed it into the recess behind the shoulder from the front side of the wheel case. This plug will become sandwiched between the front face of wheel case flange and the rear face of the crankcase when the two are assembled. If there were ever to be a revision to the wheel case casting it would be a simple matter to add additional material here.
I started the countershaft fabrication with the machining of its over-running clutch. This clutch was made up from a commonly available one-way bearing and the gear blank I used earlier to establish the distance between the countershaft and the starter countershaft. I've used these bearings in the past to make drill starter adapters for two other engines, and it seems they've always been a bit of a hassle for me to deal with. The outer race of these bearings is a thin-walled shell and is designed to be pressed into an accurate bore in a supporting sleeve. These bearings use the shaft that they ride upon as their inner race, and so the shaft must also be accurately machined and polished. 
In both my previous applications I ended up pressing the bearings backwards into their sleeves due to confusion about their required directions for rotation. Actually, I even managed to mis-install one of them twice. Removing these bearings often damages them, and so I purchased a spare for this project - fully prepared to repeat the same mistake. Two errors must have somehow cancelled along the way, though, because I finally succeeded in installing one of them correctly on the first try, I think.
Pressing these bearings into their sleeves isn't at all satisfying, and I'm always left wondering if I created latent damage. The diameter of this bearing's thin outer shell is a whopping two thousandths over its recommended bore size which is a lot of interference for a 5/8" diameter bearing. One end of the bearing has a large beveled lead, and so there may be a preferred but undocumented direction for pressing. The bearing is rather fragile outside its sleeve. If the pressing operation isn't done correctly it can be easily damaged, and so an installation tool is recommended. I made mine with a full end-face contact area and a close fit to the bearing's i.d. If the bore is a bit too small or too large, the sprags may not rotate properly for maximum lock-up. A shrink-fit can be tricky because the bearing is pre-greased, and it contains some plastic cage parts. The cold pressing operation on this particular bearing required everything my two ton press could give, and in my shop that's normally a bright red flag when dealing with parts this small. However, the bearing seemed to function properly after all the dust had settled.
The ring gear for the clutch sleeve was bored for a .0005" interference fit on a machined shoulder on the aluminum bearing housing, and it was augmented with Loctite. Three shallow grooves were machined on the sleeve to collect and spread the Loctite during the pressing operation.
The shaft, itself, was turned from Stressproof 1144. In the past, I've used hardened drill rod for the shafts used with these bearings since the shaft will serve as the bearing's inner race. However, there's always a chance that even a simple shaft will distort during the quench cycle of its heat treatment. Since the countershaft also contains some complex features including an integrally machined spur gear as well as a key slot for its slip-clutch, I decided to use pre-hardened 1144. This material is probably also a good choice for the narrow teeth of the integral 12 tooth gear that will be heavily loaded by the momentum of the supercharger during engine speed changes.
The portion of the shaft that will be in contact the bearing rollers was finish-lapped on the lathe using 600 and 1000 grit paper backed up with a flat metal bar. This lapping was followed up with metal buffing compound. Since the bearing is free to slide on the shaft, a slip-on retainer was machined to limit its aft movement. The stock shaft design had no provision to limit the bearing's forward movement. So, I added a stepped spacer behind the inner race of the shaft's front bearing to prevent the clutch from contacting the outer race of this bearing. The countershaft's rear bearing is retained in the bearing plate, and this stepped spacer also removes the shaft's thrust clearance.
In order to verify the mesh of the countershaft's newly machined integral gear with the driving main gear on the temporary main shaft, I machined the main gear. Unfortunately, although I had a gear cutter for the proper DP and number of teeth, its 20 degree pressure angle didn't match the 14-1/2 degree pressure angle of the cutter used to machine the countershaft gear. Surprisingly, as far as I could tell even under a magnifying glass, the resulting gear pair appeared to mesh beautifully. I'd probably leave well enough alone if it weren't for the 18k rpm at which the 12 tooth countershaft gear is going spin as well as the huge loads that it will experience from the momentum of the supercharger during engine speed changes. So, I've ordered yet another expensive gear cutter. The next step is to machine the rather involved slip-clutch for the rear of the countershaft. Its purpose is to absorb some of the gear train stress that will be created by the supercharger. - Terry


----------



## mayhugh1

The Quarter Scale documentation, initially released in 2003, showed a 32DP 50 tooth gear on the rear of the countershaft for driving the supercharger. In 2007 a drawing for an optional slip clutch was added to the documentation, and in 2013 its design was revised. Gunnar's engine was built according to the original documentation, and a photo of his wheel case clearly shows a simple driving gear. John's documentation is later than Gunnar's, and he included a slip clutch; but it's one of his own design. The Quarter Scale notes explain the purpose of the clutch but also mention that it's optional, untested, and may not be required. I don't know when that particular note may have been added to the documentation, but it's possible that testing eventually showed the clutch was required after all, since a design revision showed up so very late in the project's development.
When the engine speed is changed, the 10x geared supercharger follows, but its angular momentum creates stress on the gear train. The magnitude of this stress is a result of the applied torque which is a product of the rate of change of the speed and the moment of inertia of the supercharger's impeller assembly. Without a clutch in a full-size Merlin, enthusiastic use of the throttle during combat could raise the drivetrain stress to destructively high levels.
One of the highly stressed components in the Quarter Scale version is the 12 tooth gear on the countershaft. In order to achieve the rpm multiplication for the supercharger, the number of teeth on this particular gear was reduced to as few as practicable. Rather than using a separate gear, it was integrally machined into the 1144 alloy countershaft for maximum strength, but its small diameter and few number of teeth still resulted in a tooth profile that was at the lower edge of good design practice.
A slip clutch can absorb the transient energy dumped into the gear train by either the throttle or the supercharger's angular momentum and dissipate it as heat rather than dangerous gear strain. Although adding a clutch to the gear train may seem like a no-brainer, it doesn't come without cost. The clutch needs to be inserted into the gear train behind the starter which means it will add its own angular momentum to the high-revving rear end of the system. Also, its high speed rotating parts are potential sources of imbalance.
The first photos show exploded and sectional views from my SolidWorks interpretation of the clutch design. The provided documentation was an assembly drawing that isn't really clear about some of the hub and spacer details. But, basically the clutch is a steel ring gear sandwiched between a brass backing plate and a flexible brass friction disk. A spacer partially fills a gap between the two and establishes the gripping force on the ring gear. The Quarter Scale drawing lacks the dimensions to determine this gap, and so it must be empirically determined during assembly. Its value, in any event, is dependent upon the particular brass alloy used as well as the surface finish of its various parts.
There are several potential sources of imbalance in the clutch including the TIR of every component, and so the challenge became to work out a machining strategy to minimize them. The narrow widths of the parts greatly complicated their work-holding, but each was indicated-in before every machining operation. Other than zero, I wasn't sure what the final TIR goal should be, but I figured I'd know it when I saw it.
The steel hub was the first component to be machined since I planned to use it as a mandrel to machine the brass frictional parts. The ring gear was the most tedious part to machine because I had not been concerned with its final size and shape when I initially machined its huge starting blank. The numerous holes in both the backing plate and friction disk have several functions. They reduce the momentum of the rotating parts, create spring in the friction plate, and they help air cool the frictional components. A copper alloy might have been a better choice for the frictional surfaces, but soft brass was the closest material I had on hand in the diameter needed. 
The spacer was the real PITA part. It had to be very flat and very thin. I wasn't sure exactly how thin, though, because I had no idea about how the breakaway torque might vary with its thickness. The pre-assembly gap that I could measure was evidently 4-5 thousandths different from its assembled value which I couldn't measure. It turned out that only 1-2 thousandths separated a usable spacer from an unusable one. I had considered machining the spacers from thin shim stock and then stacking parts to build up the spacer, but I couldn't figure out how to align their screw holes during assembly. Individual spacers were turned on the lathe and parted off from a pre-drilled Stressproof blank before being surface ground to their final thickness. It took several spacers to zero in on the correct thickness. 
I selected a breakaway torque of 1-2 ft-lbs for the clutch as this felt like a safe maximum for the gear train. I cobbled up an adapter for my torque wrench so I could measure the torque for each spacer that I tested. A bit of freshman physics allowed me to estimate the supercharger's maximum angular acceleration while protected by the final clutch. This calculation showed the clutch would limit the supercharger's acceleration from 20k rpm to 30k rpm to about 1 second which probably wouldn't be noticeable on a model.
After machining all the parts, I trial-assembled the clutch on the countershaft so I could measure the TIR. The full ceramic bearings that I ordered for the supercharger had arrived, and so I used them to support the countershaft in a vee-block for the measurement. The TIR was disappointing with an unacceptable .002" measured at the gear teeth. Most of it appeared to come from a .005" lateral wobble created by one or both of the brass parts. Even though they had been turned on the hub used as a mandrel, neither had come out uniform around its center hole. Evidently I had not fully cleaned out the sharp corner adjacent to the hub's flange, and the close-fitting parts distorted when the mounting screws drew them against the flange for machining. I was able to correct the backing plate, but I had to make a new friction disk. 
The second assembly looked better. Both the wobble and TIR were less than a thousandth. I was eventually able to find a relative angular position between the backing plate and the friction disk that reduced the errors to less than .0005". Witness marks were scratched into the two disks so they could be reassembled with the same relative orientation.
When all the measurements were completed, I performed a final calculation just to see if the clutch had really been worth the effort required to add it. The computed moment of inertia of the clutch was less than half of what I had estimated for the supercharger, and by definition its angular velocity will be one-half as well. Therefore the angular momentum of the clutch is less than a quarter of that of the supercharger which is a relatively small price to pay for the protection it provides. As will be seen later, the torsional load of the supercharger adds unbelievable complications to the design and machining of the main shaft.
I'm anxious to play more with the ceramic bearings, and so my next step may be to work on the supercharger's bearing assembly. - Terry


----------



## mayhugh1

This post will be uncharacteristically short (for me). Due to the forum's current software issues I can only view it using my iPad, and its interaction with Safari will allow me to upload only a single photo per post. I've tried the HMEM app but lost patience trying to use it. I'm confident, though, the administrators will eventually resolve the problem while we remain patient.
The 14-1/2 degree gear cutter that I needed to machine the new main gear arrived much earlier than expected. This cutter is for the main shaft gear that will drive the integral 12 tooth gear on the countershaft for the supercharger's first 5x rpm multiplication. The 20 degree pressure angle of the main gear that I cut earlier didn't match the pressure angle of its driven integral gear on the countershaft, and so it was used only to verify the center distance between the two shafts. 
Since I ended up cutting two 32DP 62 tooth gears using cutters with two different pressure angles, I thought it was worth a photo to compare the tooth profiles of the two actual gears. Compared with the 14-1/2 degree gear, the teeth on the 20 degree gear have a bit more meat down near their root. One of the reasons that 20 degree pressure angles have become popular is that even though they're typically noisier, they can transmit more power. 
So, it may seem illogical to have used 20 degree gears throughout the engine and then switch to a 14-1/2 degree pressure angle for the strength-critical 12 tooth gear on the countershaft as well as the main shaft gear driving it. The issue I ran into, though, was that 20 degree 32DP gear cutters seem to be available only in 2-1/4" diameter compared with 1-3/4" for the 14-1/2 degree cutters. The collateral damage created to the inner bearing for the over-running clutch on the countershaft by this larger diameter cutter would have greatly shortened its life if it even functioned at all. The extra tooth strength didn't seem worth the risk especially after I added the protection of the slip clutch. A better solution might have been to make my own small diameter cutter as I did to solve similar problems on my two radial builds. However, the rpm involved in this particular application concerned me since excessive wear created by an imperfect profile might wash damaging debris into the numerous open bearings inside the wheel case.
Although there will be another handful of gears inside the magnetos, the supercharger's driven gear was the last gear machined for use inside the wheel case. Even though it will become part of the bearing cartridge in the supercharger, I was able to verify that it meshed correctly with the slip-clutch by installing a temporary Delrin bushing in the bearing plate. The pair worked smoothly together with the same one degree or so of backlash that I've been using for the rest of the gears.
The next step will be to start wotking on the bearing cartridge for the supercharger. - Terry


----------



## Parksy

Your work always leaves me gobsmacked Terry. Very impressive. I always wonder what occupation a person is or has done and whether such beautiful pieces of work is due to a lifetime of honed skills in the field or whether it is just a hobby.


----------



## xpylonracer

Some great engineering work Terry, also your written description matches the quality of your machining skills, thanks for posting.

Emgee


----------



## dalem9

All I can say is ! WOW !!!!  You are amazing .Wish I had a little of your talent  .Thanks for sharing !


----------



## mayhugh1

Thanks all for the very nice complements. 
Parksy, I was an electronics engineer during my working days, and instead of taking a busman's holiday, I took up machining as a hobby to keep busy after I retired. I spent most of my professional career solving problems using results interpreted through the eyes of various instruments. I think what I enjoy most about machining is that I now get to use my own eyes. - Terry


----------



## mayhugh1

For a number of reasons I decided to design my own bearing cartridge for the supercharger. I wasn't able to locate a supplier for the specified S3K (R6) bearings that were rated for 36k rpm, and I also had questions about a vague note on the supercharger drawing that specified the front seal as a 'piston ring type seal'. I wasn't sure if the note was referring to the use of a cast iron piston ring or a rubber o-ring, but neither sounded like a high speed shaft seal to me. The stock design also didn't include any provision for supplying oil to the bearings nor was the rear of the cartridge sealed, but a comment in the notes warned that bearing lubrication would likely be necessary.
I designed my cartridge around a pair of full ceramic bearings. 'Full ceramic' means that both the races and balls are ceramic compared with 'hybrids' which have ceramic balls and metal races. Because metal races are subject to micro-welding and corrosion, hybrids require lubrication. Full ceramic bearings do not, and they can be used in sealed environments where the presence of oil is an issue such as inside earlier generation hi-rel computer hard drives. Ceramic bearings are not recommended for impact loads even though they've become popular with performance bike and skateboard enthusiasts. They are capable of handling high rpm and temperatures approaching 180C, and so the Quarter Scale's supercharger seemed like an ideal application for them. A downside is their price. The R6 ZR02 bearings that I purchased from VXB.com were close to $90 for the pair, but when compared with the price of the castings their cost was in the noise.
I designed my cartridge to be run with or without oil, and I sealed the shaft running through it with non-contact labyrinth-like seals. Instead of intertwined fingers, the seals in my design are actually parallel steps separated by .003", and so I admit referring to them as 'labyrinths' may be a stretch. The cartridge was designed to prevent the bearings from being flooded with engine oil which is pretty much opposite to its function in a similar full-size application. 
Even though the engine and its bearings have been scaled down, the oil viscosity has not. Automotive viscosities generally aren't an issue in model engines and are even beneficial for oil control. This may not be the case for the scaled-down bearings in the high revving supercharger, especially since the oil will likely never warm up enough in typical use to thin out. The bearing heat created by the thick lubricant could create more problems than the lubricant solves. 
There's no metal-to-metal contact between any moving parts associated with the cartridge that must be protected with oil except for the slower-running driven gear, and it will receive splash lubrication from the wheel case oil. Since oil isn't required to prevent micro-welding or corrosion in the ceramic bearings, the only uncertainty is whether a light weight oil may be needed to control the bearing temperature. Considering the Quarter Scale's light duty requirements, I don't expect bearing cooling to be required. To be safe, though, I plumbed the cartridge with an oil line that is accessible from outside the supercharger housing. RF techs might recognize the repurposed microwave connector and length of hollowed out rigid coax used to fabricate the oil line. A few drops of lightweight synthetic oil can be occasionally added to the bearings through this line if testing shows it's required. 
Construction began with the machining of the housing and included boring it for a close slip fit to the bearings. I went back and forth trying to decide whether it would be best to use aluminum or steel for the housing. Aluminum would have some advantage in removing heat from the bearings, but steel would be a better choice for dampening high frequency vibrations created in the thin-wall supercharger housing by imbalances in the rotating assembly. In the end, I opted for a hefty chunk of 12L14. The end cap, combined with the supercharger's driven gear is part of the rear labyrinth and was machined from aluminum. 
I lapped a pair of aluminum spacers for near zero interference fits between the inner and outer bearing races. I may increase this interference to one or two thousandths later, when the impeller is added, if I measure any radial 'loosening-up'. I initially machined Delrin spacers with slight compression fits but scrapped them after researching Delrin's extremely high temperature coefficient of expansion.
The ceramic bearing races seem significantly looser than what I'm accustomed to with typical metal bearings, but measurement showed that most of this is an illusion created by their lack of lubricant. I inserted a temporary shaft through the assembled cartridge, and with the shaft resting between a pair of v-blocks I was able to measure only a tenth or so of run-out on the housing as it was rotated on the shaft. The friction was low enough that the assembly always settled with the gear cutout in the aluminum end-cap facing up. I estimated the cutout material to be less than a half percent of the total rotating mass; and so without oil, the friction may be low enough that I'll be able to do a reasonable job statically balancing the impeller assembly.
The shaft was also machined from 12L14. My original plan was to separate the labyrinth surfaces by only .001". I wasn't able to adequately control the thrust clearance of the shaft, though, and so I relaxed the spacing to .003". The shoulder washer for the driven gear was ground to maintain a .001" clearance between the rear face of the gear and the inner race of the rear bearing with the end bolt in place. The gear is keyed to the shaft to prevent it from spinning. This was done to avoid adding stress to the inner races when the bolt was tightened. The final thrust clearance of the shaft, and therefore eventually the impeller, came out to be just over a thousandth.
The supercharger documentation called out the rear of the shaft to be splined to the impeller similarly to what was done on the full-scale Merlin. A drawing was supplied for a 30 spline shop-made broach to spline the impeller. I could envision a lot of things going wrong with a little side project like that, including ruining an irreplaceable impeller casting. Instead, I milled a pair of slots on the rear end of the shaft for 1/16" square keys. A third slot was milled for a similar key on the opposite end of the shaft for the driven gear. 
Although I probably should get back to the wheel case and start working on the dreaded main shaft, I may next machine the impeller so I can finish up the supercharger. - Terry


----------



## Ripcrow

Piston ring seals are used in turbos on the turbine side at up to 150,000 revs if your seal design doesn't come up to your requirements.


----------



## mayhugh1

I continued on with the supercharger since it's so close to being finished, and I began by cleaning up the impeller casting. The impeller was cast with a fairly long top-end spigot that I chucked up in the lathe in order to face its bottom surface. I indicated off its rough bottom and searched for an orientation that minimized the wobble created by the spigot. The best I could do was .010", and since I was planning to leave the metal between the fins as-cast, the impeller's edge thickness would end up with this same variation. Although it wouldn't be visible after assembly, it would create balance issues would have to be dealt with. In hindsight, it was a rookie's mistake to not have first cleaned up the spigot, but I had become so complacent with the accuracy of the circular features in these castings that I got sloppy.
I removed just enough material from the impeller's bottom surface and o.d. to true them up. I then bored its center for the shaft, but after cutting off the excess spigot I saw that its interior was full of soft porous metal. Although most of it was discarded with the spigot, some of the bad metal continued on down about a quarter inch into the impeller.
I installed the bearing cartridge on the front half of the supercharger housing and slid the partially finished impeller on its shaft. As mentioned earlier, the races in these ceramic bearings are quite a bit looser than those in typical metal bearings, and not all of it's due to a lack of lubricant. With the zero pre-load spacer I was using between the inner races there was enough slop in the bearings so the outer edge of the three inch diameter impeller could be nudged over enough to kiss the floor of the housing just .007" below its bottom surface. A .002" longer spacer added a bit of bearing preload and appeared to solve the problem. 
At this point I took a couple days off to have five stints implanted into two major vessels in my heart. Last week my cardiologist saw an EKG anomaly during my annual stress test, and he ordered a heart catherization to look into it. Six hours after walking into the hospital for the test, I had been re-plumbed. Twenty-four hours after that I was back in my shop as though nothing had happened. It was a really disappointing surprise since I had no symptoms, have always been careful about what I eat, and have been vigorously working out in a gym four days a week for the last fifty years. Even now, after the procedure, I physically don't feel any different. I have a poor family history, but I guess we all deal with the genetics we've inherited.
Even though the machined bottom of the partially finished impeller ran true inside its housing, the variation in the impeller's edge thickness was a growing irritation I decided I couldn't live with. I was also concerned about the shaft keys working loose in the impeller's porous central interior. So, I decided to stint the impeller and fix both issues. 
I set up the impeller on the mill and was able to shim out all but a thousandth or so of the impeller's edge variation. I then bored out the bad metal and replaced it with a steel bushing. Using the same lathe setup I turned the bushing's o.d. for a press fit in the impeller and its i.d. for a close slip fit over the shaft. The bushing was turned extra long so that after installing it I would have a true spigot so I could finally finish machine the bottom of the impeller.
Machining the impeller's bottom was the easy part. The hard part was profiling the rest of the impeller for a close fit to the contour of the supercharger's volute in the rear half of the housing. The drawing spec'd a maximum .010" clearance to the rear half of the housing over the entire profile, but I decided to increase this to .015". I figured the bit of extra clearance wasn't going to make the difference between boost and no boost, while the extra margin would probably be appreciated down the road.
After sawing off the excess spigot, I mounted the impeller on the mill table and machined the top of the newly bushed center to its finished height. I then installed the impeller on a mandrel in my manual lathe and brought the tops of the inlet fins to their finished height and angle. The inlet fins extend into the inlet opening in the rear housing, and their top profile was just a simple 10 degree angle. The reason for finishing the central end of the impeller on the mill before finishing the inlet fins on the lathe was because of the acute reverse angle of the fins. In order to reduce the chances of the lathe tool grabbing and damaging them, I used my last narrow insert designed for non-ferrous metal; and I didn't want to take a chance on it being damaged by the steel bushing. 
The remaining profile was not only a bit complex, but being underneath the rear housing made its clearance difficult to determine. A profile for the impeller was provided on the supercharger's drawing, but it was only a starting point, and the clearance would have to be planned for my unique assembly.
I modeled the provided profile in SolidWorks and then printed it out on paper as an actual size cross-section. This allowed me to trial fit the pattern to the contour in the rear housing. Of course, the two were significantly different, and so the fitting process became an iterative combination of changes to the profile as well as to the surface inside the housing. I filed, sanded, and polished the interior of the housing until I had an acceptable match to one of my paper profiles. I then compiled a program for my 9x20 lathe to turn the profile onto a trial workpiece so I could check its fit in the supercharger housing. I used Plastigage to measure the clearance between the installed dummy impeller and the housing. I had to extrapolate the Plastigage measurement to .015" since what I had on hand would measure a maximum clearance of only .009". Once I was happy with the trial workpiece, I used the same program to cut the exact same profile into the actual impeller. The machined impeller and its clearance nicely matched those of the trial workpiece.
Only the diffuser section ring and a bit of mounting hardware remain to be machined before I can finally assemble the supercharger. - Terry


----------



## mayhugh1

A centrifugal supercharger takes in air along the central axis of its rotating impeller, and the fins use centrifugal force to rapidly accelerate this air radially outward to their outer tips. As the heavy air is slung away from the center of the impeller, a partial vacuum is left behind that draws even more air into the inlet. This high velocity air slams into the wall of the volute and piles up against the air that's already packed into the housing. This packing converts the kinetic energy of the high velocity air into static energy in the form of increased pressure, which is the goal for a supercharger. Compared with a Roots-type blower a centrifugal supercharger does a lot with its single moving part, and it doesn't heat the air nearly as much in the process. The downside, though, is that the kinetic energy imparted to the air varies with the square of the tip velocity. This means that boost falls off very rapidly with decreasing engine speed. (Glass-half-full people might say it rises very quickly with increasing speed.) The full-size Merlin used a variable pitch prop and operated over a modest rpm range which helped mitigate this shortcoming.
With the air-packed volute under pressure, a potential leak is present in the space underneath the impeller. This leak is created by the gap between the bottom edge of the impeller and the floor of the housing which is adjacent to the volute. The solution is a thin stationary ring bolted down to the floor of the housing that closely surrounds the impeller. The air flung off the impeller will then continue across the top surface of this ring before hitting the wall of the volute. This ring is referred to as a 'diffuser section ring' on the supercharger drawing. There was no detail provided on its design other than the assembly drawing showing its cross section. I had previously drilled clearance holes in the front-half housing for its eight 1-72 mounting screws. These holes were located and drilled through the centers of thin cast spokes on the front of the housing, and so their exact locations were not on a perfect bolt circle but were affected by the casting geometry. The first thing I did was measure their actual locations and compare them with my original notes.
Since the measured TIR of the mounted impeller came out to under a thousandth, I planned the gap between the impeller and ring to be .005" in order to add plenty of margin for hole uncertainties. I chucked up a 4" diameter aluminum round in the lathe and turned a portion of its end for the o.d. and i.d. of the ring while machining the workpiece extra long for a couple rings - just in case. The chucked workpiece was moved to the mill so I could drill and tap the array of holes. A witness mark was included to keep track of the orientation of the imperfect bolt circle pattern. After returning the chucked workpiece back to the lathe I parted off a ring using a right-side ground parting tool to minimize the burr on its inside i.d.. The first ring fit as hoped and was installed on the front-half housing using lowstrength thread locker on the mounting screws. 
Before finally assembling the supercharger, a few miscellaneous items had to be completed including the shaft keys as well as a nice streamlined spacer and bolt for the top of the impeller. For the time being I decided to not use any sealer between the housing halves since my previous flashlight test before adding the impeller showed no light leakage.
I plan to eventually do some systematic bench testing on the supercharger including an attempt to measure any boost it might possibly make, but this will require some special hardware to properly drive it. Rather than create an elaborate dedicated drive for a one-off test, I'd like to re-purpose at least a portion of what I have to machine for use in the electric starter. I'll let my brain work on this in the background while I continue on with the engine.
I couldn't resist, though, spinning it up by blasting compressed air into the intake. I have no idea how fast I got the impeller spinning, but it screamed like a turbine winding up and took nearly thirty seconds to slow to a stop when the air was removed. While holding the assembly in my hand I could feel no resonances or significant vibration throughout the entire rpm range that I ran it, and so for now I'll assume current impeller balance is 'good enough'. I could feel a lot of air leaving the outlet just after removing the air source, and so I know I at least have a decent diffuser. 
After gaining some confidence that it probably wasn't going to blow up in my hand, I made several sustained stress runs lasting up to a minute or so. Neither the sound nor its feel in my hand seemed to change after accumulating some ten minutes or so of run time.
I found some 0W-20 full synthetic oil in a local auto parts store and dropped a dozen drops down the oil intake. The sound of the bearings immediately changed - not necessarily better, just different - and there was an obvious increase in drag. With the same compressed air spin up, the impeller came to rest twice as fast as it did without the oil. I don't know if any of this means oil is good or oil is bad in the ceramic bearings, but the extra drag has to mean more friction and therefore more heat. I left the oil inside the bearing cartridge, but right now I don't have plans to add anymore.
So far, I'd have say this supercharger has probably been the most fun portion of this build. - Terry


----------



## grapegro

Hello Terry,
                You mentioned the long run down time of the turbo impellor. This relates to me of the history of the Merlin engine where trouble was encountered with the drive shaft of the turbo breaking when the revs were reduced quickly. Have you considered this problem.
Grapegro


----------



## 10K Pete

Terry, your work continues to be awesome!! The fits and finishes you are achieving
are amazing. I think it's safe to say than I'm not the only one anticipating the first
running of this fine machine.

Pete


----------



## mayhugh1

grapegro said:


> Hello Terry,
> You mentioned the long run down time of the turbo impellor. This relates to me of the history of the Merlin engine where trouble was encountered with the drive shaft of the turbo breaking when the revs were reduced quickly. Have you considered this problem.
> Grapegro



I hope so ...  see post 332.


----------



## stevehuckss396

Hello Terry!

I don't post much because there is only so many times you can say "holy crap!! but I want you to know that i'm still watching and enjoying the build very much. Keep up the the awesome work and Holy crap!!


----------



## Ken I

> I found some 0W-20 full synthetic oil in a local auto parts store and dropped a dozen drops down the oil intake. The sound of the bearings immediately changed - not necessarily better, just different - and there was an obvious increase in drag.



When a perfectly spherical steel ball rests on a perfectly flat steel surface - its mass is supported by the "dent" it makes in the steel = area x compressive stress. For applied loads the dent gets deeper.

The stress at the middle is basically the compressive stress that the material can stand and is therefore always damaging.

Add into that the surface imperfections and geometrical errors and it gets worse.

For a ball in a groove or a roller in a ring the contact is a line rather than a point but the same rules apply. (the stress diagrams look like squashed jelly beans with the highest stress at the centre diminishing to zero at the edges)

From this it follows that there is no such thing a a ball bearing that can run dry - it is always at the expense of diminished ratings for speed, load & life expectancy.

The relatively high shear and dynamic compressive loads that can be borne by the lubricant provide a much larger support area at lower pressure - this is the principal role of the lubricant.

The role of lubrication in rolling element bearings is extremely complex but if you are interested you should find plenty of information on line.

While ceramic bearings are more tollerant of high heat, the rules of dry compressive stress support aren't going to change.

Just something to bear in mind.

Regards,


----------



## Cogsy

I agree the bearings shouldn't be run dry. I was working for SKF when they first started making them available for normal distribution and our training had us targeting food processing industries due to food safe lubrication issues. Basically we were told full ceramics could be successfully lubricated by things like orange juice, milk and even straight water if necessary. We were told they needed some lubrication though.

Interestingly, ceramics also come as full or part hybrids as well. A full hybrid has normal steel raceways but all the balls are ceramic. A part hybrid is basically a normal steel bearing with one of the balls being ceramic. The full hybrid was primarily for insulation properties from memory, but the part hybrid used the hardness of the one ceramic ball to 'repair' micro damage to the raceway surface as it occurred from particle ingress. It just crushed the dirt particles then flattened out the damage caused to the raceway. Greatly extended bearing life in demanding environments.

Lastly, I once met a guy who built his own gas turbines and used modified deep groove skateboard bearings (608's) for his turbines. He replaced all the balls with ceramics, with no cage, and ran them at ridiculous RPM (hundreds of thousands I think). He replaced raceways often but reused his ceramic balls many times with no apparent wear.


----------



## brotherbear

I just had an epiphany ..thank you very much!


----------



## mayhugh1

The Quarter Scale's coolant pump is a dual output centrifugal unit with an impeller and volute that are very similar to those in the supercharger. Three castings were supplied for the pump including the main body, an inlet cover, and an impeller. All three took much more time to machine than expected due to their difficult fixturing and precision requirements. I was pretty happy when the time came to finally test the pump.
The pump body has a number of features that must be concentric with the impeller cavity, and a long spigot was cast into its top end to help with the machining. Similar to the supercharger's impeller, though, the body wobbled badly with the spigot chucked in the lathe's headstock. The inside jaws of my lathe chucks were too large to grip its interior so the spigot could be cleaned up. Instead, I inserted a tight-fitting Delrin plug into the cavity and supported it in a live tailstock chuck while the headstock chuck gripped the very end of the spigot. After truing up the spigot, I turned the neck of the pump body to its final diameter and added a groove for an o-ring. The pump body was supported by its neck for the remaining lathe operations, and the spigot ended up being used only to bring the neck to its final length when I parted off the body.
After the impeller cavity was bored to its final dimensions, a long narrow internal grooving tool had to be ground to open up the entry to the volute. The neck of the pump body was then drilled and reamed for a bronze bearing for the pump shaft. During these two operations I ran into the same soft metal issue encountered with the supercharger's impeller. The drilled hole had a bad finish, and even with a flood of coolant, the gummy metal fused to the flutes of the reamer. The final hole came out poorly finished, nearly ten thousandths oversize, and skewed to the axis of the body. Apparently, the metal in the thick spigot-like features on some of these castings didn't harden as well as the metal in the thin wall structures. Fortunately, this hasn't been an issue where it really matters because it could have been a real show stopper. I'm really glad now that I took the trouble to minimally anneal along only narrow bend lines when I earlier straightened the castings that were warped. Drilling and tapping all those mounting holes in gummy metal like I've seen in these spigots would have been a nightmare. In this case, the bronze bearing nicely buried the trashy metal out of sight and out of mind. Since the bearing was off axis from the pump body, I waited to finally bore it for the shaft until after the bearing was pressed and Loctited in place. The shaft bore, the pocket for a shaft seal, and the impeller cavity were all finish machined in the same lathe set-up.
The pump shaft was turned from 303 stainless. Its bottom end was tapped for a left-hand 10-32 thread for the impeller, and the unthreaded body of the shaft was polished for a nice bearing surface as well as the sealing surface for a standard rubber shaft seal. Since the shaft was also used as a mandrel for later machining the impeller, I waited to machine its top for the Oldham coupler until after the impeller was completed.
The coolant pump drawing called for a polished sleeve to be pressed onto the bottom of the shaft after inserting it through the bearing. This sleeve was to provide the sealing surface for a TC8x14x4 shaft seal that was part of a 2014 redesign. This sleeve, though, would have captured the shaft in the bearing between it and the Oldham tennon. I didn't like the fact that the shaft would no longer have been removable once the sleeve was installed. So, I modified the design for a TC6x15x4 seal that enabled me to use the polished surface of the shaft for the sealing surface and allow the shaft to be removed. Since the stock sleeve doubled as a thrust spacer for the impeller, I machined an integral spacer onto the bottom surface of the impeller as a replacement. I also bored a recess in the bottom surface for a steel spacer to provide a shoulder stop for the threaded impeller. The spacer was ground for an impeller thrust clearance of .003".
The spigot on the impeller casting was also considerably off axis to the impeller and had to be turned true so it could support the part while its center was being drilled and tapped. I first sawed off a badly warped portion at its very end which helped a little. I was worried that I was going to run into the same gummy metal problem during threading, but the portion I cut off appeared to be reasonably hard. A lot of material had to be removed to true up the spigot, and there probably wouldn't have been enough left for a repair bushing, but fortunately the threads came out looking great. The spigot was parted off, and the pump shaft was used as a mandrel for the remaining impeller machining operations. Since the shaft/mandrel was reverse threaded, rear mounted inverted lathe cutting tools had to be used for some operations, and the lathe was run in reverse with inverted front mounted tools for others. During an 'ah-ha' moment I discovered a power feed reversing lever on the Enco lathe that I've owned for some twenty years. Inlet fins were added to the impeller design in 2014 to improve the engine's cooling system. The fins were tediously profiled for a close fit to the pump body and cover just as was done for the supercharger.
The inlet cover casting required a number of machining operations with difficult fixturing requirements. Its small diameter spigot cleaned up with no issues, and its interior was machined to closely follow the contour of the impeller fins with the same clearance used in the supercharger housing. I added an o-ring groove to the cover so I wouldn't have to deal with a gasket or sealer on its narrow body mounting flange. The interior of the large inlet port was also prepared for an o-ring sealing surface. A dial indicator showed its rough cast i.d. was nearly perfectly circular. Instead of risking a boring operation I lapped it in my hand using 230 grit valve grinding compound on a wood lap chucked up in the lathe. The lap was easily turned to successively larger diameters as the lapping proceeded.
The final inlet cover operations included match drilling the two mounting flange pairs for some fourteen 0-80 mounting screws as well as the machining of stainless hose barbs for the inlet and outlet ports. Although the outlet barbs were threaded into the castings, there were too few threads in the casting for adequate seals; and so the barbs were permanently installed with JB Weld. Since John Ramm recently discovered that the i.d. of the coolant hoses had a significant impact on his engine's cooling system, I made the i.d.'s of the hose barbs as large as possible. The threads of the stainless steel pump shaft were coated with a Cu-Ni anti-seize compound before it was threaded into the aluminum impeller in order to reduce corrosion between the two dissimilar metals in the coolant.
Testing the pump by spinning its shaft with a battery powered drill through an Oldham coupler showed it to be quite capable. With the outlet hoses supported about twelve inches above a temporary one quart reservoir tank feeding the pump, it took about 20 seconds to empty the tank with the drill spinning at 1300 rpm. This corresponded to a 45 gal/hr flow rate at an engine speed of only 650 rpm. The pump also performed in reverse but with significantly less flow rate. - Terry


----------



## stevehuckss396

Fantastic.

Do you have anything assembled? How about a picture of the hundreds of parts that are done?


----------



## ddmckee54

I agree with Steve.  We've seen all these nifty bits and pieces being machined.  How about a family photo?

Don


----------



## petertha

Terry, your wood lap has me curious & intrigued. I had a similar thought about making a simple/quick/disposable MDF lap finishing tool to touch up cylinder liners (OD). On your ID lapping tool, do you somehow progressively expand the lap tool boss with a center screw or something, or do you mean you turned a new surface a couple thou larger each time?

_Instead of risking a boring operation I lapped it in my hand using 230 grit valve grinding compound on a wood lap chucked up in the lathe. The lap was easily turned to successively larger diameters as the lapping proceeded._


----------



## kvom

Based on the pics, I bet he just cuts off the used end and advances a bit more wood in the chuck before turning to the next size.


----------



## mayhugh1

Peter,
As kvom said, I just cut old lap off, pulled a bit more dowell through the chuck and turned the new diameter for the next lap. I left the cross slide at the previous diameter and just added a thou or two for each new lap. I used pine. I'm not sure about using MDF since the part gets pretty hot, and I'm not sure how the MDF will hold up. I couldn't measure any circularity imperfection with a dial indicator when I was finished. I've used similar conical laps to remove machining marks from valve seats. - Terry

I've been testing the fits of all the parts as I make them, but I've just never taken a photo of any major assemblies. I'll assemble what I have and take some photos this weekend.


----------



## ddmckee54

Mayhugh1:

It's been over a week!  I'm Jonesing for my Merlin fix.  Central Texas still there or did it get blown away?

Don


----------



## wirralcnc

Don
I'm waiting my self to see it all bolted together.
Had to get in the loft and look at my merlin castings just for a fix.

Robbie


----------



## DICKEYBIRD

ddmckee54 said:


> Mayhugh1:
> 
> It's been over a week!  I'm Jonesing for my Merlin fix.  Central Texas still there or did it get blown away?
> 
> Don


This old saying is apropos I think: "The difficult we do immediately; the impossible takes a little longer."


----------



## cfellows

I got to see Terry's supercharger first hand this past week and, like all his work, 'tis a thing of beauty.  Flawless fit and finish, and it spins like a dream!

Chuck


----------



## mayhugh1

The full-size Merlin had a dry sump oiling system that was fairly typical of the aero engines of its day. There was a pair of scavenger pumps located inside the rear end of the oil pan, also known as the lower crankcase, and a pressure pump located directly below them outside the oil pan. The second scavenger pump, which was not included in the Quarter Scale's design, drew oil through a suction tube from the front of the lower crankcase during extended dives. The Quarter Scale's pressure and scavenger pumps operate on common shafts that run between them through the oil pan. The bores for the shafts don't extend outside the engine, and so seepage around the shafts doesn't create external oil leaks. The pump's driven gear meshes with an idler that's driven by the coolant driveshaft inside the wheel case and provides a bit of mesh adjustment. Pressure reliefs will later be mounted to the external starboard side of the engine's crankcase, and copper oil lines with custom scaled fittings will eventually run over the outside of the engine.
After several days into this portion of the build I thought I'd be writing that I spent much more time deciphering the drawings for the pump bodies than I spent actually machining them. The pumps have complex shapes with several sides that require careful machining and cross-drilled holes running in and between them. Unfortunately, they're described by multiply-sectioned flat drawings intended for someone with more print reading experience than I have. All the needed information is in the drawings, but I had a really difficult time wrapping my head around the way it was presented. One or two trimetric views would have saved me days of headscratching. In the end though, while machining the pump bodies, I managed to generate enough scrap so the machining time came out greater after all.
Construction began by facing a mounting surface for the scavenger pump inside the rear of the oil pan as well as a second surface immediately under it on the outside of the pan for the pressure pump. These two surfaces must be absolutely parallel to each other to prevent the close-fitting shafts in the pump bodies from binding when they are assembled as a stacked pair straddling the pan. Their finishes also require care since they'll become the sealing surfaces that isolate the pumps from each other. The shape of the oil pan doesn't make the inside surface machining an easy task. The pumps must have gone through a redesign since the mounting bosses on the oil pan casting were designed since they don't match the envelopes of the pumps. This added to my confusion while trying to decipher the drawings.
Not part of the stock design, two pairs of phosphor bronze inserts were pressed and Loctited into the aluminum workpiece from which the pump bodies were milled. These inserts became the bearings for the pump shafts as well as thrust surfaces for the pump gears, but they created problems for some of the cross-drilled holes in the pressure pump body. A couple of these holes crossed the boundaries between the aluminum and bronze, and the drill invariably wondered into the soft aluminum. I had to plunge an end mill into the affected holes in order to straighten and prepare them for oil fittings. Compression fittings machined from standard 3/16" unions were installed in the scavenger's output port as well as the pressure pump's input and output ports. A similarly machined 1/8" compression fitting was installed in the pressure pump's gauge output. Scaled custom flare fittings will likely be used for the distribution tubing later.
A short length of 12L14 was machined into pump gear stock. The individual pump gears were parted off from it and their widths surface ground for .001" depth clearances inside the pump body pockets. A .002" clearance was machined into the pocket around the o.d. of each gear. 
For the six pumps I've previously machined for my last four engines I generally start out with these optimistically close fits but usually have to clear the interferences left by my Tormach's backlash while machining the pump gear pockets. It's been my experience that the 60-70 psi that these pumps typically generate is much more pressure than is needed or even wanted in a model engine. Even though the scavenger pump has twice the capacity of the pressure pump, John Ramm mentioned that he had to throttle his pressure pump down to some 15 psi in order to better control the oil in his Merlin's crankcase. In both my radials I had to severely restrict the oil flow into the pressure pumps to avoid similar issues. I plan to later implement a relief valve in the pressure pump's output line with a return back to the oil tank similar to what John eventually did.
Even though I could probably be much more aggressive when fitting the pump gears, I prefer bluing and tediously polishing away only the high spots that create the interference. The stacked pump pair in the Merlin design could have created a whole host of additional problems with its pair of facing gear cavities, and so I was relieved to discover that I only had to open up the drive shaft bore in the pressure pump body for a .002" clearance in order to obtain a freely turning dual pump assembly. 
The drive gears in both pumps were each broached with a pair of slots spaced 180 degrees apart to accept slip fit drive pins in the driven shaft. This provided some precision broaching practice for the operations coming up later on the rear crankshaft, but I was left with some concern about their impact on the gears' strength. These constant displacement pumps are capable of generating terrifically high stresses on the shafts and pump gears. I couldn't come up with a better way, though, to secure them to the shaft so the pump pair could still be assembled. 
The driven gear for the pump assembly is secured to the pump driveshaft with a setscrew tightened against a machined flat, and a hold-down plate fits into a groove around the gear's neck to keep both shafts in place. The hole pattern drilled into driven gear is required for access to the plate's fasteners.
I machined a temporary spacer plate to simulate the oil pan surfaces between the two pumps so I could test the completed assembly outside the engine before drilling the holes through the oil pan. With the assembly immersed in a container of oil, both pumps generated vigorous streams of oil when spun with an 800 rpm drill. For a quick stress test I installed a gage on the pressure pump and blocked off its output line. The gauge pegged at 200 psi before blowing the oil line out of the gauge and causing me to lose my grip on the pump. The pint container of oil ended up in my lap, but I considered the test a 'pass'.
I promised to post some assembly photos of the engine's progress to date, but the large white Delrin fixture that I've been using as a temporary rear drive shaft inside the wheel case prevented it from being bolted to the crankcase. Since the wheel case and everything aft of it is where I've spent my time during the past several months, I wanted to include it in the photos. The next step will be to machine the actual dreaded rear driveshaft so I can finally assemble the wheel case and take some meaningful assembly photos. - Terry


----------



## mayhugh1

In the full-sized Merlin, the crankshaft and wheel case gearing were connected through a thin splined shaft. This spring shaft used rotational flex to reduce the pounding absorbed by the gears from the engine's power pulses. It also helped to dampen potentially dangerous rotational resonances in the crankshaft itself. However, this shaft was not strong enough to handle the engine's starting torque requirements, and so a heavier outer shaft was designed to be engaged when the twist in the spring shaft reached a predetermined amount. 
The documentation points out that a need for this additional complexity in the Quarter Scale has never been proven, but it's continued to be part documentation over several design revisions. A final design was included as part of the 2014 revisions. Both John and Gunnar included earlier revisions of this two-part shaft in their engines.
Reproducing a scaled version of the Merlin's rear main shaft in a home shop is difficult because of the requirement to machine three pairs of splines indexed across three separate parts without access to custom spline broaches similar to those used by the Rolls factory. If the splines are not precisely machined and accurately placed using the only tool likely to be available - a keyway broach - the rotational load will not be evenly distributed among them. In the best case, the final result could be inferior to a conventional solid shaft; but in the worst case, metal particles could be forever fretted into the oil system as the edges of mismatched parts vibrate against one another.
The rear main shaft documentation that I have feels like a confusing collection of drawings, some of which were obsoleted by later design revisions. A short adapter, fixed into the rear of the crankshaft, though, is common to all of them. In addition to a recess to accept the main shaft's centering bushing, this adapter has two sets of internal splines: an innermost set for the spring shaft and an outermost set for the main shaft. Splines on the front of the spring shaft engage the innermost splines in this adapter, and splines on the rear of the spring shaft engage a set of internal splines at the rear of the main shaft. When the spring shaft twists under load, it turns the outer main shaft with it via the rear splines until, at about five degrees of rotation, yet another set of splines on the front of the main shaft engages the outermost set of splines on the adapter. At this point, both shafts are locked to the crankshaft.
Three options were suggested in the notes for creating the troublesome internal splines that mate with the spring shaft. The option with the highest torque capacity, and the one that best resembles the shaft in the full-scale Merlin is a high-count multi-groove spline. This option requires the creation of a special broach or the use of an EDM machine, and so I ruled it out early on.
The second option was a scaled approximation to an SAE 6-groove spline cut using a keyway broach. This option produces a nice looking result that I very much liked, and I tried for several days to implement a version of it in SolidWorks. I used partial drawings that were provided in the documentation as starting points since I didn't feel a complete workable design had been included. I ran into several issues especially because I didn't want to re-machine some interrelated wheel case parts that had already been completed according to the original drawings. The shallow splines in the main shaft would have required me to butcher up an expensive broach, and a set of matching external splines with the proper angles would have required a custom ground tapered end mill. I also couldn't come up with a way to retain the spring shaft inside the main shaft without significantly compromising the strength of the main shaft since it was too late to increase its diameter. On top of everything else, I still had no real way to guarantee a precise and uniform placement of the splines by cutting the grooves individually with a keyway broach. At the end of the day, option two would have looked really great from afar, but I would have been left with a lot of uncertainty about its integrity. I think John was able to make this option work for him, though.
The third option, and the one I reluctantly adopted, was a simple square drive for the spring shaft. A complete design for this option was provided in the documentation, and it appeared to be the supported choice in the 2014 re-design. Theoretically, it offers less torque capacity than either of the first two options, but an actual home shop implementation could very well end up stronger. It clearly provides the desired loose coupling between the crankshaft and wheel case gearing, and fitting and indexing square shafts and square broached holes is much easier than dealing with keyway broached splines. My only real objection to using it in the Merlin is that It reminds me too much of the flexible drives in my gasoline-powered yard tools. Fortunately, it won't be visible after assembly, and my tired old brain will likely bury all images of it along side several other compromises I've had to make along the way.
Three parts make up the rear main shaft assembly, and I started by machining the crankshaft adapter from Stressproof steel. The end that fits into the crankshaft was turned for a close slip fit, and the pilot bore for the square broach was drilled and reamed in the same setup. The workpiece was then turned around in the chuck so the recess for the main shaft's centering bushing could be bored. I intentionally used the runout in the chuck to offset the bushing recess in hopes of canceling some of the TIR that I was previously left with in the end of the crankshaft. I was surprised when this worked because usually when I attempt something like this it backfires and makes things worse.
The broaching of the hole for the square drive was started in the lathe using the tailstock as a press in order to help get the hole started straight, but I completed the broaching in an arbor press to avoid abusing my lathe's headstock bearings. I then moved the workpiece to the mill. It was very important that the adapter's mounting holes and outer set of inner splines be precisely indexed to the square drive hole. To do this I inserted a tight-fitting square tool blank into the hole and then selected a gage pin to use as a shim for aligning the workpiece to the mill's vise. When the milling was completed, I moved the adapter back to the lathe in order to turn a taper on its rear nose. This taper was necessary for clearance to the pump shaft's bevel gear. I added a radially drilled hole in the bushing recess so the pressurized oil feed in the rear bearing cap would also lubricate the bushing. This hole will also be used later to index the bushing to its minimum TIR position when it is permanently installed.
The spring shaft was also machined from Stressproof. After turning a blank on the lathe with generous filets at the diameter transitions, I used the mill's fourth axis to mill the square ends and to insure they were aligned to each other. A corner radius end mill was to machine the flats to avoid any sharp corners at the intersections between the flats and the cylindrical shaft.
The last shaft component to be machined will be the main shaft, itself. This part will be a much more complex, and it has several features that must be accurately indexed to one another. Its TIR will also affect the fit of three major gears that are already a part of the wheel case. - Terry


----------



## michael-au

Amazing work


----------



## mayhugh1

The last and most complex wheel case component to be machined was the rear main shaft. A disadvantage of saving it until the very end is that all of its dimensions must be spot on before it can be installed since it affects every moving part inside the wheel case. However, one of the reasons for saving it for last was that with all the other parts finished and in place, I felt I'd have the best chance of coming up with those dimensions.
Two especially critical ones involve the locations of the integral cam drive sprocket and the mounting flange that sets the meshes for the pump bevel and magneto helical gears. The timing chain doesn't flex laterally, and so the drive sprocket must end up aligned with the idler sprockets that center the chain inside its very narrow housing. By design, the bevel and helical gears are assembled as a ring gear set, and so the meshes with their mating gears is accomplished by properly locating their mounting flange. In addition, the shaft splines must end up aligned to the square hole for the spring drive to within a half degree or so.
Because of limited access and visibility inside the wheel case, the dimensions associated with the main shaft were not easily measured even as the wheel case was being built up. They had to be iteratively determined using trial-and-error machined spacers. Since the mesh of the pump gear was hidden from view by the gear itself, its depth had to be inferred from the backlash that it created in the coolant pump shaft when various spacers were placed in front of the bevel gear. Although all the shaft-related measurements taken over the past months seemed reasonably consistent, I felt it safer to assume they were only starting points for the shaft design. So, I changed my original plan and decided to make two shafts: a prototype shaft and a 'production' shaft. The prototype shaft was completely machined and its fit verified before work was started on the production shaft.
I initially set up the order of the machining operations so I could check the fit of the prototype shaft after each operation and verify or modify its design as I went along. I eventually discovered my original dimensions were accurate, but the order I had used to machine the prototype shaft had a number of problems. For example, the forces associated with broaching the square hole for the spring shaft affected the TIR of the prototype shaft. For the production shaft, I moved the broaching operation to the top of the list before any of the shaft's features were machined. A couple interference issues also showed up with the shank of the tool used to spot the front flange mounting holes as well as the end mill used to machine the cam drive sprocket. A different order for these operations solved the spotting tool issue, but I had to grind down the 1/8" shank of the 3/32" cutter used to mill the cam drive sprocket in order to prevent it from rubbing against the front splines.
As with the rest of the shafts in the wheel case, the main shaft was also machined from Stressproof - not so much for its dimensional stability as for its tensile strength and ductility. After initially skimming the outside diameter of the one inch workpiece, the rest of the operations were carried out in a four-jaw chuck to minimize any runout among the shaft's features. For the prototype shaft I mistakenly set up its work sheet using .938" as the finished o.d. for its workpiece instead of .984", and this guaranteed right from the start that it would end up in the scrap box after being completed.
For the production shaft, I faced both ends to bring it to its finished length, and then I drilled and reamed its center from each end so the square drive hole at its rear could be broached. The depth of the spring drive shaft inside the main shaft was carefully set using the i.d. reamer while the workpiece was back in the 4-jaw.
The o.d.'s of the major features were finished before cutting out the material between them. The more complex features, including the front splines, the cam drive sprocket, and the rear groove for the retainer clip were then machined. To reduce gear runout, the locating shoulders for the shaft's three gears were machined for very snug sharp corner fits. The rear of the shaft was also turned for a near-zero fit to its bearing plate bearing.
Two arrays of gear mounting holes had to be drilled/tapped into the two roughed-in flanges. The locations of these holes have been an interesting experience from the very beginning. The six tapped holes used to mount the bevel/helical ring gear set was originally arranged so the mounting screws would come out in the roots of the threads of the bevel gear. Now, the six clearance holes for these screws in the front flange had to be aligned with the twelve tapped holes used to mount the main drive gear on its rear flange. This alignment was needed so a hex wrench could pass through the tapped holes in the rear flange in order to tighten the mounting screws in the front flange. Both of these hole arrays ended up too close to the edges of their mounting flanges in the prototype shaft because of the initial machining error I made on its workpiece.
For the production shaft I also changed the method I had been using to align the workpiece in the mill while machining the shaft splines so they would be properly aligned to the spring shaft. For both the crankshaft adapter and the prototype shaft I had used pin gages as parallels between the fixed jaw of the vise and a tight-fitting square lathe tool blank inserted into the broached hole in the workpieces. I found that this alignment method had created about a two degree error between the adapter and the prototype shaft which I felt was too much. For the production shaft I inserted the spring shaft into the workpiece and then clamped a long horizontal bar to one of its flats which I then indicated to the mill's x-axis. With care, the repeatability of this technique appeared to be about +/-0.2 degrees. When I checked the error between the production shaft and the adapter it was still about two degrees telling me that most of the original alignment error had been a result of the adapter's fixturing. I machined a new adapter using the new alignment method, and found that the error between it and the production shaft had been reduced to essentially zero. My hat is off to anyone able to do this with a splined spring shaft.
A bronze bushing was pressed onto the front nose of the shaft and turned concentric with the rest of the shaft's features. The shaft will only rotate +/-5 degrees inside the crankshaft adapter, and so its real purpose is to keep the shaft centered in the adapter and on axis to the crankshaft.
The prototype shaft appeared to fit perfectly inside the wheel case with the bearing plate installed although, with so many close fits, its installation required a lot of patience. All seventeen meshed gears between the oil pump and the supercharger turned smoothly together as the prop shaft was rotated. I also exercised the gear train by driving it through both starter shafts. I threaded the timing chain down through the idler sprockets and around the cam drive sprocket to verify it had ended up in the correct position. After a good bit of testing I was finally happy that the prototype shaft fit and operated as intended. I then started all over and machined the production shaft to the exact measured dimensions of the prototype shaft. 
The next step will be to finally assemble the entire wheel case. - Terry


----------



## napoleonb

Real nice work! I'm always eagerly waiting for a new report and enjoy reading it.


----------



## mayhugh1

There were a few loose ends to tie up before finally assembling the wheel case, and I used them also as an opportunity to assemble/disassemble the wheel case several more times to make sure everything went back together consistently. This is probably the most complicated assembly I've made, and I wanted to clear up any glitches while it's construction was still fresh in my mind.
The first task was to permanently install the adapter in the end of the crankshaft. The adapter is bolted to the crankshaft with six 3-48 SHCS's, but it's also intended to be bonded to the interior of the crankshaft. I didn't particularly like the idea of permanently installing it, but I was concerned about an area just behind its mounting flange for which I had questions about its ability to support the starting torque carried by the splines. Hopefully, the Loctite adds some much appreciated margin.
Since the adapter was machined for less than a half thousandth clearance inside the crankshaft, I used Loctite 609 which is a low viscosity retainer designed to augment press fits. With such a close fit, though, I was concerned about the Loctite setting up while I was still scrambling to align the mounting holes which were also reamed for minimum clearance. In order to avoid getting the adapter embarrassingly stuck in the crankshaft, I threaded a pair of temporary studs into the end of the crank in order to guide the wetted adapter into place. I had a plastic mallet on hand, just in case, but it wasn't needed. The steel mounting screws were locked in place with blue (medium strength) threadlocker. Blue threadlocker is overkill for number three screws; but the adapter, for better or worse, was to be a permanent part of the crankshaft.
Green (low strength) thread locker was used on some of the fasteners associated with the various shafts inside the wheel case as insurance against vibration. Before locking the threads on the pump idler bracket, the mesh of its idler gear was set with the oil pumps assembled in the lower crankcase. And, before this was done, I drilled the sump for a drain for which I made up a magnetic drain plug. This feature wasn't part of the documentation, but there was a pocket cast into the bottom of the sump that seemed to scream for a drain. I hope the screaming doesn't turn out to be a warning that I overlooked something more important that was supposed to have gone in there. Since the design of the oil pumps located on either side of the bottom surface of the oil pan made the use of gaskets or sealer risky, I filled the lower portion of the pan with oil and allowed it to sit over night to verify there were no leaks. 
Forward thrust of the main shaft is ultimately limited by the depth of the shaft's splines inside the crankshaft adapter. This depth stop doesn't set the gear depths, though, as it was intended only to prevent the main shaft gear from rubbing against the wheel case housing during testing. During running, the shaft is held in position by a pair of spacers that straddle the inner race of the rear bearing located in the bearing plate. It's these spacers that set the engagement depths for the bevel and helical gears discussed previously. The widths of these spacers were determined during the wheel case build-up and verified using the prototype shaft. The front spacer is sandwiched between the rear face of the main gear and the inner race of the rear bearing. The rear spacer is held in place behind the rear bearing with a retainer clip in the groove at the rear of the shaft.
The wheel case is mostly modular which means that it was designed so it could be added to or removed from the crankcase as a completed assembly. However, there are three flange mounting screws located behind the countershaft that are accessible only from inside the disassembled case. These screws were probably added for extra support around the front of the countershaft which is especially stressed. Even though I had some misgivings about being able to align the inner and outer shafts while sliding the unit into place, it wasn't terribly difficult. When the wheel case is assembled to the crankcase for the final time, however, it will have to come apart once more for access to those three screws.
I rechecked the alignment of the timing chain inside the fully assembled wheel case. Some technique is required to get the chain threaded around the drive sprocket because of its restricted view and access. The drive sprocket is located directly over the top of the pump shaft bevel gear, and with the chain in place there is only about .020" clearance between the two. I eventually figured out how to snake the chain into place by pulling it through from the port side of the wheel case on the end of a waxed string. Because of its close proximity to the countershaft gear on the starboard side, it can only be pulled up vertically from that side. The chain isn't yet cut to length which makes working with it a little easier. It won't be shortened to length until final assembly, and threading it into place then with the housing in position is something I'm not looking forward to.
The final task was the fabrication of an oil nozzle for splash lubricating the gears and bearings inside the wheel case. The design of this part for what seemed like a simple task got away from me and grew into something that quickly became complicated. This two-part assembly is designed so oil will drip onto the main gear through a .018" diameter orifice, and windage should care of distributing the oil to the gears and bearings in front of the bearing plate. A second orifice on the end of an extended nozzle gets oil to the gear pair behind the bearing plate. There's an opening at the bottom of the wheel case to return waste oil to the sump. I formed the tiny orifice on the end of the extended nozzle by forming the tip of the soft copper tube around a drill bit. 
I've included some assembly photos of the completed wheel case and rear end of the engine. I plan to start working on the magnetos next, and so the wheel case can remain in place until they are completed. Finishing the magnetos will complete all the work involving castings. The complexity of the drawing describing the magnetos is on the order of those for the wheel case, and so we'll see if my print reading skills have improved over the past several months. - Terry


----------



## Parksy

Amazing! Everything looks just perfect! Immaculate! How do you do it?

I'm curious about how long something may take to create? Ie your rear shaft assy in post 362? Just to give me an idea on a project like this.


----------



## mayhugh1

Parksy said:


> Amazing! Everything looks just perfect! Immaculate! How do you do it?
> 
> I'm curious about how long something may take to create? Ie your rear shaft assy in post 362? Just to give me an idea on a project like this.



Parksy,
Yes, that post was pretty much all about that shaft. - Terry


----------



## pickleford75

Gasp! I cannot wait to see it run..... That is some of the finest workmanship I've ever seen, thank you for sharing.


----------



## mayhugh1

The full-size Merlin used a pair of magnetos to fire the six pairs of spark plugs in each cylinder head. The port-side magneto fired the outside plugs in both heads, and the starboard-side magneto fired the inside plugs. In case of a magneto failure, this arrangement provided for at least one of the plugs in each cylinder to continue firing. Since there's only one plug per cylinder in the Quarter Scale, the wiring was simplified by arranging for each magneto to fire all the plugs on its particular side of the engine.
The Quarter Scale's magneto housings were cast to look very similar to those on the full-size engine. A design for a distributor, compatible with a conventional spark ignition, was also provided since designing a functional magneto was beyond the scope of the project. Fitting a fairly complex distributor inside the magneto housing created some challenges involving the high voltage that arose from the scaling. The requirements for high voltage isolation didn't scale with the physical sizes of the voltage carrying components, and so the limited space inside the housings even with half the number of plugs created problems for at least one early builder.
I used a translator app to follow Gunnar's online diary of his distributor testing experiences that were plagued with crossfires and internal arcing to ground. His entries seemed to end abruptly during his efforts to modify portions of the original distributor design, and it's not clear from his website that he was ever able to overcome all the problems and get his engine to run:
http://www.123hjemmeside.dk/gunnarsorensen/47386583
The distributor was later redesigned by Dynamotive, and some of Gunnar's improvements may have been incorporated into the new design which included an improved contact block. A photo in Gunnar's diary shows the tower electrodes in his distributor sitting above the contact block similarly to those in the full-scale magneto. In the Quarter Scale, the path lengths between those tower electrodes and the grounded enclosure were marginal insurance against arc-overs. The re-design moved the electrodes deep into the contact block to increase the lengths of the surface paths between them and ground. Other improvements were made to the rotor, and John Ramm may have been the first to implement the new design in a successfully running engine. In the latest design that both John and I received, the original mechanical points used by Gunnar were also replaced with a solid state trigger.
The documentation includes a drawing sheet that clearly shows most of the machining required on the castings. A second sheet contains the distributor design, but several details are left up to the builder. I eventually had to model the distributor components in a 3-d assembly before I could begin to understand and appreciate its operation.
The main shaft in each distributor is driven at 3/2 the crankshaft speed through the Oldham couplers on either side of the wheel case. A timing disk on this shaft opens an aperture between a stationary magnet and a Hall sensor twice per revolution. The rotor is gear reduced to the timing shaft and spins at 1/3 its speed or, equivalently, half the speed of the crankshaft. The result is that for every two crankshaft rotations the rotor has six consecutive angular positions defined by trigger events that are 60 distributor degrees apart. The contact block converts these six angular positions into a 2x3 linear array of tower electrodes - one for each of the six plugs in the distributor's cylinder bank. Internal conductive paths inside the rotor and contact block created using pressed-in metal pins distribute the coil firing voltage to each plug in each bank according to the firing order 1-4-2-6-3-5. A typical firing position, in this case for cylinder number four, is shown in the cross sectional view of the distributor's partial assembly model.
The first step in construction was to machine the castings according to the drawing I had so I could have some parts in my hands to help me visualize the design. While boring the housings for the timing shaft I discovered the BOM hadn't specified a flanged bearing for the inner main bearing as shown on the drawing. While reordering these I decided to convert the outer bearing to a flanged type also since the distributor drawing seemed to describe an overly complicated mounting scheme for a flangeless bearing.
The castings for the top covers that I received seem to be less desirable early versions which are the same as those used by Gunnar but different from those in John's engine. John's covers include integral troughs for the plug wires that look similar to those in the photos of the full-size Merlins I've seen. The trough-less castings I received would be awkward to adapt, and so I'll likely machine a pair of replacements. In the full-size Merlins the plug wires were routed between the magnetos and the spark plugs through metal conduits mounted to the sides of the cylinder blocks. These tubes nicely protected the wires, but their real purpose was most likely to shield the aircraft's onboard radio receiver from the RF interference they created.
The rotor spins on a two-piece shaft in a housing which is an integral part of the contact block. The outboard portion of the shaft is metal, and since it forms part of the contact to the coil's secondary, it is at full coil potential. The inboard portion, including the rotor's driven gear, is Delrin so the 'hot' half of the shaft is kept well isolated from ground. In the stock design the rear rotor bearing is a simple Delrin sleeve. John, instead, used ball bearings on both ends of his rotors to reduce the mechanical load carried by the acetal gear and shaft. I plan to do something similar since precision bearings may allow me to reduce the size of the rotor's air gaps that are in series with each spark plug. I've worked out a reasonable solution for the isolated inboard bearing, but the outboard bearing which will be 'hot' is still a work in progress. I machined the retainer blocks for the inboard bearings and bolted them into place in the main castings. They will be line-bored later along with the rotor housing. 
Every air gap in the high voltage path between the coil and the spark plug dissipates coil energy proportional to the width of the gap. This dissipation, over time, erodes the ends of the conductors on both sides of the gap causing them to grow even wider. The tiny plug gaps associated with the Mini-Viper plugs used in the Quarter Scale make these air gaps especially significant. Anything that can be done to reduce their size and number will improve the reliability and reduce the maintenance of the ignition system. - Terry


----------



## dsage

Hi Terry:

All I can say (as usual) is Wow!. Fantastic work. I admire your ability to work through problems (and your ability to figure out you have one ahead of time).
 I'm wondering what your plan is for coils and drivers? Perhaps a couple of CDI units?
I'm looking forward to seeing  how the ignition system works out. This is always a problem for model builders because the management of high voltage is of those things that doesn't scale.

Great work.

Sage


----------



## mayhugh1

Dave,
I'll probably use a pair of CDIs. I bought a pair plus a spare of Roy Sholl's original CDI units for this build last year after hearing that that he was losing his supplier for the boards he was selling. I visited his website last night since it's probably time to bite the bullet and order the dozen ZR2 plugs I need and noticed he is now carrying the Rcxcel units. 
Thanks for the kind comment. - Terry


----------



## mayhugh1

I started work on the internals of the distributors with the most difficult parts - the contact blocks with their integral rotor housings. Since they looked like they would probably require more thought and setup time than machining time, I launched a pair of spares as well. I used white Delrin because of its excellent machinability and resistance to high voltage breakdown (500V/mil). I'd rather have been working with black Delrin, as it looks more at home on an engine, but the carbon used to color it adds so much uncertainty to its electrical properties that DuPont doesn't even specify them for the black material. Even though it makes great looking distributor caps, black Delrin really isn't a good choice around high voltage. 
I had some white round drops in my scrap collection, but they required their first machining step to be a 4-jaw offset turning operation in order to get the blocks started in the centers of their workpieces. The circular ends of the rotor housings were lathe turned before milling the rectangular portions of the contact blocks. The blocks will eventually be bolted inside the housings, but I also machined them for snug fits inside my particular castings so they'd be consistently re-mounted after the boring operations for the rotors and bearings.
After drilling the contact blocks for the tower electrodes, I machined some trial electrodes from 360 brass. In particular, I was looking for the right amount of interference to keep the 1/16" diameter pins in position during the boring operation for the rotor housing but not bend them during the pressing operations. I eventually settled on .004". Due to workpiece deflection, turning the long skinny pins without tailstock support created a taper going in the wrong direction, but it was correctable with a simple compensation program run during the finishing pass on my 9x20 CNC lathe.
I plan to use 1/8" diameter black 20 kV silicone wire for the plug wires; but I wasn't comfortable with, or maybe I didn't understand, what was being shown in distributor drawing to secure them within the contact blocks. John held his wires in place with individual Delrin sleeves, and I did something that probably ended up being very similar. I machined slotted Delrin collets for the wires. Testing showed that pressing a wire-filled collet into the block with just the right width slot compressed the silicone insulation enough to retain the wire so it would pass my 'tug' test. The collets were straight forward enough to machine, but cutting the slot was much more difficult than I expected. The i.d., o.d., and the slot width of the collet all interact to affect the amount of force that's required to press a wire-filled collet into the contact block. The collets won't be pressed into position until after the distributors are completed and the contact blocks have been weakened by the boring operation for their rotors. It's important to not get carried away with the amount of seating force since a hard pressing operation could distort the rotor housing and upset the rotor air gap. After spending an evening scrapping dozens of collets, I finally came up a reasonably consistent slotting tool made by bolting two single-edge razor blades together on either side of a 'goldilocks' spacer. With the collet resting in a wood v-block and a tiny wood filler dowel through its center, rapping the tool with a small mallet usually punched out the right slot. Somehow, I managed to get through all the parts I made without spilling blood.
The plug wires will eventually have their ends stripped and the strands wound into a circular 'bird nest' below the bottom end of the collet. After the collet is pressed into place, the strands will be captured between the bottom end of the collet and the flat head of the pin. In addition to strain relief, this should also provide a reliable electrical connection between the two. 
After pressing in the tower electrodes, the contact blocks and the rear bearing blocks were assembled in their housings so a shaft alignment hole could be drilled/reamed through them. This hole was used to pick up the centers for the boring operations for the rotor bearings as well as the opening for the rotor itself. Unfortunately, it wasn't possible to do these operations in a single setup with the components installed in the housings. The rear bearing blocks were bored for their flanged bearings and tapped for 0-80 retaining screws. A fixture was then machined to support the contact blocks so the rotor housings could be bored without distortion.
After assembly, the angular positions of the rotors will be hidden from view inside their housings, but these positions will be needed when timing the engine. An index hole, shown drilled through the outer end of each rotor housing, will align with a similar hole in the rotor to determine the rotors position. The use of these holes weren't documented, and my CAD model showed that with the coordinates provided alignment would actually occur 7-1/2 degrees before full alignment with plug number one. I altered the location of the hole in the housing to set the alignment at dead center, and I reduced its diameter from 1/8" to 1/16" since the hole was uncomfortably close to my high voltage coil contact. Also not mentioned on the drawing is that fact that the locations of the housing holes must be mirrored between the port-side and starboard-side distributors since they rotate in opposite directions. I didn't realize this until I had already drilled mine, and so I had press in filler plugs and re-drill. The plug sequences in the tower arrays must also be mirrored.
Finally, the recessed pocket for the outer rotor bearing was bored, and this finally completed the machining on the contact blocks.
In order to verify the accuracy of the boring operations, I turned a trial rotor blank for a .003" theoretical rotor air gap. I pressed in a test shaft and spun the combination in all four rotor housings while mounted in their corresponding magneto housings. The rotor spun freely in all cases, and there didn't appear to be any interference with any of the housings including the spares. Since I didn't expect to be able to reliably do so, I didn't try to reduce the clearance any further even though a .003" rotor air gap is a whopping 25% of what the plug gap will probably end up being.
The rotor-side design of the high voltage coil contact that I'm currently working with is somewhat different from what is shown in the distributor drawing, and it's shown in the exploded rotor assembly diagram. The stationary side of the coil contact will be designed later after the rotor is machined and in place.
In order to maximize the path length to ground along the outer surface of the rotor housing, the rotor housing was set back away from the metal enclosure, and the front bearing was recessed into the inboard surface of the rotor housing. Only its inner race is visible from the outboard side. Even though this bearing is at full coil potential, damaging current should flow only through the inner race and not through the balls themselves. An insulated end cap will be machined later to cover the coil connection and seal against the outboard side of the rotor housing. - Terry


----------



## mayhugh1

I didn't spend much time in the shop during the past week while two of our grandchildren were visiting, but I did manage enough late night hours to finish up the rotors.
If my brain had been plugged in before starting, I'd have realized that the large driven rotor gear could easily have been machined as an integral part of the rotor, itself. Since it wasn't, though, the first thing I did was to machine a Delrin prototype gear from which I sliced off the two gears that I needed. I'd never before used a gear cutter on plastic, and even though I thought the tooth cutting operation went smoothly, the tedious de-burring required afterward on both sides of every tiny tooth did not. My zero rake gear cutter didn't play well with Delrin, and I eventually had to lap the faces of the gears in order to clean them up. If I had it to do it over I might try grinding a single point cutter with some rake.
Since I'd already made two spare rotor housings, I decided to also start a couple extra rotors since there was some unforgiving drilling ahead related to the high voltage conductors. For minimum TIR, I planned for all the finishing operations to be completed in the same lathe setup. My goal was to at least duplicate the .003" air gap I had been able to achieve earlier with the test rotor.
I faced an end of each rotor blank and then rough-turned the diameters to leave .020" excess stock for finishing. The blanks were then moved over to my mill's fourth axis where a pair of radial holes were drilled for the rotor electrodes and a pair of flats were machined on their cylindrical sides. These flats serve two purposes. First, they open up the volume around the rotor and reduce the amount of unneeded/unwanted dielectric material rotating very close to the housing. More importantly, though, they provide a convenient way to hold the cylindrical parts in a vise at a precise and consistent angular orientation while their ends are machined. After pressing short lengths of 1/16" diameter brass rod into the holes for the rotor electrodes, the parts were returned to the lathe where their o.d.'s were finished and their centers bored for press-fit shafts. 
The ends of each rotor were then machined. The inside end was simply drilled and tapped for four 0-80 flat head screws for mounting the driven gear. The outer end machining was a little more complex because of the need to electrically connect the rotor electrodes to the coil contact. I found some 20 AWG dead soft silver wire in a local craft store that I used to connect the rotor electrodes to a contact disk machined on the stainless steel rotor shaft. A pair of .032" diameter axial holes were drilled through the outer end of each rotor so they would intersect the sides of the radial electrodes and penetrate about half their diameters. A short piece of the wire was inserted into each of these holes, and the tops were bent over into a shallow slot milled across the outer end of the rotor. The wires were cut slightly long so the pressure from the contact disk forced them into the drilled spots in the rotor electrodes. The folded-over wires in the slots were sandwiched tightly against the contact disk and held with a pair flat head screws for a reliable connection. An ohmmeter verified the final continuities. Although silver is very close to both brass and stainless steel on the galvanic reaction chart, I thoroughly cleaned and removed all traces of cutting fluids from the wire and wire holes before final assembly to insure I didn't leave an electrolyte behind that might corrode the electrical connections.
The rotor shaft is actually two separate shafts. The outer shaft was machined from stainless steel and will be at coil potential when a plug fires. I modified the shaft design provided in the distributor drawing to accommodate the ball bearings that I added to the rotor housing. I also integrated the contact disk with the shaft and added the screws to secure it to the rotor. The inner race of the outside bearing is captured between the end of this shaft and a custom phosphor bronze contact screwed into its end. The bronze contact was machined with hex flats for a nut driver, and a screwdriver slot was cut into the rear of the shaft so the pair can be easily tightened. The contact pair on the port side is left-hand threaded, and the starboard-side contact pair is right-hand threaded.
The inner shaft was machined from Delrin to maintain isolation of the 'hot' outer shaft from chassis ground. Since the rotor is held in place in its housing by the outer bearing, the rear shaft merely supports the inner end of the rotor in its bearing to maintain concentricity with its housing. The end of this shaft was threaded for a puller since after assembly it and its bearing must be pulled before the rotor can be disassembled.
Both completed rotor assemblies spun freely in their housings with no detectable rubbing. Except for the stationary coil-side contact, the high voltage portions of the distributors should now be completed. A potential problem with the distributor's basic design, though, is created by its tightly enclosed rotor. Ozone will be continually produced by the arc at the rotor's air gap, and if not adequately vented it can fill the space between the rotor and its housing after only a brief period of operation. If the ozone is allowed to build up in this space it will ionize and crossfires to unwanted tower electrodes can occur due to the lower plug firing voltage requirements of the cylinders that are not under compression. An unshielded/unprotected Hall device inside the distributor can also be affected. These gas discharges typically have a softer appearance but are only visible through a transparent distributor cap. It this does become an issue for me the discharges may be visible through the thin white Delrin wall of the rotor housing if tested in a room with subdued lighting.
The next step is to add the low voltage triggering mechanisms so the high voltage sections can be tested. - Terry


----------



## RonC9876

Terry: Most excellent work as usual. I read with interest your statements concerning the ionization of ozone gasses being produced inside of a distributor and it being the cause of possible cross-firing. I had never given this any thought and have never experienced a problem that I am aware of on any of my many engines. Maybe that's because most of my designs are not machined to the precision you are so capable of and plenty of ventilation takes place? Makes perfect sense that this would occur and could be a source of trouble. Very interesting and something else to consider with a poorly performing engine. Thanks for enlightening an old friend. Ron Colonna


----------



## mayhugh1

Ron,
You're very welcome. If you're a GM nut (I'm not) you might remember they had to ventilate even the huge distributor caps they used for their HEI ignitions back in the 70's. Terry


----------



## dsage

Hmm. Thanks for pointing that out Terry. It might explain some of the issues I have with the Howell V8 ignition. I made the (relatively small) distributor cap with a pretty tight fit over the base plate. Since it needs work anyway for other reasons I'll keep the vent idea in mind.
 I also picked up on your earlier comment about the black delrin not being as good an insulator (as the white). Another item to consider.

I have an HEI ignition on my old Corvette. How did they ventilate it. When they went to HEI there was no longer the sloppy slide up side plate to adjust the points. Which would have been a good leak for fresh air in the old distributors.

Thanks

Sage


----------



## mayhugh1

Dave,
The one HEI distributor I had experience with had an opening in the base of the distributor housing. There was a wire mesh over it, probably to keep out insects. Lots of drag racers who added high energy after market ignitions drilled a hole or two in the tops of their caps. Many for whom this solved problems thought they were venting carbon dust, but it was really ozone they were venting. Some Ford street racers created issues when they added after-market ignition systems and after market distributor caps because of their typical smaller sizes and smaller internal volumes. Drilling vent holes in the distributor caps on street cars with stock ignitions wasn't a good idea because of possible condensation problems during start-up. Most of my experience was with Ford engines, and I never understood why some of the hot rod parts manufacturers, (MSD, for example, if I remember correctly) made their caps smaller with smaller volumes. It might have been for larger aftermarket air cleaner clearance since the Ford engines had front mounted distributors. Of course, the time frame I'm talking about was during the 60's and 70's. Today, with COP, ozone inside a distributor is no longer an issue and a good thing, too, with the extremely high energy ignitions used today. - Terry


----------



## Ken I

Terry,
        A while ago I built a "mad scientist" Jacob's ladder for my grandson - one of those things where an arc propels itself upward between two electrodes - blows itself out at the top and starts again at the bottom.

What came as a surprise was that it generated copious amounts of Ozone, Nitric Oxide and Nitric Acid - the whole thing was built in a perspex tube (for Safety) - the atmosphere inside rapidly turned brown (Nitric Acid and Nitric Oxide gas).

When I was fooling around with the exposed electrodes at the prototype stage you could smell it and it rapidly became unbearable / downright dangerous and everything in the vicinity rusted.

So now I only run it outside on Halloween (it has a ventilating fan) or flush it with Argon if I want to run it indoors (without the fan)..

I would imagine an H.T. ignition is going to do much the same thing on a smaller scale because of the very short arc length.

Just a thought.

Regards,
             Ken


----------



## mayhugh1

Ken,
That corrosion you saw was also an anomaly seen inside a lot of after market high energy distributors by irate street racers who thought the 'high performance' distributor caps weren't sealing properly and allowing moisture to rust the internals. After a few thousand miles some distributor baseplates looked like they had been sitting open to the weather in a junkyard for a decade. The manufacturers told them to drill holes in the tops of their caps, but this sounded so counterintuitive that many ignored the device and went on to a different manufacturer's system. In fairness to the racers, the manufacturers were late in figuring out what was really going on because they hadn't properly tested the longitivtiy of their equipment for the street market that they were going after. Most users would have been much better off to have stuck with the OEM equipment. - Terry


----------



## mayhugh1

The trigger components for the distributor are located on the distributor driveshaft below the rotor. The distributor driveshafts are driven by the crankshaft through Oldham couplers on either side of the wheel case. Since the triggers are magnetic, the driveshafts were machined from aluminum to avoid influencing the magnetic fields at the Hall sensors mounted near their ends.

The trigger disks in the distributors of the three engines that I've previously built have all used multiple magnets mounted on nonferrous disks rotating in front of single Hall sensors. The sensors were located inside the housings of the distributors but were protected from ionized discharges by spark shields covering them. All three distributors worked reliably, and the only ignition-related issue I ever encountered was with the Howell V-4 distributor whose neodymium magnets slowly weakened over time and reduced the dwell for its transistorized ignition. The magnets' loss of strength was most likely a result of the extremely close proximity of the opposing fields of the distributor's irregularly placed magnet pairs.

The Merlin's magneto housing has room only for a tiny trigger disk, and so multiple magnets weren't an option. Instead, the Quarter Scale uses a single stationary magnet with a ferrous disk rotating between it and the sensor. A pair of holes drilled through the disk exposes the magnet to the sensor as it rotates. As a bonus, the sensor ends up mounted outside the rotor housing and safely away from the thunderstorm at the tip of the rotor.

The trigger disk is driven at 1-1/2 times the speed of the crankshaft, but a gear on the driveshaft drives the rotor at half the speed of the crankshaft. The phasing of the rotor with respect to the crankshaft is easily adjusted thanks to a pair of spacers that grip the drive gear after the assembly is tightened together by a bolt on the end of the driveshaft. Previously drilled index holes in the rotor and rotor housing align when the rotor points to tower electrode number one, and the rotor can be temporarily pinned in this position during alignment. The trigger disk is simultaneously gripped by the same spacers, and this allows the timing of plug number one's firing to also be adjusted.
The ideal material for this type of trigger disk has a high magnetic permeability so it will easily conduct and shunt the flux of the source magnet away from the sensor when the trigger is OFF. It also has a low remanence which means that over time it will acquire little magnetism of its own from the nearby source magnet since this would change the threshold of the sensor. Silicon or 'magnetic' steel is best used in these applications and is found in the laminated cores of transformers and motors. Magnetic steel is typically laminated for ac applications in order to reduce power losses, but laminating provides little benefit in a dc application. I considered salvaging the steel from an old transformer, but its laminations were too thin, and I didn't want to deal with the extra complexity involved with stacking them. A good second choice would probably have been wrought iron, but it can be gummy to machine, and I didn't have any on hand. My third choice was hot-rolled steel. Quality hot-rolled mild steel typically has half the remanence of cold-rolled steel, and even less remanence than most hardenable alloys. 

The trigger disks in the Merlin's distributors require a pair of diametrically placed aperture holes to handle the two rows of tower electrodes. In order to reduce timing jitter, the holes must be matched and carefully placed. I made my disks by turning a rod to final o.d., plunge-milling the apertures from one end using an end mill, parting off a pair of disks, and then surface grinding their faces. I verified there were no visible asymmetries by stacking the aligned and anti-aligned pair back-to-back under magnification on a snug fitting rod. 

There's probably a good reason why the apertures may appear to be excessively wide to someone who has built a more conventional distributor. Although no ignition details were provided in the documentation, the disk was likely designed to provide dwell for a transistorized ignition. With the disk rotating at 1-1/2 times the speed of the crankshaft instead of at the more familiar half speed of the rotor shaft, the apertures had to be widened accordingly. Since I plan to use CDI modules, the wide apertures probably weren't necessary.

The distributor drawing included a timing adjuster which is a two part Delrin assembly that supports the magnet and sensor while the trigger disk spins between them. Neither a particular magnet nor sensor were specified, but the timing adjuster drawing showed a 1/8" diameter by 1/8" deep flat bottom hole for a magnet. I trial tested an 1/8" long neodymium magnet with an Optek OH090U sensor that I had on hand and found that the sensor would fire through the disk apertures using the .125" magnet/sensor separation shown in the drawing. Details about how a sensor was to be consistently supported in the mount provided was unclear in the drawing. Since I had several Optek sensors on hand, I designed a mount around them with a tight fitting pocket for the sensor and a strain relief for a cable. 

I've standardized on Futaba J male servo connector cables for the sensors in all my engines. These are readily available from RC hobby shops, and I've found the connectors to be reliable and easy to work with. Using a standard connector allows the use of common test fixtures which in the past have helped speed testing and troubleshooting. A minor problem is that the order of the three sensor leads doesn't match the order of the color-coded wires in the Futaba 3-wire flat cable. When soldering a sensor to the cable, one of the leads has to cross over the other two, and so I included a milled trough in the sensor mount to allow this to be cleanly done. After soldering the cable to the sensor in its mount, a few drops of silicone windshield sealer stabilizes and insulates the connections. A cover bears down on the wired assembly inside the sensor mount and the pair are held together with the two mounting screws and a short length of shrink tubing on the adjuster arm.

After machining the first part of the timing adjuster assembly according to the drawing, I discovered a significant interference between it and the magneto housing. I modified its fit for use in testing but changed the design before machining the final parts. The test part ended up being put to good use, though.

With all the parts for the timing adjusters finally completed, I assembled the first set to check its functionality but without high voltage. The sensor fired through the aperture holes but would not turn off. The sensor's hysteresis combined with the huge flux level flowing through the wide apertures and around the edge of the disk prevented the sensor from turning OFF. The OH090U sensor is the most sensitive part in an Optek Hall sensor line which also includes the OH180U and OH360U. (The number in the part number is actually the typical flux density, in Gauss, required to turn the sensor ON.) 
A shorter 1/10" long magnet gave about the same result, and an even shorter 1/16" long magnet appeared to work but with little margin. I decided to machine a new set of thicker sensor mounts so I could experimentally reduce their thicknesses and find an optimum magnet-sensor separation. After some testing I found that .175" was near optimum using the 1/10" long magnet and the OH090U sensor, and so the whole batch of new mounts were modified accordingly.

During final engine assembly when the rotor and timing disk are initially phased to the crankshaft and locked into position with the spacers, the timing can be adjusted over a limited range by rotating the arm of the sensor mount. The adjuster rotates the magnet/sensor pair with respect to the timing disk apertures causing the plug firing angle to change. After adjustment, it's locked in place with its own screw. The adjustment range is ultimately limited by the widths of the rotor and tower electrodes. It's important for a portion of the rotor electrode to remain overlapped with the corresponding tower electrode over the entire usable range. For the electrode and rotor diameters used, the available timing range works out to a maximum of +/-9 distributor degrees or +/-18 crankshaft degrees around the electrodes' center. Since timing changes are made with respect to the trigger disk which rotates 1.5 times faster than the crankshaft, one degree of crankshaft timing change will require 1.5 degrees of timing adjuster rotation. The total adjustment range of the arm is 38 degrees. - Terry


----------



## kylenlord

Hi Terry,

I'd like to echo everyone else saying that your 12
Cyl build is just unreal, something to aspire to. Your radial builds as well I'll be referring to when I start on the Hodgson 14 cyl. 

I have a small request though, can you put spaces into your threads? I struggle to keep my place reading your post.
There's a ton of great information, a lot Im still learning too so I'm trying to take it all in.

Either way keep it up, I love seeing the progress you make.

Kyle


----------



## mayhugh1

Kyle,
I agree with you about the spaces. I actually do use them but somewhere in my process they seem to get removed. I normally compose the text on my ipad and then email it to my Windows machine from where it's uploaded. Somewhere along the way the spaces are removed. I just tried to edit my last post and add the spaces back in after the upload and that worked. I'll try to remember to do the same in the future. Glad it's been useful to you. - Terry


----------



## dsage

Terry:
 It's not your fault. There is something fundamentally wrong with entering text on this (and most) forums. For instance if you try to use a Tab to indent text - like at the beginning of a paragraph - your cursor disappears outside the text box ending the editing session. There seems to be no way to start a new paragraph with an indent. Nor can you simulate a tab by entering a few spaces. More than one space in a row gets reduced to a single space. For instance:
                                   This is a new paragraph I simulated with a carriage return and a large number of spaces at the beginning, yet you can see the spaces have disappeared before the word "THIS" as soon as I saved the message. Also I tried to enter a bunch of spaces in the middle of the line here         between the dashes -                                - and they disappear leaving only one space when the message is posted. Even if I go back and edit the message the spaces are missing and putting them back does not help.


This line started with three carriage returns so that seems to work. So you may be able to space your paragraphs by using a couple of  returns. That would help greatly.
It's all very frustrating and I wish someone would fix it because (like me) I know you try to make your posts clear and understandable and text formatting is very important to that end.

Thanks for all your work. It's amazing to follow along.

Sage


----------



## kylenlord

Great Terry, thank you. I do most of my engine browsing on the phone though it looked the same on the laptop.
Keep it up I'm looking forward to more updates. 

Kyle


----------



## dsage

Terry et. al.

I subscribe to the daily digest for this forum i.e I receive a single email with all of the posts for the day, and I just noticed that the spaces that I entered in my post while I was directly on the forum DO show up in the email version. Even though they are NOT on forum post. So it's even more screwed up than I thought.

Sage


----------



## mayhugh1

Since I had machined five sets of mounts and covers and still had plenty Optek sensors left over, I thought I'd make up three more cabled assemblies for spares while the 'art' portion of their construction was still fresh in my mind. To my surprise and disappointment the next three assemblies all had issues with the sensors turning OFF. When I rechecked the first two, I found the one containing the sensor around which the mounts had been optimized was still working reliably in both distributors. A closer look at the second assembly, though, showed it might have been only marginally turning OFF in one of the two distributors.

This is really my first experience with this particular Hall device. The ones I've used in my other engines have long been discontinued, and I'm saving what remaining stock I have of them for replacements. I purchased the Optek parts a couple years ago after reading another builder's comments about his experience with their ruggedness. He claimed to have seen accidental discharges to the sensor's ground lead with no ill effect to the part. This wasn't something I would have necessarily expected the part to survive, and so I ordered a dozen pieces for future projects. And now, here we are.

The Optek data sheet actually warns about potential turn-OFF issues with the OH090U. The 'turn-on' flux densities in Gauss are specified as 0(min), 90(typ), and 180(max). The 'turn-off' densities are listed as -100(min), 65(typ), and 100(max). Turn-off levels which are roughly half the turn-on levels as listed for the typical and maximum specs are reasonable behaviors to design around. The minimum specs aren't at all reasonable, and I originally dismissed them as unlikely anomalies that were probably so many standard deviations away from typical behavior that they would never be seen. After all, the OH090U is sold as a non-latching unipolar device, but the minimum numbers seem to imply that the field may actually have to be reversed in order to turn some sensors OFF. 

Still hoping the sensor's internal hysteresis would be proportional to the level of flux that actually turns it ON, I machined two new sets of trigger disks with smaller apertures to reduce the strength of the field applied to the device. I reduced the aperture diameters from the original .187" down to .156" and then again to .125". The disappointing results were basically that the sensors now had difficulty in turning ON as well as turning OFF. I also machined a thicker disk to make sure that saturation wasn't the issue.

Finally, I made up a fixture to carefully compare the turn-on and turn-off distances between a test magnet and the sensors in each of my five mounted assemblies but without a disk between them. The turn-on distances were very similar, but the turn-off distances varied an unacceptable factor of 2.5 among the sensors in my tiny sample size. At this point I had to conclude that either a reputable distributor had sold me floor sweepings, or this particular sensor was not designed to provide the consistency I was looking for.

Many of the specs for the Infineon TLE4905 are similar to those of the Optek device, and its data sheet lists minimums and maximums but no typicals. The turn-on flux densities converted to Gauss are listed as 70(min), and 180(max), and the turn-off densities are 50(min), and 160(max). The lack of a typical spec implies the parts probably come out of manufacturing uniformly distributed between the two extremes, and this is likely the case for the Optek parts as well. These ON/OFF ratios are very attractive for a trigger disk, and I eventually ordered the 4905's to replace the OH090U's. One of the reasons for selecting this particular part from a bewildering number of available possibilities was that its package width is similar to that of the Optek part, and so I could reuse my mounts. I had to shave off another .010", however, in order to optimize them for the new parts. I didn't modify the one Optek assembly that continues to work well with both distributors, but the sensors in the other four assemblies were all replaced. All four assemblies finally worked as expected. My distance measurements for the new assemblies showed the turn-on and turn-off distances to all be tightly clustered around similar values, and so hopefully the sensor stuff is finally behind me.

With some fifty fairly unforgiving machined parts plus the shafts, bearings, and gears, each of these distributors has ended up requiring as much effort as an entire single cylinder engine. Instead of a pair of running engines, though, so far I only have a pair of blinking LED's to show for more than a month's work. And since I have to manually spin their shafts to get the LED's to flash, my wife isn't very impressed. I think the end is in sight, but I still have three sets of housing covers to design and machine before I can finally check the distributors' operation under high voltage.

Both distributors are located at the rear of the engine behind the exhausts. This means the electrically sensitive portions of the distributors should be shielded from the oil, water, and gasoline they'll likely see during cold start-ups. The full-size Merlin's magnetos had the advantage of not being vulnerable to start-up grunge since the exhaust tips were located outside the plane's engine compartment. The Quarter Scale's distributors have an advantage of their own, though, they're not vulnerable to enemy gunfire.

The easiest covers to make were the ones shielding the timing adjusters. It seems like a shame to cover up all the painstakingly machined hardware associated with the trigger disks and sensors, but hiding the neat stuff has become common practice in this build. Other than some intricate profiling to clear the components of the timing adjuster, the machining of these black Delrin covers was fairly straightforward. Hex nuts secure them to a pair of 1-72 studs threaded into the adjusters.

The covers for the ends of the rotor housings were more complex because they contain and protect the critical high voltage coil connections to the spinning rotors. To make things more interesting, I machined the exteriors of the covers from black Delrin for appearance sake, but the interiors surrounding the contacts were machined from white Delrin for its better dielectric properties. Before machining the covers I made up their workpieces by pressing a pair of tight-fitting white Delrin inserts into the black Delrin blanks. The shapes of the covers' peripheries complicated their work-holding in the lathe, and so I machined an expandable mandrel to grip the shallow interior of its end. The Delrin's slipperiness greatly limited the depth of cut. For the rotor button, I decided on a spring-loaded phosphor bronze contact instead of the carbon button I had been considering in order to avoid carbon dust inside the relatively small volume of the cover.

The last pair of covers will be the most complex of the three. They will be designed to replace the contact block cover castings in order to provide a more elegant exit for the plug wires. I plan to design them to be similar to the magneto covers used on one of the versions of the full-scale Merlin. - Terry


----------



## dsage

Hi Terry:

I think you made the right move to steer away from the Optek sensors. Who knows how their already variable specs might have changed with time and temperature etc getting you in trouble. I too have many of these sensors but they are triggered by spinning magnets. It might be interesting for me to have a look on a scope to see how the dwell time is varying with each magnet as it passes.
  Thanks for the heads up. I'll order some of the Infineon sensors for future consideration. Keep us posted on their operation.

Thanks

Sage


----------



## apointofview

Terry,
I have been amazed at your work and want to thank you for taking the time to document all of this for everyone to enjoy !!

I am late with this suggestion but maybe future designs could use this or maybe not...  Have you ever looked into an optical sensor.  I ran one in a nitro r/c helicopter that sees crankshaft speeds in the neighborhood of 17000 rpm.  This sensor - http://www.digikey.com/catalog/en/p...opb703wz-opb704wz-opb705wz-and-opb70awz/17829   -  was triggered by reflections from a very small piece of aluminum tape on a black clutch bell and it gave rpm feedback to a governor that maintained rpm as the load of the rotor changed.  It supplies its own light and was very reliable.

Pete


----------



## mayhugh1

Pete,
Back in the early 70's I designed a capacitive discharge ignition for my brand new 6-cylinder Ford Maverick. To trigger it, I made up an optical sensor assembly using a six hole metal disk that slid down over the distributor's cam and interrupted a light beam between an led and a photosensor that were attached to the distributor's advance plate. I temperature tested the electronics to 125C in my employer's environmental chamber during the evenings, because at the time we lived in the middle of the Mohave Desert in California and trek'd across it nearly every weekend. I wasn't trying to solve any particular problem except maybe to avoid adjusting points, but in those days if it wasn't broke I fixed it anyway. Although I kept the original parts in the glovebox as a back-up, the system worked flawlessly for over three years until we left the desert to move east. During our cross-country drive I spent about an hour one evening somewhere along Route 66 in New Mexico, with my wife holding a flashlight in one hand and and a baby in her other arm, putting the points back in so we could be on our way. That experience helped me to appreciate the auto industry's move to the much more reliable variable reluctor. - Terry


----------



## mayhugh1

The distributors have top covers that protect the high voltage plug wire connections to the contact blocks. The covers I received were most likely early castings designed for the original Quarter Scale distributors that used a single row contact block. In addition to the plug wires, the coil connections to these first generation distributors, as well as the battery connections to the full-scale magnetos, were also under these covers. A pair of sketchy holes had to be drilled in the sides of the Quarter Scale's covers to provide exits for the wires. I found an online photo of the completed covers on Gunnar's engine that shows what had to be done. Similar covers used on some of the full-size Merlins included integrally cast conduits that were angled inward for the wires. Space at the fronts of the full-scale magnetos was limited, and several versions of the housings appeared over time to accommodate engine design changes as well as differences among the various Merlin models.

When the Quarter Scale's distributors were redesigned for a double-row contact block, the coil connections were moved under their own covers at the ends of the rotor housings. The top covers were redesigned with more elegant front elbow exits for the plug wires. A photo of John Ramm's engine shows an example of these later castings. They aren't much different from the magneto covers found on some of the later versions of the Merlin.

I liked the looks and functionality of the later covers much more than the castings I received, and so I designed a pair of replacements. My particular castings were usable although the 20kV wires I wanted to use overfilled them. Since the covers would end up prominently mounted at the top of the engine I really wanted a tidier solution for the wire exits. My goal was to design a set of covers that were similar to those on the late model Merlins and with a little more interior volume for the 1/8" diameter plug wires and retaining collets I was using. The space available for a front conduit is limited even more so in the Quarter Scale than it was in the full-size engines because of the addition of the timing chain cover.

I spent a few days with SolidWorks designing and printing out actual size cross-sectional patterns as a cover design slowly evolved. Since I didn't have CAD models for any of the castings, I tested my paper models against a temporary assembly of the engine's potentially interfering parts so I could estimate the clearances. The timing chain cover was the most difficult obstacle to deal with, and the magneto cover was essentially designed around it.

I initially considered splitting the cover design lengthwise and machining it in black ABS as two halves to be glued together. This would have made it possible to use a cylindrical conduit to completely enclose the exiting wires. Although not a 'must have', I was hoping to be able to install and remove the covers from the installed distributors with the timing chain cover installed, and such a conduit would have made this very difficult. The design eventually evolved into one with a three-sided exit trough that I hoped would simplify maneuvering the covers into and out of place. The open rear allowed the covers to be machined from single blocks of aluminum without compromising the shielding of the contact block from the start-up grunge.

I was able to machine each cover in just two set-ups despite all the filleting added to make them look like castings. The total machining time on my Tormach was about three hours per cover and, when finished, their shiny surfaces were bead blasted to try to match the surface texture of the castings. The color match isn't very good, but they may end up later painted black. The resulting minimum clearance to the timing chain cover tubes came out to only .020" which was half of what I had estimated from my paper pattern checks. Another close feature was the final internal volume. The six collet'd 1/8" diameter 20kV wires fit under the covers, but they have to be carefully laid out. In the end it wasn't possible to remove or install the covers on the already installed distributors after the timing chain cover was installed. The 20kV wires drove the minimum dimensions of the trough, and the final result was just too close to the timing chain cover. This only means the wires and covers will have to be installed on the distributors before the distributor is installed on the engine. Both covers were checked on both distributors, and so hopefully there won't be any unpleasant surprises during final assembly. - Terry


----------



## apointofview

Thanks Terry that explains why your not using an optical setup really well, once something bites you its hard to consider using it again. Mad Dog 20/20 comes to mind for me 
Pete


----------



## nel2lar

Terry
I just run on to your build and what a job, very nice. I am sure you are satisfied as you advance closer to completion. 
Very very sweet
Nelson


----------



## mayhugh1

With the distributors completed (I hope), I could finally check their operation under high voltage. I inserted six lengths of 20 kV plug wire into the contact block on the starboard distributor using the retaining collets made earlier. A shop-made insertion tool helped with the collet installations in the limited area at the top of the assembled distributor. My custom machined covers have an internal shoulder that wiil bear down slightly against the tops of the collets for back-up retention against engine vibration, and so it's now important that the collets be fully inserted.

Temporary terminals were soldered on the other ends of the wires for connections to the CM-6 spark plugs that I chose for testing instead of the more expensive Mini Viper plugs that will actually be used in the engine. I expected the CM-6's wider gaps would make a better worst-case test, but mainly I didn't want to risk damaging the Vipers or deforming their washers in my test fixture. I practiced synchronizing the rotor and trigger disk to a couple arbitrary crankshaft positions. A pin in the rotor index hole proved invaluable for locating and securing the position of the rotor so the trigger wheel shaft screw could be tightened.

Although it's much too early to attempt valve adjustments, I thought I would make up a degree wheel to verify the limits of the timing adjuster and to check the consistency of the edges of the sensor signals. Since I had some earlier difficulties with the sensors, and any aperture machining errors could create timing inconsistencies, I wanted to make sure the static timing jitter was acceptable before moving on with the rest of the build. I have the option of adding custom circuitry between the Hall sensor and the CDI module, and so I'm free to use the sensor's most consistent signal edge to fire the plugs.

When I started work on the degree wheel I found I had been thrown a curve that I hadn't seen coming. The only available shaft for mounting a degree wheel during final assembly will be the prop shaft. Gear reduction is used between the crankshaft and the prop shaft in the Quarter Scale and its ratio is a "closer to scale" 48:21. This screwy ratio required the 720 degree crankshaft cycle to be mapped into just 315 degrees of the degree wheel. Because the ratio isn't a nice integral number like 2:1, there was also a 45 degree gap in the wheel that's equivalent to just under 103 crankshaft degrees. If I had realized this little surprise was on the horizon, I might have considered altering the ratio to at least reduce the gap. Unfortunately, that train left the station a long time ago. The biggest issue with the wheel turned out to be wrapping my head around its construction. It wasn't all that difficult to use once I made my peace with its limitations and gained some experience using it

A cam timing diagram mapped onto a geared-down degree wheel can be easier to read, but the loss in resolution will limit the accuracy of the valve adjustments. The referenced piston's TDC will remain synch'd to the degree wheel only during the revolution on which the two were initially referenced. This needs to be kept in mind to avoid some serious head scratching later. I made a second diagram without the valve information for the opposite face of the wheel to use for checking the timing. The wheel gap causes the firing edge measurements to slip some 17 crankshaft degrees per each complete wheel revolution, and so this is another landmine that's best stepped around.

At the end of the day, the sensor's turn-OFF edges appeared to be consistent and spot on with respect to one another within the two degree measurement resolution I probably had to work with. After completing the measurements, I chose to turn the sensor's led indicator ON when the trigger disk aperture exposes the sensor to the magnet and to trigger the CDI on the opposite edge when the led turns OFF. This is the same convention used on my two radials, and it mimics the old Kettering systems where the led ON time is a mock dwell. I verified the timing adjuster was capable of advancing the timing a maximum of 18 crankshaft degrees beyond its initial setting and the plugs continued to consistently fire at this maximum advance.

For testing, I used a fixture made during my last radial build. In addition to an led driver it contains an old style S/S Engineering CDI module. The starboard distributor worked as expected, and the plugs fired in their 1-4-2-6-3-5 order while the prop was manually rotated in its normal running direction. Similar tests with similar results were obtained on the port side distributor. Before moving on to the cylinder liners, the next step will be to construct and test the actual ignition modules that will be used to run the engine. - Terry


----------



## mayhugh1

For the Merlin's ignitions I re-used some of the previous development work from my 18-cylinder radial build. The CDI modules used on that engine were older generation units previously sold by Roy Sholl. These particular units had been modified by Roy to have a half-size discharge capacitor in order to obtain an output of 30k sparks/minute. The Merlin uses the same CDI's, but without the capacitor modification. Since each Merlin ignition will be responsible for only six cylinders running at a maximum 3600 crankshaft rpm, the unmodified units should easily support the Quarter Scale's 11k sparks/minute requirement. Theoretically, going back to the original capacitor should allow these CDI's to output twice the energy per plug compared with the modified units. The additional plug current that will be available should help mitigate the Vipers' tiny plug gaps (.009" vs. .018" for the CM-6's). Although smaller gaps can offer some advantage in a rich-running cylinder, they are more susceptible to oil fouling.

Each ignition includes a small circuit board of my own design. Basically, it's just an LED driver that provides an indication of the Hall sensor's output state without the need to power up the CDI. A 'Mag' toggle switch on this board allows the engine to be timed using the Hall sensor without having to worry about generating unintentional and potentially damaging sparks. Both of my radial ignitions included a similar PCB, but after the boards were designed and populated I decided to add a pair of transient protectors across the Hall sensor inputs. These large components had to be kludged into the radial's ignition enclosures, and the results weren't pretty. I re-did the layout of the circuit boards for the Merlin ignitions and increased their size in order to accommodate the transient protectors.

The circuit boards were designed in SolidWorks, and the single-sided copper layer was milled on my Tormach using a 1/16" diameter end mill in a 3x spindle multiplier. The .030" diameter holes were drilled using an eBay circuit board drill. Fabricating a simple board in this manner is reasonable and fairly quick, but laying one out in a general purpose CAD program like SolidWorks was a long and frustrating experience. After designing the original board for the radial I didn't think I'd ever do another one in that way, but I ended up spending several more hours on it adding those two extra components.

The enclosures I designed for the radial had to be increased in size to accommodate the new circuit boards. The Merlin's enclosures were machined from a block of gray PVC that I had acquired long ago. I'd never before milled PVC in my shop, and I ended up learning a 'shocking' lesson while working with it. Sometimes when machining plastic or wood on my Tormach, I'll occasionally vacuum up some of the chips with my Shop-Vac while the machine is working. Instead of flood coolant I use a Micro-drop system, and its compressed air spray can churn up the lightweight chips and blow them everywhere. This began to get out of hand during the machining of the enclosures after a thick layer of PVC chips had accumulated over the vise and much of the table. A few seconds after beginning to vacuum up the chips, a one inch stinging arc jumped between the vise and my hand that was holding the Shop-Vac hose. This was pretty surprising since the humidity here in central Texas has been insufferable during the past month. Mach 3 went off into the weeds and took the machine's work offsets with it. I was able to recover the workpiece, but I put the Shop-Vac away and finished up using a chip brush. I'd run a static drain wire down though the Shop-Vac's hose if it weren't for the fact that it has to frequently come off so I can clear metal chip blockages at the entrance to the main canister. I've used this Shop-Vac on large black Delrin machining jobs in the past with no issues, and so this experience might be evidence of (black) Delrin's inferior dielectric properties compared with PVC.

The rear face of each enclosure includes a machined boss into which a short Futaba J female connectorized cable was epoxied. This connector mates with the male sensor cable from the distributor so the sensor can be powered up and its signal brought inside the ignition module. A short piece of shrink-fit tubing will be used to form a slip-fit cover over the junction between the two connectors in order to protect the electrical interface from the exhaust. The Mag switch protrudes through the lid of each enclosure along with a pair of LED indicators. An amber LED indicates the output state of the sensor, and the red LED warns that the 'mag' is alive. The red indicator and its dropping resistor are actually soldered to a tiny breadboard area available in one of the corners of the CDI. There's actually a pair of amber LED's so the state of the sensor can be seen from either side of the panel on which the enclosure will be mounted. I had a bit of fun with the design of the enclosure's lid and machined it to look like a finned heat sink.

The center conductors of the coil output leads were soldered to some mysterious phosphor bronze spring terminals that were in my electronic scrap collection. I made up the coil boots by supergluing a short length of 1/8" rubber tubing to the end of a 3/8" automotive vacuum plug.

After the ignition modules were completed, I used them to replace the previous distributor test set so they could be tested with the distributors and the CM-6 plugs. There was a noticeable increase in the intensity of the sparks in the plug gaps which was probably due to the higher energy output of the unmodified CDI modules. (The CDI in the distributor test set contained the half-size capacitor.) During one of my tests I became careless and forgot to connect the ignition module's engine ground to the return on the spark plug fixture and quickly blew out the sensor. Not connecting the high voltage return is, of course, a major no-no. But, I was really disappointed to learn that the transient protectors that had taken so much time and effort to add evidently don't protect the sensors after all. - Terry


----------



## 10K Pete

What can I say but... WOW! Really great work.

Pete


----------



## JaamieG

Superb work!


----------



## Ken I

You surge protectors are only going to arrest the HT after it has passed through the sensor (or its wiring).

Murphy's law is never on your side.

A delicate transistor protected by a fast blowing fuse invariably becomes a fuse protected by fast blowing transistor.

Epic build and thread.

Regards
           Ken


----------



## mayhugh1

The next step in this build was to finalize the design of the cylinder liners so the designs for the connecting rods and pistons could also be finalized. These are the last major components to be machined, and the interactions among them have to be carefully checked. This particular step wasn't one of my favorites because it involved sitting in front of a computer for the last week instead of making parts and progress in my shop. But it was an important step, and for anyone with a set of these castings it may save a lot of headaches and re-work later on. I've been told by Richard Maheu that there are between 50 and 100 sets of his castings out here somewhere.

The Quarter Scale's stock liners are probably faithfully scaled replicas from the full-size Merlin's top end and, of the parts remaining to be machined, these will likely be the most difficult. In addition to the features required to seal the combustion chambers and the coolant jackets around them, the stock slip-fit liners have a worrisome wall thickness of only .035". The Quarter Scale's stock bore is 1.35", and with a stroke of 1.5" the total displacement is nearly 26 cubic inches.

My concern with the Merlin's thin wall slip-in liners arises from my experience with the cast iron liners in the Howell V-4 which was my second engine build. Finishing the i.d.'s of its 1/16" liners to within two to three tenths of being truly circular for a proper fit to its cast iron rings ended up being much more difficult than I had expected. All the machining and finishing had to be done outside the engine block since the liners weren't pressed into place but were supported with o-rings. Not only were the machining steps and their order important, but work-holding was especially critical to prevent workpiece distortion during both machining and honing. Material selection was also important not only from a functional perspective but also for dimensional stability during and after machining. I machined liners from three different lots of cast iron before I finally had four acceptable parts. I'm sure that being a newbie had a lot to do with my problems, but the larger physical size of the Merlin's liners makes their thinner walls scary even with the experience I've accumulated since my Howell days. For this engine, I'm going to need to end up with at least a dozen usable parts.

In addition to wall thickness, there are other reasons to re-consider the design of the stock liners. Poor statistics are available on the Quarter Scale's ability to run without overheating, and John Ramm may be the only builder to have accomplished this. The stock cylinder design provides for less than a teaspoon of coolant around each cylinder, and the lack of space between bores prevents any enlargement of the jackets inside the cylinder blocks. The only way to increase the volume of coolant around the liners is to reduce their diameter, and this will also reduce the engine's displacement.

The liners also affect the static compression ratio. If the Quarter Scale's c.r. is calculated using the typical simplified model of a stock piston sitting at TDC in a cylindrical combustion chamber, the result is 7.9 compared with 6 for the full-scale Merlin. I did a closer calculation using measurements on my completed heads to account for volume reductions created by the valve heads and coolant tunnels that protrude into the combustion chambers. The result was a whopping 9.7.

High compression ratios create needless problems in multi-cylinder four stroke model engines intended to run as displays. High cylinder pressures aggravate marginal cooling systems, and they increase starting torque requirements. Starting torque is a particular concern in the Quarter Scale because of its unproven electrical starting system. John's last video,
http://www.homemodelenginemachinist.com/showthread.php?t=25754, shows him hand starting his engine because of starting system difficulties that arose from increased cylinder pressures after the rings and valves bedded in.

Finally, measurements made on my engine's completed head assemblies show that it is currently within .005" of becoming an interference engine if completed using the stock rods and pistons. Although not fatal, while doing engine timing adjustments the fully open valves will come very close to extending into the space in which the pistons move.

All these potential issues are a result of the interactions among the designs of the liners, rods, and pistons as well as an accumulation of the machining tolerances of many, many already machined parts. The liner design can be adjusted to compensate for all these issues, but changes to the liners will likely introduce clearance issues between them and the connecting rods. A reliable method for verifying the clearances between the rods and the stationary parts of the engine is needed before making any rod design changes. Rod clearance issues typically don't occur at TDC or BDC which are easy positions to sketch on paper. In order to continuously visualize what will be going on during an entire crankshaft revolution, a CAD assembly model was used. A partial SolidWorks assembly was created that included a pair of cylinders, liners, heads, pistons, rods, and the crankshaft. The virtual crankshaft was rotated in order to spot clearance issues throughout the entire range of complex motions of both the blade and fork rods. Simple models for the heads, cylinder blocks, and crankcase were created using actual measurements taken from my already machined castings. Since I already had a full model of the crankshaft, I had only to create additional full models for the as yet un-machined rods, pistons, and liners. 

The first issue revealed by the modeling was a minimum clearance of only .005" between the stock rods and the bottom edges of the stock liners during their closest approach. This insured that any reduction in the liner i.d. would definitely require a change to the stock rod design. I've included a few cross-sectional CAD snapshots taken showing the stock rods and pistons in a few locations of interest inside the stock liners. 

I began design changes on the CAD assembly model by shortening the pistons by .023" above their wrist pins in order to increase their clearances to the fully opened valves at TDC. This also had the effect of dropping the compression ratio from 9.7 to 8.6. The i.d.'s and o.d.'s of the liners were then reduced in order to increase the liners' wall thickness and the coolant volumes around them. The i.d. reduction was limited by the additional loss in compression ratio that I was willing to accept. After several iterations, I arrived at a new i.d. of 1.2" down from 1.35" and a new o.d. of 1.35" down from 1.42". This change increased the liner wall thickness from .035" to .075", and the coolant jacket volume by 80%. The new wall thickness was still a bit less than I had been hoping for, but the compression ratio had decreased to 6.2, and I wasn't willing to reduce it any further. This change resulted in the engine's displacement dropping from 27 c.i. to just over 21 c.i..

As expected, the liner i.d. reduction created an interference between the bottom edges of the liners and the stock connecting rods. Before modifying the rods, the liners were shortened by .075" which brought their bottom ends flush with the interior surfaces of the crankcase. I also added a 60 degree chamfer to the inside edge of the liners' lower ends in order to ease assembly with the ringed pistons later during final assembly. In addition to reducing the diameter of the pistons to fit the new liners, they were also shortened by .075" to match the new liners at BDC. The rods were finally modified to eliminate the interference that was created by the changes, and the minimum clearance ended up at .060" compared with .005" for the stock configuration. Removing the rod material weakened them slightly, but the mass removed from the pistons as well as the c.r. reduction most likely mitigated all the loss in strength.

Although the reductions in displacement and compression ratio may seem rather harsh, I believe they are now more in line with the expectations for a typical model engine, and hopefully they will improve its run-ability later when/if it runs. - Terry


----------



## mayhugh1

[Your surge protectors are only going to arrest the HT after it has passed through the sensor (or its wiring).

Murphy's law is never on your side.

A delicate transistor protected by a fast blowing fuse invariably becomes a fuse protected by fast blowing transistor.]

Ken,
I think you're correct. I had neglected to take into account the slow speed of the large area transient protectors I selected. I've been thinking about adding some protective spark gaps inside the ignition enclosures which is probably the only real solution. I've thought about doing this during my last few builds but have been hesitant because I really haven't had problems with blowing up Hall sensors, and the gaps will take some time to experimentally set properly so they don't become their own nuissances. - Terry


----------



## petertha

_I machined liners from three different lots of cast iron before I finally had four acceptable parts._

Hi Terry, can you elaborate on this prior experience? You mean different CI grades or suppliers or property variations in the same stick...? What determined non-acceptability? Also I've heard people mention different machining properties within core of a stick vs. near its OD. I never paid much attention if this related to drawn rods vs. stress proof vs. CI. Do you think there is something to this in CI? So what will be your material/source for this build?

Can you elaborate on the sealing aspect. I can understand the O-ring on lower side, but why not anything on upper side (red arrow)? Also, maybe I missed the purpose of the extending ledge on your revision & then O-ring beneath that?


----------



## mayhugh1

Peter,
All the c.i. material used in the V-4 was class 40 cast iron, but it had been purchased at different times from different suppliers and was, in fact, remnants from other projects I had been involved with. I had trouble with the rings sealing on the V-4, and after checking the ring fit of my first set of liners with a light source, I traced the problem to the liners, themselves, which weren't perfectly circular. After discovering that I actually needed to measure the circularity of the liners with a dial bore gage after they were machined instead of just assuming they were perfect, I learned just how difficult it was to not only machine a thin-wall slip-in liner truly circular but also how difficult it was get it to remain so.
The upper stock coolant jacket seal is just a close metal-to metal seal. I have questions about it, myself and am thinking about including an o-ring. The bottom ledge looks a lot wider in comparison to the stock liner because the o.d. of the liner was reduced above it. There is an error in that cross-section drawing, though. The stock ring collar above the o-ring is no longer required, because it was integrated into that ledge. I forgot to remove the collar from the assembly drawing of the redesigned version. I currently plan to use Stress-proof for the liners.
I, too, have had suspicions about that outer layer of metal in a centrifugally-cast c.i. rod. Many use it and purchase a 1" diameter cast iron rod when tbey need to make a one inch diameter part since the rod will typically be another eighth or so larger in diameter. I, myself, machine the outer layer away rather than take a chance on using it. I figure the manufacturer probably doesn't consider it to be of the same quality as the underlying material or he wouldn't be giving it away for 'free'. - Terry


----------



## Ken I

Cast Iron bar stock is frequently spun cast and can have all sorts of spiral graining and residual stresses in it.
Best to rough machine it, heat treat it / normalise - then ideally let it age a bit before final machining.

It can even be a sod to simply drill a straight hole down the centre.

And quality can vary wildly.

Regards,
            Ken


----------



## Charles Lamont

mayhugh1 said:


> All the c.i. material used in the V-4 was class 40 cast iron, but it had been purchased at different times from different suppliers and was, in fact, remnants from other projects I had been involved with. I had trouble with the rings sealing on the V-4, and after checking the ring fit of my first set of liners with a light source, I traced the problem to the liners, themselves, which weren't perfectly circular. After discovering that I actually needed to measure the circularity of the liners with a dial bore gage after they were machined instead of just assuming they were perfect, I learned just how difficult it was to not only machine a thin-wall slip-in liner truly circular but also how difficult it was get it to remain so.



You don't lap the bores?


----------



## mayhugh1

Charles Lamont said:


> You don't lap the bores?



Charles,
At that time on my experience curve I was using abrasive brush hones to hone the bores, but I've since swiched to laps. With the honing, I had problems with the workholding distorting the thin liners while they were being honed. My 5C collets were a major disapointment as supports, and I eventually learned I had to hold them lightly in a gloved hand with the hone in a battery-powered electric drill in the other hand. After I finally got the workholding 'in hand', I then learned about the issues involved with the material settling out days afterward and putting everything back to square one. I've used cast iron only for rings since that experience. On my last engine I heated the ring material up for several hours at 600F before roughing out the rings. I then left the material alone for several days before finishing them. I got pretty good yields on some 80 rings I made on my 18 cylinder radial. I'd have to look back in my notes to be sure, but I seem to recall it was on the order of 80%-90%. 
I'm sure thick wall liners would be less of a problem especially if they could be lapped after being pressed into the block. In my experience, thin-wall slip-in liners are quite a challenge. -Terry


----------



## Parksy

I'm curious as to how thin these liners were that you speak of Terry?


----------



## mayhugh1

Parksy said:


> I'm curious as to how thin these liners were that you speak of Terry?



Parksy,
The V-4 liners were 1/16" thick. The stock Merlin's were 1/32".
Terry


----------



## mayhugh1

With a set of revised drawings, I went back into my shop and began working on the cylinder liners. I decided to start out using 1144 (Stressproof) for the liner material because of its reputation for dimensional stability during and after machining. Even with thicker walls, cast iron still didn't seem like the right material for these particular liners because of their protruding top ends used to seal the combustion chambers. Cast iron in these thin and highly stressed sections could potentially crack when the head assemblies are torqued down to the cylinder blocks. Similar problems, believed to have been created by the rapid temperature changes inside the combustion chambers did actually plague the early full-scale Merlins. The Quarter Scale's liner drawing specifies chrome moly which is similar to the alloy used in the full-size liners. I added it to my short list of alternatives along with 12L14 in case 1144 didn't work out.

My only experience with Stressproof has been with a handful of parts machined for this engine including, of course, its crankshaft. I found it easy to obtain beautiful surface finishes except for a single lathe boring operation that I had briefly tried as a test. Although 1144 is generally considered to be free machining, its machinability is half that of 12L14, and it is 50% harder. Boring bar chatter, which I've always been able to control while machining 12L14 or 303, left me with a concern about using Stressproof for the liners.

Before fully committing to it, I thought I would perform some experiments to see if my equipment and I were capable of obtaining usable surface finishes inside the Merlin's 1.2" diameter by 2.5" deep liner bores. Although the liners will eventually be lapped, I've learned that it's best to begin the lapping process with smooth bores that are within a couple thousandths of their finished diameters. Light imperfections are easily removed, but starting out to lap three or more thousandths from a large number of undersize bores or bores with heavy chatter patterns can be the beginning of a long and messy weekend.

I saw-cut several 1-5/8" diameter Stressproof blanks that I hoped would eventually become liners. These were drilled through at 1-1/8" diameter so I could practice the boring operation on them before taking any to their final diameter. Drilling such large deep through-holes on my 12x36 manual Enco lathe turned into a grueling experience of its own. I used four tailstock drills ranging in size from 1/2" to 1-1/8". I found it best to turn entry chamfers on the blanks for the larger drills in order to cut down the excitement created while trying to get the drills' cutting edges started. There was just no rpm setting that would keep the lathe happy about what it was being forced to do. Running in its back gear at 100 rpm sometimes resulted in severe dig-in's when my tailstock feed rate got a little ahead of the spindle speed. Increasing the spindle speed to a couple hundred rpm without the back gear created bone-chilling chatter until the drill was well inside the blank. Spindle stalling then became a problem due to the lathe's drive belt slipping when, again, the feed rate wasn't just right. Initially, the drilling required about 30 minutes per blank, but it stretched out to some 45 minutes as the drills dulled.

I ended up running tests on four blanks before deciding to continue using 1144. Initial tests showed that my 9x20 CNC lathe was only marginally capable of the required boring operation. I was hoping to use this lathe since I get better repeatability on large lots of parts when I let the computer take my place cranking the hand wheels. I had previously gotten good results while turning smaller diameter 1144 parts on this lathe at 300 SFM. But, once my 5/8" boring bar with its 2-1/2" stick out started to feed into the 1-1/8" bore, I had chatter problems that seemed insolvable. The 9x20 lathes are notorious for rigidity issues associated with their lightweight compound. I wouldn't even have attempted this operation on an unmodified 9x20, but I had long ago replaced my lathe's compound with a huge block of metal. I could dial in any feed rate I wanted, but at this bore diameter the lathe was limited to a minimum SFM of about 100 by the low end torque available from its very expensive Varicon motor and its lack of a back gear. This particular boring operation really needed to be run at a much slower rpm in order to control the chatter. 

My best obtainable surface finish was disappointing and had a very prominent chatter pattern. Similar operations on free machining steels using the same lathe and tooling had always produced much better results. Early in these tests I found it necessary to move away from finishing inserts with chip breakers intended to cut steel and instead used very sharp high rake inserts designed for aluminum. My lathe was just too lightweight to handle the d.o.c.'s required for the steel-cutting inserts on 1144. Using Korloy aluminum cutting inserts, I found I could take d.o.c.'s (dia.) anywhere between .005" and .040". 

I was finally able to get marginally acceptable results by modifying a 3/4" boring bar that had been purchased as part of a set but never used because it was too large for my lathes' tool holders. After grinding down a portion of it so it could be clamped in my 9x20 tool holder, the chatter improved somewhat. The periodic pattern disappeared, but the surface finish still had rather deep ridges that I could feel.

In the midst of all these poor results I needed a sanity check to make sure my recollections of turning this stuff on this lathe hadn't been imagined. Sure enough, I was able to easily turn the 1.625" o.d. of the blanks at 500 SFM using .0025 in/rev and an inexpensive insert designed for finishing steel. The surface finish was a nearly perfect mirror.

So, I moved the modified boring bar to the Enco lathe where I was able to use the lathe's back gear to drop the surface speed down to about 30 SFM. The finish improved enough for me to feel better about continuing with 1144 for the liners. I saw-cut a total of 15 blanks, pre-drilled them, and then finish bored their i.d.'s to 1.200" +0/-.001". The o.d.'s of the blanks in the photos may appear to have also been machined, but this is because I mistakenly ordered the starting material I had been using as 'ground and polished.' The next step will be to prepare an expanding mandrel to grip the bores in the lathe chuck so the features on the o.d.'s can be turned. - Terry


----------



## petertha

Nice. Watching this closely. Very interesting on the insert cutter results. I bought a stick of 1144SP myself to try. Flying season is drawing to a close but you are making me itchy to return to the shop early. I found pre-drilling the holes kind of PITA too. Not so much the progressive size drudgery, but axial pressure wanting to push the slug against chuck jaws. Its an accurate chuck but I also didn't want to gorilla crank down & distort the thin wall. My liners require a lip anyway so roughed in that feature & that acted as a stop against the chuck jaws which helped.

Any thoughts on using these annular cutters?


----------



## Buchanan

We regularly use annular cutters to bulk remove metal . I have an adapter that fits into my tail stock taper that holds the cutter in a socket with a couple of grub screws. The only limitation is the max depth but often the job can be turned around and a 4 inch hole can be achieved. Much less swaf and a nice slug left for something else. The hole size is good and few starting problems. 
I love your work Terry


----------



## lohring

A very long time ago my company had a customer who needed to bore long, accurate holes in tubing.  He also needed a good surface finish that he was getting by honing after boring.  We made him a cutter with two square inserts set on opposite sides at a 45 degree angle.  The points were circularly ground to the finish diameter.  That makes the front of the inserts the cutting side, just like a drill or reamer.  We then made him a bar that PULLED the cutter through the tubing.  

Our customer was then able to finish the bore with one pass and get both the diametric accuracy and surface finish he needed.  The secret was pulling rather than trying to push a long boring bar and the self centering effect of the circularly ground inserts.  Of course the starting hole needs to be concentric and straight.  In your case if the hole is bored first the OD can be machined with the liner in an arbor.

Lohring Miller


----------



## mayhugh1

[Quote: Any thoughts on using these annular cutters?]

I've seen these on consignment tables at shows but never gave them much thought because I didn't appreciate what they were used for. Now I wish I'd picked up a few. I like the idea of not having to turn the whole bore into chips, but I wonder if a large one would be easier to start into a piece of steel chucked in my lathe. If not, I'm pretty sure my Bridgeport clone could handle it. - Terry


----------



## Buchanan

I have used them both in a Bridgeport and a 1963 Colchester student tailstock and they start easily (with a slow start feed and normal care) I really like them. They do need coolant and make long thin stringy swarf, but if you back off the cutter often it is nor a problem, we use  a 31mm diameter in a Bridgeport to drill holes through 45mm thick wall tube at a 27 degree angle for hand rails.  You can see the waste slug on the top slide of the lathe. this was cut from both sides. We use bath HSS and carbide tipped. The carbide are faster, you can push them harder.


----------



## wirralcnc

Terry
These are brilliant. Used them for many years. Known as rotabroach if you want to Google them. Usually have a centering pin which when used in the rotabroach holder becomes spring loaded. Can be used without centre pin and still remain very stable. In my experiences with them you need to keep weight on them or you lose the cutting edge.


----------



## bigrigbri

I would hone/lap the bores to size first after finishing the o/l.
Placing the finished bore on a close fitting expanding mandrel or a threaded and bolted one to ensure concentricity.
Working prevoiusly at a  company for 20 years making liners from 2" to 24" bore this type of machining operation was often used. Liners can be de mounted for testing and re machined with no set up necessary keeping a good roundness through the bore.


----------



## mayhugh1

In order to turn the liners' o.d. features, they were supported by their bores on an expanding collet. Although many builders routinely make such mandrels, I opted to use a commercial import that threads into a 5C collet chuck. Once installed, it was turned to fit the liner bores and then left in place on the lathe until all the machining on all the liners was completed. Before turning the soft collet for a close slip fit inside the bores, it was important to place the collet segments under a bit of outward pressure using their expanding screw. The total available adjustment range was only some ten thousandths, and since this corresponded to about a quarter turn, an initial loading of 1/16 turn was sufficient. 

Unfortunately, the runout measured at the mandrel's tailstock end varied as much as a couple thousandths when the screw was adjusted for a different diameter. The workpiece couldn't be arbitrarily taken off and on the mandrel nor flipped end-for-end between operations intended for perfectly concentric features (maybe because the bores hadn't yet been honed as 'Bigrigbri' suggested.) Since this was how I planned to use the mandrel, I had to re-indicate the workpiece each time it was remounted. This involved rotating the workpiece on the mandrel, tightening the expanding screw, indicating the o.d. used as a reference and then repeating the steps until the minimum TIR was found. Fortunately, it was always within a half thousandth or so. There were only a few features on the liners that needed to be truly concentric, but I chose to re-indicate each workpiece before every operation. Witness marks added to the i.d. of each liner with a marking pen eventually eliminated the tedious process.

One of the sketches shows the liners' features that required machining. For consistency, all the liners were machined in batches one feature at a time. A real risk with this approach, though, was that an error could have propagated throughout the whole batch of parts before being discovered. Features one and three are the most critical, and these must be concentric with each other. Feature one is the lower half of the combustion chamber seal, and number three is the lower half of the coolant jacket's upper seal.

Feature one was the first turning operation, and it also became the reference o.d. for indicating all subsequent operations. Counterbores in the heads' combustion chambers will seal against the top ends of the liners which sit above the cylinder block. These seals rely on an important machining detail described by a pair of notes - "no sharp inside corners" and ".010 R Fillet Typ" - on the drawing for the liner. I've included a close-up sketch of the area of interest for a typical seal.

A 1.405" diameter counterbore, concentric with each combustion chamber, was machined into the heads much earlier. The top end of each liner was specified to be turned with an outside diameter of 1.400" as well as a .010" radius fillet in its outside corner. It's very important that the ends of all six liners sit at the exact same height above the top surface of the cylinder block. When the head is bolted down to the block, the liners are sandwiched between them, and the sharp edge of the counterbores are forced into the liners' outside fillets to create the seals. Modeling showed there should be a .003" crush height available for deforming the soft edge of the aluminum counterbore into the hard corner fillet of the liner. Since I turned the ends of my liners using a standard lathe insert with a .008" nose radius instead of grinding a custom .010" radius cutter, I changed the outer diameter of the liners' top ends to 1.402" to obtain the same .003" crush height. 

The integrity of the seals also relies on machining that was done over a year ago when the head and cylinder block castings were bored. During those operations it was important to accurately machine all the counterbores to the same diameter and spacing to match the bores in the cylinder blocks. I was anal about machining all the counterbores on both heads to within a few tenths of one another so a common end diameter could be later used for all the liners. Back in post #61, just after completing the head and cylinder block machining, I turned a set of close-fitting Delrin fixtures which simulate a portion of the liners including their top ends and shoulders. I used them to trial assemble the head and cylinder block pairs just after machining them so I could verify the counterbores in the heads were actually aligned with the cylinder bores in the blocks. This had been one of my 'must have' machining milestones in this build. 

After the top end of the first liner was machined, it was lightly set into each head counterbore so the crush distance could be checked with a feeler gage. Depending upon the particular counterbore used for the measurement, the crush heights ranged from zero to something under .001", but most were close to zero. The explanation for this that I took away from the modeling was that even though the 'sharp' edges of the counterbores had never been intentionally broken, they likely ended up with slight chamfers up to .004" in width. I turned this into an opportunity to improve the seal by turning two different radii fillets at two different depths on the liners. I've included a drawing from my modeling to illustrate just what I actually did. Basically, a typical counterbore's chamfered edge fits nicely into the .008" radius fillet, and the .016" fillet provides a additional crush height of .002". These fillet radii match the nose radii of standard lathe inserts. The crush heights of the finally machined parts measured between .0015" and .002".

The outside diameter of each blank was next turned down to 1.500" which became the final o.d. of the liner's top shoulder as well as its largest diameter feature. A fixture was then machined for the headstock end of the mandrel to use as a positive z-axis stop. The blanks were then reversed on the mandrel with their finished top ends tightly against this stop so each could be faced to the exact same final length. This stop was used to reference the z-axis for the rest of the operations.

The coolant jacket was then machined using a DCMT insert. This 55 degree rhomboid cutter simplified the turning operation and left good looking tapered edges at the ends of the jackets. The recessed jacket provided a nice tool entry point for finish machining the coolant jacket's upper seal using a grooving tool modified with a bit of relief so it could be used for very light side-to-side turning. 

The number three feature is the lower half of the coolant jacket's top seal. The liner diameter just below the shoulder was specified to have a close slip fit in the cylinder block, but since it's not a press fit, it's not a functional seal either. Instead, the seal is formed between the top deck surface of the cylinder block and the bottom surface of the liner's shoulder. The 'sharp corner-into-a-fillet' trick can't be used for this seal because it might have created inconsistencies in the heights of the shoulders and issues for the combustion chamber seals. Instead, the upper coolant seals rely upon a pair of smooth flat surfaces pressed together by the sandwiching forces of the head when torqued down to the cylinder block. The integrity of this seal can be affected by the parallel alignment of the liner inside the bore of the block since it affects the parallelism of the sealing surfaces. This alignment is influenced by the lower coolant jacket's compressed o-ring as well as the liner collar support hardware between the cylinder block and crankcase.

As far as I can tell from my research, the liners' coolant jackets in the full-size engine were similarly sealed. There were certainly plenty of documented problems with leaks, but evidently they were eventually solved. With the change to the liner's wall thickness that I've made, there is now sufficient space to add a -027 Viton o-ring as a back-up seal. With this modification, the combustion chamber becomes the only metal-to-metal seal. Adding this o-ring may increase the assembly difficulty involved with getting the liner into the cylinder block, though. Some very preliminary tests have shown the assembly may already be fairly difficult because of the need to compress and stuff the lower o-ring into the bottom end of the assembly. Before making a decision about using the upper o-ring, I'm going to machine the liners' lower support hardware and do some actual assembly testing using a single modified liner. I don't want the o-ring groove to become one of those mistakes that propagates through the entire batch of finished parts.

The last feature to be machined was a 60 degree chamfer that I added to the bottom ends of the liners. This chamfer will provide rod clearance near the bottoms of my thicker-walled liners, but more importantly it will hopefully ease the insertion of the ringed pistons into the liners. In the photos I've seen of the full-size engine's assembly, each entire cylinder block will have to be inserted down onto the crankcase over all six ringed pistons simultaneously. - Terry.


----------



## kvom

Does the crush height mean that once installed the liners are locked in permanently?


----------



## mayhugh1

kvom,
I used the term to just refer to the extra amount of height I will have for the soft edges of the counterbores to deform and seal against the liners when the heads are torqued down to the heads. The liners won't be locked in place. I do have questions about how many times this torque-down can be done, though, and I expect it would be unwise to exchange liner locations once it had been done the first time. I currently plan to assemble them only once, but s/n the liners so I can keep track of their original locations in case the heads have to come apart for some reason. In the full-size engine, I expect the liners on each bank were selected for uniform heights during assembly, and I plan to do the same thing. I recently read that these engines had an average actual combat time of only seven hours between rebuilds, but I don't know what was meant by a 'rebuild'. I suspect the liners weren't re-used in a major over haul if they could help it. - Terry


----------



## Ken I

Terry,
        This as told to me by my father who worked on Merlins throughout the war.

In most cases a major rebuild went back to Rolls Royce and were downgraded for further use in MTB's etc that also used the engines.

Other than in-situ repairs, the engines if removed went back to Rolls and and invariably a new engine put in place.

The throttle on a Spitfire had an overboost position (I believe from 1 bar to 1.5 Bar) meant to be used in an emergency - to shake off a tail chase.
There was a "seal" - a red painted copper strip screwed across the throttle which you broke to get to overboost. If this seal was broken, then according to the "rules", the engine had to be removed and rebuilt. The pilot also had to explain why.

In practice they pushed through the seal on takeoff and used it as seen fit. 
If ground crew asked a pilot to fill in the appropriate form explaining his actions, he would be told in no uncertain terms where to shove it.

On the other hand if an inspection revealed a broken seal, the ground crew would be up on a fizzer (charge).

The seal was a tightly controlled spares item - you couldn't get one without the required report forms.

Bureaucracy occurs even in wartime.

The solution to the problem was to get a local engineering company to make a press tool to make the seal - the aircrews paid for this out of their own pockets - completely off the books.

So after every flight they simply replaced the seals and the system was satisfied.

Apparently the ruse went undetected (or a blind eye was turned) for the entire war.

So it would appear that the Merlins received a great deal more "abuse" than officially recognised.

Regards,
            Ken


----------



## mayhugh1

Ken,
Pretty cool story with rare perspective.
-Terry


----------



## mayhugh1

The lower ends of the coolant jackets are sealed with Viton o-rings that are sandwiched between pairs of supporting metal rings. These rings as well as the o-rings must be slipped onto the liners through the bottoms of the cylinder blocks. The upper liner ring bears against a shoulder that was previously machined into the liner near the bottom edge of the jacket. The lower liner collar is slipped onto the liner below its o-ring and helps keep the o-ring in place. The liner collars have flanges that will be captured between the cylinder block and crankcase when the two are assembled. These flanges must all be machined to an identical height in order to prevent crankcase oil leaks or, even worse, damage to the cylinder blocks during final assembly. The o-rings will be compressed 28% in the space available between the cylinder block and the cylinder liners, and so they don't require additional compression from the liner rings. Although it seemed excessive to me, according to the references I checked, 28% is about the right amount of compression for a .070" thick o-ring used for a static liquid seal.

When I originally decided to increase the liners' wall thicknesses, I thought I could integrate the upper liner ring into the wall of the liner, and this is what I indicated on an earlier assembly drawing. However, I had overlooked the fact that this ring had to be machined as a separate part because the liners have to be inserted through the top of the block during assembly, and the block's necked-down bore just below its top surface is too small to pass the rings.

The liner's shoulder for the upper ring is only .010" high and was previously turned with a sharp inside corner using a grooving tool. The liner ring that bears against it also had to be cleanly turned with sharp corners and a close slip fit to the liner in order to avoid assembly damage to the o-ring. In order to avoid scratching the liners or cylinder block during installation, these rings were turned from 6061. The aluminum blank, from which the rings were parted, was turned for close fits to the cylinder block's i.d. and the liner's o.d. A snug-fitting Delrin plug was temporarily inserted into the tailstock end of the blank. This plug allowed the rings to be cleanly parted without the burrs or ragged edge flashing that would typically be left behind if the parted rings been allowed to freely fall away. The plug also helped to reduce potential distortion of the fragile finished rings.

It's imperative that the o-rings be installed without damage because they will eventually become deeply embedded inside a complex assembly that should, for a number of reasons, be done only once. Working through the bottoms of the blocks to insert the o-rings into the tight spaces between the liners and cylinder block bores became an unexpected challenge. The o-rings wanted to be uniformly compressed radially before they could be slipped into place axially. I made a couple tools to help with their installation, including a ring compressor, but my results were hit-and-miss and typically ended up damaging the o-rings. During a couple days of frustrating attempts to come up with a process, scratching the cylinder block bores or the liners' shoulders, either of which could have resulted in coolant leaks, was a continual concern. I didn't remember having difficulties installing the o-ring'd liners in my Howell V-4, and after going back and reviewing the drawings I remembered that Jerry had used a groove depth for its o-rings that produced only 9% compression.

The eventual solution for my particular liners was to add an o.d. taper on the bottom end of each liner to provide an entrance ramp for the o-ring. During assembly, this ramp should convert a portion of the axial insertion force applied to the o-ring by its installation tool into a radially compressive component. The clearance chamfer that I had already added to the bottom i.d. of the liner, to ease piston ring insertion later on, left me with less space than I would have liked for the o.d. taper. It was also important to not leave a sharp edge on the bottom end of the liner that might also damage the o-ring. The space left available for the taper turned out to be barely enough. Since not even this area would have been available on the stock thin-wall liners, I'm not sure what a safe solution for them would have been. I continued using my three simple Delrin tools to practice a few trial assemblies, but tool #2, which was used to push the o-rings into the space between the liners and cylinder block was the only really important one.

Before assembly, the upper liner ring is dropped into the cylinder block bore, and tool #1 insures it rests squarely against the bottom surface of the block's deck. The bottom end of the liner is lubricated with oil and inserted through the top of the cylinder block. The liner ring is captured on the liner's shoulder as the liner is pushed through the block. When the end of the liner is within a half inch of the bottom of the block, a lubricated o-ring is set into the bore and backed up with tool #2. Tool #3, whose sole purpose is protect my hands from the liner's top sharp edges, is used to push the liner and o-ring against tool #2. This action hopefully forces the o-ring down the liner's entrance ramp and into the space between it and the block. Once the o-ring is below the bottom end of the liner, tool #2 is used to insure it is seated against the upper liner ring, and that the liner ring is seated against the liner's shoulder. A depth gage verifies the o-ring is at its proper depth below the liner's bottom end.

I was then left with the decision about whether or not to add an o-ring groove at the top of each liner for a back-up seal for the top coolant jacket. Without this o-ring, the top jacket seal will be just the originally intended .037" wide metal-to-metal seal between the bottom surface of the liner's shoulder and the top surface of the cylinder block. The use of sealant on these surfaces would likely result in inconsistent shoulder heights among the liners and create problems for the combustion chamber seals. There's only .001" clearance between upper neck of the cylinder block bore and the o.d. of the liner and very limited space for a ring compressor. I wasn't willing to reduce the metal-to-metal seal width at the top of the block for another o-ring entrance ramp. And, there is only .150" available for the .100" wide groove required for a .070" thick o-ring. Based on my experiences with the lower o-ring, I had already pretty much given up adding another one, but I turned an o-ring-grooved test part just in case. After playing with it for a short while, I abandoned the idea of a top o-ring entirely.

The final liner-related parts were the lower cylinder collars, and these were machined from 12L14. The o.d.'s are a close slip fit to the cylinder block bores, and the i.d.'s are close slip fits to the liners' o.d.'s. These collars control the alignment of the liners inside the cylinder blocks, and so they affect the parallelism of the mating surfaces that make up both the combustion chamber and top coolant jacket seals. The height of the lip that contacts the o-ring was selected to compress the o-ring only a few additional thousandths. The flanges on all the collars were ground to an identical height so the stresses on the blocks would be uniform after they are torqued down to the crankcase. Flats were milled on the sides of the collars to provide clearances to their neighbors.

Except for the lapping, the machining of the liners and the o-ring retaining hardware finally seems to be completed. - Terry

Errata... After posting, I noticed an error on the labels on the photo for the o-ring installation tools. The o.d. of tool #2 should have been labeled as being a close fit to the i.d. of the cylinder block bore instead of to the liner.


----------



## petertha

mayhugh1 said:


> .... Although it seemed excessive to me, according to the references I checked, 28% is about the right amount of compression for a .070" thick o-ring used for a static liquid seal
> .... I didn't remember having difficulties installing the o-ring'd liners in my Howell V-4, and after going back and reviewing the drawings I remembered that Jerry had used a groove depth for its o-rings that produced only 9% compression..


 
Interesting & timely. This might be what I've been struggling with on my radial crankcase face seal mockup. Just to make sure I understand, when you say 28% compression, would that correspond to a 0.050" groove depth? ex Compression = 1 - 0.050 / 0.070 = 0.28 (28%)

My 1mm section dia O-ring groove was prescribed with 0.7mm depth which would be 30%. This link for example recommends 0.8mm depth which would be 20%.
http://www.theoringstore.com/index.php?main_page=page&id=30&chapter=4

The other thing I noticed - this link for example shows an even 0.5mm incrementing section diameter progression. But the corresponding compression % is not a constant or trending up or down consistantly. Why would that be? Maybe just nominal dimensions or indirectly related to standardized tooling width?


----------



## mayhugh1

Peter,
Yes, my effective groove depth was .050". I, too, saw small variations on the order of a few percent for the recommended compression depending on the particular reference. One reference I came across said to use no more than 40% because the o-ring material would take a permanent set with an eventual loss in sealing. So, I didn't feel like 5% or so was significant enough to be concerned with. I have some expensive high flow pond pumps that have static o-ring seals that are close to 35% compressed and those rings invariably take a set, leak, and have to be replaced during my yearly maintenance on the the pumps. And then, I also have some 7 year old underwater low voltage lights that are less than 10% compressed and feel like they would never be effective seals, but they have never leaked and have never been replaced. Although the references I checked said nothing about the particular o-ring material used, I would have thought it would have also mattered whether the o-ring was viton, buna, or silicone. -Terry


----------



## Ken I

The dynamic nature of an "O" ring is that it behaves like a fluid and resists any amount of applied pressure. Up until the "O" ring starts to extrude out of the clearance then it all goes South really quickly.

So even small amounts of compression are very effective - what is way more important are clearances and surface finishes.

You only need enough preload to seal against surface imperfections - after that physics takes over.

I have used "O" rings as piston seals for destructive pressure testing of steel tubes up to 16000 psi - the only failures were because of excessive clearance.

And while we are on the subject, using two "O" rings doesn't work - next to each other or even in two grooves - particularly in a dynamic environment - they can generate enough pressure between each other to bring about extrusion failure.

Regards,
            Ken


----------



## mayhugh1

After finishing the machining on the liners I needed a short procrastination break before wading into the messy honing/lapping process. So, I thought I would take an initial stab at selecting the Merlin's starter motor. I began with a set of 'nice to have' specs which included 6 volt operation and a torque of 14 ft-lbs at 240 rpm available to the crankshaft. The 6 volt requirement was a 'nice to have' since I've been running my engines from the same small 6 volt gel cell whose voltage is compatible with the ignition modules, fuel pumps, and other accessories that I've typically added to my engines. The torque requirement came from cranking measurements that I made on my 18 cylinder radial during its build, and as a starting point I expected the Quarter Scale's requirement to be similar. The 240 rpm cranking spec might be ambitious and maybe even a little over-kill for a twelve cylinder engine, but I needed to start somewhere. A quick horsepower calculation using these 'nice to have' requirements gives (14 ft-lbs)x(240 rpm)/5252 = .64 hp or, equivalently, 477 watts. Assuming a dc brush motor efficiency of 70%, such a motor would draw (477 watts)/(6 volts)/.7 = 114 amps from my 6V battery. 

With space only for an under-two inch diameter motor, these power requirements seemed a bit excessive, and so I began again with a set of minimum 'must-have' specs. I reduced the torque requirement to 10 ft-lbs in order to adjust for the Merlin's twelve cylinders rather than continuing to assume the requirements of the eighteen cylinder engine. I considered 60 rpm to be an absolute minimum cranking speed but continued to hope for 120 rpm. I then decided I'd be willing to make the changes necessary to run the Merlin from a 12 Volt battery or else use a separate battery for the starter. With the same 70% efficiency assumption and my new 'must have' requirements, the current draw from the 12 V battery fell to about 10 amps. 

Since there is an internal wheel case gear reduction of five between the starter and the crankshaft, my dc motor requirements became 2 ft-lbs torque at 300 rpm (600 more desirable) measured at the shaft of a 12 volt dc motor. The diameter of the motor needed to be no more than 1-3/4", but its length could be as long as 4 or 5 inches.

I initially limited my search to dc brush motors because I knew they were significantly cheaper, and there seemed to be more readily available application information for using them in scratch designs. In addition, a first glance showed I was going to have to become familiar with a whole new world of jargon if I was going to navigate the world of R/C brushless motors. Finding a good brush candidate first will give me something against which to compare brushless alternatives so I can determine whether their increased performance will be worth the additional cost and hassle of controlling them.

After hours of online comparisons, I focused on an inexpensive ($9) Nichibo 775-8511FDAS dc brush motor whose specs seemed to be representative of the high output motors available in a packaging envelope I could live with. One has to be careful when comparing these little motors based on their marketing specs because the high torque, low current, and high efficiencies that are often advertised may not be available simultaneously. I've included a set of performance curves for this particular motor that I also found online. In fact, the availability of these very useful curves was one of the reasons for selecting this particular motor.

The curves for this 14.4 volt motor were generated for operation on 12 volts, and so the 12 volt axis on the left hand side of the graph may be confusing since it has little meaning. If the motor were to be operated at a voltage other than 12 volts, then the curves shown would morph into a new set of curves for the new operating voltage. 

It seems there is no standard for units of torque among the manufacturers of these small motors, and the kg-cm used by Nichibo is a little unusual. My 2 ft-lb. torque requirement is roughly equivalent to 30 kg-cm. To start the design process, I entered the horizontal torque axis at 1 kg-cm and then moved up to find its intersection with the operating point curves. Since I'll have to machine a 30:1 gear reducer to convert the 1kg-cm torque into my required 30 kg-cm, I must then calculate its impact on the motor's speed. The rpm curve is intersected at 17,500 rpm, and so my gear reducer will drop this down to 580 rpm which is (hooray!) greater than my minimum required 300 rpm and nearly equal to my more desirable 600rpm. The amperage curve intercept is at about 22 amps, and this will be the actual current draw from the battery. The power delivered by the battery will be 12V x 22A = 264 watts. The intercept with the output power curve is at 180 watts, and this will be the actual mechanical power that the motor will be putting out. The efficiency will be (180W/(264W)= 68% which agrees closely with the intercept of the efficiency curve.

I can reduce the current draw by reducing the required output power of the motor. And so for a lower output operating point I started the process again using the 0.5 kg-cm coordinate which is equivalent to .036 ft-lbs torque. In order to turn this into 2 ft-lbs, I will now need a gear reducer of 55. The new rpm curve intercept is 20,000, and the gear reducer will drop this to 360 rpm which is only slightly above my minimum requirement of 300 rpm. What I've gained from this bit of compromise is that the current draw has now been reduced to 13 amps, and the power required from the battery has been reduced to (12V)x (13A)= 156 watts. The new mechanical output power interpolated from the new intercept is 105 watts, and the calculated efficiency is now 105/156 = 67% which again compares favorably with the graph's efficiency intercept.

And so, a representative dc brush motor that appears to meet my requirements is a $9 motor that will provide 156-180 watts of output power. It will require a mechanical gear reduction of between 30:1 and 55:1 as well as a 12 V battery that can supply between 264 watts and 156 watts. The motor's diameter is 1.75" and its length is 3.8". Its shaft diameter is 5/32", and it has a milled flat.

I ordered a couple of these motors for some hands-on experience. If I don't end up using one of them for the starter, I'll at least have something to use for the supercharger tests I plan to run. The next step in the motor selection will be to find a comparable brushless motor so I can make cost, size, and performance comparisons. - Terry


----------



## Naiveambition

I anxiously await every post on this motor from the very beginning of your build, and I remember you had mentioned starter issues early on. 
At the time I was doing some brainstorming and thought of a small starter for a push mower . 
I had a John Deere 6 hp, with electric start that had a small starter and thought maybe this could be a solution. I believe it was a js30.  It could possibly fit your parameters with a quick solution as being small and strong , with the added benefit of being made for these applications .
Apologies for the lateness of my post, but I often am mesmerized by your scientific approach to your solutions, and quite simply forgot.

Mike


----------



## bigrigbri

Why not make a scale sized rotary vane motor running from a Co2 bulb or high pressure air which will give plenty of torque especially geared down.
Brilliant work so far sir.


----------



## Ken I

Terry,
         I've got quite a bit of experience in cranking out dubiously large amounts of power from small motors - for slotcar racing (a hobby) and for robotic applications (my usual line of work) where power to weight is an issue.

You can only get so much torque out of a saturated armature so the only way to get more is to spin the beans out of it and gear it down as I am sure you are well aware.

I posted on the site an article on getting more out of your A.C. motor (a lot more)  which is germane.

www.homemodelenginemachinist.com/showthread.php?t=25236

Also from my automotive experience - starter motors are not 100% duty rated - they burn out if you run them too long but normally longer than it takes to crank the battery flat. So you can overload a motor for brief periods given the relatively light time-duty cycle of a starter.
With a motor that runs close to saturation this won't help but a motor that runs at 20% saturation can be loaded to 500% for brief intervals.
The "brushless" servo motors we use in our robots are built like this they will handle 200% load for 20 minutes and 500% for 5 seconds.

Anhoo - the reason for my response is that you will need to gear it down and those ganged planetary gear drive sets used in cordless drills and pneumatic tools can be cannibalised to form the basis for your reduction gearbox.

A lot of starter motors now do just that as opposed to the direct drive types on older cars.

And as Naiveambition pointed out you can go scrounging for an actual starter built for the purpose from something or the other - none spring to mind but perhaps some other members might make suggestions.

Another thought for a compact gearbox would be a harmonic drive - I could give you a perfectly serviceable 50:1 450W unit out of a robot (too much lash for precision but still a perfectly serviceable unit.) I have a few lying around.

Just a suggestion.

Regards,
            Ken


----------



## mayhugh1

Thanks all for your informed comments - Terry


----------



## mayhugh1

The final step in the liner construction was to bring all the bores to a common diameter and then lap the i.d.'s for cast iron piston rings. Since neither the pistons nor the rings have yet been machined, the actual diameter isn't yet important. What is important is that the i.d.'s end up identical so a single diameter piston ring can be machined for use in all the cylinders. The resolution of my dial bore gage is about a tenth or so, and I was able to identically lap all the cylinder bores in my last two engines to within its resolution. So, I set the same goal for the Merlin's liners.

All twelve liners plus the three spares that were initially launched managed to survive their machining and avoid being scrapped. Initial measurements indicated all the bored i.d.'s were within a thousandth of one another, and so I was looking forward to a brief lapping session. However, the chatter marks with which I had struggled on some of the liners were deeper than I had hoped and weren't picked up by the anvils on my internal micrometer. After some localized clean-up on a couple of the worst looking parts, my dial bore gage showed the actual diameter spread was closer to .0025". This was really disappointing because the grooves on these parts ended up setting the final diameter of the entire group of liners, and what I had hoped to be just a single messy afternoon of lapping turned into days of grinding.

Each liner was engraved with a unique number so its progress could be tracked throughout the honing/lapping process. A set of worksheets was set up on which the measured i.d.'s of each liner were recorded at three different depths as the lapping progressed. With up to .0025" to be removed from many of the liners, I would normally have re-bored the whole lot, but I hadn't learned anymore about getting chatter-free bores on Stressproof than I knew when I bored the liners the first time. I zero'd the dial bore gage to the center of the spread so I could focus on deviations instead of trying to keep track of absolute numbers.

I used commercial Acro barrel laps designed for through-holes and Clover silicon carbide grease in three different grits: 280, 600, and 1000. A separate lap was used for each grit. The laps were mounted on an arbor and spun in a battery-powered drill while the liners were simply held in my gloved hand. This method of supporting the liners would have required greater care had I been working with the stock .030" thin-wall liners since a tight grip, especially needed for the coarse compound, would have tended to distort their bores. With the drill running at 300-400 rpm, the liner was slowly oscillated along the length of the lap with about half the lap being exposed at each end. The liners were always slipped onto the laps through their bottom end to avoid accidental damage to the sharp sealing edges at the tops of the liners. These sealing edges are an important reason to avoid using brush or bottle hones on the Merlin's liners.

Since the starting bore was a non-standard 1.198", I modified the stock Acro 1-1/4" brass barrels by turning them down to 1.195". With so much liner metal to be removed, I started with 280 grit grease. This coarse compound was extremely abrasive to the laps, and the grinding process removed about the same amount of material from the laps as it did from the liners. The expander bolts on the ends of the laps had to be continually adjusted as the lap wore, and it was necessary to take small steps in between many measurements in order to avoid overshooting targets. I probably made three to four measurements during the removal of each half thousandth. By the time all the liners had been ground to a common diameter, two 280 grit laps had been fully expanded. Measurements showed their starting diameters had been reduced from 1.195" to 1.180" by the grinding, and this volume of metal was nearly identical to the volume of metal that had been removed from the liners. Even though I was using barrel laps, I wouldn't consider this first step to have been a lapping operation. It was more of a controlled grinding operation used to bring all the liners to a common diameter. 

The 280 grit grease produced a surprisingly smooth and beautifully frosted finish that was free of visible machining marks or scratches. The real lapping, though, began with the 600 grit paste after the liners were all at the same diameter. During this operation only a tenth was removed from each of the nearly finished bores, and maybe a thousandth from the single lap. Each tenth took longer to remove than when working with the 280 grit paste, and so it wasn't difficult to get all the liners to precisely the same diameter with fewer measurement checks. 

I've learned during lapping that there is some technique involved with using a (my) dial bore gage. My only experience with these gages is with my own imported model, and so I don't know if a more expensive gage behaves in the same way. But mine seems to have one or two tenths backlash. When I rock the anvil back and forth inside a bore to take a measurement, I get a slightly different result depending on the direction that I rock the gage. I've learned to make it a point to approach all measurements from the same direction when making comparisons.

I finished the liners with 1000 grit compound which didn't remove any measurable amount of metal but did seem to improve the surface finishes a little. I'm not sure if the 1000 grit pass is needed or even desirable for cast iron rings, but since I used it on the cylinders in my last radial I also included it in the Merlin's liners.

My process for getting all the liners to a common diameter was not to grind on each one continuously until it was at that final diameter. Instead, I worked in small steps across the whole group of liners to finesse them all, as a group, across the finish line. This approach took more time and involved many small steps and measurements, but it helped to avoid accidents, and it better handled surprises such as undiscovered grooves or scratches. It was also easier to spread the work out over several less tiring sessions over several days when not grinding incessantly for long periods of time on the same part. Changes in the lap (and the lapper) were slowly spread out over a number of bores for a more consistent final result.

The 280 grit compound typically required about 5 minutes of actual lapping time to remove a couple tenths from a single liner, but when the times for cleaning and measurement were added, the total time was closer to ten minutes. It was important to thoroughly clean and dry the liner before each measurement to not only get consistent measurements but to also avoid damaging the gage's anvils. I used kerosene for removing the lapping grease, and it left me smelling so bad that neither the wife nor dog would come around me for days.

After the 280 grit grinding was completed, I let the parts sit for a day so I could rest up for the final 600 grit lapping step. For consistency, I used the 600 grit lapping operation to remove the last tenth from all the parts in one session. The final result was that 14 of the 15 liners finished out to better than a tenth with beautiful smooth finishes. There were no measurable circularity errors after (or even before) the lapping. The 15th liner had the deepest chatter marks, but It would have likely cleaned up with another two or three tenths pass. Since the other fourteen liners were already at the finish line, I decided that having a third spare wasn't worth the effort or risk to the other liners. - Terry


----------



## rdefrei1

Running engine from Dynamotive castings.

[ame]https://www.youtube.com/watch?v=KTPf3kZz9u0[/ame]


----------



## ddmckee54

Terry:

I check in every day or two to get my Merlin fix. It's been an immensely enjoyable ride so far. If you are talking about starters it's gotta be close to the time when this one is gonna be goin vroom-vroom. Or whatever the sound is that you've been hearing in your head when you look at this beast.

Whatchya gonna build next?

Don


----------



## petertha

mayhugh1 said:


> I used kerosene for removing the lapping grease, and it left me smelling so bad...


 
Great write-up as usual Terry. Liners look very nice.

Kerosene is probably the only solvent I don't have in my arsenal. But for whatever reason I found WD-40 removed a healthy amount of lapping compound, leaving the harsher solvents reserved for final clean. WD-40 almost seemed to disperse the grit off the metal, but maybe I was hallucinating. I found thinners I usually prefer like acetone dilutes the grease but the grit is still kind of free floating & clingy.


----------



## petertha

Ken I said:


> Another thought for a compact gearbox would be a harmonic drive  Ken


I've heard of them, but assumed they were brutally expensive. Do you have links for ones in/around this size?

Also, for model engine starter motor applications like this, would they be typically on/off or is there some (ideal) requirement to ramp up to rpm for whatever reason?


----------



## Ken I

petertha said:


> I've heard of them, but assumed they were brutally expensive.



Correct: They are fiendishly expensive as are their cousins cycloidal drives.

However look up your nearest robot supplier (Yaskawa, Fanuc, ABB, Kuka etc.) and if you speak to them nicely they might give you an "old" unit.

I would.

These are often changed out because even minute amounts of lash become problematical on a robot - but they are otherwise still perfectly serviceable as a "gearbox".

Unfortunately they typically toss them in the bin as they are no use as a "spare" so you might have to wait.

http://makeagif.com/9jh2He

Above link to a harmonic drive in action - note these things can give 50 to 100 to one reductions at 70% efficiency (mind boggling). An efficiency of better than 50% is needed in robotic & N.C. applications to maintain control over deceleration of large inertial masses (do that with a 50:1 worm drive and it will self lock because of its less than 50% efficiency (and therefore non-reversible / self locking) and the inertial load will then proceed to tear off all the teeth).

https://goo.gl/images/65ZlNB

Above link for a GIF of a cycloid in action

and what they typically look like - 

https://goo.gl/images/71F5H0

A complete and very compact gearbox / radial /axial thrust bearing assembly combined - when you see an industrial robot, each axis turns on one of these (including the main "S" axis on which the entire unit stands) with typical reduction ratios from 90 to 190:1 at 75% efficiency and zero backlash - really cool.

At first glance both of these types of drive look like they would be inefficient - just the opposite they are even more efficient than ganged planetary gear sets and can be built to interference fits to be backlash free (no really - zero lash) - but they do have to made to very exacting standards - which makes them very expensive.

They are also lubrication critical - pump in the wrong grease and the gearbox self destructs as many robot users have found out the hard way.

Sorry this post kinda got well away from the original question - a simple full on switch would only present problems if there is sufficient lash in the system to let it get a head start and result in an impact - so a soft start would be better - a simple two step would be fine - a resistive switch on at low torque to take up the lash followed a split second later by full on would be quite sufficient.

The only manufacturers I know are Harmonic Drive Systems (invented by an American CW Musser in 1957 but perfected by the Japanese).

https://en.wikipedia.org/wiki/Harmonic_drive

http://www.harmonicdrive.net/

The cycloidals I work with are made by Sumitomo

http://www.sumitomodrive.com/modules.php?name=Product&op=productBrand&brand_id=13


Regards,
            Ken


----------



## petertha

Terry, re starter motor, just happened to stumble on this Conley V8 vid. Some views of starter motor around 20:20. First I thought it looked like an RC motor, but I don't recognize the open can so maybe brushed? Its circa 2011 so not sure if that's what he still uses. 
Youtube search _Conley Factory Tour Model V8 Working 1/4 Scale Engine_

You mentioned avoiding brushless RC side if possible & I don't blame you. OTOH, they are getting quite inexpensive & available in multitude of KV & diameter flavors. You likely could utilize your same 12v drive battery as its close to 3-cell lipo ~11-12v nominal & amps are low. So the shopping list would be brushless motor, ESC rated for amp duty & cheap servo tester to throttle the ESC. Probably still $100 combined. But my electronics hits a wall with how to turn on/off though. The tester is meant to mimic TX signal & throttle motor between 0-100%. I suspect trying to insert switch [SW] between tester & ESC would cause ESC arming issues & generally be bad. Now whether the turn knob pot thingy could be modified or tricked.. above my pay grade  Anyway, food for thought if push comes to shove. Some hobby CNC-ers are making spindle motors with this configuration but its continuous vs. on/off like starter motor. This vid shows larger diameter outrunner, but same principle.

http://www.raynerd.co.uk/brushless-dc-motor-cnc-high-speed-spindle/


----------



## kiwi2

Hi,
     It's probably not on topic as far as constructing a Merlin engine goes, but I snapped the attached picture this afternoon. 
A local guy has made a set of formers to construct plywood Mosquito fuselages. This is his second one and the twin Merlins came roaring overhead this afternoon. A very impressive noise. It's amazing these engines are still operating after 70 odd years.
Do you have any plans to put your quarter scale engine into (for example) a quarter scale scale Spitfire fuselage or doesn't the scaling work like that?
Regards,
Alan C.


----------



## mayhugh1

Peter,
Thanks for the post. I didn't realize there were such things as servo testers. I was expecting I would have to design something to drive the ESC if I went brushless, but one of those looks exactly what I would need.

Alan,
I really don't have any plans for the Merlin beyond a display shelf.

Terry


----------



## ddmckee54

If you aren't familiar with ESC's and servo testers, there are a couple of things I'd recommend.
1 - I'd go with an aircraft ESC, not a car or boat ESC.  That way you only get one direction out of the ESC, instead of a bi-directional output with full stop at mid-range.
2 - I'd replace the pot in the servo tester's input circuit with a switched fixed resistor, you're building the equivalent of a retract switch.  That way the output of the ESC will either be on or off,

Don


----------



## mayhugh1

With the cylinder liners completed, the next step was to machine the pistons. As shown on an earlier assembly drawing, I had to make several modifications to the stock piston design in order to adapt it to my modified liners. Despite the fact that in the process I scaled them down by some 10%, at 1.197" diameter by .830" long, they're still the largest pistons I've machined to date. 

The Quarter Scale's pistons are similar to the 'short length' pistons used in some versions of the full-size engine. They use two rings and an oil control groove located immediately below the second ring. During the piston downstroke, oil is scraped from the cylinder wall and into this groove by the lower ring and allowed to escape into the interior of the piston through a series of radially drilled holes. Both radials that I've built had a non-trivial third ring designed specifically for oil control. Hopefully the Merlin's approach to oil control, which is much easier to implement, will perform as well. The lack of a third ring also reduces the friction that the starting system will have to deal with.

I used .003" (diametral) piston-to-cylinder clearance which is about the same clearance I used in my air-cooled radials. The deep finned heads and cylinders on those engines are efficiently cooled by the prop wash, and .003" is nearly optimum for an oil film and its protection against scuffing and piston noise. Assuming a temperature expansion of 13E-6 inches/inch/F, the piston temperature rises in the radials were most likely less than 275F. I don't expect the Merlin's heads, even with their liquid cooling, to be as well-behaved though. The prop wash won't be nearly as effective on the Merlin's heads, except for its influence on the radiator that will likely be required in the coolant loop. The full-size Merlins actually used drop-down radiators located beneath plane's airframe in order to prevent overheating during prolonged runway idling periods. For additional margin against piston expansion, the Quarter Scale's piston crowns were reduced to obtain a .008" (diametral) clearance. The piston's highest temperature rise will be at it's crown, and with only the rings providing the primary heat loss path, a little extra clearance is probably a good idea. This extra clearance extends .300" down from the top of the piston and includes both rings. 

A second temperature consideration involves the clearances behind the rings. This clearance is determined by the cylinder bore, the radial thickness of the ring, and the ring's groove depth. The ring will be in full 360 degree contact with the cylinder wall, and because its diameter is constrained by the cylinder, only its running gap can decrease as the temperature rises. The piston's diameter is free to grow, however, and its clearance to the rear of the ring will decrease. Clearance must be maintained behind the rings, and especially behind the top one, since combustion gasses pressurize this space and force the ring against the cylinder wall to create ring's seal. I machined the piston groove depths to create a radial clearance of .006" behind the rings. Even at an unlikely 500F, a couple thousandths clearance would still remain behind the rings.

The (axial) widths specified for the Quarter Scale's stock ring grooves may have been a result of the scaling since they were spec'd at .040" for use with a .039" width piston ring. This width is much greater than the published recommendations for model IC engines by Trimble, Chaddock, and Walshaw. I've successfully used their recommendations on my other engines, and so I reduced the axial groove width to .027" for use with a .026" ring.

The construction of each piston began by turning its o.d.'s on the end of a 1-1/4" 6061 round before cutting the ring grooves. Particular care was taken in choosing the feeds and speeds (1500 rpm, 0.5 ipm for a carbide grooving insert on my 9x20 lathe) to achieve good surface finishes on the walls of the grooves. The lower wall of the upper ring is also a sealing surface for the upper ring during combustion. After cutting the grooves, the pistons were parted off in the bandsaw.

Unfortunately, I had once again recorded an incorrect dimension while setting up the process sheet that I created to machine the pistons. Before realizing that I had been turning them .002" undersize, I had machined all twelve. They're sitting in the 'scrap' pile in one of the photos. I gave myself a couple days off without pay after that one. 

In order to machine the pistons' interiors, a fixture was created to support them under the mill's spindle. This fixture was designed to be turned 90 degrees so it could also support the drilling and reaming of the wrist pin holes. These holes must be precisely square to the pistons' axes to prevent connecting rod binds, and so a lot of care was put into the fixture's machining. It was finish-machined with a piston blank clamped in place after the two relief slots were cut. I probably spent as much time on that little fixture as I did on both sets of pistons up to that point. The wrist pin holes were drilled and reamed before the piston's interiors were machined, and the fixture was vertically indicated on the mill before each hole was drilled.

The final two operations included machining of shallow flats on each side of the pistons for the wrist pin retainers, and drilling the escape holes in the oil grooves. The full-size Merlins used c-clip retainers for the wrist pins, but the Quarter Scale will use hardened floating pins with soft tipped ends. Both operations were done on a rotary under the mill's spindle with the piston gripped in a machinable 5C collet. The collet was machined so it could grip the piston on either of its diameters since each operation required opposite end access to the piston. At the last minute, I increased the number of oil holes from six to ten. - Terry


----------



## mayhugh1

ddmckee54 said:


> If you aren't familiar with ESC's and servo testers, there are a couple of things I'd recommend.
> 1 - I'd go with an aircraft ESC, not a car or boat ESC.  That way you only get one direction out of the ESC, instead of a bi-directional output with full stop at mid-range.
> 2 - I'd replace the pot in the servo tester's input circuit with a switched fixed resistor, you're building the equivalent of a retract switch.  That way the output of the ESC will either be on or off,
> 
> Don



Don, 
Thanks alot for the tips. Sounds like good advice. 
Terry


----------



## mu38&Bg#

I worked for a company which supplied Conley the starter motors. They were brushed cobalt motors, but also are out of production a few years ago now. The particular one in the video was marketed under a few labels. Before that, he used Astroflight cobalt motors, until they became too costly. Last I knew, he switched to "modified" (serviceable brush type) brush rc motors with gear reduction.

Unless you need a very small motor, I'd just as soon use a brush motor.

Greg


----------



## petertha

_> so I reduced the axial groove width to .027" for use with a .026" ring_

Terry, hard to tell from your pic, but are you using those Nikcole inserts to cut the ring grooves? Technique wise, do you cut the middle groove portion like parting & then dress each face with a skim cut to final gap dimension? And how about the groove bottom - do you traverse the tool laterally a bit to ensure its a clean profile? I found this operation to be a bit fiddly & was reluctant to go in there with sandpaper, any tips appreciated.

I like your clamping setup jig, going to steal that idea. Do you target the pocket bore diameter exactly equal to piston OD & then the slitting 'unsprings' it a bit? Or do you bore with a bit of oversize clearance? I'm slowly learning the hard way how easy it is to mar or distort delicate parts.


----------



## mayhugh1

petertha said:


> _> so I reduced the axial groove width to .027" for use with a .026" ring_
> 
> Terry, hard to tell from your pic, but are you using those Nikcole inserts to cut the ring grooves? Technique wise, do you cut the middle groove portion like parting & then dress each face with a skim cut to final gap dimension? And how about the groove bottom - do you traverse the tool laterally a bit to ensure its a clean profile? I found this operation to be a bit fiddly & was reluctant to go in there with sandpaper, any tips appreciated.
> 
> I like your clamping setup jig, going to steal that idea. Do you target the pocket bore diameter exactly equal to piston OD & then the slitting 'unsprings' it a bit? Or do you bore with a bit of oversize clearance? I'm slowly learning the hard way how easy it is to mar or distort delicate parts.



Peter,
Yes, I take a pass down the middle and then skim the walls on either side. On a groove this narrow, there typically isn't room for much side-to-side. In this particular application the rear finish isn't important but for an o-ring it would be. And yes, I'm using Nicole inserts.
The piston clamping jig really is really something I also borrowed from somewhere. I bored the hole .002" oversize and I don't think I saw any spring either direction. I made one from 12L14 some time ago for another project and it did spring open a bit. The hole hoe the clamping bolt should also be drilled and tapped before cutting the relief grooves. - Terry


----------



## geo

Terry a it off topic toying with the idea of a tormach mill are you happy with your machine
Cheers 
Geo


----------



## mayhugh1

Geo,
i've been very happy with it. If you have any specific questions, send me a pm. - Terry


----------



## mayhugh1

Although there's still lots of small PITA parts ahead, the connecting rods should be the last major engine components to be machined. The Merlin uses six pairs of fork/blade rods that include big-end split bronze bearings. A single pair of these rods is about as complex as a radial's master rod, and so I spent time thinking about how I was going to go about machining them in quantity. I decided to use 7075 aluminum since it has some 80% greater tensile strength when compared with 6061 and is 50% harder. The greater hardness should provide some additional wear resistance against the hardened wrist pins. Unlike the full-scale Merlin, the Quarter Scale doesn't use bronze bearings in the rods' small ends.

I started with the simpler blade rods so I could work out the fixturing that I'll also need later to machine the more difficult fork rods. The plan was to machine the rods in cookie sheet fashion in groups of three. I prepared enough workpieces to machine three groups of three rods so I would have spares to cover mistakes along the way. 

Each workpiece was created by bolting two half-inch thick rectangular bars together so the rods and their caps could be integrally machined. The junction between the two bars would become the seam between the rods and their caps, and so the workpiece ends were finish-machined before being bolted together. The layouts of the three rods within the assembled workpieces were planned so the bolts holding the two bars together were actually the rods' 5-40 cap bolts. The heads of the bolts were sunk deep in counterbores inside the workpiece so they would not be cut up while machining the ends of the caps. Even still, extra stock had to be left on the ends of the caps and removed later in a separate operation. 

I typically prefer to support workpieces, requiring both top and bottom machining, in a vise because I seem to get better results when re-registering the parts. My supply of 7075 was pretty sparse, however. The widths of the material I had on hand wouldn't have provided the margin required around the rods to stabilize the workpiece if supported in a vise during the final machining passes. As a result, I wound up with several inefficient set-ups and lots of workpiece preparation. Since I didn't have material to waste on workpiece mistakes, this preparation amounted to machining pairs of parallel surfaces with no precise dimensions. In my shop, trying to achieve both of these at the same time is pretty risky.

The first step in preparing the blanks was to parallel machine the long edges of both bars that make up each workpiece. Exact dimensions weren't important, but since the workpieces would be flipped over for top/bottom machining, parallelism was important. The top and bottom mill-rolled surfaces of the workpiece material was already as parallel as I could hope to achieve, and so those surfaces didn't receive any special attention before drilling the holes. The clearance holes and counterbores for the cap bolts were first drilled through the edges of the narrow bars. An extra hole was included for a pressed-in gage pin that was used to keep track of the locations of the bolt holes within the workpieces. Each pin was collinear with its row of holes and spaced a known distance from them. 

The tapped holes for the bolts were then drilled into the finished ends of the wide workpieces that will contain the rods. After bolting the workpiece halves together, the top and bottom surfaces of the assemblies were lightly faced to give consistent parallel surfaces for later fixturing. For these facing operations, the surfaces of the narrow bars were used to indicate the assemblies in the vise to insure the final faces of the workpieces wound up parallel to the rows of bolt holes. To complete the workpieces, their left hand sides were squared up. At this point, three of the workpieces' dimensions had been changed after their holes were drilled, and all three workpieces were slightly different. Only the gage pins knew exactly where in the workpieces the bolt holes were and where the rods would eventually wind up.

The first operation was to bore the rods' big and small ends using the gage pins to determine their exact positions. After completion, the middle rod's big-end bore was used as X0-Y0 for all subsequent operations, but Z0 remained with the gage pin somewhere inside the workpiece. The boring operations were done with the workpieces supported in a vise. At this point I was still optimistic about using a vise for the rest of the machining, and so I bolted a huge chunk of steel to the underside of the workpiece for reinforcement. It did a good job of damping the vibrations of the thin workpiece straddling the parallels and probably improved the surface finish of the bores. However, it was still no cure for the lack of stabilizing stock between the rods and the rods and vise jaws.

After giving up on using a vise for the rest of the machining, I re-surfaced a sacrificial block that's been in my shop for years. The workpieces were bolted down to it for their top side machining which included engraving unique identifiers on each rod/cap pair. The diameter of the bolt heads was only .007" less than the finished thickness of the rod caps, and so it was important that they end up well centered in the rods. Watching them emerge from the workpiece without a scratch during machining gave me the confidence I needed to carry the gage pin references over to the fork rod machining later. Before flipping the workpieces over to complete the bottom side machining, the partially cut out rods were glued to the workpiece using Devcon 5-minute Super Gel. This epoxy kept the rods attached to the workpiece frame while they were being cut free during the bottom side machining. All the bottom side filleting was done while the parts were attached to the workpiece by only the epoxy. When the bottom side machining was completed, the workpieces were heated to 250F, and the parts literally fell free. 

The final step was to unbolt the caps from the rods so the caps could be finish machined. To save time, three caps were machined simultaneously. A set of extra-small pattern steel washers were turned to fit under the heads of the steel SHCS's. The actual machining time on each blade rod/cap pair worked out to about two hours. About half of this time was spent on the cosmetic filleting that will never be seen after assembly. - Terry


----------



## kvom

How did you machine the rounding along the edges?


----------



## goldstar31

I have just been with a Merlin engine fitter whom I served with in 1948-50 in RAF31 ( The Goldstars) Squadron when it was at RAF Hendon.

Whilst there were 2 Squadrons 601 and 604, we had 'care' of three belonging to high ranking officers. Boothman of Schneider Trophy fame but perhaps more importantly SL-721 belonging to Air Chief Marshall Sir James Robb- a 16 which is still airworthy and in Canada. 

Ironically, we were both a mere 18 years of age then-- and now 86

Ex Corporal Norman Atkinson


----------



## mayhugh1

kvom said:


> How did you machine the rounding along the edges?



Kvom,
The filleting was done with many passes of an 1/8" dia. ball mill.
Terry


----------



## nel2lar

Terry
I've watch the progress for a long time and you still amaze me on your expertise and craftsmanship. The love of machine and man, you surely have achieved the highest. 
Nothing less than beautiful.
Nelson


----------



## petertha

Terry, I find your epoxy backfilling technique very intriguing. What sort of oven temp do you bring the part up to for glue removal stage? Do you treat the aluminum in any way prior, like an oil wipe acting as a release agent? Or do you endeavor to clean the metal to encourage a good adhesive bond during machining & just rely on the heat?


----------



## wirralcnc

On the subject of epoxy can you post picture of the epoxy you use.


----------



## mayhugh1

All,
Here is an Amazon link to the epoxy:

https://www.amazon.com/dp/B002YCACJ6/?tag=skimlinks_replacement-20

 If you Google 'Devcon 5 minute gel' you'll find many places that sell it. I get mine locally from Lowes which is a home building supply house. Devcon also makes a non-gel product which works about as well but with less tensile strength, but the gel is often more convenient because it won't flow into places you may not want it to go.

I thoroughly clean and dry the parts before use. The vegetable-base coolant I use for machining has to be thoroughly removed. I used to use acetone but recently switched to hot water and dish detergent which seems to do just as good of a job. Heat is the only release agent I use. The epoxy is only good to about 200F, and so an hour in an oven at 250F cleanly releases the parts. Sometimes I also just use a torch to warm up small parts for release.

I spent a lot of time several years ago trying various epoxies that were strong enough to withstand what I wanted to do with them, but would cleanly release with moderate heat. One lesson I learned was to stay away from JBWeld. Somewhere in the bottom of my scrap pile are some JBWeld epoxied test parts that I never could get to release. - Terry


----------



## mayhugh1

Forked connecting rods were commonly used in high performance aero-engines like the Merlin to help reduce length and weight of the power plant. For a given number of cylinders, the crankshaft needed only half the number of throws compared with a conventional V-engine. V-engines using conventional rods on shared crankshaft pins, however, required an offset between the cylinder banks. The Merlin's forked rods were split in two at their big ends, and the blade rods for the opposing cylinders were thinned down to fit in between the tines of the forks. This arrangement didn't require an offset between the cylinder banks.

The Merlin's forked rod has a single, wide bearing sleeve that spans the whole width of the rod including its central gap. The blade rod doesn't run directly on the crankpin, but instead runs on the outside of the sleeve. The two rods oscillate but don't rotate relative to each other. The bearing is relatively lightly loaded and doesn't run at high speed, but the resulting reciprocating motion complicates its lubrication. As in the full-scale engine, the crankshaft's pressurized oil system will provide a protective oil film between the sleeve and the crankpin, but the Quarter Scale's blade rod will depend upon splash lubrication from sump windage.

I started work on the fork rods while the fixturing that was worked out during the Quarter Scale's blade rod machining was still fresh in my mind. I had some longer pieces of 3/4" thick 7075 material, and these allowed more separation between the parts for a more rigid workpiece. They also allowed the use of larger cutters to reduce the extra machining time required by the thicker workpieces. The width of the material, though, was identical to that of the half inch material used for the blade rods, and so pretty much all the workpiece preparation and many of the machining steps wound up being similar. The big and small end bores are the most critical operations in the rod machining. They must be parallel to each other to avoid binding the rods in the cylinder bores. Identical big end bores will also ease the bearing fitting process later.

Each fork rod has two pairs of 3-48 steel cap bolts, and so there were two rows of bolt holes in the workpiece layout. The gage pins were placed between the bolt hole rows and on the centerline of the final parts. Most of the text in the previous post describing the blade rod machining also applies to the fork rods, and so the photos should be pretty much self-explanatory.

Extra care had to be taken while machining the slot between the tines of the fork rods because a 3/16" diameter end mill with a 1-1/4" stick out was required. From experience, I've learned that this is a recipe for chatter. With only a few thousandths clearance specified on either side of the blade rod, a smooth surface finish on the walls of the slot was important. The speed, feed and d.o.c. were experimentally determined on a test part before the actual machining was begun. In order to obtain an acceptable surface finish, a roughing pass down the center of the slot followed by light finish passes on each wall were required.

Devcon may have changed the recipe for their epoxy gel since the last time I purchased it. The new product I bought for the fork rods was in a different color package and behaved differently. After baking the finished workpieces to remove the finished rods, I found they still released easily so long as the workpieces were at 120F or so. But, I allowed one to cool back to room temperature, and the epoxy hardened and regained its grip on the parts. After re-warming the parts until the gel became flexible again, the rods easily released. Unfortunately (for me) Devcon may be trying to improve their product's high temperature performance.

The final machining on the ends of the rod caps was done with the caps clamped together in groups of four. A torus end mill with a .015" corner radius was used to machine the smooth contour using many fine steps.

I didn't feel comfortable with torquing the steel rod bolts down against the aluminum rod caps, and so I turned three dozen .155" diameter steel washers with a very close i.d. fit to the bolts for use under their heads. - Terry


----------



## Parksy

Superb work as always Terry! 

I always learn something from your posts.


----------



## Ghosty

Hi All,
Only found this site the other day. Have been reading through this thread.
You amaze me on your expertise and craftsmanship. Will follow to the end.
Many years ago I came across a 1/5 build, done some looking and found it
http://enginehistory.org/ModelEngines/merlin_xx.shtml
[ame]https://www.youtube.com/watch?v=0xe1LL1IC7Y[/ame]

Cheers
Andrew


----------



## mayhugh1

To date, the only split sleeve bearings I've made were the main bearings done earlier for this engine. For those, I took a whimsical departure from common practice and went down an involved but fun path that included rolling out pure silver plate and forming shell bearings using my own shop-made press dies. The final results with their pressed-in oil grooves turned out better than expected, and the experience was certainly worth the time and effort put into it. But, having been there and done that, I wanted to try something different and, hopefully, much simpler for the rod bearings. 

While researching piston ring fabrication techniques several years ago, I came across a method being used by a model builder who was making his own cast iron rings. His technique was to measure the diameter of his cylinder bore from which he calculated a circumference, and to this circumference he added the width of the slitting saw that would be used to cut the ring's gap. This new circumference was then divided by pi and used to calculate the o.d. of the blank from which the rings were parted. Although the builder claimed his rings fit his cylinders perfectly, it seemed to me that most of the contour change needed to even get one of these rings inside its cylinder would occur at its highest stressed point directly across from its gap. His fits were evidently good enough to get his engines started, but I doubt they were perfect. I was more impressed by G. Trimble's quantitative arguments and adopted his method for making my own rings. I felt, however, that someday I might apply this builder's technique to making split sleeve bearings. With two individual bearing halves there are no concentrated areas of stress. Only one of two saw kerfs would have to be absorbed in each split bearing's contour adjustment when inserted into its rod. Since the absorption areas are much wider, a more uniform contour adjustment is possible.

I decided to finally adapt this ring-making technique to the machining of the Quarter Scale's rod bearings. To calculate the o.d. of the bearing blank, I started with the diameter of a rod's big-end bore which I multiplied by pi to obtain its circumference. To this I added twice the kerf width of the saw that will be used to slit the blank plus an additional thousandth for 'crush'.

In order to establish the bearing's thickness, I performed a similar calculation for the blank's i.d.. To the diameter of the rod journal I added .003" for a running clearance before calculating a circumference. To this circumference I added twice the width of the saw kerf and then divided the result by pi to obtain the i.d. of the bearing blank. The running clearance would have been closer to .0015" if my rod journals had ended up perfectly circular. Despite my best efforts during the crankshaft machining to prevent the Merlin's ten inch long 1144 alloy crankshaft from flexing while the journals were being turned, they wound up with circularity errors. On such a long crankshaft, grinding the journals would probably have given a better result.

The end of the rod blank was turned/bored for only one bearing at a time since I had decided to machine a custom size bearing for each journal. After machining its end to the calculated inner and outer diameters, the blank was moved to the mill and carefully slit on its exact center using a .010" slitting saw. In order to accurately locate the rather unwieldy thin bade, I marked the top of the bearing with a Sharpie and then carefully lowered the backwards spinning saw blade until it just rubbed the mark. The saw was then lowered half the diameter of the blank plus half the thickness of the blade before reversing the spindle and splitting the bearing.

After engraving the end of the bearing with an identifying number on each side of the slit, the blank was moved back to the lathe. A close-fitting Delrin rod, supported in a rotating tailstock chuck, was inserted into the end of the blank. The slit bearing was clamped around the rod using a simple shop-made Delrin clamp so everything would be nicely held together during the parting operation. After parting, but before removing the clamp, both ends of the bearing were manually chamfered with a large 90 degree countersink so the inner edges of the finished bearing would clear the journal's tiny inside corner fillets.

SAE 660, also known as 932 bronze, is probably the 'gold standard' for tin-leaded bearing bronzes, and it was originally specified for the Quarter Scale's rod bearings. This spec was later changed to a somewhat less common 936 bearing bronze which is about 10% softer than 932. I suspect this was done to reduce wear on the blade rods which were specified to be machined from 6061 aluminum. Since I used a harder 7075 alloy for my rods, this probably wouldn't have been an issue. However, I didn't have either alloy on hand in a large enough diameter, and so I ordered a $hort cored length of one inch diameter 936. I'd have wasted a lot less material with a 3/4" diameter workpiece, but no one seemed to have that diameter in stock when I placed my order.

Before launching the entire lot of bearings, I measured and recorded the diameters of all the rod journals as well as the bores of all the fork and blade rods. Using these measurements I pre-selected a best-fit rod pair for each journal and then machined a single trial bearing in order to test out the theory.

When placed side-by-side, the finished trial bearing halves don't appear to form a perfectly round circle. But, just like the commercial automotive bearings I've used, they literally snap into place inside each rod half. Under a microscope I checked the fit of the bearing's contours to the bores of the fork rod and cap before torquing the two together, and both sides appeared to match perfectly. The fact that the bearing halves are retained by the rod halves turned out to be a real convenience while installing the rods within the tight space inside the crankcase. The gap between the installed shell halves closed up to zero when the cap bolts were tigtened; and, as far as I could tell, the crush height came out as expected. I measured the inner and outer diameters of the bearing while installed in its fork rod and both agreed closely with the calculations. 

When finally comfortable with the test bearing, I spent the next few days working as a Rolls fitter but without the skill and efficiency of those who performed the same task 75 years ago. After machining and checking the fit of each bearing in its rod pair while installed on the crankshaft inside the crankcase, I recorded the i.d. numbers and the orientations of all the components along with their journal location. Since the first few sets of parts involved installing and removing the rod bolts several times, I temporarily switched to a shorter set of bolts so I wouldn't add unnecessary wear the deeper threads that will be filled later by the actual rod bolts. I chose to not leave the rods in place after performing these preliminary fits. When the wrist pins are completed, I'll recheck the fits with the pistons installed and running temporarily in a pair of opposing cylinders. Checking these pairs systematically, one at a time, will make it much easier to locate any binds that could be caused by crank machining errors. Once the rods and bearings pass this test they can be finally installed on the crank. - Terry


----------



## xpylonracer

Great machining work and equally good write-up Terry.

xpylonracer


----------



## dsage

Hi Terry:
All I can say is I'm glad you chose the Trimble method to make your rings back when you made them. I've found rings to work perfectly using his method.
 But I'm concerned about using this new method described to make circular elements including bearings.
 I also read the article you mention about making the circumference (essentially the  diameter) of the rings greater by the width of the slitting saw and think it is seriously flawed. Of course I may have misunderstood his writings.
 I have perhaps an odd way of making sense of things in my mind by extending theories to crazy proportions to see if the idea still makes sense. So in this case lets assume (for rings) you wanted to use a slitting saw with a width of 1/8"  Why would you add 1/8" to the circumference of the ring circle? The resulting diameter of the ring would obviously be WAY too large to fit the cylinder. Even if you could insert it in the cylinder it would obviously no longer be round.
 I won't elaborate any further on my concerns because perhaps I'm misunderstanding the whole process.
 You have obviously measured your results - especially the inside diameter - with great accuracy. I trust your superior workmanship so they must be correct. It just doesn't make any sense to me.
 Question: Does the bearing half slide in from the side of the rod without effort (rather than snapping it in from the top - which forces it to compress out of round)? Would it make any sense to insert a precision ground rod in the bearing with some bearing blue on it to observe the contact points? (or assemble one rod in the engine with the bearing blue). I'm going to guess that the bearings are pinched at the parting line.
  I'm just trying to understand this process better. Sorry for the distraction from your thread.

Very nice work - as usual.
Thanks

Sage


----------



## kvom

WRT Sage's question, I believe that the bearing deforms slightly when pressed into the rod end, and the extra circumference means that both halves meet with no gap from the kerf.  

Obviously the rod end diameter was made larger than the crank journal by the thickness of the bearing material.  Whether the bearing thickness is derived from the two measurements would be a question for Terry.  Since he appears to have made each bearing individually, I'm guessing each was made to fit.


----------



## mayhugh1

Dave,
I often use the same technique of exaggerating an element of an explanation in order to help understand what's going on. In this case, increasing the kerf width shows that the kerf is, indeed, an error; and this technique for making bearings is a compromise solution. I really should have given more information in my post about why I used such a thin saw blade, and so I'll do that here.

The hope was that the kerf error would be distributed around a good portion of the circumference of each half shell and become negligible or at least comparable to my other machining errors. The actual diametrical error that I'm trying to distribute is not the kerf width but the kerf width divided by pi. When I machined the big-end bores on my rods I chose to interpolate them on my Tormach instead of using a boring bar. The backlash on my particular machine is sufficient to yield circularity errors of two to three tenths which I considered acceptable since the fork rods are not intended to spin on the bearings and so any circularity error will only help hold them in place. The blade rods, though, are spec'd for close sliding fits on the bearings, but they rotate only through an angle of less than 90 degrees. With selection, I was easily able to achieve smooth sliding fits of all the rods throughout this angle, and the selections were recorded so they could be reproduced at final assembly. 

This brings me to the rod journals. As mentioned earlier, I started out having to deal with half thousandth circularity errors on some of the journals themselves due to the method used to machine the crankshaft. The measured i.d.'s of my compromise installed rod bearings ended up with their own circularity errors ranging from one to three tenths, and so my solution was to machine a custom bearing for each journal with as good of a fit as I could achieve. My worst-case clearances ended up at about three thousandths which was more than I liked, but after all this is a model engine. My back-up plan was to re-bore the bearing i.d.'s with a boring bar while the bearings were installed in the fork rod. For many applications this would have been a first order solution for making bearings. In this case, it didn't seem to be worth the effort or risk. I doubt my rod journals would have known the difference. To finally answer Dave's question - no, the bearing halves won't slide into the sides of the rods but are most easily pushed into place from the end of the rod. While free standing they have the right circumference but wrong diameter for the rod bore. - Terry


----------



## nel2lar

Terry
I am not a pro but the one piece bearing I'm woried about. The two pistons move a little bit and a solid bearing would hold it tight. Or am I looking at it wrong?
Nelson


----------



## mayhugh1

Nelson,
I'm sorry, but I don't quite understand your question. Could you please elaborate a bit further? The two rods are free to rotate with respect to each other if that is what you are asking. - Terry


----------



## Ghosty

nel2lar said:


> Terry
> I am not a pro but the one piece bearing I'm woried about. The two pistons move a little bit and a solid bearing would hold it tight. Or am I looking at it wrong?
> Nelson


 
I think what he is looking at, is there are two con rods on a single bearing set, how will the rods move independent of each other?

Cheers


----------



## mayhugh1

The bearing is gripped by the fork rod, and so the bearing and fork rod as a pair are free to rotate on the rod journal. The blade rod, on the other hand, is free to rotate on the bearing. Therefore, the blade and fork rod are free to rotate with respect to each other. Because of the angle of the opposing cylinder banks, though, the fork and blade rods really only have to move over a very limited range with respect to each other. Hope that makes it clearer. -Terry


----------



## Ghosty

Mayhugh1, thank you for the reply, and clearing this up, just that in post #459, 7th photo, it showed the bearing would be a tight fit on the single rod, then in the 8th photo it showed the bearing shells fitted to the forked bearing.
Cheers


----------



## dsage

Hi Terry:

Regarding the circularity of the bearings:
As with the rest of your superior workmanship you have thought this issue out further than most anyone else would have. As you point out the result is what counts and you have proven it out.
 Amazing work.

Thanks

Sage


----------



## nel2lar

Terry
I am more lost now than what I was earlier. If the center rod is going to rotate any amount. When it comes to rotation with the bearing on the crank is the normal thing, but to rotate the rod end on the outside of the bearing, that movement no matter how small will have negative results and the rpm that motor spins at how long will it take to gald and lock up. I think it will hurt to see that thing self destruct. 
Nelson


----------



## grapegro

Hello, Henry Ford used similar type bearings in his V8 engines from 1932 to 1942. How many thousands of those motors were sold and performed. Norm


----------



## brendanf

I think Nelson is worried that there is no lubrication being supplied to the outer surface of the rod bearing for the blade rod other than some splash type lubrication. I had a similar thought when I first saw the design.

The bearing stays in place on the fork rod, and is lubricated against the crank journal which is like a conventional engine and oil flows through the crank providing oil to that surface, but it appears there is no such system for the blade rod.


----------



## mayhugh1

I suppose I could drill a hole through the two bearing halves. This would provide a path for pressurized oil from the rod journal to reach the interface between the bearing and blade rod. In the current design, the pressurized oil from the rod journal will flow out around the ends of the bearing, and some will inevitably be wicked in between the bearing and blade rod. In addition, there will be splash from windage.
Although I had my own misgivings about the blade rod's lubrication, I reasoned it was no different from the problem of lubricating the rods' small end bearings. In a model engine these usually rely only on splash lubrication, and many designs don't even include a dedicated bronze bearing. I've seen some model engine rod designs using an end-drilled hole at their small ends to help oil entry, but many do not. I'm pretty sure I read someone's convincing analysis that concluded its small benefit wasn't worth the stress riser it could introduce on a typical model engine rod end which typically has a marginal amount of material around the wrist pin bore. -Terry


----------



## Ghosty

Mayhugh1, Your work is brilliant and I bow down to your ability, With the blade rods, maybe a 1/32" or 1/16" hole in the bearing shell now will avert any possible problems with the rods further down the road, will keep watching as you progress with the build on this masterpiece.

Cheers
Andrew


----------



## IceFyre13th

steel crank moving on bronze bearings = OK

Aluminum rod moving on bronze bearing........not so much

I suggest every rod has its own bearings so they stay in a fixed position in the rods but move freely on the crank, yes that means 1 bearing set becomes 3 sets, but will work better in the long run.

Or try to build as the real rods were, more difficult but will prevent the possible failures you may have down the road with aluminum moving over bronze.

http://www.enginehistory.org/phpbb/viewtopic.php?p=562&sid=36c9010b4523bceaaa2899b3971040ac has information on the real rod design, notice the inner bearing / outer bearing system they had.

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=10&ved=0ahUKEwjajvyauvbPAhVB6CYKHUiMC5cQFghVMAk&url=http%3A%2F%2Fwww.enginehistory.org%2Fmembers%2Farticles%2FCrankpinBearings.pdf&usg=AFQjCNH-gJWgo8p6k7t_SwjfTgOR7tkPig&cad=rja is  a PDF on how the bearings were developed.

These guy's http://www.51-factory.com/merlin_overhaul.html would be able to help more as they are the experts on the real deal.


----------



## mayhugh1

IceFyre13th,
Thank you for the references and comments. I had briefly thought about adding a second bearing for the blade rod because from an engineering perspective it just felt better. Because of limited clearances around the rods, though, it would have been necessary to remove material from the blade rods in order to make room for the bearings. And, the blade rods already look a bit anemic to me.

I totally agree with you that putting (6061) aluminum against a bronze bearing doesn't feel right. The Brinnel hardness of 6061 is 65 while the 936 bronze I'm using has a hardness of 60. There's essentially no difference between the two, and so the two parts would essentially wear each other out instead of one 'wearing in' to the other. However, I used 7075 aluminum for the rods, and it has a hardness of 150. My justification for staying with the stock design's single bearing was that this difference would probably be adequate for the bearings a model engine. I admit I have little to back this up especially since there are so few running examples of this engine, and even for those I don't know what modifications the builders might have made. - Terry


----------



## IceFyre13th

mayhugh1 said:


> IceFyre13th,
> Thank you for the references and comments. I had briefly thought about adding a second bearing for the blade rod because from an engineering perspective it just felt better. Because of limited clearances around the rods, though, it would have been necessary to remove material from the blade rods in order to make room for the bearings. And, the blade rods already look a bit anemic to me.
> 
> I totally agree with you that putting (6061) aluminum against a bronze bearing doesn't feel right. The Brinnel hardness of 6061 is 65 while the 936 bronze I'm using has a hardness of 60. There's essentially no difference between the two, and so the two parts would essentially wear each other out instead of one 'wearing in' to the other. However, I used 7075 aluminum for the rods, and it has a hardness of 150. My justification for staying with the stock design's single bearing was that this difference would probably be adequate for the bearings a model engine. I admit I have little to back this up especially since there are so few running examples of this engine, and even for those I don't know what modifications the builders might have made. - Terry



To me, and being "small scale" I would just split the single bearing into 3 bearings.....leave < 0.005" clearance or so between the "rod" and "blade rod" then you will be steel on bronze for all. Also you wont be running the split of the rod cap past the split of the bearing, something that may accelerate galling.

And like you, nothing to back up this idea.......it just sounds more "right" to me. 

I still cant wait to see this marvel running!!!!!


----------



## Ken I

I would also be concerned about galvanic corrosion between the aluminium and the bronze. (Brass and aluminuim are particularly bad - ask anyone whose used those pretty aluminium tyre valve caps on the brass tyre valve stems - after a couple of months they are never coming off).

In an oiled environment its not that big a problem as the oil inhibits current flow but if the engine stands for long period with "acidified" used oil it will tend to generate stains at point of contact.
This is mild corrosion and I'm not sure of the long term implications.

I would be tempted to replace the oil any time it becomes significantly discoloured.

At very least I would keep a careful eye on it.

Thanks for your impressive documentation that allows all us awe struck mortals to follow your awesome project.

Can't wait to hear it burble into life.

Regards,

Ken


----------



## mayhugh1

The wrist pins were machined from a length of 5/16" diameter O1 drill rod. I used the same drill, reamer, and holder to machine the holes for the wrist pins in both the pistons and the rods so their diameters would all be identical. From a couple different lots of drill rod that I had on hand, I selected a length that was a close slip fit in the bores. The wrist pins float and can move side-to-side in their cylinders, and so the liners need to be protected from them. The centers of the pins were drilled out, and a soft aluminum rivet was pressed into each end in order to buffer them from the liners. I also drilled tiny air escape holes through the centers of the rivets before they were installed.

The pins were hardened before the rivets were pressed in place. I've created extra work for myself in the past by hardening cylindrical parts after they had already been carefully fitted to their mating bores. So, I ran an experiment on a trial pin before launching the dozen or so parts I'll eventually need. After all its machining was completed, the diameter of the annealed wrist pin measured .3126" at room temperature. The pin was then placed in a triple-folded stainless steel envelope filled with argon and heated for 45 minutes at 1475F. After quenching, and a return to room temperature, the pin's scale-free diameter had increased by a whopping six tenths to .3132" and would no longer fit any of the bores. After a one hour temper at 450F and an overnight return to room temperature, the pin diameter remained at .3132". I had to polish a half thousandth off the pin's diameter to re-fit it. I searched through my stock of drill rod once more and found another length that measured .3122" that, in its annealed state, had a loose fit in the bores. I used it to make the rest of the wrist pins. After hardening, I still had to polish off a couple tenths, but polishing left the pins fitting perfectly and with nice bearing surfaces. 

The amount that heat treatment affected these particular pins was dependent on a number of factors including their size, form, material and, most likely, a number of factors involved with the quench. Looking back on my notes for the 18 cylinder radial I built, I remembered that its O1 tappets had grown only three tenths from an identical heat treatment.

Assembling the heads to the cylinder blocks and then installing the combinations onto the crankcase will be a complicated step that I hope to perform only once. The original Quarter Scale design would have allowed the rods with their attached pistons to be installed down through the tops of the cylinder blocks before the heads are installed, which might have made the process a bit easier. Because of my liner modifications, though, the rods' big ends will no longer fit through the liners. Instead, each cylinder block will now have to be inserted down over 14 studs and all six rods and pistons simultaneously after they've been pre-assembled to the crankshaft. An online ancient Rolls factory video shows the full-scale engines also being assembled this way.

My plan is to prepare everything I possibly can ahead of time to make this assembly go smoothly, including locating and clearing any binds or interferences beforehand. I've had a major concern about potential errors between the axes of the rods and cylinders that could cause piston scuffing or, even worse, binding. The Merlin's design which separated the cylinder blocks from the crankcase is a result of reliability issues discovered during testing of its original uni-block design. There was no time in its wartime production schedule to fix the problems associated with the original design, and so the Rolls engineers decided to break up the block into three separate castings. This decision added considerable complexity to the engine's manufacturing, but it evidently solved the reliability issues.

In the Quarter Scale, this three casting combination resulted in some dozen machining operations in as many different setups that affected the alignments of the rods in their cylinder bores. This issue first became a real concern of mine over a year ago while working on one of the machining setups for the crankcase. When I realized how errors from that setup, as well as from so many other set-ups to come, could stack up to affect this alignment, my hiatal hernia woke up. 

With the rods, pistons, and wrist pins completed, I could finally begin checking the rod alignments. An important first test was to install a pair of rods and their liners, one opposing pair at a time, so I could individually check the smoothness of motion of the reciprocating piston pair as the crank was rotated. For this test I torqued the main bearing caps to their final values, and I also installed the main cap cross studs which were made much earlier during the crankcase machining. In order to secure the liners in their registered positions on the crankcase, a couple simple Delrin fixtures were constructed. The same pair of fixtures were usable in all six cylinder locations. To my great relief, I couldn't detect any rod issues in any of the cylinders. 

The installed rods were checked by carefully watching the un-ring'd pistons for any twist or side-to-side rocking motion while feeling for any bind in the crank was as it was slowly rotated. Then, with the pistons at various depths in their cylinders, the rods were moved back and forth axially on their journals to the limits of their clearances while the small ends were watched for the same motion on their wrist pins. These tests weren't quantitative and they didn't include the cylinder blocks, but I came away feeling a lot better about the crankcase and crankshaft machining. A similar test will be repeated later with all the rods, pistons, and cylinder blocks installed before the heads are added.

The two head/block assemblies will eventually be secured to the crankcase with twenty-eight 8-32 studs. I was lucky to find a package of 50 four-inch long studs on a Cabin Fever vendor's table earlier this year. The packaging claimed these commercially made studs were fabricated from 60 kpsi steel, and their threads rolled. In addition to being shortened a bit, the center three inches of each stud had to be reduced to 1/8" diameter in between its threaded ends. The clearance this operation provides will allow the head/block assemblies to more easily slide down over them during assembly and reduce the difficulties involved with trying to simultaneously register all six liners and fourteen oil seals to the crankcase. It was possible to turn down only about a half inch at a time on each stud before repositioning it in the lathe's chuck. This tedious operation on the whole lot of studs required several days, including lots of procrastination time, and was one of the least fun parts of the build. 

All the rods were finally assembled to their journals using full length steel rod bolts and the custom washers made earlier. Before installing them, I drilled holes through each rod bearing pair so that pressurized oil from the rod journals could better reach the blade rods. I drilled a single hole in the fork cap bearing shell near the journal hole and a pair of escape holes through the opposite bearing half. After digesting everyone's comments and doing some more research, I think these holes and the use of 7075 for the blade rod is a good compromise and should probably have been part of the original Quarter Scale design. During my research I found an online drawing showing similar oil holes in the full-size Merlin's bearings. Finally, the cylinder block studs were threaded into place in order to verify their fits in the cylinder blocks. - Terry


----------



## petertha

mayhugh1 said:


> After quenching, and a return to room temperature, the pin's scale-free diameter had increased by a whopping six tenths to .3132" and would no longer fit any of the bores.


 
Beautiful work as usual, Terry. 

I'm glad you mentioned this issue because these fit-up subtleties are a source of head scratching (at least for me). I experienced the exact same post-hardening wristpin growth & suspect even more variation among my samples which I chocked up to my primitive torch & dunkaroo methods. Anyway, my nice sliding (annealed state) wristpin fit was no longer.

My first inclination was to lap the wristpins back down to size because they could be counted on to always grow. The plan was drill all pistons/rods identically. That lapping test turned out to be fussy work. They are short with not much grip area for the collet in order to lap the entire length eventually by flipping them around.

On a scrap (7075 Al) connecting rod I went a different route & lapped the hole with a piece of very mildly tapered drill rod to match the wristpin as a set. That actually had a nice fit & was pretty easy to do, but of course a micro bore angle. But it was more of a trail towards getting a needle lap when the time comes.

Then I got thinking about my RC engines, Many times I have had to mildly heat the piston to expand & the wristpin would then push through. I used to think it was gunk factor or maybe even distorted in duty. But I've also had brand new assemblies where this is the case. They slide nice on a brand new rod, but are much tighter in the piston. Maybe a function of those high revving designs, they want them locked down?

But I'm curious now with your tooling comment. You want the same sliding fit between piston/pin and pin/rod? What advantage does a floating wristpin within the mating piston hole provide?


----------



## mayhugh1

Peter, 
From a functional view, it would probably be better to have a slip fit on the rod and a light press fit on the piston, but doing it twelve times requires consistency I'm likely not capable of. In order to be certain the pin doesn't work itself sideways when the piston heats up, the fit would need to start out on the tight side. Then there's the issue of assembly/disassembly. I'll likely separate the two parts several times for one reason or another before they're installed for the final time, and so there's risk of damage if the fit is too tight. A 'slip fit' is a little more forgiving machining-wise than  a 'light press fit'. - Terry


----------



## kvom

I remember a post on another site where it was claimed that most drill rod is not perfectly round but likely to be tri-radial, a relic of the manufacturing process.  If that is true, you'd likely want to polish off a few tenths regardless.

I can see the first-run date coming soon.


----------



## petertha

kvom said:


> ...where it was claimed that most drill rod is not perfectly round but likely to be tri-radial


 
Interesting. That's consistent with what I discovered on some O1 drill rod. Maybe it varies by manufacturer, but I could make out 3 shiny spots after the slightest of lapping on new rod. I guess the typical +/- specs refers to equivalent largest diameter maybe? 

Anyway, it made me think hard about fits like this. You have to start somewhere & decide where the adjustment will occur. If the drilled/reamed hole is the standard based on tooling, then pin has to compensate. If the pin is the standard, then the opposite is true. I'm not convinced that lapping the piston hole in my case might not be easier, but like Terry was mentioning, every situation is different.


----------



## Ken I

FYI

Tri-lobal grinding is an artifact of poor centreless grinding set up (grinding too close or on the centreline between the grinding and regulating wheels).

I ran #2 & #3 Cincinnati centreless machines for over 20 years.

It shouldn't be there but can be very subtle - you won't get rid of the shape by papering.

It's also hard to measure without a "V" micrometer or a Tallyrond - which I've found bar grinders seldom have - until they have a major quality return cost problem - Ahh well !

It's perplexing to mike up a bar and find it undersize to a reamed hole and yet it doesn't fit (constant chord trochoid).

Regards,

Ken


----------



## Charles Lamont

Ken I said:


> It's also hard to measure without a "V" micrometer or a Tallyrond ...


You can simulate a V micrometer by resting the rod in a V-block and checking the top with a DTI. This should tell you if the rod is out of round.


----------



## mayhugh1

The crank (and now) big end rod bearings will receive pressurized oil from a manifold affixed to the main bearing caps. The tops of the caps were prepared for this manifold while they were being machined near the beginning of this build. A drawing provided in the Quarter Scale's documentation shows a soldered manifold assembly made up from soft copper tubing. Even though the manifold will be hidden inside the engine, I was hoping to come up with one that was more like that in the full-size Merlins. In the full-scale engine, the manifold was integrated into the crankcase casting, and it ran along an inside edge rather than through its center. I tried for a few days to come up with a similar solution; but crankcase obstacles, as well as my own requirement that the manifold not block access to the rod or cap bolts, seemed to dead-end all my efforts. Eventually, I gave up and designed a machined version of the original tubing manifold that functionally was pretty much the same thing.

Even in the center of the crankcase, space for the manifold between the rotating rods and the bottom of the oil pan is limited. The space above the rearmost main cap was especially troublesome because it contains the oil pump drive and driven gears. While developing my own design, I realized that the original soft tubing version had some advantage over what I was trying to do because it could be more easily snaked through and around the obstacles in this area. My rigid design wasn't as accommodating, and I had to modify the oil pump drive gear bracket in order to gain access to the oil inlet on the rearmost main cap.

I machined seven pedestals to function as oil feeds to the bearing caps as well as supports for the manifold. The complete set of pedestals was machined as a group similarly to the connecting rods using a piece of yellow mystery metal from my scrap collection for the workpiece. With carbide tooling I was able to obtain a barely acceptable surface finish, but I ran into real difficulties while drilling the inch long 3/32" holes for the oil passages through the edge of the workpiece. Even with .050" peck drilling I could hear the crunching of the hard chips being re-drilled in the deep holes. Before I could get the drilling parameters dialed in, I had broken two drills and a reamer in addition to ruining a couple parts. Even with shipping it would have been a lot cheaper to have ordered a chunk of 360 brass, but I mistakenly thought the hard part was over.

After completing the machining, I made up a soldering jig from a piece of steel that precisely duplicated the locations of the pedestals inside the crankcase. At the last minute, though, I decided to solder up the manifold while its close-fitting parts were assembled in the crankcase just to make sure there would be no fit-up issues later. As part of the original main bearing cap machining, I Loctited short nipple tubes into the tops of the caps. These tubes not only prevent the shell bearings from spinning, but they should provide more positive seals for the oil inlets. At the time, though, I was more focused on reducing oil leaks than I was on easing the final manifold installation. Now, the manifold had to be soldered together with enough precision so that all seven pedestals in the assembly could be simultaneously set down on all seven snug-fitting oil inlet tubes.

Just when I thought I had a workable plan, my mystery metal started screwing with me again. The solder-ability of the pedestals turned out to be extremely poor. This surprised me, because I didn't think there was a yellow metal out there that didn't have an affinity for soft solder after being fluxed with the flux I was using. The butane micro-torch, 60/40 solder, and fully-activated rosin flux that had always produced excellent results on all the bronzes and brasses I've come across in the past now seemed to be struggling. The metal was difficult to wet and didn't want to wick the solder in between it and either a brass or copper manifold tube no matter how I cleaned and fluxed them. Thinking that the shelf life of my flux might have expired, I also tried some plumbers acid flux; but it worked no better. I moved the soldering process out of the engine and onto the jig so I'd have better control over the torch. All I was able to accomplish, though, was to overheat the flux and contaminate the parts. I pickled them in sulphuric acid in a effort to save them; but after a couple of the better looking joints failed pressure testing, I scrapped the entire week's work and ordered a bar of 360 brass so I could start over.

After receiving the 360 brass, I machined a second set of parts using exactly the same processes I had used on my mystery metal. The improvement in surface finish was very apparent, and there were no drilling problems. This time, the soldering was effortless, and the joints turned out nice and bright with full smooth fillets. I soldered up the assembly on the jig, and after struggling to get it installed in the crankcase, I briefly reheated each joint to relieve any stresses in the assembly so it would more easily install later.

The final step was to fabricate an inlet for the center of the manifold. The side of the crankcase had been earlier drilled for a mounting flange for this inlet according to a drawing in the documentation. However, the mounting holes for the flange were shown with only .250" separation which make them uncomfortably close to the 3/32" manifold tube in between them. After the inlet tube and flange were soldered to the center of the manifold it was important that the mounting flange mate perfectly with the crankcase so it wouldn't hinder the manifold installation. The mounting flange wasn't accessible for soldering inside the crankcase, and so a second soldering jig had to be constructed. The shape of the inlet tube was complex and unforgiving, and several attempts were required to obtain one with a satisfactory fit. Fortunately, when completed, the entire manifold assembly easily slipped into the crankcase as it should. Finally, a set of gaskets were cut from 100% linen paper (rag paper) to seal the pedestals to their caps as well as the inlet flange to the crankcase. 

The worst-case clearances between the manifold and the rotating parts on the crank wound up at about .030". Final clearance to the stationary oil gear bracket overtop the rearmost cap was just over .010". - Terry


----------



## petertha

Beautiful work. What size bolts are holding the pedestals? Sorry to hear about the mystery metal detour. I was wondering maybe lead content, but looks like 360 just has as high concentration as any. Maybe that's just a welding thing I hear about re free machining (leaded) alloys? 
http://www.makeitfrom.com/material-group/Brass-Copper-Zinc-Alloy

Aluminum brass maybe?


----------



## mayhugh1

Peter,
The pedestal bolts are 2-56. I don't know if I'll ever know what that alloy really was. From its color, I had guessed it was a bronze. - Terry


----------



## Parksy

Perfect work as usual. It certainly is becoming an aesthetically pleasing piece of machinery.
It's a shame that the unknown material didn't play the game, I bet a lot of hours went into making those.

I'm led to believe that you've done it manually? If this is correct, do you use charts with demensions and follow a DRO, or is it just a matter of carefully cutting a pre marked shape by hand?


----------



## mayhugh1

Parksy,
Those parts were CNC cut on my Tormach. I wouldn't have a clue about how to make them manually. - Terry


----------



## dsage

It's a good thing you ditched the mystery metal. A fellow club member had a similar problem trying to silver solder some mystery metal - well actually I think he said it was aluminum bronze (not sure) But maybe same for yours. He did get it to silver solder with great difficulty. Luckily he tested it because the joints failed easily.
You wouldn't want it to fail. Those new solder joints look good.
   He also said it was difficult to machine which may explain your un-satisfactoy finish.

Nice work (as usual).

Sage


----------



## mayhugh1

There are some fittings related to the cooling and oiling systems that probably should completed before further assembly makes their locations less accessible. The castings seem to contain a number of undocumented provisions for plumbing coolant through the engine. Some of these may have been the result of a continually evolving Quarter Scale cooling system, and some may be cosmetic and never intended to be functional. Some are probably my misunderstanding of by-products of the casting process and totally unrelated to the operation of the cooling system. 

At the beginning of the build, I was thoroughly confused about coolant flow through the engine because many of the passages in the heads and cylinder blocks weren't continuous. As I probed my way through them, nothing seemed to make sense until I realized the passages were blocked by investment left behind by the casting process. After clearing the blockages, I was able to develop a plan for the coolant loops for which I can now machine the final fittings and block-offs.

The first of these fittings is associated with the cylinder blocks. The dual output pump will pump coolant into the engine through the outside of each cylinder block so it can flow around the liners on its way up into the heads. The coolant will enter the blocks through inlet logs that were previously assembled from aluminum tubing and machined fittings that were supplied as castings. I turned stainless barb adapters to attach flexible hoses between the pump and these assemblies. The o.d.'s of the adapters were limited by their close proximities to the rear engine mounts. For maximum flow, the i.d.'s of the cast fittings were partially threaded for the largest UNF thread that wouldn't break through their walls, and the threads were sealed with JB Weld. An aluminum plug was turned and pressed/Loctited into the final opening in the block's coolant passage located just below each inlet log.

Based on recommendations received earlier on this forum, I purchased two sealants: Hylomar M and Permatex Aviation Grade Sealer. Neither of these were available locally, but both were easily found online. The Permatex aviation sealer is thinner but otherwise very similar to the Permatex No. 2 non-hardening sealer that I've used for decades in automotive applications. Its squeeze out is much easier to clean up than the sticky mess typically left behind by the No. 2 sealant, though.

The blue-colored Hylomar M is quite different from any sealer that I've used before. There are a number of Youtube videos that demonstrate its use much better than I can describe with words.

[ame]https://m.youtube.com/watch?v=6gKbg8ah0c4[/ame]

After painting it on the mating faces of the two parts to be sealed, the solvent is allowed to evaporate for several minutes, and this leaves the sealant adhered to each surface. When the two parts are placed against each other, the interface between the layers of sealant forms an effective seal against most engine fluids. The two parts may be easily separated any number of times, but the same seal will be recreated each time they are reassembled. Some testing that I did showed that using minimally thin layers of Hylomar on a pair of metal surfaces will add a minimum of .006" between them. My first use of this sealant was on the three pipe flanges of each inlet log assembly. Its squeeze-out is also easily cleaned up. My first use of the aviation grade Permatex was to seal the aluminum tubes inside the cast fittings.

Coolant from the cylinder blocks will flow up into the heads through a number of o-ring'd transfer passages between the two. These passages as well as their transfer tubes were machined earlier during the head machining. The o-rings will be added when the heads are finally assembled to the blocks. Each head has a major coolant exit at its front and rear. The castings included only a single elbow fitting for each head, and so they will be used to direct the coolant flow out of the heads and toward the front of the engine as was done in the Merlin's aero applications. Stainless steel barbs were also turned and JB Welded to these fittings. A reservoir, wrapped around the front end of the full-size Merlin just behind its prop, collected coolant from these outlets before returning it to the pump. This reservoir had a unique and very complex shape and would have been an excellent candidate for casting, but it was evidently never part of the Quarter Scale design. I'll likely fabricate one from scratch even though I currently plan to also include a small radiator hidden under engine and cooled with a 12V fan. 

In the full-size engine, a second pair of major coolant exits at the rear of the heads was used for a number of purposes including the plane's cabin heating system, but they were likely used also for other purposes. I created block-off plates for these, although I think the cooling system might benefit from making them functional along with the front exits. There is a second pair of smaller coolant ports at the front and rear of each head located just below the main exits. The drawing for the head specified these to be tapped 10-32, but there were no further references to them in any documentation. I temporarily plugged these with modified 10-32 button head cap screws. These ports may be used for coolant temperature sensors later on.

In order to create a sketch for the block-off plates, I gathered up the manifold gaskets that I fabricated last year:

http://www.homemodelenginemachinist.com/showthread.php?p=273966&highlight=Merlin+gaskets#post273966

To my dismay, they no longer fit the heads nor the metal templates used to drill their mounting holes. The ten inch long gaskets had all shrunk about 3/16", and only a tiny fraction of the some fifty mounting holes still aligned with those in the engine. Hoping that the automotive paper gasket material just needed some moisture to return the gaskets to their original size, I used my wife's steam iron to make a few passes over one of the spare gaskets as a test. This caused it to over expand a bit, and so when I'm actually ready to install them I'll need to be more careful.

The only oil fitting that really needs to be machined and installed at this time is a tiny injector that will lubricate the prop reduction gear set at the front of the engine. This was one of those parts that my clumsy hands and poor eyesight would rather not deal with. The body of the injector was threaded 10-40 to match a previously tapped hole for it in the gear case cover. A banjo fitting and locknut were machined to complete the tiny assembly. Drilling the pair of cross-intersecting .020" holes in a 3-48 stainless SHCS required for the banjo fitting turned out to be less of a hassle than I had expected. The threading of the injector body was done manually on a lathe by turning the spindle by hand with the half-nuts left engaged until all the passes were completed. After the injector was installed, the front cover was finally sealed to the crankcase with a gasket cut from .004" thick linen paper. An oil line which will be part of an externally plumbed oil distribution system will be soldered to the banjo after the engine's final assembly.

I was never able to determine the purpose of yet another mysterious crankcase port located just behind the gear case, and so it was lined it with Tygon tubing and stoppered with a turned aluminum plug. In a wet sump engine this would have been an ideal candidate for a crankcase vent, but I found the crankcases in my two dry sump radials never required venting. In fact, the crankcase pressure pulses in those engines actually tended to assist the scavenger pump in moving oil out of the engine and into the collection/separation tank. The collection tank will require venting, however. - Terry


----------



## kvom

The Hylomar product looks like a winner for a lot of model seals.


----------



## Blogwitch

Terry,

As you may well know, Hylomar was developed for Rolls-Royce for use on their engines, we used to use it when I was in the RAF 1960's & 1970's, and when I went to work for Rolls-Royce/Bentley in the early 80's I used to go across to the engine line and they were using it on all their car engines.
Sadly the two marks were split apart not longer after I left and I think both now use their own engines, Rolls = BMW & Bentley = Volkwagon/Audi. A shame really, as the original 6 litre+ engines were bomb proof.

It has a smell you never forget and is one of the best sealants I have ever come across.

John


----------



## petertha

Interesting info on Hylomar, thanks for mentioning. I was experimenting with different gasket compounds like these RTV silicones. They sealed perfectly fine, but the issue I was facing was removal. The parts stuck particularly well. I could see where on a large FS engine part you could get some leverage & shear the bond, but I have some fiddly bits than are hard to grip & might even distort.

https://www.amazon.ca/dp/B0002UEN1U/?tag=skimlinks_replacement-20

Some one else suggested Hylomar as a good option. I'm not sure if that was because of softer durometer or maybe lower shear strength than RTV? But the video link is interesting if I understand correctly & was going to be my next plan assuming I didn't go the route of cut gaskets. 

What I then tried was a variation of that video. I painted the RTV on the aluminum part, then overlaid a piece of shiny mylar, weighted part down on a piece of glass & allowed to fully cure. Then peeled the mylar off next day. That left me with a thin coating RTV mated to metal with a good surface on the mylar side. Same treatment on the mating face. The theory is the parts would get assembled & squeezed together with pre-cured RTV & seal that way (but disassemble easier). I have different kinds of films, strangely some of them allowed curing, others did not. I'm not sure what the net thickness was but ended up putting this on the shelf for now. There are only 2 main (crankcase) gaskets I need to deal with so my inclination is to have them cut & just use the goop on some bolt heads which should remove easily with torque.

Keep us informed of your results! Inquiring minds want to know.


----------



## Ghosty

Hi All,
I use Loctite 515 flange Sealant Master Gasket, designed for metal to metal surfaces, seals very well, and can be disassembled with out damage to parts.
Cheers


----------



## mayhugh1

For piston rings, I use the method described by George Trimble in issues 7, 8, and 9 of Strictly IC Magazine. By now, I've made nearly a hundred rings using his process (that happens when you build big radials), and the only change I've made to it is to use a normalization temperature of 975F rather than Trimble's recommended 1475F.

As part of my own process, I check the fit of every finished ring in a test cylinder using a strong light source fitted to it through an adapter. This step allows me to weed out questionable rings before they end up inside an engine. I try to identify and discard rings with fit errors on the order of three tenths, or so, by checking for light leaks between the rings and the wall of the test cylinder. Over time, I've correlated the passing of this test to piston/ring combinations that usually produce the cylinder pressures expected during cranking compression tests immediately upon installation.

The yields on my rings are typically rather low and are limited primarily by the material itself. I've used class 40 gray cast iron from a number of sources, and some of the drops I've used have been relaxing around my shop for many years. The problems I invariably run into are circularity errors that show up during the final machining passes on the blanks. The magnitude of this problem varies from blank to blank, and occasionally an entire blank will produce no usable parts. I try to identify questionable material while it's still a part of a blank. Once a ring has been parted off, it becomes difficult to evaluate without being turned into a finished ring so it can be light-tested. To reduce wasted time and effort, I discard even marginal material at the front end of the blank preparation process. My yields through the remainder of the ring-making process using known good blank material are usually 80%-90%.

I prepare extra blanks because my yield of usable blank material is often less than 30%, though. Regardless of my to-date attempts to avoid them, circularity errors still manage to show up in portions of most of the blanks during their final finishing passes. I've even watched the distortion continue to grow for days after the blanks have been completed. Fortunately, I think I've finally eliminated this particularly nasty problem by pre-soaking the blanks at 950F before they receive their final machining.

My particular Quarter Scale's rings require a 1.200" final o.d., and so a good starting diameter for the raw material would have been 1-1/2". I used some two inch material that I had on hand, and so I generated a lot of waste. The diameter of these rings required the blanks to be supported in a chuck rather than a collet, and past experience has shown the circularity errors are sensitive to work-holding. The material I used came from at least two different sources and has been sitting in my shop for over three years. Three blanks were initially prepared by drilling/boring their i.d.'s .050" undersize and then turning their o.d.'s oversize by a bit more. In order to stress relieve the blanks, they were sealed in an argon-filled stainless steel envelope and heated to 950F for two hours followed by an overnight cool down. Two of the blanks were then finish machined, but the third was held back as insurance against a screw-up that might jeopardize the first two.

The blanks' final machining was begun by finish-boring their i.d.'s. The o.d.'s were then finish-turned to one thousandth oversize. Pairs of diameter measurements taken at 90 degrees to each other were recorded at three locations along the length of the blank during its machining. The measured circularity errors were on the order of a tenth along the entire length of the blanks during most of their machining; but as the machined diameter approached its finished o.d., the blanks began to show distortion. Even though the parts were lightly chucked, the final errors measured near the headstock end of the blanks approached a whopping seven to eight tenths. The errors at the tailstock ends of the blanks remained near a tenth. The outer 30%-50% ends of the blanks had errors less than three tenths which was my empirical cutoff for usable material. Fortunately, there was sufficient usable material among the two blanks to yield all the rings needed plus lots of spares. The last thousandth was polished off with 600 grit paper, and the parts were allowed to rest for a couple days before being re-checked. Fortunately, neither of the blanks got any worse.

The rings were parted off from the sweet areas of the two blanks using an .019" wide carbide cut-off insert tool in order to minimize waste of good material. Parting tends to raise ragged burrs on both the id.'s and o.d.'s of the rings, and these had to be carefully removed. I used a 1/4" diameter ground ceramic rod as a file to manually debur the rings while being careful to not mar their outer polished surfaces. All four edges were worked under a magnifier with the file held at 45 degrees and with just enough effort to remove the burrs but leave the edges sharp. The rings were parted so they had the same width as the piston groove, and so they were lapped with 600 grit grinding grease on a glass plate to polish their sides and provide a .001" groove clearance. During running, a ring will seal against the lower wall of its piston groove and provide a portion of the combustion chamber seal.

The Trimble article emphasizes the need for a straight radial break in each ring and recommends using a shop-made cleaver. Although 'good enough' results might be accomplished by simply snapping the rings, I've make enough of them to justify making a cleaver years ago. After deburring, each ring was cleaved in preparation for heat treatment.

The Trimble articles describe the construction of a fixture required to support the rings during their heat treatment. Dimensions are provided for machining the specific ring gap spreader that is key to Trimble's method for forming rings. The fixture is not at all difficult to make, but its dimensions are tied to the dimensions of the particular rings to be treated. This means that a different fixture is required for each ring size. This fixture was my third. 
With the time and effort invested in the rings to this point it's important to not spoil them by allowing them to become contaminated during the heat treatment. They and the fixture were thoroughly cleaned in alcohol. Again, I used an argon-filled stainless steel envelope with triple-folded edges to keep air away from the rings during their two hour soak at 975F. Although I originally sized my fixture to handle all the rings I needed plus several spares in a single batch, I decided at the last minute to machine a spacer so I could run two or three smaller batches. This was done for safety so I wouldn't spoil the whole lot should something go wrong during the heat treatment. - Terry


----------



## gbritnell

Hi Terry, 
After reading the original article in Strictly I.C. I started making my rings by the Trimble method. To date I have made 4-5 heat treat fixtures for the different ring sizes I've needed. I have tried other methods but have had the best luck with this one. 
gbritnell


----------



## petertha

mayhugh1 said:


> ... but as the machined diameter approached its finished o.d., the blanks began to show distortion. Even though the parts were lightly chucked, the final errors measured near the headstock end of the blanks approached a whopping seven to eight tenths. The errors at the tailstock ends of the blanks remained near a tenth. The outer 30%-50% ends of the blanks had errors less than three tenths


 
Very interesting observations. By distortion do you mean non-circular section like an elliptical shape, or its circular but different diameter than outboard material? Any personal theories why this would be occurring? Your 600 finish is very nice. And you don't bother lapping the OD section with a ring/clamp type gadget, correct?


----------



## mayhugh1

petertha said:


> Very interesting observations. By distortion do you mean non-circular section like an elliptical shape, or its circular but different diameter than outboard material? Any personal theories why this would be occurring? Your 600 finish is very nice. And you don't bother lapping the OD section with a ring/clamp type gadget, correct?



Peter,
By distortion I mean the two quadrature measurements taken on the turned diameter don't agree, and so I guess they are somewhat elliptical. I suspect the distortion is related to the workholding. On these blanks I was careful to use thick workholding spigots, but it didn't eliminate the problem. If there's a next time, I might try not boring completely through the blanks.

The blanks' o.d.'s are polished on the lathe and not touched after the rings are parted. Trying to do anything with the o.d.'s after the rings have been parted would probably do more harm than good. - Terry


----------



## DICKEYBIRD

mayhugh1 said:


> I suspect the distortion is related to the workholding


 I wonder if it's worth the trouble to make or buy an ER50 collet chuck & get a collet to hold the blanks?  ER collets create less distortion than a 3 jaw for sure and the 50 size goes up to 34mm.  That's assuming you ever want to see another piston ring for the rest of your life!

I made an ER40 chuck to fit my Emco clone's DIN flange style spindle for holding 1" thinwall brass tubing & it worked great.  You can get one & just whack it a 3 or 4 jaw for odd jobs pretty easily.  That's what I ended up doing most of the time anyway instead of going to the trouble of swapping chucks.


----------



## mayhugh1

DICKEYBIRD said:


> I wonder if it's worth the trouble to make or buy an ER50 collet chuck & get a collet to hold the blanks?  ER collets create less distortion than a 3 jaw for sure and the 50 size goes up to 34mm.  That's assuming you ever want to see another piston ring for the rest of your life!
> 
> I made an ER40 chuck to fit my Emco clone's DIN flange style spindle for holding 1" thinwall brass tubing & it worked great.  You can get one & just whack it a 3 or 4 jaw for odd jobs pretty easily.  That's what I ended up doing most of the time anyway instead of going to the trouble of swapping chucks.



Maybe.....
But, for my radials' one inch rings, I supported the ring blanks in two different 5C collets and had pretty much the same experience. - Terry


----------



## petertha

mayhugh1 said:


> ... If there's a next time, I might try not boring completely through the blanks.  - Terry


 
I'm no expert but thinking back when I made my liner testers that's maybe effect I noticed. #1 (12L14) I machined a sacrificial stub like yours & drilled right through just because it seemed easier to let the boring tool exit rather than blind hole. I made a lapping tool & when it was cutting nicely on the tailstock end it, it showed kind of a irregular stripes on the headstock end. This was a 3-jaw chuck & cranked down pretty good.

On #2 (CI) I left the full bar in the jaws to conserve material & terminated the bore ~ 0.5" ahead of the jaws with a blind hole. I don't recall having the same issue, it seemed to lap pretty consistent. But I chocked it up to less springy material.

BTW, in both cases I noticed the outboard diameter was ever so slightly larger than headstock side. Not sure if that's my lathe setup or due to extended stock / cutting deflection? Lapping is a PITA but the set diameter does reveal things like this.

I was concerned about egging the liner wall for ID finishing in the 2nd operation. Here I was able to use a collet & quite light clamp pressure. Seems to be ok but I'll know for sure when I have to make more.


----------



## napoleonb

The distortion comes from within the metal itself as you've discovered.
This is due to internal stresses and atom alignment.

Simplified it's like layin bricks, there's a certain logic in which metals are formed or bricks are layed. When removing some metal or by inducing stress (turning/bending etc.) the layout is changed and this can cause some metals to "move" to another position. 











In the first pic there arent any atoms removed but rather "chushed" together like you would in a bending/rolling/pressing situation.
During the removing process of surrounding metal (turning/milling/cutting) at a certain point situation C can become D which doesnt change the form.
But the build up tension is released in situation E the product becomes distorted (elleptical in your example)

The heat treatment removes build up stress in the part which can cause shifts in the pattern and settle's the metal in its new form. Finish turning induces much less stress which helps to keep the form. It "regenerates" the structure to form E so there's no left over stresses (or a lot less depending on the time and temperature in the oven).


The way some bar stock is made by pressing/rolling induces stress in a certain form. Making square bar stock unsuited for this kind of application.


----------



## kvom

The prior post somewhat supports my supposition that the outer portion stress relieves easier than the inner as it is more "flexible".

If you were to make rings from the "bad" portion, they might relieve back to round after being parted.  Or did you already try that?


----------



## DICKEYBIRD

mayhugh1 said:


> Maybe.....
> But, for my radials' one inch rings, I supported the ring blanks in two different 5C collets and had pretty much the same experience. - Terry


Sounds like there are other factors beyond the chucking issue but (for what it's worth) the ER system has 8 clamping elements instead of the 3 with 5C.

Could the OD blank be turned & finish honed between centers?  (Sunnen hone)  Come to think of it maybe a fixture to clamp a stack of compressed semi-finished rings then their OD's finish honed to final size??


----------



## mayhugh1

kvom said:


> The prior post somewhat supports my supposition that the outer portion stress relieves easier than the inner as it is more "flexible".
> 
> If you were to make rings from the "bad" portion, they might relieve back to round after being parted.  Or did you already try that?



Initially, it sounds counterintuitive, but no, I've never tried that. I normally discard at least the outer eighth to quarter inch. I'm no expert, but it seems to me that since cast iron is cast and not rolled, the internal stresses that Napoleonb is referring to might be found all through the material but especially on the outside depending upon how it cooled. I would guess the outer layers would cool first and lock in the volume available for the inner layers. But, as the inner layers cool, the material shrinks and maybe become less stressed. Perhaps one of the reasons for the centrifugal casting/cooling is to equalize some of this. 
In any event, I find cast iron frustrating and messy to work with, and I try to avoid using it except for one of the most critical components in every engine I build :>) Terry


----------



## bigrigbri

Continous cast iron bar is readily available in the UK dunno about the States but it is very uniform in construction and grain size.


----------



## 10K Pete

bigrigbri said:


> Continous cast iron bar is readily available in the UK dunno about the States but it is very uniform in construction and grain size.



Oh, no problem. At least two companies...

Pete


----------



## nel2lar

Terry
This might be what you are looking for. Cut the pot chuck to exactly the size if the ring, then you could face and cut the ID to exactly what you need. Maybe, check it out and it will cost less the a C note.
http://www.roviworkholding.com/category/Rovi-5C-Oversize-Collets-22
Cheers and good luck my friend
Nelson


----------



## mayhugh1

After a two hour soak at 975F, the first batch of rings were allowed to cool overnight before opening their sealed packaging. There were a few black soot deposits on the fixture, but the rings were relatively clean. Before removing the rings I burnished their collective outside diameters using a white Scotchbrite pad. The pad doesn't remove any metal, but it does remove most of the fine deposits that inevitably collect on the outer surfaces of the rings during heat treatment. These deposits are barely visible, but they leave a slightly rough surface on the rings' polished o.d.'s. More importantly, they create problems for the light test because they cause the rings to stand off from the cylinder wall. Light leaking from around an entire ring makes it appear too small in diameter for the cylinder. If left alone, these abrasive deposits will just rub off the rings and wash into the engine oil during the first few seconds of running. If a light test is to be performed, however, they need to be removed because they can hide fitting errors.

In my experience, it's typical for a few rings to become stuck together during the heat treatment. The deposits that form on the rings' outer surfaces sometimes tend to lightly bond them together at their outside corner edges. They're easily separated with a razor blade by carefully prying them apart at the inside edges of their gaps. Before I started using argon gas as an air displacer, I tried including bits of various sulphur-free papers inside the sealed package as some have suggested. The theory is that the paper will burn up, and the bit of smoke that is released will generate a reducing rather than an oxidizing atmosphere inside the envelope. Every time I've tried this, I've ended up with a gooey coating on the rings that was difficult to remove and a lot of stuck-together rings. After several tries, I switched to using argon from one of my welding gas cylinders. I've read that the rings can also be coated with a borax fluxing agent to protect them. If there's a next time, I may also try that.

While the rings from the second blank were going through their heat soak, I began finishing and testing the first batch of rings. A running gap of .004" was filed into the ends each ring using a thin diamond file. A diamond file is cleaner because it doesn't magnetize the cast iron while it's being filed. The minimum gap was verified using a feeler gage with the ring installed inside the top end of a cylinder liner. The sides of the rings were then lightly lapped on a glass plate using 1000 grit grinding grease. The fixture used for this step supported the rings by their o.d.'s unlike the i.d. fixture used for lapping the rings before they were gapped. The rings' o.d.'s were once more burnished with a white Scotchbrite pad to remove any deposits missed earlier. This was done using a simple two-part fixture made to safely grip the rings one at a time so their shapes were not stressed during the burnishing. Special care was required around the gap to prevent the pad from grabbing one of the ring's ends and deforming it.

For the light test adapter, I turned a black Delrin plug with an o.d. that was about .020" smaller than the i.d. of the cylinder. A shoulder was also turned on the plug so the ring-under-test could slip on to it. With the ring installed on the bottom of the plug and the combination sitting square in the top end of a cylinder, a high intensity flashlight was shined into the bottom end of the cylinder. Any light leaking between the ring and the cylinder wall is easily visible from above the cylinder. My criteria for a good ring was that there be no visible light except for that passing through the ring's gap. I've included a few photos of some of the test results. 

The magnitude of the errors can be roughly estimated by comparing the widths of the light leaks to the light passing through the .004" gap. Most of the errors I saw were much greater than the circularity errors in the blank material. These errors evidently resulted from the material further relaxing after parting/gapping or from handling issues during the final finishing steps. I'd like to believe that most of the rejects resulted from the former and not the latter since installing the rings on the pistons always feels like the most traumatic step in their handling.

When completed, 34 of the 49 rings parted from the two blanks passed my light test. This 70% yield was a bit lower than expected, and it reduced the net yield of the finished portions of the blanks to about 30%. Even with the poor yields I ended up with ten spare rings.

Finally, I selected one of the good rings and used it to verify the i.d.'s of all the cylinder liners machined earlier. Of the fifteen liners, eleven had no light leakage. Three of the remaining four had just a hint of a leak, but one was large enough to be scrapped. - Terry


----------



## mayhugh1

On another issue ...

One of the stents that was put in my heart last April has developed a problem, and I'm soon going into the hospital for open heart surgery that's now required to fix it. While I'm in there, the doctors also plan to repair my aorta which evidently also needs attention. I've been told to expect a long recovery time, but recovery sounds like a good thing. Although the Merlin has recently been a nice diversion from the personal loose ends I'm now scrambling to tie up, there won't be any more posts for a while. I wish everyone a safe and happy holiday. - Terry


----------



## Parksy

Here's to a quick and speedy recovery Terry. All the best and look forwards to your return with good health.

Andrew


----------



## Ghosty

Terry, All the best for your recovery, All the best to you and the family for the holidays, Hope to see more when you are up to it.

Cheers
Andrew


----------



## Ken I

If your surgeon is as skilled as you in his trade you should be fine.

Good luck & a speedy recovery.

Regards,
            Ken


----------



## ShopShoe

Sorry to hear about your heart issues.

Wishing you a successful recovery.

--ShopShoe


----------



## kvom

Best of luck with surgery and recovery.  I hear model engine shows are good recovery therapy.


----------



## ozzie46

Praying for a successful out come and a quick recovery.  

Ron


----------



## napoleonb

I hope you have a good and speedy recovery!


----------



## gbritnell

Terry, 
All the best for your recovery. Health is more important than everything else.
gbritnell


----------



## kuhncw

Terry,

I wish you all the best for your surgery and a quick recovery.

Chuck


----------



## brotherbear

I'm praying for a quick and uneventful surgery and recovery for you, Terry. May you and your's have a peaceful Holiday season.


----------



## wirralcnc

All the best for a speedy recovery


----------



## petertha

Terry, best wishes through your surgery & recovery period. Take care.


----------



## nel2lar

Terry
Best regards and a speedy recovery. Health is very important and I will be praying for you. Don't worry the surgeon has probably done hundreds by now and with luck you will not need surgery.
Get well soon
Nelson


----------



## RonC9876

Terry: Best of luck. We need you back quickly to inspire us to be better machinists. Without your high standards to emulate we will fall back to mediocrity! See you around someday soon I hope. Ron Colonna


----------



## 10K Pete

Best wishes and God speed, Terry.

Pete


----------



## Cogsy

Good luck and a speedy recovery Terry. Enjoy the down time.


----------



## michael-au

All the best, hope you have a speedy recovery


----------



## xpylonracer

Hello Terry

As all readers of your build sequence may I wish you well with your operation and I look forward to your future articles when back in the shop again.

xpylonracer


----------



## DiegoVV

Best wishes and speedy recovery Terry. It's incredible how inspiring your work is for the rest of the community. You are pushing all of us to be better machinists just to try to close the huge gap between your skills and ours. Hope to read you again soon! We'll be here waiting


----------



## sbdtasos

Terry
your health is first of all 
hope to recovery soon you are strong. 
will wait to see that engine runs ..
good luck my friend


----------



## dsage

Terry:
I wish you all the best with your surgery and hope you have a speedy recovery. We'll all be waiting for more inspiration when ever you are ready.

Something less important for you to think about during your recovery:
I might be confusing the Trimble method with several others I've read about but I believe you are supposed to make the rings a thou or two over the required OD and the last step (perhaps you left out) after heat treating and cleaving is to put a stack of rings on a mandrel that is the inside diameter of the finished rings and compress them (perhaps with a cylinder temporarily slipped over them). The mandrel is threaded on the end so you can put a washer and nut on and clamp the rings while they are compressed to tightly fit the diameter of the mandrel. Then you skim the outside diameter to the proper OD (therefore making them round).

I've always just made them to finished size and ignored the last step because my lathe usually has more run out than the amount required to be skimmed off. I haven't had a smoking engine yet right from startup (knock on wood).

All the best and we hope to hear from you soon.

Sage

Edit: I went back and looked at the many articles I have. It was Professor Chaddock that proposed skimming the rings to size as the last step. Although I had no success with it because of my equipment I'm sure Terry could pull it off. Perhaps this is a good way to get nice round rings.


----------



## jschoenly

Dad got an aortic valve a few years ago and a few bypasses while in there.  Do what they say and take the recovery seriously.  All the best to you!  Attitude is everything!  Take care!


----------



## rdefrei1

All the best Terry... Good luck and a speedy recovery.


----------



## Goldflash

Hi Terry , coming up for the 4th anniversary of my CABGx3.  
Just bought a motorbike . never felt better, but I will admit that recovery took a while. 
Good luck and welcome to the Zipper Club .. 

Ralph


----------



## Blogwitch

Best wishes and a fast recovery Terry.

Don't go worrying about anything in your shop, it will still be there waiting for you, just take your time and get yourself well before carrying on.

John


----------



## neubert1975

and all the best wishes, and fast recovery
from the guy who´s mostly lurking around


----------



## metalmad

Hi Terry
Best wishes Mate!
Pete


----------



## gmac

Terry;

Take your time with the recovery - top priority :thumbup:. I for one will go back to the start of this fantastic thread and bide my time while I wait for your return. Keep us posted on your recovery.

As a newbie to model machining you have no idea how much this thread has inspired and educated me.

Get well !

Cheers Garry


----------



## mayhugh1

Thanks everyone for your well wishes - they seemed to have worked.
It's been just over a week since my surgery, which went pretty much as the doctors expected, and after a week I'm finally home from the hospital. I'm still in some pain, and it's difficult to take even moderately deep breaths, but it's up me to work through that and re-build my endurance. I'm still very loopy from the pain medication I'm taking, and so it will be at least another week before I trust myself enough to go back into the shop. I was told I wouldn't be able to lift more than five pounds or so for the first couple weeks of recovery, and so before I went into the hospital I spent some time machining the parts and fixtures I would need for the Merlin's final assembly. Final assembly, which will be the next step, will require more patience and thought than strength, and so I should be up to handling it soon. - Terry


----------



## Cogsy

Great to hear of a positive result Terry. Don't rush back into the shop though - take care of yourself. The Merlin will be waiting for you.


----------



## petertha

That's awesome news Terry. All the best in your healthy recovery.


----------



## ShopShoe

Glad to hear that you got home OK. Take it easy. We are following your work but we have the patience to wait for you to do it no faster than your recovery allows.

Best Wishes.

--ShopShoe


----------



## brotherbear

Terry, I am so pleased to hear that your procedure went well and you have made it home. The success of all the effort you take, to humbly share your knowledge and skills with others is an inspiration to me. I pray your recovery will continue, free of complications.


----------



## Ghosty

Terry,
Glad to see everything went well. Take the time to recover, the engine will still be there, if you do something silly you may not, a lot of us are learning more from you being here.

Cheers
Andrew


----------



## editor123

mayhugh1 said:


> On another issue ...
> 
> One of the stents that was put in my heart last April has developed a problem, and I'm soon going into the hospital for open heart surgery that's now required to fix it. While I'm in there, the doctors also plan to replace my aorta which evidently also needs attention. I've been told to expect a long recovery time, but recovery sounds like a good thing. Although the Merlin has recently been a nice diversion from the personal loose ends I'm now scrambling to tie up, there won't be any more posts for a while. I wish everyone a safe and happy holiday. - Terry


Having had an aorta valve replacement 5 years ago, I can tell you that the post recovery period is much longer than the surgeons will tell you. The sternum may heal in 12 weeks but the nerves stay sensitive for up to 2 years. Also, do the post operation physical therapy. You may feel OK but a three month stint in therapy will astound you with the results. If therapy is not prescribed, force the medical team to do so.
Of course, now the cardiologist tells me the next valve emplacement will be just through a small cut in my groin, like when they did the Angiogram.:thumbup:


----------



## nel2lar

Terry
I do not know if being a member of the zipper club is that great but better than the alternative. Pray all goes well, looking forward to see that little Merlin run.
Nelson
The best of a Christmas Season


----------



## cfellows

Hi Terry,

I had wondered why we hadn't seen you at Rudy's for the past couple of months.  Glad to hear everything went well.  I hope you have a complete and speedy recovery.

Chuck.


----------



## mayhugh1

Originally, I wasn't going to make any gaskets for this engine other than those made much earlier for the intake manifold. Many of this engine's scaled flanges are tiny with myriads of screw holes, and I thought I would rely on the large number of screws holding the sections together to also seal them. After less than an hour into the final assembly, though, I changed my mind. Much of the Merlin's assembly will be an exercise in patience, and it didn't take long to realize that I didn't want to go through it a second time because of leaks that might have been avoided the first time around. The Merlin's design provides lots of opportunities for leaks - some fifty coolant seals per head.

Final assembly began rather arbitrarily with the forward portion of the wheel case. The already partially assembled case was taken apart and removed from the engine so a gasket, cut from .004" thick linen paper, could be used to seal it to the crankcase. Twenty-three screws hold the wheel case to the crankcase, and six of them are located inside the wheel case behind its multitude of gears. After being stripped down so the internal mounting screws could be added, the wheel case internals were reassembled as far aft as the supercharger flange. The crankshaft was carefully re-checked for binds as each component was added to the wheel case. When the head/block assemblies are installed later, the friction added by the ring'd pistons will likely be too high to detect any binds.

The next sub-assemblies to be completed were the cylinder blocks. An earlier post at
http://www.homemodelenginemachinist.com/showpost.php?p=284553&postcount=419
covered the process and special tools I came up with to install the liners in the cylinder blocks without damage to their o-rings. The final installation was just as difficult as I remembered it being back then when I practiced it several times on one of the liners. Although at this point I couldn't be absolutely certain, I'm reasonably sure all twelve o-rings wound up installed without damage.

The combustion chamber seals created when the heads are finally assembled onto the cylinder blocks was detailed at
http://www.homemodelenginemachinist.com/showpost.php?p=284308&postcount=414 .
Each head/block pair includes fourteen o-ring'd coolant transfer tubes running between them as well as another fourteen o-ring coolant seals around the bottoms of the stud tubes. An additional fourteen coolant seals are used on the tops of the stud tubes of each head. Before attempting these sub-assemblies, I wanted to double check the integrities of the valve and spark plug seals to reduce any chance of having to separate them again later. Each valve seal had previously been verified by pulling a vacuum behind it through its port and then measuring its resulting leak-down time:
http://www.homemodelenginemachinist.com/showpost.php?p=273401&postcount=233 .
These tests, however, didn't include possible valve spring effects since I held the valves closed with my fingers during the tests, nor did they include possible leaks at the Viper plugs' tiny sealing flanges. A last minute valve sealing issue can sometimes unexpectedly arise from a non-square spring failing to hold its valve uniformly on an otherwise perfectly formed seat.

I made a simple fixture that would allow me to pressurize each individual combustion chamber with both valves held closed by their springs and a spark plug screwed into its port. An -026 o-ring just happened to fit the corner recess in the combustion chamber intended to receive the top end of the cylinder liner, and so I only had to turn a piece of Delrin with the correct o.d. to hold the o-ring in place. Each combustion chamber was pressurized to 30 psi and then allowed to leak down to 10 psi after switching off the air supply. The individual leak-down times combine like paralleled resistors, and the final results for each cylinder were very close to what I expected from my previous individual valve measurments. 

Waste oil from the heads returns to the sump by flowing down and around the enclosed stud bolts. Stud tubes inserted in the tops of the heads surround the upper portions of the studs. Holes drilled around the upper peripheries of these tubes allow oil to enter them on its way to the sump. Since the stud tubes pass through the coolant jackets in the heads, they must be sealed to the heads at both their tops and bottoms. Twenty-five percent compressed Viton o-rings seal the bottom ends of the tubes. My original plan for the top seals was to use a gasket sealer, but since I've had a lot of time on my hands recently, I thought I would, instead, make a set of gaskets. The gaskets were cut from a new US dollar bill which is made from high quality .004" thick linen paper. (I've had a sample of this paper sitting in motor oil for over a year with no sign of deterioration.) The gaskets are simple washers with a .312" o.d. and a .210" i.d., and in this application it's very important the i.d.'s be concentric with the o.d.'s.

I first punched the gasket i.d. using a piece of brass tubing sharpened into a punch with a small 45 degree countersink. The punched stock was then moved to a gasket punch/die set where the washer was punched out. The gasket's i.d. was held concentric to the punch's o.d. using a centering spacer temporarily shoved up through the gasket's i.d. from the bottom of the die. The process was slow, but it created accurate washers with crisp edges. A pair of these washers were stacked to create a .008" thick gasket under the head of each stud tube. In all, 56 washers plus some spares were required, but I was able to cut them all from a single dollar bill. 

After installing the fourteen o-ring'd coolant transfer tubes in the top of the cylinder block, the fourteen gasket'd stud tubes were inserted into the head, and Viton o-rings were slipped over the bottoms of the tubes sticking through the bottom surface of the head. The head was then carefully set down on top of the block so all 28 tubes aligned and sealed along with the six liner flanges. The pair was then bolted together with the twenty-eight 3-48 auxiliary head bolts whose holes were drilled and tapped earlier during the head machining. Miraculously, all 62 features aligned perfectly. The resulting gap between the head and block measured .052" indicating that the auxiliary head bolts were not sufficient on their own to draw the tops of the liners into the combustion chambers the additional .002" needed to crush the corners and complete the seals. This wasn't totally unexpected since the real purpose of the auxiliary head bolts is for convenience while assembling the head/block pair to the crankcase. The fourteen 8-32 studs that will later draw each head/block assembly down to the crankcase will exert the force required to completely close these seals. - Terry


----------



## sbdtasos

Terry
as always your work is magnificent
ps if you have leakage problems with dollar you can use the 20 euro


----------



## xpylonracer

Welcome back Terry, seems you are straight back into the job in hand.

xpylonracer


----------



## michael-au

Good to see you back working on the merlin


----------



## Ken I

Who'd a'thought the Dollar was cheaper than gasket paper.

Really good quality linen paper - nice lateral thinking.

Glad to see you are up and functional - mentally as well - after your op.

Regards,
            Ken


----------



## mu38&Bg#

Heh, he could still take it to the bank and get a new dollar bill.


----------



## kvom

Cheapskate.  I use Franklins for my gaskets.  ;D


----------



## nel2lar

Terry
Is great that everything worked out. I guess it give us better sense of how fragile our bodies can be. 
A Happy Healthy New Year
Nelson Collar


----------



## mayhugh1

The next step in the Merlin's final assembly was a major one - the assembly of the cylinder heads and blocks to the crankcase. Because of the modifications made to my liners, the only way this could be done was to slide the pre-assembled head/block pairs down over the pre-installed studs and ring'd pistons in the same way the full-size engines were assembled. The purpose of the previously installed auxiliary head bolts is to hold the head/block pairs tightly together while this particular step is performed. 

The Quarter Scale's unmodified stock rods and liners, on the other hand, would have allowed the rods to pass completely through the liners permitting a more piecemeal assembly. In this case, the blocks would be first installed on the crankcase so the rods and pistons can be slipped down through the tops of the blocks to be bolted onto the rod journals. The heads may then be finally installed on the blocks. This assembly method does away with any real need for the auxiliary head bolts which may be why the Quarter Scale's head drawing refers to them as optional. 

In my case, assembly began by installing the studs on the decks of the crankcase. Delrin oil seals were then pressed into the bottoms of the blocks using a simple shop-made insertion tool. These oil seals prevent the oil flowing down and around the studs on its way to the sump from leaking out the sides of the engine. After installing the pistons on the connecting rods, the head/block assemblies were lowered down into position over the studs. The tapers turned into the bottoms of the liners were invaluable for guiding the ring'd pistons into their cylinders. Without these tapers, a pair of piston installation tools operated by an extra set of hands would probably have been needed. This assembly method also greatly benefits from the studs being turned down a bit between their threaded ends so there is some 'wiggle room' available to the assemblies while they are being inched down into position. I've included a photo of a full-size engine rebuild going through this very same assembly step.

Tightening down the flange nuts on the tops of the studs not only secured the head/block pairs to the crankcase, but the head/block pairs were pulled together another .002". This crush height collapse was an indication that the liners had been pulled into the heads to complete the combustion chamber seals. The auxiliary head bolts could then be finally torqued. These particular assemblies are probably the most critical in the entire build, and hopefully they won't have to come apart during my lifetime. In a full-size engine rebuild they're separated using an overhead hoist to pull the head/block pair against the weight of a fully loaded crankcase. A similar operation might be performed on the Quarter Scale, but great care would have to be taken to reduce risk of damage to its castings. 

After assembly, the friction added by the piston rings increased the rotational torque requirements on the crankshaft to the point where it became very difficult to manually turn the crank using the prop shaft. Of course, this isn't totally fair since the prop shaft's gear reduction nearly doubles the torque required through the prop shaft. At this point, the starter shaft sticking out from the wheel case is the most convenient way to turn the crankshaft, and its operation was verified using an adapter mounted in a battery-powered drill. The crankshaft torque requirement will increase again once the timing chain is installed, and the overhead cams are being driven. When the engine is timed and compression is added, the crank will become very difficult to manually turn. All this is adding to my misgivings about the engine's seemingly fragile starting system. On a more positive note, the connecting rods ended up nicely centered in their pistons, and so the numerous dimension changes that had to be made to accommodate my short crankcase casting seem to have come out OK.

With the cylinder head/block assemblies in place, the intake manifold could be finally installed. Hylomar was used during pre-assembly to seal the manifold's three components together. These components were drilled/tapped almost twenty months ago using fixtures to simulate the engine's final deck heights and angles.

http://www.homemodelenginemachinist.com/showpost.php?p=266334&postcount=81 

The manifold gaskets made at the same time to seal the intake manifold to the heads had, over those twenty months, shrunk nearly 5/16" and would no longer fit the heads. Spritzing the gaskets with water and carefully heating them with my wife's laundry iron re-hydrated the material and brought the gaskets back to their original size. A total of 128 SHCS's are used to secure the manifold subassembly to the heads. I was a bit concerned about all these previously match-drilled holes actually lining up during final assembly, especially after my unexpected gasket problem which also changed its thickness. Fortunately, every screw went back into place with no issues.

After the intake manifold was installed, the mounting flanges of the coolant block-off plates and exit fittings were sealed with Permatex Aviation grade sealer. The entire coolant jacket in each head assembly, including its nearly fifty internal o-rings and gaskets, was then leak-checked. Each head jacket was pressurized to 10 psi by injecting compressed air into its coolant entrance fitting while its exit fitting was temporarily plugged. Unfortunately, both head assemblies quickly leaked down. Using a piece of plastic hose as a stethoscope to locate the source of the leaks, I discovered that some of the tapped holes in the lower row of mounting holes for the exhaust tips had broken into the coolant jackets. When the holes were originally drilled, I vaguely recall flagging this as a potential issue during final assembly, but I evidently forgot to record a warning for myself in my notes. 

I hadn't planned on installing the exhaust tips until after the spark plug wiring was completed and tested, but I chose to install them now so the leak checks could be completed. A bit of non-hardening thread sealant applied to the ends of all the screws in the lower row of exhaust tip mounting holes in both heads easily sealed those leaks. However, I then discovered a pinhole defect on the outside of the starboard head casting that was evidently deep enough to also penetrate the coolant jacket. My makeshift stethoscope worked much better than I had expected. Although the pinhole was barely visible, the whoosh of air that streamed from it during the test was very pronounced and easily located. I enlarged the pinhole with a small drill and backfilled it with JB Weld. A Mity-Vac was used to pull a vacuum on the coolant jacket to help draw the epoxy down into the defect before it was allowed to cure.

I continued using the stethoscope to probe inside the spark plug ports looking for possible liner leaks inside the combustion chambers. I also probed in and around the gaps between the head/block pairs as well as around all the intake mounting screws for any signs of leaks. Fortunately, I found none. After repairing the pinhole in the starboard casting, the leak down times of both heads had increased to nearly a minute which was essentially the noise floor of my cobbled-up tester. 

One piece of advice that I might offer to anyone who gets a chance to build this engine is to plan for a good rotisserie engine stand early in the build. Over time, mine has evolved from being a nice-to-have convenience to a must-have necessity. At this point in the build, the engine weight is some twenty-five pounds, and I continually find myself rotating the engine on its stand to just the right angle so I can best install the next screw. There's no safe bottom nor sides for this engine to rest on without risking damage to some machined part or irreplaceable casting. The only practical way to support this engine is by its motor mounts which are integral to the crankcase casting. Bolting these to an engine stand allows total access to the entire engine during construction. - Terry.


----------



## Ghosty

Terry,
It is really coming together quickly. Great work.

Cheers
Andrew


----------



## ddmckee54

Terry:

Looks liked you're getting real close to the point where you can quit making the engine noises and let the Merlin speak for itself.

It's been a Helluva ride so far, but I'm pretty sure that the light you've been seeing at the end of the tunnel is not another train.  I've no doubt that the Merlin will be purring for you soon, maybe snarling depending on the throttle setting.

Don


----------



## petertha

Looking SO good, Terry. 
Re that hylomar, when you paint the opposing part surfaces & it 'flashes off'. Does that mean its essentially bonded/cured? Or there is a specific time to mate the parts? ie. could you paint each, leave that way overnight & do the bolt-up next day for example & still have the removal/re-seal capability?


----------



## mayhugh1

Peter,
My understanding is that there is just a minimum flash-over time. You should be able to paint the two surfaces and then assemble them a day later - Terry


----------



## Charles Lamont

petertha said:


> Re that hylomar, when you paint the opposing part surfaces & it 'flashes off'. Does that mean its essentially bonded/cured? Or there is a specific time to mate the parts? ie. could you paint each, leave that way overnight & do the bolt-up next day for example & still have the removal/re-seal capability?


As I understand it, there is no question of a cure or bond. Hylomar comes out of the tube fairly soft to allow it to be applied, and all that happens is that a solvent evaporates leaving the sealant stiff and gummy. It is supposed to remain in that state indefinitely. The instructions say (I am not going out to the shop to look) something like 'torque down, leave an hour or two and torque again' as it will continue to squeeze out for a while.


----------



## gbritnell

Terry,            BREATHTAKING!!!!!!!


----------



## rdefrei1

This is a "dream engine" what a beauty.

Congrats.


----------



## dsage

WOW.

That's a beautiful sight. So much so I had to go back several times to look at your assembly pictures and marvel at the fact that it looks so perfect. Here's hoping that it fires right up and you never have to open it up again. Especially after the procedure you went through to put it all together.

:thumbup:

Amazing work.

Sage


----------



## mayhugh1

Thanks, all ... -Terry


----------



## kvom

> Here's hoping that it fires right up and you never have to open it up again.



The dream would be to cast all the exterior cases in transparent plastic to be able to see what's inside.


----------



## kuhncw

Looking at your assembly photos, it is easy to think I'm looking at a full scale engine build.  Beautiful work, Terry!  

Chuck


----------



## Hopper

Meticulous work, mate. I stand in awe, at both  your skills and your patience!


----------



## neubert1975

Hopper said:


> Meticulous work, mate. I stand in awe, at both  your skills and your patience!



what the gentleman just said :thumbup:


----------



## mayhugh1

With the wheel case and heads assembled to the crankcase, the timing chain and its cover could be finally assembled and installed. The Merlin's overhead cam drive system was greatly simplified for the Quarter Scale version, but it was designed more than a dozen years ago around a 3/16" steel roller chain that has since become obsolete. A year ago, I purchased an engineering sample of this chain that had been gathering dust in a Nordex salesperson's office. (Nordex.com was the recommended supplier for this chain in the Quarter Scale documentation.) I was told that this particular sample as well as a pair of connecting links were the last of their kind in their inventory since this chain had long ago been superseded by .1475" pitch products. The Quarter Scale's documentation mentions the .1475" chain as a possible alternative, but I wasn't sure that its fit had actually been verified in the cover design supplied in the documentation. So, I machined the timing sprockets in my engine around my piece of obsolete chain.

Just after machining the sprockets and chain cover components a year ago, I tested the fit of my chain in a partial assembly of the aft portion of the engine. At that time, I was mainly concerned with verifying the clearances of the chain inside its cover, and so I took a few liberties with some of the difficult accesses required for the trial assembly. I wasn't able to re-use them during final assembly, and so the chain and cover installation turned into a bit of an ordeal.

I spent the better parts of several days working out a sequence of steps for their installation. I kept notes along the way so I wouldn't have to re-derive the process should the engine ever need to be disassembled. I've included those steps in the next paragraphs even though I realize they will be of interest to only a couple readers who currently own the Merlin castings:

The retaining screws on the hubs of the port and starboard cam drive sprockets are first loosened so the sprockets can spin freely of their camshafts. The two idler sprockets are installed in the wheel case, but the central tensioner must initially be left out to get access to the crankshaft sprocket. The rear half of the main cover is installed on the top of the wheel case and temporarily retained with a single center mounting screw. The port-side head cover with its two cover tubes is then installed on the port head, and the lower ends of the tubes are inserted into the rear half of the main cover. The tubes are a snug fit in the head cover and, with care, will remain in place during during assembly.

A piece of stiff chord (I used waxed cable lacing chord) is then fed down through the left-most port-side cover tube and down over top the idler sprocket. Some deft manipulation with a long probe and tweezers will be required to get the chord routed around the crankshaft sprocket and up and out of the wheel case. Because of very limited clearance around the crankshaft sprocket, any knot tying the lacing chord to the chain will likely be too large to pass around the sprocket. So, a length of thin high strength thread (I used .010" diameter upholstery thread) is tied between the lacing chord and the chain. While rotating the crankshaft, the chain can be pulled down through the leftmost port cover tube, over the idler, around the crankshaft sprocket, and then up and slightly out of the wheel case. Again, some assistance from a long skinny probe will likely be required to get the chain properly started on the crankshaft sprocket. Once on the sprocket, though, the chain is pulled up about 1/4" above the wheel case chain cover mounting flange. The starboard-side head cover along with its two cover tubes can then be installed on the starboard head. The rest of the screws may then be inserted in the rear half of the main cover. Again, while rotating the crankshaft, the chain is pulled by the thread up and over the idler sprocket, through the right-most starboard-side cover tube, and then over and around the starboard cam drive sprocket.

The central tensioner sprocket can then be installed in the top of the wheel case. This has to be very carefully done to avoid dropping its parts down into the wheel case which will then have to disassembled to retrieve them. The chain may then be pulled completely around the starboard cam sprocket, down through the inside starboard cover tube, and around the bottom of the tensioner sprocket while rotating the crankshaft. The chain is then finally pulled up through the inside tube of the port-side cover and onto the port-side cam sprocket where it will meet up with the rear end of the chain. 

The chain must now be shortened to its final length which is 116 links excluding the connector link. With the tensioner sprocket set to minimum tension and after a final check for tautness, the roller pin to be removed is marked with a Sharpie. With the engine well covered with a protective cloth, a Dremel tool can be used to grind away a peened end of the roller pin so it can be pressed out and the excess chain removed. The connector link is then installed while the two ends of the chain are held in alignment on the cam drive sprocket with a pair of adjacent sprocket teeth. The pins on the connector link are .030" longer than the pins on the chain. I was concerned about them rubbing against the inside of the chain cover, and so I ground them down to about .015". I don't know if there is a preferred orientation for the connector link's keeper that's dependent upon the chain's direction of travel, but I oriented mine as shown in one of the photos. Testing showed the chain and connecting link moved smoothly through the cover with no sign of rubbing - a result that continues to astound me. As I've said before, my hat's off to the designer of the chain cover. It's not only functional, but for a component that wasn't part of the engine's original design, it wound up asca nicely integrated sub-assembly. Finally, the front half of the main cover can be installed along with the remainder of the mounting screws.

With the timing chain installed, the valves could be timed to the crankshaft. First, the lash on all the rockers was adjusted to .004". The engine's cam card shows the intake valve beginning to open 10 degrees before its piston's TDC. The firing order is 1A-6B-4A-3B-2A-5B-6A-1B-3A-4B-5A-2B using the Merlin convention that 'A' is the starboard bank, and 'B' is the port bank. The crankshaft was rotated so that piston #1 (front-most piston) in the starboard bank was at TDC and the degree wheel (http://www.homemodelenginemachinist.com/showthread.php?t=24153&page=40) on the prop shaft was zero'd. The crank was then rotated back 30 degrees or so to remove backlash and then rotated forward to 10 degrees BTDC. Using a wrench to turn the milled hex on the front of the starboard cam, the cam was rotated until a D.I. indicated the #1 intake valve had opened .005". The retaining bolts on the starboard side cam hub were then tightened to lock in the starboard side valve timing. The crankshaft was then rotated 60 degrees until piston #6 (rear-most piston) in the port bank was at TDC, and then the process was repeated. 

With the chain cover installed, the air/fuel connecting tube between the supercharger and the intake manifold could be machined and installed. This nearly one inch diameter tube runs through the center of the timing chain cover with very little clearance. It delivers the pressurized air/fuel mixture to the intake manifold from the supercharger. This tube wasn't machined earlier because its design depended upon measurements involving the finally assembled manifold, chain cover, and supercharger.

The front and rear ends of the tube were grooved, respectively, for -022 and -023 Viton o-rings. Its o.d. was turned for a chain cover clearance of .010". The height of the mounting flange of the connecting tube's elbow was finally machined in order to set the tube parallel to the axis of the engine. A thin linen paper gasket was cut to seal the elbow to the top of the supercharger. - Terry


Addendum ...
I've been doing more searching for the 3/16" pitch roller chain, and I may have found some in stock at:
http://www.powertransmissiondepot.com/artifact/3113516/ .
I ran across this website after reading a request for help on a pocket bike forum. It seems that this particular chain was used by a Japanese manufacturer in one of its pocket bikes, and an owner was trying to find a source for it so he could repair his bike. Another reader pointed him to this particular supplier who claims to currently have it In stock.


----------



## Cogsy

Looking fantastic Terry! If the chain rotates clockwise in the picture showing the connector clip then the clip is on backwards (at least that's what I was taught with motorcycle chains). It may not be important to you with your fully covered chain but with an exposed chain it's possible for a piece of debris to contact the clip in motion, putting force on the clip in the direction to remove it.


----------



## mayhugh1

Cogsy,
Thanks for the information. I forgot to draw a direction arrow on the photo, but the sprockets do turn counter-clockwise. - Terry


----------



## mayhugh1

The supercharger has been completed for some time but can only now be finally bolted onto the rear of the engine. It'll be held there with a couple dozen 1-72 SHCS's that will have to be inserted through the front side of the rear wheel case flange amid numerous obstacles. Most of the screws will have to be tightened a fractional turn at a time using a ground down hex key, and so this will be another assembly step that I prefer to do only once. 

My original plan was to perform some bench tests on the supercharger before it was installed on the engine. There's an SAE standard that deals with such testing, but it's a heavyweight and well outside the scope of this little project. My primary goal was to stress the supercharger with several minutes of full-speed full-load running before installing it on the engine. However, with a few shade tree measurements I should also be able to gain some insight into its effect on the engine's performance.

To spin up the supercharger for testing I used the Nichibo 775-8511FDAS dc brush motor (http://www.homemodelenginemachinist.com/showthread.php?t=24153&page=43) that I purchased earlier. I found an inexpensive speed controller on eBay that was adequate for some rpm control. I machined a 32 pitch 48 tooth brass driving gear for the motor's shaft as well as a mounting plate to secure the motor to the supercharger's housing. The number of teeth on the drive gear was selected to spin the supercharger at twice the rpm of the motor in order to obtain a maximum 36k rpm. This rpm will match the speed of the supercharger running on the engine at a maximum crankshaft rpm of 3600 rpm.

For my first measurement, I sealed a 42 gallon (5.6 cubic ft) plastic trash bag to the end of the supercharger's outlet tube. After a 36k rpm spin-up, the bag was fully inflated in just under 10 seconds. Although this may seem more like a parlor trick than a meaningful measurement, it allowed me to estimate the supercharger's maximum flow rate at (5.6 cubic ft)/(10 sec) x (60 sec/min) = 33.6 cubic ft/min. 

The engine's airflow requirement can be computed using CFM = engine displacement x rpm x volumetric efficiency / (1728x2). The 1728 converts the cubic inch displacement to cubic ft, and the 2 corrects the four stroke engine's rpm to account for its two revolutions per cycle. My engine's displacement is 21 cubic inches. For a maximum crankshaft rpm of 3600 and an estimated .8 VE, the engine's maximum air flow will be around 17.5 cubic ft/min. Since supercharger's flow rate is about twice the airflow requirement of the engine, the supercharger should at least not act an obstruction in the engine's induction system. The question, though, is whether the supercharger can increase the engine's volumetric efficiency by increasing the pressure in the intake manifold above atmospheric.

For the next measurement, I blocked off the supercharger's outlet tube with a rubber stopper. The stopper was through-pierced with a barb to which was connected an automotive-type boost pressure gage. At 36k rpm, the gage showed the supercharger building one psi of boost.

One psi above atmospheric isn't much, and as several with experience in this area have previously commented, 36k rpm isn't sufficient to build significant boost from a supercharger of this size. While playing with the test setup I felt like I could have easily achieved another pound of boost with another 10k rpm or so. However, I'm not willing to extend the engine's maximum rpm to 4600 rpm. 

In any event, I managed to accumulate some ten minutes of running time on the unit which improved my confidence in its ability to hold up to the stresses that it will endure in the running engine. I expect any real effect on the engine's performance beyond improving the air/fuel distribution in its huge intake manifold will likely be marginal, but for talking purposes I can honestly say the supercharger does generate measurable boost. The supercharger was then finally installed on the engine. - Terry


----------



## aonemarine

Frick man, hurry up!  Quit you job, work 23.5 hours a day or what ever...I need to hear this baby run!


----------



## Ken I

Flow and pressure curves for vane type charges show a fall off in pressure at stall - running it with a closed port might be doing it a disservice - it may do better dynamically.
All said its not going to be much but as you have observed, it won't be an impediment.
Can't wait for this to roar into life.

Regards,
            Ken


----------



## dsage

A new series just came to Netflix (here in Canada anyway) called "Plane Resurrection". The first episode is on the Mustang (the British Merlin Engine version). There is a guy in England that took on restoring a Mustang and the Merlin Engine in it. Now he finds himself rebuilding a couple of engines per year and having done 30 or so, so far. Lots of interesting clips of work on his engine, old clips of original engines and comments about them. A wonderful episode.
Terry: Don't get in any dog fights with yours. Apparently since the cooling system is on the bottom, they were vulnerable to being damaged by enemy fire. 

Sage


----------



## Blogwitch

I have watched those Sage.

The one that caught my eye was the battle of Britain Hurricane which had a very early Merlin fitted, cylinder block and heads, all one casting.

John


----------



## dsage

Yes indeed. I had only started watching the series while I posted about it before and was surprised that the second episode (the one you mention) was about another Merlin equipped aircraft. A very interesting and well made series (so far).

Thanks

Sage


----------



## mayhugh1

The only paint I have planned for the Quarter Scale is a matte black finish on its valve covers. For this I used an oven-cured product called Gun Kote which is a durable ultra-thin finish available from Brownells as well as others. After being cured for an hour at 325F, the finish is impervious to engine fluids, and there are several Youtube videos attesting to its durability when applied over a properly prepared surface. I've used this paint on custom motorcycle parts that have been in the weather for more than a dozen years and they still show few signs of wear. The only issue is its current cost. A 6 oz. rattle can is around $32 which is 300% more than I paid several years ago when I last bought what I think is the same product under the label 'Brownells' Baking Lacquer.' A less expensive paint could certainly have been used, but I was concerned about a thicker coat washing out the shallow 'Rolls Royce' badges cast into the sides of the covers.

I made a pair of gaskets for the valve covers as well as a gasket for the lower crankcase. For these I used 1/64" rubberized automotive sheet gasket rather than the shrink-prone brown fiber material used earlier to make the intake gaskets. Of course, these gaskets also required clearance holes for a truckload of 1-72 mounting screws. In order to get them all in the right locations I first set the valve cover down on top of the gasket. Using a length of pointed drill rod with a close fit to the covers' bolt holes, I transferred the locations of the holes onto the gasket as light dimples. A simple hole punch was made up from a short length of brass tubing by sharpening one of its ends with a small 45 degree countersink. After removing the valve cover from the gasket, the punch could be precisely centered over each dimple with the help of a second piece of pointed drill rod slipped inside the tube punch. Once in position, the rod was withdrawn and the punch given a couple light taps with a small hammer. With the gasket backed-up with a sheet of thin cardboard between it and an anvil, the tiny holes came out perfectly punched. The punch had to be resharpened every dozen holes or so, but two of them lasted through the hundred-plus holes that I ended up punching in the three gaskets.

The magnetos (actually, the distributors) can't yet be installed because once they are in place they will complicate the installation of some of the engine's oil lines. These lines will emanate from a pressure relief valve housing that's yet to be installed on the starboard side of the crankcase. The next step, therefore, was to machine this assembly so the engine's oiling system can be first completed.

The valve housing, which actually contains a couple functions, is the last component to be machined from the Quarter Scale's documentation. I spent several days studying its drawing and trying to decipher its functionality, but I wasn't able to make my peace with it until after I had actually completed its machining. Then, I had to make some modifications to it to correct for my misunderstandings of its operation. 

Part of my initial confusion was caused by the mounting hole pattern that I had already machined into the crankcase. I had faced, drilled, and tapped a number of mounting hole bosses that were originally cast into my particular crankcase; but evidently it had been designed for an earlier version of the valve housing. The housing in my drawing requires only two mounting holes, and its backside was intended to be machined to fit the complex contour of the crankcase. I began by modifying the design of the valve housing to match my already machined crankcase. A much bigger problem, though, was that I didn't appreciate what the designer of the valve housing was trying to accomplish, nor did I completely understand the interaction between the valves inside the housing.

The housing contains two valves which, in the documentation, are labeled as high and low pressure relief valves. Pressure regulation is a good idea in an lubrication system using a constant displacement oil pump because of the extremely high pressures that can be generated (80-100 psi in my radials, for example). And, it's almost mandatory in a dry sump system in order to prevent the pressure pump from getting too far ahead of the scavenger pump. It's easy to provide a tank of froth-free oil for the pressure pump to draw from, but the scavenger pump is left to fend for itself in the engine's sump. In a model engine it spends a lot of its time sucking air and re-priming until the engine's sump is filled with waste oil that has drained back from the engine's upper end. The only way the scavenger pump is then able to catch up is if its pumping capacity is higher than that of the pressure pump. Fortunately, the Quarter Scale's pump designs try to provide for this.

Relief valves work by blocking off oil flow using a spring-loaded plunger sitting in a seat. When the oil pressure on the plunger exceeds the spring pressure, the plunger is lifted, and a portion of the oil is allowed to escape through a 'return to tank' line. This action creates an adjustable pressurized source of oil that can be used to lubricate a portion of the engine; and the excess is simply returned to the system's oil tank.

The Quarter Scale's valve housing, however, contains two pressure relief valves in series. A high pressure relief valve supplies oil to the crankshaft, but its 'return to tank' line is actual&#322;y the input to the second valve. This second valve is a low pressure relief valve that supplies oil to the rest of the engine. In the stock design, its 'return to tank' line is actually a return to the engine's sump through a passage in the rear of the valve housing. This creates a potential problem because it means that the entire output of the pressure pump, including the 'tank' returns of both relief valves, ends up inside the engine where it can overwhelm the scavenger pump if the pressures and flows are not precisely balanced. 

John Ramm mentioned that the sump in his engine routinely over-filled causing excess oil to be spit out the engine's exhausts. He improved the situation by adding a third pressure relief valve with a true 'return to tank' just ahead of the stock high pressure relief valve. Feedback concerning this issue may never have made it back to Dynamotive for an ECN because John may be the only builder who only recently got one of these engines to run long enough to see it. I've attempted to solve the issue, however, by modifying the design of the stock valve housing so the low pressure 'return to tank' line real&#322;y does return its excess oil to the tank rather than dumping it into the engine's sump.

The Quarter Scale's high pressure relief valve also happens to function as an anti-drain-back valve by preventing oil from draining back out of the engine when it's shut down. Before I understood the interaction between the two relief valves, I thought this was its primary purpose; and I mis-labeled it as such on the housing that I machined. I added a gage port to the housing so the low pressure relief valve would not have to be blindly adjusted. When I machined the pressure pump long ago, I included a gage port on its body which will be used to set the high pressure relief valve. 

The next step will be a tedious one that includes making up and routing the various external oil lines. I've not been looking forward to this because I can already tell it's going to be one of those tasks that I'm never quite satisfied with. I've bought a lot of miniature copper tubing to play with, but I'm sure most of it will end up as scrap. I've gotten a head start on the easiest one - the high pressure line feeding the crankshaft. It required only three tries to get a satisfactory result, but I still have to machine and solder a mounting flange on its far end. -Terry


----------



## Buchanan

Absolutely fantastic!   May I ask, with the greatest respect , Will you try to make the oil control block look like a casting. It would blend in with  the the lost wax castings of the engine so much better .


----------



## mayhugh1

Hi Buchanan,
I agree with you that it would look better if it were blended into the crankcase to look like part of the casting. I added it as a bolt-on, though, because that was the the way it was handled on the full-size engines. Maybe it should be painted, though. - Terry


----------



## Buchanan

Sorry Terry.
 I did not explain myself properly. What I was trying to say was to make the bolt on block look like a separate part but make it look a little more like a casting itself. I am in complete admiration of your work in every way, what ever you do.
Deryck


----------



## mayhugh1

This is what I find amazing:
http://buchananclocks.com/astronomical-extraordinaire/


----------



## Ghosty

mayhugh1 said:


> This is what I find amazing:
> http://buchananclocks.com/astronomical-extraordinaire/


You are not the only one, love those type of clocks, I know I don't have the ability to do that type of work. 
Your work on this engine would be pushing me to limits I don't have, Keep up the great work.


Cheers
Andrew

[ame]https://www.youtube.com/watch?v=iYA13MVMgVA[/ame]


----------



## Buchanan

Thank you very much,  but not the reply I expected.


----------



## Blogwitch

Deryck,

If you are into full sized aircraft and engines you would find that most ancillary valves that you are looking at are in fact machined from solid bar, very rarely are they cast unless they were just a cross or T joint, which would be fairly simple to hold and machine, and even then, most of those would be manufactured from billet material.

To make a casting for such a small and most probably an "off the shelf " part would just be too expensive to hold and machine.


John


----------



## Rustkolector

Terry,
I can't say it any better than has already been said.....OUTSTANDING WORK.

In the future you can find more color options and much lower prices on Gun Kote direct from kgcoatings.com. I have used it for many years and it adheres to brass and aluminum better than any other finish. Great stuff. 
Jeff


----------



## Buchanan

John.  If it is true to scale I have absolutely no problem . If not, its Terry's engine and it is beautiful.I do not have an in depth knowledge of aircraft engines but I can understand you. I just assumed that the valve would have been a die casting. Thanks for the adjustment.
Buchanan


----------



## mu38&Bg#

https://www.flickr.com/photos/[email protected]/3444679767/in/album-72157615730935253/

While the original was a casting, it does not detract from the work being here.


----------



## mayhugh1

Dieselpilot,
Thanks for the photos. They contained details I hadn't yet come across in my own research -Terry


----------



## dischn2

Hi Terry,
can I help you with the original drawing of the housing? 
You are doing a great job, but this brass part is ugly .

Dirk 

View attachment 607929.zip


----------



## Buchanan

Oh dear, what have I started. Terry, keep it like it is. It's your engine.   
Deryck


----------



## mayhugh1

No problem... 
One of my reasons for posting is to gather comments and opinions from others to use or to not use. The post by dischn2 and the 'like' by cheese.cake.701 seemed a bit suspicious, though. I've been afraid to open that zip file.&#128128;


----------



## gadabout

That file is ok, I opened it and its a drawing , very detailed of a relief valve

Mark


----------



## dischn2

Hi Terry
I am sorry that you misunderstood my posting. I had to zip the tif file because I am not allowed to post tif files and the file size was also restricted. 
Actually the drawing shows the original oil relief valve housing for the V-1650-7 Packard Merlin. I thought I could help you with it 

Dirk


----------



## rdefrei1

I did open the file and it's a legit Engineering Drawing. 
It's just a compressed file (.zip)


----------



## rdefrei1

I was able to change the file extension to JPG.


----------



## mayhugh1

dischn2 said:


> Hi Terry
> I am sorry that you misunderstood my posting. I had to zip the tif file because I am not allowed to post tif files and the file size was also restricted.
> Actually the drawing shows the original oil relief valve housing for the V-1650-7 Packard Merlin. I thought I could help you with it
> 
> Dirk



Sorry for my misunderstanding. Thanks for your help. -Terry


----------



## mayhugh1

The Quarter Scale documentation suggested machining scaled AN816 37 degree flare fittings for connecting the oil lines to the relief valve housing. For the housing's two output lines I machined a pair of single piece flanges that were intended to only look like threaded fittings. I used faux fittings on these two lines because the runs made up from the rigid tubing were just too short and didn't have the flexibility required to undo a threaded connection. One of my goals in plumbing the oil system was to do it in such a way that the individual lines can later be opened up for maintenance (to verify flow, replace gaskets, etc.) without the need for a lot of secondary disassembly.

Three additional oil lines branch off the far end of the low pressure line at the rear of the engine. These lines feed oil to the internals of the wheel case as well as the camshafts and rockers in the engine's top end. Unfortunately, they need to be routed in the busiest section of the engine and right up against the chain cover and starboard-side distributor. 

A sketch in the Quarter Scale's documentation recommended anchoring a stack of banjo fittings to the top of the wheel case to create a union for these lines. In my particular case, this would have required some heroic bends in the 3/32" copper tubing used for the lines. Several days were spent trying to come up with something that looked decent but was still accessible. Bare aluminum (tig) welding rod and lots of trial-and-error was used to develop shapes for these three oil lines. Simple grooved mandrels turned from wooden dowels were used to form the bends. Along the way, I machined lots of brass fittings that ended up not being used. One batch of parts ended up being inadvertently machined from the nasty mystery brass that created so many problems for the crankshaft oil manifold.

I wanted the flanged fittings that were used at the rear of the engine to be as small as possible, but their mating surfaces needed enough area to provide leak-free joints. I didn't want to use sealer on any part of the oil system for fear of it finding its way inside a tube and creating a blockage. The tubes were soldered to the fittings with a tiny butane torch while they were bolted onto the engine in their final positions and with their sealing surfaces parallel and making full contact. The challenge while forming the complex bends was to not only make them pleasing to the eye but precise enough so they slipped easily into position.

Eventually, I created a custom union for the four lines on the starboard side of the engine just forward of the distributor and barely out of the way of its plug wires. Yet another set of fittings was machined to accommodate the bends coming out of the union. A really troublesome line needed to be run to the input fitting on the top of the wheel case. This single line created 90% of the rod and tubing scrap shown in one of the photos. The union isn't rigidly attached to the crankcase but is well supported and held in position by the four tubes attached to it. This was done to reduce the stresses on the solder joints. After all the oil lines were completed and finally in place, each was removed, one at a time, so linen paper gaskets could be added.

Those who have been following this build, and didn't like my brass relief valve housing, may not like the brass union either.  It's bigger than I would have liked, but it will be hidden behind the distributors and plug wires when they are installed. - Terry


----------



## Buchanan

Love it Terry. Pipe bending can be a nightmare, your's look beautiful.  

Buchanan


----------



## Ghosty

Terry,
Beautiful work as always. Will keep watching.

Cheers
Andrew


----------



## DICKEYBIRD

I can't help but say this project for one man to accomplish is no less a feat than NASA's moon landings in the 60's!


----------



## ddmckee54

Terry:

If they don't like your oil lines, let them build their own 1/4 scale Merlin.  Then THEY can try making scale oil lines and you can complain that the resulting oil leaks aren't scale sized.

Don


----------



## tms6401

Absolutely incredible build!!  There are no other words that haven't been used many times already. You must get an incredible feeling of satisfaction every time you look at or touch this engine.

Tom


----------



## camm-1

What can I say more than amazing beautiful and exelent skills of everything Terry!


----------



## Blogwitch

Terry,

As they say, it is just as easy to make two as it is to make one.

So if I send you a couple of hundred bucks, will you knock one off for me? 

John


----------



## mayhugh1

Thanks all for your kind comments ...

In order to wrap up the coolant system components that are actually mounted on the engine, a means must be provided to return the coolant from the outlets on the fronts of the heads to an external off-board radiator. In the Merlin's aero applications the full-size engines used a header tank for this.

For me, the header tank was one of the most difficult to understand (and ugliest) components on the Merlin. The Quarter Scale documentation contained little information about configuring a coolant system for the model and nothing at all about this tank. Dynamotive's Youtube video shows a scratch-built tank installed on its prototype, but this was a late attempt to solve the engine's overheating problems. 

The full-scale tank, hidden beneath a plane's cowling, took on a number of different shapes depending upon the model of the engine (there were 57 variants) and the airframe in which it was installed. On an engine stand it would have been situated well below the prop wash and appear to provide little cooling benefit.

A revelation concerning its real purpose occurred when I came across a re-builder's online photo showing its internals. The tank wasn't at all what I had expected and was filled mostly with air. Its actual purpose was to isolate a pair of large diameter (expansion) coolant return lines from the engine's heat so they could de-aerate the coolant before it was returned to the radiator.

Since I plan to display and (hopefully) run the Quarter Scale on a test stand, I chose to fabricate a functional header that was more appropriate for that set-up. The engines I've seen displayed in simulated Spitfire or P-51 mounts are very impressive, but they greatly limit access to areas of the engine that will likely require some fiddling to get it running for the first time. These mounts would certainly demand a header tank, though, that was more reminiscent of the one in the first photo.

I started fabrication of my header by forming a length of 3/4" diameter stainless tubing into a 200 degree five inch diameter bend. The 3/4" die set that I own for my tube bender happened to be very close to the required diameter, but the last 20 degrees of the bend had to be muscled in using a vise and a large clamp. In order to prevent the tubing from deforming, I filled the starting workpiece with Cerrobend.

I've learned through experience that a lot of Cerrobend headaches can be avoided if the time and effort are taken to use it properly. In order to avoid overheating the metal, it was melted in a beaker sitting in a pan of boiling water on our kitchen stove. While the metal was being heated, one end of the tube was tightly corked and filled with ordinary cooking oil. The oil is really necessary to keep bits of Cerrobend from later sticking to the interior of the tube, and one of the reasons for not overheating it with a torch is to prevent scorching the protective oil. The oil was poured out of the tube just before filling it with the molten metal. The other end of the tube was then quickly corked so the workpiece could be plunged into a sink filled with ice water. The fast chill added some ductility to the Cerrobend. After the bends were completed the tube, with its two open ends pointing up, was re-heated in a large pan of boiling water. The Cerrobend poured out cleanly with no 'cling-ons' and was reclaimed in a scrapped muffin mold.

Machining began by notching the tube for a pair of inlet fittings that will eventually connect the header to the engine's outlet fittings through a pair of short pieces of flexible hose. These fittings were lathe-turned from 303 stainless and then tack-welded to the tubes. This particular stainless alloy isn't really weldable, and so the fittings were soldered to the tubes. I used a 96% Sn, 4% Ag solder alloy available from TM Technologies (kit #ABS-0065 includes the flux)
https://www.tinmantech.com/html/soldering.php
I previously used this particular product, recommended to me by Petertha, to fabricate the fuel inlet tubes for my 18 cylinder radial. 

I wanted the tube and its fittings to appear as a single sculpted part, and so I buttered the solder onto the assembly as though I was doing auto body lead-work. The next several hours were spent with files and emory paper metal-finishing the result. It's less frustrating to perform the initial shaping with a file that doesn't tend to load up with the soft solder. I have two round chainsaw files that work nicely, and one of them was used for most of the work.

A pair of outlet fittings was next machined for the bottom ends of the header. Each of these two piece fittings included a hose barb that was permanently threaded into a lathe-turned 45 degree elbow which, in turn, was joined to the header tube with 620 Loctite.

The flexible hose couplers would not, by themselves, provide adequate support for the header tank against the engine's vibration. And so, two band clamps were formed from .010" stainless shim stock and added to the lower ends of the header. These bands secure the header to bolts already present on the front of the prop drive cover. 

The color of the Ag/Sn solder wasn't a perfect match to the stainless steel and was something of an annoyance for an assembly that was going to be in full view at the top of the engine. While trying to decide whether or not to paint the header, I noticed a slight shadow under one of the front fillets that I thought had been previously polished out. This made me suspicious of my soldering that, up to that point, I had been so happy with. So, I decided to pressure test the header. The disappointing result was a very slight leak at the edge of the fillet. This indicated that the solder had evidently not wetted the seam which was located a good eighth inch under beneath the fillet, and so there was likely contamination as well.

Merely re-heating the joint would probably not have been a reliable fix because there was no way to clean and re-flux the affected area. So, I unsoldered the whole assembly, ground away the weld tacks, and separated the parts so I could start over. After removing all traces of the soft solder, I brazed the pieces together using a gap-filling (35% Ag, 26% Cu, 21% Zn, 18% Cd) brazing alloy available from McMaster Carr. Large thick fillets can be obtained with this particular alloy, and they flow out more controllably doing away with the need for soft solder 'buttering.' The final metal finishing was made more difficult by the harder filler, but the assembly didn't leak when It was completed. 

The now yellowish fillets left no doubt about whether to paint the header, and so I used the remainder of the matte black Gun-Kote purchased earlier for the valve covers. The full-scale header tanks were typically painted white in order to reduce the absorption of the engine heat surrounding them. In my case, the coolant will likely be hotter than the immediate surrounding area, and so the black paint seemed more appropriate. - Terry


----------



## ddmckee54

Judging from the amount of work that you put into your "simple" coolant header I'm guessing that your last project for this engine will be an in-flight variable pitch prop with forged prop blades, maybe even de-icing boots.  Just funnin' with ya Terry.

I have learned so much just from watching you build your engines and the testing you do to build them that it isn't even funny anymore.  You just continue to amaze.  

If you're going to build one of these beauties for John, how many orders do you need before we can get a group discount?

Seriously, how are you ever going to top this one with your next project?

Don


----------



## DICKEYBIRD

ddmckee54 said:


> Seriously, how are you ever going to top this one with your next project?


I think if I were Terry, I'd probably retire from being retired for a while before starting something else!


----------



## Barnbikes

ddmckee54 said:


> Judging from the amount of work that you put into your "simple" coolant header I'm guessing that your last project for this engine will be an in-flight variable pitch prop with forged prop blades, maybe even de-icing boots.  Just funnin' with ya Terry.
> 
> Don



I thought he was going to build a 1/4 scale plane to put the engine in.


----------



## DiegoVV

Everytime I see posts from Terry or from Keith5700 I can´t help to envy their knowledge and craftmanship level. Every single piece they make deserve to be exposed in a museum. Go ahed with these builds!


----------



## wirralcnc

1/6th scale pratt whitney r1830. Combine the skills of machining castings and radial engines.


----------



## kvom

Learn something every time.  I have a Cerrobend ingot but have never used it.  The trick about oiling the inside of the tube before pouring in the metal is useful info.

Waiting anxiously for the first run video.


----------



## cfellows

Really incredible work, Terry.  The fit and finish on that pipe-work is unbelievable.

Chuck


----------



## mayhugh1

The full-size Merlin's carburetion evolved continuously during the engine's development which seemed to span most of its life. Dual venturi updraft units manufactured by SU, Stromberg, and Bendix were used over time. In 1943, a form of throttle body injection replaced the Merlin's updraft carburettor, and metered fuel began being pumped directly into the supercharger. 

Similar to the full-size Merlin, the Quarter Scale's supercharger inlet casting was designed to accommodate a (scaled) Stromberg carburetor that had been planned for the engine but never actually implemented. I've included a photo of an early carburettor mounted on the full-size Merlin's inlet casting for comparison with the Quarter Scale's casting. Since the Quarter Scale 
Stromberg never materialized, the metering area on the front of the casting was available to builders for their own carburetors.

The Quarter Scale documentation included some discussion about selecting a carburetor for a scaled engine. The only concrete recommendation that came out of it, though, was a Honda GX120 unit manufactured for an industrial 4 hp single cylinder engine. This carb is still available, but its .456" diameter venturi feels a bit oversize. It wasn't at all clear whether one of these units had actually ever been tried on Dynamotive's prototype. The notes do mention that it had run reasonably well, although without a supercharger, using a commercial RC carb with a .350" diameter Venturi.

I had good luck with the Perry carburetor that I used on my 18 cylinder radial:
http://www.homemodelenginemachinist.com/showthread.php?t=21601&page=36
The model 1401 with its .312" venturi came up quickly and was not overly difficult to tune even on gasoline. The engine idles and transitions well, and the settings have remained stable over time. So, I decided to try a similar unit but with a .340" venturi on the Quarter Scale.

My plan was to adapt the Perry carb, running on gasoline with an alternate idle disk, to the metering area on the front of the supercharger inlet casting in such a way to retain continual access to all the carb's adjustments. It was also important that the carb be easily removable for experimenting with other size units since the Quarter Scale's huge induction system and supercharger are still big unknowns for me. Finally, the end result had to look like it belonged on the the rear of a Merlin rather than the front of an RC plane.

I discovered that a 1/2" solderable copper pipe elbow perfectly fit the standard .550" diameter o-ring'd neck of the Perry carb. This elbow became the smooth transition that I needed between the input of the supercharger and the output of the carb. The large venturi area in the starboard-side inlet passage was reduced and sealed to the elbow so the supercharger can draw only through the carb. A tapered aluminum reducer was machined to provide this seal as well as the transition between the output of the copper elbow and the input of the supercharger. The assembly was made permanent by backfilling the rear of the reducer and elbow with JB Weld. 

The carburetor will draw its fuel from a bowl whose level will be regulated by a recirculating loop driven by an electric pump. A constant level fuel bowl will allow a lot of freedom later when selecting a location for the engine's fuel tank. It will also provide consistent fuel delivery to a large engine that will quickly consume a lot of fuel. I've used a similar scheme on the last four multi-cylinder engines I've built. A float-regulated bowl could work as well, but tiny floats can be difficult to get working reliably.

The fuel bowl was to be tucked inside the casting's port-side inlet passage adjacent to the carb. The throttle shaft had to be lengthened with a two inch extension in order to clear the bowl and to extend the throttle lever beyond the inlet casting for access from the rear of the engine. 

The carb bowl was machined from a single block of brass, and then four inlet/outlet tubes were soldered to it. The most critical tube is the return outlet whose height establishes the level of fuel in the bowl. The fuel's surface tension interacts with the edge of the return tube to stabilize the level somewhat above the end of the tube, and this can become an annoyance in a limited capacity bowl. I've attempted to solve this numerous times in the past with the design of the return tube, but I usually end up shortening the tube anyway. Arbitrarily reducing the fuel level can create problems in a small bowl since not only is the bowl's capacity reduced, but the turbulences generated near the inlet and outlet tube can aerate the fuel before it reaches the carb. The carb's inlet should be located at the bottom of the bowl and as far as possible away from these tubes. 

This time I tried rolling over the end of the return tube to form a thin-edge bell-mouth, but I still ended up having to lower the height of the tube more than I had hoped. The bowl's inlet tube is designed to supply its fuel to the rear of the bowl and away from the carb inlet and the bowl return. The carb inlet at the bottom of the bowl allows the bowl be easily emptied for storage.

The goal was to stabilize the fuel level at a quarter inch below the carb's spray bar, and this was verified by setting up a temporary alcohol recirculating loop. The fuel pump, commonly available in RC hobby stores, is the same one used on my other engines. Its components will later be re-packaged in an aluminum machined housing. This pump is a high volume 6V-12V unit designed to quickly fill the tank in a large RC plane. For my application I inserted a .022" diameter orifice in series with the input line to the carb to limit the flow rate and reduce the turbulence generated inside the bowl. For fine tuning, a 50 ohm rheostat will also be placed in series with its 6V power source. In operation, the pump is easily tuned by listening for a consistent drone before the engine is started. This particular pump is designed and recommended by the manufacturer only for methanol, but as far as I can tell it contains no components chemically incompatible with gasoline. I've run four gasoline engines using these re-packaged pumps and have had no issues ... so far.

At this point, the carb and its fuel bowl are sitting, unsecured, in the metering area on the front of the supercharger inlet casting. The final step will to be to machine a cover or covers to secure the assembly and shield its components from the prop wash. - Terry


----------



## Ghosty

Terry,
Got to love copper plumbing fittings. Have used them for a lot of things over the years. Still love the work, and will keep looking.

Cheers
Andrew


----------



## dsage

Great work as usual Terry. It looks like the fuel comes up very close to the top of the reservoir. I'm wondering if, once you put the top on the reservoir, capillary action will attract the fuel and form a meniscus with the lid and the side wall and interfere with the drain. Perhaps if the drain were more in the middle of the reservoir or the reservoir were much deeper than the normal fuel level this could be avoided. Tough to tell from pictures. Not sure what the lid looks like either maybe it adds to the height of the reservoir interior?


----------



## mayhugh1

dsage said:


> Great work as usual Terry. It looks like the fuel comes up very close to the top of the reservoir. I'm wondering if, once you put the top on the reservoir, capillary action will attract the fuel and form a meniscus with the lid and the side wall and interfere with the drain. Perhaps if the drain were more in the middle of the reservoir or the reservoir were much deeper than the normal fuel level this could be avoided. Tough to tell from pictures. Not sure what the lid looks like either maybe it adds to the height of the reservoir interior?


Dave,
Once the gasket is added, it lifts the lid the thickness of the gasket. I should have mentioned that I ran the loop again with the lid assembled, and it seems to run OK. Because of space limitations I just didn't have much choice on where to place the tubes on this one. I probably should have butchered the casting and made the bowl bigger and more square, but I wasn't sure how well I'd be able to hide the crime scene. - Terry


----------



## petertha

Very nice Terry. Once you have a handle on running characteristics, I'm sure you can replicate the important dimensional guts of the Perry for a 'period look' of the outer body if you so choose.

Entertainment side note - I just stumbled on a Netflix 6-part series called Plane Resurrection. Part 1 is a P-51 Mustang, part-2 is a Hurricane. Amongst the rebuilding, some teaser shots of the engine & ancillaries. Gives some appreciation of engineering mechanics of that era. And the correspondingly huge work effort to those who restored them back to flying conditions.


----------



## mayhugh1

In order to wrap up work on the carburetor, I needed only to secure it to the engine. In homage to the Merlin's original designers, I turned a simple sheet metal bracket into a half dozen complex machined parts. I drew a line, though, at using the same number of fasteners they would have used to hold everything together. 

The fuel bowl was secured to the metering area of the inlet casting with a pair of interlocking machined brackets that also form a bearing (of sorts) for the throttle shaft extension. Thanks to some poor planning, the fuel hose between the bowl and the carb ended up with a tight bend that could have collapsed over time, and so a spring was slipped inside the hose. 

The carb cover was more involved because of the complex shape of the carburetor body. I wanted the carb's inlet to end up vertical and pointing downward, but I also wanted to be able to choke the carb by holding a finger over its intake. Another copper elbow fitting, o-ringed to the carb's inlet neck, solved both requirements nicely. The fitting was soft soldered to a machined brass top plate which, in turn, was bolted to a pair of endplates attached to the inlet casting. The covers were bead blasted and painted with flat gray Gun Kote which, after its oven cure, was impervious to gasoline. Other than the throttle shaft extension, the only other modification made to the carb was the machining of a new and longer-than-stock idle stop screw. Finally, a gasket was cut from rubberized automotive gasket material to seal the inlet casting to the bottom of the supercharger. 

An important loose end that I tied up while waiting for the Gun Kote to arrive was the testing of the oil system including all the plumbing and the pressure relief valves. There was no practical way to include the engine's oil pump in this particular test, but it had already been thoroughly exercised in a previous test.

For a pressurized oil source I cobbled a 50 ml syringe into the input of the pressure relief valve, and I attached gages to the high and low pressure lines so the operating points of the relief valves could be set. The first test identified a fitting whose 1-72 mounting screws needed a bit more tightening. Before any relief valve adjustments were made, the high and low pressure lines each hard-pegged the 15 psi gages I was using. After setting the high pressure line to 15 psi and the low pressure line to 6 psi, I found obvious evidence of oil reaching all the crankshaft bearings as well as those in both camshafts. The output of the wheel case oil feed line was buried deep inside the engine by this time, but since the timing chain seemed to be wet with oil I assumed it was working. The oil feed to the prop gear was also hidden, but there seemed to be oil returning from it to the bottom of the crankcase. I was happy to see the pressure readings responding to the adjustments as expected and to see oil flowing in the low pressure tank return line. Up until this point I wasn't sure that I fully understood how the tandem relief valves were going to work. - Terry


----------



## dalem9

Truly amazing . Great work .


----------



## ddmckee54

Looking good Terry.  You've got oil leaking from where you want it to leak, and you've stopped the oil leaking from where you didn't want it to leak.

Out of idle curiosity, what's the Merlin's all up weight so far?

Don


----------



## gbritnell

The extra work on the carb pieces is icing on the cake. Well done!
gbritnell


----------



## kvom

It's hard to believe it's been 2 years since post#1.  The finish line is in sight.  :thumbup:


----------



## DICKEYBIRD

kvom said:


> It's hard to believe it's been 2 years since post#1.


What's mind boggling to me is the truly prodigious  amount of painstakingly researched & documented work of the highest caliber he's completed in those 2 years.


----------



## mayhugh1

I spent several days working on the design of a display/running stand for the Quarter Scale before I realized that I really needed the final design of the electric starter. Since it will have to be shoehorned into a crowded area at the rear of the engine, it will likely affect the design of the stand. Even though I've always considered an electric starter to be a nice-to-have option that could be added later, I've continued my background search for a suitable motor.

Back in post #423, just after I had located my first candidate dc brush motor, Naiveambition suggested that I take a look at motors actually designed for starter applications in small gasoline engines such as those used in yard equipment, etc. Following his advice, I located some small 12V permanent magnet brush motors being sold as replacement parts for some popular go-kart and scooter engines. Some of these were being offered by Chinese suppliers on eBay for just over $20 plus free shipping, but I wasn't able to find any electrical or dimensional specs on any of the ones that looked interesting. After some procrastination, I ordered a couple different units hoping that I might at least be able to appropriate some useful components from them.

I've included a photo of the two motors that I received which shows them lying along side the Nichibo that I already had. The new motors are physically a bit larger than the Nichibo, but either could be made to fit into the available space if a custom offset gear box is used to adapt them to the wheel case. These motors are some 30% heavier than the Nichibo, and while playing around with them I discovered that I needed to be careful and tightly hold onto them when they're energized.

One of the motors has a built-in 6:1 speed reducer and a measured current draw of some 10 amps at its 2300 no-load reduced rpm. The motor without a speed reducer draws 12 amps at an unloaded 16 krpm. In comparison, the Nichibo's current draw at its unloaded 16 krpm is only 2 amps. It's likely that these motors were designed for some serious torque - probably as much as five or six times more output than the Nichibo. After less than a minute of running the housings of both motors become too warm to hold while, in comparison, the Nichibo with its internal fan seems capable of continuous operation.

At first, I was enthusiastic about designing a starter around one of these new motors, but after some thought I began having misgivings about their high outputs. If blindly installed in the Quarter Scale, they could be capable of breaking parts in the engine's seemingly fragile starting system. The problem that I'm dealing with is that I need a motor with just the right amount of torque plus just a little more, but I really don't know what that right amount is. Eventually, I realized that I may have to iterate the starter's design in order to determine its real requirements, and so I decided to begin with a conservative design based on the Nichibo. An alternative approach would be to start with one of the high torque motors and to use an electronic speed controller to adjust its output. I actually don't have a technically sound reason for starting out with the Nichibo, and I may end up changing course after getting further along into the starter's development. Just in case, though, I've ordered a 40 amp speed controller.

Most of the complexity in the Quarter Scale's starter will lie in the offset gearbox required even by the Nichibo to move the motor off the axis of the wheel case starter input shaft so it can clear the engine's supercharger and coolant pump. In order to begin tying down some of the design variables, I selected a 30:1 gear reduction ratio which was determined earlier to be nearly ideal for the Nichibo and, hopefully, not unreasonable for the other two motors. I also chose 48 DP for the gears not only because I needed to achieve a rather large reduction ratio in a relatively small area, but because I already had a nearly complete set of 48 DP gear cutters. 

I would have liked to have started with a 12 tooth pinion on the motor shaft in order to achieve the target reduction with the smallest diameter gears. However, the Nichibo's shaft is .157" in diameter, and it has a half-diameter milled flat over half its length. I had some concern about the strength of a minimum diameter pinion fitted to this particular shaft, and so the gear reduction was begun with a 16 tooth pinion. Unfortunately, the pinions are integral to the shafts in the other two motors, and they also appear to be metric. 

The envelope of the gearbox was determined by trial-and-error using SolidWorks patterns printed out full-scale and then cut and trial-fitted to the engine. I previously designed the wheel case starter input shaft to use an Oldham coupler, and so the location and form factor of the gearbox output shaft had already been defined. After some thought as to how the gearbox might be assembled, I designed its complex top cover as a separately attached component to the wheel case, and I made it independent of the gear train. The gear train, itself, is a standalone testable assembly on a sub-plate which doubles as the bottom cover of the gearbox, and it includes the mounting details for the motor(s). The gearbox will be lightly packed with grease, and bronze sleeve bearings will be used on all the shafts. 

The next step is machine all these parts and assemble them into a first-pass starter. - Terry


----------



## Ken I

Just to chip in with some observations on electric motors / starters.

Starter motors are not 100% rated and burn out  if run continuously - they are generally rated to "kill" the battery.

What you can get out of a motor is limited by the torque / saturation of the iron core rotor - so go for more revs and gear down.

I've used those Nichibo motors for odd jobs (like a slotcar tyre grinder) and have run a 9V up to 24V - WTH a D.C. motor just spins faster. But to get one of those to crank your monster (I'm estimating 420cc) you'll need to rev the beans out of it and gear down (seems to be your thinking).

Those motors are frequently used on cordless screwdrivers etc. with a convenient double planetary drive reduction system which might save you on reinventing a gearbox.

Your power supply should be able to establish a current limit and therefore a driving torque limit.

I'm guessing there is already some sort of engage / disengage mechanism or roller clutch in the hand crank drive etc. so what follows is probably redundant.

You will need an override roller clutch (sprague) so that the engine cannot drive  the starter motor - it will over-rev and explode. Even short "hunting" of the motor can apply enough overdrive torque to do damage (bent teeth and shafts).
If your gear down ratio is large your efficiency can fall below 50% and the gearbox is non-reversible (self locking) and the engine cannot overdrive it (might lock up your hand crank if directly linked) - it can only start to break things - the sprague becomes mandatory.

Most starters these days use planetary gear drives to gear down and a solenoid / stirrup lever to engage the pinnion / sprague (via a splined shaft).

Older inertial types used a helical spline which "threw" the pinnion into engagement - overdrive by the engine simply returned it.

One problem was that hunting of the engine during start up would throw the pinnion out of engagement and led to that annoying grind, crank, fire, wheee, grind cycle of a failed start up on a cantankerous engine.

A cure for this (a Bendix patent I think) was the addition of a spring loaded radial detent pin which locked the pinnion in the engaged position - this only disengaged centrifugally one the pinnion's rmp's were about double the starter's nominal (overrunning on the sprague it's not overruning the motor). You hear this as a distinct whine and spin down after the motor starts.

The downside was if the motor failed to start the pinnion remained in engagement and made push starting that more difficult - almost locking up the engine. You would struggle (typically locking the wheels when you "dump" the clutch) and then you would hear the "whee-clunk" as you got it to disengage - thereafter it was back to normal.

Can't wait to hear this run - awesome work.

Regards,
            Ken


----------



## tornitore45

https://www.pololu.com/category/22/motors-and-gearboxes

Just a point of reference.

Mauro


----------



## tornitore45

> If your gear down ratio is large your efficiency can fall below 50% and the gearbox is non-reversible


Can you explain that?   I know is true because I have experienced that with very high compounded ratios, typical is a cordless drill where you can tighten the chuck without the motor turning backward.  However, intuitively you would think that 50% efficiency holds both way and if it works as reduction should at least turn as multiplier, even accepting the fact that the frictional torque is multiplied.
I suppose the statement is not just a practical rule but a fact of physics, which escapes me.


----------



## Ken I

tornitore45 said:


> I suppose the statement is not just a practical rule but a fact of physics, which escapes me.


Yes it is a rule of physics - to do with friction but the proof is complicated.
Perhaps easier to consider a small angle wedge lifting a heavy load - it doesn't matter how heavy the load it won't dislodge the wedge until the wedge angle matches the friction angle - at that point if you do the calculations you will find the system efficiency is 50% 

Regards,
             Ken


----------



## mayhugh1

Ken,
Thanks very much for the information. The comment sbout an excessive gear ratio also caught my attention. There is a sprag clutch between the starter and the crankshaft, but both the electric starter and the manual drill starter shaft will be on the same side of it. This means that when the drill starter is being used, the gear reducer will need to turn. Do you think my 30:1 reducer will be an issue? -Terry


----------



## mayhugh1

I'm afraid I was able to answer my own question. It turns out that a rule of thumb used by designers is to allow 10% efficiency loss per gear contact, and I have four gear contacts in my design. I cobbled up a four-contact gear motor with parts from a junked water softener timer. It had a reduction ratio of only 15, and I could barely spin it from its output shaft.
This isn't a problem that I had considered but it's serious enough to scrap my original design. I spent yesterday preparing the blanks with their pressed-in bronze bearings so I could begin machining the parts today, and so the timing of all this is pretty good. 
Adding a second sprag clutch is an option, but now using one of the other motors with an electronic speed controller is beginning to look attractive. I have some more thinking to do. Again, Ken, thanks for your helpful comments. - Terry


----------



## tornitore45

Thank you Ken, the inclined plane explanation makes sense.


----------



## editor123

You can  limit the torque by limiting the current to the motor (or volts if you prefer).


----------



## Ken I

Terry,
         I thought that might be the case and I was concerned you might have "missed a trick" (been there - done that).

Straight cut spur gears typically give 94-98% efficiency but that's for ground gears mounted on ball / roller bearings - slightly less for helical because of the end thrust.

That 50% efficiency limit is something I have to live with every day in my line of business - robotics - we use high ratios with high inertial loads - but if you fall below 50% the gearbox self locks under deceleration and you cannot control it with the servo drives - the gearbox self destructs in short order. This most commonly occurs because the customer used the wrong grease in a 200:1 cyclo drive - dropping its 70% down to 40% - destruction follows in as little as 3 days.

Home made gears on plain bearings might just go to 90% and it compounds.

0.9^4 = 65%
0.85^4 = 52%

You are probably sailing too close to the wind with 4 gears.

The additional sprague is probably the best option to unload the the hand crank shaft (external starter) otherwise its likely to impose more load on the hand crank than the engine itself.

Glad to have been of some help - or as Thomas Edison said - "another useful piece of negative information".

Regards,
            Ken


----------



## mayhugh1

While re-thinking the starter design, I realized that I had forgotten about the pair of gears inside the wheel case that interconnect the manual and electrical starter shafts. This beveled gear set is a 2:1 reducer. That is, when the manual shaft is driven, the electrical shaft follows at twice the rpm. These gears divide by two the load seen by the electrical starter compared to that seen by the manual shaft, but from the manual shaft's perspective they are yet another gear set that will contribute to its lock-up. It now seems that any gear reducer used in conjunction with the electrical starter should be isolated with a one-way clutch.

Before further complicating my already complex Nichibo design with the addition of a such a clutch, I decided to take a serious look at the high torque starter motors I've been recently collecting. I have no electrical data on any of them, and I really hate blindly lashing electrical stuff together. But, I real&#322;y don't know the starting torque requirements of the Quarter Scale well enough to be sure the Nichibo is actually capable of starting the engine even while running at its ideal operating point. It loks like some experimenting is going to be required after all.

I just received the third and last eBay motor that I had ordered earlier. This one is a component in a starter for a John Deere JS-30 (6.75 hp 90 cc) lawn mower, and it was another suggestion from Naiveambition. This motor looks similar to the Nichibo, and its measured unloaded current draw and rpm are also similar; and so I'm not sure it fits my current definition of 'high torque.' The starter includes a 6:1 gear reducer. The motor has a 12 tooth 30 DP pinion gear pressed onto its shaft, but for some reason its 72 tooth driven gear is a non-matching 32 DP.

I thought my next approach to a starter might be to simply power one of the high torque motors with an electronic PWM controller and completely discard the troublesome mechanical gear reducer. My reasoning was as follows.

A typical gasoline engine requires a cranking speed of 100-200 rpm in order to reliably start. The small engine starters based upon the permanent magnet motors that I'm currently looking at typically use a 6:1 gear reducer. This means that these motors are capable of supplying the torque needed to start their engines while spinning between 600 and 1200 rpm. Of course, this assumes there is no additional gear reduction between the starter and the engine.

The Quarter Scale should have similar rpm starting requirements. Although its 350cc displacement is considerably larger than the engines these starters were designed for, the Quarter Scale's displacement is distributed over a number of small cylinders with small compression bumps rather than one or two large ones. Inside the Quarter Scale wheel case there is a built-in 10:1 gear reduction between the electrical starter shaft and the crankshaft. Therefore, the Quarter Scale's electrical starter shaft will spin need to spin at least between 1000 and 2000 rpm while cranking the engine at its starting rpm.

Hopefully, at these rpms, one of the fit-for-purpose starter motors will be capable of supplying at least enough torque to start the Quarter Scale. The downside of using a motor with the potential of supplying even more torque than required is that the engine's starting system must be stout enough to handle the starting power including the occasional abuse of an inadvertent fault such as a temporarily blocked prop. With some modification, a PWM controller should be capable of limiting the available torque to just what is required and at the same time provide a soft start to reduce shock to the gear train. 

A new housing was designed. With no gear reducer, the need for an offset went away, and the motor was centered on the axis of the starter shaft. The diameter of the new housing was selected to fill the available space and included a notch to clear the pesky coolant pump. I designed the complex upper portion of the housing to attach to the wheel case independently of the particular motor used. The bottom plate of the housing, which is also the mount for the motor, was designed around the John Deere motor with the intention of modifying it for one of the other motors should testing show it to be inadequate.

An issue arose with the motor's pressed-on pinion gear. I didn't want to pull the gear from the shaft for fear of damaging the motor should it need to be replaced later. The steel Oldham shaft had to be blindly splined so it could be driven by the pinion. I didn't need to perfectly match the splines to the gear teeth, but they had to be stout enough to handle the torque that the resulting socket would be required to handle.

The only way I could think of cutting the splines in my shop was to mill them. I laid out the tooth profile of the pinion gear and then approximated a socket around it using a circular pattern of twelve .075" diameter drilled holes arranged around a plunge-milled center hole. Standard small diameter end mills typical&#322;y don't have the half-inch flute length needed to remove the material left among the holes. But, in my collection of eBay carbide circuit board cutters, I found one that did. A .075" diameter cutter running at 0.5 ipm took a while to do the job, but the result turned out great. When completed, the pinion was a perfect slip fit inside the socket.

It was satisfying to finally start machining the components of the housing since I'd been drawing and re-drawing them for a couple weeks now. The housing and its bottom plate were machined from aluminum, and the splined Oldham shaft was machined from 12L14. The Oldham coupler was turned from 1144 Stressproof. 

A CCM9NW 40 amp PWM controller, available everywhere including Amazon:
https://www.amazon.com/dp/B00RFDFL54/?tag=skimlinks_replacement-20
was used to control the motor from a 12 volt UPS battery. I selected this particular controller since its PWM frequency is switch selectable for 240 Hz, 2.2 kHz, or 22 kHz, and without some testing I didn't know the best frequency to use. An external pot is used to control the duty cycle of the waveform, and therefore the power, applied to the motor.

The first test involved spinning the crankshaft at 150 rpm without the spark plugs installed. I began with a PWM frequency of 22 kHz. The measured voltage at the terminals of the motor was 2.1 volts indicating a PWM duty cycle of about 18%. The average current draw from the battery measured 5 amps which, under an 18% duty cycle, indicated a peak current of 28 amps. 

I then gripped the prop shaft as tightly as I could with a gloved hand to add some additional load to the starter. The motor easily overcame my grip, and at 150 rpm the voltage rose to 2.8 volts and the average current to 13 amps. At the new 23% duty cycle the peak current had risen to 56 amps which was actually beyond the recommended 40 peak amp maximum of the PWM controller. Assuming a motor efficiency at this operating point of, say 40%, I estimated (.4 x 2.8 x 13 x 5252 / 746 / 150) the torque delivered to the crankshaft (after the wheel case 10:1 gear reduction) to be about 0.7 ft-lbs which is considerably less than my earlier guesstimate of 10 ft-lbs at this point needed to eventually start the engine. 

I performed similar tests using the other two available PWM frequencies, but 22 kHz worked best by far. The available torque decreased with decreasing frequency, and the duty cycle had to be considerably increased to obtain the same rpm. Switching noise emanating from the motor was very audible at 2.2 kHz, and at 240 Hz the available torque was so low that I could easily stall the prop shaft with my hand. 

The next step was to repeat the tests with the spark plugs installed to provide a more realistic load on the starter. I re-ran the cranking test as I installed the plugs one by one. I could detect trouble as soon as the first plug was installed. The motor baulked at turning over as soon as that cylinder hit its compression stroke. Running the PWM wide open wasn't sufficient to get the starter to turn the engine over with just two plugs installed. Fortunately, my battery powered drill, driving the manual input, could still easily turn the engine over under the same conditions.

After a bit of actual hands-on experience, I'm gaining some appreciation for the torque levels I'll need to be dealing with on this starter. My concern about breaking parts inside the wheel case has also gone up a few degrees. I now better understand why John Ramm starts his engine by hand slapping the prop. - Terry


----------



## stevehuckss396

Holy smokes everything looks good. How close are you to a test fire? It looks about 90% done so i'm guessing your right about half way. ;D


----------



## mayhugh1

Well, there's still a running stand, control panel, gages, oil tank, coolant tank, fuel tank and pump, radiator, and of course this #@$% starter. -Terry


----------



## kvom

Might be late to the party, but can you not get an idea of the needed torque from a torque wrench attached to the shaft?


----------



## mayhugh1

kvom said:


> Might be late to the party, but can you not get an idea of the needed torque from a torque wrench attached to the shaft?



Kvom,
Yes, you can. That's how I came up with the estimate I'm currently using. The problem is that you need to spin the crank with the torque wrench at the same speed you intend to crank the engine when starting it. The cylinders' compression creates the lion's share of the load that needs to be driven, and because the cylinders leak down during cranking, the load is rpm sensitive. - Terry


----------



## Ken I

Terry,
        There is just so much "wow factor" to this engine already - but how about a scale Coffman starter. Some Merlins were equipped with such. Start it with a bang !

The RC guys use similar frame size motors in higher power D.C. and PM rotor three phase - all of which crank out serious power - might be of use to you.

Regards,
             Ken


----------



## dsage

Hi Terry:

Besides the "cool factor" of having a built in starter motor is there a reason you have discounted simply starting the engine with an electric drill on the shaft you already have available? That way you avoid all the worries about extra gears couplings and associated lock-up issues. I'd hate to hear about a disaster inside the engine.

Sage


----------



## tornitore45

This is at the very top of "Craftsmanship Museum" quality.
Is there going to be a party for the christening of this engine?


----------



## napoleonb

I am still enjoying every update and the tremendous amount of research which is going in building this beautiful engine!


----------



## mayhugh1

dsage said:


> Hi Terry:
> 
> Besides the "cool factor" of having a built in starter motor is there a reason you have discounted simply starting the engine with an electric drill on the shaft you already have available? That way you avoid all the worries about extra gears couplings and associated lock-up issues. I'd hate to hear about a disaster inside the engine.
> 
> Sage


Sage advice 
It was originally 75% cool factor, but now it's a challenge that's hard to walk away without a solid technical excuse for doing so. Most of the breakage concern is with the entire starter system including the drill shaft input. If I can properly control the torque and speed from the electrical starter, I may not make things much worse. -Terry


----------



## mayhugh1

I disassembled enough of the John Deere motor to see that internally it looks very similar to the 775 Nichibo for which I have electrical data. The 775 portion of the motor's part number indicates a standard physical size, but from what I've noticed during my online research the electrical specs can vary somewhat from one 775 motor to another. Since my unloaded rpm and current measurements of the two motors were nearly identical, I'm assuming the motors are the same except for some cosmetic differences. The John Deere version has a plastic boot wrapped around its lower end to block off air vents that would otherwise allow grass clippings inside the motor while the Nichibo has a stator flux shield wrapped around the outside of its housing.

After taking some time to think about the disappointing and puzzling tests that I ran a few days ago, I believe I now have an understanding of what happened.

The speed of a dc motor is directly proportional to the voltage applied to its terminals, and its constant of proportionality is Kv in rpm/volt. When a fixed voltage is applied to an unloaded motor, it will run at its unloaded speed and draw its unloaded current. When mechanical load is applied to the motor, its speed will decrease and its current will increase. Both of these changes are linearly related to the size of the load, and the slopes of their straight-line relationships are available from the motor's data. They can also be measured, but a calibrated mechanical load isn't a typical fixture in a home shop.

For the Nichibo motor, the speed decreases 71 krpm per ft-lb., and the current increases 268 amps per ft-lb. The maximum torque that the motor can supply is called its stall torque, and for the Nichibo this is .32 ft-lbs. The current at this torque is called the motor's stall current, and for the Nichibo this is about 88 amps. In general, as the Nichibo curves show, operating a motor near its maximum torque can be very inefficient, and the resulting internal dissipation will shorten the life of the motor. In briefly powered starter applications this may not be a major concern, but the motor's wiring and controls must be able to handle the additional wasted current.

As the load on the motor increases, its speed will drop, and its current will increase as predicted by the two linear constants. These constants are fixed by the physical design of the motor and are independent of the applied voltage. If the motor is spinning faster than desired under a given load, though, the applied voltage can be decreased to drop the speed of the motor. Likewise, if the motor is spinning slower than desired under a given load, the applied voltage can be increased but only up to the maximum working value specified for the motor.

An efficient way to manually vary a battery voltage applied to a motor is with the use of a PWM controller. This device will efficiently switch the voltage applied to the motor on and off at a high rate and at a duty cycle that can be manually controlled. The effective voltage applied to the motor will be the average value of the PWM waveform. The frequency of the switching should be much greater than the motor's ability to respond to speed changes. My tests on this particular motor showed that 240 Hz was much too low, 2.2 khz was OK, but 22 khz was much better.

The crude load test that I ran while gripping the prop shaft with my hand got the motor to draw 13 (average) amps while spinning the crankshaft about 1500 rpm. The measured average voltage applied to the motor was 2.8 volts. Therefore the duty cycle of the PWM worked out to be 2.8v/12v =23%, and all seemed well. I didn't realize at the time there was trouble brewing under the covers. The peak current supplied to the motor by the controller was 13a/.23 = 56 amps, and this was higher than the controller's continuous 40 amp rating which I mistakenly assumed was spec'd in terms of average current and not peak current.

The third test was performed with some of the spark plugs installed in order to approach the load that the starter will need to handle. Everything went wrong during this test. The motor wouldn't spin, the pot had little control over the controller's low output voltage, and the average measured current was off-scale at 30 amps.

After mulling over the tests and discovering my error about the misinterpreted current rating, I realized the controller was probably at least part of the problem. I replaced the 12 volt battery I was using with a pair of series-connected batteries which I hoped would allow me to source a little more power to the motor through the controller. This change got the motor just barely spinning with three spark plugs installed, but there were still significant hesitations at each of the three compression humps. The starter sounded very much like an old big block Chevy trying to start after its starter and solenoid had been over-heated by the engine's headers. 

This test seemed to confirm that the controller was probably most of my problem. After installing all the spark plugs, I threw caution to wind and removed the controller completely so I could briefly energize the motor directly from the battery. The motor abruptly woke up and effortlessly spun the crankshaft. Over a number of test cycles I was able to measure the crankshaft spinning at 620 rpm while drawing 77 amps from the battery with 10 volts across the motor's terminals.

Although a lawn mower engine starter would likely have no issue with running at such an operating point, I'm uneasy about stressing the Quarter Scale's starting system with some 2-3 times more power than required because the motor is spinning faster than needed. If it weren't for my concern about the robustness of the starting system I would probably just add a starter relay to what I already have and be done with it. I have to admit that that its current high-pitch whine sounds pretty good.

Spinning the engine with the starter eventually became infectious, and I spent a lot more time playing with it than I probably should have. I was careful to keep the bearings and cylinder walls doused with oil since I don't yet have the oil pumps connected. As an aside, I placed a finger over the carburetor intake during one of the cranking tests. The suction was very strong and a good indication that the induction system is probably working as it should.

Even though the starter system has already survived several minutes of cranking time, I'd still like the ability to control its speed, and a PWM controller is still the most efficient way of doing this. This time I went shopping for one in the RC car/truck world where 70 amp brush motors need to be controlled. In this specialized marketplace the controllers are called ESC's (electronic speed controllers), and they're much smaller and more capable than the general purpose controller I've been using. Once more, eBay came to the rescue:
http://www.ebay.com/itm/302145096583

I don't know what extraterrestrial technology the manufacturer of this PWM is using to be able claim 320 amps continuous operation within such a small package. Even though this time I realize they're talking about peak current, my expectations aren't high. 

Seemingly, the main issue with adapting an ESC to a non-RC application is that these controllers have an input control port of their own that expects a small signal PWM control waveform from a servo. Fortunately, this input can be generated and manual&#322;y controlled by yet another piece of ($6) specialized RC hardware called a servo tester. Alternatively, some simple circuitry based upon a 555 timer can be breadboarded to do the same thing. My concern is that the ESC/servo tester combination that I've ordered may include some extra built-in intelligence to support bi-directional and dynamic breaking operation that could get in the way of my plans to use it as a simple single direction speed controller. - Terry


----------



## napoleonb

Perhaps its possible to test load the motor by winding a weight on a rope with a pully directly connected to the motor. The same goed the other way round if this method can turn the engine over you can determine the power needed with some rpm's. It has to be a relative long rope but i assume its possible.


----------



## Ken I

mayhugh1 said:


> I don't know what extraterrestrial technology the manufacturer of this PWM is using to be able claim 320 amps continuous operation within such a small package.


Some of those use MOSFET transistors which have switched resistances better than relay contacts so the power losses are very low hence not a lot of heat.
Also for RC work this negates the need for a "full on" relay bypass - ditto in Slotcar hand controllers.

My experience with PWM systems is that there is sufficient inductance / capacitance in the output to give pure DC under load - you can't normally pick up the the PWM signature until you are close to or exceeding its rating.

I have yet to see a low voltage DC motor that you can't run at 2 - 3 times maximum voltage - apart from the caveat that it might not physically handle the rpm's and fly apart.

napoleonb's callibration suggestion is a good one - I used this very trick to calibrate a slotcar dyno (rolling road) that I built.

It looks like you are getting close to solving this.

Regards,
Ken


----------



## petertha

mayhugh1 said:


> http://www.ebay.com/itm/302145096583
> I don't know what extraterrestrial technology the manufacturer of this PWM is using to be able claim 320 amps continuous operation within such a small package.


 
I'm not familiar with that ESC or surface/car variants, but would have to agree... 320 amps seems <cough> optimistic. Sold with 14 AWG wire & cheesy bullet connectors that would make great fuses no less. Beware of ebay type stuff

Some of the car stuff on HobbyKing for example is ~what I would have guessed, sub-70A. 
https://hobbyking.com/en_us/speed-controllers-esc-1/car/x-car.html

Example 160A air ESCs look something like these. Re peak, correct. Vendors don't spec it as much anymore, but it used to worded like 100A continuous, 250A burst and **burst=3 secs duration, proper cooling yada-yada. I've seen +400A pumped through older gen 120A ESC's 2-sec bursts but that's a $$ magic smoke competition.
http://www.castlecreations.com/en/fixed-wing/phoenix-edge-hv-160-esc-010-0103-00
http://www.castlecreations.com/en/phoenix-edge-lite-hv-160-esc-010-0114-00

RC ESC's are getting very sophisticated & application-specific these days & I don't want to lead you astray. Most, unless they are hard wired into toy level ready-to-go models need to be programmed. Or worded another way, you may not receive it programmed in a state you require. This isn't quite as bad as it sounds but its very brand specific. In the case of Castle for example, you buy a USB>ESC cable called a CastleLink, download their free software, it recognizes the exact ESC model# & recommends any firmware updates. Then you just toggle desired checkbox entries & click save. The minus is extra effort & cost, the plus is total control: motor specs, F/R direction, source voltage, timing, current thresholds, ramping, de-select any undesirable things like governor. 

I haven't done exactly what you are doing but I would expect this would give something like a servo tester box the best chance to be the 'rpm controller' to the motor replacing the RC transmitter throttle signal.

And while we are busy blowing the budget  many brushless motors come in compact inline planetary gear drive flavours, 4.x:1 and 6.x:1 are typical
http://neumotors.com/planetary-gearboxes/

This might be helpful. You can pick motor/ESC/battery voltage combo's & it spits out various power outputs, efficiency, overload warnings & other curves of interest. Unfortunately you would have to trick it with propeller load, but might yield some insight
http://www.castlecreations.com/flight-calcs


----------



## mayhugh1

The 320 amp ESC and servo tester arrived. Neither came with instructions, but I was able to figure out the ESC's power-up calibration procedure by reading some online manuals for other manufacturers' RC equipment. I did some initial testing with the motor outside the engine until I was reasonably sure the combination was going to behave itself. After installing the motor on the engine, I got it to spin the crank for a few seconds before it died. As foreseen by Peter, the ESC's light duty power connector burned up and had to be removed. The connectors on its motor leads soon developed similar problems also had to be replaced.

I was able to make a couple brief tests to verify the controller was indeed capable of running at duty cycles approaching 100%. This was something I'd not been able to do with the previous PWM controller. Even though it had a cooling fan, the ESC became excessively hot after less than a minute of runtime. In short order, the motor refused to crank the engine because it too had become overheated.

The motor requires a minimum duty cycle of some 75% in order to crank the engine. During each test, the time spent searching for just the right operating point was evidently subjecting the motor to a lot of abuse. With an operating point located near 80% of stall, internal dissipation became a major issue during the time spent time dallying.

After this last experience I've concluded that my original idea of manually controlling this motor in this application is impractical. Adding fixed control isn't reasonable either since the engine load and battery output can be expected to change with time.

As I've accumulated more and more cranking time on the Quarter Scale, I've gained confidence in the ability of its internals to hold up under power from the John Deere starter motor. So far, the wheel case is the only component that hasn't been an issue. Even though the oil and coolant pump loads haven't yet been added, I'm close to deciding to just use this motor along with a starting relay. Before finally deciding, though, I plan to look at one more motor: an 820 size brush motor from a DeWalt hammer drill. 

In the meantime, I'm wrapping up the remainder of the Quarter Scale's final assembly that can be done while the engine is still on its assembly stand. - Terry


----------



## petertha

Sorry to read of the setback Terry. Maybe a blessing in disguise. The other potential complication with ESC's when interpreting specs is, as a general rule, ESC's don't like running at sustained partial throttle. Worded another way, the ESC need to be sized appropriately to accommodate that. I know that's not your motor when its all sized, just thinking more this testing and R&D sizing mode. 

This issue has to do with FET switching (and that's the red line of my electrical competence ). But using a real world example, a motor drawing 50 amps on say a slightly undersized 35A continuous rated ESC might do that just fine at full throttle. But the setup trying to control partial throttle, low rpm typically goes thermal. Unfortunately, that generally means even more amp rating headroom = more $. That's kind of where I was going with the inline gear drive. The motor might be doing 30K at full throttle but say 4K at the shaft & operating in a happier band. But they are spendy.

Under a 'too much motor' potential damage scenario, I'm sure you've thought about clutch mechanisms & forgotten much more than I know. But I *just so happen* to be recently familiar with a clutch mechanism on my lathe that came into question. Its a relatively simple cup with 2 threaded holes. In each hole is a set screw + spring + bearing ball. It mates its opposing drive shaft which has a straight V groove. Progressive spring tension = higher torque. At a the point of decoupling it disengages... and makes for a heart stopping racket. Maybe something along these lines with a pre-set disengagement limit would at least protect the engine?


----------



## mayhugh1

The last bit of assembly that can be done while the engine is still on its assembly stand is the final installation of the distributors and spark plug wiring. The wires on the full-size Merlins were routed to the plugs through straight sections of metal conduit attached to either side of the engine. In addition to organizing and protecting the wires, the conduit reduced electrical interference to the aircraft's onboard radio. The plug wires also had metal braids around them that not only enhanced rf shielding but also offered some protection against chaffing.

Not being concerned with radio interference, I ran the Quarter Scale's unshielded wiring through Delrin tubes for a similar look. Rigid black Delrin tubing isn't readily available, and so I drilled out the centers of a pair of half-inch diameter rods. The rods' centers were drilled/reamed to 3/8" in order to pass the bundles of six 1/8" (20 kV) plug wires. The exit holes for the wires were drilled at a shallow angle to the long axis of the tube so the wires could be easily fed through the conduit without damage. The tubes were attached to the cylinder blocks just below the coolant manifolds with three metal brackets. The Quarter Scale's documentation doesn't address the ignition system, and so I'd been wondering for some time about the purpose of three unused screw bosses on the manifold fittings.

Before installing the distributors, I rechecked the valve lash and cam timing before adding the valve covers. A borescope was used to peer inside the cylinders through the tiny side-mounted plug holes to determine the TDC's. The previously constructed degree wheel with its weird gap was invaluable for setting and measuring the cam timing. Even though I had synchronized the cams to the crankshaft back in December while recovering from my surgery, verifying the timing was pretty scary since now would have been a bad time for a mis-machined cam to show up to the party.

After feeding the numbered plug wires through the conduit, a shop-made insertion tool was used to press them in the distributor contact block. Slotted Delrin sleeves, inserted around the insulated ends of the wires, grip and hold them securely in the block so their bird-nested ends can make consistent electrical contact to the tower electrodes. When the distributor's wire cover is installed it bears down against the tops of these sleeves for added security.

The trigger disk is driven directly from the Oldham shaft, and an end screw is used to lock its orientation with respect to its reference piston's TDC. When tightened, this screw also locks the orientation of an internal distributor gear that drives a gear on the rotor. This arrangement allows the rotor to be aligned to the reference tower electrode even with the distributor already installed on the engine.

With the crankshaft rotated so the #1 starboard cylinder is at TDC of its power stroke, the starboard distributor with its Oldham coupler was installed on the engine. The trigger disk locking screw was loosened, and the rotor manually rotated until it was directly under the #1 tower electrode. This alignment was determined using a #52 drill inserted through the index hole on the face of the rotor housing. It will pass through a similar hole in the rotor when the rotor is aligned with the #1 tower electrode. Before tightening the locking screw, the trigger disk was also rotated to set the initial spark advance. This took a few tries since it must be done by trial-and-measure. I used 10 degrees initial advance. The Hall sensor arm on either distributor can be later rotated toward the front of the engine to add up to an additional 20 degrees advance. A machined cover which protects the trigger disk and magnet is left off for now, but it will be installed later after the engine is running and the final advance determined.

The plug wires were left long so temporary connectors could be soldered on their ends for connection to a bank of test plugs. Finally, the engine was spun by its drill starter to verify the plugs in each bank were all firing in their proper order.

The same procedure was repeated for the port-side distributor. The TDC of the #1 port-side cylinder was used to set up this distributor since its rotor index hole was also set up for tower electrode #1.

The boots for the spark plugs were made up of modified 1/8" x 1/8" right angle rubber automotive vacuum fittings (VACU-TITE 47409). The electrical connection to the plug electrode was made by rolling up a 1.1" stripped length of the stranded conductor into a ball before pushing the wire into the boot. I normally use more complicated but also more positive electrical connections inside the plug boots in my engines. The tiny size of the Viper plugs fought me on everything else I tried, though. The 1/8" plug wires are snug fits inside their boots, but I added a short length of shrink tubing to help keep them in place and to improve their appearance. - Terry


----------



## sbdtasos

OOO my good
Terry can not wait hear this engine ...........
your work is excellent i can not find words..
i admire your passion
good work continue your excellent work


----------



## cfellows

Words fail me Terry.  That is among the finest pieces of model engine workmanship I have ever seen.   I honestly don't understand how you do it.

Chuck


----------



## Ken I

cfellows said:


> That is among the finest pieces of model engine workmanship I have ever seen.



Not to mention the finest documenting of such a project.

Awesome work.

Regards,
Ken


----------



## mayhugh1

Thanks, all...

The DeWalt 820 motor (396505-21), used in a number of the company's battery-powered tools, has been adopted for use in large scale hot-rodded trucks by a number of RC enthusiasts. I couldn't find any real data on it other than some hobbyists' subjective comparisons between it and their high end Traxxas 775 motors. There seemed to be enough enthusiasm surrounding it, though, that I thought it was worth a quick look before finally wrapping up the starter work.

After realizing that my cranking tests haven't yet included the oil and coolant pump loads nor the inertial load of the huge four blade prop that's yet to be installed, I began wondering whether the John Deere motor will actually be up to the task. Hopefully I'll luck out and the extra loading will just drag the cranking speed down to where I wanted it in the first place. But, if the additional loads turn out to be too great, it would be nice to have a backup.

My own cursory measurements on the DeWalt showed an unloaded 15.5 krpm at 4.4 amps compared with 2.2 amps at 22 krpm for the 775. Although the DeWalt looks heftier than the 775, it's really only a bit larger. Its case is thicker, and its bearings and brush assemblies also look beefier. Cogging is much more noticeable in the DeWalt than in any of the other motors that I've tested and probably accounts for some of its excessive unloaded current draw.

I had to fabricate a new mounting plate for attaching the DeWalt to the Quarter Scale, but I was able to re-use the wheel case adapter machined earlier for the John Deere motor. I also had to make a new socketed Oldham shaft to insert over the DeWalt's pressed-on 28P 15t pinion. The machining of the even narrower .42" long splines for this gear, with its additional three teeth, really pushed the limits of the little .060" circuit board cutters used to cut them. Before I was finished I had broken a few of them.

The measured crankshaft cranking speed using the DeWalt was 855 rpm at 75 amps. I retested the John Deere in the same setup with the same battery and identical high-current connections. The result was 660 rpm at the same 75 amps. From these tests I concluded the DeWalt was putting out about 30% more torque than the John Deere.

The DeWalt motor was designed with a ventilated case and an internal fan for extended operation. It won't overheat as quickly as the John Deere which is sealed to operate in a harsh environment. Although I designed the DeWalt's mounting plate so most of the ventilation ports face toward the rear of the engine, I machined a pair of shields to cover those that still faced forward. A bottom cover, similar to the one on the John Deere, was also made to shield the motor's open brush assembly from the engine's oily wash. I turned both covers from black Delrin and machined slots in them for the fan's air intakes and exhausts.

I made a short Youtube video showing the Quarter Scale being cranked in both its manual and electric start modes. In the video, I used the John Deere 775 motor as the electric starter and my 3 year old Ryobi One 18V drill on the manual shaft. I don't have any video editing software or I would have spliced in a third run using the DeWalt. As things turned out, the runs with the two motors were so similar that a second video wouldn't have been all that i
interesting.

[ame]https://m.youtube.com/watch?v=KfAOr2m5GGc[/ame]

I hope this wraps up the work on the starter. It turned into a bigger deal that I had anticipated, but the learning experience made it all worthwhile. My current plan is to use the John Deere motor since it seems to best meet my current needs. If I run into problems with overheating, or if its torque later becomes an issue, I'll have the DeWalt ready to go as a backup.

The next step is to come up with a running/display stand for the engine. I'll likely design it in parallel while fabricating some of the running gear needed to go around the engine to make it run. - Terry


----------



## petertha

That looks darn encouraging. And the engine is even more glorious in video. Way to go.


----------



## kvom

How many turns of the crankshaft would you expect it to take before it fires?  I assume that if it fires quickly then the load on the starter motor would be of very short duration.


----------



## mayhugh1

Kvom,
Probably (at least I hope) the longest cranking time will be the several seconds it takes to prime the carburetor. - Terry


----------



## mayhugh1

The Quarter Scale documentation recommends using a spin-on oil filter between the oil pump and the engine's pressure relief valve housing. An oil filter might be overkill, but it's worth a couple visual effects points. The smallest filters I could find in our local auto parts stores were 2.7" dia. x 2.6" tall motorcycle filters which are still large for a quarter scale engine. I eventually decided on a WIX 57712 filter only because it was painted black, and its i.d. information was printed on an easily removable label instead of being silkscreened directly on the filter itself. A mount was required so the filter can be eventually installed on the display stand right up next to the starboard side of the engine. 

Oil filter mounts are readily available, but one advantage of making my own was that I was able to locate the input and output fittings where needed for a neat placement of the oil lines. For no good reason, I had always assumed that oil flows into one of these filters through its center hole and flows out through the surrounding holes. Fortunately, I did some checking before machining my mount and discovered that I've had it wrong all these years. It turns out that it's best for oil pressure to push the filter media against the metal support screen in the center of the filter. If oil flows in the reverse direction, it can rip the media away from the screen.

The 20x1.5 mm stud for the mount was turned from O-1 drill rod and then hardened before being Loctited in the mount. Standard 3/16" compression fittings were used since they match the ones used on the pressure pump and relief valve housing.

After bead blasting the mount and installing the filter, the whole thing seemed just too big and out of place for the engine. I went looking online for something smaller and came across an obscure post from someone on social media who had just purchased an oil filter for his push lawnmower and was poking fun at it because of its tiny size. I looked up its part number from the photo he had posted (Oregon 83-030, replacement for Briggs & Stratton 795990 filter), and sure enough Amazon had both of them in stock. 

After receiving one each of them, it was obvious that their 1.9 inch diameters were much closer to what I was looking for, and so I started all over. I was hoping to at least reuse the PITA threaded stud that I had made for the first mount, but the new filter used a slightly different 3/4"x16 stud. Since I had to make a second pass through the mount design, I added some cosmetic improvements, and final result turned out to be well worth the do-over. I'm even becoming attached to filter's yellow body. - Terry


----------



## dsage

Nice looking job. Smaller is better.
 Nice finish. Is the black powder coat? 

Sage


----------



## Ken I

mayhugh1 said:


> For no good reason, I had always assumed that oil flows into one of these filters through its center hole and flows out through the surrounding holes. Fortunately, I did some checking before machining my mount and discovered that I've had it wrong all these years.



It simply will not flow the other way - the rubber seal behind the inlet holes acts as a non-return valve.
In most cases the filter is spring loaded ("oil bypass valve" in your diagram) and if it becomes clogged, this flap and filter can back up against the spring allowing unfiltered oil to flow through. The logic being dirty oil is much better than too little or no oil.

Regards,
Ken


----------



## mayhugh1

Sage,
I just painted it with some of my left-over GunKote, - Terry


----------



## mayhugh1

With some 1300 hp on tap, the Merlin's coolant system could be called upon to remove up to a megawatt in waste heat from the engine. In aero applications the engine was under the plane's cowling and didn't receive the full benefit of cooling air moving past it. Airframe manufacturers were typically required to add a hefty radiator below the engine. Low altitude strafing runs made the P-51's underside susceptible to damaging debris, and so a distributed set of radiators was eventually developed for it. Each of these radiators had a spring-loaded check valve that shut off coolant flow to it in the event of damage.

The tiny sample size (two) of actual running Quarter Scale Merlins, that I'm aware of, seems to show they are susceptible to overheating even while idling. Although a major cause for this could be limited coolant flow through the heads due to investment left behind by the casting process, I made earlier modifications to the coolant jackets in my particular engine to increase the coolant volume around its cylinders.

In addition, a belly radiator will be attached to the running stand just below the front of the engine. I considered fabricating a custom radiator from scratch but decided my time would be better spent packaging a pair of 80 mm radiators used by some of the PC gaming enthusiasts to cool their over-clocked components. I didn't include a link, but these radiators can be readily found in various sizes on Amazon or eBay by searching for 'PC Radiator.' I was dubious about their quality since they looked too good to be true at less than $10 each, and so I bought a spare that I cut open for inspection. I especially wanted to make sure there was an internal baffle separating the input and output fittings to ensure coolant would actually be forced to flow through the cooling tubes. I was impressed with their quality, and one of the 80 mm radiators would look right at home on the front of a model V8.

The combined core volume of the two radiators I used is 18 cubic inches. This is nearly equal to the Quarter Scale's displacement, but it's still half the cooling capacity I really wanted. Doubling the volume of the radiator below the engine would have spoiled the esthetics; and so to make up some of the difference, I'll likely add a coolant reservoir at the rear of the running stand. 

I machined a housing to support the two radiators side-by-side with 12V cooling fans attached directly to their rear faces. Since the packaged radiators will be set back a considerable distance from the prop without a shroud, the fans were added in hopes of improving the efficiency of the radiators. The 30 cfm low profile fans pull a lot of air through the cores even without the high pressure area that will be created later on their front faces by the prop wash. The fans are set up to pull air through the cores from front to back, and it's possible they might even allow running the engine without a prop.

I've had a 6"x8"x2" chunk of aluminum in my scrap collection for years just waiting for the right project to justify hogging out its interior. After machining the block with the exterior features of the radiator housing, I turned a three-flute hogging end mill loose on its interior. The high chip rooster tails were a lot of fun to watch since I don't typically remove such high volumes of metal in a single operation. When finished, a couple hours later, I had a rather extravagant one pound housing and eight pounds of chips. 

Since there was some excess real estate on the front of the radiator housing, I engraved the logo for North American Aviation, the manufacturer of the P-51 Mustang, across its top. This company later became part of North American Rockwell, which later became Rockwell International and is now a division of Boeing.

A pair of input hose barbs were turned from 303 stainless and mounted to the front of the housing. The housing's two inch thickness, though, became a limitation for some of the interconnecting hoses inside the housing. Although I pocketed the inside of the rear cover, there was still insufficient height to insure the two input hoses would remain kink-free. A couple of 90 degree automotive vacuum fittings seemed to solve the problem. A circular panel connector was added to bring the 12V power into the enclosure for the fans. Finally, each side of the assembly was pressure tested by plugging its output fitting and pulling a vacuum on its input fitting.

If the radiator housing looks overbuilt, it's because I plan on using it as a structural member in the running stand. The next step will be to design the stand. -Terry


----------



## Ghosty

Terry,
The 80mm radiators that you have are only a single tube, you can get the same size ones with twin and triple core. They may be more efficient than the single tube ones. The radiator setup you have done looks spectacular.

Cheers
Andrew


----------



## stragenmitsuko

Another good source for small radiators are motorcycles . 
They can be found in all kinds of sizes for little money . 
My daughter's littke 50cc bike has a radiator thats about twice the palm of my hand . 
I know , I had to weld it last year 

About the engine , I do realise it is not what it is intended to , but as  the original merlin had indeed over a 1000 Hp , what output would you expect from the 1/4 scale . If it would be simply scaled down that would still be 250 ish . 
Wich is more then most cars round here in Europe . 

Pat


----------



## Charles Lamont

stragenmitsuko said:


> About the engine , I do realise it is not what it is intended to , but as  the original merlin had indeed over a 1000 Hp , what output would you expect from the 1/4 scale . If it would be simply scaled down that would still be 250 ish .


It does not work quite like that. Remember it is scaled in *three* dimensions. For a rough idea 1000 / ( 4 x 4 x 4 ) = about 16.


----------



## gbritnell

HI Terry,
The largest rad I have, capacity wise, on all of my engines is the one on my 302 V-8. At the time I built it, late 80's, there were no forum or Internet as we know it so building miniature engines was totally an experiment. When I completed the engine I played with several designs but didn't have much luck. I ended up going to an automotive radiator shop with the finished engine and explained what I needed. At that time you could still get rad core material in different sizes. These were used for heater cores. I purchased one that fit my size requirements and made the top and bottom tanks. Jump ahead 30 years. While finalizing the build of my Flathead engine I figured I would do the same thing but the industry has changed so I ended up making my own. The biggest problem with these little engines seems not to be in the water capacity but rather trying to get enough airflow through them. On my V8 there is only noticeable air flow when revving the engine up so when it sits idling the heat starts to build up and even with the good sized core it's just a matter of maybe two or three minutes before it needs to be shut down for a cooling period. 
These little engines make a fair amount of heat, probably more than one would suspect, so trying to make 'scale' cooling systems just won't work.
I'm really looking forward to even just a couple of minutes of running of the engine. It should be glorious!
gbritnell


----------



## ICEpeter

Hello George,
Regarding your 302 V-8 radiator do you have a couple of pictures of that radiator and the dimensions / capacity of the radiator? 

Any information on the coolant flow through the radiator and its effectiveness re water temp in / water temp out / temp drop across radiator?

That information would be of great interest not only to me but I am sure to others as well, thanks.

Sorry Terry, did not want to interfere with your excellent post and description but was itching to ask George these questions.

Peter J.


----------



## mayhugh1

George,
I think you're definitely right about the major problem being airflow through the radiator. The tiny spaces through the core of a model engine radiator present a significant resistance to flow; and without a proper shroud, the air being pulled in by even a well-designed fan will just come in from around the sides of the radiator. Shrouds can be a pain to make and can detract from the engine's appearance, and so many of us leave them out. Jerry Howell, though, got it right on his V-4.

On an aero engine with a big spinning prop there will be a high pressure area built up on the front face of the radiator. This should help force some the air through the core, but how much is difficult to estimate. I suspect that the further back the radiator is placed, the less air will flow through it. Again, there's a compromise with esthetics. I added the fans on the Quarter Scale's radiators to guarantee a minimum flow, but they will be on/off switchable in case I get lucky, and the prop pushes more air through the cores than I'm expecting. - Terry


----------



## kvom

Assuming you're going to demo this and the other radials at shows, I guess that like George they won't  be run for very long at a time.  And with a big prop, it'll be outdoors.  If you were to bring it to CF or NAMES, can the engine run indoors successfully without a prop?


----------



## tornitore45

Prop or NO prop?   Is the prop providing Flywheel effect or there is enough rotational inertia inside the engine?


----------



## mayhugh1

I don't want to get ahead of myself, but the single run of the original Quarter Scale prototype memorialized on Youtube by its original designer, was made without a prop. With a cylinder firing every 60 crankshaft degrees, the inertia of the prop probably isn't as important for keeping an engine running as it would be on a one or two cylinder engine. Most of the V-4 and V8 models I've seen don't have significant inertial loads.
I don't think I'd try running one of my radials without its prop. Those engines would probably heat up pretty quickly without the prop wash to cool them. It's pretty scary standing close to either of them, but especially the 18 cylinder, while it's running. If I'm lucky enough to get the Quarter Scale running, it'll probably be even scarier. - Terry


----------



## geo

Terry
Off topic but what spark plugs did you use in your howell v twin 
Regards Geo


----------



## Ken I

FYI some of those warbird belly radiators were raised up and down via a hand crank to prevent stone damage during take off and landing.
If you came in to land with your wheels up or your radiator down you would have a red flare shot at you by the ground crew to remind you.
Followed by a chewing out by the squadron leader.

Regards
Ken


----------



## mayhugh1

geo said:


> Terry
> Off topic but what spark plugs did you use in your howell v twin
> Regards Geo



Geo,
I used the Rimfire VR2L (long reach) plugs in my V-4.
Terry


----------



## mayhugh1

Much of the progress on the running/display stand for the Quarter Scale was pretty slow and frustrating due mainly to the difficulties I had in getting started. I spent lots of hours trying to come up with something that looked good, but the functional requirements I had placed on it kept getting in my way. For example, to make storage and transport a little easier, I wanted a stand that would support the engine high enough above its base to clear a 26" prop. The resulting tall proportions, though, detracted from the engine's appearance, and a lowly coolant reservoir that's yet to be made will end up at eye level. The stability of the whole assembly, especial&#322;y while the engine is running will also have to be watched due to its high center of gravity.

I didn't want to settle for four boring legs sticking up from a baseplate, but the already completed radiator and oil filter had specific locations where they needed to be mounted. More complication came from another requirement that the stand not block access to the engine for maintenance and minor tweaks later on. This meant unfettered access to pretty much everything aft of the engine's rear motor mount. 

To gather some ideas and help me get started, I studied all the online photos I could find of statically displayed full-size Merlins. With no need for a prop or running gear, most of the stands I saw were pretty well proportioned and looked at home under their engines. Youtube examples of stands supporting full-size running engines, though, seemed give priority to function over form and lacked the novelty I was looking for. I came away with a real appreciation for why the three quarter scale Merlins for which I've seen photos were all displayed in faux aircraft mounts.

I began my design by using an Apple iPen and tablet to sketch dozens of concepts directly on photos taken of my engine sitting on its assembly stand. When I had something that I thought was worth a second look, I created a detailed model of it in a SolidWorks assembly that included a crude model of the engine. These iterations went on for more than a week until I had come full circle and was back to one of my very first sketches.

My final design consisted of four tall legs sticking up from a baseplate. I tried to make the legs look less tall and a little more interesting by fashioning each from a pair of mitered square tubes. I even added a pair of compound intersections to the front legs which I knew would complicate their construction. At this point, though, I was so impatient to start welding that I ignored the fabrication difficulties that I was building into the stand.

It's very important that the mounting pads on the top ends of the four stand supports end up in the same plane so the Quarter Scale's cast motor mounts are not stressed when the engine is bolted down to them. I've learned from working with these castings that the heat treated metal can range in consistency from gummy to brittle, and I didn't want one of the final steps in the project to end up cracking or twisting the crankcase. I was pretty sure that after all the welding on the stand was completed, the tall supports wouldn't be rigid enough to allow any residual distortion to be removed by machining. And so, the fixturing and finish welding needed to be carefully planned.

The stand was fabricated from one inch square tubing having an 1/8" wall thickness. I began by rough cutting the tube lengths for the supports on a bandsaw and then carefully milling their ends for the best possible fit-ups. The first few pieces were cut extra long since I expected a few tries would be needed to get my brain wrapped around the setups required on the mill. At the same time, I also began fabricating the fixtures to support the mitered pairs during welding. After struggling with the fixturing nightmare I had created, I went back into the design and modified it to use a common angle for all the joints including the compound ones. This also helped reduce the confusion I had been dealing with while trying to keep straight the parts for the port and starboard sides of the stand. Using a common angle required only a single simple welding fixture since the supports on either side of the stand were now identical.

After welding up the four individual leg assemblies I was able to grind their top mounting pad surfaces before finally welding them to the stand's framework. After welding the leg assemblies to the stand, I relieved the stresses with a torch while keeping the four ends with the mounting pads still clamped to their fixture plate. After the assembly had cooled, the mounting pads were coplanar within a thousandth or so which was much better than I had expected. The fixturing and welding sequences had done their jobs, but the long sides of the stand's frame ended up with a slight bow that created an annoying rock when the stand was sitting on a flat surface. There was no way to correct the frame without affecting the alignment of the mounting surfaces, and so I just welded pads on the bottom four corners of the frame to raise it slightly above the bow.

I couldn't yet plan the locations of the running gear that will eventually be added to the stand to support the running engine since none of it has yet been designed. Hopefully, inspiration for it will arrive after the engine has been sitting on the stand for a while. The various tanks, gages, and electrical hardware will be located behind the engine, and so I welded a pair of vertical brackets to the rear of the stand to support them. A vertical row of through-holes was drilled and tapped in each one so the various components can be individually added later as modular assemblies. I also welded a pair of cross supports to the floor of the stand to support a drip tray.

This completed the fabrication of the stand. After verifying it actually fit the engine, the stand was primed and painted a shade of military green. The stand was too large to fit in an oven to cure Gun Kote, and so I used (rattle can) Rustoleum which I've used for many of my projects over the years. The color I wanted wasn't available in one of their gas resistant automotive paints. Their non-automotive paints aren't promoted for their gas and oil resistance, but I've found they stand up pretty well if allowed to cure for a week or so before exposure to them. - Terry


----------



## Henry

WHAT A BEAUTY!!!! I have been following the creation of this jewel and it amazes me, thank you for sharing this process, documentation and  your great work! waiting for the sound.


----------



## Buchanan

Terry . 

That is an absolute beauty. The stand is just right as well. 

Love your radiator. 

Buchanan


----------



## gbritnell

A stand befitting a masterpiece! Not much else to say.
gbritnell


----------



## rdefrei1

That's a beauty what a marvelous art.

I would suggest making a scale P-51 Mustang Spinner shape.
If you want I could send you the drawings or the 3D file I have.

Cheers, Roger.


----------



## mayhugh1

Roger,
I'd be happy to take a look at what you have. I sent you a personal email.
Terry


----------



## AAFitArm

Looks awesome! You could always do an approximate copy of the airframe mount! It'd just have to be cantilevered out the front.


----------



## ddmckee54

So tell me Terry, when you're working on the engine do you pause periodically to pat it on the head covers and say "Let's get ready to RUMBLE"?

Just askin',
Don


----------



## kvom

I can imagine Terry sitting there thinking, "I better slow down on getting this thing finished, 'cause what the heck am I going to build next"?


----------



## wirralcnc

Sleeve valve engine ???? 

View attachment 1494360719859.jpg


----------



## bananarchy

Incredible work. I agree on the sleeve valve - the wow factor on this is hard to beat, and about the only way to go from here would be a Bristol Centaurus or a Napier Sabre.


----------



## mayhugh1

Before moving the engine from the rotisserie assembly stand to its new static display stand, I tried, while I still had easy access, to address some oil leaks that I'm already seeing. Although the leaks themselves probably won't be of interest to anyone, one of the techniques that I used to fix them may be.

My original plan to rely on the large numbers of screws holding the supercharger cover, wheel case cover, and prop drive cover halves together for metal-to-metal oil sealing turned out to be pretty naive. Oil from some of my earlier tests has been collecting on the interior floors of these sections and has been seeping through the junctions between their halves. At this point the seepages are minor and mostly just annoying, but they will likely grow worse after the engine is running and being temperature cycled. If I had it all to do over, I'd use Permatex Aircraft Sealer between the halves of all three sections and not be concerned, as I originally was, with the issues it might create for a future disassembly. As far as I'm concerned, disassembly right now isn't an option, and so I decided to try something much easier.

There is a product sold by Eastwood called Diamond Clear Coat

http://www.eastwood.com/eastwood-diamond-clear-dtm-and-painted-surfaces-aerosol.html

that's designed to clear coat bare metal. I've used it on polished aluminum and steel motorcycle parts for years, and they continue to look bright and shiny. The coating remains flexible and doesn't yellow or peel even in our hot Texas sun. One of my more demanding applications for this product has been on a piece of kinetic yard art that included a lot of polished copper. After over five years in the weather, that copper looks the same as it did the day it was coated. The satin version of this product is essentially invisible on castings.

I loosened about a dozen screws on the lower portions of each of the three seeping sections and wicked in several doses of acetone from a tiny eye dropper to remove the oil from the mating surfaces. Then, using a fine plastic pipette, I carefully directed a bit of sealer into the seam between the halves where it wicked in between the surfaces. This product has the viscosity of water and is quickly drawn into the tiniest cracks. Since I usually purchase the coating in aerosol cans, I had to collect some in a paper cup in order to apply it with a pipette. It's also available in quart cans, but with a higher viscosity. I retightened the screws while the coating was curing, and after several days there doesn't appear to be any sign of seepage. 

There was a somewhat bigger leak at the oil pump located on the bottom of the lower crankcase. This leak is the result of a marginal boss on the lower crankcase onto which the oil pump was mounted. The boss seems to have too little area and too few screws to provide a reliable metal-to-metal seal between the lower crankcase and the oil pump. It may have been designed for an earlier version of the oil pump. A gasket isn't appropriate here since the crankcase is being used as the pump cover, and the use of even a thin sealer would affect the pump's clearances. This time I didn't loosen any screws. After thoroughly cleaning out the oil, I wicked sealer in between the portion of the pump body that was overhanging the mounting boss and the crankcase surface around the perimeter of the boss. The narrow space around the boss easily retained a healthy bead of sealer while it cured. Again, this appears to have fixed the problem.

A final leak of even more significance was again underneath the engine but at the adapter for the coolant pump. The originally specified pump shaft bearing inside this adapter was an open type which allowed oil to easily pass through it and flood the area above the pump seal. I replaced the open bearing with a more difficult to find sealed equivalent. More importantly, though, I also replaced the .004" thick gasket that I had been using between the crankcase and the flange of the adapter with Hylomar sealant. 

Hylomar was also added between the rear mounting surface of the oil pump pressure regulator housing and the side of the crankcase. I had previously overlooked potential leaks here due to some unused mounting screw holes behind the regulator when it was installed a couple months ago. 

After all my efforts to get the stand's four mounting pads coplanar to machinist-level tolerances, I realized after setting the engine down on the stand that I had never actually machined the bottom surfaces of the Quarter Scale's motor mounts. What my aging mind had confused was the facing of the top surfaces of those mounts which had been necessary for the fixturing required to line bore the crankcase. The top surfaces and not the bottom surfaces were machined because the crankcase was inverted for the boring operation. To absorb the 'rough' cast bottom surfaces I inserted .030" thick pads made from automotive gasket material between the stand's mounting pads and the engine's motor mounts.

The placement and orientation of the oil filter looked reasonable in my SolidWorks model, but after bolting it onto the actual stand it was obvious that the routing of the oil lines to it was going to be awkward and their lengths excessive. I machined a black Delrin adapter to alter its orientation to improve the appearance of the routed 5/32" copper feed lines.

I plumbed as many of the interconnecting coolant lines as I could using 1/4" i.d. clear Tygon tubing. The clear tubing is only temporary so I can more easily verify coolant flow while the engine is running. It will eventually be replaced with black hose.

The next step is to fabricate and install a coolant tank on the rear of the running stand. - Terry


----------



## Blogwitch

Terry,

Showing these pictures and text proves that none of us are infallible and that you are in fact human and not a reprogrammed robot.

Beautiful work, as usual.

John


----------



## Ken I

Terry,
         I read a 1946 air minstry test report which gave the Spitfire a thrust of 2.77lbs per HP at takeoff power of 1375 HP = 3800 lbs thrust.

Some musings...

Now your motor is 1/4 scale - for each scale halving the capacity is 1/8 but the specific HP doubles so it's 1/4 - so a rough guess would put your engine at 86 HP - that's too much (200 HP per liter).

So if you were to assume a fairly sporty 100 HP per liter then your motor is going to be in the 40 HP realm and therefore capable of producing something like 110 lbs thrust.

How are you going to restrain the horses - I'd hate to see it fly away.

Just out of interest what are you expecting to get out of this engine ? (I know that's not the intent.)

I remain overawed by this project - fantastic work. More than that, thanks for the documentation effort to have all us lookenpeepers along for the ride.

Regards,
Ken


----------



## kvom

Last photo was a teaser.  We want to see the whole engine on its stand.  :thumbup:

WRT Ken's musings, the thrust will depend on the prop pitch and RPM, so takeoff power might not be what we'll see.


----------



## Lakc

Wonderful work.


----------



## Stieglitz

I'm with you ripcrow!


----------



## mayhugh1

Ken I said:


> Terry,
> I read a 1946 air minstry test report which gave the Spitfire a thrust of 2.77lbs per HP at takeoff power of 1375 HP = 3800 lbs thrust.
> 
> Some musings...
> 
> Now your motor is 1/4 scale - for each scale halving the capacity is 1/8 but the specific HP doubles so it's 1/4 - so a rough guess would put your engine at 86 HP - that's too much (200 HP per liter).
> 
> So if you were to assume a fairly sporty 100 HP per liter then your motor is going to be in the 40 HP realm and therefore capable of producing something like 110 lbs thrust.
> 
> How are you going to restrain the horses - I'd hate to see it fly away.
> 
> Just out of interest what are you expecting to get out of this engine ? (I know that's not the intent.)
> 
> I remain overawed by this project - fantastic work. More than that, thanks for the documentation effort to have all us lookenpeepers along for the ride.
> 
> Regards,
> Ken



Ken,
If you look back at the photo labled 'painting completed' on post 676, the stand is sitting on an outdoor bench where I usually run my engines. I usually clamp the big engines down to this bench when they're run. There are two feet sticking out the bottom rear of the Merlin's stand that I plan to clamp down with c-clamps to this bench. The pitch of the prop I plan to use is not very aggressive, and at a max rpm of 3600, or so, I don't expect the engine to be able to even pull its own weight and that of the stand which is currently about 50 lbs. - Terry


----------



## ddmckee54

Terry:

Slightly OT but definitely related.  Back in post #680 it was suggested that you make a scale P-51 spinner.  That got me wondering how they originally made the spinners back in the 40's.  Were they spun out of sheet as the name implies?  I doubt that they were carved out of billet, maybe welded up out of stamped sections?  Do you know, or does anybody on the forum know?  It would be very cool if a video existed showing how this was done.  I imagine you've just about worn out your screen watching the videos of both Rolls and Packard assembling the Merlins.

Don


----------



## kvom

I found this contemporary article that discusses spinner design without describing the way they were made.  However, a drawing on the second page shows that they had numerous parts.

https://www.flightglobal.com/pdfarchive/view/1940/1940 - 3291.html


----------



## MrCat63

I would suspect they were spun from aluminum and then mounts and supporting structure added.  Much the same way they are still made.  Here's a modern spinner being made.

[ame="https://www.youtube.com/watch?v=yrTDBW6q7Xg"]https://www.youtube.com/watch?v=yrTDBW6q7Xg[/ame]


----------



## gld

That was very interesting, Thanks for posting. That fellow was putting some heavy mussel into  that tool.


----------



## gunna

Always a pleasure to watch a real craftsman at work, no matter what he is producing.
Of course, that applies to Terry as well!
Ian.


----------



## mayhugh1

Because of overheating concerns with the engine, I wanted to provide it with a robust cooling system, but I didn't want a large assemblage that overshadowed the engine itself. In addition to the 18 cubic inch belly radiator, I added a reservoir to increase the volume of coolant in the system. Additional coolant can extend the running time of a model engine that's prone to overheating when heat extraction from the coolant isn't adequate.

I considered two possibilities. The first was to add a fan-cooled radiator mounted to the accessory rails at the rear of the running stand. As Ghosty pointed out earlier, there are double and triple tube radiators available that are similar to the ones used in the belly radiator. I purchased one of the triple tube models since it would have nearly doubled the amount of coolant in the system and also provided an efficient mechanism for removing heat from it. I tried to integrate the radiator into the accessory mounting scheme that I had planned for the stand; but the radiator's form factor kept getting in my way, and its input and output fittings were difficult to deal with.

In the end, I opted for a custom machined reservoir that fits in between the stand's accessory rails. I designed it around a sizable chunk of aluminum in my scrap collection that had enough volume in the right proportions to add another 45 cubic inches of coolant. I machined an array of cooling fins into its rear for a bit of heat removal, but considering typical model engine runtimes (and the fact that the fins are shielded from the prop wash) they're probably more cosmetic than functional.

Although my main objective for adding the reservoir was to increase the system's coolant capacity, its heat extraction might have been improved a bit by reducing the thickness of the fins and increasing their number. After deciding to cut the eight inch long array of 1" x 3" fins with an end mill, though, the machining time would have become an issue for anything much thinner than a couple tenths of an inch. A more efficient way to have cut them in my shop would have been to use a carbide tipped circular blade in my radial arm saw. But, my saw's rather worn table was going to require some significant refurbishing to get results I'd be happy with. This particular operation would have been an ideal candidate for the right angle milling attachment that I once considered purchasing for my Enco mill.

My Tormach with a 3x spindle speed multiplier spent nearly three hours cutting the .2" thick fins using a 3/16" cutter spinning at 13 krpm. The full-width 10% deep roughing passes in the valleys between the fins left significant chatter marks on them, and so I had to run an additional pair of time consuming finish passes on either side to clean them up.

A 1/2" 3 flute hogger was used to remove the 45 cubic inches of chips from the tank's interior. Hogging out the relatively large three inch deep cavity was a new experience for me, and it required another couple hours machining including the time needed to recover from a clogged-flute cutter. The Micro-drop coolant system that I use doesn't perform very well in such deep voluminous operations even with all its settings max'd out.

I didn't want to end up with any leaks especially since the reservoir will eventually sit directly above the engine's ignition modules. I drilled and tapped holes for some 45 2-56 screws that will be used to seal its gasket'd cover. The bottom of the tank was drilled and tapped for a 3/8" stainless steel hose fitting. A hose from this output fitting will feed the input of the coolant pump on the engine. Hoses from the belly radiator will return coolant from the engine to a pair of 1/4" hose fittings that will be machined into the top of the reservoir's cover.

The side of the reservoir was machined for a sight gage so the level of coolant in the tank can be monitored. After cutting the vertical viewing slot, a groove for an o-ring was machined around its perimeter. A trimmed glass microscope slide sits in a machined recess against the o-ring in order to seal the viewing slot. A bezel, screwed into the side of the reservoir, holds the glass window in place against the o-ring. The exterior of the tank was bead blasted and painted with matte black Gun Kote. In order to improve the visibility of the coolant level inside the dark tank after the lid is installed, a white backplate was mounted inside the tank just behind the viewing window to reflect exterior light back out through the coolant.

I designed an overly elaborate cover for the reservoir with the fittings for the return hoses integrated into its top along with a 3/4" threaded o-ring'd port for a filler cap. This cover became my part from hell after two workpieces with a total of nearly ten hours of machining time in them wound up on the scrap pile. The first was the result of a storm related power glitch during machining, but I have to take full credit for the second one.

To wrap up the cooling system I still need a filler cap and a means for draining coolant from the lowest point in the system which is where the two return hoses will exit the radiator. I was hoping to complete both of these before my hip replacement surgery which is scheduled at the end of the week. I spent much more time than expected on the lid, and so they'll have to be done later. It's been pretty painful for me to walk or even stand during the past several months, since a slight defect in my right hip has, over time, caused it to wear out prematurely. I'm not sure what my recovery is going to look like, but it will likely keep me out of my shop with all its tripping hazards for a few weeks. - Terry


----------



## stragenmitsuko

mayhugh1 said:


> I designed it around a sizable chunk of aluminum in my scrap collection . - Terry



Quite a piece of scrap that is


----------



## brendanf

Terry,

I wish you well on your recovery, I know myself and a few more will be going through with drawl as we anxiously wait for your next update..


----------



## grapegro

Hello Terry, I hope your recovery is as good as your achievement in engineering. King regards, Norm


----------



## rdefrei1

Terry, have a good recovery....


----------



## ShopShoe

I wish you the best and a good recovery. Do what they tell you and you'll do well.

--ShopShoe


----------



## Ghosty

Terry,
I wish you well on your recovery, you will be up dancing again in no time.

Cheers
Andrew


----------



## napoleonb

I wish you a speedy and full recovery! And as always I'm loving your updates.


----------



## neubert1975

Good recovery 
i am sure you will come through it just fine :thumbup:

A what a beauty your engine is, nice work


----------



## Ken I

I just love your eye for and determination to get the aesthetics right - the results are simply gorgeous.

Get well soon.


Regards,
Ken


----------



## nel2lar

Terry
I must have missed something. What is going on with all this recovery time?
Praying for the best outcome.
Nelson


----------



## tornitore45

Same here, I can't find any post indicating a cause for recovery.  Whatever is the problem wish you feeling well soon. Miss you at the last BBQ.  We pulled the trailer to Buffalo, there is a model engine show in Sept and I show off my stuff will be back early Oct.


----------



## Cogsy

Terry is off having hip replacement surgery from memory. Like everyone else, hoping you have a quick and easy recovery. I must say I'm in no hurry for this build to be over though - I really enjoy the frequent updates which will soon cease once the build is complete.


----------



## neubert1975

nel2lar said:


> Terry
> I must have missed something. What is going on with all this recovery time?
> Praying for the best outcome.
> Nelson



post #699


----------



## nel2lar

Cogsy said:


> Terry is off having hip replacement surgery from memory. Like everyone else, hoping you have a quick and easy recovery. I must say I'm in no hurry for this build to be over though - I really enjoy the frequent updates which will soon cease once the build is complete.



Thank you Al, that is something we in this country go through a lot. I wonder if it has something to do with how hard we work? Terry speedy recovery.
Nelson


----------



## mayhugh1

My hip surgery went pretty much as the doctors expected. A physical therapist had me up and walking only four hours after the operation, and I was home from the hospital the following day. The surgeon used a relatively new 'superpath' procedure that minimizes the need to cut tendons or muscle tissue around the joint. For anyone interested, a step-by-step (and blood-free) animation is available online that shows all the cool specialty tools that were used:
[ame]https://m.youtube.com/watch?v=qIjiqI9D5cA[/ame]

Post-op pain was a big issue for me though. Two of the three pain meds sent home with me controlled it, but they kept me constipated, nauseous, and continually loopy. I was so miserable that I decided I'd rather deal with the pain. I switched over to the third med that did little for the pain but did reduce the loopiness.

I tried to get back into my shop about a week after the surgery, but I had a lot of trouble concentrating, so I took another week off. I restarted the build another week later with a pair of trivial carrying handles for the running stand. I finished them, but with great difficulty, and so I decided it would be best to wait another week before attempting anything more substantial. I'm including photos of the tiny bit of progress I did make even though it's hardly worth mentioning.

The project's weight has been slowly growing, and the total including the engine and running stand is now at 53 pounds. I knew the whole assembly would wind up heavy and awkward to move around, and so I planned a pair of carrying handles for the front and rear ends of the stand. Since they shouldn't have been at all difficult to make, I used them as a warm-up to get back into the project. I machined them from a couple pieces of 7075 bar stock which is an alloy that I much prefer working with compared to 6061. Its extra hardness leaves a beautiful surface finish right off the mill, and the chips don't tend to stick to the cutters in deep milled cavities like they do in the more gummy aluminum alloys. I carefully planned the cutting and filleting paths so the parts wouldn't require any secondary work before being painted and installed.

I machined the topside of the first workpiece and then flipped it over in order to machine its bottom. I guess my mental state still wasn't at 100% because when I flipped the part over I mis-referenced the workpiece by exactly .125" along the mill's positive x-axis. I didn't realize I had a problem until after the part was completely machined nor did I understand how I had gotten it wrong. When I machined the second part, I managed to make the same mistake but this time in the negative x-axis direction. At this point I decided I'd take some more time off before doing any more machining. Over the next few days I was able to recover the two mis-machined parts with a lot of filing. 

I find that when I work on one of these long term projects, certain parts can become forever associated with the cards being dealt out by life at the time. I'll likely never have any fondness for those two black handles. - Terry


----------



## Ghosty

Terry,
It's good to hear that you are getting over the op. You will be back to your old self in no time. The carry handles look great.

Cheers
Andrew


----------



## dsage

Hi Terry:

The handles look good.
Is there a reason you use the sticks and glue rather than tabs in your Gcode. I'm always looking for new techniques and the sticks look quick and easy.
Thanks

Dave


----------



## tornitore45

Glad to see you are back.  Take it easy on the shop, mis-machining a part is annoying but machining a finger is worst.


----------



## Buchanan

Terry, I have been thinking about you a lot the last while, Very pleased you are well and on the mend. 
Regards 
Deryck.


----------



## RonC9876

Terry: I know what you mean about trying to concentrate through pain. I will not take anything stronger than Tylenol for the nerve pain in my legs and back. It doesn't help much but I can't stand the feeling of being doped up on narcotics, not to mention the other nasty side effects. Anymore, I barely am able to get in any shop time. Pain will ruin the enthusiasm needed to press on with even the simple tasks. At least you are in recovery. I have no hope of that. Take care and take your time getting back. I have nothing to say about your project. It deserves more than words to describe it. Ron


----------



## nel2lar

Terry
So glad everything went well, even the loopy. The anesthesia is the worst part of surgery. May you be back to a good norm as soon as possible. Now you can look forward to live with a little less pain. 
Be well my friend
Nelson


----------



## petertha

Terry, your perseverance through this immaculate engine project & your recent physical hurdles is truly inspirational to me.


----------



## Cogsy

Glad to have you back Terry. No need to rush back into the shop. As I said before, I don't want the build to end too soon as I thoroughly enjoy reading the updates which will obviously stop on completion...


----------



## mayhugh1

Thanks again, all, for your comments. i feel like I'll be back to normal in a few more days. 
Dave, I've not yet never tried using tabs on a workpiece. This stick and glue thing just seems easier although it is expensive for multiple parts. I heated the parts in a oven at 190F and while wearing gloves I literally pushed the parts free of the workpiece and rubbed any remaining epoxy off with a popcicle stick. - Terry


----------



## mayhugh1

A panel used to mount the two enclosed ignition modules that were constructed nearly a year ago was machined next. This panel was designed to be bolted to the accessory rails at the rear of the stand immediately below the coolant reservoir. This arrangement protects the susceptible electronics from any potentially oily prop wash, and it allows relatively short and direct connections to the engine. The CDI modules inside the enclosures require 6 volts for operation. Since the current plan is to use a single 12 battery to start and run the engine, a 12V/6V converter will be located elsewhere to provide the required voltage. A copper braid connects the ground planes of the ignition modules to a common point on the rear of the engine. This braid provides the high voltage returns for the spark plugs.

The only machining required on the plate were the cutouts for the Hall sensor connectors and the high voltage and ground wires that run between the ignition modules and the engine. What turned out to be a bit of a hassle, though, was replacing the booted connections on the ends of the high voltage coil wires from the modules. The straight boots I previously made up didn't look quite right in the final assembly, and so I decided to change them to right angle types. I can usually find suitable vacuum fittings in the local auto parts stores to make up just about any ignition or plug boot that I need, but the commonly stocked fittings wouldn't stretch over the large diameter towers that I had machined on the distributor covers. After a couple days of searching, I located some fittings intended for 'ancient' automatic transmission vacuum modulator valves. I was able to cut them down to make a pair of right angle boots that could be reliably and repeatedly installed/uninstalled without coming apart. I've included a couple self-explanatory photos of the boots' construction.

It occurred to me that the Tygon tubing I was using in the coolant loops had a temperature rating of only 145F which was much too low - especially for the runs exiting the heads at the front of the engine. I found other transparent and translucent hoses available with higher temperature ratings, but they were typically sold only in large and expensive rolls. I eventually found some short (12") lengths of reinforced translucent silicone tubing on Amazon, of all places. This tubing has a maximum service temperature rating of 400F and, from a distance, looks a bit like braided metal hose. 

I also machined the cap for the coolant reservoir. I drilled a small vent hole in its center which I'll most likely plug later. I haven't yet decided whether I'll allow pressure to build-up in the coolant system since I'm a little concerned about all those o-ring seals between the cylinder blocks and heads holding pressure. I still need to come up with a drain for the coolant system, though, before declaring it finished.

Slowly, but surely, progress is returning. - Terry


----------



## nel2lar

Terry
Very nice and looks like completion is in sight. You have done an amazing job and you documentation is super. I enjoy seeing the different ways you use to complete a part, never thought about epoxy. It is always nice to have the tool in your box for the job at hand. 
Thank you and much comfort in your healing.
Nelson


----------



## editor123

Just a word of caution about using dual ignition systems. We tried it on one of the supercharged V-8s and found that electrical crosstalk fired both systems at random times, even using dual distributors.
The other problem we found was that the CDI systems had a built-in timing advance but it was set up for a 2-cylinder engine. With all the pulses coming in for a V-8, full advance was reached before the engine got started. This, of course, created a 'small' problem.


----------



## Buchanan

Terry. That is looking wonderful. I also really like your choice of colors.

It makes it so much more like a full size. The casting look that you have on your machined components like the top of the tank is awesome.  I have a daily check  to see if there is any more progress. Lovely. 

Buchanan


----------



## mayhugh1

The coolant reservoir was mounted at the top of the accessory rails so its coolant level could be set slightly higher than the coolant level in the heads. This will allow the engine to be filled from the reservoir, although any air trapped at the tops of the heads may require some time to work its way out. The coolant pump at the bottom of the engine will take in coolant from the bottom of the reservoir and pump it up into the heads. With reservoir level at the top of the engine, the pump will see approximately the same head pressure at both its input and output ports. With minimum pressure across the pump there will hopefully be a healthy coolant flow through the engine. The return hoses from the radiator will return coolant to the reservoir through fittings located just above the reservoir's coolant level.

The oil tank will be mounted on the front of the oil panel just below the ignition panel. This location will place the pressure pump's input below most of the oil column inside the tank which will aid oil flow (not really necessary) and help prime the pump. A shut-off valve will be added to prevent the tank from draining its contents into the engine during storage. I've learned from my radial builds that this can happen if there is even the slightest leak through the pump. The output from the scavenger pump, on the other hand, will return oil to the tank through a fitting located above the tank's oil level making drain-back through it a non-issue. The return-to-tank line from the low pressure regulator will return excess oil to the tank through a similarly elevated fitting. The bottom of the tank will also have a magnetic drain plug.

The panel to which the oil tank will be mounted contains two oil pressure gages. The high pressure gage will be connected to the pressure pump whose output has been tentatively limited to 15 psi by an adjustment on the high pressure regulator. The low pressure gage will be attached to the low pressure regulator whose output has been tentatively limited to 6 psi.

The space available on the oil panel directly behind the oil tank was used to mount a pair of 12V/6V converters to generate the required voltages for the ignition modules. These took the form of very inexpensive buck converters available in six packs from Amazon: 
https://www.amazon.com/gp/product/B01GJ0SC2C/?tag=skimlinks_replacement-20

I chose to power each CDI from its own converter even though the output of a single converter could have supplied more than enough current for both CDIs. A cavity was milled into the panel to completely enclose the converters. It was probably over-kill, but they operate at 400 KHz, and so the shielding provided by the enclosure should improve the electrical system's noise immunity. The enclosure will also protect the electronics from engine soot and oil. After installation, the converters were tested by running them with 7W loads for several hours. There was nothing special about the size of the load - I just happened to have some five ohm power resistors handy.

The eBay oil pressure gages I used were something of a hassle to mount because they weren't designed for the typical U-brackets used on most other panel gages. I bored close-fitting openings through the one inch thick panel and, after testing the gages, I secured them in the openings with a bit of silicone. While I was at it, I also machined a decorative bezel on the panel around each face.

The 'generator' cover for the 12V/6V converters includes a pair of pressed-in light pipes so the blue indicator leds on their circuit boards could be made visible through the cover. The light pipes were turned from clear acrylic rod and polished with automotive paint buffing compound. An extra-fine oil-based Posca paint pen was used to fill in the machined engravings on the finally painted panel and generator cover. Blade terminals were JB Welded into the top and bottom sides of the panel in order to provide tidy electrical connections to the converters later.

The next step is to machine and install the oil tank. Since it appears that it will be competing with the throttle for space, I'll first need to work out the details of the throttle linkage and control. - Terry


----------



## Ghosty

Terry, more great work, a thing with the power supplies, I would fit them with some heat sinks, I use the same voltage regulators and the IC can get very hot. I use little 10x10mm heat sinks and 3M double sided heat sink tape.

Cheers
Andrew


----------



## mayhugh1

Ghosty,
Thanks for the warning. When I ran my four hour 7 watt output test (12V in, 6V out) I checked all three semiconductors and none were more than barely warm to the touch. I'll likely use a third one for the fuel pump which I may not be able to run as conservatively, and so I may need a heat sink for it. - Terry


----------



## mayhugh1

The oil tank was machined separately from the oil panel and bolted to its front. I limited its volume to something under a third of a quart to avoid overfilling the crankcase with oil should the scavenger pump fail to keep pace with the pressure pump. This is a well known issue with the Hodgson radials which also are dry sump engines. A common workaround for those has been to carefully regulate the oil flow into the pressure pump with a custom drip feeder similar to the ones found on medical iv bags.

The tank's form factor had to be massaged in order to avoid infringing upon the area required by the throttle linkage which happens to want to occupy the same space. I haven't yet decided whether I'll machine a quadrant lever or just make a simple push/pull control for the throttle. I cobbled up a test linkage, though, to make sure that I left room for either. The tank's final dimensions worked out to require a four inch deep cavity if machined from a single workpiece. Since this would have required an extra long end mill that I didn't have, I fabricated the tank from two chunks of aluminum to end up with a three inch deep body and a 1-3/8" high cover. The two pieces were joined together with a gasket and a handful of screws.

A sight gage and a provision for a screw-on filler cap were machined into the body and cover, respectively. The sight gage is identical to the one fabricated for the coolant tank and was added to the starboard side of the oil tank which makes it rather difficult to see. This was done so I could access all the controls and gages while standing to the rear starboard side of the engine. I'll likely run the engine while it's secured to a long metal workbench that's in my backyard, and I didn't want to create an unnecessary need to cross over the plane of the engine's spinning prop.

The two previously installed oil panel gages were plumbed to their pressure sources using 1/8" copper tubing. The lines between the oil tank and the two oil pumps in the lower crankcase will be later run using 5/32" copper tubing. The compression fitting for the pressure pump line was drilled/tapped into the lower front side of the tank, and a similar fitting for the output of the scavenger pump was machined into the top cover. The return-to-tank hose from the low pressure regulator will also be plumbed into the top cover through a hose barb. A ball valve was inserted in the line between the tank and the pressure pump. Its main purpose is to shut off the oil supply during storage, but it could also provide some crude flow control if needed. The oil filler cap will be vented so that pressure build-up in the tank created by crankcase gasses being pumped into it by the scavenger pump are relieved. I also added a drain plug at the bottom of the tank.

I'm a little embarrassed to admit that I went so overboard with the design of the tank's cover. In the end, a simple block top would probably have looked better than the over-cooked piece that I came up with. It got away from me and became one of those parts that I made like I did just because I could and eventually soaked up so much time and effort that I just couldn't scrap it. 

I'll likely work on the throttle linkage next before finally installing the oil tank. The throttle will be much easier to deal with before installing the oil tank lines. - Terry


----------



## SilverSanJuan

Absolutely stunning workmanship!  :thumbup:


----------



## Ghosty

Terry, Looking at your last photo in post #731, you need some covering to cover the pickup wiring, it just looks out of place. I use this https://hobbyking.com/en_us/wire-mesh-guard-black-6mm-5m.html on my electric stuff.
I listed the black, I used the red in my boat as all the drive and engine are red.
The engine and acc look great, can't wait to see it finished. 
Hope this helps.

Cheers
Andrew


----------



## mayhugh1

Thanks, Andrew, that's a goid idea. I just ordered some.
Terry


----------



## mayhugh1

Both the Spitfire and the P-51 Mustang used a quadrant throttle located on the wall of the cockpit within easy reach of the pilot's left hand. Although a simple push control would probably be more practical on the rear panel of the Quarter Scale's running stand, I decided to try to use a quadrant control there also. Since I'd already designed one that's been working well on my two radials, I made a third for the Merlin. 

The quadrant's base was machined from black Delrin, and the lever was cut from 3/16" aluminum plate. Delrin provides a slick bearing surface for the lever, and so the base was designed so its walls can pinch the flat sides of the lever to provide some rotational friction. A locking nut, embedded in one end of the base into which a SHCS used as the throttle shaft is threaded, allows the amount of friction to be adjusted.

For no apparent reason, when I built them, I set up the throttles on both of my radials to increase the engines' rpm when the levers were pulled back. However, I recently discovered from online photos of both the Spitfire and Mustang cockpits that convention seems to be to decrease the engines' rpm when the throttles are pulled back. I opted to not correct my error at this point, though, so that all my engines will operate identically even if non-conventionally.

After playing around with a suitable mounting location for the throttle, I realized that the best place for the engine's tachometer would be on the control panel just above the throttle. Even though I had a really frustrating experience with the eBay aircraft tach that I purchased during my 18 cylinder radial build, I ordered yet another one for this engine. It's a totally different model, supposedly working, and again it comes from an overseas salvager. Unfortunately, the area on the running stand immediately behind the tach is where I'm planning to mount the fuel tank, and so I need to know the depth required behind the panel for the tach. Some aircraft panel gages can be surprisingly deep, and the seller with whom I'm dealing doesn't seem to waste time answering emails after receiving his payment. So, I decided to wait until I have the tach in my hands before doing any more work on the throttle.

In order to continue making progress, I switched over to working on the fuel pump that will be used to drive a recirculating fuel loop between the fuel tank and the carburetor bowl. Basically, I just repackaged the main components of an RC filler pump that I purchased from a local hobby shop. Inside the unit I used, a composite pump is driven by a 6V-12V electric motor through an Oldham-style coupler. So, I just transferred the motor and pump into my own custom machined aluminum housing. The manufacturer recommends using only alcohol-based fuels with their stock unit, but I've been using their pumps on my gas powered model engines for several years now with no issues.

I also cleaned up a few loose ends that had accumulated during the past few weeks. Since the oil panel was now complete and finally installed, I was able to wire the ignition modules to the 6V generators and plumb the copper lines between oil tank and the oil pumps. I also machined the oil tank's filler cap which I made identical to the one on the coolant tank. I'm still procrastinating, though, over the drain valve that's still needed at the bottom of the coolant system. 

The tracking info for the tach shows that it should be delivered in two days, and so my next step will likely be to resume work on the throttle. - Terry


----------



## Ken I

mayhugh1 said:


> The coolant reservoir was mounted at the top of the accessory rails so its coolant level could be set slightly higher than the coolant level in the heads. This will allow the engine to be filled from the reservoir, although any air trapped at the tops of the heads may require some time to work its way out.



Terry - you might like to try this automotive trick - vacuum the coolant system from anywhere (typically the filler cap) - once it has fully pulled down a vacuum (also proving there are no leaks) you fill via the drain valve (or anywhere else you might prefer) - the vacuum "sucks" all the coolant into all the voids regardless of location and complexity.

This is often how automotive assembly plants fill brake systems and coolant systems without having to bleed them.

You might also need to degas your coolant before "sucking" it in - just to eliminate any dissolved gasses that might froth up.

I know a couple of engines that can be damaged if these "voids" are not bled before use - normally such engines have a bleed valve at the highest point - ignore it at your peril when refilling the engine.

FYI

Regards - Ken


----------



## mayhugh1

Ken,
Good tip... thanks.
Terry


----------



## IceFyre13th

Just outside on a break from work......our place is next to an airport full of older aircraft.

As I am sitting there a MkVIIII Spitfire takes off, I have seen plenty sitting static at museums and such, but never before heard one flying........oh my god, I want that engine in my car......its sounds beautiful!!!!!!


----------



## ddmckee54

Used to be that hearing the sound of these engines was if not commonplace, at least it wasn't a rarity.  Now days most of us have to pay for the pleasure of hearing a Merlin, an Allison, or even a P&W radial.  IceFyre you are one lucky SOB.

Don


----------



## mayhugh1

I received the tachometer along with a hand-written sketch from its eBay seller describing how it had previously been hooked up. I watched eBay for months waiting for a tach to become available with specs similar to this one. Its description said that it had come off a 6 cylinder aircraft and used a wire-wrap type impulse trigger generated from the coil wire on the engine's magneto. Aircraft tachs come in a wide variety of types, both electrical and mechanical, and the jargon associated with them can make your face hurt. As described, the tach I purchased would have easily dropped into the Merlin with its dual magnetos and twelve cylinders. Generating a trigger by wrapping a few turns of insulated wire around the unshielded coil wire of one of its magnetos would have been trivial. And, it would have provided the same input needed to display the Merlin's crankshaft rpm as it did in the original 6 cylinder single-magneto application.

The first thing I did was to apply 12V to the tach's power pins. This caused the needle to immediately move to zero - a very good sign. The issue that I ran into, though, was that the note now described its input as having come from a cabled magnetic sensor (not included) that had been screwed into the vent port of a Bendix magneto. I suspected the sensor was probably just a Hall device, though, since the sketch showed its cable had three wires: +V, Gnd, and Signal. Fortunately, the tach outputs that I had brought outside my ignition modules were Hall sensor outputs although I had been looking forward to using a much simpler wire-wrap trigger.

I made up a six magnet trigger disk and inserted it into a drill chuck in the spindle of my Tormach. I also breadboarded some test circuitry that duplicated the front-end electronics of one of my ignition modules including its Hall sensor which I connected to the sensor input terminals on the tach. With the disk spinning at 400 rpm, though, the tach read an unexpected 1600 rpm instead of 800 rpm.

I opened up the tach's housing and discovered it contained the CS8190 air core coil driver IC that I had used to make the tach driver for my 18 cylinder radial. 

http://www.homemodelenginemachinist.com/showthread.php?t=21601&page=31

Since I was pretty familiar with the circuitry associated with that particular IC, I was comfortable with adjusting the calibration pot to change the output reading. After turning it all the way down to zero, though, the tach still read some 1200 rpm. There was a fixed resistor in series with the pot, and so I soldered a second one across it in order to reduce its net value to something less than half. This modification then allowed me to dial the reading to exactly 800 rpm.

I traced out the trivial signal conditioning circuitry connected to the chip's input pin and concluded it would not likely have handled the ac waveform from a wire-wrapped trigger pulse. Unless my thinking is screwed up, it's hard to see how this tach actual&#322;y came from a 6 cylinder engine unless it was a two stroke. There's a lot of additional functionality on the tach's circuit board including a second calibration pot, but I didn't bother trying to figure out what it might be. Curiously, the front of the tach face contains 'Made in USA,' but there's no other markings anywhere on it to identify the manufacturer.

The rear of the tach will ultimately end up in a rather nasty area on the running stand just below the oil tank drain plug and probably near the filler for the fuel tank. Its housing isn't all that well sealed, and so a protective cover for its rear will need to be fabricated. All its electrical connections are made through a DB-9 connector on the rear of its housing, and so I made up a potted assembly covering the wire connections on its mating cable connector. - Terry


----------



## Ken I

6 x 400 rpm = 2400ppm = 4800rpm for a single cylinder (one pulse per two revs).

To get 1600rpm it had to be a three cylinder. Or a 1 1/2 cylinder  two stroke or redundant spark. 

Puzzling.

Ken


----------



## mayhugh1

The electrical panel will be the bottom-most panel to be installed at the rear of the running stand. It will support the throttle and tachometer as well as a panel voltmeter plus three or four toggle switches that will be used to control the engine's electrical functions. The fuel pump will be mounted to the front of the electrical panel, and so it will also contain a voltage controller for the pump motor. Due to their large physical size, the high current (80 amp) starter components will be mounted on a separate panel that will be bolted the starboard side of the stand near the starter motor.

The panel, itself, is made up of three parts: a front plate, a rear plate, and a mounting block for the tach. The front plate and meter mounting block were rough machined separately before being permanently joined together with Loctite'd screws. After joining, the pair was finish machined. The throttle and tach will be mounted to the front plate which is also pocketed to provide clearances for the voltmeter and panel switches that will be mounted to the rear plate. After assembly, these two plates will form a protective enclosure around the meter, the switches, and their wiring.

The tachometer will be shoehorned into the space above the throttle. The throttle control rod, which would have been difficult to relocate, barely clears the side of the tach. The narrow slot in the front plate through which the rod passes was just one of the reasons why the tach mounting block was machined separately from the front plate. The extremely long 1/8" end mill that would have been used to machine the slot in the thick front plate while clearing the meter block would have chattered badly while literally chewing through the slot. The other reason, though, was that I didn't have a suitable block of aluminum to create them as a single part.

Before machining the rear plate, I performed a trial assembly of the front plate, tach, and the throttle. This was probably just one of several trial fits to come. The entire panel assembly would have been a good candidate for modeling before doing any machining. But, since a lot models would have had to be created for the non-machined parts, I decided to just fit things as I go. I don't normally like working this way, but my process standards seem to be yet another thing that's shriveling with old age. 

Two of our grandkids are coming for a week long visit, and I don't plan to do much more on the build while they're here unless it's to sneak in a few late-night-can't-sleep hours. Anyway, it's probably a good time, while there's still a lot of space left, to step back and make sure that something important isn't being left out. - Terry


----------



## kvom

I notice you use rougher endmill for aluminum.  Any advantages there?  I've only used them on steel.


----------



## mayhugh1

Kvom,
I've been experimenting with the three flute roughers in aluminum for a while now. They seem to be quieter for the same metal removal rate compared with a two flute cylindrical cutter, but I haven't made my mind up about them yet. They're trickier to use without flood cooling since the flutes tend to load up in aluminum, but I can still get maybe 50% greater removal rate with them. - Terry


----------



## mayhugh1

Before doing much more that might complicate its installation, I added the drip pan original&#322;y planned for the stand underneath the engine. A box brake was used to form a shallow five-sided tray from 16 gauge steel, and its corners were tig-welded closed. After painting the tray with Rustoleum texture paint, it was attached to the cross supports on the floor of the stand. I've used this particular paint in model engine builds before (most recently, the Merlin's rotisserie assembly stand) because it's inexpensive and resistant to most engine fluids after being allowed to air dry for three or four days. The 'multicolor' version easily covers up significant surface defects (ugly welds, deep scratches, panel beating marks, etc.) with a thick, durable, and remarkably uniform looking finish.

I also finally completed the coolant loop between the radiator and the return inlets on the coolant reservoir. Even after a lot of thought, I wasn't able to come up with a drain cock that looked at home under the engine, and so I scrapped the idea completely. Instead, I'll just disconnect the return hoses from the coolant reservoir when the system needs to be drained. I machined three sets of spreader bars for the hoses, though, in order to tidy up their routing.

For completeness, I finished up the wiring for the electric starter even though all the work that I've put into the engine's starting system may have been for naught. John Ramm (the only builder I'm aware of to get a running engine completed from these castings) recently informed me that the steel bevel gears in his Merlin's starting system had a very short life that seemed to come to an abrupt end just after his engine's rings seated and cylinder pressures rose. This is why you'll see him slap-starting the prop in his Youtube video. I've had major misgivings about the robustness of the starting system design ever since coming to grips with the incredible complexity inside the wheel case. I took great pains in setting up the starter gears during the wheel case construction, and my modifications to the geometry of the cylinders effectively lowered the static compression ratio about a point and a half. I guess my starter's durability remains to be seen.

I mounted the starter components on a hand-formed sheet metal panel mounted to the starboard side of the engine just below the starter motor. Ten gage 'noodle' wire was used for the high current wiring. 'Noodle' wire is something I recently discovered in a local hobby store. It's an ultra-flexible silicone insulated wire, and in this particular gage it has an impressive 1050 strand count. For the starter solenoid I used a 120 amp SPST automotive accessory relay that I found in a local auto supply store. The starter switch is a red-cover momentary toggle reminiscent of the P-51's original starter switch.

A pair of 6 mm hex binding posts for the 12 volt battery input were mounted in a terminal block machined from black Delrin. Both the starter motor and the rear electrical panel will receive their power from these posts. Hopefully, the short term current carrying capability of these posts and their associated wiring will be adequate to handle the engine's 80 amp starting current requirement. Troughs were milled into rear of the block to accommodate the huge wire. Metal inserts were pressed into the block's machined barrier terminals to handle the connections running off the starter panel.

The starter panel was designed to be a standalone sub-assembly. The 12 volt power cable from the radiator fans was terminated on the starter panel but will be continued to a control switch that will be mounted on the electrical panel at the rear of the stand. The fan cable as well as the 12 volt power feed for the electrical panel will continue from the terminal block to the electrical panel through quick connect blade terminals on its rear side. 

The remainder of the noodle wire was used to make up a pair of battery cables. Since I had taken liberties with the current carrying capabilities of several of the starter components, I energized the starter motor several times while checking the various connections for excessive temperature rises. 

The next step will be to finish up the rear electrical panel. - Terry


----------



## Ghosty

Terry,
For the coolant, have you looked at the Evens Waterless Coolant (https://www.evanscoolant.com/products/high-performance-coolant/)
May be worth a look as it would not have to be drained, as normal coolant or water would.

Cheers
Andrew


----------



## mayhugh1

Ghosty,
Thanks for the tip. I've not seen this before and will look into it.
Terry


----------



## Cogsy

That coolant looked interesting so I had a brief look at the specs which were a little surprising. The manufacturer gives the specific heat capacity figures at 90 C (and I think it's safe to assume they chose this temp because that's where they get the the highest figure) of only 2.633 J/g.K. This is a far cry from the SHC of water at 4.186 J/g.K. For that don't know, specific heat capacity is the amount of energy (heat) that one gram of water absorbs to increase in temp by one degree (celsius or Kelvin). So this 'coolant' will only absorb 2.633/4.186 * 100 = 62.9% of the amount of heat as the same amount of water, for the same increase in temperature. Also very interestingly, the coolant has a flash point of a mere 120 C (the point at which it gives off enough vapour to ignite in air) which is far less than it's boiling point of 191 C. To top it off, despite being marketed due to it's waterless qualities, it is hygroscopic and will absorb water if exposed to the atmosphere (like in a coolant header tank).

So to summarise, it may catch fire if the cooling system overpressurises, the cooling system is likely to overpressurise as its efficiency is only around 63% that at which is was designed to be when operated with water as coolant, and it's likely to contain water soon after you install it. Personally, there's no way I would be running this stuff in any vehicle(or model) of mine.


----------



## kvom

I doubt the flash point issue is a concern is reality since there shouldn't be any air other than at the top of the radiator, and no spark there to ignite it.  The peak operating temperature of the engine  would determine if there is any concern.  The obvious advantage is not needing to drain the system to prevent corrosion.  The specific heat capacity is lower but since it boils at a much higher temp than water the total cooling capacity may be greater or equal assuming that the engine can withstand coolant that much hotter. No boiling means no pressure rise or boilovers.

An interesting option.  I may be interested in using this in my offroad Jeep, which has an issue with overheating on hot days.  It actually has two smallish radiators and a 6.0 V8.  I have to remember to turn on the rear fan manually when the temp gauge goes too high.  $45/gallon isn't cheap, but if it never boils over or leaks it should last a long time.


----------



## Cogsy

I'd have to disagree on a couple of points. With the liquid experiencing a larger change in temperature (with the higher boiling point to account for the SHC change) there is more thermal expansion and that extra volume has to go somewhere - ie into a header tank, or vented to atmosphere, neither of which are sealed and therefore exposed vapour occurs. Of course it is susceptible to water absorbtion at this point in the header tank also. The bigger deal with running with a higher coolant temperature is the higher temp of the components the coolant is supposed to keep cool. With the engine running over design temp I'd imagine all sorts of problems to arise with things like fuel vapourisation within lines and stability of some materials like plastics, hoses, manifold fittings and even bearings (for example, most general rolling bearings have an upper temperature limit of less than 150 C,maybe less, above which they will permanently deform and will not return to correct shape upon cooling). So I don't believe the increased boiling point is much/any benefit and I suspect your Jeep will have worse overheating problems. Of course I could be wrong and I'd be interested in seeing the results of a trial if anyone does try it out.


----------



## kvom

The literature states that the hottest area of an engine is right around the cylinders (makes sense).  And there the temperatures can cause water to flash to steam.  Steam has no capacity to absorb more heat, plus can cause pitting over time.  If that does in fact happen then the specific heat capacity would be reduced over the theoretical value.

I'm going to ask some mechanics I trust about it.  A vehicle might need a higher reading temp gauge and some changes in the computer to avoid going into limp mode.


----------



## kvom

Just had another thought and checked the specific heat capacity of antifreeze solutions.  50% ethylene glycol lowers it into the mid 3s.  Of course the Merlin probably doesn't need antifreeze.


----------



## stragenmitsuko

That is exactly the reason why a coolant system is pressurised nowadays . 
To raise the boiling temp and thus avoid the flash steam problem . 

I just did an engine rebuild , and long story short , I had a faulty radiator cap . 
The system remained at atmosferic pressure and as soon as the engine was shut off 
it started to boil . 

As far as I know , water has one of the highest thermal capacity and is by far the best choice for cooling . Just needs some anti corrrosion and antifreeze additions . But mostly it's simple plain water . 

This offcourse is my ecperiance with cars , not models . 

Pat


----------



## editor123

kvom said:


> The literature states that the hottest area of an engine is right around the cylinders (makes sense).  And there the temperatures can cause water to flash to steam.  Steam has no capacity to absorb more heat, plus can cause pitting over time.  If that does in fact happen then the specific heat capacity would be reduced over the theoretical value.
> 
> I'm going to ask some mechanics I trust about it.  A vehicle might need a higher reading temp gauge and some changes in the computer to avoid going into limp mode.



No, steam does have the capacity to absorb more heat or we would not have super-heated steam systems such as locomotives and nuclear submarines.

BTW, Barry Hares in Birmingham built the first Merlin V-12 if I remember correctly. Several others have built running Merlins as well. Some from casting kits and others from bar stock.

Here is a YouTube video of it: [ame]https://www.youtube.com/watch?v=0xe1LL1IC7Y[/ame]


----------



## ddmckee54

Maybe it's just me, but I've got nothing but a black box where the YouTube connection is supposed to be.

Link broke?

Don


----------



## kvom

After some research on the Evans product, I think it's probably not for me in the Jeep, and probably not for the Merlin.  Here's a test a competitor product ran:  http://www.norosion.com/evanstest.htm

The competitor (No-Rosion) may make sense as adding it to water may eliminate the need to drain the cooling system.  I also found this article about the proper type of water to use in an engine where corrosion is an issue (esp. aluminum).  I'm now thinking HyperKuhl with straight water for my Jeep.

http://www.onallcylinders.com/2016/09/09/coolant-additive-guide/

An interesting sideline to this build regardless.


----------



## grapegro

Having had many years of experience in the motor repair industry, One of the main reasons of overheating in high revving engines, make that water pumps, is that at higher revs, cavitation can take place with poor design  of impellers. Sharp edges at the tip of the impeller should be avoided. Norm


----------



## dairwin

Interesting post, regarding the non water coolants.  I was invited to consider using this product in my Merlin.  (Cooling of the real engine can be a problem for prolonged ground running).  I looked at the specs for this material, but decided to concentrate on improving conventional cooling with improvements to the radiator air flow, fitting an effective cowling, and changing settings on the propeller.  I also added cooling fans on the backside of the coolant/oil cooler block to achieve prolonged running temperatures.


----------



## Cogsy

ddmckee54 said:


> Maybe it's just me, but I've got nothing but a black box where the YouTube connection is supposed to be.
> 
> Link broke?
> 
> Don


 
It's not just you, it's a weird issue with the forum software and Internet Explorer currently. Until it's fixed, using some other browser will allow you to see the videos.


----------



## petertha

Cogsy said:


> It's not just you, it's a weird issue with the forum software and Internet Explorer currently. Until it's fixed, using some other browser will allow you to see the videos.


 
Yup, opened up in Chrome & the embedded video displays & runs perfectly vs. black screen in IE. I just went through a similar IE rigmarole on another forum with sporadic picture displays. Hope the issue gets resolved.

Anyway, as usual, beautiful workmanship!!!!


----------



## josodl1953

This Merlin was on display on the Model Engineering Exhibition in London, way back in 1982. It seemed to me to be scale 1:5 or even smaller. It was an amazing piece of engineering.

Jos


----------



## mayhugh1

I delayed the starter wiring as long as I could in order to avoid accumulating a lot of unnecessary play time on what might be a limited life starter. However, there's something really neat about an electric starter on a model engine, and I ended up running down two 12 Amp-Hr batteries while 'testing' it. I could be using a battery with more appropriate capacity (and terminals), but the ones I have might be a little less stressful on the engine's starting system.

Afterwards, I removed the manual starter shaft and bearing housing so I could inspect the starter bevel gears which are all visible from behind the cover. I didn't yet see anything suspicious about the teeth - just the expected wear patterns on their phosphate coating. The patterns looked normal, and so I just re-coated the gears with gray moly grease and replaced the cover. I also filled the oil tank so any further cranking could begin pumping oil throughout the engine. I allowed the engine to sit for several hours with the oil tank's ball valve open so gravity could help prime the pressure pump. The copper oil distribution lines were previously filled with oil when they were installed, and so all that was left to do was to pre-fill the oil filter.

The good news was that the high pressure oil gage was now registering a couple psi while cranking the starter. The bad news was that I had a pretty significant oil leak on the underside of the engine. Even though it's been in plain sight ever since the lower crankcase was assembled, this leak has been difficult to pinpoint because of its totally unexpected location. Oil has been leaking from the bottom machined surface of the scavenger pump because of an imperfect fit of one of the bronze bearings pressed into the aluminum pump housing. The bearings for the pump shafts were pressed into the housing's workpiece before any machining was done. The floor of the housing ended up rather thin after machining, and this evidently uncovered latent damage created by a poor pressing operation. I had been assuming all along that the oil on the underside of the pump had been coming from far more likely places above it. 

My fix was to JB Weld an aluminum plate to the machined bottom surface of the pump housing. The outer contour of the plate was machined to match the pump housing so it would completely cover the bottom surface of the pump and look as though it belonged there. After installing the plate, the engine's underside finally remained dry.

I then completed the machining of the rear and front plates that make up the electrical panel. Cutouts for a panel voltmeter and four toggle switches were machined into the rear plate. The voltmeter monitors the battery voltage; and, in addition to a main power cutoff, the switches apply power to the magnetos, fuel pump, and radiator fans. The outputs of the switches on the rear plate connect to their loads through blade terminals on the front plate. A pair of connectorized cables between the front and rear plates compete the circuits between the two while allowing the panels to be easily separated for maintenance. 

The fuel pump was mounted to the front side of the front panel. A buck converter located on the inside of the rear panel supplies voltage to the pump motor so the fuel flow can be regulated. A screwdriver adjustment, accessible on the rear panel, controls this voltage and the fuel flow.

Including the tach, two CDI's, and three buck converters, there's a lot of electronics associated with the electrical panel that could be damaged by an inadvertently reverse-connected high capacity battery. Therefore, I added a protective diode in series with the main power switch. I was able to come up with a Schottky power diode that had only a .3V forward drop at 3 amps of current.

During testing, I ran into a problem with the starter wiring. When I wired in the starter relay I had forgotten that one side of the motor's brushes was grounded to the motor housing. I managed to wire the relay into the wrong side of the motor, and all was well until the negative side of the battery's accessory loads were connected to the chassis. This inadvertently bypassed the starter relay and caused the starter to be energized as soon as the battery was connected to the terminal block. Pretty much all the starter wiring had to be re-done to correct the problem.

The build's final steps are soon coming up and will include the fuel tank and a system to fill and drain it. -Terry


----------



## dairwin

Terry - interesting post.  I do not have knowledge of this engine or castings, but the real engine also leaks from various points including the scavenge pump assembly.  The oil finds its way to sit on top of the water pump impeller housing.

Regarding your wiring harness; do you have a wiring diagram?  Will you use an oil pressure cutout switch as a safety?

David.


----------



## tornitore45

Love the vintage voltmeter, all analog gauges and classic look switches.  Digital gauges would be so out of place.

Terry, slow down we are out of state till October and would hate to miss the premier.


----------



## ddmckee54

OOOOOOHHH, tied wiring bundles!:thumbup:  You ARE going old school on this one, very appropriate.

Don


----------



## Buchanan

Terry , I really like your period engraving on your panel, not to mention everything else that you have done. It is beautifull.


----------



## mayhugh1

dairwin said:


> Terry - interesting post.  I do not have knowledge of this engine or castings, but the real engine also leaks from various points including the scavenge pump assembly.  The oil finds its way to sit on top of the water pump impeller housing.
> 
> Regarding your wiring harness; do you have a wiring diagram?  Will you use an oil pressure cutout switch as a safety?
> 
> David.


David, 
I didn't originally include a wiring diagram because I didn't think it would be of interest. Here is a sketch of what I did, though. No, I'm not planning for an oil pressure switch. - Terry 
p.s. Did you work on these engines in a previous life?


----------



## dairwin

Terry, I work on them in this life, but only for ground running and just as a hobby.  I have a small collection of RR Merlins which I research and rebuild, with their correct propellers.  I am interested in anything Merlin, hence my appreciation of those on this forum who endeavour to build working examples.

https://www.youtube.com/user/dairwin2000

David.


----------



## dsage

OMG. What a video. And two engines at once if you watch one of the other videos. That must be something to hear / see in person. Fantastic enough just in video !!

Thanks for the link.

Great work Terry and David.


----------



## dairwin

We try to run two engines together; the resonance of two Merlins is certainly a memorable.  However, we can align with other engines to produce the same harmonic.  This year I have also displayed my engine with a Bristol Hercules radial.

I am part of a small group of fellows around the UK who own and restore WW2 aero engines for ground running.  We attend large public shows on a non profit basis, so that enthusiasts of all types can get close access to the engines after they are run and ask questions, etc.

It's great fun and I get to meet many veterans and others with an interesting story to tell.

David


----------



## dairwin

Terry - thanks for the circuit diagram.  I was interested to see how you powered the various loads, and note you use a power relay.  Are you intending to use fuse protection?

There is some similarity with my harness, below.  I also have a charge circuit side, as the engine drives an original generator which charges through a carbon pile voltage regulator.  A bit unnecessary, but completes the electrical loop back to the batteries.

David 

View attachment DAI Sheet 1.pdf


View attachment DAI Sheet 2.pdf


----------



## mayhugh1

It looks as though the mounting hardware for the fuel tank will be the last machined parts required for this build. I didn't have any suitable stock on hand to use for turning a cylindrical metal tank, and so I used the same 10 oz high density polyethylene tank that I used on both of my radials. These particular (Sullivan) tanks are usually available from my local hobby store. I like using them on model engines that consume lots of fuel because their translucence provides continual feedback on the amount of remaining fuel. The downside is that they look somewhat RC-ish. On my 18 cylinder radial I hid the tank inside an aluminum shell, but the backlighted slot that I added to retain some visibility didn't work as well in bright sunlight as I had hoped. For the Quarter Scale, I designed a set of banded support brackets to give the tank an industrial look.

These tanks come with a few accessories that were designed for use with glow fuels. For my application they had to be replaced with gasoline compatible parts. One of these was a very flexible silicone pick-up hose terminated with a 'klunk'. A klunk is just a heavy metal nozzle that keeps the end of the pick-up hose submerged in fuel during flight. The klunk wasn't heavy enough to ensure the stiffer gasoline-compatible Tygon pick-up tube would always remain in contact with the bottom of the tank. So, before inserting it into the tank I soldered the three metal tubes together in a subassembly with the pick-up angled downward. This kept the pick-up, return, and vent tubes properly oriented even while the tight-fitting external hoses were being twisted onto them. The stock silicone stopper used to seal the tubes to the tank was also replaced with a gasoline compatible version.

Another RC fuel-related component that I like to use is a filler valve designed to remotely fill the tank without disturbing the metal tubes sealed into the stopper at its end. This valve has a FILL port that's accessible at the end of a manually extendable o-ring'd nozzle. In its RUN position the valve is simply a pass-thru for the tank's output line.

It's important to provide a way to drain the fuel system for storage since pump gas has a short shelf life. This is complicated by the fact that the fuel tank is mounted near the bottom of the Quarter Scale's eighty pound assembly. Fortunately, the electric fuel pump can assist with this. The heights of the various components in the fuel loop were chosen so the fuel in the carb bowl will drain back into the tank when the fuel pump is shut off. In order to drain the tank, however, the return hose from the bowl must be pulled from the fuel tank and directed into an external container. The pump is then run until the system is dry. In order to avoid constantly messing with the tank's metal return tube, an alternative and more robust return port was mounted on a bracket next to the tank.

Finally, an inline fuel filter was inserted in the input line going to the carburetor bowl. This line also contains a .018" diameter restrictor to reduce the turbulence inside the carb bowl. The size of this restriction was empirically determined several months ago during the design and initial testing of the fuel loop. Once all the fuel components were installed, the tank was filled, the pump control voltage optimized, and the system carefully checked for leaks. 

With the fuel loop finished and running, it occurred to me that all I had to do was bump the starter switch to see if the engine would 'pop.' The stand was sticking off the edge of my messy and overcrowded workbench, the propeller wasn't installed, coolant hadn't yet been added, and the carb's settings hadn't been touched since taking it out of its package. Against my better judgement, though, I couldn't resist pressing the starter switch. I was startled when the engine fired right up and ran. All I recall now is thinking how great it sounded, but in all honesty I was too dumbfounded to appreciate what was going on. After three or four seconds of hot exhaust in my face that ended up blistering a lip, I spotted the oil tank valve which I had forgotten to open. I hit the power switch to shut everything down, but I'm sure I kept on smiling. The next thing I did was engrave a warning placard about the oil valve which I bolted to the engine stand next to the starter switch.

I finished off the valence on the rear control panel, but I have a few more cosmetic ends to tie up before focussing on running the engine. If I don't tend to them now, I'll be too busy playing with it, and they'll never get done. Then, they'll end up being the only things I see later on when I look back over the finished project. I also need to round up a camera for a video. - Terry


----------



## kvom

Magic moment is fast approaching.


----------



## Buchanan

So you started it,th_confused0052  And you only give us a 3 line description of it running! Congratulations!

Buchanan


----------



## michael-au

Will be nice to see the video of it running when you make one

Fantastic workmanship


----------



## Charles Lamont

I'm not moving out of this chair.


----------



## dairwin

Terry - the return line from the carb to the tank; is that a pressure relief return from the pump or a ullage drain?

David


----------



## prophub

Terry,
Awesome work! Glad to hear it fired right up. Add me to the list of people waiting for the video! I've been following this build and your radial builds since I'd like to build the radial as my skills progress. You should be able to drain the tank from the fill valve. To fill the tank you could use something like this http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXJGS5&P=7#mults by rotating the handle forwards and to take fuel out, just rotate the handle backwards. It would save some wear and tear on the engines fuel pump.
Shawn


----------



## ShopShoe

Slight OT

For those following this, Jay Leno recently posted a video of demonstration Merlin (Packard) that he has acquired. He does a pretty good walk-around of its features and then gets it running. Whether you love or hate Jay Leno, the engine is pretty well described. It shows how Terrys model is so incredible to incorporate so many of the things that make a Merlin a Merlin.

[ame]https://www.youtube.com/watch?v=GYcKdK7hmEo[/ame]

BTW, Terry, I like your dashboard better than what Jay has.

ShopShoe


----------



## ICEpeter

Hello Terry,
Congratulation on your success. You are very close now. At some point in your thread there was a discussion regarding the cooling fluid to be used in your Merlin engine and various possibilities were suggested.

One possibility that I did not notice in the discussion is the possible use of a low temperature heat transfer oil and I wonder whether it might be possible and could be suitable for your Merlin if the Merlin heat load matches the heat transfer capabilities of a heat transfer oil. Don't know much about heat transfer capacity etc. of low temperature heat transfer oils but they are extensively used in food processing applications for example.

Peter J.


----------



## ddmckee54

OMG - It's alive?

You didn't think it would run?  Yeah - right, just like Howard Hughes was only doing a "Taxi" test of the Spruce Goose.  

Probably had to chisel the grin off your face, fried lip and all.

Congrats on the first run.  You ARE going to video the second run, right?

Don


----------



## mayhugh1

One of the last ends to tie up was the protection of the electrical connections inside the Futaba connectors used on the Hall sensor cables going to the ignition modules. This involved making a pair of protective covers by shrinking a length of heat shrink tubing over the connector while leaving a bit of overhang on its open end. A mating male connector, used during the shrinking process, prevented the open end from closing up. The cover slides over and protects the seams between the mated connectors on the ignition modules. Silicone was used to seal the cable to the rear of the tubing.

The step that I've been dreading since the beginning of this project was filling the engine with coolant. The are 76 coolant seals in the engine, and 52 of them are inaccessibly buried in the head assemblies. Although I vacuum tested those assemblies just after the heads were married to the cylinder blocks, my gut never made its peace with this particular feature of the engine's design.

I slowly filled the whole system with about 1-1/2 liters of automotive anti-freeze while checking for leaks, and then I left the engine sitting for several hours. Placing the coolant reservoir at the rear of the engine so it was level with highest point in the coolant loop was a great help, but another half inch or so of height would have been even better. If I had it to do over again, I would add a second filler cap to the top of the header tank at the front of the engine. 

Sure enough, a bit of seepage showed up near the front of the starboard head assembly and also near the rear of the port assembly. With the engine filled with coolant but still no prop, I attempted to start it with the carb settings untouched (or so I thought) from my previous accidental start. I got a few pops and then nothing. After several seconds of cranking, raw fuel began pouring out of the carb's intake. My first thought was that I had an issue with the fuel loop. If the pump pressure is too high, excess fuel can be forced out of the bowl vent and create a similar symptom. However, after additional testing, I realized the flooding occurred only while the engine was being cranked. 

I was about ready to remove the carburetor (Perry 9400) when I noticed the starboard coolant return hose rubbing against the high speed needle. I could see the hose changing the needle setting as the throttle was moved back and forth. The o-ring friction that's supposed to stabilize the needle setting against vibration wasn't adequate against the moving silicone hose. A simple tie-wrap solved the problem. The remarkable thing about all this was that the throttle had been moved many times since that hose was installed, and yet somehow the needle ended up at just the right setting to allow the engine to start up so easily the very first time. 

At this point the needle was sitting at 2-1/2 turns open from its fully closed position which happens to be close to the recommendation in the application note that came with the carb. I went back over my notes for my last radial build that used a very similar Perry carb. That engine had run best with a needle setting 3/4 turn from fully closed. 

I reset the needle to 3/4 turn and let the engine sit for a few hours to dry out before attempting a restart. This time the engine started up and ran although a bit rough. I could tell from the exhausts that the cylinders in the starboard bank were firing only intermittently. This time my wife was videoing the run on her iPad. 

[ame]https://www.youtube.com/watch?v=2lw-6he7qFY[/ame]


While running there's no oil or smoke coming out of the exhausts - a very good sign, but the coolant leaks opened up some as the head temperatures rose. After shutdown, about a teaspoon of coolant dripped from the engine.
After allowing the engine to cool I made another run. This time I could feel the throttle response beginning to show up, and the engine easily rev'd up even though the starboard cylinder bank was still only intermittently firing. Before quitting for the evening I was able to eliminate the Hall sensor and ignition module as the source of the problem. The problem seems to be in the starboard distributor, and I may have a small phasing issue with the rotor. 

I was pleasantly surprised to see the engine which has so much internal gear friction run as well as it did without the benefit of prop momentum. The electric starter also seems to be holding up.

My next step is to figure out the distributor problem and accumulate additional running time before adding the prop. I'm hesitant about adding the prop because I'm not comfortable with running the engine inside my shop with it installed. The engine is very heavy and is going to require a back-breaking effort to navigate it through my crowded shop and get it outside. I want to minimize the number of times I'll need to do it. I then plan to replace my wife's video with one in which the engine is running on all cylinders and with its prop.

The coolant leaks, though have really let the air out of my sails. Most of the engine will have to be torn down to properly address them. Frankly, I think chances are high that if I decide to do it, I will just move the leaks around instead of eliminating them. I'm also very concerned about separating the heads from the cylinder blocks without damaging either or both. I'll need to think more about this before deciding if it's the way I want to spend my winter.

In any event, I've taken a few photos of the final assembly as I don't expect the project's external appearance to change. But who knows? I made need them this winter. - Terry


----------



## dairwin

Excellent first run Terry.  Seems readily willing to turn over and run despite the gear friction.

David


----------



## mayhugh1

David,
Do you engines leak coolant? 
Thanks
Terry


----------



## Ghosty

Terry, Congrats on the running engine. There was no way this would not run, all the effort, checks and rechecks that you have done over the build.:thumbup::thumbup:

Cheers
Andrew


----------



## dairwin

mayhugh1 said:


> David,
> Do you engines leak coolant?
> Thanks
> Terry



No.  Oil yes.  I would like to know more about the seals used in your engine, but the main area of coolant leakage in the Merlin is the seal between the bottom of the cylinders and the crankcase.  There is a triple rubber seal (like 3 o-rings side by side) which provides the lower seal.  Tope top seal is a barrel shaped brass connector with two o-rings.

I run my engines with 35 percent antifreeze (ally friendly type) and deionised water.

David


----------



## RonC9876

Terry: Congratulations! What a mind blowing piece of work you have created! I could feel your nervousness as you powered everything up and hit the starter. Always scary starting a new engine especially one as complicated and work intensive as this one. So many things that can go wrong. But it has passed the test with flying colors. It runs! Maybe those coolant leaks are something you could get used to. Tearing this monster down would be a nightmare and as you said might be counterproductive. I have an oil leak on my Novi that showed up after my scavenge pump quit during a long run due to a stripped thread on the main bolt that drives it. I dread taking the engine apart and have been running it with a diaper underneath. I have tried all manner of ideas to stop this leak without taking the engine apart but it continues to drip. The worst part is that the source of the leak has remained hidden. It almost seems to be leaking through osmosis. I cannot pinpoint where it comes from. It bugs me to no end and a tear down is in the future for sure. It runs so well now and I am afraid that I might cause some other problem taking it apart. Torture!


----------



## ShopShoe

Terry,

Congratulations.

I think I've read every post on this thread and looked at every picture. Every part of this build is phenomenal. You've met every obstacle and solved all the problems. All that is left is peanuts (or chicken feed, as the old-timers said). As others have said, this is a work of art. 

The video shows it's a runner. I remember early in the project when you were talking about warped castings and etc. and suggesting that this might turn out to be a display. BUT IT RUNS.

I am convinced that you will resolve the unevenness and the leaks somehow and look forward to seeing how or what you decide.

For now, enjoy the success and take a breather.

I can't say congratulations enough times

--ShopShoe


----------



## cfellows

Congratulations, Terry.  Great to hear it running.  I look forward to seeing the engine in person when you're ready to show it off!

Chuck


----------



## mayhugh1

dairwin said:


> No.  Oil yes.  I would like to know more about the seals used in your engine, but the main area of coolant leakage in the Merlin is the seal between the bottom of the cylinders and the crankcase.  There is a triple rubber seal (like 3 o-rings side by side) which provides the lower seal.  Tope top seal is a barrel shaped brass connector with two o-rings.
> 
> I run my engines with 35 percent antifreeze (ally friendly type) and deionised water.
> 
> David


David,
The 28 top seals are short aluminum connectors each with a single o-ring. The 12 top liner seals are metal-to-metal press-fits. The 12 bottom liner seals each have a single o-ring which is sandwiched between between the liner and crankcase deck. All pretty much scaled down from the full-size engine. My leaks seem to be one or more of the top seals. The coolant has wicked throughout the entire gap between each head and cylinder block, and so it's difficult to pinpoint its location. Right now, I get about a teaspoon of coolant that drips out immediately after a run. If I wipe that up, nothing else seems to show up until the next run. I'm slowly making my peace with it. 
 I just hope I can resist adding some kind of snake oil sealer to the coolant. I used Barsleaks some 30 years ago in an old beater car I had, but I don't remember how well it worked. They have so many different types nowadays, but their website is very poor about explaining the differences between them. i expect my problem is rubber-to-metal, and I'm guessing those types of products are intended for metal-metal leaks. - Terry

p.s. I just remembered that I didn't answer your question about the return line from the carb bowl. When the pump is pumping it fills the carb bowl, and any excess fuel not used by the engine is pumped back into the tank. When the pump is shut-off, gravity will eventually empty the bowl back through the pump because the bowl is physically higher than the tank, it is vented, and the bowl's input line is at the very bottom of the bowl. Hope this answers your question. - Terry


----------



## DICKEYBIRD

mayhugh1 said:


> I just hope I can resist adding some kind of snake oil sealer to the coolant. I used Barsleaks some 30 years ago in an old beater car I had, but I don't remember how well it worked.


Congrats on finally tasting the sweet taste of success!  I really admire your perseverance on finishing the engine itself _and_ the documentation of the process.:thumbup:  Like me, I'm sure everyone that's been watching this thread feels excitement every time you post an update.

If it makes you feel any better, as part of the regular scheduled maintenance antifreeze drain/refills on the Jaguar V-12's we service at the dealership, it is required by Jaguar that 2 "sticks" of Bars Leaks are installed along with the new antifreeze.


----------



## dairwin

Hi Terry - I was just updating my earlier posting with more detail, but you seem familiar with the real set up (so I won't!).

The overall top fit of the liners and cylinder head (both early and late Merlin) is quite critical and not easy on the first attempt.  The later two-piece heads involve some care regarding bending/flatness and accommodated by different torque setting of the end pair of nuts.

From earlier photos of your engine, it seems to have a two-piece head.  The objective is to achieve the same compression on each liner, i.e., that the liner/head contact is at the same point such that the torque of the head nuts achieves a uniform compressive force.  I am sure you will have paid great attention to this.

Assuming the above has been followed, any leak from the top is likely to be minor.

Given that you have mentioned a teaspoon of coolant, I would consider running the engine for a while and monitoring the coolant loss.  You may find that the seal seating improves and the coolant loss reduces.  I would consider this, before taking the heads off again.

I would not use any leak-stop fluid.  Best to understand the source, even if it is not fixable.  The reported leak rate is low at present and with time may seal completely.  I would also resist using any non-water coolant.  Just my opinion.

Thanks, re the pump return.  The Merlin pump gearing provides a slow return of fuel through the pump.  If an Amal pressure regulator is fitted, then there is no appreciable leak back and the engine can be restarted the next day without any line priming.

DAI


----------



## Rustkolector

Terry,
Your Merlin has been, and continues to be absolutely the most awesome build I have ever seen. Congratulations!

However, as one who has seen a lot of real engine failures, your comments on coolant leaks reminded me of a model engine crankshaft I had to remake due to a head gasket failure and automotive ethylene glycol (EG) antifreeze mixing with crankcase oil. I have always had reservations about using ethylene glycol based antifreeze in my model engines, but I need it since I attend shows in the dead of winter. EG can be devastating to engine bearing journals when it mixes with engine oil. Unless you are absolutely convinced that a cooling system failure can never allow antifreeze to come in contact with your oil, I would look for another type of coolant that is anti-corrosive yet more oil friendly, even if it has little or no anti-freeze value. You can always drain it. I am sure you have considered this issue somewhere along this lengthy build, but I wanted to mention it just in case. 
Jeff


----------



## petertha

Its beautiful Terry, congrats!


----------



## Cogsy

Outstanding conclusion to an immense project. What an amazing piece of mechanical art!


----------



## Twizseven

Having recently been in a Lancaster bomber on taxyruns the fantastic sound from the Merlins is replicated by your engine.  Congratulations on a phenomenal build and the most comprehensive build documentation I have ever seen..
Colin


----------



## Stieglitz

Hi Terry, Thanks for sharing you are an inspiration!
Allen.


----------



## mayhugh1

I seem to be plagued with a signature screw-up that has affected my last three engine builds including this one. Regardless of all my care and pre-testing, I continually manage to sabotage the distributors in such a way to cause the rotors or timing disks to lose crankshaft synch during the engines' very first runs. In the Quarter Scale's starboard-side distributor, a pinch bushing was machined a little short and allowed both the rotor and trigger disk to slip. In the 'first pop' video, the starboard cylinder bank started out firing very intermittently and then eventually not at all. The abrupt stop was caused by a jump in timing that created a backfire through the carburetor and a resultant stall - not a good thing for the supercharger gearing.

After machining a new bushing and re-timing the engine, it finally fires consistently on all twelve cylinders, and all the exhaust turnouts now heat up uniformly. The engine starts almost immediately with the electric starter and within five seconds or so using the slower drill starter. After tuning the carb, the throttle response is smooth up to about 3/4 full throttle which is as high as I've run the engine so far. The best performance seems to be with the Perry's high speed needle set open about 3/8 turn from fully closed. The tach wasn't initially working, and so I wasn't able to measure the actual engine speeds. As a reminder to myself to not blip the throttle and abuse the supercharger, I tightened up the lever in the quadrant throttle to make its action very stiff.

So far, the timing hasn't been changed from its initial 10 deg setting. I plan to wait until the prop is installed before experimenting with it since the load will likely affect the timing and probably the carb's settings as well. 
I've managed to run about 25 ounces of fuel through the engine so far in a number of one minute runs. Although others have their favorite break-in procedures, I like to condition a new engine by temperature cycling it with a number of short runs separated by thorough cool-down periods.
With all cylinders now firing, the engine is considerably louder. The exhaust turnouts probably have something to do with this since the Merlin is considerably louder than my 18-cylinder radial.

After resolving the timing problem, I spent a couple days tending to a number of smaller issues. I replaced the high pressure oil gage which was damaged during the engine's very first start-up. The high pressure regulator wasn't yet properly set, and when oil pressure came up for the first time the 30 psi gage was pegged and left with a 7 lb. offset. Fortunately, I was able to replace the gage with an identical looking 60 psi model. I also re-adjusted the oil pressure regulators. I set the high pressure regulator to 40 psi which is the oil pressure seen by the crankshaft and rod bearings. The low pressure regulator was set to 20 psi. This is the oil pressure seen by the cams, the front drive, and the wheel case. I'm currently running the ceramic supercharger bearings dry except for any wheel case oil that finds it way into the bearings which I expect is non-zero.

The non-working tach was a puzzle since it had been thoroughly tested beforehand. I eventually discovered that the artwork used to mill the interface boards in the ignition modules left a bridge that degraded the tach driver outputs. The end mill used to remove the copper from the circuit boards had been too large to fit between an important pair of traces related to the tach output. The CAM software, whose prime directive is to not gouge legitimate part material, ignored that particular area of the board and left copper between two critical nodes. The ignitions themselves weren't affected, and since I used a hand-made driver breadboard to test the tach, I didn't catch the flaw in the circuit boards until now. Once located, though, the problems were easily corrected with an Xacto knife.

A Texas hurricane has brought rain into our area that will continue for much of next week. So, instead of a final outdoor video, I cleared an area on my workbench so my wife Mary could video the engine running with the prop installed. For this video, I bumped the timing up to 15 degrees and slowly varied its running speed between 1100 and 2000 rpm. The engine wants to rev higher, but its operator isn't quite ready. I'm not yet sure how low the engine will idle because the throttle is currently against the carb's idle stop at 1100 rpm. My custom carb mount makes any change to this stop a little less than straight forward, and so I need to go back and review my construction notes. - Terry


[ame]https://www.youtube.com/watch?v=0tOUQt5fem0[/ame]


----------



## Ghosty

Terry,
ABSOLUTELY BEAUTIFUL, is all I can say.th_wavwoohoo1
Don't worry about model of the month, it should be model of the year, decade, century.

Cheers
Andrew


----------



## Ken I

Absolutely stunning - I'm dumbfounded at the craftsmanship and attention to detail - your documentation alone deserves outrageous praise.

Having followed this post since the get go I've been mesmerized every step of the way.



Ghosty said:


> Don't worry about model of the month, it should be model of the year, decade, century.



Couldn't agree more.

Hall of Fame quality for sure.

Regards,
Ken


----------



## gbritnell

Terry,
With all the superlatives used many times I'll just say what an outstanding creation. The work, attention to detail and documentation are first class. Congratulations!
gbritnell


----------



## kvom

So, what's next?


----------



## IceFyre13th

kvom said:


> So, what's next?



Of course, build of the month.......Year.


----------



## dairwin

mayhugh1 said:


> <snip>  "As a reminder to myself to not blip the throttle and abuse the supercharger, I tightened up the lever in the quadrant throttle to make its action very stiff."
> 
> A good idea.  I also have a throttle friction control, so I can not bump the throttle.  There are two separate throttle return springs in the event of control disconnection.
> 
> "The engine wants to rev higher, but its operator isn't quite ready. "
> 
> I know the feeling!  The max I have run my engine, with low propeller pitch (variable pitch prop) is 2,500rpm and -3psi boost.  Torque roll on rapid throttle advance, also has to be avoided.
> 
> Nice video Terry.  Sounds great.  Any more info on the coolant leakage?
> 
> DAI


----------



## mayhugh1

I don't yet know if the Quarter Scale is going to be prone to overheating, but over time I plan to carefully extend the runs while keeping an eye on the engine temperatures. The cooling system does appear to be removing heat from the heads. Another one of my concerns about this engine has been the capacity of its scaled-down coolant pump whose impeller looks awfully small. After a one minute "prop-less" run at 1500 rpm, my last measurements showed an intake manifold temperature rise of 24F, a header tank rise of 42F, a radiator rise of 23F, and a reservoir housing rise of 9F.  After the 1-1/2 minute 1800-2000 rpm prop run in the second video, the intake manifold rose 50F, the header tank rose 60F, the radiators rose 12F, and the reservoir housing rose 19F. That little pump certainly seems to be pushing coolant around the system.

The coolant were a disappointment, but they're fairly minimal and don't seem to be getting any worse. It's not worth going through a complete teardown to try to fix them especially since I'm not sure what I would do differently. After reading Jeff's comment about the danger that ethylene glycol presents to the bearings if it gets into the oil, I drained the oil for inspection. The oil was clear although it had darkened a bit as expected, and I could detect no antifreeze odor. Another piece of good news was that there was only 60 ml of oil in the lower crankcase which indicates the scavenger pump is keeping up nicely with the pressure pump.

Since most of the leaks seem to be occurring just after the engine has been run, it occurred to me that a pressure rise in the system during its hot soak may be overwhelming the o-ring seals located between the heads. I'm currently running the coolant system with an unvented cap, and I may not be allowing enough volume in the reservoir for expansion. On the other hand, there could be a lot of trapped air in the tops of the heads above the seals, and therefore not a lot of coolant to leak out.

So, I machined a neck extension for the filler cap on the coolant reservoir. This neck makes topping off the reservoir a little easier and allows the level of coolant to be increased a bit more which might help displace any air in the system. The neck also  allowed me to install a hose fitting so I could add an expansion tank. A temporary expansion tank was cobbled up from a plastic syringe body.

I completely filled the reservoir with coolant and closed up the system with its unvented cap. During a one minute run at 1200 rpm, about 15 cc of coolant was forced into the expansion tank. When the engine cooled, it was all sucked back into the reservoir. I still had a coolant drip, but it was less than before. Even though the overflow tank isn't period, it probably makes sense to keep it and so I"ll machine something that looks better. 

Unless I run into something that might be of real interest, this will probably be my last post on this build. I'd like to thank everyone for their encouraging comments and constructive tips during the past 2-1/2 years. I'd especially like to thank John Ramm who patiently answered my email questions about his experiences during his own build. Richard Maheu, the designer of the Quarter Scale, also deserves to be recognized for the labor of love that he spent some ten years creating. 

I have a number of things that need tending to around the house and shop. The break will also give me a chance to think about a next project. I hope to be  back. -  Terry


----------



## kvom

I had a discussion on an offroad forum about using just distilled water as coolant, which conducts more heat than antifreeze.  With the addition of a product like Hyperkuhl, corrosion is eliminated.  Might be worth looking into.


----------



## mu38&Bg#

Excellent work. Cooling systems are tricky stuff. It may be worth monitoring the pressure of the cooling system or doing a pressure test. Though temperature could come into play. I had a car which passed a cold pressure test, but leaked water into a cylinder when parked hot. Some idea of cooling capacity could be determine from the radiator specs (if supplied) and fuel consumption.

As a side note, put together a compilation of your photos and video to post to YT before somebody else does to profit from your work. I saw this the other day and was disappointed to see a video of Keith5700's V-10 had earned 150,000 views in a couple days, half of what Keith's own engine running video has reached in almost a year. The guy made a compilation of his forum photos. Being a compilation it's likely protected and earning ad revenue on a bit of video editing of other's work.


----------



## Ca-g

Terry,
thanks for the fun. I've rarely seen such skill and reasoning power...
Chris


----------



## napoleonb

Congratulations on your fine build and results!
It has been fun and a great learning experience to tag along reading your posts.


----------



## editor123

Terry,
I sent you an email on this forum about featuring your engine as a Centerfold Article in a future issue of Model Engine Builder.


----------



## dsage

I knew Jay had lots of cars but I didn't know he also had a Merlin. And a real fancy one at that.

https://www.youtube.com/watch?v=GYcKdK7hmEohttp://

   Terry, maybe he'd be interested in seeing yours. I know he liked Lou's Duesenberg. Maybe you can get on one of his Jay Leno's Garage episodes. (On Youtube).


----------



## Charles Lamont

dsage said:


> I knew Jay had lots of cars but I didn't know he also had a Merlin. And a real fancy one at that.



It's a matter of taste I know, but for 'fancy' I'd say 'blinged-up beyond reason'.


----------



## mayhugh1

After accumulating an hour or so of numerous shakedown runs, the engine abruptly stopped one day just after a full throttle test. The prop appeared to be sickeningly trapped between a pair of hard stops separated by what I measured to be some 390 crankshaft degrees. Right after this happened I had to go out of town for a week, and so I had something to think about while I was gone.

When I returned, the first thing that I checked for was a piston striking a valve being held open by a dislodged seat that had become wedged between the valve and the head. This possibility was high on my worry list because during construction one of the seats that I pressed into the head needed suspiciously less force than the others. Repairing this, assuming an irreplaceable casting hadn't been damaged, would require separating a head from its cylinder block, and this was something that I hoped I would never have to do.

After draining the fluids and returning the engine to its rotisserie assembly stand where it would be easier to work on, I removed the valve covers so I could manually exercise each valve. All seemed OK.

My next guess was that a rod bolt had come loose, worked its way out of its cap, and was hitting the oil manifold mounted to the tops of the bearing caps. I rotated the rotisserie 180 degrees so I could remove the lower crankcase (oil pan) and was surprised to see that everything beneath the oil pan looked OK. The symptom had changed, though, and now the crankshaft had much less free rotation. The cylinder bores, as much as I could see of them, had nice shiny mirror surfaces; and only one showed signs of minor piston skirt scuffing. 

I turned the rotisserie back over so I could insert a borescope in the spark plug ports of the number two and five cylinders in both the port and starboard banks. The pistons in these cylinders were near the tops of their strokes, and now the crank was completely seized. Everything I could see inside the four combustion chambers, though, looked reasonable.

As an aside, I was really impressed with how clean the Viper spark plugs looked. They looked essentially new. I initially feared I'd have continual fouling problems with these tiny plugs which are mounted on the sides of the combustion chambers. Since they're located in front of the exhaust ports, though, the exhaust heat may be helping to keep them clean. There was a lot of coking, however, on the cooler walls of the huge exhaust ports cast into the heads outside the combustion chambers.

The center bearing cap, which was machined extra wide, establishes the crank's thrust clearance to something just under a thousandth. I then thought perhaps that some debris had found its way into this gap to create a bind. I removed the center bearing cap, which also required removing the oil manifold, but the crank was still stuck fast.

Although it didn't start out feeling like a starting system failure, the symptom now seemed to be pointing to an issue inside the wheel case. I removed the manual and electric starter shafts so I could look inside the wheel case with a borescope. The starter gears still looked good, but my visibility inside the wheel case was too limited to determine much else. 

I was mentally preparing myself to begin disassembly of the wheel case when I decided to first remove the front drive cover. With the symptoms I had been seeing, I had no reason to suspect the problem was in there. Inspecting the front drive, though, would at least eliminate the last of the easy stuff. As soon as I pulled the cover, I saw two halves of a mangled screw laying in the bottom of the housing. One of the six button head cap screws that attaches the large driven prop gear to the prop shaft had backed out and fallen in between it and its drive gear. Three of the other screws were also on their way out. 

The problem was created by a too small circular pattern for these six fasteners. The screw heads ended up too close to the fillet on the gear hub. When tightened, the heads dug into the fillet around the hub instead of bottoming on the flat surface of the flange. The vibration of the prop load likely caused them to back out over time. Two of the still-loose screws had too much thread damage to be safely removed without breaking them off. I was able to retighten them, but for good measure I first flooded them with a wicking grade of thread locker. Before replacing the other four fasteners, I turned down the diameters of their heads so they no longer touched the hub fillet. I also installed them with blue Loctite. The high spots on the damaged gear teeth cleaned up with a fine file.

I was able to take advantage of some of the unnecessary disassembly to better seal a few annoying areas around the lower crankcase that had been seeping oil. In fact, I discovered my two coolant leaks weren't created by the dreaded o-ring'd transfer tubes between the heads and cylinder blocks after all. They turned out to be associated with the coolant distribution manifolds on either side of the cylinder blocks. These, I was eventually able to fix.

To my relief, after reassembly, the engine fired right back up, and I seem to be back where I started. Actual&#322;y, considering that the drip pan no longer has coolant in it, I'm considerably better off. 

So far, I don't believe the engine overheats, but I'm still working on determining that for sure. The cooling system seems to be sufficient for the three minute runs I've made so far, but I could sure use a temperature sensor inside the header tank. 

When shutting the engine down, I've learned it's best to first kill the fuel pump and let the engine run itself out of gas before powering down. If not, fuel that was sucked up to the input of the supercharger will rain back down the long vertical intake and drip out through the carb's intake when the engine stops. In this engine that's actually quite a bit of gas. - Terry


----------



## dairwin

Terry - sorry to hear about the reduction gear bolt problem, and pleased to learn the damage is minor.  On the full scale Merlin, these bolts are necked and fitted from the rear side of the gear flange with nuts and split pins.  The bolt shaft is machined to fine tolerance and the fit of the gear to the flange very important for the equivalent load across the mesh.

Shutting down the engine; fuel off and let it starve is the best way to evacuate fuel from the inlet.  I shut off the fuel and let the revs drop, and eventually the 'low oil press' switch trips the mags to stop the engine itself.

I would like to see a video of a full load run.  Something I can never do!

David


----------



## Ghosty

Terry, very sorry to hear and see the damage, is it repairable, or will you have to cut a couple of new gears?

Cheers
Andrew


----------



## ///

Ghosty said:


> Terry, very sorry to hear and see the damage, is it repairable, or will you have to cut a couple of new gears?
> 
> Cheers
> Andrew





mayhugh1 said:


> ...
> The high spots on the damaged gear teeth cleaned up with a fine file.
> ...
> To my relief, after reassembly, the engine fired right back up
> ...


----------



## dsage

Whew 
Terry, you should be a mystery novel writer. You had me on the edge of my seat through that whole read.
Glad to hear it isn't (too) serious. I hope the loctight is enough to hold those screws. But now that there are properly seated you should be good.
 Good work.
:thumbup:

Dave


----------



## tornitore45

> Terry, you should be a mystery novel writer. You had me on the edge of my seat through that whole read.



I was thinking the same.  All these write-up should make a good novel, better that the Guy Lutard " Machinist's Bedside Reader".

I hope Terry has a soft copy compilation, saved.


----------



## ShopShoe

Terry,

I've said it before, but you continue to amaze...

I followed your inspection and diagnostic post just like it was another part of the build and I continued to be impressed by the way you think and logically work through the process to success. This model engine is just about the most complex mechanism on this forum, but your descriptions keep all of us following along as if we would have to do something similar tomorrow.

Thank you for the additional details about other things you noticed in the tear-down as some of those things will transfer to other things we do.

Thanks again,

--ShopShoe


----------



## nel2lar

Terry
I've followed many builds but none like yours. You have a very special way of showing and explaining that anyone can follow. The greatest thing we can feel your excitement and your sorrow when thing are not quite right. You are an amazing person both in talent and words. Maybe one day we will meet. I did not follow when the storms were going on, was your place alright with all the bad weather?
Very impressed
Nelson


----------



## V22

If only Terry could somehow get this content into a book. I would be the first to place an order. The content here is truly astonishing. This should really be preserved.


----------



## mayhugh1

nel2lar said:


> Terry
> I did not follow when the storms were going on, was your place alright with all the bad weather?
> Very impressed
> Nelson



Nelson,
Thanks for asking. Here in central Texas we got only a bit of wind and about 6 inches of rain from Harvey. If it hadn't been for a high pressure area that had settled over us, the story might have been a lot different. - Terry


----------



## RonC9876

Terry: I can't imagine how you survived the week away from your engine just itching to find out what had happened and fixing the problem. I would bet that it was hard to sleep during that time. Glad that the problem was relatively minor and was easily fixed. All the things that could have happened had to be working over your mind and body. Take care and here is hoping that nothing like that happens again.


----------



## mayhugh1

I thought I'd pass along some observations to those with their own sets of castings, based upon my experiences with the running engine during the past several week.

The average fuel consumption turned out to be about an ounce of gasoline per minute, and so the ten ounce fuel tank that I used is a reasonable size. The engine now has about 1-1/2 hours of running time on it, and has burned nearly three quarts of 92 octane gasoline (Truefuel).

The heads warm up to 180F in about 30 seconds (consistent measurements made along the exteriors of both heads), and they've remained there during the 2 minute  runs that I've made so far. The coolant pump circulates an impressive amount of coolant, and the temperature of the rear reservoir housing has reached 150F during the longer runs. So far, all the running has taken place inside my shop, and I haven't tried to extend them because of fumes. With the current radiator and reservoir sizes, though, I wouldn't feel comfortable with running any longer than a couple minutes. The cooling issues I'm seeing would certainly limit the engine's use in a flying scale model which was one of Dynamotive's original visions. The engine starts easily when cold but sometimes labors the starter when hot.

There's a lot of heat in the prop wash, but it's mostly exhaust heat. I generally allow the radiator fans to run several seconds after the engine has been shut down, mainly to give some purpose to the otherwise useless fan switch that I installed. The fans, of course, remove heat only from the coolant in the radiator since there's no circulation when the engine isn't running.

The engine doesn't blow smoke or oil out through its exhaust, and so the rear of the stand stays much cleaner than I had expected. Water, which is a normal byproduct of combustion however, collects inside the sooty exhaust tips during the first 30 seconds or so of running until the engine temperature rises enough to vaporize it. This is a common occurrence in automobile tailpipes while the engines are warming up. A bit of this soot collects on the two rearmost exhaust tips as well as the top covers of the distributors. 

The Perry 9400 carb seems well matched to the engine and performs well with gasoline. I ended up with the high speed needle open between 3/8t and 1/2t from its fully closed position. The carb's mixture disk didn't have to be changed to accommodate gas and is still sitting at its stock neutral setting. The engine starts easily in the shop's 70F - 80F ambient, and so far, choking hasn't been necessary. This will probably change when the shop's temperature drops 20F this winter. Starting is consistent so long as the previous run was terminated by shutting off the fuel pump so the engine was forced to run out of fuel. If not, gasoline settles inside the enormous intake and drains down through the supercharger's long vertical input where it soaks the carb, puddles in the drip tray, and leaves an overly rich condition for a restart. Shutting the engine down in this manner also tends to clean up any rich-running plugs.

The engine accelerates smoothly with a fixed timing of 20 deg BTDC. Performance seems relatively insensitive to any timing between 10 and 25 degrees.

After all was said and done, I still have some coolant leakage. About a teaspoon of coolant collects in the drip tray every day or so - just enough to be irritating. I expected and was prepared to tolerate some oil seepage, but leaking coolant is a different matter. After punching some trial and error pinholes in the bottoms of a number of paper cups, I was able to experimentally determine that the leak is roughly equivalent to a .020" diameter hole. I had been suspicious of the coolant seals, but now I believe there is yet another porosity issue with one of the castings. The leak is small enough, though, that I can't even be sure on which side of the engine it's on, but fortunately there's no sign of it in the oil.

I repaired two starboard head porosity leaks that I discovered when pressure testing the heads last winter just after assembling them to the blocks. My guess is that this leak is probably in the same casting, and my original setup wasn't sensitive enough to show it. Porosity issues are ideal candidates for a number of stop-leak sealants, though, and I'm currently experimenting with some solutions. If I were willing to wait several more months, investment that's probably still hiding in some of the coolant passages might begin circulating and plug it.

I removed the front drive cover to make sure the previously Loctite'd screws holding the large driven gear to its shaft were still in place. This time I noticed that the 1/4-28 bolt in the nose of the crank that secures the drive gear to the front of the crankshaft had loosened up. Since the drive gear is keyed to the crankshaft, I wasn't expecting a problem with this particular bolt. But, while I was in there, I blue Loctite'd it as well. For being one of the simpler portions of this engine, the front drive has been the source of a number of unexpected problems. The forces associated with driving the engine's huge prop evidently deserved more attention than I initially gave them.

The electric starter has been a great convenience, and so far the starting system has held up well. It now must be close to having accumulated a hundred start cycles including the initial testing it endured. The starter motor and battery that I ended up with turned out to be a fortuitous combination. They provide enough torque to quickly start the engine but not so much so as to break things when faced with a prop blockage.

The starter, along with the front drive, seem to confirm something that I continue to see on every complex project I'm involved with. The things that tend to give the most trouble are those that don't receive their share of worry. - Terry


----------



## dairwin

Continued good luck with the engine Terry.  More videos when you can!

David


----------



## tornitore45

> The things that tend to give the most trouble are those that don't receive their share of worry. - Terry



After a lifetime of design engineering I can say this quote should be repeated at the introduction of any engineering course or text.


----------



## Ken I

Terry,
        I have built a number of pressure decay leaktesters for the automotive industry for both engine blocks and cylinder heads.

A finish machined head or block is typically permitted 5cc per minute (air leak) from the coolant galleries and 1cc per minute from the oil galleries under 5 Bar test pressure.

This seems to be the generally accepted level at which porosity type leaks will generally self heal.

Unfortunately they don't always self heal and we had one head come back from VW that passed test and when tightly tested was found to be pretty much exactly 1cc per min @ 5 bar and never self healed but this seems a rarity.

Problem - you cannot measure zero so some allowance needs be made.

Another routine the industry follows is to test the raw castings prior to machining(so as not to waste valuable machining on "scrap) and 10cc is the pass limit for further machining and anything over 100 is scrapped. Castings falling between 10 and 100 are parked outside for 3 months to "weather" - most pass on retesting after "weathering".

I don't think I would sweat the coolant leak - keep an eye on it - as long as it continues to diminish then it will probably self-heal - if not then go the Barsleaks method or similar - I have found this works best if you use the Barsleaks with water only - no other additives or glycol which seem to inhibit the self-healing process.

Regards, Ken


----------



## Cogsy

I'm going to throw this out there, just so you have it for reference. On full-sized equipment with smallish coolant leaks (although nowhere near as small as yours is) adding a portion of ground black pepper (finely ground, 'dusty' stuff that makes you sneeze when you put it on your eggs, not chunky pieces) will generally solve the issue. I guess in the same way as your pieces of investment would 'fill the hole', the pepper clogs the leak. One advantage of the pepper as opposed to chemical additives is that it is completely inert and won't damage anything else it comes in contact with, and a coolant flush will get rid of any excess.

As for chemical additives, I have successfully used 'Stop Leak' which is a brand available down here as a clear liquid with fine particles of copper in it. It's basically liquid glass which sets in the hole (somehow, maybe magic). The big drawback is the heat needed to set the chemicals. Typically they need 30 minutes of engine operation at running temperature to activate, which obviously you can't do. Again not a problem you're likely to encounter, but I once used a chemical solution on an old 4cyl Nissan/Datsun engine with a slight head gasket leak. It fixed the gasket but basically welded the rings into the piston on the leaky cylinder. I went from using 1/2 a litre of water a week to 1/2 a litre of oil instead.

I'm sure you'll get it sorted. I second the call for more videos of this mighty beast too!


----------



## ICEpeter

Hello Terry,
I am not sure how applicable this method could be without dismantling all or parts of your engine to solve your coolant leaking problem but I solved my radiator leaking problem using a Loctite anaerobic product (Loctite 648 retaining compound) by forcing the compound through the fissures in the radiator under 60 PSIG and managed to seal the radiator completely, holding up to 60 PSIG air pressure after without any leakage.
In the casting industry they use the same process to seal porosity in castings prior to machining and sealants for that purpose are available in larger quantities but not in the open market. It seems these sealants can only be obtained form the actual user (A foundry) in smaller quantities.
http://loctite.ph/php/content_data/LT1244_TT_Automotive_Porosity_Sealing_By_Design.pdf

Peter


----------



## mayhugh1

I've used stop-leak sealers with mixed results in the old beater cars that I owned when I was much younger and poorer. Even with what little I knew at the time, something just didn't feel right about pouring thick brown sludge from a yellow plastic container into the radiator of the only car I had and depended upon.

If you visit today's online automotive forums you'll find many questions about whether these products actually work. Lots of 'experts' respond positively, and an equal number swear they'll cause immediate self-destruction of an engine. The truth is somewhere in between because there are different kinds of leaks and different kinds of stop-leak products.

The most difficult (practically impossible) leaks to fix for any significant amount of time are head gasket leaks, large radiator holes, burst hoses, and leaking water pump seals. Stop-leak products containing long fibers and/or sodium silicate (water glass) may help long enough in the first two cases so one can return home from a trip and make a proper mechanical repair. The only thing they can do for a leaking water pump seal is to clog up its weep hole so the problem is out of sight for a while. And nothing, except maybe a silicone tape wrap, is going to even temporarily repair a burst hose.

Candidates for long term repairs, though, are casting porosity problems and some freeze plug leaks. General Motors, in the nineties, routinely added their own stop-leak product to the coolant in a number of models as they came off the assembly line. GM had issues with casting porosity, and they hadn't yet learned to reliably seal aluminum heads to cast iron blocks. Their ACDelco coolant sealing tablets are still available and continue to be used today by some shops when performing flushes and coolant changes on these older cars. GM eventually terminated their use in new vehicles after developing their long-life DexCool coolant because their sealant tended to shorten the life of their new coolant's anti-corrosion package. Once dissolved in coolant, the tiny organic particles from these tablets continually circulate throughout the engine. The material (ground up walnut shells and ginger root) tends to find its way into small defects and seals them for pretty much the life of the coolant. When time comes for a coolant change, the engine is flushed, and new tablets are added to the new coolant.

These problems weren't limited to U.S. auto manufacturers. The 1990 Jaguar XJ-S Driver's Handbook (page 176) recommends adding two 135 ml bottles of Jaguar Radiator Leak Sealer to the vehicle's radiator after every coolant change, probably for the very same reasons.

This brings me to the Quarter Scale whose coolant leak I have good reason to believe is due to a porosity problem in one of the block or head castings. I researched the stop-leak products currently available so I could make an informed decision before irreversibly dumping someone's snake oil to the Merlin's coolant system. 

I decided early on to avoid the common silicate-laden products because of my fear of the glass particles eroding the numerous tiny o-ring seals in the engine. As an aside, coolants themselves, unless labeled 'silicate free', may contain their own silicates whose purpose is to scrub the walls of the engine's coolant passages. The owner's manual for my Honda Valkyrie specifically warns that silicate-free coolant must be used or the water pump's factory warranty will be voided.

The second group of sealants that I eliminated from consideration were the products containing copper flakes. Although the manufacturers of these products claim they can be safely used in engines with aluminum heads and radiators, this doesn't make a lot of sense to me. I was careful to use only aluminum and stainless steel materials in the Quarter Scale's coolant system in order to avoid issues with galvanic corrosion. Using a stop-leak product that stuffs copper particles into a hole in an aluminum head in the presence of an eventual electrolyte would seem to guarantee that the hole will eventually grow larger. In addition, I didn't like the idea of continually circulating metal particles past the seals in the Quarter Scale, and especially around the one in its tiny water pump. So, I eliminated the aluminum particle sealers as well. I also crossed off my list the sludgy-looking fibrous sealers, just because. And so at this point I had eliminated all the stop-leak products available at my local auto parts stores.

The two products that I did consider had to be ordered online. The first was claimed by its marketing to be a polymer only product. It's a (very) expensive product sold under the name Titan Block Stop Leak on the Titan Sealer website and also under the name Dura-Seal Engine Block Sealer on the Dura-Seal website. Curiously, both websites look very similar and have exactly the same contact information. The second product was the inexpensive ACDelco sealant tablets described earlier. These are available through Amazon as well as several other online sources.

My own testing included the inspection of the sealers under a microscope after samples had been mixed in their proper proportions with coolant. I wanted to be sure that most of the particles were small enough to seal a .020" hole, and that there were an insignificant number that might be large enough to block the tiny coolant tubes in the Quarter Scale's radiators. Both sealants passed this test. 

Next, I measured the time it took for a 100ml mixed sample to plug a leaking paper cup whose bottom had been perforated with five .060" holes. Both products plugged the leaks rather quickly - less than 10 seconds for the Titan Sealer and about 30 seconds for the ACDelco Sealer.

The last comparison was to allow the mixed samples of each sealant to sit undisturbed overnight in a clear container. The Titan product contains thousands of tiny polymer flakes in a thick carrier that isn't miscible in the coolant. This carrier hardens when exposed to air, and its likely purpose is to not only cement the flakes inside large defects but also to fill pinholes that are too small for the flakes. It's important that this particular product settles beneath the coolant in the bottom of an engine when it's shut off and away from any possible air pockets. After sitting for only several minutes, the Titan sealer separated out from the coolant and into a coagulant at the bottom of the container. The fine polymer particles appear to remain in suspension in the goo. 

The coolant itself is the carrier for the particles from the dissolved ACDelco tablets. These particles remained in solution in the coolant, also near the bottom of the container, but quickly spread throughout the coolant when lightly agitated. There was no evidence of a goo or sludge that was reminiscent of some of the sealants I've used in the past.

In the end, I chose to use the tablets over the Titan sealer for a couple reasons. The goo bothered me because it would tend to settle at the bottom of the coolant system, and in my case that would be inside the water pump. I was concerned that during long storage periods the goo might thicken and cause the tiny pump to seize. In addition, adding the Titan sealer to the Merlin's coolant system felt like a somewhat irreversible decision. If I later changed my mind and wanted to remove it from the engine, I'd have to work quickly to remove it before the carrier had a chance to air harden.

Since there is about 1-1/4 liters of coolant in my particular Merlin, I dissolved 3/8 of a tablet in about 200 ml of coolant before adding the mixture to the coolant reservoir. This dosage followed the manufacturer's recommendations. I immediately ran the engine for a minute or so to circulate the material. After a cool down period, I made another one minute run after which there was no more sign of leakage. It's now been over two weeks with considerable run time on the engine and the seal is still intact. - Terry


----------



## 10K Pete

The only coolant system sealer I've ever used was "Alum-a-seal" which is a finely divided aluminum powder, nothing else.  It never failed to stop the leak and never fouled a coolant system. I, and a half a dozen mechanics I've known, swear by the stuff. My Dad introduced me to it back around 1960. He'd been using it since air was new.

I may still have a tube of it somewhere....

But here it is..

https://www.goldeagle.com/product/alumaseal-radiator-stop-leak-powder

I've seen all the others clog, fail and otherwise make a mess...

Pete


----------



## rswinberg

Terry,
Awesome build. I have the same castings but haven't made a chip yet.
Where did you get the prop?
Thanks,
Randy


----------



## mayhugh1

Randy,
I got mine here:
http://www.aircraftinternational.com/Products/Propellers/BielaCarbonProps.aspx

Terry


----------



## rswinberg

Thanks Terry.


----------



## bazmak

This thread and Buchanans clock are my favourite builds.Simply because
they so far ahead of most projects and way beyond both me and many others
No disrespect to others but these two posts in particular bring to most model 
engineers the heights to which mere mortals can go


----------



## kvom

I'd add George Britnell to the list of people who's posts I always read.


----------



## 10K Pete

I must agree. This is the sort of heady stuff that keeps this mere mortal inspired...

Pete


----------



## Ardent

If anyone knows of a set of these castings that is for sale, or may become so, please let me know. I realize what theyre worth and simply waited too long to order from the 1/4 scale site, the email is no longer active there, tried to contact to see about any remainders. 

This thread has been better than any book I could have packed to camp. Im flying helicopters in a remote work camp sixty degrees north and there are some long nights this time of year. Was very much appreciated.


----------



## rswinberg

Ardent

I have a complete unmolested set that may become available. Also includes complete set of valves, springs, retainers, clips, and valve guides.
[email protected]

Randy


----------



## Ardent

rswinberg said:


> Ardent
> 
> I have a complete unmolested set that may become available. Also includes complete set of valves, springs, retainers, clips, and valve guides.
> [email protected]
> 
> Randy



Thanks Randy, email sent look forward to hearing.

Angus


----------



## BillH

I think I will stick to locomotives!


----------



## Herman staal

Good evening.

I have a big intrest in the quartelscale merlin engine. But found out the castings are not avalible anymore.

I had contact with a danish builder who built on of  this engines and got it running. 

He told me that from what he have heard about 50 of those casting sets were sold. Only few of them completed them.

Is there or does somebody on this forum knows who has a set of castings and would like to sell them.

Hope i could get a set of this.

Best regards 
Herman staal


----------



## rswinberg

Herman,
I have a complete un-touched set, plus valves, guides, seats, retainers, and keepers.
Randy
[email protected]


----------



## Herman staal

rswinberg said:


> Herman,
> I have a complete un-touched set, plus valves, guides, seats, retainers, and keepers.
> Randy
> [email protected]


 
You got mail


----------



## gdrhbb

mayhugh1 said:


> I came across two online references to help me with machining the Merlin crankshaft. The first is a thread by a Belgium builder 'Zapjack' who fabricated this exact part with some 200 hours of work over a period of two months nearly three years ago. It's located at
> http://www.homemodelenginemachinist.com/showthread.php?t=18747
> He first published his build on a French forum and then cross-posted its highlights on HMEM in 2012. The original non-English forum where he posted his realtime build as well as an additional two year's work on his Merlin is located at:
> http://www.usinages.com/threads/rolls-royce-merlin-v12-echelle-1-4.42350/
> Unfortunately, his posts faded away in 2014 after completing the crankshaft, prop shaft, and cylinder liners as well as the crankcase and some of the cylinder block machining.
> The second reference is George Brittnel's crankshaft tutorial inside his V-8 flathead build thread starting at:
> http://www.modelenginemaker.com/index.php?topic=3846.210
> Since I have some limited four axis CNC capability, my hope is to combine the information in the two threads and take advantage of my Tormach's fourth axis. I don't if my particular CAM software can be convinced to continuously machine the offset throws from billet, but it's worth several days of experimenting to see just what it can do. Hopefully, I can at least come up with g-code for some of the tedious roughing.
> Work started on the crankshaft by sawing off a 10-1/2" length of 2-3/4" diameter 1144 steel. I've not used this particular alloy before, but it comes highly recommended for crankshafts by George. I bought a piece long enough for two parts just in case my learning curve takes an ugly turn. I purchased the metal from an online supplier who advertises it as 1144 Stressproof or 'equivalent'. The 'equivalent' sounded ominous, but their price was nearly half that of the other online supplier that I've used used in the past for material not available in my scrap collection. Since Stressproof is a brand name, I'm not sure it's legal to use it to advertise a generic equivalent.
> Anyway, after facing and center drilling one end, I turned the o.d. down to 2-1/2" over as much of the length as I could before flipping it around, facing and center-drilling the opposite end and then turning the rest of the o.d. After cutting through the black outside layer I was relieved to find the material turns pretty similarly to mild steel. The chips resemble those from free machining steel, and the surface finish is similar. An amazing thing I noticed was the material's consistent o.d.. The run-out at the end of the 10.5" long un-machined round was only .002" after being chucked in my lathe's 3-jaw without tailstock support. The material I purchased was their low-end cold-roll, but it is also available as precision ground and polished.
> After studying the crankshaft drawing I realized just how complex this part is. The webs are not identical, and there are many machining features associated with them. Another wrinkle is that each bearing and crank pin is bored-through in order to reduce weight. In addition, both ends of each of these bores must be counterbored for end plugs since internal oil passages supply pressurized oil from the mains to the crank pins. The workpiece I'm starting with weighs 18 pounds, and the weight of the finished part will be only 1-1/2 pounds. A lot of metal has to be removed from some very difficult to reach locations.
> The first and probably most important decision to make is how the workpiece will be held for offset turning. George's offset end blocks looked good to me as they positively grip both ends of the heavy eccentrically rotating load. When I tried to adapt his technique to my crank I realized the four-sided headstock block he used for his 90 degree throws would not work with my crank and its 120 degree throws. I looked at using a hexagonal end block but I wasn't happy with two of the four jaws gripping on the corners of the block. A 12-sided polygon would work, but it wouldn't have long enough sides to handle the crank's 1-1/2" stroke in my 4-jaw.
> Zapjack center-drilled the ends of his workpiece for center-turning on each of the three offset axes. I don't have much experience with center-turning, but supporting the weight of this workpiece between two centers concerned me. None of Zapjack's photos showed his headstock drive, but I can't imagine it was merely a conventional drive dog.
> I decided to both center-drill and mill reference flats on both ends of the workpiece. Currently my plan is to use the center-spots to locate the workpiece between centers while finish turning the crankshaft. However, I will also add a head support block similar to George's to secure the crankshaft to my lathe's faceplate. The tailstock end will just be supported in an offset center-drilled spot by either a live or dead center. Most of the material will be initially roughed out on the mill and probably with the workpiece held horizontally in a vise. If I run into problems and have to come up with a plan B, at least I'll still have the flats and center-drill references to work with.
> A first pair of reference flats was milled into each end of the workpiece while it was held horizontally in a vise. The workpiece was then stood vertically in the mill and clamped against an indicated reference plate using a ground block between the flat and the plate. I was relieved that this rather dicey set-up was actually able to hold the workpiece truly vertical and was rigid enough to mill the additional flats. Zapjack actually removed the table from his mill so he could perform a similar operation. The 120 degree center-drills were then drilled, and the remaining two flats were milled on the perimeter. Both ends of the workpiece were similarly machined but an additional nine holes were added to the front-end. These will eventually be tapped and used to secure a driveshaft to the front of the finished crankshaft.
> Because of its complexity and the need to modify its dimensions to fit my 'short' crankcase, I modeled the crankshaft in SolidWorks so I could better understand what I will be up against. This crankshaft looks like a part that can be easily ruined by lapse of attention. It also looks like it will be the most complex part I've ever attempted to machine. It wasn't too long ago, when I was intimidated by what now looks like a pretty simple crankshaft in my 18 cylinder radial. - Terry
> 
> View attachment 77211
> 
> 
> View attachment 77212
> 
> 
> View attachment 77213
> 
> 
> View attachment 77214
> 
> 
> View attachment 77215
> 
> 
> View attachment 77216
> 
> 
> View attachment 77217


Hello, I really need this drawing very much. I love it. Do you have any plans to sell it?


----------



## mayhugh1

gdrhbb,
I'm sorry but it's copyrighted material, and I can't supply it. Others have been down this path trying to purchase the drawings from the original author even though the castings are no longer available, but his position has been firm and he won't allow them to be distributed outside the casting set. Your best bet is to purchase the set of castings and drawings from Randy above. You're going to need the castings to build the engine, they are very rare, and if Randy is willing to sell his you may not have another opportunity.
I don't know what your skill set is, but if you decide to purchase the castings and go on with the project, you should get a few other engines under your belt before attempting the Merlin. It will take only a single slip up to ruin an irreplaceable casting, and many of them will require straightening. Best of luck to you and keep us advised of your progress. Everybody loves a Merlin. - Terry


----------



## gdrhbb

Randy？Excuse me, who is it


----------



## mayhugh1

gdrhbb said:


> Randy？Excuse me, who is it


He's the person you communicated with in post 843 above. 

By the way, I happen to remember that there was a change to the crankcase casting that ended up making later versions of the crankcase slightly longer than earlier verdions. There was a warning about this issue on the Dynamotive website when it was still active a few years ago. This casting modification changed some rod locations from what was given in the drawings. Mine happened to be one of the ones that required these changes. In fact these changes rippled on up through the entire engine. So, before you start machining the crankshaft, make sure you have the actual crankcase casting that you'll be using in your hands. - Terry


----------



## elliot9797

I’m in need of this complete casting set-can anyone help?


----------



## elliot9797

Terry-did you end up using glow ignition, or magnetos?


----------



## mayhugh1

elliot9797 said:


> Terry-did you end up using glow ignition, or magnetos?


Elliot,
I used a spark ignition with two CDI's. The distributors were disguised to look like magnetos. - Terry


----------



## CJD

I realize this is an old thread...but...

I just bought a set of the basic engine castings from an estate sale.  It appears to have the castings for the basic engine, groups 1 through 4.  I wondered if anyone has a line on the castings listed in groups 5 through 9 that hey would be willing to sell.  These include the "bonus" items like the intakes, supercharger, carbs, magnetos, and a few other items.  I would even be interested in a complete set of castings that include all the groups.

Thanks,

John


----------



## goldstar31

My old Merlin fitter mate- 12" to the foot guy has just passed the Grand Lodge above but his favourite TB-731.  ( JM-R) is still airworthy-- from 1949.
So is dear old VP-981, the DH Devon C1 which later became the hack for the Battle of Britain Memorial Flight.  Gypsy Queen 71's.  I used to joy ride in it instead of playing soccer.


----------



## CJD

Well, got the castings.  They came with valves, keepers, springs, seats, and rockers.  They did not come with the rear gearbox or supercharger.  I have a couple projects to finish up, and then I'll get serious about looking the Merlin over and come up with a game plan.  This build will be complicated by the fact that Dynamotive is shutdown and does not respond to any attempts to contact Richard.  I am missing all the documentation to the rear gearbox, but I actually look at that as a plus, as there are a few things I do not like about the original gearbox and cam drive plan.

Terry, your build documentation here will be invaluable, as the plans leave a lot to be desired.  I believe this is a first generation set, as the initial castings are dated 1996, and the final contacts with Richard were in 2000.  The original owner was receiving the castings as they first became available.  

Still interested in any castings still out there...


----------



## Alec Ryals

gdrhbb said:


> Randy？Excuse me, who is it


Too many dang old coy rights !


----------



## CJD

I finally got the heads and cylinder blocks.  I can see right away that the cylinder spacing is going to be an issue due to differences in the casting shrinkage between the crankcase, cylinder block and heads.  The documentation is not what I am used to in technical drawings.  I am afraid Richard was intentionally sparse with details about measurements, and he has shut down all contact with the outer world.  It appears he sold the castings to help finance his side of the project, and kept the details (and copyright) close to his chest.

I have decided to build the engine virtually in Autodesk Inventor before even thinking about breaking a chip.  That will allow me to finalize all the details in cyber world, as I can see immediately that it would be easy to back myself into a hole otherwise.  Once I get going I will break my project off into its own thread.  Even with the issues ahead, the castings are truly mesmerizing to look at.  I can understand the effort that Richard put into them, even though I feel it's a shame he refuses to sell any of the copyrighted documentation.  It's it lot of work that will never be put to good use.


----------



## skylark

goldstar31 said:


> My old Merlin fitter mate- 12" to the foot guy has just passed the Grand Lodge above but his favourite TB-731.  ( JM-R) is still airworthy-- from 1949.
> So is dear old VP-981, the DH Devon C1 which later became the hack for the Battle of Britain Memorial Flight.  Gypsy Queen 71's.  I used to joy ride in it instead of playing soccer.


The Spitfire 16    JMR.  was Air Chief Marshal  Sir James Robb   personal aircraft  when it was based at  RAF. Northolt  (  hence the marking  JMR. )  This was fitted with the   Packard Merlin 266  1,372 hp.  -  I last new this to be flying with the Air Gunnery School at Exeter in 1953.  - Where is it now?


----------



## goldstar31

RAF Northolt at the time pf SL-721 and  the other 2 Vip Spitfires was a satellite to Hendon.

I was stationed  At Hendon there 1948-1950


----------



## Alec Ryals

Love to see some photos


----------



## goldstar31

Norman Franks  First in the Indian Skies give some aircraft details. It is inaccurate as Franks was going off someone one's recollections. Sadly not very true.   Four  VIP aircraft - 3 Spits and Devon  VP-981 were in the care of my mate in 31 but they were 'not on strength' so to speak. James Marshall Robb's kite was  JM-R replicating his intials on  SL-721.  I'm keeping quiet about one 'jockey; but  there is one helluva story about Boothman and the Sneider Trophy.     Although Robbs Spit appeared in Warbirds of Canada, his plane never went to war. It hdn't any guns LOL but somewhere and I think  Warbirds again and Jimmy ob. there are the lads on B Flight with the Proctors.  Tucked away was probably a  French Nor1000 or otherwise a ME108 Taifun.  My mate helped to put it together.
Devon  vp-981 is far more interesting. It was actually DH Dove originally but was  sort of a cousin to our  Devons whivh were replacing our Anson 19's. It 'beonged' to the Air Officer Commanding in Chief Coastal Command and flew with a bass fiddle across the seats as a liferaft. Well,  it was Costal Command.
In early 1950 the message came through "subsmash' A British submarine was in trouble and the dan marker had surfaced off Sheerness on the River Thames.  981 was in for a service in Tech Wing R&I  and my phone rang pn 19.  I was boss of the Signals billet then.  ' Corp, do you kmow what a Danbuoy is because 981 is on the Peri  trck across from you. Catch i  i was sitting opposite.  We flew at f all feet over Buckingham Palace with the Roya Standard flutering and down the docks of the London river.
 We got there to find that  the sub had been  spotted and the lifting gear had  come from Portsmouth in the night. We were too late and the deaths on truculent were appalling and it  was a wing dip in salute and  home for tea.  Days later, I'd been jabbed for  a trip in an ambulance Anson 12.  The  RAF Regiment corporal and were the best shots with 9 millie Sten( I'm deaf now)  and thing quitetted down and SL-721's engine basher and I were off into Civvy street. Johnny went to BR RAcing and  here me-ahem.
VP-981 was then sent as the hack to the Battle of Britain Memorial Flight and was superseded by a proper Wartime Dak.  50 years to the date of the Crash we tool the girl friend and the sistr of the 2 of the 3 crew and we kept in touch until John's death last year.  
So the two of us  are left- Eddie my top clerk has gone as well.  

When this pandemic is over, walk the haunted hallows of Hendon and move up to the National Arboretum to the RF 31 Goldstar memorial . Read the names of the  great people of th past.
there is a comfortable garden seat for your convenience. I put it there inmemory of my late  father in law by my late wife on behalf of ALL of us.


----------



## CJD

Alec Ryals said:


> Love to see some photos



Of the engine castings or the guys days in postwar England?


----------



## goldstar31

CJD said:


> Of the engine castings or the guys days in postwar England?


It is a misnomer on both counts. It was never 'post war England'. WW2 as such waa over but in months our former Allies were our enemies. Conscrpription in the UK lasted and lasted as did rationing and the last of the conscripts  would have been born in 1938 and those who survived would be old  ruins like me in mid 80;s and errrrrrr older!  Many would die s fresh faced youths in the many conflicts  from Russian occupied Berlin to  as ffar as the Far East. Communism was rife and deaths on- as a WW1 poet would have said 'On a Foreign Field that is for ever England' I'm sorry but as someone who was in a bit of it after 6 years of  WW2, I was there watching some of us horribly burn to death- and would be forgotten. 
Our Forgotten 14th Army and an unarmed RAF 31 Squadron would echo the words from the Greek:-

When you go home
Tell them of us
For your  tomorrow
We gave out today
Again with the closing of WW2 in Europe and long before Enola Gay would change  the World forever, the   Merlin engine was dead. Our Sptifires would not escort  both American and British bombers and the  up rated American P-51D's fitted with  American Merlins were no match against the Ferman jets and rockets which  were coming 'on stream/.  Thankfully  bombing by Allied and British bombers had reduced them.   But the V1's and then the V2;'s ere getting through- and I slept for most of my conscription in a 'Doodle bugged' billet. All this  ballyhoo about  tipping a V1  with obsolete Spitfires and on stream Typhoons and coming on Stream Meteors was  largely journalism.  It was not until the launching sites were overun by  the poor bloody infantry that  the attacks ended.
By the end of  what people call the end of WW2, the  famous Spitfires were  resigned to 'Toy for High ranking officers' and Auxiliary weekend airmen who had the vast life expectancy of 400 hourd flying time.
By 1960, even these venerable  little jockey fellows  would be flying DH Vampires.

All that would be left were carrier borne Seafires in Korea being hopelessly out gunned by jet powered Mig-15's over Korea.
By September 1949- I had reached the dizzy heights  of the rank of Hitler and Napoleon and  hd lready seen my 'boys'( they were all older than me) die= there was a job in the deveping British civilian aircraft industry in a scant few months. What did we have to show the World and me at farnborough Air Show?
And these Meteors would become - widow makers,  the much vaunted Brazon out of Filton would end as  scrap and  the then thrilling DH Comet 1  would  shake itself and everyone on board- to death in a year.
Perhaps wisely, I had seen enough and would switch to running my own little air travel business- on the side  and in my lunch hours( 20 minutes) and I watched prices of property prices  go into orbit. Like that Meor with the re-heats? I would fly comfortably and reasonably safe at a faster speed than was ever achieved in level flight in the best of Spitfires with filed rivets whatever.
Five years aho, I did what a  decent old survivor would do.

The Brits now have a National Arboretum to recall those  who did their  best and paid their  efforts in death for you and me. There is the Star of India which lists the commanding officers who led  from long before the Royal Air Force was concocted- from the cavalry.  Perhaps I am the oldest survivor now of a Squadron that  is only a fading memory. People get old or the lucky ones do and a seat is always welcome.  As Sole Executor and sole beneficiary and Trustee, there is a simple wooden seat- from my wife to her Dad- who was part of it.
I'm still making money from air travel and , as I don't want it- apart from the fun- am giving it- like my mates to deserving charities- much of it to the other survivors from those dreadful days.
My story, my events, my life --- because I was THERE.


----------



## CJD

What kills me the most is that the US offered surplus P-51's for $100 a piece in 1946.  After the Korean war they re-offered them for $500.  Imagine the investment if you tucked a hand full of those in your back yard!


----------



## Jennifer Edwards

10K Pete said:


> The only coolant system sealer I've ever used was "Alum-a-seal"
> 
> my father also introduced me to the stuff. Even would seal a small head gasket leak long enough to get you home. Amazing stuff!
> 
> one small 1”x3” tube would do the trick.


----------



## goldstar31

CJD said:


> What kills me the most is that the US offered surplus P-51's for $100 a piece in 1946.  After the Korean war they re-offered them for $500.  Imagine the investment if you tucked a hand full of those in your back yard!



This echoes the book about a  pair of Merlins in a  gunboat after the WW2 as  Nicholas Montserrat's the Dhip that Died of Shame.   So long ago, and I almost forgot!
 I recall the  Wembley Cup match 1949 and the hundreds of Government surplus aircraft that were parked around RAF Hendon for the matc'h. They were then 'dirt cheap- beyond my pocket, of course.
The years moved on-
 there w as 31 Squadron's  annual reunion and  ex- officers in their rusty old cars and a once scruffy sergeant and I  paring our gleaming Mercedes  as far away as possible from them.  Roly Sahib was the owner of a  scrap yarf on the Tyne-- and I was -rather well off with a small trave business and property abroad-- and all that I had had previously was  a Govdernment surplus Royal Observer Corps uniform with only a cap badge, a pair of chevrons and  'seagulls' on the shoulders.

But men are also forgotten  and a Royal British Legion branch- an important City one and it was  £30, 000 short and ready for closure and there once heroes would be dumped.  I was a member who never had time or inclination to attend but they got £15,000 from  my little group. of just over 3,000 Freemasons to help.
The World changes- men as well as P-51D's are forgotten but more importantly  the men and women.

In the story of the engine fitter of SL_721 JM-R he was deafened by one of the 3 Spifires.  I finally got him a War Pension  50 years after his ears had been blown out.
It took our Government 70 years to get us both  hearing aids.
So I must agree most strongly and Thank You

Norman


----------



## goldstar31

Hi Jennifer

Thank you for the information but  I always  thought that R_R stuff was Hylomar

Are you still perched in Brid?   Family are - when there is a chance on the windy end of Flamborough Head.

Best Wishes

Norman


----------



## mrehmus

In 1959, you could buy a P51 for $500 and the V-12 (still in the crate) for another $500 from a stockpile in Long Beach, CA. The Mustangs were standing firewall down and the engines in crates alongside a building.


----------



## CJD

Wellseal is the magic goo developed by RR to keep the Merlin heads sealed.


----------



## CJD

Well, I have spent the last couple weeks collecting manuals on the Merlin.  Also studied the Ramm videos of his engine running in Australia.  He does not document the build at all, but it is obvious he worked out the cooling issues.  I have owned several V12 Jags...and honestly the cooling is very similar.  The thing to remember is the Brits are very big into external piping.  We Americans always look for ways to do it internally...and often miss the obvious.  Cooling is plumbed differently on pretty much every aircraft in which the Merlin was installed.  I will have to lean towards the P51D for my build, naturally.

Making headway on digitizing all the parts too.  I will have to CNC the entire rear gearbox and supercharger sections.  

Also starting to collect metal for the non-cast parts.  I plan to stick with the phosfor bronze on the bearings (can't bring myself to use silver on a wearable part, although bronze costs almost the same these days).  The crank and prop shaft will be 4340 steel.  I am sure that is overkill, but 4340 is still the premier metal for crankshafts in any engine.


----------



## CJD

I am restoring a full-size, wrecked 1940 Stearman, which is taking most of my time.  I am still working on programming the castings into Inventor during odd times.  Once I am ready to start, this project should go a lot faster than previous endeavors with these castings, using CNC and thread-milling instead of 2000 tapping operations.  All but the cylinder blocks are now programmed into the virtual world of CAD.


----------



## tornitore45

> thread-milling instead of 2000 tapping



Many of the Merlin screws are #2.  Are you sure you can thread mill the holes?  And give up the trill of tapping a casting you worked on it for 200 hrs.


----------



## L98fiero

tornitore45 said:


> Many of the Merlin screws are #2.  Are you sure you can thread mill the holes?  And give up the trill of tapping a casting you worked on it for 200 hrs.


Harvey Tools sells them down to #00 thread, $73 USD With a mill that small you wouldn't want too much backlash in your machine!  Harvey Tool


----------



## CJD

Yes, I have the proper thread mills all purchased and ready to go.  The biggest issue I foresee is the tiny drill bits gumming up with the aluminum.  I'll have to find the proper mix of speeds, feeds, and lubricant.


----------



## mayhugh1

The problem I ran into is that for several of those castings with all their screws, the bosses for them weren't precisely spaced for whatever reason. Since I wanted the screws in the exact center of their boss, I indicated each under a spindle microscope. While I was there hovering over the boss, it just made sense to go ahead and spot and drill the hole. I also had to heat straighten nearly every casting of any significant length that typically had long rows of screws. The Merlin will fight any attempts to automate its construction, and you'll have to have the patience to play by its rules. I'm a fan of CNC, but it just wasn't useful on this build.  
Make sure of what you're doing on those heads with the dimensions that don't agree with the drawings. I had the same problem, and the changes you'll have to make to your drawings will spill over into the rest of the engine and many of the drawings of other parts will have to be changed, and you'll be compensating for those changes during the entire build.
It's my understanding that the head castings were so troublesome to manufacture that they almost tanked this project. My drawings in fact included a set of functional but esthetically poor looking heads that could be machined from billet. These were provided to builders as a back-up plan in case the cast heads never materialized. I also spent countless hours digging investment out of its coolant passages. You'll need to study the intentions of the coolant system in the head and make sure the passages are connected and free-flowing as they should be. Mine weren't and required a lot of remedial work. - Terry


----------



## CJD

That's why the digitizing has been going so slow.  As you say, each screw boss is off a bit...I have been taking the time to mic each difference as I digitize the castings into Inventor.  The flip side is that, as you note, Terry, my programming likely will not work on any other set of castings.

I only have the basic drawings, and finding the missing ones is no longer an option since Dyno has distanced himself from the project.  It's a shame he wants to lock in the copywrite to prevent copying, yet he won't sell them either.  That may be a blessing for my project, as my castings will be completely digitized, so I can work on size and placement issues long before the first cutter touches aluminum.  The other beauty is that I can run the final program without a cutter to track the accuracy, and only once all the bosses are located exactly run the cutters.

The trade off is I am spending the many, many hours on the computer to save hours on the mill.  I am likely spending more total time, all said.  We'll see how it goes once the Stearman is out of the shop.


----------



## Ken I

As an apprentice, one of my early machine shop supervising artisans gave me some sage advice - he was watching me charge into a job without really thinking it through and he said "You can't put the machine in reverse and put the material back on !".
That thought always hovers into my mind each and every time I take a cut.
Sadly it hasn't always stopped me making mistakes.
But time spent planning sure as hell beats time spent remediating errors.

Regards, Ken


----------



## ajoeiam

Ken I said:


> As an apprentice, one of my early machine shop supervising artisans gave me some sage advice - he was watching me charge into a job without really thinking it through and he said "You can't put the machine in reverse and put the material back on !".
> That thought always hovers into my mind each and every time I take a cut.
> Sadly it hasn't always stopped me making mistakes.
> But time spent planning sure as hell beats time spent remediating errors.
> 
> Regards, Ken


Grin - - - - that's one reason my welding skills also improved!


----------



## CJD

Here's the Stearman.  A before and after on the frame.  Long way to go...


----------



## josodl1953

How about the wings and tail section?

I'm planning to build a model Stearman for my Edwards .. sometime... in the distant future...
Jos


----------



## CJD

Hey Jos,

The Stearman wings and tail are even worse!  They are put up in storage. Since I am working out of a 2 car garage and can only work on one part at a time.  Here is a picture of how the plane came to rest...pretty much says it all!?!

Back to the Merlin, The relatively new "AirCorp Library" website now has some very good information on the Merlin.  In addition to a complete set of detailed drawings of the entire engine, they have all the associated manuals.  They even have complete factory drawings of most WW2 aircraft.  In fact, I am toying with my next project to build a P-51 right off the original plan sets!  All the destroyed parts on my Stearman can be duplicated from the original Boeing drawing sets.  All this available for almost nothing...yet Dyno won't let us copy his papers?!?  The second picture is one of the broken flying wire lugs that I pulled off the Boeing plan and CNC'd from 4340 steel.  I think it's pretty cool all this information is at our fingertips!

Anyway, I am missing the rear gearbox castings from the 1/4 scale set I bought.  The great thing is that I can reference the original drawings that Dyno likely used.  That will actually simplify my project, as the castings wound up being a bit of a disaster...shrinkage appears to be what killed the entire project.  Using CNC from factory drawings, and machining from billets, all those issues can be avoided.  At least that's the plan...I'll keep everyone updated when I finally put the tools to the metal...


----------



## Bentwings

mayhugh1 said:


> Don,
> Thanks alot for the tips. Sounds like good advice.
> Terry


I was just directed to this thread and build today. I do remember the casting kit from years ago. I wanted to get the set and do this engine.  I could see much better then but I really did not have reliably shop to build and work in at the time. I’ll try and backtrack this group to satisfy my ire to see one of these completed.   Msleave for now.

byron


----------



## Bentwings

Ken I said:


> Terry,
> I've got quite a bit of experience in cranking out dubiously large amounts of power from small motors - for slotcar racing (a hobby) and for robotic applications (my usual line of work) where power to weight is an issue.
> 
> You can only get so much torque out of a saturated armature so the only way to get more is to spin the beans out of it and gear it down as I am sure you are well aware.
> 
> I posted on the site an article on getting more out of your A.C. motor (a lot more)  which is germane.
> 
> www.homemodelenginemachinist.com/showthread.php?t=25236
> 
> Also from my automotive experience - starter motors are not 100% duty rated - they burn out if you run them too long but normally longer than it takes to crank the battery flat. So you can overload a motor for brief periods given the relatively light time-duty cycle of a starter.
> With a motor that runs close to saturation this won't help but a motor that runs at 20% saturation can be loaded to 500% for brief intervals.
> The "brushless" servo motors we use in our robots are built like this they will handle 200% load for 20 minutes and 500% for 5 seconds.
> 
> Anhoo - the reason for my response is that you will need to gear it down and those ganged planetary gear drive sets used in cordless drills and pneumatic tools can be cannibalised to form the basis for your reduction gearbox.
> 
> A lot of starter motors now do just that as opposed to the direct drive types on older cars.
> 
> And as Naiveambition pointed out you can go scrounging for an actual starter built for the purpose from something or the other - none spring to mind but perhaps some other members might make suggestions.
> 
> Another thought for a compact gearbox would be a harmonic drive - I could give you a perfectly serviceable 50:1 450W unit out of a robot (too much lash for precision but still a perfectly serviceable unit.) I have a few lying around.
> 
> Just a suggestion.
> 
> Regards,
> Ken


I’m just starting to learn about stepper motors. These can be pretty strong in small sizes with some careful thought I’d think a planetary gear trace could be mad roughly cylindrical.encasing the often more or less square shape of steppers. There ar some complicated drivers  available but I have not progressed that far yet. Just something to think about. These little motors can produce amazing torque fo their size.

byron


----------



## pascal

mayhugh1 said:


> I'm going to try to justify some of the craziness that I'm about to apply to these very expensive parts with some background theory. Precipitation hardening is a common way of strengthening 356 aluminum which is a popular casting alloy. To promote this process, certain impurities such as magnesium and silicon must also be present in the aluminum melt. As the castings cool these impurities form simple compounds which gradually, over time, come out of solution (precipitate) and they end up distributed throughout the casting. These precipitates harden the casting by preventing its plastic deformation (bending or stretching) when it is put under stress. These precipitates strengthen the casting, but they also make it brittle. This hardening process is kicked off just after the castings solidify, and it continues for hours to days or even weeks later depending upon the casting's storage temperature. Because of this process's dependency upon time, it is also commonly referred to as age hardening.
> A casting that has been age-hardened has little tolerance to bending, twisting, or stretching. If a 356 casting warped during its solidification, and if it requires straightening before it can be finish machined, then it must be annealed. This can be done by heating the casting to about 700F and then allowing it to air-cool. The common shop technique of using an acetylene torch to create a soot coating for use as an annealing temperature indicator also works for 356. If, after straightening, the part is left in its annealed state, significant strength will be lost. For 356 the tensile strength loss can be as great as 10,000 psi. Unfortunately, a 700F annealing is not high enough to kick off another age hardening cycle.
> The casting can be re-hardened, though, back to its maximum strength by heating it to 1000F for a dozen or so hours and then quickly quenching it. What makes this difficult to do in a home shop is the fact that aluminum melts at 1035F, and so careful temperature control is required. There is also a chance that the casting will deform under its own weight if it isn't properly supported. In addition, air-cooling needs to be minimized which means the quench tank needs be located within seconds of the furnace.
> Unlike the more familiar hardening process associated with steel, precipitation hardening does not occur immediately after the quench. The metal may remain soft enough to be straightened for up to a full day after the quench.
> Production castings should normally be straightened by the foundry before age hardening has progressed to any significant extent. An even better solution, of course, is to design the part so warpage is a minor concern, and the casting can be corrected by finish machining. The Merlin castings were not straightened by the foundry, and their thin-wall and complex cross sections make them very susceptible to warping that may not be correctable solely by machining. Straightening, after the castings have been allowed to harden, was therefore left to the end-user.
> Since this is a totally new experience for me, I felt it would be best to practice on some scrap cast parts I picked up long ago from my favorite scrapyard. My practice pieces, which are louvered vents, were sand cast from 356 and allowed to age-hardened for many years.
> I decided to immediately answer a question that was in the back of my mind, and that was just how much could I permanently deform one of these castings without annealing. After breaking two practice parts, I realized the answer was 'pretty much nothing at all.' The rest of my practice was done using only annealed parts.
> I eventually developed a process, after cracking a few annealed practice parts, for controlling the pressures I used to bend the castings. I learned to clamp the parts down firmly and to use positive calibrated stops to quantitatively limit the distance that an edge was being pushed. Rather than using a press I typically used my own strength and body weight in combination with fulcrums, levers, and clamps so I could maintain a hands-on feel for what I was doing. I found it was important to proceed in small deformation steps of .005" at a time and continually return to the surface plate to check my progress. I also decided it was best to not aim for perfection but to stop at the point where measurements showed I could machine the remaining defects away without negatively impacting the part's appearance. Since I had decided to not even attempt age-hardening in my shop, I tried to minimize the areas that I annealed. Before attempting any straightening, I located the major axis of the warpage using a surface plate, and I tried to anneal only a narrow region along that axis. I then applied my straightening efforts across this axis. After a full day of experimenting I had gained enough confidence to start on the Merlin parts.
> I first selected the three crankcase-related castings. I was able to machine flat the bottom surface of the main casting with respect to the crankshaft bores in order to obtain a reference surface. The front gear case turned out to be the major problem area on this part. It was out of perpendicular by almost .050" over its 5" height. I annealed a line across the gear case just above the top deck of the crankcase. After clamping the crankcase with its reference surface down to my drill press table, I clamped a long piece of wood to the gear case to which I applied the straightening force. With a pencil mark on the wood as a moving pointer I carefully monitored the distance the part was being pushed. After a half dozen tries which included returning to the surface plate to check my progress after each push, I had finally bent the gear case to within .015" of perfection. At this point I was able to machine its cover mounting surface flat and perfectly perpendicular to the reference surface in order to meet the drawing dimensions with no noticeable impact on appearance. I then machined the rear of the crankcase to its finished dimension. The decks for the cylinder heads will be done later, since they can be cleaned up with just finish machining.
> The gear case cover was relatively simple to correct because its major warp was also about a single axis. The documentation warned that this rather rigid part might have to be widened, and the drawings included the design of a complex 'stretcher' to attempt this. I'm thankful that my particular cover, which is a fairly rigid part, didn't require this really scary correction.
> The oil pan was considerably more complex and problematic. Being rather flimsy by design, it was warped across two separate axes. In addition, it's width had to be spread to match the crankcase. When checked on the surface plate, one corner of this part was initially almost 1/8" higher the other three. This part required almost a full day to correct, and I ended up annealing practically the whole casting. Fortunately, the oil pan is not a structural part, and the loss in strength that it likely suffered is not important. In the set-up for its final flange machining, the pan had to be packed with plastic modeling clay in order to dampen the chatter created by the mounting flange machining. I used high relief aluminum-cutting Korloy carbide inserts for all the machining operations and was able to obtain excellent surface finishes on both the annealed and un-annealed areas of all three castings. - Terry
> 
> View attachment 75254
> 
> 
> View attachment 75255
> 
> 
> View attachment 75256
> 
> 
> View attachment 75257
> 
> 
> View attachment 75258
> 
> 
> View attachment 75259
> 
> 
> View attachment 75260
> 
> 
> View attachment 75261
> 
> 
> View attachment 75262
> 
> 
> View attachment 75263
> 
> 
> View attachment 75264
> 
> 
> View attachment 75265
> 
> 
> View attachment 75266


----------



## pascal

mayhugh1 said:


> The Rolls Royce V-12 Merlin, was one of the best known, if not most influential, WWII aero engines. It was deployed in the British Spitfire and later replaced the Allison in the American P-51 Mustang. I recently purchased a set of quarter scale castings from a small San Diego start-up that originally planned to build and sell completed quarter scale Merlins nearly a decade ago.
> http://www.quarterscalemerlin.com
> The parts I received were investment cast and can be best described as large pieces of (expensive) jewelry. They share most of the realistic features and intricate detail with the equivalent parts on the full-size engine. Photos of the castings are available here:
> http://www.quarterscalemerlin.com/castings/
> I've no experience in working with castings, and was a little taken back by the notes accompanying them. The notes warned, in several places, that being long, complex, and thin-walled, they will likely require straightening and, in some cases, heat treating.
> The set I purchased includes castings for a functional supercharger, but it's not clear whether its scaled development was ever fully completed and just how much of it became a part of the prototype that was produced. The original designers opted for a glow plug engine, and so the magneto development may not have been completed. Finally, the notes mentioned fuel distribution issues with the Merlin's scaled-down intake manifold. The developers eventually designed an alternate configuration with multiple carburetors in order to get a running prototype, but the drawings didn't include information on its design. Over-heating issues were also mentioned, and a prop didn't show up in the published video of their running engine. Working these issues will add some interesting challenge to the project, but I'd rather additional development work wasn't going to involve very expensive and perhaps irreplaceable castings.
> I've been able to find online evidence of three other builders who have tackled this project using these particular castings. One posted his crankshaft build on 'the other' forum but he never returned after creating his own piece of art.
> My plan is to spend the first few weeks evaluating the castings I have so I can better understand the issues involved with getting them ready to machine. My first goal will be to see if I can get the major crankcase components straightened and fitted together with minimal machining. -Terry
> 
> View attachment 75234


HI mayhugh1

very impressive work.
I want to build same engine.
Can you help me with or if its avaiable cad, cast and drawin?
thanks 
Pascal


----------



## rlo1

Wow, that is some next level work.  DId not know about annealing Aluminum.  Good Read!  Good Work.


----------



## Bentwings

pascal said:


> I remember this project from many years ago there was an active forum for a while I wanted the casting set as I had machine shop availability atvthe time the castings were just too expensive . There were numerous posts about them being very weak and often breaking or cracking while machining  I YHINK there was quite a set of drawings available to I don’t remember if I actually purchased these   Atvthe time the general feeling drifted to carving the parts from solid bar stock 6061 or even higher strength alloys. Even then these were quite expensive tonourchbraw materials.   If I remember there were probably 3 engines produced that ran . As far as the supercharger , even back then it was well known that model  scrolls superchargers and centrifugal ones didn’t work well at best they were great fuel mixture beaters. It’s surprising that  mixture issues came up but air with gas or alcohol in it just does not like to turn corners well . Often the fuel drops out and you have a lean condition for one or more cylinders . This happened even in full sized racers.  I’ve had supercharged cars for many years as well as race fe cars . This is a common problem even there  the Hogson radials have a centrifugal impeller that actually does a good job of mixing furl  but I YHINK push comes to shove  it would show mixture variation cylinder to cylinder      Were I to build this Merlin today I’d make a full set of solid model   Assemblies to check the design then look into cnc machining . The oil pan and valve covers are really thin so they would be tough to machine nicely. I YHINK I might look into pressure forming these parts as sheet metal   The crankshaft would be a real issue if any serious power were applied
> HI mayhugh1
> 
> very impressive work.
> I want to build same engine.
> Can you help me with or if its avaiable cad, cast and drawin?
> thanks
> Pascal


----------



## Bentwings

pascal said:


> after reading and posting I looked this up again
> I tried to get backninbtobyhecsite but I couldntbitvtookbsvlittlevmessingvaroundcwith quarter scale Merlin and related things but I finally foundvitbibstillncsntvgetvavclickabke site address but muchbofvyhebokd stuff is still yherevifvyoubdidcaround  in the Ed this was actruev2/4 scal except for fasteners   In my mind it’s a good example of full scale that really does not scale well  down to 1/4 or 1/5  if exactness is desired . You end up with wired sizes  of hole bores pistons rings bearings. That would be much better adjusted to more or less standard sizes
> 
> 
> Then how did that scary  wrinkle cream site get stuck atvthe end of this thread yikes!
> The site is called scale Merlin .com  I YHINK I was not able to cut and paste the site   I don’t think the castings are available but there is a drawing set noted . Check it out . I’ll look it up again and see if I can get a tag able site .
> HI mayhugh1
> 
> very impressive work.
> I want to build same engine.
> Can you help me with or if its avaiable cad, cast and drawin?
> thanks
> Pascal


----------



## Bentwings

I probably commented this before .

In my opinion I YHINK rather than exact scale. Is probably not the best idea . My idea would be around possibly using parts that you can purchase   . Make the model “ about scale”.   Look toward using standard fasteners metric or imperial     I YHINK a cad model would be essential   Then maybe 3 d print the parts and build a plastic  model  so it could be seen where could be useful concessions . I’ve built  amber of large scale Rc model airplanes   I subscribe to “ if it looks scale , it’s pretty close “. A good example was a “ semi scale” gun sight I made it had many features that were notable on the real one but in the end it was terrible “ but it look like it was scale to the unknowing “     I had countless good moments on this atrocity .   Even real pilots thought it was good .   I had a semi scale pilot  positioned so he appeared to be looking correctly into the thing  if if you  were to measure this’ll  stuff you would probably just shake your head and walk away .  You can scale plastic models  an come close  but practically  being able to make it look scale yet functional is the real challenge   As I noted the crankshaft would be a real work of art   Eve with modern cnc  just machining some thing that small out of 4340 or tougher steel  would be a challenge. Just look around at small engines and especially large scale Rc planes.  A two cylinder crank is pretty tough most are built up  so some pretty close size work involved    Look at a Hogson 18 cylinder crank. It’s built up  some have mad it press fit others have made it slip fit assembly using various   “ fixing” means  . I have a 4 cylinder double acting engine it has only  mm main and rod bearings    I haven’t put it under heavy load  yet  but I’ve already designed an outer bearing  support for the overhung flywheel  it’s probably not really necessary as I’ll most likely not power a heavy load no run at high speed  for long periods   But 6 mm is pretty small  shaft  I just wanted double hung bearing rather than single over hung bearing . 
Just my yhoughts


----------



## CJD

It's been a while, as the Stearman project is taking most of my free time, but after 2 years of working here and there, I have managed to measure and digitize all of the Merlin castings.  I am now working on machining and building the engine in virtual space.  The beauty of this is that any mis-matching in the castings becomes immediately obvious.  I can then take care of fixes in virtual space, long before the first CNC cutter touches a casting.












Here is an example.  This next picture shows the front gear cover installed on the block.  The cover is a bit too large, so the screw holes do not perfectly line up.  Some of the screw holes can be seen punching through the block casting!  I then have the opportunity to realign the cover or re-locate the screws as appropriate to ensure there is not a problem.  The front cover is shown translucent to aid in viewing the internal gears and bolts.







The pictures above also show some of the machining operations started.  In other words, the main bearing webs have been virtually machined to reflect the fit of the bearing caps, and the cross bolt drillings are located in both the block and bearing caps.  The cylinder decks have also been planed flat and indexed to the crank bore.

Terry, if you are still out there, this thread is invaluable to me, as I received my castings from an estate sale, so I do not have all the notes and documents.  I am depending on your detailed posts to obtain recommended screw sizes and a lot of  other important information about this build.  Thanks!

My time frame is still infinite.  I expect the Stearman to take at least another 2 years.  I work on the Merlin project virtually when away from the house on business trips.  With luck, I will have the virtual work completed about the time the Stearman is compete, and I can start the CNC machining shortly after.

I'll try to give (virtual) updates now and then...

Cheers,

John

Oh...a quick glimpse of the Stearman...


----------



## Bentwings

CJD said:


> by all means keep up with the cad models   I was going to purchase the original drawing set and do as you are doing .   Once you make really corrected models maybe you could do 3 d printed models an really assemble as intended .  IE make a desk top plastic model
> It's been a while, as the Stearman project is taking most of my free time, but after 2 years of working here and there, I have managed to measure and digitize all of the Merlin castings.  I am now working on machining and building the engine in virtual space.  The beauty of this is that any mis-matching in the castings becomes immediately obvious.  I can then take care of fixes in virtual space, long before the first CNC cutter touches a casting.
> 
> View attachment 142338
> 
> 
> View attachment 142339
> 
> 
> Here is an example.  This next picture shows the front gear cover installed on the block.  The cover is a bit too large, so the screw holes do not perfectly line up.  Some of the screw holes can be seen punching through the block casting!  I then have the opportunity to realign the cover or re-locate the screws as appropriate to ensure there is not a problem.  The front cover is shown translucent to aid in viewing the internal gears and bolts.
> 
> 
> View attachment 142340
> 
> 
> The pictures above also show some of the machining operations started.  In other words, the main bearing webs have been virtually machined to reflect the fit of the bearing caps, and the cross bolt drillings are located in both the block and bearing caps.  The cylinder decks have also been planed flat and indexed to the crank bore.
> 
> Terry, if you are still out there, this thread is invaluable to me, as I received my castings from an estate sale, so I do not have all the notes and documents.  I am depending on your detailed posts to obtain recommended screw sizes and a lot of  other important information about this build.  Thanks!
> 
> My time frame is still infinite.  I expect the Stearman to take at least another 2 years.  I work on the Merlin project virtually when away from the house on business trips.  With luck, I will have the virtual work completed about the time the Stearman is compete, and I can start the CNC machining shortly after.
> 
> I'll try to give (virtual) updates now and then...
> 
> Cheers,
> 
> John
> 
> Oh...a quick glimpse of the Stearman...
> 
> View attachment 142341
> 
> 
> 
> View attachment 142343


----------



## ajoeiam

CJD said:


> It's been a while, as the Stearman project is taking most of my free time, but after 2 years of working here and there, I have managed to measure and digitize all of the Merlin castings.  I am now working on machining and building the engine in virtual space.  The beauty of this is that any mis-matching in the castings becomes immediately obvious.  I can then take care of fixes in virtual space, long before the first CNC cutter touches a casting.
> 
> 
> 
> 
> 
> Here is an example.  This next picture shows the front gear cover installed on the block.  The cover is a bit too large, so the screw holes do not perfectly line up.  Some of the screw holes can be seen punching through the block casting!  I then have the opportunity to realign the cover or re-locate the screws as appropriate to ensure there is not a problem.  The front cover is shown translucent to aid in viewing the internal gears and bolts.
> 
> 
> 
> The pictures above also show some of the machining operations started.  In other words, the main bearing webs have been virtually machined to reflect the fit of the bearing caps, and the cross bolt drillings are located in both the block and bearing caps.  The cylinder decks have also been planed flat and indexed to the crank bore.
> 
> Terry, if you are still out there, this thread is invaluable to me, as I received my castings from an estate sale, so I do not have all the notes and documents.  I am depending on your detailed posts to obtain recommended screw sizes and a lot of  other important information about this build.  Thanks!
> 
> My time frame is still infinite.  I expect the Stearman to take at least another 2 years.  I work on the Merlin project virtually when away from the house on business trips.  With luck, I will have the virtual work completed about the time the Stearman is compete, and I can start the CNC machining shortly after.
> 
> I'll try to give (virtual) updates now and then...
> 
> Cheers,
> 
> John
> 
> Oh...a quick glimpse of the Stearman...
> 
> View attachment 142341
> 
> 
> 
> snipped most of the pics/visuals



Hmmmmmm - - - - where did you get your information (drawings etc) for the "Stearman" - - - I'm assuming that its an airplane. 

TIA


----------



## Shopgeezer

ajoeiam said:


> Hmmmmmm - - - - where did you get your information (drawings etc) for the "Stearman" - - - I'm assuming that its an airplane.
> 
> TIA



Wow and a real airplane at that. This must be a restoration project. What is the history of this one?  Is the engine running or will you have to tear that down too?


----------



## Scott_M

To CJD
You should really start your own thread on both the Stearman and the Merlin. Right now it is at the end of 45 page post. Good luck on anybody finding it again. 
Not to mention going "off topic" on Terry's excellent post.

Scott


----------



## CJD

Yeah, I hear ya'.  I'm only able to post every 9 months or so on the Merlin, and the Stearman is definitely "off topic".  I only mention the Stearman to explain my slow progress on the Merlin.  Once I am able to work enough to post regularly, I will start my Merlin's own thread.  It deserves it's own thread, since it is a completely different approach to the same engine project.  Right now I just don't have enough info to start a new thread...plus it serves to "bump" Terry's great thread every few months!

Bentwings...The thought of printing one of these engines crossed my mind.  The digitizing I have done is really all that is needed to print.  It would be best to "fix" the casting problems that I built into these particular parts, but that is rather easy once the parts are built in virtual space.  In fact, I bet 3D printing in metal wouldn't be as pricey as making castings.  I am not really interested in printing a Merlin, but if anyone else is, let me know.  Unlike Dyno, I would be willing to share my Inventor files.


----------

