Quarter Scale Merlin V-12

[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]

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]

... 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]

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]

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]

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]

... 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.