# 270 Offy



## mayhugh1

Before deciding to build Ron Colonna's 270 Offy, I wanted to familiarize myself with the original full-size engine. I came across a link with a number of photos that describe the full-size assembly of a slightly later version of this engine:

https://www.hotrod.com/articles/assembling-270ci-offenhauser-indycar-engine-step/

Zeroing in on the model builders' major concern with the Offy is its use of a one-piece crankcase. The crankshaft is supported inside the crankcase by four main bearing webs. In the full-size engine, these two-piece split webs are assembled onto the crankshaft before it's dropped vertically through the rear of the crankcase. The webs have ears that are shrink fitted to notches machined inside the crankcase, and in order to finally seat the crankshaft assembly, the crankcase must be expanded with heat.

Ron's quarter scale Offy uses the same arrangement, but his three webs are four-piece assemblies. Using access ports on either side of the engine, the webs are assembled around the crankshaft while it's inside the crankcase. The access ports on the full-size engine are large enough to clear the hands and tools needed for final assembly. In the model, however, where even more assembly is required, the limited access provided by the scaled down ports have been the reason for its reputation as an 'engine assembled in a bottle'.

Being a visual person, I heavily rely on pictures and drawings to interpret a design, and I tend to get lost in textual descriptions. Since Ron's design is divided among all three, I decided to create SolidWorks models of some of the engine's key components in order to test my ability to follow the documentation.

For having just four cylinders, the engine is quite complex but a thing of real beauty. Even though the full-size engine was constructed from several complex castings, Ron was able to machine a faithfully scaled replica from bar stock using a basic mill, lathe, and lots of skill. Since my manual machining skills are not on par with his, I also needed to see if my Tormach was going to be of any help in machining some of the more complex parts that I had already spotted.

The photos contain CAD renderings of some of the models that I created. Except for a few liberties taken to fill in some missing minor dimensions, the models should be accurate representations of Ron's design. In order to avoid a copyright discussion, let me say up front that I realize these models are just another embodiment of copyrighted work currently available from Ron and that they're not available.

One of the critical steps in machining the crankcase is the milling of the pockets for the four ears on each of the three main bearing web assemblies. The design of a long reach shop-made fly-cutter is provided in the documentation to help with this. Mismatches in the depths of these notches will combine with machining errors in any of the four parts making up each of the three webs and create a misalignment of its particular bearing. Although this problem can be mitigated by line boring a pre-assembly of the webs inside the crankcase, their intricate in-place assembly around the crankshaft would still remain.

In addition to the connecting rod assemblies, the sixteen head bolts that secure the head to the block and the block to the crankcase must also be torqued through the 3/4" wide access ports. Even though I can't begin to visualize this very intricate assembly, I can certainly appreciate why it's been described as being done inside a bottle.

My next step is to modify the crankcase model to simplify the crankshaft assembly. In particular, I plan to split the crankcase and use conventional main bearing caps. I'm also going to look at a slightly different head bolt arrangement to try to come up with a bit more robust and serviceable head gasket. Before committing to the project, my goal is to model something with same outward appearance of the original model that I think I'm capable of building and assembling.

If I decide to go forward with the project, Ron has also offered to share his recommendations for improvements based on his experiences with building the engine and running it now for over a decade. - Terry


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## Ghosty

Looks interesting, will be following along, If it is any thing like your other engines, it will be a masterpiece


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## Tim1974

Same hear love your work..


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## oldboy

I have a copy of Ron's pans recently purchased.  I wil be watching this with interest.  Love your work, you are brilliant if 
I could be 1% as good I would be happy.

Barry
Australia.


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## petertha

Hope you ultimately decide to go for it Terry.


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## mayhugh1

To create a model for the split crankcase, I started with two identical copies of the stock crankcase and, at the crankshaft centerline, literally cut away the top half from one copy and the bottom half from the other copy. This wasn't the most efficient way to begin since the CAD software will continue to remember and associate the invisible thrown-away portions with those actually retained, and this will waste precious resources on my ancient XP computer. However it was a quick way to get started, and it reduced the chances of making unintentional changes to the original design.

The stock internal features were cut away and replaced with three integral webs for the main bearings. Since I plan to machine the interiors of the unassembled halves on the mill, I enlarged the cutouts around the crankshaft counterweights in order to accommodate the fillets that will be left behind by a 3/8" ball end mill. These cutouts could be made smaller if, instead, they were lathe bored per the original documentation.

Mounting holes were added for cap screws to rejoin the halves and also for a pair of dowel pins to register them. The teardrop scars along the lower half's sloping sides created by counterbores for the screw heads should be the only outward indication that Ron's original design was altered.

Dados machined into the tops of the webs inside the lower crankcase half will be used to register the bearing caps to tenons machined into their undersides, and the final assembly will be line bored. The screw hole locations for mounting the circular rear housing were also altered slightly to accommodate the crankcase split. Grooves for o-rings to seal the side covers were added around the access ports straddling the split. Neither a gasket nor sealer will be used between the crankcase halves, and so a few more o-ring grooves were added to the ends of the mating flange on the lower half to seal a couple potential oil leaks.

Attention was focused next on the block. The original design uses long 5-40 studs running up through the roof of the crankcase to secure the block to the crankcase and the head to the block, requiring major disassembly for head gasket servicing. I originally planned to machine the block as an integral part of the upper crankcase half, but the risk added to the whole crankcase by so much additional machining caused me to reconsider. Instead, I kept the block and upper crankcase as separately machined items but joined them into a 'semi-permanent' assembly. The two are joined with a number of 3-48 SHCS's that are threaded up through the roof of the crankcase but stopping short of penetrating the wet interior of the block. I added a groove on the bottom of the block for an o-ring to seal the two surfaces against oil leaks. Once assembled, the pair shouldn't require separation. O-ring grooves were also added around the block's side cover openings to avoid dealing with sealant or gaskets pierced by the cover's forty 0-80 mounting screws.

The last component to be modified was the head. Eliminating the long studs through the crankcase and block allowed a bit more flexibility in the locations of the head bolts. The only change made to the head was a slight repositioning of the head bolts to provide a little more 'meat' for the head gasket. The head will be secured to the block using sixteen SHCS's threaded through the roof of the block and into the bottom surface of the head. The holes for the tubes that will return top end waste oil back to the crankcase were also moved slightly inward to gain clearance for the o-ring on the bottom of the block.

Since I don't yet fully understand the engine's lubrication system, I've not included the oil passages in either the crankcase or the head. None of these passages really have to change from the original design, but the elimination of the four-piece main bearing webs will create an opportunity for some simplification. This should become more apparent after I get some actual parts in my hands. The next step is to allow these models to simmer for a few days and then begin the machining of the crankcase. - Terry


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## petertha

I bought this book a while back when the softcover came on sale. It has a pretty decent array of clear B&W pictures & quite a few line drawings. Not sure if it will help with the specific build, but provides interesting history of the era. 
https://www.amazon.ca/Offenhauser-L...s=offenhauser&qid=1566091842&s=gateway&sr=8-1


Are you making it to same scale as Ron's design?


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## gbritnell

Hi Terry,
Through the years of building engines probably the one job I disliked the most was line boring for the crankshaft. It seemed like every engine I built required a different bar and set-up. The larger engines weren't too bad but the smaller engines were just a flat out pain. We as builders take liberties in building our engines, just as you are making to Ron's original des


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## gbritnell

I apologize for the abbreviated response above. When trying to use my Ipad it loves to reload some web pages, this one especially.
I'll start again.
Through the years of building engines probably the one job I disliked the most was line boring for the crankshaft. It seemed like every engine I built required a different bar and set-up. The larger engines weren't too bad but the smaller engines were just a flat out pain. We as builders take liberties in building our engines, just as you are making to Ron's original design. It's virtually impossible to completely scale an engine down from the full sized copy and have it work.
While you're in the designing stage here's something you might look at. Rather than line boring my engine blocks I now cut a rectangular slot for the bearings. This does two things, first and foremost it eliminates the line boring process and second it adds greater accuracy to the whole main bearing part of the build.
The bearing slots can be made one of two ways, the first is to make the slot wide enough to accommodate the bearing and its mounting holes and the second is to make the slot large enough for the bearing with the mounting ears on top of the the split crankcase. To make the bearing I machine them to whatever configuration I'm going to use then make a fixture to hole them. Center is picked up and the bearings are bored to the required diameter. Who says that bearings have to be circular inserts. It's common full sized engine practice but for our model engines who cares. It's not like you're going to be replacing bearings every season, but if you did you just machine up some new blocks, mount them in the already made fixture and bore them.
Just a thought.
gbritnell


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## lohring

Not to be critical, but did you consider using the original Offy crankshaft bearing  design with the split crankcase?  If you allow a little float it should be easy to align the bearings before firmly bolting them to the crankcase.  You could then dowel them in place.

Lohring Miller


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## ozzie46

Thank you so much George, you just saved my V-8 block. Drilled it in the mill/drill. rear is higher than front. Will mill it out and use your square bearing idea. 


Ron


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## johnmcc69

More great work Terry, always a good read.
-Nice CAD work.
 John


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## mayhugh1

George

Thanks very much for your suggestion on using square bronze inserts for the main bearings. At first I wasn't sure I fully understood how you were achieving the alignment without line boring, and so I spent time going over your straight-six build on the Model Engine Maker forum. I noticed that a lot of fitting was required at the end to get the crank spinning freely and that your final conclusion was that you'd probably not recommend the technique for journals larger than .437" (the Offy's are .500"). However, you've got me thinking about a hybrid approach that uses these bearings along with line boring to eliminate the typical inserts. I think I'll probably be able to re-use the boring bar and fixture plate that I made up for the Merlin (if I can find them).- Terry


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## Mago

Another Offy 270
I was fortunate in having  Ron Colonna's  "building the 1/4 scale 270 Offy" manual,  as without it construction would have been even more difficult.
Whilst not having to exactly follow his methods it is a valuable starting point.
I used both metric screws etc and BA for the very small connections. This required redrawing many parts to ensure that they were not going to foul something or break thro where they should not.
I think it's a model worthwhile building.

Mago

Not quite finished.


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## sition

nice


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## mayhugh1

I combined the comments from George and Lohring into an alternative split crankcase model using solid bronze circular main bearings. This approach is cleaner and a little closer to the technique used in the original design, and it does away with the need to deal with fragile shell bearings. I'd still likely line bore the final result, though. Both bearing halves are secured to the lower half of the crankcase with a pair of 6-32 cap screws with the upper half of the crankcase being machined for clearance around it. - Terry.

p.s. Thanks Petertha for the tip on the Offenhauser book. I've placed an order for one.


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## lohring

Thanks for the credit, but my solution was cruder.  I believe you will still need to accurately line bore both the seats in the crankcase halves and the bronze bearings.  My plan was to make each of the bronze bearings separately and then face mount them to webs in the crankcase.  That way there would be some play for alignment and you could then drill for dowel pins to maintain the alignment.

Lohring Miller


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## mayhugh1

Construction of the crankcase began in typical fashion by band sawing a couple chunks of aluminum into rough workpieces that will eventually become the upper and lower halves. After squaring them up and leaving an eighth inch or so excess stock all around, their dimensions were recorded. Working from the centerlines of each, the locations of the two registration dowel pins were determined and their holes drilled/reamed. These dowels are primarily for convenience during machining since the ten close-fitting SHCS's that will eventually secure the halves together will also ensure they're consistently assembled. In the event that one of the workpieces has to be scrapped, the dowels can be helpful in creating its replacement.

Working on the bottom of the temporarily clamped-together assembly in the mill vise, the earlier recorded dimensions were used to locate and drill the holes and counterbores for the ten cap screws straddling the assembly's centerline. After tapping the holes in the upper half, the pair was assembled using all the fasteners. The remaining excess stock was then removed from the assembly while keeping the screws symmetrical about its centerline.

The upper half was then removed and set up in the mill with its interior surface facing up. After drilling and counterboring the holes for the block mounting screws as well as the top-end oil returns, its interior was completely machined. Excess stock was left on the bores for both the rear housing and front bearing to allow them to be finished in a later operation with the lower half. The bores through the three central webs, however, were finished to their final dimensions. These bores aren't critical since they only provide clearance around the bronze bearings that will be installed in the lower half.

Measurements were made on four of the five bores that I could conveniently access using a lathe-turned test bar. My purpose in doing so was to determine if the same machining technique can be used to create the more important bores that will support the three bronze bearings in the lower half. The results were better than I expected. Although all four bores came out .002" oversize, they were all in line within a couple tenths and, as best I could tell, were perfectly round. The test bar snapped into place with no light visible between it and any of the webs.

A bit of a disappointment, though, was that the bores' centerline was offset from the centerline of the workpiece by .003" due to a calibration error in the digital probe used to set the initial work offset. Almost the same error showed up on the x-axis causing its machining to be offset to the left by about the same amount. Fortunately, these errors have little significance in the top half since they only affect clearances.

Even though quite expensive and substantial looking, the probe I use seems overly sensitive to handling and periodically requires a painful alignment procedure. After recalibration, the errors were back to just under a thousandth.

The next step will be to machine the interior of the crankcase bottom half. The current plan is to use the same cutters and tool paths used for the upper half and to finish machine the bores for the bronze bearings. Similar to the upper half's machining, excess stock will be left in the bores for the rear housing and front bearing. - Terry


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## Ghosty

Will be watching this one as well.


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## e.picler

Congratulations, it will be another brilliant work from you.
Will be following with great interest. I also have the plans and the book.

Edi


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## kvom

No grass growing under your feet.


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## stragenmitsuko

I'm watching


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## mayhugh1

For the machining of the crankcase's lower half, I used the same tooling and tool paths used in my experiment with the upper half. With the probe error corrected, the centerline of the final result ended up within a thousandth of the workpiece's centerline. The holes for the cap screws that will secure the bearings in the webs will be transfer-drilled later when the bearings are in place.

The two halves were then assembled so the access ports could be machined into both sides. The sizes of those ports didn't look at all unreasonable on my computer screen, but I was struck by just how tiny they really are once I had actual parts in my hands. My hat's off to the builders who actually assembled their engines through them. They really aren't necessary with a split crankcase, but I didn't want to change the engine's appearance by leaving them out.

Although there's plenty of machining left to do on the crankcase, most of it will alter the shapes of its workpieces and make them more difficult to hold in a vise for later operations. The remaining crankcase machining won't be done until after the bearings are installed and the block is machined.

I iteratively machined some disks to use as gages for measuring the actual diameter(s) of the bearing bores. Remarkably, all three came out to be 1.5005" which was just a half thousandth over their target value. Measurements using the same gage disk in each web showed the bores to be in line to within a few tenths, and their center axes to be flush with the top surfaces of the webs. This was good news since it means the crankcase won't have to be line bored before installing the bearings. If I'm careful, and with some luck, I may also get away with not having to line bore the installed bearings.

The next step will be to machine the bearings. - Terry


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## petertha

Wow, impressive start. What alloy did you select for the crankcase?


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## mayhugh1

Petertha,
Sorry I missed your question. I don't know for sure what the alloy is since I used a piece of unmarked scrap, but it appeared to machine like 6061. - Terry


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## mayhugh1

SAE660 bronze was used for the split crankcase's main bearings. Machining began by skimming the 1-3/4" o.d.'s of a pair of three inch long rounds. After facing away half their diameters, they were bolted together and machined as an assembly to create a set of three clamshell bearings. Reserving one inch for a work-holding spigot, the material I used was long enough for a fourth (spare) bearing.

The top halves of the bearings came from the first workpiece set up on the mill. About half of its diameter was machined away except for its spigot. There were no critical requirements on this operation except for its surface finish, but the same setup was to be used for the second workpiece whose machining was a little more demanding. While fine-tuning the setup's accuracy and rigidity in preparation for the second workpiece, I managed to screw up the first workpiece. An already well-worked drop was scrounged up for a replacement that had barely enough excess stock to be usable.

In order to end up with a uniform height for the centers of all three bearings, the second workpiece had to be carefully fixture'd under the spindle so precisely half its diameter could be removed over the whole area of interest. Before starting, the y-axis DRO was zeroed over the axis of the workpiece so it could be used as a reference to locate the bearings' mounting holes.

Without disturbing the finished second workpiece in its setup, the first workpiece was temporarily clamped to it using a pair of hose clamps, and the bearings' mounting holes were drilled and counterbored. All eight holes were tapped through both workpieces so screws could be used to hold the assembly together for the remainder of its machining

The assembly was moved to the lathe and its o.d. finish-turned to match the bore measurement made earlier in the lower crankcase. The center was also through-drilled and reamed for the crankshaft's .500" journals. Unfortunately, the drill wondered off course in the deep bronze material leaving behind an unacceptable .006" runout. This was corrected using a sharp insert in a long skinny lathe boring bar. This operation was run under power feed with a spindle speed of only 60 rpm to eliminate chatter. When completed, the measured TIR was essentially zero, the bore was smooth and concentric with the bearings' o.d.'s, and I had a new spec for the crankshaft journals.

The boring bar was used to open the bore up to .514" since I had a length of .513" drill rod that I could use as a test bar to check the alignment of the installed bearings. It will also be used later to pickup the axis of the installed bearings when it comes time to bore the front and rear of the crankcase for its outer ball bearings.

Before parting off each bearing, its accessible face was finished using a gage pin in one of its bolt mounting holes as a center reference for the bearing's width. An internal oil groove was also turned inside the bore. Because of a small kerf allowance, each parting operation was started with a thin parting tool and then finished with a hacksaw (stationary spindle, of course). An expanding mandrel was then used to grip each bearing so it could be faced to its finished width.

Before separating them, the bearings' halves were numbered to insure consistent reassembly. The bearings passed a quick sanity check while seated, but not bolted, inside the crankcase with the test bar rotating freely.

The lower crankcase was returned to the mill so shallow counterbores could be machined at the locations for the bearings' mounting bolts and provide flat starting surfaces for their spotting, drilling, and tapping operations. The temporarily tapped holes in the bearing halves were reamed for clearances needed around their mounting bolts and then carefully checked under a magnifying lens for burrs that might interfere with the bearings' fits.

I found it best to install all three bearings along with the test bar as an assembly and to tighten the bolts as though I were installing a head. Just before finally tightening them, I used my upper body weight to bear down on all three caps which seemed to snap the bearings into place.

The test bar is only a thousandth under the bearing bores, and even though it was snug, it could be spun using a two-finger grip. I installed/uninstalled the combination several times to make sure its assembly was consistent. I did discover that all six bolts have to be fully tightened in order to spin the test bar indicating that one or more of the bearings is springing back out of its seat when its cap is loosened. After the assembly had been allowed to sit overnight, seating evidently improved a bit since the test bar spun much more freely. Measurements on the test bar showed it's in the center of the crankcase and parallel to its sides and bottom to within tenths.

I doubt that I'd get any better result with a final line boring operation, and so this wraps up work on the main bearings until the crankshaft is available which will likely require some minor fitting. Since its the safest place to store them, the bearings will be left installed in the crankcase for the remainder of the build. - Terry


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## mayhugh1

I received an email asking how I'd go about making and installing the main bearings in the split crankcase without line boring and without the use of CNC. Here is how I was originally planning to install a set of square bearings before deciding to make things more difficult by using the circular bearings:

Set the crankcase up in the mill, and using a cylindrical end mill, machine a rectangular slot through the three webs on the centerline of the crankcase. Machine a set of bronze blocks for press-fits in the slots. With the blocks installed, drill/thread a pair of bearing mounting holes through the blocks and into the crankcase for temporary holding screws for the next operation.
Using a .500" diameter ball end mill, mill a semicircular slot down the crankcase centerline that's .250" deep.
Machine a set of three bearing caps and secure them in the mill vise. Mill the same hemispherical slot through the tops of the three caps as a group, and then drill/ream the clearance holes for the bearing mounting screws.
Install the caps with either a test bar or the actual crankshaft in place and fit if required. - Terry


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## joerom

Thank you for posting this incredible work..It got me moving again..We all benefit from your efforts...……...


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## mayhugh1

There are two remaining operations related to the support of the crankshaft. These include boring the front of the crankcase for a front bearing and boring its rear for a circular housing that will contain a rear bearing and oil seal. Both of these bearings, though not identical, are ball bearings. The test rod running up through the central bronze bearings will be used to pick up the centers of both of these operations.

As long as it's properly located, the exact diameter of the rear bore isn't critical since the rear housing can be turned to fit. In fact, it'll be turned a few thousandths oversize to allow the housing to locate itself on the crankshaft before being tightened down. The rear bearing will be positively retained in a counterbore in the rear housing, and will be used to limit the crankshaft's aft thrust.

The diameter of the front bore is more important. The front bearing in the original design is retained in the crankcase by a one thousandth interference fit. I'll likely try to reduce this fit to a couple tenths to accommodate the split crankcase and then take advantage of the oil pump housing located inside the gear case to retain this bearing. This bearing can then be used to control the crankshaft's forward thrust.

In order to continue progress while still studying the gear case design, I tackled the simpler rear operation first. After indicating its center, the previously roughed-in bore was finished on the mill using a boring head. The mounting holes for the rear housing were also drilled/tapped. The mounting hole locations in Ron's design were selected to overlay the eight very deep mounting holes for the removable bearing webs. In my case, I used just four holes that were equally spaced about the crankcase halves.

The rear housing could then be machined. A starting workpiece was created having a healthy work-holding spigot that wasted more material than was actually used. Machining began in the lathe on the forward side of the housing so all its critical features could be completed in the same setup. This ensured the bores for the bearing and oil seal were concentric with the housing's mounting lip and that all three were normal to the flat mounting surface that will end up against the crankcase.

While still set up, I added a face groove for an o-ring immediately adjacent to the mounting lip in order to seal a potential oil leak between the two. This required a special tool ground from a .040" drill bit that was soft soldered to a piece of steel. This tool was originally made for a similar operation in the Knucklehead build.

After the rear housing's frontside operations were completed, the part was flipped around and gripped by an expanding mandrel inside the bearing bore so the rear machining could be started on the lathe. The rear side contains a circular groove with vertical walls that would have required a pair of right and left hand boring tools to complete on the lathe. Since the part had to be moved to the mill for a number of hole drilling operations, I decided to mill the channel instead of turning it.

The bearing was pressed into the rear housing, but the oil seal won't be added until much later at final assembly. With a bushing pressed onto the rear of the test rod in order to bring its diameter up to match the i.d. of the rear bearing, the rear housing was trial-fitted to the crankcase. After tightening the housing down to the crankcase, the test rod continued to freely rotate as it did before. - Terry


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## PhilWroundrockTX

Terry - The Design/modifications, tool making/modifications, and actual build are consistently amazing to me.  This one too is looking good!


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## mayhugh1

The front-end machining on the crankcase includes a bore for the front crankshaft bearing and a pocket for a gear case containing bearing recesses for a pair of driven gears. One of these gears will eventually connect the crankshaft to the gear tower, and the other will drive the water and oil pumps. The Offy uses a dry sump oiling system, and its pressure and scavenger pumps will eventually be located inside the gear case.

The crankcase was set up in the mill vise and indicated for access to its front end. The location of the bore for the crankshaft bearing was picked up from the test rod running through the three bronze bearings. The rear bearing in the rear housing and the starter bearing in the not-yet-machined front cover each have a bit of 'wiggle' room since they're bolt-ons to the crankcase. The front bearing, though, will be hard fixed to the crankcase and must be on the same axis as the main bearings.

I was concerned about attempting an interference fit for the front bearing since I was unsure of just how much interference could be tolerated while drawing the crankcase halves closed. If the flat surfaces of the crankcase halves don't completely close against each other, not only will there be an oil leak, but the axis of the front bearing may end up displaced from the axis of the main bearings and create a bind in the crankshaft. On the other hand, too loose of a fit will allow the bearing to spin in its bore and damage it.

Boring the perfect fit would require more luck than I was willing to risk and couldn't be tested without removing the crankcase from its setup. So, I opted for a one thousandth oversize bore that would provide a clearance that I could later shim out - something that's possible with a split bore. Aluminum foil as thin as .0005" is used by some candy manufacturers on their chocolate treats and can be a sweet source shim stock.

The remainder of the gear case machining was completed including bores for the two driven gear bearings which were also bored a thousandth over. Although I'd have preferred zero interference fits for these bearings, the front cover will eventually contain a matching pair of bearings, and there's no way to align bore them in pairs. The front cover's wiggle room will likely be taken up by the starter bearing, and unavoidable errors in locating the positions of the two bearing bores will make the cover difficult to assemble unless the bearings have some wiggle room of their own. When assembled, there will most likely be enough friction created by positioning errors to prevent the gear bearings from spinning in their bores.

A trial assembly of the crankcase halves around the front bearing was successful. I found that adding a thousandth shim around only the upper half of the bore allowed the crankcase to close tightly around the bearing and allow the thousandth-under test rod to freely rotate inside all five bearings.

One of the things that attracted me to the quarter scale Offy is its faithful adherence to the original engine's great looking appearance. The painstaking detail in many of the model's individual parts will provide a number of interesting mini-projects with their own short term satisfactions that'll help keep me interested in such a long term project.

The first of these parts is the front cover. It encloses the gear case and contains the starter bearing which will be the sixth crankshaft bearing. Other than rearranging its mounting bolt pattern to accommodate the crankcase split, I duplicated Ron's design. It's finished periphery will provide a template for the later machining the crankcase's lower sloping sides. The magneto mounting bracket was an integral part of the casting for this part in the original engine. Ron attached a separate bracket to the cover with hidden screws and blended the seams with fillets of metal-filled epoxy. I used my Tormach to machine the cover and bracket as a single part. There isn't room for a front shaft seal, but Ron included a groove for a 12 mm x 1mm CS o-ring around the bearing's i.d. that should be effective against oil leaks.

My first serious mishap in this project occurred while removing the overhanging excess stock from the rear of the cover in preparation for its rear face machining. The large multi-insert facing cutter that I was power feeding in my manual mill grabbed the overhanging lip and pulled the end of the part partially out of the vise. This stalled the cutter until I was able kill power to the spindle. There was no damage to the already machined top surface, but there was a deep gouge on the part's back surface. With all the effort invested so far, I felt there was nothing to lose by trying to salvage the part with a tig-welded repair. The welding created some of its own damage to the topside surface, but the final result was much better than expected with no visible trace of the repair.

As it turned out, my biggest concern was with the mill itself since I had to hammer the R8 cutter out of the spindle using a long drift in place of the draw bar. The cutter had spun inside the spindle bore and was jammed against what remained of the collet key pin. Fortunately, TIR checks on the spindle bore showed there was no apparent damage, and re-tramming the mill seemed to return things to where they were before the accident.

With the cover installed on the crankcase, there's still no sign of binding of the test rod, but the friction of the cover's o-ring has added significant drag. - Terry


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## petertha

mayhugh1 said:


> . Aluminum foil as thin as .0005" is used by some candy manufacturers on their chocolate treats and can be a sweet source shim stock.



Can't you visualize Terry in a chocolate shop - "I'll take 20 feet of that foil please .... aaand I guess 2 of those Eau Claire's to go... in a box please!"
Glad your scary incident didn't damage the machine. Nice TIG repair.


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## PhilWroundrockTX

Again precision and results beyond my comprehension capabilities - AMAZING! What is the surface finish inside/out on the front cover after the TIG repair? Looks perfect - almost like bead blasted?


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## mayhugh1

Phil,
It is bead blasted. The texture left behind by the grit I have (whatever it is) seems to do a good job of simulating  a casting at this scale. Plus, it hides machining marks with minimal effort. - Terry


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## gmac

Terry;
If you wouldn't mind could you briefly outline your equipment/materials/method for bead blasting? Please and thank you. Your builds, for me, are like an educational PhD!! 
Cheers
Garry


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## mayhugh1

Garry,
I have a 24" x 24" x 36" bead blaster cabinet bought 25 years ago from Eastwood Products. It's no longer sold, but equivalents are available from Harbor Freight. I use glass beads purchased from the Local Harbor Freight which are, I believe, 80 grit. I've been using the same media for over 20 years and so its probably a bit finer than when originally purchased. The air supply is 90 psi from a large compressor.


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## mayhugh1

So far, I've been focused on parts associated with the crankcase in order to look for problems that may have been created by the split. The cylinder block should be the last of these and, when completed, the remainder of the build will pretty much follow Ron's original design.

The reason for replacing the long studs running through the block with separate upper and lower mounting screws was to simplify the engine's assembly and make head gasket servicing less traumatic. This creates the need for flat surfaces under the heads of the head bolts that will eventually run up through the roof of the block. Since most of the block's interior will be gutted, the real issues are only with the screws in the block's extreme outside corners. The heads of these four cap screws will wind up partially inside the front or rear walls of the block, and so one of the block's first machining operations was to create surfaces for them.

After preparing a starting workpiece with finished outside dimensions (the block's sloping sides will be machined later), four holes were partially drilled up through its bottom for the heads of the cap screws that will be in the corner head bolt positions. Their flat surfaces were created by running a same-size drill bit with a ground-flat nose back into the holes. The holes were then back-filled with aluminum plugs that were turned, coated with Loctite, and pressed in place leaving about an inch gap inside the workpiece for later insertion of the screws.

After the Loctite cured, the plugs were blended into the block's bottom surface with a light facing pass. The block was then set up in the mill with access to one of its sides and its interior hogged out.

Sixteen 3-48 blind tapped holes were then drilled into the bottom of the block to attach it to the crankcase. Since the block will eventually contain coolant, these holes don't penetrate its interior. Sixteen mounting screws sounds like a lot, but they may allow me to do away with the o-ring I had been planning to use to seal the block to the crankcase. The cylinder sleeves will be sealed to the block, but not to the crankcase, and so there's a potential for an oil leak through the seam between the two. The top of the block was then drilled/reamed for the head bolt clearances, the oil return tubes, and the water passages. The 5-40 cap screws that will be used for the head bolts were trial-fitted in the four corner positions.

After initially roughing them in, the bores and counterbores for the cylinder sleeves were finished using a fixed-setting boring head. The Offy's head gasket history is a bit tarnished, and some of Ron's own experiences are detailed in a section of his manual. Some of these problems may be caused by the minimal clearances between the head bolts and the tops of the cylinder sleeves. Although I was able to massage the locations of the head bolts and increase these clearances from .016" to nearly .050", after holding an actual block in my hands, I regretted not reducing the diameter of the sleeves (and pistons) to pick up a little more margin. Finally, I machined a couple .020" Teflon head gaskets to make sure I'll be able to hold onto the clearances I do have. - Terry


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## Mike Henry

Would silicone rubber gaskets be an option for model IC engines like the Offy?


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## mayhugh1

Mike,
Silicone rubber would probably work well around the coolant passages and oil return holes, but I'm not sure how well it would stand up to combustion pressures. Silicone also dissolve in gasoline  and so that would need to be considered as well. - Terry


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## Mike Henry

Terry,

I didn't know that silicone was affected by gasoline so that's a new learned thing for the day.

I was thinking that silicone is easy to laser cut with even one of those hobby lasers and doesn't suffer from cold flow the way that Teflon can, at least to my limited knowledge.  They both have similar upper temperature limits as well.  That would make it easy to cut complex shapes with less effort.  As you say, it could still have application where fuel is not involved.

Beautiful job on the Offy, by the way, and it looks like you still getting good use from your Tormach mill.

Mike


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## gmac

Terry;
Thanks for the reply on bead blasting.
Cheers Garry


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## mayhugh1

Much of last week was spent modeling the complex gear tower which includes a pair of front and rear halves, end caps, and a tightly integrated take-off block for the magneto. After a lot of frustration, I still don't have an assembly that I trust to begin machining. My wife would say it's because I can't follow instructions, and to an extent she'd be right. I've found a few online screen shots from those that have gone before me to be invaluable.

I took a break from the tower and returned to removing chips from the crankcase since its modeling had been completed. With the foundational machining done, I felt it was safe to finish up the external profiling that will finally give the crankcase its distinctive shape. Other than several o-ring grooves that are still planned, its bottom and both sides were finish machined. The bottom was milled using a tiny ball cutter in order to create an array of cooling fins with rounded tips and filleted roots.

The exhaust fan on my bead blasting cabinet is currently out of service, and so the photos show the machined surfaces straight off the mill. Some cleanup will be required, but that will become more obvious after the surfaces are bead blasted for the first time. - Terry


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## mayhugh1

The crankcase side covers are nearly identical to those on the full-size engine and add realism to the model but a couple tricky parts to machine. The covers contain an array of tall cooling fins like those on the bottom of the crankcase but, instead of being flat, they're smoothly contoured over a pair of bulging pockets that hold the crankcase breathers. Ron provides instructions and a design for the shop-made cutter that he used to make his covers, but I wasn't certain of my ability to duplicate his manual effort. Examples are out there from others who have, however.

My initial modeling was done expecting to follow Ron's method, but the radius'd fins on the crankcase turned out so well that I decided to try something similar on the side covers. The design I eventually arrived at created so many surfaces that my ancient XP computer had barely enough resources to handle the resulting CAM load. The total machining time worked out to be nearly eight hours per cover with much of it required by a 15k rpm 3/32" ball cutter running at 17 ipm.

A piece of MDF temporarily glued to the bottoms of the starting workpieces prevented the finished parts from being damaged when they were finally cut free. It also dampened some potential chatter-causing vibrations during the large-tool roughing and semi-finishing steps. Due to record setting 100F+ days we've been having down here in Texas, the machining was spread out over several evenings to reduce the probability of me or the Tormach suffering a heat stroke. The photos show a few of the machining steps.

The covers not only seal up the engine's access ports, but they also contain the crankcase breathers. Ron scaled the engine's original crankcase ventilation scheme right down to the oil baffles inside the breathers. Unfortunately, its performance didn't scale as expected, and the atmospherically vented breathers created a frustrating oil control issue. Ron's eventual solution was to vent all four breathers into the engine's oil tank.

The breathers were machined from a single piece of stock without their internal baffles. In order to minimize the number of plastic hoses later on, I connected the two breathers on each cover together with a short length of thin wall stainless tubing. Hoses will eventually connect the rear breathers to the oil tank. The o-rings that I had originally planned to use to seal the covers to the crankcase were replaced with simple .010" thick teflon gaskets. - Terry


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## petertha

Very nice. 
I've often wondered, do you happen to know if Ron had access to a real Offy to touch or take closeup reference pics? Or was this design entirely based on books & such? Certainly captures the striking features that's for sure.


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## mayhugh1

Ron told me he didn't have access to an actual engine but used published photos and info about the engine to come up with his design. I have to agree - it had to have been an incredible amount of work. 

After putting up my last photos, something about my breathers doesn't look correct. I just discovered that I transposed two dimensions and machined them too short. So, I'll be doing them over. It's a good thing it wasn't me coming up with the original design. - Terry


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## RonC9876

Terry: I thought I would let you know that I only vented the front cover of the engine to the oil tank. The rear breathers were blocked off to the atmosphere. The direction of the engines rotation tends to throw oil against the front cover. That is where oil wants to escape while running. Venting the rear cover to the oil tank wasn’t necessary. Can’t hurt though and keeps things symmetrical I guess.
As far as what I had to work with designing the engine; I had only photos and the article in Hot Rod magazine showing a 270 being assembled by an Asian fellow. I believe his name was “ Chickie Hiroshima” or something close to that. I am bad with names. He apparently worked for Offenhauser at the time. This would have been back in the 50’s. The article was most informative. It gave many of the dimensions of journal sizes, cam timing diagrams, listings of various things that could be ordered special to make an engine unique to the person ordering one. I should be able to come up with the name of the guy who put the article together, but as I said, I am bad with names. He wrote for Hot Rod magazine and wrote a book on souping up the small block Chevy V-8 engine. My older brother used to drag race and he relied heavily on this book when building his engine. He even aquired a Lathem blower that was next in line to be installed but he was drafted before he ever got around to that. This was in 1963 or 64. Good times with many memories.


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## RonC9876

I checked with my brother. The guy’s name was Don Francisco.


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## mayhugh1

Ron,
Thanks for the reply. I've misunderstood your email to me last month:

'The next thing I changed was the design of the crankcase breathers. Again trying to follow the prototype, I tried controlling the oil entrapment in the blow by with internal baffles. Due to the reduced distances involved with the model, oil would come out the breathers especially when throttling down from high speeds. It takes a while for the scavenge pump to catch up with all the oil in suspension and the oil level in the crankcase would rise temporarily, and would push out the breathers. I solved the problem by eliminating the baffles and piping the breathers on each side together and running a fuel tubing line from one breather back to the oil tank under the base. Air holes to the atmosphere were eliminated. The engine breathes into the oil tank."

But just to be clear,  since I'm getting ready to re-machine the breathers, there is a left and a right cover and a front and a rear breather on each one. Are you saying that you vented only the front breather on the left cover to the oil  tank and then blocked off the other three breathers? Thanks. - Terry


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## RonC9876

Sorry for the mix up. The two breathers on the one cover are tied together as you have done and vented to the oil tank. I call the cover on the intake side of the engine the front cover and the one on the exhaust side the rear cover. That isn’t correct terminology, but just how I mentally think of the engine. I am always looking at the engine from the intake side and think of that as the “ front” of the engine although it is not. I should be more careful as to how I explain things.


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## mayhugh1

Thanks Ron. That clears it up. - Terry


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## mayhugh1

I re-machined the four breathers so they're now at the proper height above the side covers. Both breathers on the port side are functional and plumbed together so they can be vented into the oil tank per Ron's recommendations. The breathers on the starboard side are now only cosmetic.

The block covers, like the side covers, are finned and were machined similarly; but the fin spacing is only 1/16" compared with 3/32" on the side covers. This spacing was designed for a slitting saw, and so the 1/16" ball end mill that I used to radius the fins extended the machining time even further. Since it's flat, the port side cover is fairly simple, but the starboard cover is complicated by its internal coolant manifold and the integral flange required for the water inlet pipe. The manifold is a lengthwise milled cavity in the backside of the cover that's permanently enclosed with a J-B Welded ported plate. I left a .020" thick glue line all around the cover for the epoxy - something learned during my previous build. My cover plate has a dog ear covering up a small machining error in the cavity.

The block will be full of coolant, and so the cover seals require thought. Each cover will be secured with forty 0-80 cap screws, but those by themselves may not be enough to provide a water tight seal. Since I prefer using sealers only as a last resort on models, I originally planned to o-ring the covers to the block, and my initial modeling included grooves in the block for .040" o-ring cord. With so much machining already in the block, I decided later to move the grooves to the covers. However, after completing its machining, the thin port side cover wound up with some warp that would have made its grooving difficult. In the end, I settled on a pair of .010" thick Teflon cover gaskets.

The sides of the block aren't parallel but have 1.7 degree sloping sides that may have their origins in the draft angles required by the original engine's sand casting process. I delayed machining these sides until after all the other block operations were completed since the resulting trapezoidal shape would have been difficult to fixture. I machined the block's sides on my manual mill and then used the Tormach to drill the eighty .047" cover mounting screw holes. In an attempt to keep the fixturing consistent, I first machined a pair of 1.7 degree angle blocks that I used to support the part in both mills' vises.

When it came time to drill the holes, I found fixturing the block to be more difficult than expected. With the part resting in the vise on the stacked pair of 1.7 degree angle blocks, its small-area ends weren't sufficient by themselves to maintain alignment of the block along the mill's y-axis as the jaws of the vise were tightened. Even after clamping a machinist square to the fixed jaw of the vise for use as a y-axis reference edge, some trial and error with paper shims was required to get the part indicated properly.

I picked up a lot of small hole tapping experience during the Merlin project, and so the block's eighty 0-80 tapped holes weren't a concern. One of the photos shows the simple tap holder and support block that I used along with plenty of WD-40 to tap all eighty holes with the same tap and without incident.

Finally, the water inlet pipe was bent from 1/4" 303 tubing using a three wheel Rigid bender before silver-soldering it to a stainless steel flange. A Teflon flange gasket completed the assembly. - Terry


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## johnmcc69

Beautiful work!
 I just LOVE that bead-blasted finish!

 John


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## RonC9876

Harry Miller knew how to make an engine pretty as well as functional. A design that was hard to beat and has stood the test of time.


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## PhilWroundrockTX

Looking Great! Thanks for the detailed description of how it's done. Then looking at the pictures one can really appreciate all the hidden precision detail and effort required to produce such an outstanding piece.


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## mayhugh1

The gear tower is a fairly complex assembly of gears designed to connect the overhead cams to the crankshaft. The tower also includes a 'magneto block' containing one of two sets of bevel gears that will eventually drive the magneto. The water and oil pumps will be driven from a separate 60 tooth take-off gear located below the crankshaft. The Offy's gears span four separate subassemblies not including the split crankcase, and their exact locations will be affected by the use of any gaskets or sealers between these assemblies. Because of the large number of high rpm gears and their loads, accurate tooth profiles and spacings will be important for their longevity.

Before finishing the tower's modeling, I thought it best to have the actual gears in my hands so their running spacings could be verified and adjustments made to the model if necessary. I've twice before run into issues with new gear cutters producing poor tooth profiles although these were probably a result of mislabeling. Except for the scavenger oil pump, the Offy gears are all 48 DP. I have several known good 48 DP cutters, but unfortunately a new one had to be purchased for this build.

Several of the gears are identical, and so it made sense to slice multiple copies of the same gear from long pre-machined blanks. Ron recommends making the gears from casehardened mild steel as was done in the full-size engine. However, I have no experience with casehardening and was concerned about using the gears as learning tools. With no way to control the process or to measure the final result, I was worried about over-hardening and embrittling the tiny gear teeth especially those on the 60 tooth gears. Instead, I machined most of the gears from 1144 which has a Rockwell C hardness of around 25. The hardness of mild steel gears (even those purchased from Boston Gear) are equivalent to only 1 or 2 if they were to be compared on the same scale. Stressproof's tensile and yield strengths (important specs even under a hard skin) are twice those of mild steel.

The stresses that the crankshaft sleeve gear will see are a bigger concern to me especially since physical limitations require it to be attached to the crankshaft using only Loctite. I machined this gear from O-1 drill rod which, after a 1475F quench, was tempered at 375F. Its final hardness and tensile strength should be roughly twice that of Stressptoof, leaving its Loctite bond to the crankshaft as its weakest link

As often seen on commercial gears, I typically chamfer the corners of o.d.'s of my shop-made gears. I left the Offy's gears, though, with full width tooth contact for a bit more durability. The widths of the gears were finally finished on a surface grinder.

The oil pump gear stock was machined from 360 brass. The pressure pump gears are also 48 DP, but the scavenger gears are 32 DP. The individual gears will be parted off from their blanks later when I'm more familiar with the lubrication system. A set of shafts and spacers finished up the nuisance parts associated with the gears.

The nose of the test rod that I've been using as a dummy crankshaft was machined to temporarily accept the hardened sleeve gear so the fits of the two 60 tooth driven gears could be verified. The meshes of these two gears with the crankshaft gear span the split between the two crankcase halves, and from previous measurements I knew the distances between the gear centers were on the order of a thousandth within theoretical. The three gears turning freely with minimum backlash was something of a minor milestone for the project.

A fixture for testing the 40 tooth gears was also machined to verify the meshes and spacing between them. Its design was small subset of the gear tower and was also used to tweak the end mill parameters for the bearing fits. These three gears also turned freely with minimum backlash at their theoretical spacings.

Finally, a bearing removal tool was ground from a long hardened hex wrench. Counterbores will be added behind the bearings in the gear tower so the bearings can be removed as necessary using this tool. These counterbores and the tool were also part of the testing done in the above fixture. - Terry


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## RonC9876

Terry: after about a year or so of running with the case hardened gears, I had a tooth break off one of the gears. That tooth went through most of the gear train and wiped out most of the rest of them. I machined another set from 1144 . Ten years later, the second set has held up very well. Like you said, one overhardened tooth was all it took to make a mess. Live and learn.


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## mayhugh1

RonC9876 said:


> Terry: after about a year or so of running with the case hardened gears, I had a tooth break off one of the gears. That tooth went through most of the gear train and wiped out most of the rest of them. I machined another set from 1144 . Ten years later, the second set has held up very well. Like you said, one overhardened tooth was all it took to make a mess. Live and learn.



Ron,
Thanks for the reply. I may re-think the crankshaft gear now. - Terry


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## petertha

Hi Terry. What is your procedure for verifying tooth depth of cut on these little gears? For example do you zero contact the cutter to the stock, in-feed X amount according to the book value & that's it? Or maybe cut some teeth on either side of the stock at some slightly shallower depth, then (somehow?) measure & adjust in=feed vs. the target from there? I've never done any, hence the question.

So the conclusion on material is to use 1144 SP and leave it at that unhardened - no heat treating of any kind?


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## mayhugh1

petertha said:


> Hi Terry. What is your procedure for verifying tooth depth of cut on these little gears? For example do you zero contact the cutter to the stock, in-feed X amount according to the book value & that's it? Or maybe cut some teeth on either side of the stock at some slightly shallower depth, then (somehow?) measure & adjust in=feed vs. the target from there? I've never done any, hence the question.
> 
> So the conclusion on material is to use 1144 SP and leave it at that unhardened - no heat treating of any kind?


Peter,
I cut gear teeth according to the book. I make sure the diameter that I assume for the cutter includes its runout in its holder. The blank is fixture'd so its runout is less than a thousandth. The total depth of cut for the Offy gears was .045" which I did in three passes: two at .020" and a final at .005". I always verify the result afterwards by making sure there is no more than a degree or two of backlash with the  gears meshed at their theoretical running spacing. 

I'm still deciding whether I'll re-temper the crankshaft gear to make it a bit softer, but the others will definitely be left in 1144 especially after Ron's comment. - Terry


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## mayhugh1

The gear tower is a multi-part assembly consisting of a front and rear half topped by a pair of cover caps. After installation, the circular openings at the top of the tower should wind up concentric with the camshafts so their driven gears will mate properly with the driving gears inside the gear tower.

Backlash will accumulate from six tandem-driven gears between each camshaft and the crankshaft. If care isn't taken to properly mate each gear pair, excessive slop during throttle blips may create shocks that over-stress the teeth of the gears especially those at the ends of the train.

The eventual mates with the camshaft gears will be affected by the stacked assembly of the upper crankcase half, the block, the head, the cam boxes, and the gaskets between them. I already had a fairly complete model of the head, but a cam box model was still required to verify the gear mates with the camshafts. With no gaskets, its model showed concentricity offsets on the order of .005" with both horizontal and vertical error components.

A .020" thick Teflon head gasket is currently planned, and the head will be shaved by that amount to accommodate it. The total head height can also be adjusted as needed to reduce the vertical components of the concentricity errors. Currently, a .0025" thick vinyl gasket will also be used between the block and the upper crankcase half. This gasket material will be the same craft vinyl:

https://www.amazon.com/gp/product/B01N7YH58Y/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1

used for some of the gaskets in my previous Knucklehead build. It turns out that .0025" will exactly compensate for a machining error stack-up already measured in the height of the block above the crankcase. My current modeling shows that a .005" Teflon gasket between the cam boxes and the head will reduce the vertical and horizontal offset errors enough to drop the concentricity errors to around .0025".

Machining errors in the head and cam boxes will additionally affect the final choices for the gasket thicknesses. Modeling showed it was safe, though, to machine the gear tower pretty much according to its original drawing. I did, however, adjust its height for a .0025" gasket between it and the crankcase. Some tweaking to the head and/or cam boxes may also be required to achieve acceptable mates with the camshaft gears.

The rear half was the first portion of the tower to be machined. Since both of its sides were to be machined, the part wasn't cut free from its workpiece during its front side machining. Instead, after milling around its periphery down to about half the part's thickness, the groove between the semi-finished part and the workpiece was filled with epoxy. The workpiece was then flipped over so the backside machining could be completed with the epoxy holding the part in place. When the backside machining was completed, the part was heated to 300F and the part cleanly released.

With the completed rear half of the gear tower resting in place on the crankcase and with a .0025" gasket between them, the first critical gear mate (60 tooth gear in crankcase mated to the 40 tooth gear in gear tower) was checked and appeared to be nearly ideal with the gears turning freely with just a hint of backlash. The tower was then fully populated with gears, and all turned freely. The backlash at the ends of the two gear trains appeared to be just a fraction of a degree. 

The next step is to finish the modeling of the tower's front half so the actual part can be machined. - Terry


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## petertha

Terry, once the craft vinyl (Oracal  651) is cut, do you make any attempt to dissolve the adhesive prior to installing on the metal face? I can see on one hand where some tackiness might be good in that it stays put, but then maybe the opposite when you remove. Are they reusable?

The cumulative gear backlash during throttle variation is a really good point. I'm still not clear on your mitigating procedure though. Was the test fixture somehow variable that you could tweak the center to center gear distances right? And then once satisfied, you somehow measured resultant shaft centers & replicated these using DRO to the real part? In the test fixture do you measure play gear by gear, like hold one gear, wiggle the the other, adjust... then proceed down the line?

_A fixture for testing the 40 tooth gears was also machined to verify the meshes and spacing between them. Its design was small subset of the gear tower and was also used to tweak the end mill parameters for the bearing fits. These three gears also turned freely with minimum backlash at their theoretical spacings._​


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## mayhugh1

Petertha,
I don't try to reuse the gaskets. It's easier to replace a damaged one with new material. Once it's in place, I treat it as a new permanent surface on the part.mSo far, I've used this stuff only in unpressurized areas to prevent oil leaks where sealer might have typically be used.

With respect to the gears, the particular test set I used was only to verify the gears would turn smoothly with a hint of backlash at their theoretical spacings. If they hadn't passed that test they would have been re-made. 

I have made test sets in the past where I could vary the distance between the gears to see what my margins were around the theoretical spacing. There were too many cascaded gears in the Offy tower to start playing with spacings to conform to poorly made gears though. - Terry

p.s. Another effect of gear slop can be large valve timing changes during sudden speed changes. Their effects are probably overwhelmed by the carburetor vacuum changes though.


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## minh-thanh

mayhugh1 !
Can you show me how to make  a surface like that?
That surface is great !


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## mayhugh1

minh-thanh said:


> mayhugh1 !
> Can you show me how to make  a surface like that?
> That surface is great !
> View attachment 111737


Minh-thanh,
Thanks for the complement. After machining, the surface was glass bead blasted. There's more information about my particular setup, which is nothing special, several posts above this one where someone else asked a similar question. - Terry


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## minh-thanh

mayhugh1 said:


> Minh-thanh,
> several posts above this one where someone else asked a similar question. - Terry


I missed that.
Thanks mayhugh1 !


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## mayhugh1

The backside of the front half gear tower contains a mirror image of the rear half's six bearing and gear pockets. An additional complication is the magneto drive block which is a forward extension of the tower and contains the right angle drive components needed for the magneto driveshaft. In the full-size engine, this block was an integral part of the tower's front-half casting. To simulate the original engine's appearance, Ron suggests bolting the magneto block to the tower and blending the two together with aluminum-filled epoxy fillets.

I came up with two more approaches that were considerably more complex but avoided the need to color match epoxy to the tower. The first approach was to split the drive block housing into two pieces. The rear piece, including its blending fillets, would be machined integrally with the gear tower. The front half, a separately machined part would be bonded to its rear half with screws and a nearly invisible Loctite seam.

The second approach, and the one I ultimately used, was to machine the entire block as part of the tower. This required considerably more machining on a hefty workpiece that was turned mostly into chips. Since the block stands over a portion of the tower, the workpiece had to be repositioned three times to get the needed spindle accesses. The third setup was required to machine some cosmetic features on the side of the block. Inevitable errors accompanied the re-referencing and tool changes that were needed, and a couple seams that couldn't be hidden with bead blasting required some manual cleanup. The long reach finishing cutters that were needed inside the deep workpiece created their own issues with surface finish and machining time.

The front-half tower's first machining operations were the bearing and gear pockets on its backside. After verifying their fit with the already completed rear half with all the gears, shafts, and bearings installed, the workpiece was flipped over for its lengthy front side machining. More than half of the nine hour machining time was spent roughing in the shape of the tower. After the finishing operations, a quick-dry epoxy was poured over the periphery of the part to keep it connected to the workpiece during its final machining.

A portion of the workpiece had to be cut away to gain access to the port side of the drive block. This side contains some contouring added to the design to smooth the transition of the block into the tower. Once this area was machined, the part was returned to its original position with its backside facing up so the periphery could finally be machined. The front half of the gear tower has a convenient bead around its periphery that allowed the part's front and back surfaces to be machined and the cut free of its workpiece without leaving an annoying seam. This bead, a part of the original engine's casting, was probably used to help remove the front tower's half during maintenance/disassembly. This final operation separated the part from its workpiece with a slot milled around the outside of the bead. The epoxy kept it safely attached to the workpiece until it could be removed with heat. After a half hour in a 300F oven, and while still hot, the (Devcon 5 minute) epoxy could literally be rubbed off the part. - Terry


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## RonC9876

Looking good!


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## propclock

You just made my morning! 
I always enjoy following your builds. Very inspirational. 
I guess I should make something this morning before they turn my power off.
California.


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## bobden72

I have the drawings and the book for building the "OFFY" and is going to be my next build.  After seeing your build though  I don't know if I can do it justice but will give it a damn goo try.


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## mayhugh1

The cam gear covers bolt onto the upper ends of the gear tower and will eventually enclose it around the camshafts' driven gears. These covers are small in size and rich in detail and will be troublesome parts to machine. They'll wind up in prominent locations at the top of the engine, and so the effort they'll soak up won't go unnoticed. I scrapped four parts and the better part of a week coming up with a pair of covers that I was satisfied with. Again, my efforts were focused on CNC machining them from single blocks of metal. Ron describes a somewhat simpler method for creating them from several manually machined pieces.

I started with a pair of 2" x 2" x 3/4" aluminum blocks and was able to mill most of the parts' intricate features while working on their topsides. Once I completed this step on my first pair of parts, I noticed the covers' thicknesses were .005" less than that of the assembled gear tower. Both the covers and the tower seemed to match my understanding of the drawings, but I felt the thicknesses should probably match. So, I added another .005" to the cover design and started over with a second pair of parts.

Work holding issues showed up during the second step which involved opening up the sides of the parts to accept the cam box and end plate covers. This step included cutting the parts free of their workpieces on their exact centerlines. I built up temporary epoxy bridges to hold the parts in place during the milling operation that would free them from their workpieces. But, with little excess stock to adhere to, the epoxy failed on both parts and the cutter scarred them as they were freed. Yet another pair of parts had to be started.

The final machining steps opened up the interiors of the covers for the clearances needed around the cam gears. This was done in two operations using 1/8" diameter end mills and working down through the bottoms of the parts. The first roughing operation was performed with a cylindrical cutter, and the finishing operation done with a ball cutter. The finished diameter of the opening had to be increased slightly beyond the dimension given in the cover's drawing in order to accommodate the fillet left behind by the finishing cutter.

After machining, the covers' mounting screw locations were transferred to the temporarily assembled gear tower, and its eight 2-56 holes were drilled and tapped. The bores for the end plates were also finished using a boring head, and their 0-80 mounting screw holes were drilled and tapped. The pair of openings on the backside of the assembled tower shown in the last photo may look mis-machined, but they're designed to fit around the ends of the sheet metal covers that will later enclose the cam boxes. - Terry


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## Gabe J DiMarino

My one piece cover.


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## nj111

I do enjoy reading your build threads, all very informative, excellent photography,  lots of great ideas, thank you for sharing your knowledge and techniques!


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## mayhugh1

I was hoping to tie up the ribbons on the gear tower and have at least one fully machined, gasket'd, and working assembly with moving parts that I could show off. However, the plans call for a trough to be machined into its backside for the purpose of carrying pressurized oil to the engine's top end. Since I'm not comfortable with beginning work on the engine's oiling system by starting in its middle and working outward, the tower will have to be torn down later for some additional machining.

The tower/drive block combo has a number of cover plates that are easy to machine and, after polishing, add nice contrasting touches to the tower's simulated cast aluminum surface finish. The more challenging parts, though, are the internals of the magneto drive block. Ron's parts list calls out what are now obsolete Small Parts numbers for the miter gears that he originally used. However, I wasn't able to cross-reference them to currently available parts. The BOM shows them as 48 DP, but the G479-Y and G461-Y eighteen tooth 48 DP miters currently available from Boston gear appear to be too small to handle the modifications implied in the drive block's assembly drawing.

I happened to have a pair of Boston Gear G462Y 32 DP 16 tooth gears left over from an earlier project that I decided to use. I increased their original .188" bores to .2495" and turned down their o.d.'s from .536" to .480" in order to fit them inside the drive block's half inch bore. My modifications were very similar to the ones shown in the drive block's assembly drawing, but I was initially puzzled about why the drawing also seems to show most of the output shaft's gear hub machined away.

It was then that I realized that my drive block's housing is wider than it's supposed to be. There are several dimensions associated with the drive block that are left for the user to fill in, and evidently the value that I'd estimated for its width from a Xeroxed photo in the manual was incorrect. The reason why this width is important is that there must be room between the drive block and the magneto for a faux coupler between the two. Embedded in this coupler will be a pair of magnets needed to trigger a Hall device located on the side of the magneto. (Although the manual recommends making the magneto's input shaft from stainless steel in order to minimize field distortions around the magnets, I made the drive block's output shaft from stainless as well.)

Rather than re-machine the drive block, I designed a new inboard cover that would allow me to move the output shaft's inboard bearing entirely within the housing. I'm fairly sure I picked up enough space for the coupler, although it too may require a minor redesign. These changes turned out to require shortening the hub of my miter gear after all. It's probably important that these gears be bored for tight press-fits onto their shafts since, after shortening, there may not be enough surface area for Loctite to adequately hold them, if loosely fitted, in place. The inertial loads of the coupler and magneto won't be insignificant during abrupt speed changes at the rpm's this engine will be capable of.

Fitting the gears inside the drive block would have had to be done blindly, so I cross-bored a scrap piece of metal to try to duplicate it. After opening an inspection window on its top, I was able to iteratively modify the gears and begin the shimming process for an optimum engagement. The fixture got me into the ballpark, but I had to complete the process inside the actual housing. In previous miter gear (distributor) applications, I've had gravity to help out with setting the engagement depth for silky smooth low-backlash operation. Gravity seemed to work against the right angle drive's engagement, however, and setting up its gears was a lengthy and tedious process.

The drive block's components complicate the assembly and disassembly of the gear tower. Although the miter gear and its 20 tooth drive gear must be hard pressed onto the block's input shaft, the bronze shop-made bearing which is captured between the two must turn freely on the shaft and slip into the drive block during assembly. Simultaneously, the rear end of the input shaft must slip into the ball bearing located inside the rear half of the gear tower. I've included photos of my two shaft assemblies showing the shims I used. I didn't include any dimensions since they would apply only to my particular (mis-machined) drive block. The output shaft's outboard bearing is a slip fit inside my drive block, and so I added a spacer between it and the nose of the miter gear to prevent the bearing from walking inward during normal operation.

The next step will likely be to machine the cylinder liners so I can finish up the block. - Terry


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## Scott_M

Hi Terry
As always, beautiful work !
But I really wanted to thank you for sharing your mistakes as well  and the really awesome and clever engineering used to right the wrong. You always come up with an elegant solution.

Many thanks for sharing !

Scott


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## mayhugh1

The Offy's cylinder sleeves will be sealed inside the coolant-filled engine block using Loctite. Each sleeve has a machined ring around its top end that will fit inside a recess in the head. The bottom ends of these rings will be sealed inside similar recesses that have already been machined around each bore in the top of the block. Unlike the Merlin that used these rings for metal-to-metal seals, the Offy will use a head gasket. When machined and assembled according to the drawings, up to .125" of each ring will wind up inside the head depending upon the thickness of the head gasket. This means that matching the heights of the sleeves above the Offy's block won't be critical as it was in the Merlin, but each sleeve will have three diameters and an inside corner that will require careful machining.

The drawings specify Stressproof for these sleeves which, in comparison with 12L14, offers improved corrosion resistance in a liquid cooled engine. During efforts with the Merlin's Stressproof liners, I struggled to obtain bores with surface finishes that wouldn't require inordinate amounts of honing.

Stressproof turns easily on both my 9x20 Wabeco and 12x36 Enco lathes, and fine surface finishes are easily obtained using tooling with carbide inserts designed for steel finishing operations. When boring, however, the rigidity of the cross slides on both lathes is lacking, and the resulting chatter at the ends of typical boring bars that fit my lathes limits the quality of a finished surface in Stressproof. This isn't an issue with similar operations on 12L14 using the same machines, but Stressproof's 2x hardness and .5x machinability creates problems for boring operations in my shop.

The solution I eventually worked out began with drilling out the cylinders to within .050" of their final diameter using a series of drills. My Enco lathe's back gear was then used to reduce the spindle speed to 100 rpm for use with its slowest possible (.0047"/rev) power feed rate. A much slower feed is available from the Wabeco and, even though I replaced its lightweight cross slide long ago with a large block of metal, its VFD doesn't produce usable torque below 300 rpm.

I used a 3/4" diameter boring bar that had to be notched to fit my lathes' tool holders. The insert was a Korloy TCGT32.51-AK with a .032" radius nose and three polished razor edges designed to turn aluminum. This combination, along with dark thread-cutting oil, produced an acceptable bore inside Stressproof, although the insert's life was extremely short. I was able to complete two sleeves per edge, with the second one having somewhat poorer surface finish.

Depth of cut is important. If it's too shallow, even the Korloy insert will skip across the surface and spoil its finish. If it's too deep, the insert will wear out even faster and produce a poor result. I found .020", or so, (diameter) to be a sweet spot. With .050" excess stock remaining after the drilling operations, I had a couple chances during machining to calibrate the lathe's DRO for consistency between parts. The goal was to bore all the sleeves to within a thousandth of one another in order to minimize the amount of (messy) honing that would be needed to bring them all to the same diameter. Since the piston rings will be machined to fit, the final honed diameters aren't important so long as they're identical.

I had enough 1144 of the correct diameter to make four parts plus a spare. The spare was finished along with the rest of the sleeves for later use as a light-test fixture that will be used to select the rings that will be used in the engine.

Before beginning machining, a Delrin plug gage was turned to exactly match the two diameters already machined into the block. These were mic'd and their measurements recorded as targets for the sleeves' o.d. machining. This same gage will be used later to machine the cylinder recesses in the head.

Using a convention steel finishing insert, the sleeves' o.d.'s were turned with fine but unpolished surface finishes before starting the drilling and boring operations. A parting tool was used to turn the sharp inside corner needed to seat each sleeve inside the block. The top outside edges were slightly beveled to later aid insertion of the head down over the block. A short taper was also machined in the bottom of each cylinder's bore to ease insertion of the ringed pistons during final assembly.

When machining was completed, each sleeve was marked with a unique number so its progress could be tracked during honing. Record keeping isn't all that important with a small batch of cylinders, but when honing a sizable lot, wear on the lap itself can drive the process around in frustrating circles. Initial bore gage measurements showed four of the sleeves were starting out within a few tenths of one another, but one outlier was a full thousandth over.

A barrel lap and 280g Cloverleaf paste was used to bring the four cylinders up to the outlier's i.d. Once this was accomplished, faint machining marks left over from boring could still be seen on three of the five cylinders - probably the second bores from the insert's edges. These machining marks with their familiar period of some 200 spindle revolutions, often show up on my Enco during power-fed finishing passes even when turning. I've inspected the lathe's easy-to-get-to gears for defects but have never been able to pinpoint their exact cause. The marks left during turning polish out quite easily, and so I've just been living with the problem. They're a real PITA inside a cylinder bore, however.

I spent a few hours trying to clean them up with 600g paste, but ultimately had to return to using 280g to make any real progress. Final polishing was done with 600g, however. Some .003" eventually had to be honed away from the cylinders' i.d.'s to obtain five clean bores within a tenth of one another. The actual machining time for each bore was about an hour, and honing wound up adding another. - Terry


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## petertha

Hi Terry. What Loctite flavor will you use for bonding the sleeves into the block & what target annular gap? Reason I ask is I'll be bonding my bronze valve cages into aluminum heads in the near future & I just happened to notice some new product lines. Or at least new to me since I don't really check in all that frequently. Not sure they will be much difference over what I have, but I've also gotten in the habit of dating my adhesives & mine might be getting on a bit with age. I'm not even sure what shelf life is on these products, but I had a run of 'let-go's' in another hobby that I traced back to ancient Loctite, so not an area of expense I want to gamble on.

I think you have done all your liner builds without a tool post grinder preceding lapping stage. Do you feel it doesn't offer a worthwhile advantage over your current methodology, or yet another nice-to-have that Santa is not taking the hint? LOL

Do you have any plans to lap the liner OD's or they are coming off the lathe well enough?


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## mayhugh1

Peter,
The plan is to 680 Loctite. The annular gap is between a half and one thousandth. I'm using the o.d.'s as they came off the lathe. The finishes were good enough and they fit the block without polishing.

The toolpost grinder is an interesting idea. Have you seen any commercial units suitable for a cylinder bore or are they typically shop-made? - Terry


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## Gabe J DiMarino

Dumore makes them Thremac  also.


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## michelko

I had good results with the loctite 648 as sealing the liners into the block AT my bugatti bild.  No leackage so far.
Michael


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## petertha

mayhugh1 said:


> The toolpost grinder is an interesting idea. Have you seen any commercial units suitable for a cylinder bore or are they typically shop-made?



Terry, I have a Themac TPG. What little testing I did on my prior liner prototypes suggest it will work for me to bridge the gap between lathe single point turning & lapping, hopefully with more control & consistency. I think we have chatted on this before but I think my plan might be a bit more bass-akwards to the 'better' approach, which is to make the liner bores the same ID/deviation/finish by whatever means & size the rings from that. I'm trying to simultaneously hit a target bore dimensional specs with the final finish, which is probably added complexity. Part of the reason for this PITA process is to use commercial (OS-FS-56) rings, at least for my first build. Ultimately I will make my own rings because that is the way forward for any subsequent engine & then I will have a comparative reference.

Once my heads are done, liners will be the next thing to tackle so I will be in better position to show results & comment. One of the challenges of TPG's is general lack of appropriate stones of proper OD, thickness, grit & type (aggravated by the country I live in). So I bought a 1/4" thick surface " grinding wheel & had some discs water jetted out. That seemed to work but I may have chosen too fine a grit out of naivety. I learned later on that amazing finishes can be had with what I would have considered coarse grit. They cut better & run cooler etc. although I was taking squeak passes off like less than 0.0005". I hav some more things I want to ry in terms of dressing angles though. Progressive DOC measurement is another another vital ingredient to success I discovered. I could not count on my cross slide DRO & for sure not the dial on grinding ops. I mounted a tenths DTI on the cross slide to monitor progress & its rather disturbing how much things move around just tightening the cross slide & under power. So more to come on all this later I hope...

I have looked at lots of homebrew TPG designs. I'm no expert but I think what drives the cost of commercial units are attention to detail on the bearing assembly. Usually premium grade angular contact bearings, geometry, lubrication & methods to compensate under running/temperature conditions. Also ID boring means the rpms are getting up there, which means vibration & balance & (typically flat) vs pulley belts come into play. So add all this up & it starts looking a lot like a Dumore or Themac. There is one set of plans that looks decent though & the fellow seemed to know his stuff. i can provide details if you like. Brand name TPG's come up in Ebay & the like but how does one judge condition. I've heard, at least for Themac, they will do a teardown/rebuild to their specs for X $. 

There are probably lots of less stringent grinding applications where brand name TPG's are probably overkill. They are rather big & clunky, but that suites their purpose. I'm mulling buying a decent quality Asian motor/spindle with integrated ER collet for 'make it shiny' applications. But I don't think it would be up to task for a series of liners, even factoring in new bearings every so often. Although I would love to hear findings from others who went this route (and measured the results).  

Thanks for Loctite info.


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## awake

A continuing work of art!

I'm an utter newbie with respect to building an engine, much less something of this amazing detail and quality, so I hesitate to offer any suggestions ... but though I have not yet built an engine, I have been an active home-shop machinist for around 14 years. So with trepidation and humility, hoping I am not guilty of going too far off topic, here goes:

With respect to the problems you had with boring the StressProof ... I have gotten excellent results machining stress proof with HSS tooling. In fact, I have generally gotten excellent results machining the vast majority of materials using HSS tooling - I have been surprised that so many of the builders here seem to use carbide exclusively, even on machines that arguably would do better with HSS.

A stout boring bar definitely helps, of course, and so does a stout way to hold it. For much of the boring that I do, I mount a tool in my quick-change tool post. But when I need the ultimate in rigidity, and especially a larger size boring bar, I turn to an "Armstrong" style boring bar holder. No, not the lantern tool post tooling; rather something like this:







This is one of the very first projects that I made on my lathe, for my lathe - very easy to make, and works extremely well. Here are pictures of the components and assembled unit:









Again, I hope that I am not going too far off topic - if needed, I will be glad to delete the post!


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## John Antliff

I use my Quorn grinding spindle for similar jobs and it has a TIR of 2 tenths.  I tried 3 times to better that but each time the spindle came out at 2 tenths again!   I then found out that the lathe mandrel had a 2 tenths TIR which is why I could never better it.   The Quorn spindle design uses angular contact bearings with a spring box and an oil bath and compares favourably with commercial TPGs.  It's a good design and produces very acceptable results.   I also have problems finding good quality internal stones so if anyone knows of a reliable source please post details.


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## mayhugh1

The cylinder sleeves were sealed to the block with Loctite 680. The annular gaps between them were on the order of a thousandth and so, even though their fits were very close, the liners slipped into the block without distortion of their bores. Four oil return tubes were similarly installed. These will return waste oil to the crankcase from the engine's top-end so a scavenger pump can then draw it out to an exterior oil tank. The tubes were cut from hard thin-wall stainless steel tubing having a .120" o.d. and a .096" i.d. One of the photos shows a top view of the assembled block. The three pairs of holes between the cylinders are passages for coolant flow from the block to the head.

Uncertainties in the engine's lubrication system have been holding up the completion of a number of nearly finished assemblies, and so I hope to start working on it next. - Terry


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## ShopShoe

Interruption, sorry.

I just re-read post No. 81 and decided I might like to make your Boring-Bar Holder.

Did you drill or bore the holes for the bar before cutting the cylinder-shaped piece in half? Or was there some other order of operations?

Thank You,

--ShopShoe

PS: I always admire the totality of your skills in making all kinds of things.

--SS


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## awake

ShopShoe,

I'm happy to share more details. As I mentioned, this was one of the very first projects I made, some 14 years ago, so my memory is a bit fuzzy ... but as best I recall, made the outside cylinder from a piece of heavy tubing, onto which I welded a top. I then drilled the hole for the 5/8-18 threaded portion to protrude through. Next I turned the inside cylinder, sized to a close sliding fit with the outer cylinder. The bottom of this inside cylinder was turned to act as the "t-nut," and the top was turned down and threaded to 5/8-18. Finally I made a nut, threaded 5/8-18, which will fasten everything together. Here is an important point: the size of the inside cylinder stops short of the top of the outside cylinder, so that when it is assembled and the nut is tightened, the nut pushes down on the outside cylinder while pulling up on the inside cylinder, and in the process locks the tool to the compound t-slot.

Now with the tool assembled and locked together, I put a 1/2" drill bit in the lathe chuck, and moved the carriage over to drill the first (smallest) hole through both the outside and inside cylinders at once. I loosened the nut and turned the outside cylinder 120° while keeping the inside cylinder in its original orientation, re-tightened the nut, then used a 5/8" drill bit to drill through the outside cylinder, enlarging the hole in the inside cylinder in the process. Once again I loosened the nut, indexed the outer cylinder by 120°, re-tightened, and drilled through using a 3/4" drill bit.

Once the drilling was completed, I dissassembled everything and used round files to elongate the hole through the inside cylinder to provide clearance - this allows assembling the unit with the largest size (3/4") boring bar while it is loose, and makes sure it doesn't bottom out on the inside hole when it is tightened. (Alternately, I could have drilled through just the inner cylinder with a 13/16" or 7/8" drill.) Finally I cut the outer cylinder in half on the bandsaw at the center line of the holes, and used a file to ease the edges.

In use, the outside cylinder (now in two pieces) is turned so that the desired size of boring bar is lined up with the hole through the inside cylinder. The boring bar is inserted through and lined up on the lathe axis, and the nut is tightened down, squeezing the boring bar securely between the lower and upper halves of the outer cylinder while simultaneously squeezing the inside cylinder's "t-nut" up to lock the whole unit in place. The boring bar is automatically on-center, but of course you have to cut the holder(s) for the tooling that the boring bar will take so that the tool will be on center - that, or plan to grind the tooling as needed. I made my boring bars to take square HSS tool bits that I can grind to the needed shape.

Obviously, you can make this design to fit whatever size(s) of boring bars you want. If I were to do it again, I would skip the 1/2" and 5/8" sizes (since I can do those fine using my QCTP), and instead make this unit to fit a 3/4" and a 1" boring bar. (I would also produce a better finish, especially on the deburring - looking at this, I can tell it was one of my first projects!) With larger stock, you could make the design fit as large a boring bar as you wish.

I hope the explanation makes sense - the explanation is probably longer / more complicated than the actual making of the project!


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## ShopShoe

Thank You awake.

The holder looks so simple that I imagined fewer steps in the process. It clearly is a clearly-thought-out design and very elegantly made.

Thank you for your complete explanation. I think I can speak for everyone as well as myself to say how much we appreciate detailed explanations and complete sharing of methods.

I can also say that in reading your explanation I could see some other situations where that particular set of techniques could be used to make other bits and pieces.

Thanks again,

--ShopShoe


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## mayhugh1

The Offy's lubrication system isn't trivial. Although I browsed its design while working on other parts of the engine, the last week was spent totally focused on it. Its complexity is difficult to convey in a few 2D parts drawings, and so I created a 3D model based upon information in the manual that I modified for the split crankcase.

The two pumps (pressure and scavenger) are machined into a stacked pair of 3/16" aluminum plates and topped off with a 1/16" thick cover. The pumps are mechanically coupled and sit between the crankshaft which drives them, and the water pump which is driven from their common shaft.

The pump assembly is located inside a recess in the front of the crankcase, immediately behind the front cover. Drilled passages in the floor of the recess behind the pumps carry oil from the bottom (pressure) pump to the main bearings. Waste oil that collects in the crankcase is drawn out by the upper (scavenger) pump and returned to an exterior oil tank. Compared with the original one-piece crankcase, the redesigned main bearings in the split crankcase greatly simplify oil distribution in the bottom end.

An interesting feature of Ron's crankcase oil returns is their different diameters. They're designed to equalize oil accumulation between the bearings and reduce chances of the scavenger drawing air. I carried this detail over to the split crankcase as well.

Getting oil to the engine's top end is considerably more complicated, and care will be needed to prevent leaks and pressure loss along its tortuous path. The top end will actually receive oil from the scavenger pump. A portion of the oil that would otherwise be returned to the tank is diverted to the top end through a needle valve located on the side of the engine. This oil, though, must be pumped across any clearance that exists between the pump assembly and the side wall of the crankcase recess that it's mounted in. So, this fit must be snug.

After crossing this boundary, the oil flows through a vertically drilled passage in the side of the crankcase and then into a horizontally milled trough underneath the gear tower. It then continues up between the gear tower and engine block inside a milled channel in the rear of the tower. Before crossing another boundary to reach the head, a portion is turned back into the tower in order to drip lubricate its gears and bearings. The remainder enters the head on its way through the cam blocks for distribution in the top end via the hollow camshafts. Top end waste oil will be returned to the crankcase through the four vertical tubes already installed in the block.

The 'snug-fit' requirement (among others) concerns me, and so I took a break from modeling to find out how much of an issue it might become since an o-ring seal in this location doesn't seem practical. I wanted to experimentally determine how close of a fit I might expect for the pump assembly inside my already machined crankcase. A thousandth clearance should allow the assembly to come in and out of the recess without damage to either and maybe keep leaking oil and pressure loss at manageable levels. Another issue, however, is that the rear bearing for the pump assembly will sit in a pocket in the bottom of this recess, and it too has already (and maybe prematurely) been machined.

The recess was part of the lower half crankcase machining done much earlier on my Tormach using CAM tool paths that I can reuse. However, effective cutter diameter and machine backlash can unpredictably affect the fit I'm hoping to achieve. In order to get the best possible result, I machined three trial pump blanks using the same tool paths and end mill that was used to machine the recess. I modified the CAM of two of the blanks by adding a thousandth to the outer perimeter of one and subtracting it from the other.

To verify the alignment, a bearing pocket was added to the rear of each trial blank using the same CAM and cutter that was used to machine the pocket in the crankcase. A dummy bearing was used between them during the fit checks. The CAM parameters for the trial blank that gave the best fit were saved for use later when the pumps are actually machined. Even though there was a perceptible gap between the two, it was small enough to prevent a .001" feeler from passing between them.

I've provided some renderings from the modeling. I made use of a SolidWorks feature that I recently discovered that permits an x-ray view behind an individual surface. The head and cam box models aren't yet finished, and so they aren't included. I also have some o-ring and gasket details to work out.

After a full week in front of the computer, I desperately needed to return to the shop and make an actual part. I was fairly certain that its design won't change, and so I machined the oil manifold that will eventually connect the engine to its oil tank. A hose on its top barb will supply oil to the pressure pump, and the bottom hose will return scavenged oil to the tank. - Terry


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## awake

The amount of work in just the oil distribution is staggering. When all of this engine is done ... it will be a testament both to craftsmanship and to perseverance!


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## oldCB

awake said:


> The amount of work in just the oil distribution is staggering. When all of this engine is done ... it will be a testament both to craftsmanship and to perseverance!




For sure...........considering building a 2.4L Ford OHC engine , kinda cheating would use my assembled model as a pattern?


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## RonC9876

mayhugh1 said:


> The Offy's lubrication system isn't trivial. Although I browsed its design while working on other parts of the engine, the last week was spent totally focused on it. Its complexity is difficult to convey in a few 2D parts drawings, and so I created a 3D model based upon information in the manual that I modified for the split crankcase.
> 
> The two pumps (pressure and scavenger) are machined into a stacked pair of 3/16" aluminum plates and topped off with a 1/16" thick cover. The pumps are mechanically coupled and sit between the crankshaft which drives them, and the water pump which is driven from their common shaft.
> 
> The pump assembly is located inside a recess in the front of the crankcase, immediately behind the front cover. Drilled passages in the floor of the recess behind the pumps carry oil from the bottom (pressure) pump to the main bearings. Waste oil that collects in the crankcase is drawn out by the upper (scavenger) pump and returned to an exterior oil tank. Compared with the original one-piece crankcase, the redesigned main bearings in the split crankcase greatly simplify oil distribution in the bottom end.
> 
> An interesting feature of Ron's crankcase oil returns is their different diameters. They're designed to equalize oil accumulation between the bearings and reduce chances of the scavenger drawing air. I carried this detail over to the split crankcase as well.
> 
> Getting oil to the engine's top end is considerably more complicated, and care will be needed to prevent leaks and pressure loss along its tortuous path. The top end will actually receive oil from the scavenger pump. A portion of the oil that would otherwise be returned to the tank is diverted to the top end through a needle valve located on the side of the engine. This oil, though, must be pumped across any clearance that exists between the pump assembly and the side wall of the crankcase recess that it's mounted in. So, this fit must be snug.
> 
> After crossing this boundary, the oil flows through a vertically drilled passage in the side of the crankcase and then into a horizontally milled trough underneath the gear tower. It then continues up between the gear tower and engine block inside a milled channel in the rear of the tower. Before crossing another boundary to reach the head, a portion is turned back into the tower in order to drip lubricate its gears and bearings. The remainder enters the head on its way through the cam blocks for distribution in the top end via the hollow camshafts. Top end waste oil will be returned to the crankcase through the four vertical tubes already installed in the block.
> 
> The 'snug-fit' requirement (among others) concerns me, and so I took a break from modeling to find out how much of an issue it might become since an o-ring seal in this location doesn't seem practical. I wanted to experimentally determine how close of a fit I might expect for the pump assembly inside my already machined crankcase. A thousandth clearance should allow the assembly to come in and out of the recess without damage to either and maybe keep leaking oil and pressure loss at manageable levels. Another issue, however, is that the rear bearing for the pump assembly will sit in a pocket in the bottom of this recess, and it too has already (and maybe prematurely) been machined.
> 
> The recess was part of the lower half crankcase machining done much earlier on my Tormach using CAM tool paths that I can reuse. However, effective cutter diameter and machine backlash can unpredictably affect the fit I'm hoping to achieve. In order to get the best possible result, I machined three trial pump blanks using the same tool paths and end mill that was used to machine the recess. I modified the CAM of two of the blanks by adding a thousandth to the outer perimeter of one and subtracting it from the other.
> 
> To verify the alignment, a bearing pocket was added to the rear of each trial blank using the same CAM and cutter that was used to machine the pocket in the crankcase. A dummy bearing was used between them during the fit checks. The CAM parameters for the trial blank that gave the best fit were saved for use later when the pumps are actually machined. Even though there was a perceptible gap between the two, it was small enough to prevent a .001" feeler from passing between them.
> 
> I've provided some renderings from the modeling. I made use of a SolidWorks feature that I recently discovered that permits an x-ray view behind an individual surface. The head and cam box models aren't yet finished, and so they aren't included. I also have some o-ring and gasket details to work out.
> 
> After a full week in front of the computer, I desperately needed to return to the shop and make an actual part. I was fairly certain that its design won't change, and so I machined the oil manifold that will eventually connect the engine to its oil tank. A hose on its top barb will supply oil to the pressure pump, and the bottom hose will return scavenged oil to the tank. - Terry
> 
> 
> View attachment 112475
> View attachment 112476
> View attachment 112477
> View attachment 112478
> View attachment 112479
> View attachment 112480
> View attachment 112481
> View attachment 112482
> View attachment 112483
> View attachment 112484
> [/QUOTE
> 
> 
> 
> 
> 
> Terry: My engine has been running for twenty years now and I have never had a problem with the lubricating system I designed. I pondered a long time on just how to do it. I admit it is a bit difficult to employ, but it has worked flawlessly. I am happy to say that you were able to understand exactly how it works. Using the scavenged oil to lube the upper end and making the flow adjustable with the needle valve on the side is probably a little unorthodox, but it all works perfectly. I came up with this design at the very end of construction. I left it till the very end because I knew it would be difficult to get it all to fit and actually work. I don’t know how it is done on the full sized engine. I had very little info from which to work with. It is what it is!


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## mayhugh1

RonC9876 wrote:
[Terry: My engine has been running for twenty years now and I have never had a problem with the lubricating system I designed. I pondered a long time on just how to do it. I admit it is a bit difficult to employ, but it has worked flawlessly. I am happy to say that you were able to understand exactly how it works. Using the scavenged oil to lube the upper end and making the flow adjustable with the needle valve on the side is probably a little unorthodox, but it all works perfectly. I came up with this design at the very end of construction. I left it till the very end because I knew it would be difficult to get it all to fit and actually work. I don’t know how it is done on the full sized engine. I had very little info from which to work with. It is what it is!]
---------------------
Thanks Ron. That's what I hoping to hear! - Terry


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## mayhugh1

The two pump bodies and cover were machined from 6061 aluminum. There's a lot going on inside them with limited space for screws to hold them together. Both sides of each were lapped on a glass plate with Time Saver to minimize leaks. Since the thin top cover was likely to be troublesome, I initially tried machining it from a piece of 14 gage steel that I planned to grind perfectly flat on my surface grinder. I wasn't able to control its warpage during grinding, however, and so I instead machined three covers from sheet aluminum and then selected the flattest one to work with.

It was encouraging to hear from Ron that the Offy's lubrication system has been performing well for him since I had been concerned about the pressure pump's seemingly small size. My only change to Ron's original design was some rerouting to accommodate the modified crankcase, but this required relocating some of the oil channels inside the pump bodies. Before irreversibly drilling the crankcase, I thought I'd better assemble and test the pumps outside the engine just to make sure there won't be any surprises after final assembly.

I made up a simple fixture to which I could mount the pump assembly and connect some hoses so I could operate the pumps outside the crankcase. This fixture was also used to ream the final diameters of the shaft holes through the stacked pump assembly while it was doweled together and bolted down to it.

The pressure pump's small size make it susceptible to even small accuracies in its machining. A gear pump's transfer volume can be easily calculated and used as a sanity check on its machining. The volume moved through a gear pump per revolution is given by:

Vol = pi/4 * (D^2 - d^2) * T

where D is the o.d. of the pump gears, d is their i.d. measured across the roots, and T is their thickness. Once this volume is determined, the flow rate at any rpm can be found by simply multiplying it by the rpm.

There's a 3:1 gear reduction between the Offy's crankshaft and its oil pumps. At 5000 crankshaft rpm, the theoretical flow rate of the Offy's pressure pump works out to be 5.8 cubic inches per minute and 13.1 cubic inches per minute for its scavenger pump. The expected pressures aren't easily calculated, though. For the simple pumps we typically make, their machining typically limits the maximum pressures they can develop. In the past, I've measured as much as 100 psi.

I tested the Offy's pump assembly while mounted in my fixture and being spun by a drill at roughly 1700 rpm in order to simulate their operation in the engine at 5000 rpm. The pressure pump's open-end flow rate was 3 cubic inches/min, and the scavenger pump's flow rate was 9 cubic inches/min. The scavenger pump was 30% lower than theoretical, but the pressure pump was nearly half of what I expected. I also measured the blocked-output pressures to be 15 psi and 50 psi for the pressure and scavenger pumps, respectively.

Although I was satisfied with the scavenger pump, the pressure pump results were disappointing. Under a microscope I could see no visible clearance between the pump body and the teeth on its gears. But, while removing the assembly from the test fixture, I noticed it and the rear surface of the bottom (pressure) pump were wet with oil. Suspecting leaks at the rear of the assembly, I made a .005" thick Teflon gasket to seal these two surface together. I remeasured the pumps' performances and found the blocked-output pressure of the pressure pump had risen to 25 psi, and its flow rate had increased to 5.2 cubic inches/min. The scavenger pump's flow rate also increased to 12 cubic inches/min.

The addition of this rear gasket brought the flow rates up to within 10% of their theoretical values and their maximum output pressures to levels that I'm comfortable with. I've included a CAD rendering of an x-ray view looking through the bodies of both pumps. Keeping in mind that the pumps are on different levels, there should be no internal leakage between them except possibly through the central driveshaft. If the bottom pump isn't sealed to its mounting surface, however, there's a potential for its output to leak to the outside world or even into the scavenger pump's low pressure input. Similarly, the scavenger pump could find its own path to the outside world.

More importantly, if there is a leak on either of the pumps' inputs, priming during starting and/or idling can become a problem. All my testing was done worst-case with the pumps located several inches above the oil reservoir. During testing but before adding the gasket, the pressure pump had to be manually primed with a syringe and again after standing overnight. The gasket seemed cure this. The pumps were disassembled/reassembled several times over as many days to make sure their operation remained consistent after adding the gasket.

The common drive shaft running through the pump assembly combined with the pumps' .001" gear face clearances probably account for the current limitation on the pressure pump's maximum output pressure. Based on my earlier experiences with the Knucklehead, though, 25 psi should be more than adequate especially since there is no pressure relief valve. The pumps were disassembled one final time in order to drill the transfer hole through the side of the bottom pump body that will be used to supply oil to the engine's top-end. - Terry


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## ddmckee54

Where did you find that HUGE safety match that you were  using in you photos?  Make it yourself?  Gonna' do a build thread on it too?

Your reputation for excellence is well deserved.

Don


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## petertha

Very nice work indeed. Some basic questions if you don't mind

- is the higher capacity of the scavenger pump relative to the pressure pump related to some basic lubrication pumping rule of thumb. Or maybe particular to this engine implementation? You mentioned _the top end will actually receive oil from the scavenger pump. _I don't quite get why the pressure pump couldn't feed another separate area of the engine on a separate branch. How does the needle valve factor in this?

- how do you select tooth form for when it comes to pumps? I assume bigger or smaller teeth influences rate & pressure but any words of wisdom in that regard? Are they conventional spur gear profiles?

- what will you be using for oil (specifically I'm interested in viscosity)

- on the scavenger pump side, what happens if it drains the crankcase sump or otherwise sees intermittent oil & air? Especially since its capacity is higher as mentioned. Does the pump care as long as its lubricated or slowly heats up spinning like this? I've never understood this aspect. Can the crankcase ever be drawn down below atmospheric?

- anything to know about the oil supply/return tank from your previous engines? Does return oil foam at all (allowance for extra volume). Does it have an ideal position relative to the pumps (like gravity feeds pump elevation).


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## mayhugh1

Peter,

Lots of questions... 

The scavenger pump is usually larger than the pressure pump in order to insure the oil level doesn't have a chance to build up in a sump-less engine and cause problems. The scavenger may at times draw air, but it should be capable of re-priming.  Builders of the Hodgson radial found that the size of its scavenger wasn't great enough to prevent the engine from filling with oil and locking up, and so a gravity drip fed had to be added to the engine to prevent the crankcase from filling with oil and locking up the engine. 


The oil will foam, but in a well design system, the air will have a chance to settle out in the return side of the tank. I even saw some evidence of foaming during the bench tests described above. Unlike my radials, I'm hoping to be able to set the Offy's oil tank below the engine. 


I'm speaking for Ron here, but yes, the top-end could receive its oil from the pressure pump along with the bottom end. In fact this is what was done on the Quarter Scale Merlin. But, a pressure relief valve was required to properly divide the flow between the critical bottom end and the not so critical top-end. What Ron did was actually pretty clever. He dedicated the entire pressure pump to the critical bottom end and diverted a fraction of the scavenger's return to the less critical top end. A simple needle valve can be used to control this fraction while observing the two flows without having to deal with difficult to set pressure settings.


Spur gears are typically used in constant displacement pumps, but if you look back on my Knucklehead thread you'll see I tried a different profile, just for fun, that I felt would be more efficient. Then, I spent several weeks dealing with its monstrous flow that I didn't want or need. 


I don't know what you mean by 'bigger or smaller teeth.' The equation for transfer volume clearly depends on the size of the gears used, and the size of their teeth depend upon their diameter. Remember, the space between the teeth are the buckets that carry the oil around the outsides of the gears to the pump's output.


I've tried oil viscosities between 5W20 and straight 80 weight, and frankly I'm not sure I see much difference between any of them in my model engines. I now typically use whatever happens to be left over from my last auto oil change. 


Good Luck. Can't wait to see your radial ... Terry


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## kvom

Tongue in cheek comment on Ron's engine:  I've seen it at several shows over the years and heard it more often.  The noise in running is such that it rarely if ever runs more than a minute at a time.  Makes me wonder if the oiling system is super-critical for short runs like this.  Disclaimer:  I know nothing about IC engine lubrication.


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## mayhugh1

kvom said:


> Tongue in cheek comment on Ron's engine:  I've seen it at several shows over the years and heard it more often.  The noise in running is such that it rarely if ever runs more than a minute at a time.  Makes me wonder if the oiling system is super-critical for short runs like this.  Disclaimer:  I know nothing about IC engine lubrication.



I've often wondered myself if splash lubrication alone isn't sufficient for these model engines. With a roller (ball bearing) cam, leakage past the valve stems might be enough to mist lube the top end. The pressurized oiling systems that some of these more challenging models have could very well be unneeded although interesting complications. - Terry


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## RonC9876

kvom said:


> Tongue in cheek comment on Ron's engine:  I've seen it at several shows over the years and heard it more often.  The noise in running is such that it rarely if ever runs more than a minute at a time.  Makes me wonder if the oiling system is super-critical for short runs like this.  Disclaimer:  I know nothing about IC engine lubrication.


The reason for short runs at the shows is two fold. First,If I allow the engine to run for any extended period, I get flak from people saying it is too loud and their conversations are being interrupted. Secondly the water pump and cooling system is totally insufficient for the heat this thing generates. Lubrication has never been a problem. The oil tank sits at the bottom of the wooden base used to support the engine. It has it’s own oil filter and the pumps prime without incident every time, even after sitting for months. I already discussed the cooling problem with Terry. The set up needs a positive displacement pump.


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## KennyMcCormick315

kvom said:


> Tongue in cheek comment on Ron's engine:  I've seen it at several shows over the years and heard it more often.  The noise in running is such that it rarely if ever runs more than a minute at a time.  Makes me wonder if the oiling system is super-critical for short runs like this.  Disclaimer:  I know nothing about IC engine lubrication.





mayhugh1 said:


> I've often wondered myself if splash lubrication alone isn't sufficient for these model engines. With a roller (ball bearing) cam, leakage past the valve stems might be enough to mist lube the top end. The pressurized oiling systems that some of these more challenging models have could very well be unneeded although interesting complications. - Terry



commercial model aviation 4-cycles are lubricated solely by blowby and they last for decades working far far far harder than any of the models posted on this site ever do.


It isn't that critical on this scale. It's quite impressive when someone goes to the trouble of giving one full pressure lubrication but, for the majority of the models on this site that never see a day of honest work in their entire existences, they'd be lubed just fine by splash alone.


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## Ironmanaz

Blowby  is identical to the fuel/air mix coming thru the intake manifold (reason for the PCV valve). How does this lube anything?
Maybe with premix?  Considerations on my BR2 build....


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## awake

I wondered the same thing! But then again, I'm so new to all of this that I have questions about nearly every post. I'm trying to pace myself on how many things I ask about ...


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## KennyMcCormick315

Ironmanaz said:


> Blowby  is identical to the fuel/air mix coming thru the intake manifold (reason for the PCV valve). How does this lube anything?
> Maybe with premix?  Considerations on my BR2 build....



Model aircraft engines have a _lot_ of oil coming in with the fuel. 15-20 percent of the total fuel volume, depending on blend. Mine suck down an 18% lube package, of that, half is castor oil and half is synthetic. Rest of the fuel is, for the most part, methanol with a whiff of nitromethane for that extra kick.

Same exact fuel my 2-cycles run on, in fact.

If you want to simplify lubrication...and ignition...on your BR2 build, aim for a CR of around 7.5:1 and use model aviation fuel in it. Glow plugs use a quarter-20 thread and the fuel is designed to work with them. Give 'em 1.5v on startup and, once it's warmed up, it should self-sustain from there.

Some of the larger ones run on gasoline, use a CDI ignition system, and use the same oil that your strimmer uses. Saito recommends a 16:1-20:1 mix in theirs.


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## gadabout

KennyMcCormick315 said:


> Model aircraft engines have a _lot_ of oil coming in with the fuel. 15-20 percent of the total fuel volume, depending on blend. Mine suck down an 18% lube package, of that, half is castor oil and half is synthetic. Rest of the fuel is, for the most part, methanol with a whiff of nitromethane for that extra kick.
> 
> Same exact fuel my 2-cycles run on, in fact.
> 
> If you want to simplify lubrication...and ignition...on your BR2 build, aim for a CR of around 7.5:1 and use model aviation fuel in it. Glow plugs use a quarter-20 thread and the fuel is designed to work with them. Give 'em 1.5v on startup and, once it's warmed up, it should self-sustain from there.
> 
> Some of the larger ones run on gasoline, use a CDI ignition system, and use the same oil that your strimmer uses. Saito recommends a 16:1-20:1 mix in theirs.



Glow plugs are 1/4 32 thread


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## KennyMcCormick315

gadabout said:


> Glow plugs are 1/4 32 thread


Oh, they're fine thread? Huh. Well, either way, they're all standardized to a common thread. 5/16 hex.


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## mayhugh1

I'd been procrastinating over a number of loose ends related to the Offy's oiling system, and so I decided to tie them up before the holidays. First, the crankcase passages behind the pumps were drilled using the holes' coordinates and a previously machined drilling template as a sanity check. Two of the risky small diameter holes were nearly five inches deep. After starting out with jobber length drills, I switched to aircraft drills that I had on hand, but their long flute-less shanks tended to heat up and bind inside the holes even at half depth. I eventually switched to using long Guhring drills, but in order to reach full depth I could only grip the upper eighth inch of their shanks. The drilling of these two passages was sketchy, but I managed to get through it without breaking off a drill deep inside a finished crankcase.

The oil manifold holes on the lower front side of the crankcase were trivial in comparison. A .010" thick Teflon gasket was made to seal the manifold to the crankcase.

The tortuous path between the scavenger pump's output and the engine's top-end was completed up through the top of the gear tower. A 2-56 grub screw located in the side of the engine will eventually control its flow. A 3.5mm o.d. x 1mm thick o-ring seals the passage as it crosses the boundary between the crankcase halves. Another o-ring groove was machined around the transfer trough between the gear tower and the crankcase to control oil leakage at their intersection with the block. This groove was designed for a standard 7mm o.d. x 1mm thick o-ring under 10% compression.

A machined passage on the rear surface of the gear tower carries oil from the transfer slot up to the head. After entering a shallow drilled passage in the head, the oil splits into two streams that will carry oil to the cam boxes for eventual distribution to the top-end. A groove for a length of 1mm o-ring cord stock was machined around the vertical passage on the gear tower in order to seal it to the block/head assembly.

The rear face of the front cover had to be slightly modified to clear the pump assembly. A .010" thick Teflon gasket was added to seal it to the crankcase. Finally, mounting holes for the water pump were added to its front side.

An exploded assembly drawing shows the parts behind the front cover related to the oil pumps. Parts for the water pump and starter shaft components will be added later as they are machined. - Terry


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## Jon James

mayhugh1 said:


> I'd been procrastinating over a number of loose ends related to the Offy's oiling system, and so I decided to tie them up before the holidays. First, the crankcase passages behind the pumps were drilled using the holes' coordinates and a previously machined drilling template as a sanity check. Two of the risky small diameter holes were nearly five inches deep. After starting out with jobber length drills, I switched to aircraft drills that I had on hand, but their long flute-less shanks tended to heat up and bind inside the holes even at half depth. I eventually switched to using long Guhring drills, but in order to reach full depth I could only grip the upper eighth inch of their shanks. The drilling of these two passages was sketchy, but I managed to get through it without breaking off a drill deep inside a finished crankcase.
> 
> The oil manifold holes on the lower front side of the crankcase were trivial in comparison. A .010" thick Teflon gasket was made to seal the manifold to the crankcase.
> 
> The tortuous path between the scavenger pump's output and the engine's top-end was completed up through the top of the gear tower. A 2-56 grub screw located in the side of the engine will eventually control its flow. A 3.5mm o.d. x 1mm thick o-ring seals the passage as it crosses the boundary between the crankcase halves. Another o-ring groove was machined around the transfer trough between the gear tower and the crankcase to control oil leakage at their intersection with the block. This groove was designed for a standard 7mm o.d. x 1mm thick o-ring under 10% compression.
> 
> A machined passage on the rear surface of the gear tower carries oil from the transfer slot up to the head. After entering a shallow drilled passage in the head, the oil splits into two streams that will carry oil to the cam boxes for eventual distribution to the top-end. A groove for a length of 1mm o-ring cord stock was machined around the vertical passage on the gear tower in order to seal it to the block/head assembly.
> 
> The rear face of the front cover had to be slightly modified to clear the pump assembly. A .010" thick Teflon gasket was added to seal it to the crankcase. Finally, mounting holes for the water pump were added to its front side.
> 
> An exploded assembly drawing shows the parts behind the front cover related to the oil pumps. Parts for the water pump and starter shaft components will be added later as they are machined. - Terry
> 
> 
> View attachment 112870
> View attachment 112871
> View attachment 112872
> View attachment 112873
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> View attachment 112875
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> View attachment 112877
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> View attachment 112879


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## Jon James

OT.
Hi Terry,
I am building the Hodgson 9 cyl.  I have referred to your build thread many times.  It has been very helpful to me. I especially appreciate your crankshaft process.  It is a much better way to go, with guaranteed accuracy.  
Thank you very much for sharing your expertise with all of us. 
Of course I am watching your Offy build. Best of luck. 
Regards
Jon


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## petertha

Hi Terry, I don't have any deep drilling jobs ahead of me, but I was intrigued by the challenge you had to overcome. What kind of diameter were these holes? What seemed to be the best chip clearing strategy, like short pecks, or drill X amount & complete drill withdrawal? What kind of cutting fluid?

Sidenote, I was having some issues drilling good, straight 0.118" holes in C544 bronze with conventional drills. I switched to a short carbide which went better. Then I tried a parabolic that looks a lot like that Guhring & it went much better despite being HSS & a bit longer length than the carbide. Very different chip removal. Unfortunately, I also decided to try a cream type cutting/tapping 'fluid' that's been kicking around the shop so now I have to separate the two variables to see if the benefit was more one or the other.


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## mayhugh1

Peter,
The two deep holes were .093" and .125" in diameter. After getting to half depth I was drilling about .050" at a time and then fully withdrawing. I used WD-40 for the lubricant. The Guhring drills are parabolic. I've found the .093" ones though are too flimsy to start such a deep hole because of so much initial stick-out. I drilled them all manually so I'd 'feel' my way through the process. I was really disappointed that the aircraft drills didn't work, but in hindsight I could have ground down their shanks for some relief. Just glad it's over. An operation that risky is best done early before the part accumulates so much machining time.


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## mayhugh1

Just after beginning this build, I received an email from Ron concerning a couple areas in the Offy's design that he felt needs improving. One of these is its cooling system which is currently limiting the engine's runtimes. Ron feels the existing water pump isn't capable of flowing enough coolant through the head's tiny passages.

The current pump is a centrifugal design that's similar to those used in full-size engines. Its impeller, however, is a no-frills straight four blade design with a diameter necessarily limited by the starter shaft that will be located just above it. Ron's suggestion was to replace the pump with a constant displacement design.

Although constant displacement pumps are commonly used with more viscous fluids such as oil, the pumps I've been using to deliver gasoline to the carburetors on my other engines are gear types and have been working well (actually, too well). The pressure and flow requirements in those applications have been practically nil giving me little feel for their performance in a water pump application which will be sensitive to the pump's machining. In the best case, its drive torque could become an issue since it will be driven by the scavenger pump's brass slotted shaft.

Before switching pump types, I decided to compare their performances. My current plan is to construct both of them with outside envelopes similar to Ron's original design. A mocked-up coolant loop similar to the Offy's will be used to make some comparative measurements. Fully completed versions of both pumps should also allow a comparison of their performances later on the actual running engine.

My version of a centrifugal pump is shown in the photos. Its stainless steel impeller is a seven blade seat-of-the-pants design that could most likely be improved by someone who knows what they're doing. Although I increased the blade height from .250" to .312", the impeller's diameter and dual ball bearing supports are identical to those in Ron's pump.

A cover with an integral hose barb was also machined from stainless steel. A flanged tube will connect the pump's output to a similar tube on the block. The pump body itself was machined from 6061 aluminum. It was lapped to the cover and secured with enough 0-80 mounting screws to hopefully avoid the need for a gasket. The bearings are stainless steel and the space between them will be sealed with either graphite string or silicone coated o-rings.

Coolant enters the center of the pump where it picks up kinetic energy from the spinning impeller. The expanded volume near the pump's exit converts some of this energy into a static pressure rise at the pump's outlet. An optimized design within the same space might trade some impeller diameter for a surrounding volute for even higher pressure. Since the energy gained by the fluid should be proportional to the square of the impeller's diameter, I just assumed bigger was better. I didn't know how to account for it, and so cavitation might be a problem.

I hope to have a completed gear pump after the holidays. - Terry


----------



## awake

That is some impressive work! I'm eager to hear the results.

FWIW - I've seen and heard of gear pumps often in connection with oil, but never water - wonder if the gear pump needs the higher viscosity?


----------



## Charles Lamont

I have some knowledge of centrufugal pumps and may be able to confuse you a bit.

First, consider the radial flow through the impeller. You are going from a small diameter to a large one with a constant axial dimension of 5/16". The flow though the inlet has to fill up all that space round the periphery of the impeller, so the radial component of the exit flow velocity is going to be very small. It would be more normal to sweep the blade height to, oh, something like half the pipe bore at the periphery. This is often done by putting a generous bell mouth radius then a slight taper on the inside of the inlet flange.

Second, because of the tight radial clearance, you are preventing any significant flow through the impeller for about two thirds of its periphery. As there is no proper volute, you may find a bit more radial clearance improves matters. Your broad blades are helping you here.

Your outlet arrangement does not help. It would be better if it were tangential. As we see it in the photos: downwards, immediately to the left of the tongue. At the moment you have built up a nice tangential flow velocity and then you just crash it into a wall.

In tiny pumps like this, drag and leakage are significant factors. Make sure the axial clearance between the impeller and the flange is as small as possible (leakage) but putting an outer shroud on the impeller might well not be an improvement because of the increased friction losses.

Without going into the maths, I would say qualitatively that the blade curvature you have is suitable for giving you about as much pressure as you are likely to be able to get. Tiny centrifugal coolant pumps are at a disadvantage in the respect as they will always run at far below their ideal speed. If, on the other hand, it is more flow you need, as may well be the case, then straight vanes, roughly tangential to the eye diameter would be better.


----------



## Charles Lamont

Another thought. Reading about engine cooling the other day I found that as an estimate you can tke about half the engine power output as being the amount of heat to be rejected by the cooling system. Same source (Judge - Modern Petrol Engines - 1955) suggests a temperature drop across the radiator of 15-20° C. From this you can calculate the necessary flow rate.


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## Mike Henry

awake said:


> That is some impressive work! I'm eager to hear the results.
> 
> FWIW - I've seen and heard of gear pumps often in connection with oil, but never water - wonder if the gear pump needs the higher viscosity?



We used magnetically coupled gear pumps in an R&D lab to pump water and even ethanol and it seemed to work fine.  I believe that the manufacturer specified different gear and seal kits depending on the fluid being pumped.


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## RonC9876

My Sealion uses a gear pump as a water pump. It pushes a lot of water through small passages and keeps the engine cool. Designed by Westbury in the 1950’s I think. Proven design.


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## awake

Good to know - learned something new!


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## ddmckee54

Charles:

You said in Reply #112 - "more flow you need, as may well be the case, then straight vanes, roughly tangential to the eye diameter would be better".

I'm going to ask stupid question, assuming a CW rotation of  the impeller, how would the vanes be oriented?  In my head I can see two different tangential vane orientations and I'm pretty sure one of them is wrong.

Don


----------



## Charles Lamont

From left to right - increasing flow and decreasing pressure


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## mayhugh1

Before moving on to the gear pump, I decided to test my already completed centrifugal pump. Being anxious to try out some of Charles' suggestions, I also wanted to verify the methods I had used to seal the pump before replicating them in the geared version. My testing was to initially include visibly monitoring the circulation inside a clear plastic loop followed by standalone pressure and flow rate measurements at a couple different pump speeds.

Spinning the pump with a battery powered drill was unwieldy and caused me to spend more time mopping up water than making tests. After cobbling up a test bed around a badly abused Sherline lathe, I was able to spin the pump up to 2000 rpm leaving my hands free to play with the loop. This speed was equivalent to 6000 crankshaft rpm on the Offy.

The Offy will hold some 3 cubic inches of coolant with nearly 90% of it around the sleeves inside the block. A suitably scaled radiator will later add another half cubic inch or so. The dummy coolant loop was made up from a clear plastic bottle and an array of clear plastic tubing to approximate the coolant passages inside the head. The loop's total volume worked out to be just under 4 cubic inches. The flexible tubing allowed me to reconfigure and modify the heights of the various components in the loop and to change the pump's working head pressure.

Although a centrifugal pump isn't self-priming, there's no problem in actual use since it will sit in the lowest part of the coolant loop. Without an overflow tank, some provision should be made to displace air by adding coolant to the loop at it highest point in the engine. In the Offy, a convenient point will be near the end of its water outlet pipe. The array of tiny coolant passages inside the head will tend to trap any air left inside the system, and this can allow the combustion chambers to overheat.

The pump's dismal performance showed up immediately. Below 1000 rpm (3000 crank rpm) there was absolutely no flow through the loop with the simulated block sitting at its proper height above the pump. At 6000 crank rpm there was still no flow until the block was lowered to the same level as the pump. By changing a pulley in my setup I was able to double the rpm and obtain what I would estimate to be a marginally useable flow with the block sitting about an inch above the pump.

I then modified the impeller as suggested by Charles. I radially tapered the height of the blades as shown in one of the photos, and I also reduced the impeller's diameter to allow some circulation around it. The modified impeller did perform better but, below 6000 crank rpm, the pump still could not circulate water around the loop with the block sitting at its required height above the pump.

The flow rate didn't become acceptable until some 12,000 crank rpm when yet another problem showed up. All six connecting passages between the head and block are essentially in parallel. Once circulation began, only one or possibly two of these simulated passages actually flowed coolant leaving much of the 'head' stagnant. Even at 12,000 crank rpm, the centrifugal pump didn't produce enough pressure to promote flow through more than two passages. The diameters of the return tubes in the water outlet pipe on the engine will be graduated to encourage uniform flow across the entire head, but my test bed didn't include this feature.

Based on these tests, I have to conclude that my pretty-looking centrifugal pump would be pretty much non-functional on the Offy. However, I'm not sure its performance is that much different from similar pumps typically used on model engines. Inside a running engine, air expansion and diffusive heat flow through the liquid itself can produce an effective flow giving the impression the pump is doing its job. I remember the first few days of testing my Howell V-4 with its efficient shrouded radiator, overflow tank, and magnetically driven water pump impeller. Even though the expansion tank appeared to be functioning and the radiator was warm, I happen to notice one day that I had forgotten to install the o-ring 'belts' on the water pump pulley. This, along with my experience of the past few days, wouldn't leave me surprised to learn that the centrifugal pumps in many of our model engines may not be doing much of anything.

The bit of good news was that the seals, including the rear silicone coated o-ring seal, appeared to do their jobs and can be carried over to the gear pump. - Terry


----------



## dnalot

Hi

Have you considered a vane pump


----------



## H Pearce

Hi,

Are you still using the original flat cover on the pump? The clearance between the impeller and cover is critical, it needs to as close as possible any gap even a small one will cause a large loss in efficiency. This small clearance needs to follow the blades all the way down to the outside tip. Their needs to be some space for the water to exit the impeller, ideally a volute housing for proper flow. Best common  example would be a turbocharger compressor, you can clearly see the shape/flow even from the outside. Different medium but same idea.
Regarding a gear pump, the main potential issue I can see is the lack of lubricant for the gears. Guessing the engine won’t be run for long so shouldn’t be a problem? Keep in mind as it is a positive displacement pump it can make allot of pressure, not sure if the water jacket would like that.
With a bit of tweaking the centrifugal pump should work fine...


----------



## bluejets

There is insufficient "water cut" section in your design.
Made the same comment to another vane water pump the other day.

https://www.homemodelenginemachinist.com/threads/demon-v8-multiplied-1-5.31580/page-6#post-332292

post #102


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## gbritnell

Terry,
While I agree that there is a certain amount of thermosyphoning of the water and therefore while running an engine the radiator does tend to heat up (model T cooling system) the introduction of a pump should assist in the cooling effort. Not having a CNC machine I machine my impellers with straight vanes but offset from the centerline to give the desired flow across the vanes. My pump body has the outlet tangential to the inside bore of the pump. I have made the impeller shaft bore two different ways, one on center with the housing bore and one with an offset center to form what has been referred to as a cutwater. I have never tested the flow rate of these pumps but even after just a few seconds of running an engine I can feel heat circulating through the radiator. 
Your impeller design should work great but I agree with the other posters that you need to make your discharge port tangential to the pump bore. 
Attached is the drawing for the pump on my 4 cylinder engine. This design has somewhat of a cutwater that is simpler to machine without CNC. The pump draws water from the block then pumps it to the radiator. 
gbritnell


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## mayhugh1

I spent several days designing a gear pump and then, just before starting its machining, I began having second thoughts. The Offy's coolant system is a pump located in the bottom of a closed loop that's completely filled with coolant. Since the water columns at the pump's inlet and outlet are at the same height, it should be capable of circulating the coolant with minimum pressure across it.

Wall friction within the tiny head passages in the upper part of the engine could conceivably create a flow bottleneck and increase the pressure requirement of the pump, but this can be calculated using Poiseuille's law:

Q = (pi * r^4 * P) / (8 * n * L) ,

Where Q is the flow rate,
P is the pressure drop,
r is the radius of the restriction,
L is the length of the restriction, and
n is the fluid's viscosity.

Plugging in values for an 1/8" diameter restriction that's 6" long (typical of one of the Offy's head passages) and using the viscosity of water shows that only .0023 psi is required for each cubic inch per minute flow. Full-size automobile engines typically turn their entire coolant volume over one to two times per minute. For the same turnover rate, the Offy's 3 to 6 cubic inches per minute should require no more than .014 psi from the pump. (For a sanity check on the math, visualize blowing through a short soda straw.)

It doesn't seem likely that removing waste heat from the Offy's head can be significantly improved with a gear pump capable of producing tens of psi pressure. It's more likely that the pump would have to be severely throttled back to prevent coolant leaks from an already questionable head gasket.

Setting aside my first attempt, a well-designed centrifugal pump should have little problem circulating coolant through the Offy. I carefully considered the comments received on my first pump before taking another stab at it. I improved the tangential exit and water cut and added some semblance of a real volute. Since there was a definite advantage to retaining the same impeller diameter, space for the volute was created by increasing the diameter of the pump body and then notching it for clearance around the starter shaft. Although still not ideal, the volute's geometry was considerably improved. The height of the impeller was also increased by 30%. I don't normally like making so many simultaneous changes while working my way up a learning curve, but it's getting time to move past this part of the project.

A few material changes were also made to improve the pump's long term corrosion resistance. It turns out that aluminum and stainless weren't the best metals to put into wet contact. Both the pump body and cover are now 7075 aluminum with the impeller was machined from Delrin. An integral Delrin sleeve also replaced the front ball bearing, and the impeller can now limit its own thrust with minimum wear to the cover. The coolant will eventually become a 50/50 mix of anti-freeze and water which will provide some lubrication and corrosion resistance.

The number of impeller blades was reduced from seven to six and their thickness increased some 30%. The impeller has a 1/4" diameter pressed-in metal shaft with a rear end that remains supported in a ball bearing similar to the original pump. Silicone grease packing and an o-ring in front of this bearing makes up,the pump's rear seal.

Since I previously saw a performance improvement with fish-mouthed impeller blades, I machined two impellers for this pump. One has full height blades, and the other one is fish-mouthed. Research showed the backward curved blades I'm using (or else offset straight blades) are the best performers for non-compressible fluids. Without CNC capability the extra machining effort required for curved blades probably isn't worthwhile.

Testing...
The new pump performed much better compared with my first attempt. It visibly circulated water through the simulated loop at effective crankshaft speeds as low as 500 rpm. In this pump, the full height impeller performed 30% better than the fish-mouthed impeller. At an effective 5000 crankshaft rpm, the pump was capable of producing a 12" water column (0.43 psi) with the full-height impeller and a 9" column (0.32 psi) with the fish-mouthed impeller. While producing a 3" water column, the full-height impeller flowed 54 cubic inches/min at an equivalent 5000 crankshaft rpm. At 500 crankshaft rpm it produced .040" psi while pumping water at 5 cubic inches/min. Even at such an optimistically low idle speed, this new pump should have no problem pumping coolant through the Offy. - Terry


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## dsage

Looks good. As usual. Thanks for sharing all the details.


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## propclock

Fantastic! I have been following and was very interested in this result. 
all the model pumps I have seen/built have close tolerances from the impeller to the case .
Thanks for all your R&D. a true fan of yours.


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## awake

I love your detailed testing and reporting of results - and glad you got it working!


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## Charles Lamont

I like the new pump and am pleased you are now getting a satisfactory output. Out of curiosity I took your 54cu in/min flow and 3" head and calculated the power output (Q x P), but I am having difficulty believing my own figures. I make the flow rate 0.015 litre/sec and the pressure 0.00736 bar, from which I get a power output of 0.01  watt !?


----------



## mayhugh1

Charles Lamont said:


> I like the new pump and am pleased you are now getting a satisfactory output. Out of curiosity I took your 54cu in/min flow and 3" head and calculated the power output (Q x P), but I am having difficulty believing my own figures. I make the flow rate 0.015 litre/sec and the pressure 0.00736 bar, from which I get a power output of 0.01  watt !?



I got the same results. I didn't know what to expect for the pump power. I guess the engine shouldn't have any problem handling  it. Interestingly, if the water is replaced by 40W oil, the power required for the same flow rate theoretically jumps up to 2 Watts. - Terry


----------



## Charles Lamont

I have thought about it a bit more and, surprisingly, it seems reasonable, if you see what I mean. It is worth remembering that Earth's gravity exerts on an apple a force of about one Newton. To lift an apple a metre in a second requires a Watt. So lifting a tablespoon of water three inches in a second is going to be quite a lot less. I think it has to do with human perception of different forms of energy: a watt of heat is nothing, a watt of light miserable, a watt of sound almost adequate, and a watt of mechanical work quite appreciable. So a small engine will pump what we perceive as quite a lot of water but will light only a few tiny bulbs. BTW, your pump will also be horribly inefficient, and has friction in the bearing and seal, so it will need more than 0.01W to drive it.


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## mayhugh1

Calorie consumption is another quantity whose perception borders on the unfair. In the gym last night I sweated on a stair stepper for half an hour. When done, it indicated I had climbed the equivalent of a 90 story building and in the process consumed only 175 calories - barely what was in your apple.   - Terry


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## awake

Clearly we need to petition our governments to pass legislation redefining the value of a calorie!


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## mayhugh1

The starter yoke is the carrier for starter shaft's forward bearing, and it's the engine's attachment point to the front motor mount. Being a prominent and distinguishing feature of the engine, I didn't want to alter its appearance. Although relatively straightforward to cast, the yoke would be a difficult part to machine from billet even with access to CNC. I purchased the pdf version of the files just before beginning this build, but I in fact bought a printed copy of the manual nearly twenty years ago just to learn how Ron had made this particular part.

Remarkably, it was to be machined from an aluminum bar with a 3/4" starting thickness before being formed around a steel mandrel using heat and a mallet. Ron didn't specify the alloy he used, but after researching the (non)availability of suitably thick 3000 or 5000 series bendable bar stock, I concluded he probably just used 6061. A full-size template is provided in the drawing package, but after cutting out a cardboard replica to trial fit to my partially assembled front end, I discovered a nasty interference with my redesigned water pump.

The outlet on Ron's pump exits below the starter yoke. The relocated outlet on my pump improved coolant flow but was now blocked by the side of the yoke. In order to clear the interference, the pump had to be rotated at least 20 degrees clockwise to get the outlet under the yoke. Each degree of pump rotation added a degree to a second angle that was going to have to be added to the pump's already tightly bent outlet tube. The clearance slots added to the pump for the starter shaft required the machining of a new pump body and cover. Since the pump's internals weren't modified, though, its previously measured performance should remain intact.

The starter shaft will eventually be supported in a bronze bearing pressed into the yoke, and so the yoke needs to be accurately formed and positioned on the engine so the starter shaft winds up collinear with the crankshaft.

Work on the yoke began with experiments to form 180 degree bends in 1/4" thick 6061 scrap bar stock. I constructed the mandrel suggested in the plans which was designed undersize to accommodate spring back. My initial tests showed negligible spring-back, and so I made a new full-size mandrel. I also added a shoulder bolt to securely anchor the workpiece in a guide slot machined into the mandrel. It's very important that the final part be symmetrically formed around the bore for the starter bearing. The addition of the mounting bolt adds consistency to the fixture, and it provides for inevitable alignment tweaks after the yoke cools.

My first attempt at a 180 degree bend was performed on a 1/4" piece of scrap that had been annealed in an oven at 775F for two hours. It bent smoothly without opening up its grain structure, but the heavy hammering required would most likely damage the delicate features on the actual part. My next attempt was to apply heat to the workpiece using a torch only along the bend lines and at a significantly higher temperature so the part could be formed using much lighter hammer blows. Some practice was required to avoid heat damage to the part which my large acetylene rosebud tip tended to do. My less brutal mapp torch just couldn't deliver enough heat. Forming was done using a two pound metal hammer buffered by a piece of 1" x 3" oak.

After gaining experience with scrap bar stock, the actual pre-machined yoke was easily formed on the very first try. My experiments didn't come up with an estimate for a stretching allowance, and so the arms of the yoke were machined long and trimmed later to fit. My wife assisted with the torch while I was busy with the hammer and oak plank. A machinist square insured the initial fit was very close, and only minor tweaking was needed to get the yoke to slide onto the front of the engine in perfect alignment with the crankshaft.

The installation of the bearing and the mounting of the yoke to the engine will be completed after the starter shaft is machined. - Terry


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## dnalot

Nice job bending aluminium. I am a aircraft & power-plant mechanic. I have had many occasion to repair or replace damaged parts that were formed. We would send the material out to be annealed to a soft state before we would form it and then send it out to be heat treated for hardness. And then we would reform the part again because the heat treating process would warp the part a little. Again , very nicely done. 

Mark T


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## mayhugh1

Before beginning work on the starter shaft, I tied up a few loose ends on the engine's lower half. Although I haven't yet given any thought as to how the engine and its running accessories will be mounted, I machined the front and rear motor mounts. They'll come in handy later while working on the top end. I also machined the drive tenon on the end of the water pump's impeller shaft so I could finally assemble the new pump.

Returning to the starter shaft, I drilled clearance holes through the sides of the yoke for its mounting screws and then transferred their locations to the crankcase halves for drilling and tapping. A test rod used during this step insured alignment among the yoke's starter shaft bore and the main bearings in the crankcase. With the yoke in place and its bronze bearing installed, the starter shaft's dimensions could be verified before it was machined. A last minute decision was to not permanently install the bronze bearing in the yoke. Instead, it will be held in place with a setscrew hidden by the front motor mount. This will allow the bearing to be replaced, if ever necessary, without having to make a new yoke.

The starter shaft was machined from 1144. During cranking, a one-way bearing pressed into its rear end will grip the nose of the crankshaft which will also be machined from Stressproof. During my Knucklehead build I learned something that Ron already knew: 1144 isn't hard enough to withstand the rigors of a sprag clutch. His solution was to Loctite a hardened ring onto the nose of the crankshaft. Since I was already working in the area, I machined and hardened a couple of these rings for use later on. The original drawings show a .060" deep clearance flat that must be ground on this ring to allow the nose of the crankshaft to slip past the 60 tooth oil pump drive gear on its way into the front cover ball bearing during final assembly. The plans also call for adding a replacement piece back into the ring after assembly. This bit of voodoo initially raised concern, but fortunately the split crankcase allows an assembly sequence that totally avoids the need for a notch.

After assembly, the starter shaft is held captive inside the yoke between a thrust surface on its bronze bearing and the main ball bearing in the front cover. A 3/8" hex machined on its outside end will be gripped during cranking by an adapter in a battery-powered drill.

Care was required during installation of the one-way bearing in the end of the starter shaft. Not only must it be installed in the proper direction to crank the engine clockwise (when viewed from the front of the engine), but the actual bore diameter is very important. The .750" diameter bearing is designed to be pressed into a .750" diameter bore regardless of what one is likely to measure as the o.d. of its thin drawn metal shell. The bearing's outer race depends upon it being installed in the proper size bore. A short length of rod stock inside the bearing adds some extra support during the pressing operation which, of course, must be accurately started to avoid damaging the bearing.

I'm looking forward to the next mini-project: the magneto which, like the Merlin's, will be a distributor in disguise. - Terry


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## stragenmitsuko

a true work of art ...


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## RonC9876

Terry: That Voodoo notch became necessary when the original smaller starter clutch was unable to handle the compression load for any length of time. I kept going larger and the interference with the gear became a problem. Cutting the notch and adding the piece back in works quite well and has never caused a problem. I fretted over that modification but it worked out well!


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## PhilWroundrockTX

mayhugh1 said:


> Before beginning work on the starter shaft, I tied up a few loose ends on the engine's lower half. Although I haven't yet given any thought as to how the engine and its running accessories will be mounted, I machined the front and rear motor mounts. They'll come in handy later while working on the top end. I also machined the drive tenon on the end of the water pump's impeller shaft so I could finally assemble the new pump.
> 
> Returning to the starter shaft, I drilled clearance holes through the sides of the yoke for its mounting screws and then transferred their locations to the crankcase halves for drilling and tapping. A test rod used during this step insured alignment among the yoke's starter shaft bore and the main bearings in the crankcase. With the yoke in place and its bronze bearing installed, the starter shaft's dimensions could be verified before it was machined. A last minute decision was to not permanently install the bronze bearing in the yoke. Instead, it will be held in place with a setscrew hidden by the front motor mount. This will allow the bearing to be replaced, if ever necessary, without having to make a new yoke.
> 
> The starter shaft was machined from 1144. During cranking, a one-way bearing pressed into its rear end will grip the nose of the crankshaft which will also be machined from Stressproof. During my Knucklehead build I learned something that Ron already knew: 1144 isn't hard enough to withstand the rigors of a sprag clutch. His solution was to Loctite a hardened ring onto the nose of the crankshaft. Since I was already working in the area, I machined and hardened a couple of these rings for use later on. The original drawings show a .060" deep clearance flat that must be ground this ring to allow the nose of the crankshaft to slip past the 60 tooth oil pump drive gear on its way into the front cover ball bearing during final assembly. The plans also call for adding a replacement piece back into the ring after assembly. This bit of voodoo initially raised concern, but fortunately the split crankcase allows an assembly sequence that totally avoids the need for a notch.
> 
> After assembly, the starter shaft is held captive inside the yoke between a thrust surface on its bronze bearing and the main ball bearing in the front cover. A 3/8" hex machined on its outside end will be gripped during cranking by an adapter in a battery-powered drill.
> 
> Care was required during installation of the one-way bearing in the end of the starter shaft. Not only must it be installed in the proper direction to crank the engine clockwise (when viewed from the front of the engine), but the actual bore diameter is very important. The .750" diameter bearing is designed to be pressed into a .750" diameter bore regardless of what one is likely to measure as the o.d. of its thin drawn metal shell. The bearing's outer race depends upon it being installed in the proper size bore. A short length of rod stock inside the bearing adds some extra support during the pressing operation which, of course, must be accurately started to avoid damaging the bearing.
> 
> I'm looking forward to the next mini-project: the magneto which, like the Merlin's, will be a distributor in disguise. - Terry
> 
> 
> View attachment 113673
> View attachment 113674
> View attachment 113675
> View attachment 113676
> View attachment 113682
> View attachment 113683
> View attachment 113684
> View attachment 113685
> View attachment 113686
> View attachment 113687


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## PhilWroundrockTX

Hey Terry,        I'm always in awe of the art/perfection/creativeness/etc of your work and really enjoy the detailed documentation of your processes along with fine photos of projects both in progress and finished pieces. Know I'll never get to your level of work but am inspired to improve both my projects and start keeping notes to help in future similar efforts. Thanks and can't wait to see and at some point hear the Offy!


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## Tim1974

Same here I love the thread allways good reading and very nice work


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## mayhugh1

A bright red magneto prominently mounted on its front end seems to be a signature feature of the Offy 270. The quarter scale's version is really just a distributor meaning its high voltage will be generated elsewhere. Ron sneaked his voltage into the enclosure through the magneto's 'Points' terminal in order to maintain the illusion of a magneto. This innocuous-looking terminal that would have been at several hundred volts potential in the full-scale engine will ride at several thousand volts potential in the model.

The high voltage's side entry complicates the design of the rotor. A slip ring rather than the simple button contact found in conventional distributors was used to complete the path to the rotor. In order to avoid metal-to-metal wear and potential metal dust that could create leakage paths inside the distributor, the actual coupling to the rotor was accomplished through an air gap. Since this gap is in series with the model's tiny plug gaps, it robs energy from the ignition system.

My first inclination was to retain the slip ring but eliminate the air gap with a spring-loaded carbon brush assembly. After prototyping it, though, I had second thoughts about the inevitable carbon dust I'd noticed around commutators in some of the dc motors I'd disassembled.

Eventually, I decided upon a conventional rotor with its axial contact button. Similar to Ron's distributor, the high voltage is brought into the enclosure through an end-mounted terminal on the cover. However, I modified the cover to accommodate a wire running through a drilled passage between this terminal and the pressed-in button contact. One of the photos shows the voltage path through the modeled cross-section of the modified cover.

Although not obvious from the resulting hue in my photos, the cover was machined from red Delrin. The tower electrodes were turned from phosphor bronze and hard pressed into the top of the cover. The rotor contacts on their ends were exposed after boring the opening for the rotor. The side mounted screw terminal was made up with a threaded insert screwed into the cover. The interconnecting wire is sandwiched under the pressed-in button at one end and soldered to the insert at the other.

Finally, the four high voltage towers were threaded for plastic wire retaining caps similar to those in the original design. Excess material left on the cover's mounting flange will be removed later after the enclosure's details have been finally worked out. Those details depend upon the design of the rotor which in turn was waiting upon a proven cover. With it now in hand, work can continue on the magneto which for the most part will follow Ron's original design. - Terry


----------



## petertha

Very nice, Terry.

I noticed the FS engine mags had very prominent ignition wire tower caps. Any idea what purpose that served? Seems like the ones on aircraft mags of the era were slimmer.

Do you have any tricks for finishing Delrin? Yours looks like it came from a mold. Seems like my attempts just get dull & fuzzy.


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## mayhugh1

Petertha,

I'm not really sure. Some of the full scale magnetos had metal enclosures, and taller insulators on the towers would provide needed isolation from ground. Aircraft magnetos probably benefit from all the path length they can get in order to combat leakage due to the effects of lower atmospheric pressure and/or condensation.

I keep Delrin wet with coolant during machining. The cover was cut with an 1/8" ball endmill running 12 ipm at 5000 rpm. - Terry


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## RonC9876

Terry: a spark gap in series with the plug can be a good thing. Spark intensifiers were and still are sold and some people swear by them. The additional gap is said to allow the voltage to build before the plug fires. At any rate it is said that the added gap only adds about a hundred ohms more resistance to the circuit. Ionized air is basically a short circuit. All I can say is that as designed, the magneto/ distributor has worked flawlessly over the years and the ignition has been great to 13 thousand rpm. I don’t run the Offy over 10 thou now days. Had other parts fail pushing it just to see how fast it would go!


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## stevehuckss396

I have personally seen 10k rpm from Ron's engine. Scary but freaking awesome. The ignition system was flawless.


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## mayhugh1

stevehuckss396 said:


> I have personally seen 10k rpm from Ron's engine. Scary but freaking awesome. The ignition system was flawless.



I don't doubt it. I can't resist tinkering though. - Terry


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## awake

Incredible finish on that delrin. Looks like something is engraved on the top - maybe the cylinder numbers for each position?


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## mayhugh1

awake said:


> Incredible finish on that delrin. Looks like something is engraved on the top - maybe the cylinder numbers for each position?


Yes, the plug wire numbers are engraved on the top of the cover.


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## mayhugh1

The body of the magneto was machined from the same chunk of red Delrin used for the cover. One of the photos shows a model of its cross section including the gears and bearings that will be installed later. Some minor changes made to the original design included the addition of a second (outboard) bearing for the input shaft as well as positive stops for all the bearing retainers. After twenty years, the Small Parts part numbers provided in the plans for the 2:1 miter gear set have become obsolete, but Boston Gear's L159Y-G, -P appear to be equivalents.

For the trigger device, I'm using an Infineon TLE4095 Hall effect transistor. It's supported inside a close-fitting cavity on the inboard side of the magneto's body. A machined end cap, that will later double as the input shaft's bearing retainer, holds it securely in place. Testing showed this particular device is reliably triggered through as much as a quarter inch of air by an 1/8" diameter x 1/16" thick Neodymium magnet. A pair of these magnets will be mounted to the end of an adjustable sleeve attached to the magneto's driving shaft leaving the running gap much less than half this amount.

A cosmetic end cap was lathe turned for the outboard side of the magneto. It closes up one of the openings used to access the interior of the body during its machining. The retainer for the upper rotor bearing was turned from white Delrin. After assembly, it will remain sandwiched between the magneto's cover and a machined recess in the body after assembly.

Except for the rotor, whose tip will include a .003" 'spark intensifying' gap, this completed the machining of the magneto's Delrin parts. Its platform on the crankcase front cover was drilled for mounting screws, and the alignment of the magneto's input shaft bore with the right angle drive block shaft was finally verified.

The next steps will be to machine the rotor and to modify and install the stock gears and bearings so the unit can be exercised under high voltage. - Terry


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## propclock

Just my 1.414 cents worth(square root of 2) I make many ignitions for 
Myself and BAEM members. I really like the Dave Sage IGBT design.
I have shrunk it to ~1"square and use SMD components.
Instead of Hall sensors I really like the use of a simple reed relay.
Not an issue in your case but halls are sometimes placed in the HV 
distributor cap and they get zapped, continuously.  A reed has no problem with this . The switching current is ~1ma. They are fast ! 
and draw NO current when not active or in the timeout mode .
And a hall draws ~10ma continuously. Finally if a ground is available,
not in your case, only 1 wire is required , gnd (the distributor) and trigger wire.  
Reeds are cheap and almost indestructible, but made of glass. 
I usually get mine from Electronic Goldmine but I have some super small ones made for the pacemaker industry. (not readily available)
Just my input.


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## mayhugh1

Propclock,
Thanks for your insightful comments.

I built my first two engines with transistor ignitions (TIM-6 variations) but then switched to CDI's because the coil, the energy storage element in a transistorized ignition, just doesn't scale very well and is difficult to hide or disguise. The capacitor in a CDI is a much more efficient energy storage element making the whole ignition considerably smaller than an equivalent transistor ignition and so easier to deal with. Some have mentioned using COP coils, but since they're designed for single plug high energy applications, they probably require a lot of current.

I've personally never had problems with Hall devices even when using them inside distributors. I can remember blowing only one, and that was due to my carelessness. I understand the issues associated with using them, though, and can fully appreciate why many would rather avoid them.

By the way, Doc1955, who occasionally posts on this forum, has built some impressive and realistic looking coils on Youtube. Although they're still a bit large for my taste, he's probably got them as small as is practical. I haven't tried my hand at winding one, because I've never ginned up the interest in dealing with the cumulative corona damage that can occur in the windings. I don't know how Doc's coils are holding up over time, but he may be getting away with just filling their containers with paraffin wax.

I've been purchasing Roy Sholl's CDI units. Even though they're pricey, they appear to be well crafted, and my experiences with them have been positive. - Terry


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## dsage

Terry:
Maybe I'm interpreting your drawing incorrectly  It looks like the sensor top EDGE is sensing the magnet. According to the spec sheet the face of the sensor with the writing on it is the sensing face. Not to say it won't work on edge (I guess) but...

BTW I looked on Digikey for TLE4095. Not found.
Was it a TLE4096?


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## dsage

I think Roy says his CDI modules are rated for about 11,000 rpm on a single cylinder engine. (They are from the model airplane industry). Ive tested them as such. The high voltage is petering out at much higher rpm. The HV power supply can't recover quickly enough to charge the capacitor fully.
That would be only 2750 rpm on a four cylinder engine. Just saying...
Having said that I run one of his older modules on my Howell / Sage V8 and it runs ok, but I never rev it more than about 3,000 for fear of it coming apart.
If you're going to impress folks with the high rpm (ala Ron) you might have problems.


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## mayhugh1

...... Maybe I'm interpreting your drawing incorrectly  Itlooks like the sensor top EDGE is sensing the magnet. According to the spec sheet the face ofthe sensor with the writing on it is the sensingface. Not to say it won't work on edge (I guess)but...
BTW I looked on Digikey for TLE4095. Not found.
Was it a TLE4096? ......

Dave,
I have the branded side facing the magnet. I double checked the data sheet and that's what it is calling for. I purchased a number of these 4095's during my Merlin build and am not surprised they're no longer available. The market lifetime of Hall sensors seems to be pretty short. - Terry


----------



## dsage

mayhugh1 said:


> ...... Maybe I'm interpreting your drawing incorrectly  Itlooks like the sensor top EDGE is sensing the magnet. According to the spec sheet the face ofthe sensor with the writing on it is the sensingface. Not to say it won't work on edge (I guess)but...
> BTW I looked on Digikey for TLE4095. Not found.
> Was it a TLE4096? ......
> 
> Dave,
> I have the branded side facing the magnet. I double checked the data sheet and that's what it is calling for. I purchased a number of these 4095's during my Merlin build and am not surprised they're no longer available. The market lifetime of Hall sensors seems to be pretty short. - Terry




Good stuff. I guess I was interpreting the drawing incorrectly. I hate it when you find a good part and it goes obsolete. Sometimes they make it better though. Then you have to find what they changed it to.
Thanks


----------



## mayhugh1

dsage said:


> I think Roy says his CDI modules are rated for about 11,000 rpm on a single cylinder engine. (They are from the model airplane industry). Ive tested them as such. The high voltage is petering out at much higher rpm. The HV power supply can't recover quickly enough to charge the capacitor fully.
> That would be only 2750 rpm on a four cylinder engine. Just saying...
> Having said that I run one of his older modules on my Howell / Sage V8 and it runs ok, but I never rev it more than about 3,000 for fear of it coming apart.
> If you're going to impress folks with the high rpm (ala Ron) you might have problems.



Good point on the rpm limitations. It's worth some testing that I'll probably do even though I doubt I'll ever rev mine as high as Ron (assuming my engine actually does run).  My understanding of Roy's spec is that it is 'sparks per minute' and not rpm. And so, I think (hope) you're spark calculation is off by a factor of two. - Terry


----------



## dsage

mayhugh1 said:


> Good point on the rpm limitations. It's worth some testing that I'll probably do even though I doubt I'll ever rev mine as high as Ron (assuming my engine actually does run).  My understanding of Roy's spec is that it is 'sparks per minute' and not rpm. And so, I think (hope) you're spark calculation is off by a factor of two. - Terry



Of course your engine is going to run.
Was it sparks per minute? I don't recall. Whatever. it's something to consider. Also I found there wasn't much spark energy so if you have high compression there could be an issue as well. My George Britnell V-twin has about 8:1 and I think the CDI could be contributing to it's poor running. I have yet to try one of my drivers and a full sized coil to see if it runs any better.
Whatever the case you'll work it out.


----------



## RonC9876

Guys: I am still using the old Floyd Carter designed board with a Modelelectric coil and powered by two 2 volt lead acid cells wired in series for four volts. This ignition has proven to be both reliable and capable of firing four plugs to high rpms. The difference with my engine is that I also use an electronic advance board designed by David Bowes to advance the timing as the engine gains rpm. I could never get over 8000 rpm without it. The initial timing had to be set at about 15 degrees advance. If the initial advance was set any earlier than that the engine would backfire and destroy the needle clutch used to start it. It also would hurt my wrist. This engine is powerful. With the electronic-advance board, I can set the initial timing at about 10 degrees, which helps with starting and idling, and then get up to 40 degrees of advance on the top end. I had a lot of fun running at these speeds till parts started failing. I had a gear tooth break off and destroy the whole gear train and I had a crankshaft break in half also. But I learned a lot about ignitions and timing on these small engines. From the beginning I knew this engine had the power to destroy itself. I proved it several times!


----------



## dsage

LOL.
You certainly do push it to the max. Always makes me cringe when you give it "the Beans"
But such a wonderful running engine.
Thanks Ron.


----------



## tornitore45

I have blown several Hall Effect devices until I realized my spark box was connected wrong: feeding the HV to the chassis and the ground to the plug tip.
As a professional power engineer I am ashamed to to confess it.
No more failure after that.
The secret in pacific coexistence of sensitive and power electronic is in understanding and controlling the GND net.  Return currents from power elements should never be allowed to run through a wire extended to a low voltage sensitive element.


----------



## mayhugh1

I've enjoyed working on the magneto, and despite my efforts to stretch out its construction, it's sadly coming to an end. Like the water pump, it's one of the few sub-assemblies that I'll be able to check off as fully tested before the engine is completed.

One of the photos shows its internals just before being installed inside the body. The thickness of the spacer behind the gear on the input shaft was trial/error trimmed to set the pinion depth for smooth operation and nearly zero rotor backlash. The end of the magneto's 3/16" input shaft was machined with the male half of an Oldham coupler. It meshes with the female half machined into the end of the 1/4" shaft sticking out from the drive block.

The white Delrin rotor has a relatively thick brass tip electrode and a .003" running gap between it and the tower electrodes. A flat phosphor bronze spring provides positive electrical contact between it and the high voltage button in the magneto's cover. An 0-80 flat head screw holds the pieces in place inside a close fitting slot in the rotor. The rotor is a snug fit on its shaft with a 2-56 grub screw adding insurance against slippage. A witness mark engraved on the top flange of the magneto's body will be used during final timing adjustments to locate the rotor directly under the #1 tower electrode.

Ron's last post resonated with me. Although I don't plan running above the full-size engine's 6k rpm rating, I'm having second thoughts about the current lack of timing control especially during starting. Even with a modest 10 deg fixed advance, I get occasional attention-grabbing kickbacks when starting my Knucklehead. Not having been through Ron's original development work, I'm not yet as comfortable as he is with the engine's starting system whose teething pains included the nose of a crankshaft that I don't want to machine more than once.

Ron mentioned that his engine's timing is controlled with a board purchased from David Bowes. David designed and sold a PIC-based controller for his EVIC-111 engine published in the final issues of Strictly IC magazine during 2001-2002. As expected, after contacting him, I learned these boards are no longer available although his website is still here:

http://rbowes1.11net.com/dbowes/index.htm

Hardening the controller electronics against ignition EMI was probably no easy feat, and I'm impressed Ron's board is still working after all these years. Although it would be an interesting challenge to design an electronic advance, my last minute decision was to simply add a manual control to the magneto.

This change involved scrapping the already completed end plate and replacing it with one that can manually rotate the Hall sensor 20 (distributor) degrees. This will allow retarding the timing during starting but provide up to 40 degrees (crankshaft) advance while running. The photos show the new advance-able end plate that will now house the Hall device. Since this rather complex part required some involved fixturing, I made several spares while still set up.

I wasn't confident in the friction between the Delrin body and the new advance plate being able to maintain its setting under vibration, and so I added a fixed metal back-up plate between the two. The plate was machined while sandwiched between a couple pieces of sacrificial aluminum, and so there was no effort involved in adding a couple extra pieces to the stack for experiments. The photo shows the piece of .005" thick stainless shim rolled into a beveled washer that I finally used. Although the advance arm can later be controlled by the throttle positioner, an obtrusive non-original linkage would be required.

I didn't do myself any favors with the tiny space that I left for soldering the connections to the sensor. If I were doing it over, I'd make this portion of the arm a little longer. After coming up with a soldering fixture, I installed sensors and cables in all the plates I made and backfilled them with JB-Weld.

The Oldham coupler between the magneto and the gear tower's right angle drive block is concealed by a faux aluminum housing that contains a pair of trigger magnets. Three setscrews lock this housing to the drive block's shaft in order to fix the ignition timing to the engine's camshaft. Preliminary testing showed the magnets triggering the sensor as expected, and so the next step will be to come up with the ignition module so the entire system can be finally tested with actual spark plugs. - Terry


----------



## petertha

I've had to marry quite a few awkward wiring harnesses together for RC work. 

For things that need to be soldered, my go to method is a small plate of something heat resistant like glass & if necessary 'shim' supports from arborite scrap. And Kapton tape. You can usually get everything pre-positioned & aligned so your only remaining task is applying heat & solder to the joint. The Kapton wont burn or let go under the heat.

For joints that see any kind of vibration or hard bends or torturous routing that might strain solder joints, I've become fond of these pure silver crimp tubes. They sell a special plier & its foolishly easy to make crisp strong joints. The resistance is as good or better than solder. 
https://www.amazon.ca/Beadalon-Vari...alon+silver+crimp+tubes&qid=1583118989&sr=8-1

Sometimes you just cant get teeny sections of heat shrink tubing into tightly constrained wiring bundles so I like this stuff. Paint it on the exposed conductors with a detail brush & it makes a nice insulation layer.
https://www.amazon.ca/Permatex-8512...=liquid+electrical+tape&qid=1583119638&sr=8-5


----------



## tornitore45

Is there a reason why you twisted the red and black wires?
Is to match the already defined connections sequence at the end not shown?
What is the white piece under the Hall device?


----------



## RonC9876

Terry: I love your advance set up. I designed a mechanical advance for my Sealion using fly weights working against a garter spring . It causes the magnet disc to rotate in the advance direction as the rpm increases much in the same way as the advance used to work on older model cars. It works very well, but it advances very quickly and gives  the advance very suddenly. The electronic module advances the timing in several steps and does it smoothly. Great job on your design as usual.


----------



## mayhugh1

tornitore45 said:


> Is there a reason why you twisted the red and black wires?
> Is to match the already defined connections sequence at the end not shown?
> What is the white piece under the Hall device?


Mauro,
I had to twist two of the wires to keep the color coding consistent with my other projects: red=Vcc, black=gnd, and white=signal. I can usually buy a 32 AWG version of the cable that more easily handles the twist, but the local Hobbytown didn't have any in stock and I couldn't find any on Amazon. The white piece is a sliver of Teflon used to protect the wood soldering fixture. It wasn't part of the final assembly. I wasn't entirely happy with the final parts, but they passed my 'tug' tests still working with no shorts to the housing, and so we'll see. - Terry


----------



## Ghosty

Terry, here is some that may help.
https://hobbyking.com/en_us/twisted...835&indexName=hbk_live_magento_en_us_products
Or
https://hobbyking.com/en_us/twisted...835&indexName=hbk_live_magento_en_us_products

Cheers


----------



## mayhugh1

Ghosty said:


> Terry, here is some that may help.
> https://hobbyking.com/en_us/twisted...835&indexName=hbk_live_magento_en_us_products
> Or
> https://hobbyking.com/en_us/twisted...835&indexName=hbk_live_magento_en_us_products
> 
> Cheers


Ghosty,
Thanks. That's the 22 AWG that I used. It's 32 AWG that I'd like to locate. - Terry


----------



## Ghosty

Terry,
That may be a lot harder to find as even the model world does not use it much anymore. Only found these https://hobbyking.com/en_us/30cm-se...412&indexName=hbk_live_magento_en_us_products May be worth looking at as they are on sale.
Cheers
Andrew


----------



## mayhugh1

Ghosty said:


> Terry,
> That may be a lot harder to find as even the model world does not use it much anymore. Only found these https://hobbyking.com/en_us/30cm-se...412&indexName=hbk_live_magento_en_us_products May be worth looking at as they are on sale.
> Cheers
> Andrew



Yep ... those out of stock parts are the ones.


----------



## Ghosty

They are in stock in the Australian wearhouse

Cheers
Andrew


----------



## petertha

30 & 32 AWG here in various flavors. He is my go-to crack dealer for good quality plugs, pins, crimp tool...).
http://www.hansenhobbies.com/products/connectors/wire/servo_ec/
Check his write-ups on RC wires, they are not all created equal.

Strangely no AWG specified but I can attest to good resistance in long lengths. Its very thin & supple. We only really get fussy with the fine stuff when gram counting is the issue.
https://www.hyperflight.co.uk/produ...a-light-servo-twisted-extension-cable-3-7-g-m


----------



## mayhugh1

petertha said:


> 30 & 32 AWG here in various flavors. He is my go-to crack dealer for good quality plugs, pins, crimp tool...).
> http://www.hansenhobbies.com/products/connectors/wire/servo_ec/
> Check his write-ups on RC wires, they are not all created equal.
> 
> Strangely no AWG specified but I can attest to good resistance in long lengths. Its very thin & supple. We only really get fussy with the fine stuff when gram counting is the issue.
> https://www.hyperflight.co.uk/produ...a-light-servo-twisted-extension-cable-3-7-g-m


Thanks for the tip.
I ordered some from Hansenhobbies.
Terry


----------



## gbritnell

Hi Terry,
The engine is coming along great! Like you I had been using 32 gauge Futaba wire for my Hall hookups but the supply seemed to dry up. I then ordered 32 ga. wire (individual lengths) white, black and red wire from Mcmaster-Carr. I twist my wires together so it actually made it easier to do. I will order some from Hansen and see how it works.
As far as ignition timing I have been pretty lucky. My 302 is set at 30-35 degrees and it starts without kickback and will go from idle (about 1200 rpm) to full rev very nicely. I can bring the idle down by retarding the ignition and adjusting the carb but I think it's more a case of the scale flywheel not having enough inertia. 
My V-twin has ungodly compression but has never kicked back. The timing on that is about 20 degrees BTDC. I have no way of changing the timing while the engine is running so I don't know if the overall operating characteristics would be better or worse. 
My inline 4 cylinder engine has linkage hooked from the carb to the distributor and the initial timing is about 10-15 degrees. At full song the timing goes to about 30 degrees. 
My Holt is set to 15 degrees and the points are on a moveable base so I can adjust the timing while running. Curiously on the Holt timing doesn't make much difference other than change the sound the engine makes. That engine isn't meant to be a fast revver so it's not important. 
I have seen Ron's engine run many times and it's very impressive (loud also) I can't wait to see how yours does. 
gbritnell


----------



## petertha

Just curious what makes 32 AWG wire more desirable in this application?


----------



## ddmckee54

Just a thought, but 30 AWG grey flat cables are readily available up to 40 conductors.  Strip off as many conductors as you need and mark the conductor on one side with an indelible marker.  As long as you consistently number the conductors starting with the marked conductor, you can build your own custom flat cables in almost any width.

Sure the colored cables look pretty, but you can rob grey flat cables out of most defunct PC's.

Don


----------



## mayhugh1

petertha said:


> Just curious what makes 32 AWG wire more desirable in this application?


The smaller diameter wire is more in scale with the rest of the engine, and it can be potted for strain relief in smaller cavities in smaller parts. -Terry


----------



## mayhugh1

As with most of the other engines I've built, an electric fuel pump will eventually supply gasoline to the carburetors. In this case, the pump will probably be hidden in a faux fuel cell on the floor of the engine stand. Since an electric starter isn't being used, I'll be able to get away with a 6V battery and no dc/dc converters.

The enclosure for the 'Engine Control Module' was machined from a block of gray PVC. Although there's no wasted space inside, it came out much larger than I would have liked. Rather than trying to hide it, I dressed up its exterior and will leave it in plain sight on the display stand. It was bead blasted to remove its shiny exterior surface in order to make it look like a pot metal casting.

A Magnum CDI from S/S Machine provides the high voltage for the ignition. A simple board of my own design located between it and the Hall sensor provides a trigger indicator that doesn't require the CDI to be powered up. It provides a convenient timing indicator during setup and troubleshooting that doesn't require hassling with the high voltage. The module receives the battery voltage and Hall trigger signal and outputs the spark plug voltages to the magneto and a manually controlled dc voltage to the fuel pump. I also added provision for the possibility of an electric radiator fan. After verifying the various controller functions, the next step will be to cobble up a fixture to run the magneto at speed so the ignition's performance can be tested with spark plug loads. - Terry


----------



## dsage

Nice work.  Everything hiding in plain view. I like it.


----------



## PhilWroundrockTX

NICE! All of design, appearence, function (anticipated) and documentation are the highest level. Congrats again.


----------



## awake

That looks so good - hard to believe it is milled plastic rather than cast aluminum!


----------



## Gabe J DiMarino

Sand blasted after he milled it give the impression of it being cast.


----------



## michelko

Wow, awesome work. The case reminds me on a MSD Streetfire Ignition Module.

Regards Michael


----------



## mayhugh1

You're close. Here's the one I used as a model:


----------



## mayhugh1

It was simple enough to throw together a test fixture for the completed ignition, but like most things in my shop that start out simple, it grew into a project. I wanted to use the spindle of my Tormach to drive the magneto since it can be easily and accurately spun up to 5 krpm - a perfect range for testing. However, I wasn't sure if the EMI radiated by the plug wires might create problems for the Tormach's electronics or the computer controlling it. The fast rise times of a CDI's EMI-rich secondary waveform is one of the reasons CDI's fell out of favor with the automotive industry. Even though they're capable of generating impressively long arcs, stray capacitive coupling of their steep leading edges created difficult to control cross-fire problems in full-size engine applications.

I didn't want a rigid mechanical connection between the mill's spindle and my fixture that might damage the magneto should EMI cause one of the axes to take off on its on. So, I used a breakaway Delrin coupler between the two. This required the magneto and its trigger disk to become a standalone assembly with its own input shaft. What should have been a one hour side project turned into a full day of throw-away work.

The scope photos were collected using a high impedance probe coupled to the output of the CDI through only the stray capacitance between the two. Although they're accurate snapshots of the actual waveforms, they provide no real information about voltage levels. The extremely fast rise times in the CDI's ringing outputs are an order of magnitude faster than anything created by an equivalent transistorized ignition. Each lobe on each waveform can potentially create a unique discharge, and after-market suppliers didn't miss their opportunity to promote CDI's as 'multi-spark' systems. The short durations of these sparks, however, limit the energy carried by them even while jumping impressively wide gaps in display cases on part suppliers' counters. In a model engine where less than a mIllijoule is probably needed to reliably fire a plug, they're hard to beat when the importance of the ignition's small physical size outweighs its cost.

The ring or resonant frequency of the output of a points or transistorized ignition is limited by the large inductance and interwinding capacitance of their low Q energy storage coils. The external capacitor nearly always used with mechanical points will dominate any stray capacitance and keep its resonant frequency in the tens of kHz. The small inductance and interwinding capacitance of the CDI's output transformer pushes its ring frequency into the tens of MHz and leaving it heavily dependent upon stray wiring capacitance. This effect is evident in my measurements where a minor change in stray capacitance between my initial bench setup and the later one on the mill dropped the resonance from 67 MHz to 25 MHz.

Although I don't know how much actual energy the S/S Magnum CDI is really capable of, I saw no significant drop in its output in my four cylinder test over an effective crankshaft range of nearly 5k rpm. After ten minutes or so at full speed everything seemed to be still working, and so it looks like it's time to begin work on the cylinder head. - Terry


----------



## dsage

Very nice setup for testing.
Out of curiosity have you ever tried building a pressure chamber for a spark plug? I never got around to it (yet).
As you know ignition system performance changes significantly with pressure and fuel / oil etc. I wonder how the S/S unit performs under "real" conditions? I have several of them and I've always wondered if they are the source of poor running. Although my V8 seems to be ok at <5k. The maximum I feel it's mechanically safe to run it.
Would be an interesting test since you have such a nice setup made there. (variable air pressure via regulator to the chamber to simulate and record compression).
It has always surprised me that my scope has never been affected by the EMI considering they have processors in them these days. I see yours was pretty close by.
My Fluke meter just sitting on the bench (un-connected) near a CDI freaks out. But then DVM' generally have little shielding.
Nice job.


----------



## dsage

BTW. You might be able to estimate the energy output of the CDI unit by the energy input.
I'm sure you are more capable in the math for that one.
I once saw a voltage divider-like setup using a series stack of well spaced zeners to drop most of the HV output and a final resistor to ground where you could measure voltage across the resistor to make a real measurement.
I never bothered making that (yet) either.


----------



## propclock

Hi Dave your FPGA driver for a CoilOverPlug Coil drives my
blown V8 with  compression ratio ~>10 at over 7 krpm  no problem.
Also Every Day Practical Electronics had an issue devoted to
spark energy. A whole! bunch of zeners and a pic chip to measure the 
energy.


----------



## dsage

Yes my driver works well but as Terry pointed out (and I agree with) it's a lot nicer to be able to hide the ignition system - not easy with a full sized coil. I like to hide the ignition in the small wooden plate / box below the engine. That's also why I'm using the CDI units (for the most part). Terry's solution was really nice.
Yes I think that article is what I referred to concerning a real way to measure the ignition output. I'd like to build one of those. I need to find a cheap source for high power zeners (a couple of dozen as I remember it).
Not sure how to do the calculations on such a spike of power from a CDI though.


----------



## mayhugh1

Dave,

I once tried making the measurements you're asking about in order to determine just how much energy is needed to fire the plugs in a model engine. I first tried using a variable spark gap and the Paschen curve to account for the pressure inside the cylinder. However, this didn't include the effects of a wet fuel which I suspect are also important. My very shaky guesstimate from those tests came out to be somewhere between 3 and 4 mJ. 

I later used a TIM-6 and a scope connected to its output through a voltage divider while running my Howell V-4 and graphically computed the energy in the output voltage waveform with help of its current waveform. As I reduced the coil voltage, I found the plugs continuing to fire below 2mJ and not showing signs of misfiring until somewhat below 1 mJ. Using the ignition's average current draw and making some efficiency assumptions gave me a similar result.

I didn't know how to handle the complex multi-spark waveform in Roy's (at that time, his 'old' style) CDI. I was able to trace out its schematic, however, and make some assumptions about the capacitor and it charging voltage. In those days, Roy also offered an 'off-menu' high rpm option that used a half-size capacitor. (I eventually used a pair of these CDI's in my 18 cylinder radial.) Making ratio'd comparative tests between the two versions of his CDI with their two different size capacitors, I eventually reached the conclusion that the minimum number was probably around 1 mJ which has been my assumption ever since. During all  my testing, however, I forgot to include cold-start-up conditions. Of course, actual compression as well as the placement of the plug in the cylinder are also important variables.

I think federal safety guidelines assume .1 mJ is capable of non-pressurized ignition of volatile gases, and the one full-size Ford Kettering ignition that I analyzed back in the seventies happened to put out 8 mJ. I've read, but not personally verified, that some modern day full-size ignitions are using 75 mJ to help meet clean air regulations. - Terry


----------



## dsage

Thanks for your efforts and observations.
I assumed (as usual) you had done a thorough analysis of systems along the way. One of the other reasons they've gone away from CDI systems in cars is that a conventional coil when discharged gives a (relatively) long burn time as opposed to the very fast (albeit high voltage) spike of a CDI. In troublesome conditions the long energy release can be beneficial. I think this is also why the CDI systems went to multi-spark. Since the longer spark /arc was beneficial but not possible with a CDI the old saying "if at first you don't succeed...." so they give out multiple quick sparks. Better ??
Ford has what they call  "a multi-strike system" using  coils at low rpms where I suppose it might  help cold starting.
As I mentioned I'd like nothing more than to use my driver and a COP coil but when the ignition system is bigger than the engine I don't like the looks of it so I've resisted.
That said George Britnell uses an external ignition box (some using my drivers) and you don't seem to notice it along side his wonderful workmanship. So maybe I should change my thoughts on spending so much on the S/S CDI units.
Thanks again for your observations.


----------



## stragenmitsuko

The spark energy meter was described in the epe magazine february 2016 .
It used 30 zener 5watt diodes , wich cost abt half a $ each .
It looked quite an interesting circuit , so I was tempted to build it , but never got round to it .
I must have the article somewhere as a pdf should any potential builder like to take a look at it before purchasing the magazine .





Pat


----------



## srobovak

Hi Terry, What's the size of those capacitors you use on the "Trigger Indicator Board"? You don't have them in your schematic. Thanks - Branislav


----------



## mayhugh1

srobovak said:


> Hi Terry, What's the size of those capacitors you use on the "Trigger Indicator Board"? You don't have them in your schematic. Thanks - Branislav



Oops,  they're a 10uF tantalum in parallel with a .01uF ceramic. - Terry


----------



## Ghosty

Terry,
 Looking at the wiring diagram, the hall device is powered when the PWR switch is turned on, Not switched on with the IGN switch, any reason for this? Just thinking out loud.
Cheers
Andrew


----------



## mayhugh1

Ghosty said:


> Terry,
> Looking at the wiring diagram, the hall device is powered when the PWR switch is turned on, Not switched on with the IGN switch, any reason for this? Just thinking out loud.
> Cheers
> Andrew



The PWR switch powers up the Hall device so I can see the trigger indicator without powering up the CDI which is what the IGN switch does. The Hall device remains powered when the IGN switch is turned ON allowing it to fire the CDI. - Terry


----------



## mayhugh1

The head will probably be the most complex part on my version of Ron's Offy. It's eight multi-angled surfaces and arrays of internal passages require lots of patience and attention. My confidence in getting it right the first time was so low that I decided to run two parts in parallel. One, a 6061 'mule', will be used to verify my setups and test the risky operations before machining the 7075 'production' part.

A few changes made to the original design included shaving the head's bottom surface to accommodate a .020" head gasket. Modifications made earlier to the block to pick up additional gasket material around the cylinders have also altered the locations of several of the holes. The thread depth of the head mounting screws was increased a bit, and I added stock to the head's top surface for integral flanges that will increase the thread depth of the water pipe's mounting screws.

Ron appears to have used VR2L spark plugs with 1/4-32 threaded bodies. The documentation shows them mounted high up in the head with their electrodes not quite inside the combustion chamber. This appears to have been needed to keep a portion of the plug's wrench hex above the top surface of the head. There isn't enough clearance between the internal coolant passages for a recess around the plug to handle a standard socket. Smaller diameter Viper Z1's would eliminate the problem, but in the end I stayed with the VR2L's. I was able to un-shroud the plugs by using a smaller recess that will require a turned-down socket for plug installation.

Construction began by squaring up a pair of blanks with the head's outside finished dimensions. The conical combustion chambers and assorted holes for the head mounting screws and oil and water passages were the first features to be machined. The lengthwise internal coolant passages were later drilled and connected with four cross-drilled passages. The open ends of the cross passages were sealed with close-fitted Loctited aluminum plugs that were additionally secured with steel pins.

The exact angles of the 36 degree cam box deck surfaces are very critical as their accuracy will later affect the mesh between the camshaft and their drive gears inside the gear tower. To insure the precision of this machining step, a pair of 36 degree angle blocks were first machined. These blocks accurately cradled the head in the mill vise for these operations and provide a precise reference point for them. Since both deck surfaces are identical, the head was flipped, around and the exact setup and steps were used to machine both sides.

After completing and verifying both cam box deck surfaces on the mule, I managed to install my 'production' part upside down when I milled its second surface. Mules aren't supposed to be able to reproduce, but so far with a 60% completed head I now have two and counting. I hated to lose my first production head because I didn't have anymore 7075 material. - Terry


----------



## petertha

Been looking forward to these parts! 
What kind of drill is that? (0.137" x 5" deep)


----------



## mayhugh1

petertha said:


> Been looking forward to these parts!
> What kind of drill is that? (0.137" x 5" deep)



Petertha,
It's a Guhring parabolic drill.
Terry


----------



## mayhugh1

Work continued on the head with sealing up the two long internal coolant passages still open at its rear. As with the cross-overs, the ends were capped with Loctited aluminum plugs that were additionally secured with steel pins. Final machining blended the plugs invisibly into the head except for the pins' color differences

The two parallel sides remaining after the cam box machining were used support the head during its topside machining. Excess stock on the head's upper surface was used to add a few extra features. The drawings show Loctited inserts around the spark plug wells to simulate water shields. A portion of this stock was used to machine the shields directly into the head. I also added three flanges for the water outlet pipe that allowed me to raise its mounting screws out of the internal coolant passage running directly below it.

For some reason, during the machining of the combustion chambers on the bottom side of the head, I drilled the holes for the spark plugs. This was a mistake as I've made it a rule to machine each plug's mounting surface just before drilling and tapping its hole (with no deburring) in the same setup. I've learned the plug must be perfectly perpendicular to its mounting flat or its cylinder will be plagued with leaks. Fortunately, I was able to recover from the error since the upper and lower surfaces of the head were perfectly parallel. After re-registering the spindle over each hole from the topside, the plug well was machined and the hole tapped using a spindle tap holder.

A couple loose ends included tapping holes in the head's front surface for attaching the gear tower. As indicated in the drawings, the clearance holes for these mounting screws actually go through the centers of gear shafts inside the gear tower. The internal passages just inside the head's front surface for carrying oil to the top end were also drilled. Because of a ripple effect of the split crankcase, these had to be altered from those in the original drawings and angled past the just-drilled mounting holes in order to meet up with the relocated transfer port on the rear of the gear tower.

The last two surfaces to be machined were those for mounting the intake and exhaust manifolds. These surfaces are 96 degrees off vertical, and the axes of their ports entering the combustion chambers are at 112 degrees. The intake and exhaust plenums are mirror images of one another. The head was cradled in an adjustable angle block during the machining of the first surface, but with no orthogonal surfaces remaining afterwards, a pair of custom angle blocks supported the head during the second surface's machining.

This will be my first experience with a multi-valve multi-carb set-up, and the current plan is to use four O.S. 25LA carburetors with .21" diameter throats. Being more conservative than Ron, I reduced the diameters of the ports at their intersections with the valve cages from 5/16" to 3/16". Each port is blended smoothly into its plenum with a slightly oval intersection with its cage.

I would normally have installed the cages before machining the ports, but this head has been so problematic that I didn't want to wind up scrapping sixteen finished cages if I screwed up the head during one of its final machining steps. As it turned out, the third one made it to the finish line. Now, a fixture will have to be created to machine the openings in the sides of the valve cages before they're installed.

The last step was to plug all the openings and then bead blast and scrub clean the head's exterior to match the rest of the engine's simulated cast appearance. I'm not sure why it didn't occur to me earlier, but if I were starting over, an indexed 4-axis setup would have eliminated the need for so many unique setups. - Terry


----------



## awake

As always ... incredible!


----------



## johnmcc69

Beautiful machining!
What is the purpose of the "connector troughs"?
 Any particular reason you bead blasted the combustion chambers & head mounting surfaces?

 John


----------



## mayhugh1

johnmcc69 said:


> Beautiful machining!
> What is the purpose of the "connector troughs"?
> Any particular reason you bead blasted the combustion chambers & head mounting surfaces?
> 
> John


John,
I decided to bead blast the head (and other) mounting surfaces to give some 'bite' to the teflon gaskets that I'll be using. I once tig-repaired a (full-size) aluminum head for a pretty knowledgeable hotrod friend and when finished, I faced its mounting surface to a beautiful mirror finish. When he came by to pick it up, he told me my finish was too good and would never seal to the gasket. He had me re-setup the head and re-skim it at a higher ipm To  leave very light machining scratches. I don't know if the first one really would have leaked, but I do know the second one didn't, and I always remembered how adamant he was about that imperfect finish.

The troughs create a flat reference surface for installing the valve cages. The Offy doesn't use lash adjusters, and it's going to become important later that the valves are all installed at uniform heights. I'm curious about how well that's going to work out. - Terry


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## Cessnadriver

awake said:


> As always ... incredible!


Terry so glad to see you back at!  You set the benchmark for all hobby machinist!


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## dsage

Terry:
What grade / grit / etc are you using for your bead blasting?
Looks amazing as usual.


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## mayhugh1

Dave,
I believe it's 80 grit glass bead material bought from my local Harbor Freight many years ago. I use a cabinet bought from Eastwood in 1995 and run 90 psi air pressure. The material has never been changed out and so it's probably finer that when it started out. - Terry


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## dsage

Looks like a nice finish. I use something rated as MIL10 from Blast-O-Lite. It's really fine. Feels like water if you fill your hand and let it run out between your fingers. It gives sort of a satin finish with 90lbs or so pressure. It's perhaps a bit too fine.
Which is why I asked. I was trying to figure out how coarse it has to be to give a finish like you're getting without ending up with a bag I might never use.
Thanks


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## mayhugh1

After completing the head, it was trial assembled with the block and gear tower and measurements taken to reconcile the dimensions in my Solidworks model. In particular, before starting work on the cam boxes I wanted to make sure the camshafts are going to wind up properly aligned with their driving gears inside the gear tower. A fixture block bolted to the top of the head was used to help verify this alignment. The block was bored for a test shaft to support the already machined camshaft gears so their meshes with the drive gears inside each arm of the gear tower could be checked. Once verified, the locations of the camshafts inside the cam boxes and the related gasket thicknesses were finalized.

The bolt-on cam box covers that will enclose the camshafts were the first parts of the top-end assemblies to be fabricated. The documentation suggests cold forming these 16 gage sheet aluminum covers over a mandrel using a mallet and vise. With the metal forming completed, the bottom edges of the long sides are to be machined to fit inside a pair of 1/32" wide grooves milled into the top surfaces of the cam boxes. These covers will contain the top-end waste oil until it can returned to the sump through passages in the block.

I tried Ron's suggestion, but found dealing with the small covers' tight bends difficult. Sixteen gage aluminum feels like it should be easy to form until you try to bend a six inch wide piece around a half inch mandrel. My first few tries would have required a lot of work to clean up the surfaces marred by the forming process. And then there would still be the issue of achieving a pair of straight sides to be uniformly machined down to a thickness of .032".

Instead, I decided to make a set of dies to form the covers using my shop press. The covers came off the press nearly perfect and, other than height trimming, needed only to be closed up another .010" in a vise to reach their target width of .705". The heights if the parts were rough trimmed and then fit-checked using a gage having a pair of 1/16" wide parallel slots milled into its surface. A fixture was then used to support the parts for their final trimming and facing operations. The final fits were verified in a gage block containing a pair of 1/32" wide grooves identical to those to be machined into the cam boxes. The photos show the various steps involved. The covers will be later trimmed to length, and their front ends' machined for close fits inside the gear tower. After completing the top-ends, they'll likely be polished. - Terry


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## mayhugh1

The cam boxes are surprisingly complicated parts with densely packed features and little free real estate. The fasteners that will secure them to the head will also retain the bearing caps making the cam boxes extensions of the head rather than standalone subassemblies. This means that if the valve train components are not to affect the fit or subsequent alignment of the camshafts, the bearing caps must fit tightly between their guide rails.

Before starting construction, I made a few simplifications to the design. Rather than use sleeve bearings, the camshafts will be bedded directly into the 6061 bearing blocks. The cam bearings will be lubricated by pressurized oil pumped through the center of the camshaft, and so wear shouldn't be an issue. A second change involves the cup followers used to prevent side loading the valve guides. The camshaft supplied in the documentation uses straight-flanked lobes and followers with 2-d contoured surfaces that require keying to prevent them from rotating. In order to eliminate the keying, I plan to radius the camshafts' flanks and use flat top followers that can rotate. The bearing caps will also be machined with integral rather than bolt-on brackets for the cam box covers.

A sacrificial 'mule' was invaluable during the head machining, and so I started out making three cam boxes. The first step was to square up a workpiece for three nested parts to be machined in 'cookie cutter' fashion. Their nearly twenty hour machining time was spread over several days. A number of those hours were use to machine the 1/32" wide grooves for the covers. With even a 5k rpm spindle, I'd never have the patience to manually perform those multi-pass 0.7 ipm grooving operations.

The cam bearings' lower halves were machined directly into the cam boxes after developing an interpolation routine on scrap material that would produce an accurate profile. This routine was consistently repeated for all five bearings on each cam box in order to wind up with a reasonable facsimile of a line bore operation. The same routine will be also be used to machine the bearing caps.

When I originally laid out the array of parts, I spaced them for a 3/16" cutter to finish machine their outer perimeters before they would be band-sawed free of the workpiece. When it came time for this final operation, without thinking I compiled it for a 1/4" cutter which was a better choice for what was going to be three deep grooving operations. I watched in horror as the cutter traveled between parts with no apparent safety gap between them. After stopping the machine, I reviewed the CAM software to see if I had just ruined two of the three parts. Unbelievably, I had originally spaced the parts .250" apart, and since I had inputted .249" for the new cutter's diameter, the parts were unharmed. Sometimes the ball drops on the right side of the net.

After band sawing the boxes free of the workpiece, they were faced to their final heights using measurements obtained earlier from the test block used to verify the cam gear mesh inside the gear tower. Fortunately, all three parts came out to be identical. Their heights were machined so that with a .005" Teflon gasket between the boxes and head, the center distance between between the cam driving gear inside the gear tower and the camshaft driven gear is .004" greater than the theoretical on my SolidWorks model. This distance resulted in just a bit of detectable backlash. This backlash was difficult to measure because the mesh between the two gears of interest is down inside the upper arm of the gear tower. To see it, the driving gear must be held stationary with a needle probe.

A couple test caps were machined to work out their fixturing and to verify their fits. The workpieces used were short bars machined for snug fits between the caps' guide rails. The cam boxes had to be temporarily threaded for these trial fits, but they will be reamed out later. The next step will be to machine the front caps which must be installed for the end-turning operations still needed on the cam boxes. - Terry


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## awake

Absolutely incredible work!


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## mayhugh1

The front camshaft bearing caps are a little different from the rest and are to be installed and finish machined along with the boxes' front ends. Their stepped circular ends are natural candidates for a lathe operation. Their already machined top surfaces are pretty delicate, and so I made up a two-piece cradle to protect them from the lathe's 4-jaw chuck. Just after finishing it though, I discovered my chuck's through-hole was too small to handle the long parts with their offset centers. After boring out the chuck to the ends of its worm gears there still wasn't enough clearance, and so I gave up and moved the parts to the mill.

Supporting tall skinny parts in a mill vise can be sketchy because the leveraged cutting forces always seem to be greater than expected. In the past, I've had similar parts slip out of position during cutting even when centered and securely tightened in a vise. For this setup, I added side supports as well as some additional end mass to reduce cutter induced vibration. This setup was used to machine both ends of each box.

After completing the ends, the long sloping sides of the boxes could finally be machined. Fixturing for these 9 degree facing operations grew into a 'thing' because I added a .040" high vertical strip along the top edges of the boxes to provide a nice transition between the box's sloping sides and its covers. Inaccuracies in the setup for these operations would create a variation in this strip that I wouldn't be able to live with.

A pair of custom angle blocks was machined to support the parts at the angles needed to machine both faces. The blocks were designed so the parts would be locked in place against internal reference surfaces with shims used as wedges. There isn't enough surface area on the boxes' finished circular ends for a trustworthy grip in the vise, and so a pair of sacrificial rings were made to be inserted over them. After some experimenting, it wasn't difficult to align each cam box to the mill's y-axis to within a thousandth.

With the cam box machining essentially completed, the covers were trimmed to their final lengths. A recessed clearance ring was manually filed around the front of each cover to allow it to slip under the gear tower's bolt-on cover cap. A wrap of tape around the front of the cover provided a guide line for a safe-edge file. A .003" vinyl gasket will be used during final assembly to seal the covers to the gear tower.

Finally, the boxes's follower bores were plugged with rubber stoppers and their top surfaces bolted face down to a piece of protective wood so the boxes could be bead blasted to match the rest of the engine. The covers were brightly polished.

The next step will be to machine, fit, and install the remaining bearing caps. - Terry


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## tornitore45

Do not mean to teach a cat how to climb trees but as reference for similar situations...
When the part is to tall and stick out the shallow vise too much I found that I can turn my vise 90 degree. (long side of jaws vertical)
I use a machinist grinding vise which is easy to flip but even a Kurt vise can be set up on angle plates.


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## tornitore45

Terry, I think it would been easier and faster to have built a full scale Offy.


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## dsage

Wow !!
Some tedious and tricky work completed there. And as usual done to perfection.
Fabulous.


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## mayhugh1

The bearing caps were machined one at a time in multiple setups from blanks made up earlier to fit snugly between the cam box guide rails. This wasn't an efficient way to make a dozen identical parts, but after fine tuning the steps and getting usable pieces I continued on with what seemed to be working. A small advantage to making them one at a time was that a tiny setup error didn't wind up spoiling a large batch of parts. Since the cam box 'mule' was still alive and well, I made a set of caps for it as well.

Originally, when compiling the routine used to machine the bores in the cam boxes and bearing caps, I used a target diameter of .217". Although I could expect the diameters to be identical, I couldn't rely on the cap bores winding up precisely centered between the guide rails. Inevitable differences in the setups of the parts created small differences among them giving the caps a 'handedness'. After best-fit installing them, a finishing reamer was used to clean up the bores.

The .217" diameter was selected to precede the .2185" chucking reamer that I planned to use for final cleanup. With its spiral flutes and tapered nose, it was usable as a hand reamer. The flutes were long enough to bridge pairs of adjacent caps, and so I let the reamer find its own way through each bore while holding the cam boxes in my hand.

When finished, a .218" polished test rod fit snugly in all three cam boxes while a .217" diameter rod rotated freely. To avoid mixing them up, the caps' locations were engraved on their back sides. Finally, an end cap was machined to close up the rear of each box.

With all five bores in each cam box verified in line and with consistent diameters, the next step will be to machine blanks for the camshafts. - Terry


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## Art K

Terry,
I have been lurking during this build. I have Ron's book as well and have much of the engine drawn up in Alibre. This process has taken me about 2 years. Before starting on this journey I had never done an assembly. There is so much about CAD I don't understand or forget by the time I use it again, but the more I work on it the easier it becomes. I really like some of the things you've done with this build and will continue to follow along. Great work by the way!
Art


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## mayhugh1

I started four camshaft blanks from a length of half inch diameter Stressproof (1144) that I had on hand. It wasn't originally advertised as ground and polished, but it looked and measured remarkably consistent.

The first operation was to drill a 3/32" diameter hole through each work piece for an oil passage that will eventually distribute top end oil. The Guhring drill that I used was long enough, but the 6-3/4" blanks had to be drilled from both ends. Before continuing, I set them up in the mill and machined a shallow groove along their full lengths. I used the grooves as reference marks to consistently return the parts to the lathe so I could machine their features in small groups across all four blanks. Using this method with simple crib sheets didn't require a lot of thinking during machining and helped me avoid part-spoiling mistakes.

Machining started at the gear end of each blank where I immediately ran into a requirement for a 7/32-40 thread. Although taps and dies are available for this rather uncommon UNS thread, I couldn't find information on its major and minor diameters. Using the UNF thread equations, I machined a few nuts that I later used to verify the threads on the shafts. My parts fit together nicely, but they may not play nicely with someone else's.

A flange on the front end of each camshaft will seat inside an already machined recess in its cam gear, and each pair will be bolted together using one of these nuts. Each gear and flange was drilled with circular hole patterns having identical bolt circle diameters but unequal numbers of holes. These hole patterns create a vernier for setting the engine's timing. During final assembly, a locating pin between the two will be able to establish the timing with a two degree resolution.

Beyond the threading operation, the rest of the machining was done using a carbide grooving insert in an indexable lathe toolholder. I spent a full day trying to automate the machining on my Wabeco D6000, but in the end it lacked the rigidity to handle the 1/16" wide insert that I wanted to use. I eventually moved the parts over to my 12X36 Enco lathe where I manually machined them.

The diameters of the five bearings on each shaft were initially turned to .2170" since that was the diameter of the test rod that turned freely in all three cam boxes. The bearings had to be polished down to .2155", however, in order to duplicate the results with the test rod. The .0015" difference is the effective increase in the shaft's diameter created by the TIR's of the five bearings. The run out of my 5C collet and chuck combination happens to be .0015". With no attempt to limit the TIR of each bearing during its machining, I could have reasonably expected an increase in each shaft's effective diameter equal to the rms sum of five .0015" TIR's which works out to be .0034". Although I hoped using the reference grooves would have prevented any run out, they did seem to help out by a factor of two or so. - Terry


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## tornitore45

4 hole in the flange   8 holes in the gear   Why?    45* adjustment?

I bet drilling 3/32 hole through a total of 28" of material was a teeth clenching business


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## kvom

I'm surprised you didn't thread mill those threads.  Is there a reason you couldn't modify the plan to use a more common thread?


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## mayhugh1

Kvom,
I think the reason the 7/32-40 was specified was that its major diameter happens to correspond to the already being used .218" diameter of the camshaft. I'm not sure about your question about thread milling. Since the parts were being turned in the lathe, I just threaded them in the lathe as well.

Mauro,
The text explains the vernier created by the two different hole patterns.


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## L98fiero

mayhugh1 said:


> Machining started at the gear end of each blank where I immediately ran into a requirement for a 7/32-40 thread. Although taps and dies are available for this rather uncommon UNS thread, I couldn't find information on its major and minor diameters.


Here's an online calculator for pretty much any parallel UN thread UN imperial screw thread calculator Should help next time.
LaVerne


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## mayhugh1

L98fiero said:


> Here's an online calculator for pretty much any parallel UN thread UN imperial screw thread calculator Should help next time.
> LaVerne


Thanks!


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## mayhugh1

About that cam timing vernier ...

The camshaft gear has 40 teeth and, since it turns at half the speed of the crankshaft, each tooth is equivalent to 720/40 = 18 crankshaft degrees which is too coarse for meaningful valve settings. A part of Ron's camshaft design is a vernier that increases the timing resolution from 18 degrees to 4.5 degrees.

A flange at the end of the camshaft is drilled with a circular hole pattern containing four holes spaced 90 degrees apart. This flange seats inside a recess in the cam gear which is drilled with an eight hole pattern having the same bolt circle diameter. The holes in the cam gear are spaced 46.125 degrees (with 37.125 degrees left over between the last pair). The difference, in cam gear degrees, between adjacent pairs of flange holes is 92.25 - 90 = 2.25 cam gear degrees which is the new resolution i.e. one quarter of a cam gear tooth).

A pin inserted through one of the holes in the cam gear and into one of the holes in the flange selects one of four possible camshaft orientations available within that single cam gear tooth. With the crankshaft rotated into position for the timing adjustment, the camshaft is rotated so a pin can be inserted into the best-fit hole pair and then secured with one of the special nuts.

Eight flange holes could have also been used to increase the resolution by another factor of two. A point of diminishing returns is eventually reached due to errors in the actual locations and diameters of the holes, and so Ron may have felt little was to be gained beyond four.

I machined all the engine's gears several months ago from common blanks made and tested at that time. I missed the 46.125 degree spacing requirement for the cam gears discussed in the final assembly section of the manual and mistakenly drilled them 45 degrees apart. Fortunately, I had several extra gears left over from the original blanks and was able to re-drill three new cam gears from the original blanks. - Terry


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## tornitore45

Yap, when you said the word vernier I guessed the hole pattern was not symmetric despite the difficulty from detecting it from the picture.
That is something to keep in mind building another engine.  I could have easily done that on my radial, where there was ample space on the ring-gear/cam-disk interface to make a high resolution vernier.


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## RonC9876

Terry: I have tried to explain the vernier idea to other builders of this engine in years past. Very few people have been able to grasp the concept on their own. Your explanation of it is excellent. Great job as usual!


----------



## Richard Hed

mayhugh1 said:


> Thanks!


Whoa!  I have been having to refer to Machineries Handbook all the time for this info on the calculator.  What a pain that is.  Thanx for this.


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## propclock

I first saw this on my 1962 Alfa Romeo twin camshafts. Wow I thought this is cool. 
But forgot to use it on my own engines. Thanks for the reminder.


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## Herk

Every pushrod Triumph engine I have ever worked on has been the same way.  4 different ways the cam gear can be installed, each 1/4 tooth different.  About 2 cam degrees or 4 crank degrees different per 1/4 tooth.


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## merlin

Porsche 911 motors do it with 17 holes in the sprocket over 16 holes in the cam on the same bolt circle. Set the cam valve timing, find the one hole that best lines up, install a pin and lock it with a large jam nut.


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## ALEX1952

In my youth many years ago, offset dowels were used. With patience very fine adjustments could be made.


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## Jan Dressler

Porsche "Fuhrmann" engines (4 cylinder horizontal opposed "Boxer", quad camshaft) used two bevel gear driven horizontal shafts to drive the lower camshafts of each cylinder bank, then two vertical shafts driving the upper camshaft from the lower one on each side.

Besides it is not very trivial to adjust those 8 bevel drives (the ones on the lower camshafts each having two pinions meshing with the same gear on the camshaft), timing adjustments are made by changing the positions of the pinions on the splined shafts, using a similar vernier system...  Only that it is possible on both ends of the 4 shafts, and timing adjustments for the lower camshafts affect the upper ones as well, so have to be "reversed" if you don't want a change there.
Each of these adjustments means that you have to take apart everything again - And in the end, the adjusting possibilities are still so crude that if you want to be correct to 1° you have to use offset keys for the cams (each cam is keyed to the shaft).

In the end, I did make a whole model of the camshaft drive including cams, rockers and valves in CAD to simulate what changes are needed to achieve the correct valve timing. Still, you better keep the doors locked when working on these engines...

Somehow back to topic, incredible work on the Offy! I am a long time lurker here, but these threads are an inspiration really.


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## mayhugh1

I curved the flanks of my cam lobes so I can use non-keyed flat top followers. Sketches of the lobes, which are otherwise identical to Ron's, are in the photos. His documentation mentions the option of undercutting the cams to compensate for lost motion created by valve clearance in order to match the specs of the full-size cam. I selected the flanks' radii and centers to achieve a similar result with a slightly more aggressive valve opening.

The lobes were machined on my Tormach using a rotary machining operation. This 4-axis operation keeps the center of an end mill in contact with the tool path during coordinated moves of the x, y, z, and A axes. Unfortunately, the end mill's dished cutting face leaves grooves in the non-flat areas of the part. With the tool continuously moving up and down, the effect is similar to trying to drill flat holes with an end mill. The tool leaves excess material behind at its center which, in a four axis operation, shows up as a pair of grooves on either side of the cutter. Although they can be cleaned up with a file, they can be several thousandths deep depending upon the particular cutter.

These grooves can be nearly eliminated with a truly flat-bottom cutter. A local tool grinder reground a couple of my 1/4" end mills to use with this same operation during my Merlin build. However, the flat center-cutting edges are vulnerable to chipping and excessive wear, and the tool can quickly lose its advantage. To increase its lifetime, I roughed in the lobes with a conventional end mill and saved the fragile cutter for the finishing passes.

One of the photos shows two pairs of test lobes that I machined into a piece of scrap 1144 with this operation. One pair was machined using a conventional end mill and the other using the flat bottom cutter. The lobes machined with the flat tool are directly off the mill while the lobes machined with the conventional cutter received a few minutes of filing before I remembered to take the photo. Grooves created by the flat bottom tool are plainly visible (and felt) but easily removed with abrasive paper.

Each lobe pair was machined using a minimum amount of rotary axis stick-out. Although a tailstock was part of the setup, the long skinny shafts required additional support below the cutter. Since the stick-out had to be re-adjusted for each lobe pair, a simple degree wheel attached to the tailstock end of the shaft was used to reinitialize the starting angle for each lobe cutting operation.

I made up some sanding sticks to finish the lobes' surfaces by gluing abrasive paper to wood craft sticks. These are quick and easy to make by the handfuls, and they helped avoid altering the machined contours.

The lobes and bearings will be lubricated by oil pumped through the camshafts. Twelve #70 holes supply oil to these surfaces on each camshaft. They were manually drilled using a sensitive drill feed and a simple custom V fixture for support. A stream of compressed air kept the drill and hole free of the 1144's chips which tended to become magnetized and make an already difficult operation even more risky. Finally, the shafts' ends were threaded and plugged. The front plugs were drilled through with a #78 drill in order to supply oil to the cam gears.

Three of the four original blanks wound up as completed camshafts, and so I now have a spare intake cam. (Some late night carelessness resulted in one of the shafts being sliced in half.) Measurements were taken and recorded for each lobe on each camshaft. The diameters of both the heels and the heights of the noses vary +/_.003" around their mean values. These measurements will be needed later because the Offy doesn't use lash adjusters. In the full-size engines, the lengths of the valve stems were filed to adjust clearances. The manual mentions a .005" valve clearance which may be what results when everything in the valve train exactly matches the documentation. In my case, an assortment of followers will likely be required. - Terry


----------



## kvom

Did your CAM generate the tool paths/g-code?  I had come up with a way to do it via a self-written Java program and a DXF of the lobe, but haven't needed to actually do the work.

What would be the result using an endmill > 2x lobe width, offset so center never comes into play?


----------



## mayhugh1

kvom said:


> Did your CAM generate the tool paths/g-code?  I had come up with a way to do it via a self-written Java program and a DXF of the lobe, but haven't needed to actually do the work.
> 
> What would be the result using an endmill > 2x lobe width, offset so center never comes into play?


The operation I used was part of my CAM software. It was Sprutcam's first entry into the 4-axis market 13 years old and has probably been greatly improved since. The 'beta+'
version that I'm using is pretty primitive.

I think the wider the tool, the better the result. My Merlin's lobes were 1/8" wide and needed much less cleanup than the Offy's .2" wide lobes. The Knucklehead's lobes were 1/16" wide and needed no cleanup. I believe the cutting edges in the dished center of an end mill are at a 1 degree or so angle, and so will always be an error with a conventional end mill. It can be made smaller, though, with a larger diameter cutter. A torus type end mill should also help. To be honest, I'm not entirely sure why my truly flat cutter still leaves marks unless it's a combination of tram and a-axis errors.- Terry


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## petertha

Terry, re the sanding sticks, I used to do them onsey-twosey as required. But I like using them so now make them batch mode. I spray a sheet or half sheet of wet-dry paper with 3M adhesive, lay it abrasive side down on a cutting mat. Then just press the coupon stick down on it, cut directly to the edge with Exacto so the paper is flush. Flip & do the other side. I use thinner Popsicle sticks just to use up scraps of the stickied paper, but they are kind of hit & miss quality IMO. Some are not quite as flat as they appear and/or have a bit of curvature. The wider tongue depressors are worse. 

So then for a period I was using strips of MDF or hardboard which is hard, smooth & cheap. But those kinds of wood can swell if it gets liquid saturated or even a bit of cutting oil. And when you remove the paper to re-use it can , it can peel back a bit of wood or leave glue residue so you have to touch it up a bit. So my latest method is nicely fly cut 3/16" aluminum strips about 1" wide x 3/16 thick. I made about 10 of them. They make a real accurate backing & any glue is readily removed with solvent & one of those plastic razor blade thingy's. Then away you go again.

When I made the valves for my radial I found the 'full width' really helped get the finish & diameter consistently across the length (work-in-progress pic). After that I decided more aluminum sanding sticks were warranted,

If you want a softer feel for feathering over gentle curves, you can use the same concept with velco stock to the tool. Then just buy hook & loop paper. Unfortunately you have to look a bit harder for wet/dry type paper suited to metal vs. woodworking (disc sander) paper. And lowest price is more predominantly circles (for disc sanders) which nets shorter sticks. Food for thought.


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## tornitore45

I like the brass support in the middle.


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## dsage

Terry:
I'm wondering about your choice of cutter diameter when you are milling the cam lobes. I believe with a finished cam the diameter of the lifter is important otherwise the geometry of how the lifter follows the cam is impacted. Too small and the edge of the lifter contacts the cam. Not sure if too large also has issues.
I'm wondering if the same would be true when you are machining the cam with what is essentially the same geometry as a lifter. Is it possible the cams are over / under cut due to the diameter of the cutter? What consideration do you have for the size of the cutter?

After finishing a cam lobe have you ever tried setting up a dial indicator with a nose the same diameter as your planned lifter. Rotate the cam keeping track of rotational degrees (using the A-axis rotary on you mill) and actually measure the opening / closing degrees and lift / duration to see if the lobe acts as designed? 
I've played around with this a lot and have found  the lobes are not exactly as expected. They are "close enough". I can't account for where the error occurs.
Thanks


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## tornitore45

> I'm wondering if the same would be true when you are machining the cam with what is essentially the same geometry as a lifter. Is it possible the cams are over / under cut due to the diameter of the cutter? What consideration do you have for the size of the cutter?



This is an issue it has always bugged me, and have not quite formulated a clear understanding.
Is easy enough to specify a cam in polar coordinates.
For every angle: machine an infinitesimal angle at a specific distance from the center, with a an infinitesimal tool diameter.  Theoretical, but this is just to establish the geometry.
If the lifter had an infinitesimal diameter (an indicator ball) then the lift profile as read by the indicator would match the specification.
BUT
A real cutter does also cut "ahead" into the yet to be machined part of the cam.   Will the cam be over cut when we come to machine the next location?  Or there will still be metal to shave away.
A small roller lifter "reads" the cam on a vertical radial bit a large flat lifter "reads" the cam on a radial that is not vertical but at the point where the tangent is horizontal.

I understand that Terry concerns with the tool shape are not related, the groves are anomalies in the axial extension of the cam.
One alternative could be to use the side of the end mill which will cut straight even a wide cam.  But that is only possible with a single cam, impossible on a long shaft with multiple cams.


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## dsage

I think you are re-iterating pretty much what I was saying.
"The proof is in the pudding" as they say. That's why I asked if he has ever checked the specs on the cams after machining them using the actual lifter (or if a flat lifter with a flat tip on the indicator the same diameter). I have, and although I don't machine them this way mine don't come out exactly as expected.
BTW I grind them with a very large (8" dia) grinding wheel so it's sort of the same but different .
The process of taking tangent cuts as per the old camcalc program seems to be very good but it leaves a bit of filing to get rid of the facets. Then after filing where does that leave you??
This is why machining cams is a bit of a black art. The machining process has to take into account all of those little things.
Yes side milling seems to be (probably) a more accurate scheme because the cam program takes into account the diameter of the cutter. An inside profile is a good example. They come out perfectly regardless of shape as long as the cutter is not too large for an inside corner. I have made cams this way making pairs of lobes held in a fixture. But then the pairs need to be assembled on a shaft. Sort of a pain.
When ground on a professional machine the pattern the grinding wheel follows IS NOT just a large diameter version of the finished cam.
It's a bit of a black art.


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## mayhugh1

I've never checked the cams for accuracy other than with a degree wheel in the engine when it came time for setting the timing. This only involved checking the opening and closing times and the locations of the lobe centers. And yes they've always been, as you say, 'close enough'.

When one has four axes to work with, there are a multiple combinations of axis movements that can cut the same profile. I've always been curious about how CAM programs make this choice especially since I was thinking about making one of my own before this operation was released.

The software I have assumes it is working with a truly flat cutter (which in most cases it's not), and it keeps the center of that cutter in contact with the tool path. During the tool path calculations, any movements that might gouge the part are checked for and disallowed. You can watch the extra movements that are inserted in order to avoid the "cutting ahead" gouges that Mauro talks about. When running, the A-axis isn't just turning continuously while the z-axis moves up and down. The A-axis often pauses and sometimes reverses while the y-axis makes some back and forth movements of its own. I've always assumed it was doing this to avoid gouging the part with the cutter's front edge. The whole process is pretty interesting to watch. Sometimes when making these movements, however, the depth of cut is greater than the conservative value that I typically enter into the parameter list, and it is probably here that my truly flat cutters are susceptible to damage.

I wouldn't think commercial cams for any application are cut with end mills. Rotary cutters and grinding wheels avoid the problems that I run into. I don't know if my 13 year old CAM software was ever improved to avoid this issue or if there is another way of using what I do have to work around it. For example, there is an option to keep the front of the cutter in contact with the tool path instead of its center, but I've never gotten that option to compile my particular version. - Terry


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## kvom

Given that a cam lobe is convex, a flat tool tangent to any point can't touch any other point.  So I don't understand why gouging could come into play as long as the path keeps the tool tangent to the intended surface.  The A axis should be able to move continuously.


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## mayhugh1

kvom said:


> Given that a cam lobe is convex, a flat tool tangent to any point can't touch any other point.  So I don't understand why gouging could come into play as long as the path keeps the tool tangent to the intended surface.  The A axis should be able to move continuously.


Good point ...


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## dsage

Perhaps when you get down to a small finish cut this is possibly true. But if the cutter diameter is small compared to the size of the cam, the "corner" of a flat cutter can be cutting before the center if you rotate the cam blank into the cutter. If the cutter is very large then the corner is not an issue but there is still some point other than the center of the cutter touching the work before the center (where your calculations are for). The exception would be if you use a ball nose cutter.
Of course if the software is calculating possible collisions of the edge and adjusting for it (as Terry suggests his software does) then it probably a non-issue. But without some allowance for the diameter / corner of the cutter you cannot just rotate a cam into a flat cutter without some un-intended pre-cutting ahead of the center where you intended the cutter to be cutting.


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## Peter Twissell

Dsage - it is true that the 'corner' of the cutter will, as you say, cut material from the blank before the centre of the cutter arrives at the required location, but the material removed by the 'corner' is always material which will be removed by the cutter centre as the blank continues to rotate.
My approach with such operations is to try to make the machining operation replicate the final application as closely as possible.
The cam ring for my radial has only two cam profiles (although each has three lobes) so it was possible to machine it with the side of an endmill. By using an endmill of the same diameter as the roller followers, it was relatively straightforward to machine the cam to the desired lift/angle profile.
My mill (Sieg X3) has the facility to rotate the head through 90°, allowing horizontal axis milling. With a cutter larhe enough to allow the mill head to clear the fixturing, I would probably use this configuration to cut cams on a long shaft.
Incidentally, the large diameter of a radial engine cam ring (relative to the roller followers) means that the contact point between cam and follower is always very close to the theoretical contact point of a zero diameter follower, when measured as an angle about the cam centre. This also means that lateral loads on the follower are relatively small.


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## dsage

Peter Twissell said:


> Dsage - it is true that the 'corner' of the cutter will, as you say, cut material from the blank before the centre of the cutter arrives at the required location, but the material removed by the 'corner' is always material which will be removed by the cutter centre as the blank continues to rotate.



I don't agree. Consider the geometry in the first picture below. Also consider that this is a finish pass so all of the rough material is removed already so the cutter is supposed to just barely touch the surface. The center of the cutter is at the desired / calculated cutting point. If you simply rotate the cam clockwise you can see that without any intervention by the software that the left corner of the cutter will contact the cam BEFORE the center does. Hence the corner of the cutter is going to gouge the cam. Without proper software it is better to do the geometry using the left edge of the cutter (not the center). If you had made the cam from the start using the center as the cutting point  then you'd have a cam shape with the gouge already machined and you be oblivious to the error in the profile. It would "look" ok but it wouldn't be exactly as intended if measured.
The situation gets worse if you have a larger cutter - in the second picture. The top of the cam would be truncated if you rotate the cam.
The only marginally better situation is if you use a ball nose cutter - third picture. BUt then you're left with grooves around the cam face unless you do very very small step overs (requiring multiple passes).
BTW if you are side milling a contour shape around the cam (as you say you do) without using the A-axis then the geometry is like the third picture. All cam programs are fully aware of the point where the mill is contacting the surface so it should work out fine. As does any contour milling operation.
The key to using a flat cutter is having some software that knows the tool diameter and can calculate where the actualy cutting is going to take place. As apparently Terry's software does.


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## tornitore45

The point where a flat tool touches the horizontal tangent is not always aligned with the cam's center of rotation. To avoid cutting metal that should not be cut one must be willing to move the spindle axis back and forth from the rotary table axis. Not a very practical approach on a manual mill.  This back and fort movement is what Terry noticed on his CNC machine. His software knows that the tool tip is going to cut ahead so it backs out to keep the porward periphery of the tool on the cam axis and the other side of the tool is riding far high over previously cut area.


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## byawor

I cut this one on wire EDM from your dimensions straight flanks. wanted to do the one with radius but could not decifer the center
and radius for the big arc. 
bob


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## mayhugh1

Bob.
I didn't notice I'd omitted the centers of the flank radii. SolidWorks was happy with the flanks being tangent with the heel and nose circles and didn't warn me that I'd not specified their centers. Here are updated sketches with those centers:


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## awake

dsage said:


> I don't agree. Consider the geometry in the first picture below. Also consider that this is a finish pass so all of the rough material is removed already so the cutter is supposed to just barely touch the surface. The center of the cutter is at the desired / calculated cutting point. If you simply rotate the cam clockwise you can see that without any intervention by the software that the left corner of the cutter will contact the cam BEFORE the center does. Hence the corner of the cutter is going to gouge the cam. <snip>



Dave, it looks like, from your pictures, that you are depicting a straight-flank cam. If the flanks are radiused, wouldn't that change things?


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## byawor

so would it be x.5869 y.2317? Nice thing about this way its only a few lines of code, a good guy with a good machine could get it exact with a surface finish that would need no touch up. Also if so desired could harden the material prior to cutting. Bad thing not so easy to attach to shaft with the right timing. Just did it out of interest would never tackle this engine.
Bob


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## MikeG

Hi all, I was just remembering a dear friend....Ron Bement............google him and his offy.

Regards
MikeG


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## Peter Twissell

Dsage, you're absolutely right about the cutter corner digging in.
I had in mind a cam with convex flanks, but even then, if the cutter axis remains aligned with the cam base radius axis, it will dig in.
My radial cam has straight flanks and they were machined by moving the mill table to create a surface tangent to the base radius.


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## kvom

A program following a flat flank wouldn't rotate the table until the start of the next non-flat section.  The tool would move along the Y axis as well as Z to maintain tangency.


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## mayhugh1

With four valves per cylinder, the Offy's head isn't to be taken lightly when it comes to its seats and seals. Fortunately, cages were used to improve the odds of getting concentricity between the valves and their sealing surfaces.

My starting material was 3/8" diameter 544 phosphor bronze. Each blank began with polishing its diameter down to .373" using with 400g paper. I used 1/8" rather than 3/32" for the diameter of the valve stem hole to improve my chances of drilling/reaming it straight through the center of the blank. The mouth of the cage which was bored in the same setup. The side entry port was drilled using a v-block setup in the mill before returning to the lathe where the perch for the valve spring was turned.

The final step will be to manually cut the seat using a piloted seat cutter. With the cages located so deep in the head, however, my favorite seat cutter won't be able to reach them after they're installed. If I don't make a new one, the seats will have to be cut and tested the before the cages are installed. In any event, since they're .002" undersize, the cages will slide into the head without distortion where they'll be sealed and secured with high temperature Loctite.

At the beginning of this build, Ron warned me that he had run into problems with his exhaust cages slipping out of position. The shear strength of a Loctite 620 (hi-temp, slip-fit) bond between two properly prepared steel parts at room temperature is about 2.5 kpsi. Accounting for usage with aluminum and a 400F operating temperature, I estimated that 400 lbs would be required to dislodge one of the Offy's cages from its head.

I prepared a test with four .002" undersize bronze blanks installed in a 1/2" thick aluminum block with Loctite 620. With the adhesive fully cured and the block's temperature somewhere between 300F and 400F, all four cages slipped under only a 200 pound load. This 2X discrepancy with the data sheet may have been a result of using bronze in aluminum since Loctite's parameters appear to be dependent upon the actual metals being bonded. Two hundred pounds force on a cage would be roughly the result of a 2500 psi combustion pressure.

I repeated the test using Seal Lock's Fluid Weld which is a similar but new (to me) product mentioned in another thread on this forum. The results were essentially the same. Although I wouldn't expect such a high combustion pressure inside a model engine, Ron's warning has convinced me to also pin the cages inside the head.

The exact lengths of the stock cage subassemblies and their installed heights in the heads are critical to setting the ends of the valve stems a sufficient distance under the cam lobes for operation with the followers. The travel of the valve inside its cage is limited by contact of the loaded spring collar with the top of the cage. The stock parts provide just enough travel for the required .10" lift so long as the valves are sunk into their cages with the .030" wide seats that Ron used. The valves can't be made any longer and still operate with reasonably thick followers. Since I plan to use much narrower seats, I shortened the top ends of the cages by .050". This provides a comfortable margin for the lift requirement without robbing material from the followers.

While working on the valve cages, I also machined the spring collars to break up the monotony of working on the cages. I (hopefully) made way too many spares but thought it wise to do so while I was set up and my workflow seemingly working. The spring collars were designed for use with E-9 commercial external retaining rings. I also made lots of extra collars since those are the parts that typically go flying across the shop during assembly. - Terry


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## dsage

Terry:
There has been a series of live seminars recently by Henkel - the makers of Loctite. They stress that Loctite does not work well with "non-active metals". I think that means metals that do not contain copper (but don't quote me on that). In any case there is a primer that you need to add to the joint that adds the necessary ions to the joint before assembly. There is also a new product that replaces the common blue 242 that has the activator in it. It is 243. Blue may not be strong enough for your application but I believe there is an equivalent in red.
I think they posted those seminars on their Youtube channel after they went live.
They stress throughout the seminars that they are available any time for consultation. You should give them a call. I'm sure they can fix you up with the proper product to use.
The info is also available in their catalog but I've found the catalog difficult to read.
Ask the experts.


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## awake

Very nice! And glad the cut wasn't any worse. I did a number on my hand when trying to drill some wood angle blocks with a forstner bit, holding by hand. I found out that wasn't such a good idea ...


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## tornitore45

Ouch!


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## kvom

Love the Sunday updates.


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## Richard Hed

I won't tell you what I did, but the same results.


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## mayhugh1

Since I'll likely cut the valve seats before installing the cages, I'll need a way to test them independently of the head. I designed a simple leak tester around the Offy's cages, but the concept could be easily applied to others. It works by allowing me to pull a vacuum behind a seated valve so the leak-down time of its seal can be determined. My goal for similar measurements in a head has been at least ten seconds for a leak-down from 25 inHg to 15 inHg.

The body of the tester is a short piece of bored-through one inch diameter Delrin. The front of the bore was internally grooved for an o-ring that seals against the front o.d. of the cage under test. The cage's side entry port is open to a second internal groove that's connected through four longitudinally drilled holes to a plenum in the rear of the tester. In use, the plenum is evacuated using a Mity-Vac hand vacuum pump. With a perfect valve (or a thumb) on the seat, the tester will pull down and maintain a maximum vacuum of some 25 inHg after after a few pulls on its trigger.

In the past I've leak-tested my valves after installing the cages, and this required adapting the pump to the ports on the head. The valve guide ends of the cages also had to be sealed to prevent leakage around the valve stems from affecting the measurement. A silicone cap slipped over the rear of the cage usually took care of this. With the entire cage inside the tester, this seal isn't necessary, and the testing cycle is actually quicker and easier.

I had a spare valve left over from my Howell V-4 build that happened to be a perfect fit to my Offy cages with their .125" valve guides. I cut a .007" wide seat on one of the cages, and the combination held a 25 inHg for a few minutes. To be certain I was actually measuring the seal, I put a tiny scratch across the seat and retested. This time, I could only reach a few inHg, and it leaked down almost immediately. - Terry


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## gadabout

Terry, I am interested to know if testing the cage and valve with the Spring ,retainer and keeper would change the result? It shouldn't I think but was wondering if you had tested that way!
Regards
Mark


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## tornitore45

Rough force calculation
Average Vacuum   20" Hg
Atmospheric pressure  30" Hg  ~ = 15 PSI
Pressure on the valve   10" Hg ~= 5 PSI

1/4" Valve area    0.25 3.14/16 = .05 sqinch  Neglecting the stem.

Force on valve   0.25 Lbs

Kind of low, the spring will certainly pull harder, but than again if the leakdown is good under test conditions it may be better with the spring.


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## awake

Terry, what a great idea! The one thing that makes me pause is that in my only build to date, I waited to drill the side entry port until I could drill through the head and valve cage at the same time. Do you run into any trouble drilling the side port before assembly? Do you assemble the valve cage into the head using Loctite?


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## petertha

dsage said:


> In any case there is a primer that you need to add to the joint that adds the necessary iron to the joint before assembly.



In another post I referenced my experience with Loctite going off appreciably faster in this exact application, bronze valve cages in aluminum head. It was kind of heads up getting them installed rather quick-ish without adhesion kicking in half way through insertion. I wonder if primers accelerate this even more? There wasn't a lot of reference to this accelerated cure time aspect, seems like usually its recommended for more sluggish bond situations.


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## mayhugh1

When I leak-check my valves I always apply pressure with my thumb to hold the valve against the seat to simulate the action of the spring. I once estimated this thumb force to be two pounds which is what I typically strive for when choosing the spring rate and installed height of my springs. I usually, but don't always, get a valve to seal well enough to measure an acceptable leak-down time without some thumb pressure. Once the valves are installed in the head, the vacuum can then be pulled through a port as a final check with the springs installed, but you'll now be including any leakage around the valve stem which isn't fair, and sealing this area with the installed spring is much more difficult. Grease on the stem would work but be messy.

If the valve is polished free of machining marks while still on the lathe (easy to do), and the cage properly machined, the leak down time will be a few minutes on the very first try and won't need to be tested anymore. If there are some machining scratches left from the seat cutter, then you'll get an intermediate result and then have to work some to extend the time beyond the ten seconds. I never use the valve to do this (lapping) because the valve typically isn't the problem and I don't want to transfer a seat problem over to a perfectly fine valve. I'll polish the seat using a wood or felt bob and extra fine TimeSaver or metal polish. If the seat requires a lot of work, you stand the chance of changing its geometry some. If the cage isn't yet installed, you have the option of starting over with a new one.

The trick is to not scratch up the seat with the seat cutter. A close fitting pilot lubed with oil and oil on the cutting edges makes the process go smoother with fewer chatter-induced scratches. - Terry


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## mayhugh1

Awake,
I too was concerned about drilling the ports through the cages because I'd never done it that way before. The only problem I (actually my thumb) ran into was a poor work hold down scheme, and I wouldn't recommend mine to anyone. I used a 60 degree v-drill so I could do the spotting and drilling in one go. Since my port diameter was .187" In diameter, a standard size cutter was available. - Terry


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## mayhugh1

Dave,

Thanks for the Loctite tips. My frustration with Loctite is their bewildering product line with so many choices and subtle differences among them that I'm always left wondering if I'm using the right product and using it correctly. I waded through a lot of Youtube fluff but gave up before getting any real help with my application.

I was surprised at how easy it was to reach an application person at Henkle. (Just dial 1-800-LOCTITE and press '1'.) I learned a lot in the few minutes I spent with a pretty knowledgeable person on the other end. I was told that 620 was still my best choice if I really needed a 400F service temperature. I'm not really convinced that I do and, as you mentioned, there are newer and easier to use products with temperature resistances up to 350F.

I finally understand the active/passive metal stuff. In addition to being anaerobic, Loctite needs free metal ions to kick off its bonding process. Loctite doesn't bond to these ions. They are only used to activate the adhesive. The bonding occurs to the metals being joined, and different metals end up with different bonded shear strengths. The bonded shear strength of aluminum is 80% that of steel, and the bonded shear strength of bronze is 40% that of steel. Numbers on the bonded shear strength of bronze to aluminum weren't available.

Loctite can find the ions it needs on the surfaces of iron, steel, nickel, and copper. Loctite calls these 'active' metals. On the other hand, metals such as aluminum, stainless steel, titanium, magnesium, and black oxide'd or plated parts aren't 'active', and without an activator the bonding process may take days or weeks to occur, or it may never happen. If an active metal is being bonded to an inactive metal, Loctite will find the ions it needs on the active metal surface, and no activator is required. If two inactive metals are being bonded, an activator is required. Although it's also referred to as a primer, it's doesn't work like most of us would think since Loctite doesn't actually bond to it. A Loctite primer is just a copper salt in a fast drying solvent that leaves behind copper ions on the surface it was applied.

A primer can be useful even between two active metals to speed up the curing process especially if there is a big gap or if the parts are cold. The optimum gap for 620 is between .002" and .004". The downside is that if a primer is used, the ultimate bond strength will be 80% of what it would have been with no primer.

I also found out that 620 requires a 24 hour cure at 175F in order to achieve a full-strength high-temperature bond. This was something that my earlier test didn't include. I'm plan to repeat my test with my new found knowledge. - Terry


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## petertha

Interesting stuff. So maybe the accelerated cure for aluminum/bronze has more to do with the bronze having abundance of copper (80-90% in most alloys) even though the %Cu in aluminum is small?


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## mayhugh1

The problem with aluminum might be the oxide on its outer surface. - Terry


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## dsage

mayhugh1 said:


> Dave,
> 
> Thanks for the Loctite tips. My frustration with Loctite is their bewildering product line with so many choices and subtle differences among them that I'm always left wondering if I'm using the right product and using it correctly. I waded through a lot of Youtube fluff but gave up before getting any real help with my application.
> 
> I was surprised at how easy it was to reach an application person at Henkle. (Just dial 1-800-LOCTITE and press '1'.) I learned a lot in the few minutes I spent with a pretty knowledgeable person on the other end. I was told that 620 was still my best choice if I really needed a 400F service temperature. I'm not really convinced that I do and, as you mentioned, there are newer and easier to use products with temperature resistances up to 350F.
> 
> I finally understand the active/passive metal stuff. In addition to being anaerobic, Loctite needs free metal ions to kick off its bonding process. Loctite doesn't bond to these ions. They are only used to activate the adhesive. The bonding occurs to the metals being joined, and different metals end up with different bonded shear strengths. The bonded shear strength of aluminum is 80% that of steel, and the bonded shear strength of bronze is 40% that of steel. Numbers on the bonded shear strength of bronze to aluminum weren't available.
> 
> Loctite can find the ions it needs on the surfaces of iron, steel, nickel, and copper. Loctite calls these 'active' metals. On the other hand, metals such as aluminum, stainless steel, titanium, magnesium, and black oxide'd or plated parts aren't 'active', and without an activator the bonding process may take days or weeks to occur, or it may never happen. If an active metal is being bonded to an inactive metal, Loctite will find the ions it needs on the active metal surface, and no activator is required. If two inactive metals are being bonded, an activator is required. Although it's also referred to as a primer, it's doesn't work like most of us would think since Loctite doesn't actually bond to it. A Loctite primer is just a copper salt in a fast drying solvent that leaves behind copper ions on the surface it was applied.
> 
> A primer can be useful even between two active metals to speed up the curing process especially if there is a big gap or if the parts are cold. The optimum gap for 620 is between .002" and .004". The downside is that if a primer is used, the ultimate bond strength will be 80% of what it would have been with no primer.
> 
> I also found out that 620 requires a 24 hour cure at 175F in order to achieve a full-strength high-temperature bond. This was something that my earlier test didn't include. I'm plan to repeat my test with my new found knowledge. - Terry




Wow! Great stuff Terry. Thanks for taking the time to share that. I have also found their literature very confusing and after seeing their recent presentations (which I also found confusing) the take away I got from it was to give them a call. I'm glad you did and passed along what you learned. I too have had issues with loctite in some conditions. Even those that (apparently) should have been ok. But I always chocked it up to old product or poor fit up.
Perhaps not clean enough?
I also found out from their presentation they have yet another product line for "not so clean" applications and another that you don't even have to put on the threads before assembly. They say it wicks in from outside and still locks the threads.
It's all sort of black magic. I'm glad you got some guidance.
Please report on the results of your new tests.

Thanks again


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## awake

Yes, very helpful information. Thanks for sharing!


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## mayhugh1

The Offy's valves started out as a handful of 2-1/2" long blanks that I band-sawed from a 3/8" 303 stainless rod. A valve will be turned on each end of each blank with a half inch work-holding spigot left between them.

To begin, the blanks' ends were faced and center-drilled while keeping in mind the valve stem diameter will be only 1/8". They were then moved to the Wabeco lathe where each valve was turned using a pair of programs. The first (roughing) operation left .040" excess stock for a second (finishing) operation. The blanks were held in a 5C collet chuck with their far ends supported by the tailstock. A 5/32" diameter phosphor bronze dead center was turned and mounted in the tailstock to allow a DCMT21.51 lathe tool to access the entire blank.

Dimensional accuracy wasn't a consideration during the roughing operations which were completed on all the blanks before moving on to the second operation. The goal for this step was to leave .002" excess stock on the stems for manual finishing. With care, the Wabeco will hold a thousandth or so over several consecutive parts, but model engine valves can be tricky. Even with tailstock support, part deflection can be inconsistent and difficult to control. Too little axial force from the tailstock will allow the stem to deflect when contacted by the tool, and a portion of the stem will wind up oversize. Too much force during turning can create wear on the tiny dead center or on the part itself and, in fact, can flare its end. The resulting clearance will again allow part deflection.

The stem diameter was measured at the completion of each finishing operation and, when it seemed appropriate, a correction was applied to the program before the running the next part. The finishing operation was run on all the parts before going on to the manual polishing steps.

The diameters of the valve stems were manually finished with abrasive paper. On several parts that had been wrongly corrected and ended up with 3 or 4 thousandths excess stock, the manual finishing took more time than the turning operations. The stems were polished to their final size (.001" under the valve guide bore) using 400g, 600g, and then 800g paper. The seats received only very light polishing with 600g and 800g paper since the second turning operation left them with the correct geometry and a very fine surface finish. Each stem was continually mic'd during finishing and the final result verified with a test cage. The final polishing was performed with a dab of red buffing compound on a clean shop towel which left the valves with a mirror finish. Each was leak-checked with a test cage before being parted from its blank. All leak times times measured greater than a minute.

After parting the valves from the blanks, their faces were finished while safely gripped in a shop-made PVC split collet. This same collet was used to hold the valves while their stems were being trimmed to their final lengths. Each stem was trimmed for the same height above a test cage. The valves were completed by cutting the .020" wide grooves for the spring retainer clips after which the leak-checks were repeated. - Terry


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## mayhugh1

I made two more Loctite tests and got essentially the same results as before. One of the tests included Loctite's 7471 activator, but it didn't seem to make much difference. Henkle told me that would probably be the case since the bronze cages would supply the ions for a cure that aluminum could not.

I allowed both test assemblies to cure undisturbed at room temperature for a full 72 hours before stressing them. In both tests, each bronze slug held tight under a 200 pound load applied at room temperature. I then heat cured the assemblies for an additional five hours at 300F and while still hot, all the pins slipped under the same 200 pound load. The heat cure should optimally have lasted 24 hours, and it didn't occur to me until later that maybe the assemblies needed to return to room temperature to complete the cure. It's also possible, however, that a high-strength high-temperature bond may not be possible between aluminum and bronze. Aluminum's temperature coefficient of expansion is so much greater than that of either bronze or the Loctite itself, that the expansion difference may be a problem.

On the other hand, Loctite's published data for bronze isn't all that different from my results. The shear strength of 680 on aluminum is 80% that of steel and on bronze it's only 40%. My results with aluminum/bronze aren't that far away from their 40% number.

I didn't use an activator when I installed the cages in the Offy's head since it showed no improvement in my test, and according to Henkle it degrades shear strength for all metals by 20%. In order to help install the cages at the same height above the head, I made some tapered Delrin plugs to locate and secure them to the head through the port openings while curing. Before assembly, the aluminum bores were scrubbed with acetone-wetted Q-tips, and each cage was lightly polished one last time using 800g paper to remove any surface oxide that might have formed since they were machined.

A .005" to .007" wide seat was manually cut into each cage and leak-checked with its partner valve just before installation. For some reason, the leak-down time of every valve/cage pair was greater than a minute with no additional work required on any of the seats. Only a few valves required a bit of thumb pressure to achieve a nearly perfect seal. In some hundred seated valves I've installed, I don't recall ever having an issue with a valve, but the seats have always required at least a few minutes of polishing with Time-Saver and/or metal polish in order to pass my leak-down test. For this step I used a dedicated valve or even a felt or soft wood bob for lapping/polishing, but I long ago quit using the actual valve that would end up in the engine.

And so, something about my cage machining process has favorably changed. One difference is that I bored the mouth openings using a tiny boring bar rather than a drill and/or ball end mill as I've done in the past. Another difference is that the Offy's cages are slip fits in the head rather than being 'lightly' press fit.

My seat cutter is a commercial 12 flute 45 degree piloted chamfering tool that I've used in the past and currently available from Midway:

PTG Interchangeable Pilot Muzzle Cylinder 45-Degree Chamfering

This time, instead of using it dry, I oiled the flutes and pilot with 30 wt oil which seemed to make its cutting action much smoother. I was careful to remove all traces of oil from the seat with solvent before performing its leak check since oil on the seat's surface will invariably make it look better than it really is.

The cage installation was completed by drilling and pinning the cages to the head using Loctited steel dowel pins as shown in the photos. This last step was risky although probably needed, and so I made a practice run on my 'mule" head using a couple spare cages and the custom machined angle blocks made earlier. - Terry


----------



## bobden72

mayhugh1 said:


> I made two more Loctite tests and got essentially the same results as before. One of the tests included Loctite's 7471 activator, but it didn't seem to make much difference. Henkle told me that would probably be the case since the bronze cages would supply the ions for a cure that aluminum could not.
> 
> I allowed both test assemblies to cure undisturbed at room temperature for a full 72 hours before stressing them. In both tests, each bronze slug held tight under a 200 pound load applied at room temperature. I then heat cured the assemblies for an additional five hours at 300F and while still hot, all the pins slipped under the same 200 pound load. The heat cure should optimally have lasted 24 hours, and it didn't occur to me until later that maybe the assemblies needed to return to room temperature to complete the cure. It's also possible, however, that a high-strength high-temperature bond may not be possible between aluminum and bronze. Aluminum's temperature coefficient of expansion is so much greater than that of either bronze or the Loctite itself, that the expansion difference may be a problem.
> 
> On the other hand, Loctite's published data for bronze isn't all that different from my results. The shear strength of 680 on aluminum is 80% that of steel and on bronze it's only 40%. My results with aluminum/bronze aren't that far away from their 40% number.
> 
> I didn't use an activator when I installed the cages in the Offy's head since it showed no improvement in my test, and according to Henkle it degrades shear strength for all metals by 20%. In order to help install the cages at the same height above the head, I made some tapered Delrin plugs to locate and secure them to the head through the port openings while curing. Before assembly, the aluminum bores were scrubbed with acetone-wetted Q-tips, and each cage was lightly polished one last time using 800g paper to remove any surface oxide that might have formed since they were machined.
> 
> A .005" to .007" wide seat was manually cut into each cage and leak-checked with its partner valve just before installation. For some reason, the leak-down time of every valve/cage pair was greater than a minute with no additional work required on any of the seats. Only a few valves required a bit of thumb pressure to achieve a nearly perfect seal. In some hundred seated valves I've installed, I don't recall ever having an issue with a valve, but the seats have always required at least a few minutes of polishing with Time-Saver and/or metal polish in order to pass my leak-down test. For this step I used a dedicated valve or even a felt or soft wood bob for lapping/polishing, but I long ago quit using the actual valve that would end up in the engine.
> 
> And so, something about my cage machining process has favorably changed. One difference is that I bored the mouth openings using a tiny boring bar rather than a drill and/or ball end mill as I've done in the past. Another difference is that the Offy's cages are slip fits in the head rather than being 'lightly' press fit.
> 
> My seat cutter is a commercial 12 flute 45 degree piloted chamfering tool that I've used in the past and currently available from Midway:
> 
> PTG Interchangeable Pilot Muzzle Cylinder 45-Degree Chamfering
> 
> This time, instead of using it dry, I oiled the flutes and pilot with 30 wt oil which seemed to make its cutting action much smoother. I was careful to remove all traces of oil from the seat with solvent before performing its leak check since oil on the seat's surface will invariably make it look better than it really is.
> 
> The cage installation was completed by drilling and pinning the cages to the head using Loctited steel dowel pins as shown in the photos. This last step was risky although probably needed, and so I made a practice run on my 'mule" head using a couple spare cages and the custom machined angle blocks made earlier. - Terry
> View attachment 116691
> View attachment 116692
> View attachment 116693
> View attachment 116694
> View attachment 116695
> View attachment 116696
> View attachment 116697
> View attachment 116698
> View attachment 116699


Terry could you give me a link for Midway and the  12 flute 45 degree piloted chamfering tool please. Have goggled but can not find them.


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## stevehuckss396

There is a. Link in his post


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## bobden72

stevehuckss396 said:


> There is a. Link in his post


Ah yes missed that thanks.


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## petertha

Really good stuff on the testing info, Terry. 
So that I'm clear, is pinning the valve cage on this particular engine because the top of the cage does not dead-end into a counterbore within the head like on other engines? You only have the circumference OD bond area to keep it put?


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## mayhugh1

petertha said:


> Really good stuff on the testing info, Terry.
> So that I'm clear, is pinning the valve cage on this particular engine because the top of the cage does not dead-end into a counterbore within the head like on other engines? You only have the circumference OD bond area to keep it put?


Correct...


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## mayhugh1

The valve springs were tackled next so the valves could be assembled in their cages. Their diameter and installed heights have already been defined by the cage geometry. The remaining parameters are dependent upon the force needed to hold the valve closed at the spring's installed height. For this, I selected 2 lbs based upon my experiences with earlier builds. An online spring calculator:

Spring Calculator & Instant Quote - Quality Spring, Affordable Prices

was used to iteratively solve for the rest of the parameters after selecting the wire material and diameter. I used .022" diameter music wire left over from another project, and after a few minutes with the calculator I settled on:

.300" o.d.,
.82" free length, and
4.5 turns .022" music wire.

The calculator predicted a 3.5 lbs/inch spring rate for an acceptable force of 1.8 pounds to hold the valve closed at an installed height of .30". The force required to fully open a valve will be 2.1 pounds.

A .195" diameter mandrel was used to wind the springs on my lathe using a shop-made tool post wire feeder. I wanted an inactive turn on the ends of the springs that I could grind flat so they will sit vertical on their perches and not rub the interiors of the followers. Engaging/disengaging the lathe's power feed to produce closed ends required a lot of practice, and I wasted a shameful amount of wire in the process.

The springs were normalized for 6 hours at 350F in an oven to heal the micro-cracks created by the winding process. They were then tumbled overnight in a vibratory tumbler with walnut shells and polishing compound for a bright finish.

Measurement of the force required to tip each installed valve off its seat agreed very closely with the predicted 1.8 pounds.- Terry


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## dsage

Great stuff. I learn something every time you post. I've never heard of the normalizing of the springs. But then I've never had one break either which I assume is the reason you take that step (to avoid breakage) ?
Nice finish. Such attention to detail.
Thanks


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## mayhugh1

Thanks, Dave,

The heat treatment step helps the spring retain its spring factor over time.

I used to 'pin shoot' at a local gun range many years ago. This is a handgun competition in which you shoot at five bowling pins while trying to knock them off the back a wide table faster than your opponent. I used a 45 caliber semi-automatic that I specially built to absorb the recoil of a powerful round that I hand-loaded especially for this weekly competetion. The gun used a special recoil spring that I had to hand wind. At the end of each evening of competition, I could feel the spring weakening and it's effect on my time between shots, and so a new one was used for each competition.

After coming across an article on spring making, I learned about the heat treatment step that spring manufacturers use and so I tried it. It increased the lifetime of my gun springs nearly an order of magnitude, and so I continued to use it on all my hand made springs ever since. 







My gun weighed 8 pounds and so wasn't legal for national competetions, but it cleaned up locally. - Terry


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## dsage

Standing like that those trophies remind me of a bunch of plastic army guys from my childhood. Very nice collection. Congratulations
 Great tip. I'll have to start doing that.
Thanks Terry.


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## mayhugh1

From a machinist's standpoint, the cam followers will compensate for the machining errors that have been accumulating in the valve train. From an engine builder's perspective they provide a method for setting the valve clearance. After installation they won't be adjustable and can't be used to compensate wear, but in a model engine wear is typically less of a problem than a lash adjuster that won't hold its setting. The full-size engine didn't use lash adjusters either - probably for reliability reasons. Hydraulic lifters were still fairly new at the time and probably not yet race proven.

I used .372" for the diameters of the followers so they'd be sliding fits in the .375" cam box bores. The first step was to reduce the diameter of a length of 3/8" drill rod using abrasive paper and a shop-made ring gage. While still in the lathe, the rod was parted into some thirty .290" long blanks, each with a shallow hole drilled in one end as a start on their interior machining. The followers' lengths were chosen to keep them entirely within the cam boxes to avoid rubbing or binding in the head. I wanted each valve stem to push against a truly flat surface inside its follower, and it turned out the most efficient way to accomplish this was to pocket the interiors of the followers on the mill. I initially tried to bore them on the lathe, but tool deflection became a problem around a nub that tended to form at the center of the bore.

A custom holding fixture was used to cycle parts quickly through the mill where a pocketing routine machined their interiors. Based upon measurements of the valve stem heights, a variety of depths was used with allowances for the tops of the followers that would be finished later. The parts were then heat treated and tempered at 300F. After heat treatment, their outsides were polished on the lathe with the help of a quick change mandrel fabricated from a wood dowel and a couple o-rings. The parts were easily slid on and off the mandrel while the lathe was running. Their interior polishing was done with Scotch-Brite but took longer since they had to be gripped in a collet with the lathe continually started and stopped.

After polishing, the top of each follower was ground on a surface grinder as needed to realize a .007" lash clearance (including the .005" cam box gasket) for each valve. The spread in the final follower thicknesses was .004" with a couple outliers at .008". Step feeler gages made up from brass shim stock were used to measure the clearances.

Final assembly of the head required drilling out the ten holes in the cam boxes which up to this point had been threaded for the screws securing the camshaft bearing caps. The cam boxes, through their bearing caps, were then bolted to the head using longer screws in holes previously threaded into the head. The delicate teflon gaskets made up earlier for use between the boxes and head were a bit tricky to keep in place during assembly. After assembly, compressed air forced into the oil feed port at the front of the head could be felt leaving the oil holes drilled through the lobe heels of both camshafts indicating the top-end's oil distribution path was likely clear. The camshafts smoothly opened and closed the valves in the completed assembly as hoped (whew!), and the lash was verified one last time.

Fabrication of the water outlet pipe should finish up the remaining work related to the head. - Terry


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## Charles Lamont

As impressive as ever. What is the wall thickness of those followers, and why did they not go way out of round when quenched? (Mind, you, with a fit that sloppy they would probably be OK if they did.)


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## mayhugh1

Charles,
The wall thickness is .015". I too was concerned about distortion, but a few test pieces moved maybe a tenth or so. Just in case, I added the extra thousandth clearance which turned out to not be needed. Perhaps the parts are small enough and being essentially hollow they can't help but be uniformly quenched. They were heat treated in three batches. Each batch was sealed in a stainless steel package filled with argon and heated to 1475F for an hour. The package was held over a can of old transmission fluid and its bottom cut off so the parts could randomly drop into the oil. I could see them still glowing red as they slid out of the package. One part from each batch was file checked to make sure it had indeed hardened. All three batches were tempered at the same time a day later. - Terry


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## mayhugh1

You wouldn't think something as mundane sounding as a water pipe would be much of a challenge, but this one turned into one of the most difficult parts so far in this build. The water outlet pipe is actually a three-input manifold that will return coolant to the radiator from three internal passages in the head. Coolant flow in this engine is a known issue, and the walls of its scaled-down manifold are necessarily thin. The water pipe is a prominent part that will sit at the very top of the engine, and so in addition to providing important functionality it needs to look good.

The main body started out as a 7" length of 5/16" brass rod whose interior was drilled out in three contiguous passages using 1/4", 3/16", and 1/8" drills. The entire o.d. was then taper turned starting with the .312" diameter on one end and ending with .187" on the other.

My first two attempts collapsed while turning the taper and, after some study of the drawing, I realized that a portion of the 1/4" i.d. section had been designed with a wall thickness of only .008". I eventually reduced the diameter of the drill for that section to 7/32" but ran into similar problems elsewhere. The drills for the deep 1/8" and 3/16" sections tended to wonder off course in the brass and leave a paper-thin wall at their intersection. These problems were invisible until after the unwieldy taper (with its own challenges) was turned. Then, they'd typically appear as innocent looking blemishes in the surface finish that might not show up until hours later. Some remained invisible until they wrinkled under the soldering heat. Reducing the diameters of the smaller passages wasn't a good option since it would have restricted an already limited coolant flow. Several tries using a combination of parabolic drills and reamers was required before I got my first of several usable main bodies.

The documentation contains a helpful template of the manifold. A full-size photocopy was glued down to a block of wood and used as a forming guide. A pair of grooved Delrin rollers was then machined and attached to the block and used to form the tubing.

Before bending the main body, its small end was annealed and temporarily soldered closed. Its interior was then coated with cooking oil - a release agent for Cerrobend. The Cerrobend was melted in a beaker sitting in a pan of boiling water to prevent overheating it. Immediately after its pour, the manifold was placed in a glass of ice water to crystalize and strengthen the Cerrrobend against cracking under the bending stresses. When the bend was completed, the tube was gently warmed with a torch, and the Cerrobend drained out cleanly.

The first of several difficult silver-soldered joints attached a mounting flange to the end of the main tube. I made a (low thermally conductive) stainless steel soldering fixture to hold the manifold parts in alignment during soldering. My preferred method for soldering is to include the solder in the fixturing so I only have to hand feed heat rather than the solder. The flange mounting holes are so close to the tube though that even after turning down the heads of the hold-down screws, the flux and solder tended to flow around them and attach them to the flanges. This was eventually solved by switching from stainless to plain steel screws, turning down their heads, and then blackening them using a cold bluing solution. For good measure, I also added temporary mica washers, cut from a TO-3 transistor insulator, under the heads.

The remaining two inlet tubes were also drilled out from solid rod, taper-turned, and bent according to the template. Ron recommends using thin wall brass tubing for these, but I was concerned about the tiny contact area that would be presented to the main body. One of my weak-walled main bodies failed under the heat one of these soldering steps. I also had problems with the hidden entrance holes in the main body being inadvertently soldered closed. The curved inlet tubes made it impossible to drill these out, and the only solution was to start over. I went through almost two six-piece batches of machined flanges before the manifold was finally completed.

Soft soldering would have eliminated a number of problems that took a lot of time to work out. It did, however, weed out a defective manifold that might have otherwise failed on a running engine. Strength-wise, soft soldering would have been fine for the flanges which had machined recesses for the tubes. I'm not so sure it would have been reliable for the butted intersections between the two auxiliary tubes and the main body.

In any event, I stuck with Silvaloy 355 for all five joints since I'm confident it can be nickel plated. I'm not so sure about plating the tin/lead solder that I have on hand. I plan to test this as well as a non-lead alloy later.

Although the manifold is currently bright and shiny, its finish will eventually dull and look like something more appropriate on a steam engine. The next step will be to try my hand at DIY nickel plating so I can maintain the authenticity of the part with white metal. - Terry


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## srobovak

Hi Terry,
Nice looking manifold. 
I didn't quite get the reason why to turn the taper on the outside... For the looks?
Looking forward to the next step.
cheers, Branislav


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## tornitore45

Is that a sheet of Silver Solder draped on the main piece when soldering the second inlet?


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## awake

Sounds like a lot of work and trouble, but the final results are beautiful!


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## mayhugh1

Branislav,
I think the purpose of the taper inside the main body was to equalize the coolant flow in each the three lines coming from the head. In the full-size engine, that main tube was probably a rolled and seam welded affair whose outside naturally took on that same taper. 

Mauro,
Yes

Terry


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## mayhugh1

I was originally going to fabricate the manifold from stainless steel so I'd have it in white metal. In hindsight, that would have been madness. Ron's version in brass got me thinking about nickel plating - something I've been wanting to try for some time. There are a lot Youtube videos on DIY plating, and the one by Doc1955 who occasionally posts on this forum is as good as any.

Plating requires an electrolyte, a low voltage dc source, and a pure nickel anode (all available from Amazon). The most commonly used electrolyte can be made by dissolving a couple online-available nickel salt chemicals in water (a.k.a. Watt's solution), but another (nickel acetate) can be made from ordinary kitchen ingredients i.e. plain white vinegar and salt.

Also available is a Watt's-based kit from Caswell that contains nearly everything needed. An advantage of this fairly expensive option is that it will also include some proprietary chemicals for a bright finish right out of plating solution.

Unfortunately, I wasn't able to find any end result comparisons. Nickel acetate doesn't seem to be commercially popular - maybe because of an incompatibility with the industry's 'secret sauce' brightening agents. I initially experimented with nickel acetate since I already had everything needed on hand. My test parts turned out so well that I continued on with it.

The first step was to make the lead acetate. This involved adding table salt to 1-1/2 quarts of white vinegar in a wide mouth canning jar. The electrolyte can be used over and over (it even gets better with use), and so I used a jar with a spring lock top that I'll use for both plating and electrolyte storage. A pair of pure nickel anodes (purchased from Amazon) was then lowered into the vinegar, and 5 VDC from a wall wart power supply was applied across them.

I found little guidance on how much salt to use, and my three tablespoons turned out to be more than was evidently used in any of the videos. The salt will control the conductivity of the electrolyte which in turn will affect the speed and (maybe) the quality of the plating. In this first step, a solution of nickel ions is being created for later use in the actual plating process. Over time, the color of the solution will turn greenish-blue indicating that it's ready for use. How fast this happens will also depend upon the salinity of the solution. In the videos that included current measurements, tens of milliamps through the solution was common, and the electrolyte creation process took overnight. My own measurement indicated 2.8 amps, and my electrolyte appeared ready for use in about an hour.

Although my DC supply was capable of even more, the relatively high current draw was concerning. Everything I'd read indicated best plating results will be obtained while using low currents. These sources were referring to Watt's electrolyte, though, and so I wasn't sure if the same applied to nickel acetate. I decided to continue on.

The part to be plated is connected to the negative terminal of the supply, and one or more nickel anodes are connected to the positive terminal. Hydrogen bubbles immediately begin forming around the part, and in my case they temporarily fogged the solution. The bubbles tend to agitate the electrolyte making additional stirring unnecessary. Plating occurs quickly - in just a few minutes. Other than pulling the part up for inspection, it's difficult to judge when you're done.

Thicker plating will likely result from longer plating times, but quality nickel plating is measured in tens of microns even in plating shops. I suspect, with no evidence to back it up, that if very long times were attempted, a rough uneven finish might result from second order effects related to the shape of the part with respect to the shape of the electrode. The wire hanger used to hang my parts built up an ugly rough finish rather quickly.

The importance of proper surface preparation is stressed in any reference on plating. Even when done commercially, nickel plating isn't thick enough to fill in machining marks or surface scratches. Except for its color, a part's surface will look the same after plating as it did before plating. The part also needs to be absolutely free of any oil or grease including finger prints.

I finished all my parts with 1000g paper and a white Scotch-Brite pad while supported on a fixture to avoid finger prints. Most of the manifold's metal finishing was done while the tubes were on the lathe and still straight. Its soldering fixture was used to hold the completed manifold during final polishing. I found I got better results if the final polishing was done immediately before plating rather than over a tarnished surface. All parts were dip cleaned in acetone, air-blown dry, and then hung in the plating solution without being touched by hand.

The 2-3 minute plating time on all my test parts looked great. A couple soldered flanges using both 60/40 and nearly pure tin solder took nickel plating well. When removed from the electrolyte, all parts had a smooth gray satin finish which would be suitable for some applications. They might have had a brighter finish if the Caswell kit with its secret brighteners had been used.

For the manifold, I wanted something that looked like chrome. Even the brightest nickel finish, though, has a slight yellow tinge compared with chrome. Using red rouge buffing compound on a strip of micro-fiber cloth, I was able to buff its surface to a bright reflective finish that was close enough. - Terry


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## stevehuckss396

Have you looked into the "next step" and see what it would take to chrome plate. You seem to have 95% of what it would take and it would sure look stunning in chrome.


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## Cogsy

I've done a tiny bit of chrome plating with a very similar setup to what you're using, but running the charge directly through the applicator 'brush' to apply the chrome solution. I chromed directly over my nickel plating attempt because the nickel looked slightly yellow and I wanted the chrome effect. Here's a picture of my exhausts to show the difference in nickel and chrome LINK - note the nickel is nowhere as yellow in person as it looks in the picture, but against the true chrome is is very evident.

Edit to add - I just noticed how yellow my picture looks. It seems the white balance was off target on my camera - the light pieces of the marble table are actually white, so the yellow exhaust is really just slightly yellow and the chrome one is true chrome colour.


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## dnalot

Well done. You are correct in your assumption that plating time has an affect on the surface quality. Too long or to much current will yield a rough surface. My power supply lets the voltage float and you set the amperage to what you need. To figure that, multiply the surface area (sq in) by .07. Fifteen minuets will build up around .00030" of plating. If you want more buildup repeat the plating.  If you need to fill in scratches or pitting plate first with copper and sand smooth. Repeat if necessary.


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## mayhugh1

stevehuckss396 said:


> Have you looked into the "next step" and see what it would take to chrome plate. You seem to have 95% of what it would take and it would sure look stunning in chrome.


Steve,

I looked into chrome plating but felt it wasn't something that I could easily dip my toes into like I did with nickel plating. An expensive Caswell kit is probably the most practical way to get into it, and the chemicals involved are a hassle to keep around a limited space shop for occasional use. Maybe someday though ...  -Terry


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## Mike Henry

Finish.com is a forum that focuses on these sorts of activities and the forums there might be of interest to some here.






						World's #1 Metal Finishing Resource since 1989
					

Answers to every anodizing, plating, powder coating, PVD, galvanizing & metal finishing need. The Home Page of the Finishing Industry®, the world's longest-running, most popular & authoritative source.



					www.finishing.com


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## Charles Lamont

mayhugh1 said:


> ... chrome plating but felt it wasn't something that I could easily dip my toes into ...


LOL


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## mayhugh1

The exhaust system includes a complex set of pipes that are virtually identical to those on the full-size engine. The model's exhaust is made up of several pieces of 5/8" and 1" diameter seamless 304 stainless tubing. There isn't a straight piece among them, and so a lot of metal forming/joining is involved. Basically, it's a much larger version of the just completed water manifold.

The first step was to fabricate the megaphone style collector. Its conical shape was created by first cutting a v-shaped wedge out of a six inch length of 1" diameter tubing. This was a pretty messy operation that consumed nearly a dozen Dremel-style abrasive cut-off disks and one Covid mask. The collector's shape was formed around a custom tapered mandrel. With the slotted tube resting in a v-block, gentle persuasion from the ram of an arbor press around the periphery of the tube soon had the seam closed up tight. A piece of leather wrapped around the tube prevented it from being marred.

I chose to tig weld the seam rather than solder it so the heat created later while silver-soldering the exhaust pipes won't be an issue. However, the poor thermal conductivity of thin stainless steel can create an unbelievable amount of weld distortion. The gap was small enough that filler rod wasn't needed, but I used it anyway to avoid a slight depression along the length of the collector.

The mandrel was used to stabilize the shape of the collector during welding. A notch was milled along its length to provide a gap behind the seam to keep it out of the weld puddle. The mandrel kept the collector circular and wrinkle free, but shrinkage along the seam created a subtle bow along the collector's length that actually improved its appearance. The tube wound up shrunk so tightly around the mandrel that it had to be pressed off.

The siamese'd ports in the head will require the circular ends of the exhaust tubes to be expanded. A swaging tool was machined and case-hardened in order to prepare the tube ends for soldering to the exhaust flange. A few test pieces were swaged so measurements could be taken for the flange's machining. The exhaust tubes will eventually be soldered in shallow recesses machined into the outer side of the flange. These recesses will help stabilize the assembly during soldering and provide some additional surface area for the solder. A back-up plate was also made to support the thin exhaust flange during soldering. Finally, a couple Teflon flange gaskets were cut using a vinyl cutter on my Tormach.

The next step will be to form the exhaust tubes which must be bent on a 2" bend radius. My 5/8" tube bender works on a 3" radius, and so I have some thinking to do. - Terry

edit:  the caption on the first photo should read '... 270 Exhaust'.


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## tornitore45

How was the weld ground and polished to be invisible?


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## Steamchick

Brilliant! I am impressed. Carry-on, as I am enjoying your work. Excelent story and explanation. Well supported with pictures. You'll be able to sell this story to a magazine when finished. Let us know the magazine so we can read the full story as well.
Thankyou!


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## mayhugh1

tornitore45 said:


> How was the weld ground and polished to be invisible?


Mauro,
After some initial filing, the collector was put back on the mandrel which was put back into the lathe and it was polished while spinning. - Terry


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## mayhugh1

The Offy's exhaust ports are connected to the collector through 5/8" diameter stainless steel tubes. A drawing in the manual shows these tubes being derived from 90 degree bends formed on a 2" radius. This is a pretty tight radius for 5/8" hard tubing, and even though my tube/pipe bender has a 5/8" die, its bend radius is 3". The difference didn't seem significant until I tried laying out a paper exhaust using the larger bends. The tube intersections became even more difficult; and the overall look was, well, ugly. So, I spent several days making and testing a 2" die for my bender. One of the photos shows it next to the bender's original cast iron die.

I tested the die using some stainless drops in my scrap collection. I had a few pieces of 5/8" tubing in three different wall thicknesses: .035", .049", and .065". The new die created near perfect bends in the .065" and .049" tubing, but the bend cross-sections in the .035" tubes were noticeably oval-shaped. They were improved when filled with Cerrobend, though.

I continued using the original roller that came with the bender since, after a bit of re-work, it fit the tubing perfectly. I accidentally discovered it was important to not snug the roller up against the tubing before sweeping it around the die to make the bend. Without a quarter inch or so gap, it invariably marked the tubing. Using the bender in this way seemed counterintuitive, but its instruction manual was clear about closing the roller against the tubing.

I ultimately settled on .049" for the tubing wall thickness since there's little space on the exhaust flange for a .065" wall thickness after the tube is swaged. And, since I'll probably have to make a lot of bends before I get four tubes properly fitted, I didn't want to deal with the Cerrobend. The swaging tool I'd already machined was designed for .035" tubing, and so a new one had to be made to avoid scrapping the already finished exhaust flange with its tube recesses.

The ends of the tubes must be swaged after they're bent, and this creates a work-holding problem. Since the swaging operation requires everything my half-ton arbor press can deliver, a stout fixture that won't mar the tubing is required. My solution, shown in the photos, was a clamshell machined from a couple pieces of red oak.

For practice, I soldered some of my swaged test pieces to a dummy flange to compare the three varieties of silver solder that I have on hand: Silvalloy 355 (from Brownells), Prince & Izant 50 ni3, and some cadmium bearing Silvalloy 35 (purchased from McMaster- Carr). The cadmium bearing solder flowed noticeably easier and would create the need for less metal finishing, but the Silvalloy 355 gave the best color match to stainless. Since I'm currently planning to polish the finished exhaust, I'll likely use the Silvalloy 355. If I knew I was going to paint the finished exhaust, I'd for sure use the Silvalloy 35. The solder manufacturers recommend the black (rather than white) flux for metals with tough oxide coatings such as stainless steel. I tried both, and the joints were definitely wetted better by the black flux.

I used up on testing what little .049" wall thickness tubing I had on hand and am currently waiting on some to arrive. Unfortunately, it seems to be lost in transit, and the supplier wants to wait a few more days before shipping a replacement. - Terry


----------



## Peter Twissell

Nice work!
I've recently been assembling the exhaust system for my radial, all in stainless at 1.5" diameter. I cheated by designing the system to use available mandrel bends. Still, there were plenty of parts required machining and tig welding. My tig skills are limited, so some filing is involved to achieve an acceptable result.
I can only manage a couple of hours at a time - filing stainless steel soon drains the enthusiasm!


----------



## gbritnell

Hi Terry,
When I first built my small tubing bender it would bend SS up to 5/16 but with the roller type shoe in some tubing it would leave an impression at the end of the bend. I changed the roller shoe to a rectangular shape ( rectangular block with the necessary radius cut into it) and that eliminated the depression at the end of the bend.
gbritnell


----------



## tornitore45

> I've recently been assembling the exhaust system for my radial, all in stainless at 1.5" diameter.



1.5" diameter?  what kind of a model is that? Sounds like a full scale engine.


----------



## Peter Twissell

See topic 'Gert Big Radial'


----------



## Peter Twissell

https://www.homemodelenginemachinist.com/threads/a-gert-big-radial.31859/


----------



## tornitore45

Peter Twissell said:


> https://www.homemodelenginemachinist.com/threads/a-gert-big-radial.31859/


Interesting, to put it mildly.


----------



## Peter Twissell

Thanks (I think), but let's not pollute this thread any further.


----------



## kinggt4

Beautiful work!  You are a very talented guy.  A few Q's: I noted you have a Tormach - what model?  Does the glass beading remove the tooling marks or do you need to finish the parts before blasting?  Thanks for the great presentation.
George


----------



## mayhugh1

George,
I have an original 1100 which I purchased about a year after Tormach started production,  and I've been very happy with it. It's probably been used a dozen hours per week since received and has been very reliable. Yes, the machining marks quickly disappear in the bead blasting cabinet with no other finishing required. - Terry


----------



## kvom

Are you running PathPilot now, and with the TTS holders?


----------



## mayhugh1

kvom said:


> Are you running PathPilot now, and with the TTS holders?


Still running Mach 3 because I use the same computer for my mill and lathe and don't have the room for two set-ups. I always use the TTS toolholders except if I'm going to rough out a lot of material with a 3/8" or 1/2" cutter. - Terry


----------



## mayhugh1

After my piece of 304 stainless tubing arrived, blanks for the four exhaust tubes were formed using the special tools made earlier. Silver solder doesn't play nicely with poor fit-ups, and the Offy's exhaust has eight interconnected joints to deal with. The collector's taper makes things more interesting and will affect the order of assembly.

Construction began with the machining of a ferrule to provide a temporary slip joint between the collector and the #1 (front) exhaust tube. This ferrule was silver-soldered inside the exhaust tube and made to have a snug fit inside the collector for consistency while fitting up the other three tubes.

An orientation was selected for the collector that placed its welded seam on the opposite side of the exhaust tubes. As mentioned earlier, shrinkage occurred along the seam as the weld puddle cooled and created a slight bow in the collector. When tig welding a seam in a piece of stainless tubing, a nice bead can be laid down on the outside surface under the protection of the shielding gas. On the inside however, unless shielding gas is also flowed through the tube, nasty carbides will form on the backside of the seam. (Sone welders call these boogers.) These carbides are difficult to drill through and damaging to tooling, and so an orientation that avoided them was chosen. As a result, the exhaust will end up directed slightly away from the the engine. A fortunate result was that with respect to the exhaust flange, the bow compensated for some of the collector's taper and made machining the fish-mouthed tube ends a bit easier.

The #1 tube was the first to be soldered to the exhaust flange. This step established the alignment of the entire exhaust with respect to the engine and in turn affected the machining of the remaining three tubes. It was carefully fixture'd and solidly supported during soldering. I forgot to take a photo of this important setup before soldering, and so I went back later for a staged photo.

The rest of the puzzle involved machining the ends of the other three tubes so they'd fit up closely against the collector while sitting inside the recesses machined for them in the exhaust flange. I started with the #4 tube and worked my way forward. Another oak clamshell was made to accurately grip the bent/swaged tube blanks while their ends were prepared. It was used to support the blanks in the bandsaw for rough trimming as well as in the mill during their final machining. Thanks to the bowed collector, 90% of the final end preparations could be accomplished using ball end mills. Only the #2 tube required fine tuning with a file.

The three completed tubes were then soldered to the exhaust flange using the collector as an alignment tool. The flange solder joints that I practiced earlier required a lot of metal finishing due to my left-hand trying to feed the solder while I was blinded by the flame of an over-sized acetylene torch. So, I came up with a technique to take me out of the operation except for holding the torch.

Pads were machined from .003" thick silver-solder ribbon that I fluxed and inserted in the machined recesses in the exhaust flange under the tubes. Rings of 1/32" solder were formed and inserted down over the tube just above the flange. (Forming silver solder is a lot like forming music wire.) With some torch manipulation, I was able to draw the pad solder up and the ring solder down to fill the gap around the tube in the flange recess. This resulted in joints that required little clean up.

After finishing up the soldering on the exhaust flange, I noticed it had acquired a slight warp. After straightening it, the fit of the #2 tube to the collector was now more than I wanted to see. Although the soldering fixture had originally been ground flat, a heat-induced warp occurred in its weak area between the #2 and #3 exhaust openings. Rather than bend the warp back into the flange, I'll deal with the gap while soldering the flange.

With all four tubes attached to the flange, the last and now even more difficult soldering operation will be to attach them to the collector without creating a mess needing days of filing. I have some more solder practice ahead with the gap filling silver solder I've ordered. - Terry


----------



## Charles Lamont

Don't forget the 'finger holes' in the trumpet!


----------



## mayhugh1

Before the collector was finally soldered, the ports for the exhaust tubes needed to be drilled. There were just three 7/16" holes, but they had to be drilled through a tapered thin-wall 304 stainless steel tube which was problematic.

The mandrel that was used to form the collector's taper was repurposed as a sacrificial backup to reduce the trauma of the drill breaking through the collector's wall. With the mandrel held in place with a vise stop, soft jaw material was used to safely support the tapered tube. I came across this material several years ago in a Youtube video that showed it off supporting a raw egg while its top was machined.

'Soft jaws' is sold by Tormach as a jar of beads that when heated in hot water becomes a pliable mass of plastic. A pair of wood end blocks aligned the collector in the mill vise while the pliable material was packed around it. A heat gun was used to extended its working time. The vise jaws were left slightly open (.050" or so) until the material cooled and hardened to a Nylon-like consistency.

The holes were spot-drilled with a 3/8" 60 degree v-drill, and then drilled using a 7/16" carbide drill. The sound coming from the mill told me it wasn't happy with what was going on, but I ended up with three round holes in an undamaged collector,

This was my first experience with Tormach's soft jaw product, and I found it a little messy to work with. Unless it's at the right temperature, it tends to stick to fingers and anything else it contacts. I was concerned about it sticking to my vise, which I attempted to protect with plastic sandwich wrap. My concerns were unfounded since once the material cooled, it completely unstuck itself and was ready for reuse. Soft Jaws isn't something I'd routinely use, but in this case it solved a difficult work-holding problem.

Despite being advertised otherwise, the Silvaloy 355 (56% Ag) that I used on the exhaust flange wasn't a color match to stainless steel. I decided to use it in ribbon form only inside the close-fitting joints on tubes #3 and #4. I couldn't locate a suitably colored wide gap solder for tube #2. Instead, I used Silverbraze 50ni2 (50%Ag, 20%Cu, 28%Zn 2%Ni) which is advertised specifically for 300 series stainless steels but with tight fit-ups.

The exhaust assembly was heated while supported in a fixture that used a weight to pull the collector tightly against the tubes as the solder ribbons melted. The two close-fitting joints came out as expected, but hand feeding the Silverbraze into the #2 tube's wide gap was much less satisfying. After globbing on enough solder for a generous fillet, I realized I'd have to do the same for the other two joints so they would match. This hadn't been part of the plan, but once I got started, it was difficult to stop. I used the tapered mandrel one last time in a jury rigged horizontal rotisserie that helped keep additional solder in place. The result was pretty much the mess I'd hoped to avoid.

After spending a full day filing and sanding, the exhaust was finally polished using a new technique I'd been recently considering to avoid the risk of a buffing wheel. Starting with an 800g final sanded surface, I used a cloth rag in shoeshine motions with 1200g Clover lapping grease to buff the complex shaped exhaust to a chrome-like finish. - Terry


----------



## gbritnell

Terry, 
Truly remarkable outcome on the header. When I built the header piped for both my inline 4 cylinder and flathead V-8 engine I had the same questions as you for making the openings in the collector pipe.
My collector pipe was formed with the first cylinder (bend) I made a mild steel fixture plate with the same bolt mounting holes. I used the fixture for fitting the subsequent pipes and for silver soldering. To make the openings in the collector pipe I drew a magic marker line around each pipe joint then used a Dremel grinder to make the openings, just staying away about the thickness of the pipe wall. I did it this way because the attachment points were more elliptical than round.
gbritnell


----------



## kvom

Can you explain the "collector pipe" for someone ignorant of IC engines?  Where is it in the finished exhaust?


----------



## gbritnell

The collector pipe is the main tube which 'collects' the exhaust gases from all the cylinders pipes.


----------



## kvom

Now I get it.  The holes are where the three tubes are soldered.


----------



## ddmckee54

I was wondering if you were going to open up the collector for the #2, #3 and #4 pipes before you soldered them - or if you were going to try and open them up through the openings in the exhaust flange.  Did the edge of the openings try to distort any while you were soldering them?

Don


----------



## mayhugh1

ddmckee54 said:


> I was wondering if you were going to open up the collector for the #2, #3 and #4 pipes before you soldered them - or if you were going to try and open them up through the openings in the exhaust flange.  Did the edge of the openings try to distort any while you were soldering them?
> 
> Don


There wasn't any distortion...


----------



## mayhugh1

The Offy's documentation invites the builder to experiment with alternative solutions to the engine's induction system. In addition to Ron's four carb setup, I've seen an online photo of another builder's single Perry carb sitting on a custom tubular manifold.

However, I very much like the looks of Ron's four carb design even though it will likely require a lot of effort to get properly working. It was designed to be reminiscent of an injection system that was available on the full-size engine. Ron used four air bleed carburetors similar to the latest tiny O.S. nitro units available in hobby stores. One of the problems with these simple commercial carbs is that each requires the addition of a remote needle valve and a pair of interconnecting hoses to become functional.

I spent several days trying to come up with a design based upon four O.S. 15LA's that didn't require a mass of out-of-scale Tygon tubing. The carb's form factor, however, made it difficult to hide the needle valves within a believable looking assembly. I eventually decided to start from scratch and design my own quad carb body with an integrated fuel bowl where I hid the needle valves. It's still something of a work in progress and will likely continue to evolve as I make parts for it. I already machined the airhorns to break up the monotony of sitting in front of a computer for the last two weeks. They were the only parts of the design that didn't seem to change daily.

Currently, the fuel bowl has a capacity of about 1.5 ounces. I also completed a design based upon a larger bowl that would have allowed me to eliminate the fuel tank altogether. After a few days of looking at it, though, I realized it was overwhelming the appearance of the engine.

I've included a number of Solidworks renderings of my current design along with notes detailing some of its features and dimensions. - Terry


----------



## kvom

Does this mean that the carbs are the last parts needed to finish?


----------



## tornitore45

Very nice.   How will you adjust the needle of each cylinder?


----------



## mayhugh1

kvom said:


> Does this mean that the carbs are the last parts needed to finish?


I still have the crankshaft, rods, pistons, and rings to do.


----------



## mayhugh1

tornitore45 said:


> Very nice.   How will you adjust the needle of each cylinder?


That, I'm not sure of (yet).


----------



## prophub

Hi Terry,
I always look forward to your posts as I learn so much from them and appreciate you taking the time to document things as you do.
Could you explain how you made the airhorns for the carbs?  They seem like a simple part but I can't figure out how they are made. Are you using form tools for the outside and inside? Are the tools the same radius for the outside of the airhorn and the inside and one is just convex and one concave? How do you keep a consistent thickness to the walls?
Sorry for all the questions!

Thanks!

Shawn


----------



## mayhugh1

prophub said:


> Hi Terry,
> I always look forward to your posts as I learn so much from them and appreciate you taking the time to document things as you do.
> Could you explain how you made the airhorns for the carbs?  They seem like a simple part but I can't figure out how they are made. Are you using form tools for the outside and inside? Are the tools the same radius for the outside of the airhorn and the inside and one is just convex and one concave? How do you keep a consistent thickness to the walls?
> Sorry for all the questions!
> 
> Thanks!
> 
> Shawn


Shawn,
I turned them on my little Wabeco CNC lathe. I used two operations - the first with a 35 deg rhombic insert to turn the outside contour. A hole was then drilled through the center of the blank so a second operation using a boring bar could turn the interior. I designed the Horns in SolidWorks to have a similar thickness throughout except for the outside rim which I made with a circular cross section. The curve was a spline that I played with until the shape looked good to me. I know you were hoping to hear about some clever manual operation that I had managed to come up with, but I'm sorry to say I'm not that clever. - Terry


----------



## prophub

Terry 

Thanks for the quick response! You're willingness to answer questions and share your knowledge is very much appreciated. I'm sure there are many people here like me who are learning so much from people like you. 
I made a airhorn once but it was just a simple one with straight, angeled sides. Thanks for sharing how you made yours!

Shawn


----------



## Tim1974

He is the master And I thank him too love the posts just incredible work a reel inspiration


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## dsage

tornitore45 said:


> Very nice.   How will you adjust the needle of each cylinder?



Perhaps a small tube into each manifold that you can measure vacuum at and cap off after. The old school way of tuning multiple carbs.


----------



## lohring

mayhugh1 said:


> That, I'm not sure of (yet).


Model boaters have used a flow meter to adjust needles.  The pressure comes from a standard propane cylinder feeding into the fuel line.  The needle flow rate is read on the Dwyer ball gauge with the pressure adjusted on the propane bottle to a standard on the Magnehelic gauge.  We usually used 40" of water.  This was most helpful for setting a new engine to numbers from similar engines and for adjusting needles for air density changes during the day where the correct setting is approximately known.  

In your case you might find the flow at the recommended needle setting of a suitable OS carb, then set your needles a little richer.  It will be easy to equalize the flows from each carb despite manufacturing variations.  Below are a couple of pictures.  It's easy to build.  You can probably find a model boater with one for sale for under $100.  

Lohring Miller


----------



## BaronJ

mayhugh1 said:


> Shawn,
> I turned them on my little Wabeco CNC lathe. I used two operations - the first with a 35 deg rhombic insert to turn the outside contour. A hole was then drilled through the center of the blank so a second operation using a boring bar could turn the interior. I designed the Horns in SolidWorks to have a similar thickness throughout except for the outside rim which I made with a circular cross section. The curve was a spline that I played with until the shape looked good to me. I know you were hoping to hear about some clever manual operation that I had managed to come up with, but I'm sorry to say I'm not that clever. - Terry



Hi Terry,

Those horns would be a nice exercise in metal spinning.


----------



## mayhugh1

dsage said:


> Perhaps a small tube into each manifold that you can measure vacuum at and cap off after. The old school way of tuning multiple carbs.


Nice idea. I just added them to the design. As you say, they certainly can't hurt, and they'll make the induction system look more techie. - thanks.  - Terry


----------



## thefishhunter

Wow, a chance to add something to one of Terry’s builds (I usually just lurk in awe 

if you add the manifold ports, then a set of carbs sticks (4 mercury filled tubes similar to the single one shown above.) are what we have always used to sync motorcycle carbs. They are relatively cheap, hang from handlebars or frames and allow you to get the manifold vacuum signal to be equalized at all 4 carbs.
This is used two ways, you can just cycle the starter (no ignition) and measure the vacuum to set the throttle blade position is equalized.
Secondarily, with the engine running, you can adjust your needle balance at idle to again get an equal reading, again to get the engine to “balance” across all 4 carbs.
You can get a set at just about any motorcycle shop or online.


----------



## RonC9876

Just a note on how I adjust my carbs. I remove the exhaust manifold and look directly into the combustion chambers while the engine is running. I adjust each needle for a nice blue flame at the exit of each combustion chamber. I watch for a consistent flame throughout the throttle range. Easy and I get consistent results.


----------



## Peter Twissell

I once tried to tune a motorcycle carb using that method.
It took months for my eyebrows to grow back.


----------



## BaronJ

Hi Peter, Guys,



Peter Twissell said:


> I once tried to tune a motorcycle carb using that method.
> It took months for my eyebrows to grow back.



Somewhere kicking about I have a kit of parts which includes a clear glass topped spark plug and a bottle of cleaning fluid.  I can't recall the name at the moment.

But you took a plug out and replaced it with the glass one and tuned the carburetor for a nice blue flame in the glass plug.  I recall that it was very good with SU and Webber carbs.


----------



## michelko

That is called colourtune

Michael


----------



## Peter Twissell

I have a colourtune plug, but it comes with dire warnings about using it at anything other than tickover, so I don't see the point.


----------



## BaronJ

michelko said:


> That is called colourtune
> 
> Michael



Thank you Michael !
I've been pondering over that name all afternoon.

Peter:  I don't recall any dire warnings like that, I do know that it was a right bugger to clean the inside of the glass though.


----------



## mayhugh1

Thanks all for your comments. I'd never heard of color tuning before. It sounds like what Ron did. - Terry


----------



## Ghosty

Terry, They can be found at Gunson Colortune See Through Spark Plug Kit G4074
I bought one back in the 80's for setting the idle tune on 4 cylinder bikes, hard to set top end on a bike, as you need the engine under load
Cheers
Andrew


----------



## johwen

mayhugh1 said:


> That, I'm not sure of (yet).


Johwen Here You can use a tachometer to adjust each needle to maximum revs at fixed throttle setting or a vacuum gauge but you need to have a balance pipe or drilling on the engine side of the throttles to balance the vacuum across all cylinders once again adjust each to reach highest reading. Hope this helps John


----------



## awake

I generally adjust my carbs by cutting back on bread and sweets ...


----------



## dsage

LOL


----------



## mayhugh1

Construction of the Offy's induction system began with the machining of its two main components - the quad carb body and the fuel bowl. Just after machining the carb body, I became concerned that the throttle barrels were probably uncovering the air bleed passages a little too early. So, I plugged them and their adjustment screw holes and drilled four new sets on the opposite sides of the throttles. This also resulted in a change in the direction of operation of the throttle which wasn't necessarily a problem. But, I never really liked my push-pull throttle design with its awkward two-axis motion, and so I'll likely replace it with a rotating lever.

In my earlier post I forgot to include a cross-sectional CAD view through the center of the carb body showing details of the Venturis. I've included one here that also shows the updated air bleeds. The continuation of the Venturis using tapered bores through the throttle barrels is a feature lifted from one of George Britnell's carburetor designs. None of the simple commercial air bleed carbs that I've seen use it, probably due to the additional manufacturing cost. The manifold vacuum taps suggested by David Sage were also added to the final part - Terry


----------



## gbritnell

To use a term taken from my kid's language 'Sweet'
gbritnell


----------



## Art K

Reminds me of a pair of Weber carbs.
Art


----------



## BaronJ

Art K said:


> Reminds me of a pair of Weber carbs.
> Art



Reminded me of Air horns !   Do they play  la cucaracha.


----------



## mayhugh1

Each needle valve assembly includes a jet with a .022" dia. orifice and a .030" diameter adjustable needle. In addition to metering fuel into the engine, the four assemblies also secure the carb bowl to the carb body. The tops of the jets are sealed to the carb body by a Teflon bowl gasket, and their bottoms are o-ring sealed to the inside floor of the bowl. Nuts threaded onto the bottoms of the assemblies protruding through the bowl will compress the o-rings and then hold the bowl tightly against the bowl gasket for a (hopefully) leakproof 'four barrel' carburetor.

Both halves of each needle valve assembly were lathe-turned from phosphor bronze, and all features associated with the needles themselves were turned in the same setup to insure concentricity. A sensitive drill attachment in the tailstock was used for the .022" diameter flow passages. The adjustable bodies are threaded 10-56.

The orientations of the pickup tubes are limited by the space available inside the bowl. Their hole locations were determined while the jets were threaded in place and, after drilling, the jets were numbered with their locations in the carb body. An alignment fixture was used to soft-solder the pick-up tubes to the jet bodies.

The adjustable needles were designed around .030" diameter sewing needles that were epoxied inside their own threaded bodies. The carb adjustments will be done through the bottom of the carb bowl while o-rings seal the needles to the jets. In order to provide a consistent starting point for the four needle adjustments and to prevent damage to the seats, a slip-on Delrin collar limits the travel of the needle into the jet.

During construction, with the needle bodies fully threaded into the jets and tightened against the collars, the sewing needles were slipped through the needle bodies and seated in the jets before being epoxied in place. As such, these collars provide safe indicators of when the needles are fully seated. Marks engraved on the sides of the needle bodies will give visual indication of their settings with respect to their fully closed positions. Finally, the needles were match-numbered with their jets. - Terry


----------



## propclock

As usual , inspiring , and humbling  for us mere mortals.  Thanks for your work


----------



## mayhugh1

The throttle barrels were machined from 5/16" drill rod, and their bores inside the aluminum carb body were lapped with Timesaver for a smooth sliding fit. Grub screws in the carb body ride in grooves machined into the barrels and retain them inside the bores during rotation. The barrels' Venturis were machined from both sides using an 1/8" ball end mill and a tapered boring program running on myTormach.

The throttle arms were machined from 303 stainless. The clevises rotate on threaded studs Loctite'd in their ends. Instead of the push-pull throttle control in my original design, I simply extended one of the arms for a rotary control.

I'm currently gathering the materials (and knowledge) for a last minute decision to color anodize the carb bowl. If it turns out well and I get a reasonable color match to the red magneto housing, my next step will be to tackle an oil/fuel combination tank that I'll also anodize before I dispose of the chemicals. - Terry


----------



## dsage

Terry:
Just a word of caution on anodizing. I would be careful anodizing something that has already been sand blasted. Try a piece of sand blasted scrap first of the same alloy. (Which I have no doubt you'll do).
Also I've found if you want a good color match between pieces do them all together in the same batch. In my experience (lots of it) the chances of getting the colors exactly the same between two batches is difficult. There are a lot of variables to be juggled in anodizing and getting them exactly the same between batches is difficult unless you have a professional setup. (temp/time/acid strength/ current density/ color bath concentration and ph /dipping time/ sealing time and temp - to name a few).
Black being the exception. Black is usually black but it can go bad too. Some colors are very difficult - red being one of them.
I'd hate to see your wonderful and beautiful workmanship spoiled by an anodizing job gone bad. And it can go very bad for no apparent reason.

Caswell Plating has a lot of good information and reliable supplies.





						Caswell Inc
					






					www.caswellplating.com


----------



## mayhugh1

dsage said:


> Terry:
> Just a word of caution on anodizing. I would be careful anodizing something that has already been sand blasted. Try a piece of sand blasted scrap first of the same alloy. (Which I have no doubt you'll do).
> Also I've found if you want a good color match between pieces do them all together in the same batch. In my experience (lots of it) the chances of getting the colors exactly the same between two batches is difficult. There are a lot of variables to be juggled in anodizing and getting them exactly the same between batches is difficult unless you have a professional setup. (temp/time/acid strength/ current density/ color bath concentration and ph /dipping time/ sealing time and temp - to name a few).
> Black being the exception. Black is usually black but it can go bad too. Some colors are very difficult - red being one of them.
> I'd hate to see your wonderful and beautiful workmanship spoiled by an anodizing job gone bad. And it can go very bad for no apparent reason.
> 
> Caswell Plating has a lot of good information and reliable supplies.
> 
> 
> 
> 
> 
> Caswell Inc
> 
> 
> 
> 
> 
> 
> 
> www.caswellplating.com


Thanks for the advice Dave. I actually never bead blasted the bowl that I'm planning to anodize. It was polished, but not buffed to a high luster like the air horns were. Unfortunately, I had already Loctite'd the brass inlet/outlet tubes, and since I don't know how they'll affect the process, I just finished drilling them out. I'll likely do some test parts as you suggest, but if you have any other tips, I'd be glad to hear. So far, my knowledge comes from a couple Youtube videos. -  Terry


----------



## dsage

Sorry I was going by post 347 that shows the bowl (as well as the body). It looked blasted as well. Bad angle I guess. Anodizing covers NOTHING. So the starting finish must be as good as what you're looking to end with.
Good you drilled the brass out. It would have messed up the whole process and possibly dissolved the brass.
There are a lot of Youtube videos on anodizing. Some not so good.
As mentioned you might want to look through the Caswell information (reliable). They tout the LCD (low current density) process. i.e lower current longer time. They have a Forum on there somewhere.
There are too many tips to go over here. For sure use an adjustable constant current supply. Not a battery or battery charger. You need to be able to calculate and control the current. It's key to the process.
There is a formula for the time required to anodize vs the current and the thickness of desired anodized layer. A quick search found it here but there are likely better resources.





						How to calculate anodizing time for different load sizes
					

How to calculate anodizing time for different load sizes



					www.finishing.com
				



But it's well described on the Caswell Plating anodizing forum. Search for "720 rule".
I usually calculate current / time for 0.75mils of anodizing layer. Any less and it might not take the dye well. Up to 1mil is ok. Nothing to be gained (IMO) to go any more. More takes more time then you get into temperature problems with the bath. If the temp of the bath goes much above 80deg F the anodizing may be removed as fast as it is developed. Best to go low current longer time.
As mentioned do all the pieces in one setup if you're going for other than black.
By the looks of it you might need a pretty large tank to hang everything and to avoid the bath getting too hot. Knowing you, you can probably calculate the wattage (current voltage) on the tank and the temp rise and how much it can self cool. 
A few of other points.
Agitate the bath. Bubbles are produced that can stick to the parts and stop the current flow / anodizing. I use a plastic paint sturrer on an aluminum shaft driven by an electric screwdriver and hang that off to the side of the tank. Crude but it works. Some tanks have pumps and coolers.
Never hang anything but aluminum or titanium in the tank.
I use #11 dead soft aluminum wire to hang parts and I can usually find a threaded #6 or #8 hole in the part to force screw it into. It's soft enough ti does not damage the trhread. You can wrap the wire around the part but it will leave a non-anodized mark where it touches - and those types of connections usually always fail. Aluminum MIG wire seems to burn up before you're done. Wrong allow I guess.
There's no way to start over. The anodizing is very hard and can only be removed my lye or another caustic substance. Then you're in real trouble.

I'm sure you'll figure it out. But to be honest it can be risky on a perfect part.
Have you considered powder coating?? A lot less variables to manage.


----------



## mayhugh1

The carburetor was finished up by color anodizing its bowl to match the engine's red magneto. Since my total knowledge of DIY anodizing comes from a couple Youtube videos and Dave's comments above, I was prepared for the possibility that I might end up machining a whole new part. Basically, the home version of color anodizing aluminum involves electrolytically depositing a one mil thick layer of porous oxide on a well-cleaned part. After a brief soak in dye, the part's surfaces are sealed using boiling water.

The surfaces of the 6061 aluminum carburetor bowl were finished and cleaned before receiving a final three minute dip in sodium hydroxide (diluted solution of drain cleaner). This last cleaning step etched the part's surface to a frosty gray appearance - a fairly nice finish on its own. Similar to nickel plating, though, the anodized layer will be too thin to noticeably change the appearance of a part's surface. After a rinse in distilled water, the carb bowl was hung in a small plastic container filled with electrolyte.

A proper electrolyte is a 15% solution of sulphuric acid. Battery acid (30%) purchased from a local auto parts store was diluted with distilled water. Acid concentrations greater than 15% risk the oxide being dissolved as fast as it's being deposited, and so more isn't better.

The carb bowl, which will become the anode in the process, was connected to the positive terminal of a low voltage power supply. To create a cathode, thin sheets of lead were formed around the inside wall of the plastic container. A proper power source is one capable of constant current operation since the resistance of its load will change as the non-conductive oxide layer builds up around the part. I used what I had on hand, though, which was an unregulated variable voltage supply capable of several amps and voltages up to some 18 volts. I used an operating point of 2 amps which required about 12 driving volts. The voltage setting had to be tweaked after several minutes into the process in order to maintain the 2 amps. The 2 amp operating point came from a Youtube video demonstrating the anodizing of a part similar in size to my own. Two amps was also close to the value calculated using the '720 rule' recommended by Dave.

Some of the water in the electrolyte will be decomposed into its hydrogen and oxygen constituents during anodizing. Oxygen will collect around the positively charged part while hydrogen collects around the lead cathode. A rough visual check should show twice as many hydrogen bubbles compared with oxygen bubbles.

For a hanger, I initially used a piece of 3/32" titanium welding rod bent into a hook through one of the holes in the end of the bowl. After a few minutes, the anodizing current abruptly dropped to zero. I replaced the titanium hanger with a similar piece of (4043) aluminum rod but got the same result. I thought my 60 year old power supply was teetering on failure, but I eventually discovered the electrical connections between between the hangers and the part were failing due to oxide build up on the hangers. One of the two holes in the bowl happened to be threaded for a 6-32 hose barb. After running a die over the end of an eighth inch aluminum rod, it was screwed into the hole and used as a hanger with no further problems. Dave had warned about this very issue. Strangely, even though the hangers in the Youtube videos looked a lot less robust than either of my initial attempts, there was no mention of any difficulties with them.

About 60 minutes later the part was removed from the electrolyte, rinsed in distilled water, and immediately immersed in a jar containing the dye which had been warmed to 140F. I used 'scarlet red' Rit dye obtained from a local fabric shop, but dyes especially formulated for use with metal are also available. The color's darkness increases with the part's time in the dye, and after about two minutes it was close to the color of the magneto. After withdrawal, it was rinsed one last time and then dropped into a pan of boiling water for about 20 minutes. This closed the pores of the oxide and sealed the color into the part's surface.

I was concerned that the ends of the bowl might not anodize since they had no direct exposure to the cathode. That turned out to be a non-issue, and I was surprised to see that even the inside of the bowl came out as nice as the outside. - Terry


----------



## dsage

Phew !! (sp?)
Am I glad you had success. I was truly worried for your part. There are a lot of pitfalls in the process and I'm glad none caught you up too badly. I'm also glad the current disconnect was recoverable. Sometimes I purposly put a #4, 6 or 8-32 threaded hole in a hidden spot just for the purposes of anodizing.
I had no doubt that you'd research it and would have success. Good job.
The bowl looks beautiful.
I will add one thing. I've found the Rit dyes to fade over time especially if you put them in the sun. Shouldn't be a problem for you. I did a long term test by masking off half of a red anodized piece with black electrical tape and putting it in a window for (??) a long time. Strangely the commercial red dye I did the same test on actually got darker (much darker). I guess you only did the one piece. A good thing because I mentioned there could be a color difference between pieces done in separate batches. I figured this all out when I did several gauge rings for my friends off-shore race boat. They were red and turned out really nice. But he sold the boat a couple of years later so I never saw what happened to the color after sitting in the sun most of the time.
Great job.


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## ddmckee54

Now that is some outstanding bling!


----------



## mayhugh1

I found this item on Ebay. I've seen them come up before, but they're usually sold before I can post a URL. Evidently, a die cast manufacturer (GMP) started producing and selling these 1/6 replicas of the Offy 270 in 2002. Production continued through 2010 and although I've never seen one, there should be a lot of them around. It seems it was one of their first products, and they made lots more. These Offys probably don't have functioning internals, but their exteriors look very realistic. - Terry


----------



## Richard Hed

mayhugh1 said:


> I found this item on Ebay. I've seen them come up before, but they're usually sold before I can post a URL. Evidently, a die cast manufacturer (GMP) started producing and selling these 1/6 replicas of the Offy 270 in 2002. Production continued through 2010 and although I've never seen one, there should be a lot of them around. It seems it was one of their first products, and they made lots more. These Offys probably don't have functioning internals, but their exteriors look very realistic. - TerryView attachment 118472


How much is the bidding on it?


----------



## awake

Nope - it doesn't compare to what you are building!


----------



## mayhugh1

Richard Hed said:


> How much is the bidding on it?











						GMP Offenhauser Offy 255 CI Race Car Engine Motor With Stand 1 6 for sale online | eBay
					

Find many great new & used options and get the best deals for GMP Offenhauser Offy 255 CI Race Car Engine Motor With Stand 1 6 at the best online prices at eBay! Free shipping for many products!



					www.ebay.com
				




$329


----------



## Richard Hed

mayhugh1 said:


> GMP Offenhauser Offy 255 CI Race Car Engine Motor With Stand 1 6 for sale online | eBay
> 
> 
> Find many great new & used options and get the best deals for GMP Offenhauser Offy 255 CI Race Car Engine Motor With Stand 1 6 at the best online prices at eBay! Free shipping for many products!
> 
> 
> 
> www.ebay.com
> 
> 
> 
> 
> 
> $329


If this is FUNCTIONING I would thimk this is a good deal, but if not, then it's just a decoration or an anchor.


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## mayhugh1

Our 100+ degree days have been lasting well into the evenings during the past several weeks, and so I've been in our house working on a design for the Offy's fuel and oil tanks.

I so much wanted to do something novel with them and ended up wasting a lot of time on a faux bell housing and gear box in which I hoped to hide them. The fuel pump provides flexibility in placing the fuel tank, but it also takes up a lot of its own space. In the end, its size and form factor created so many problems that I finally gave up the idea.

The Solidworks renderings instead show what I finally ended up with. A plain combination tank was something of a disappointment especially after putting so many hours into the gear box. I added cosmetic detail to keep it interesting, but the accompanying extra machining time will increase my chances of spoiling the part along the way.

The tank's construction began with a 3-1/2" x 3-1/2" x 10" chunk of aluminum. After squaring up a workpiece, a pair of holes were drilled through its ends and then their exits plugged. Later, when the the interior of the tank is machined, these inside holes will be tapped for hose barbs and interconnecting hoses.

The plugs immediately created problems. Since I hope to anodize the tank, the plugs' alloy need to match that of the tank. They were turned for .001" slip fits inside the holes but, even with primer, neither Loctite 620 nor 680 would cure even after 24 hours and additional heat. I knew slip-fit aluminum inside aluminum is a problematic application for Loctite, but I'd hoped the primer would kick off the curing process. My eventual solution was to make threaded plugs and secure them with red thread locker. After installation, the plugs were hard pressed into the ends of the workpiece using a hydraulic press.

All four holes would have exited inside filleted edges in the ends of the tank where the zig-zag patterns of the threads would have been visible even after the pressing operations. After the plugs were installed, the filleting was redesigned to make the holes exit through flat areas.

Since I'm not an early morning person, the tank's machining will be done during the late nights of the next week or so when the outdoor temperatures are in the low 90's. - Terry


----------



## BaronJ

Hi Terry,

Both the Chinese and Japanese use a lot of superglue for that kind of application !  Have you tried it instead of Loctite ?

I've had issues with getting loctite to bond aluminum, Cyanoacrylate adhesive has worked for me !


----------



## mayhugh1

The first machining operations on the combo tank were on its complex underside where I was able to reuse some of the CAD/CAM developed for my Knucklehead's fuel pump enclosure. Even though the two inch long 3/8" diameter end mill used for the tanks' deep pocketing operations was pretty noisy, the surface finishes came out surprisingly nice. With daytime outside temperatures still hovering around 100F, the tank's 20+ hour machining time was spread over several late evenings.

After half an hour into the bottom side machining, I realized I'd mounted the workpiece upside down in the vise. This was a problem because of the previously cross-drilled holes. After being plugged they were no longer visible from the outside, and since my ambiguous Sharpie 'topside' label managed to confuse me, I had immediately gotten off to a bad start.

The purpose of the cross-drilled holes is to create internal passages that will eliminate the need for external hoses between the fuel tank and pump. After machining away the excess stock in the valley in between the tanks, I was able to plug three of the mis-drilled passages, but my modeling showed the fourth was going to wind up as a groove across the finished top surface of the oil tank. Since I was still in the early stages of the tank's machining, I was able to save the workpiece with some last minute design changes that reduced the tank's height.

I later ran into a problem with the limited computing resources in my ancient XP computer that I use to run my dozen year old CAM software. The tank's large and highly detailed top surfaces continually crashed the software during the tool path calculations. I eventually had to divide the model of the tank's top surfaces into several smaller pieces and keep track of the connections outside the CAM tool. This required even more design changes to the tank whose workpiece had already been roughed out.

The photos show some of the machining steps as the workpiece evolved into a finished tank. Still remaining is a bottom cover and a pair of filler caps. I've probably lost my opportunity to anodize the tank due to a poor late night decision to plug the mis-drilled holes with Loctite'd threaded steel fasteners. In any event, the tank's size would likely have been a stretch for my little home anodizing setup. Instead, I've located some gasoline resistant paint that appears to reasonably match the color of the magneto. - Terry


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## dsage

That's one heck of a nice piece of work Terry. I'm amazed at the finish. Almost looks like a stamped stainless item except for the thickness. Beautiful as usual.


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## propclock

Always amazed! could you detail how you went from the final cnc stage to the final polished stage. 
Is it just hard hand work?  I know you often bead blast . Possibly blast then polish?  
Thanks for all your posts.


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## mayhugh1

Propclock,
What you see in the photos is directly off the machine. No manual clean-up. It was, in fact, the reason for the long machining times and the inadequate computing resources in the computer that did the tool path calculations. I usually set the CAM up to leave no more than a .0003" scallop and sometimes leave it at its default setting of .00016" scallop. 

The bead blast step is usually just bead blasting. Sometimes there will be an issue with referencing the workpiece in multiple setups and I'll end up with a 'seam' that I'll need to manually fix. This is almost always caused by an error on my part. I just bead blasted this part a few hours ago, and it won't need any manual clean up. I was going to paint the tank but have since decided to leave its bead blasted surface as is. - Terry


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## propclock

Thank you.


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## ddmckee54

Terry:

Just out of idle curiosity, what was the machining time on the tank?


Don


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## mayhugh1

. . . 'a little over 20 hours' . . .


----------



## mayhugh1

After machining a bottom cover plate, the individual tanks were leak-checked. I don't yet have the proper size o-rings for the bottoms of the tanks, and so the o-ring grooves were temporarily filled with Viton cord. A machined slot across the cover's top surface between the two tanks will provide a drain for the motor and pump compartments in the event of a leak. After installing the components for the pump, the fuel tank was filled and the loop exercised for several minutes feeding the Offy's carburetor bowl. The engine control module constructed earlier was used to supply the pump's control voltage to hopefully avoid any surprises later.

After bead-blasting the tank I had second thoughts about all that red paint, but I didn't want to leave it's surface in bare metal either. Instead, I sprayed it with matte gray Gun-Kote. I've used this oven-cured paint on several other projects, and its gasoline resistance puts it on the short list of robust gas tank coatings. The filler caps were done similarly in matte black.

The engine's display stand was cut from a sheet of 1/4" hot rolled plate and painted with Rustoleum textured paint which nicely covers its beat-up surface. After a several day cure, it will become sufficiently resistant to gasoline. A functional radiator is still needed, but it will require a hole through its center for the starter shaft, and so I'm considering drill starting the engine from its rear. In the meantime, though, I plan to start work on the crankshaft. I thought I'd already ordered a chunk of Stressproof for it, but it's nowhere to be found. - Terry


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## minh-thanh

*mayhugh1 !*

You always do everything perfectly !


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## tornitore45

Love that tapping operation.


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## Scott_M

Hi Terry
Awesome as always !!!
Not sure if you knew that panel mount XT60 connectors are available. Or if your design would tolerate them, they do need a bit more room and require some possibly ugly screws. But wanted to make sure you knew about them. Here is an Amazon link, but they are available from any good RC dealer.
amazon.com/XT60E-M

Scott


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## mayhugh1

No, I wasn't aware of those Scott. Thanks! - Terry


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## Chiptosser

An other little bit of magic!    More art for the heart!


----------



## mayhugh1

I came up with 9.7 for the quarter scale Offy's stock compression ratio which agrees favorably with the 9.5 specified in the manual. I couldn't find a head gasket in the drawings and so one wasn't included in my calculation, but Ron has mentioned solving leaks using a gasket and sealant. The .020" Teflon head gasket that I plan to use will drop my c.r. to 8.7, but I've also decided to reduce the stroke from 1.094" to 1.000" to further reduce the compression ratio to 7.8.

Crankshaft construction began by band sawing a 9-1/2" length of 1-3/4" diameter Stressproof (from Speedy Metals) which was long enough for a pair of end spigots. The spigots were faced and center-drilled, and the entire workpiece o.d. was skimmed. After moving the workpiece to the mill, a pair of vertical reference flats were machined on its ends. The workpiece was then clamped vertically on the flats and, after carefully indicating the center hole, a pair of holes were center-drilled for the crank journal turning operations. The other end was similarly prepared.

It's important that the offset center-drills be identically placed on both ends of the workpiece. The axes of the crank journals must wind up parallel to the axis of the main journals to avoid binding the pistons in their bores. These were later verified to be parallel within a thousandth or so using a dial indicator with the workpiece mounted between centers in the lathe. If needed, the spigots were long enough to give another chance or two to get it right.

Since most of the crankshaft will be machined between centers, a drive dog similar to the one constructed during my Merlin's build was made to fit the faceplates on both my lathe and the fourth axis rotary on my Tormach. A pair of setscrews snugged against protective pads on the crankshaft's flats secure it to the drive, and the drive is secured to its faceplate while monitoring the workpiece TIR with a dial indicator.

The main journals were roughed out using the mill with the workpiece supported in a vise and manually indexed in 60 degree increments leaving a minimum of .038" stock for later finishing. After returning the workpiece to the lathe, the main journals were semi-finished to .525" diameter (finished diameter will be .512"), and the workpiece was skimmed once more. The resulting TIR of the main journals as well as the rest of the workpiece was essentially zero at this point. After being left undisturbed in the lathe for a day, however, the TIR of the journals (and much of the workpiece) had increased to some .002".

The warpage was disappointing. Not all 1144 alloys behave the same, and 'Stressproof' is manufactured to minimize warpage but evidently doesn't totally eliminate it. A single-piece multi-cylinder model engine crankshaft is one of the most difficult parts to accurately machine. For my own education, I decided to carefully track all the important TIR's through each of the remaining machining steps. Out of curiosity, I left the workpiece in the lathe undisturbed for 24 hours at two different orientations to see if gravity made a difference, but nothing changed.

The workpiece was then returned to the Tormach where the rod journals were hexagonally roughed similarly to the mains but this time using a four axis indexed setup. In addition to the tailstock, the center of the workpiece was stabilized with a fabricated support.

The workpiece was returned to the lathe where the TIR's of the main journals were re-measured. They had actually improved to .001" indicating that the workpiece had moved around some more. The rod journals were semi-finished in several steps to .550" (finished diameter will be .530"). The spaces left behind by the roughed-in rod journals were temporarily filled with close-fitting metal spacers during these turning operations to prevent bending moments during the cutting operations increasing the TIR of the journal being cut. Since a spacer can't be used with the journal being cut, some runout from a real-world cutter will be expected. I'm still working to see how small I can make this. - Terry


----------



## mayhugh1

The two lathe tools shown in one of the photos in my previous post were used to turn the crankshaft journals. Both of them use sharp carbide grooving inserts that were shop modified. The gold colored insert is .120" wide, and in order to reduce chatter its center was notched out. The outer sides of the insert and the insides of the notch were relieved with a diamond burr to allow shallow side-to-side turning. After relieving the insert, its holder had to be ground down to avoid rubbing on the workpiece. At 80 rpm, this tool was capable of turning the main journals to a predictable diameter with a smooth surface finish using a d.o.c. of .010" (dia). Unfortunately, the holder wasn't stiff enough to work as well on the rod journals which required more stick out.

The rod journals were turned using the black .204" wide insert. The stock insert already had relieved outer sides, and so relief had only to be added to the insides of the notch. This insert was also capable of acceptable surface finishes, but its huge contact patch even with the added notch combined with the flex in the system to make actual d.o.c.'s somewhat inconsistent. Turning all four journals to a common diameter was hit and miss, and when I had somehow managed to get all four journals to within a thousandth of .537" I stopped. The TIR's all wound up slightly less than a thousandth.

The rod journals were finished in .008" d.o.c. (dia) steps, and the TIR and diameter of each was checked after every pass. The technique that gave the best results was to start the turning operation in the center of the journal and then power feed to its leftmost side and stop. After reversing the feed direction, the cutter was power fed to the rightmost side. The feed direction was reversed again and the cutter once more power fed to the leftmost side. Because of space limitations, the journals could only be mic'd in their very center, and so it was important to not leave behind a narrow and difficult to detect ridge in the center of the journal. All operations were performed with the lathe in back gear and set to 80 rpm, and so the process was pretty time consuming. The journals were finally polished at 400 rpm using 600g paper.

Earlier, when roughed out on the mill, excess stock was also left on the webs on either side of the journals. This was removed next using a pair of repurposed boring bars. At this point, the offset turning operations were complete with (hopefully) no further need for the offset center-drills. The close-fitting rod journal spacers will remain in position until the crankshaft is completed. I didn't see any change in any of the TIR's that I continually measured during the rod journal turning operations.

The workpiece was re-installed in the lathe with the crankshaft's main axis between centers. With some care in positioning the drive dog and adjusting the tailstock pressure, I was able to get the main journal TIR's matched to the values measured before and after the rod journal turning operations. Even with the rod journal spacers in place, however, it was possible to more than double the runout with too much tailstock force. The excess web material left on either side of the main journals was removed next.

The workpiece was returned to the mill where the rear (ball) bearing and flywheel retaining surfaces were hexagonally roughed. It was then returned to the lathe so these areas could be semi-finished with a conventional turning tool. Again, all the TIR's remained consistent with those previously measured.

The workpiece was returned to the mill where the front (ball) bearing surface was roughed in. The Offy crankshaft has a skinny extended nose that will eventually receive a Loctite'd drive gear and a hardened nose for the starter clutch. This troublesome section will weaken the workpiece and likely create problems for the main journal finishing operations, and so this portion was left for later.

After returning to the lathe, the front (ball) bearing surface was semi-finished. At this point none of the TIR's had changed since that mysterious overnight movement after the initial main journal semi-finishing step. I began final finishing the main journals with the front (ball) bearing journal which went perfectly. However, after finishing the center journal, I found its TIR had ballooned to .004" - likely due to workpiece flex.

After grinding a razor sharp HSS tool and indicating it in the toolpost, I was able to scrape away most of the runout by manually rocking the spindle back and forth over the journal's high spot. With no way of putting material back though, I ended up with a .005" undersized journal. The results were essentially the same with the other two journals even with the HSS tool.

I roughed in the two ends of the crankshaft so it could be trial fitted in the crankcase lower half without the front and rear ball bearings. The fit wasn't as sloppy as I expected, probably because the three TIRs aren't lined up with respect to one another. In any event it will become worse as the engine is run and the bronze bearings become 'wallowed' out.

I decided to scrap the part and start over. I rechecked the snugness of the rod journal spacers, and even though they felt correct, I can't help but think they were at least part of the problem. Since I'm now reasonably confident with the stability of the material, on my next attempt I'll likely finish the main journals before even roughing in the rod journals. - Terry


----------



## thefishhunter

Beautiful work as always. Round two should come out perfect.

I do have a question about your last post. What is the reason for the reduction In the compression ratio from the plans?


----------



## mayhugh1

thefishhunter said:


> Beautiful work as always. Round two should come out perfect.
> 
> I do have a question about your last post. What is the reason for the reduction In the compression ratio from the plans?



Thanks,
Reducing the compression ratio will reduce the combustion pressures and take some of the stress off the head gasket. This engine has some history with head gasket issues, and since I'm not building one to run on a dynamometer I thought I'd take some easy steps to make life a little easier later.


----------



## dsage

Hi Terry:
What's your reasoning behind roughing out the journals on the mill rather than avoiding all the back and forth and just taking it easy and turning them fully on the lathe? I can understand the time saving but it seems the careful re-measurement of TIR upon each return to the lathe would be time consuming also. No?
Just wondering. I never thought to do it that way.


----------



## mayhugh1

Dave,
The reason for roughing them out on the mill is that on the lathe I'd have to use the same deep grooving tool for roughing the narrow space between the webs. With just the .010" d.o.c. that I seem to be able make on steel with these tools on my lathe, it would not only take a long time but be pretty stressful. - Terry


----------



## dsage

Makes sense. and (as usual) a very smart idea. I'll give it try
Thanks


----------



## wthomas

Hi Terry:
    Excellent work.  From my experience on full scale cranks I would recommend you leave .005" to .010" on all the main and pin
diameters till after you have finished the sides of the pins and mains.  Also I would indicate the side movement of the cheek
closes to the tailstock when you you tighten the tailstock.  You could put enough pressure on the tailstock to make it move only
.001" then back the tailstock off and bring it back up to almost the same place with no bending pressure on the crank.
     Another thing to consider is to rough mill the pins and sides close to round or round in the mill where you have less pressure on the rest
 of the crank and then do the same for the mains.  The less stock you have to remove between centers the less stress you are putting on the 
pin and mains.  This is the way I have found to have the least problems because you have less unbalanced weight stressing the centers.
                Keep up the good work I really enjoy the photos and information.


----------



## mayhugh1

wthomas said:


> Hi Terry:
> Excellent work.  From my experience on full scale cranks I would recommend you leave .005" to .010" on all the main and pin
> diameters till after you have finished the sides of the pins and mains.  Also I would indicate the side movement of the cheek
> closes to the tailstock when you you tighten the tailstock.  You could put enough pressure on the tailstock to make it move only
> .001" then back the tailstock off and bring it back up to almost the same place with no bending pressure on the crank.
> Another thing to consider is to rough mill the pins and sides close to round or round in the mill where you have less pressure on the rest
> of the crank and then do the same for the mains.  The less stock you have to remove between centers the less stress you are putting on the
> pin and mains.  This is the way I have found to have the least problems because you have less unbalanced weight stressing the centers.
> Keep up the good work I really enjoy the photos and information.


All great suggestions. Thanks a lot. I'm incorporating them in a new work flow while waiting on more material to arrive. I wish I'd planned for two, but I hate paying those shipping costs. - Terry


----------



## propclock

Just my opinion, My friend Dwight Giles  reminds me when he makes his V8 cranks
they are rubber, and can be bent back into shape. A soft hammer can fix a lot of 
the stress induced warping. Also he tends to over correct and wait a day, yep it grows back. 
So in short, wack it ,or press it, don't cut it.  Also another member of our club says,
This is why I built my tool post grinder. He grinds all of his cranks. 
I truly appreciate all of you work and the sharing of your experiences. 
Thank You.


----------



## petertha

propclock said:


> This is why I built my tool post grinder. He grinds all of his cranks.



Propclock, not to detract from the thread, but I would really like to see how you arranged your TPG in a lathe environment with supporting tailstock. I have a Themac TPG that I use occasionally. It works well enough for cantilevered work extending from the jaw. I used it to grind cylinder liners that way for my 5-cyl radial. But as soon as I bring the tail stock into the equation, it wants to occupy the same real estate as the TPG even with the TS quill fully extended. I would probably have to run a 6" wheel to get TPG spindle to clear the (adjacent) TS. And then I'm running out of cross slide travel as it extends towards operator.

I've even set the TPG on the back side of work, mounted to a baseplate on my cross slide. That has some advantages. It eliminates some of the vertical stack-up associated with TPG on compound (less vibration from multiple sliding surfaces). Allows bigger wheels in theory, although I think my TPG is kind of orientated to max 3-4" based on pulley selection & fixed motor rpm. But doesn't solve the lateral conflict issue of TPG spindle & tailstock. Maybe a function on my lathe's apron casting footprint or tail stock size... but its generically a common 14x40 lathe.

I'll stop here & gladly start a new post on this subject because on the surface it seems like grinding is a great way to sneak up on a critical dimension like journal surfaces. I can post some pics that better show what I'm trying to describe with words.


----------



## mayhugh1

Propclock,
Thanks for the comments. In this particular case though, the TIR's result from the journals being oval and so bending the crankshaft won't help. The oval'ness's came from system flex during turning and was probably mostly caused by inadequate support between the rod journal cheeks while the main journals were being finished.

Petertha,
I feel your pain. I recently purchased a Themac J45 tool post grinder through ebay and ran into exactly the same problem. Mine required wheels with 1/2" center holes, but I couldn't find grinding wheels for it that would fit between the cheeks of my 3/8" wide journals. I then found a spindle adapter for 1/4" center hole wheels, but then the only wheels I could find with enough diameter to clear the adapter were Cratex-type resin bonded wheels. I wasn't sure these were suitable for what I wanted to do but I decided to give it a try anyway. I ran into the same interference with the tailstock. There was just no way to use it with a tailstock.

I also have an old Dumore TPG that I acquired through a local estate sale 15 years ago, It's 1/3 hp and doesn't have enough power for anything much larger than the mounted stones you would normally use in Dremel. It has even greater problems with the tailstock. I probably now have some $1k invested in tool post grinders, parts, and wheels for them and still haven't been able to do anything real with them. - Terry


----------



## ICEpeter

mayhugh1 said:


> Propclock,
> Thanks for the comments. In this particular case though, the TIR's result from the journals being oval and so bending the crankshaft won't help. The oval'ness's came from system flex during turning and was probably mostly caused by inadequate support between the rod journal cheeks while the main journals were being finished.
> 
> Petertha,
> I feel your pain. I recently purchased a Themac J45 tool post grinder through ebay and ran into exactly the same problem. Mine required wheels with 1/2" center holes, but I couldn't find grinding wheels for it that would fit between the cheeks of my 3/8" wide journals. I then found a spindle adapter for 1/4" center hole wheels, but then the only wheels I could find with enough diameter to clear the adapter were Cratex-type resin bonded wheels. I wasn't sure these were suitable for what I wanted to do but I decided to give it a try anyway. I ran into the same interference with the tailstock. There was just no way to use it with a tailstock.
> 
> I also have an old Dumore TPG that I acquired through a local estate sale 15 years ago, It's 1/3 hp and doesn't have enough power for anything much larger than the mounted stones you would normally use in Dremel. It has even greater problems with the tailstock. I probably now have some $1k invested in tool post grinders, parts, and wheels for them and still haven't been able to do anything real with them. - Terry



Hello, 
When I decided to grind the crankshaft for the two engines I was building, I run into the same problem regarding the reach of the grinding wheel into the journals with conventional aluminum oxide grinding wheels. 
Consequently, I decided to use two dia.six inch CBN wheels with different particle concentration to rough out and final grind the journals for diameter and side clearance. The resulting tolerances and clearances came out very well. The unfortunate result was that my bank account took a serious hit, although I kind a expected that.
I posted quite a while ago some pictures on HMEM that showed the set up with the CBN wheels and my cam / crank grinder.

Peter J.


----------



## petertha

I seem to recall your post ICEpeter. If you could locate your link or find your pics I would certainly appreciate seeing them.

I created a new post on toolpost grinding. I'll leave it to you guys if you want to carry on discussion there or not. I'm starting to share Terry's sentiment. I had much bigger plans for the TPG compared to what I've been actually able to accomplish thus far. But that could also be lack of experience or good ideas on my part.





						Toolpost (or other) grinding in the lathe
					

I thought it might be beneficial to share information & experiences on this subject because it seems to come up often. The typical reason behind grinding in general is to achieve a high degree of accuracy as well as surface finish. Personally, I am interested in what you have achieved with...




					www.homemodelenginemachinist.com


----------



## Foketry

mayhugh1 said:


> Propclock,
> Thanks for the comments. In this particular case though, the TIR's result from the journals being oval and so bending the crankshaft won't help. The oval'ness's came from system flex during turning and was probably mostly caused by inadequate support between the rod journal cheeks while the main journals were being finished.
> 
> Petertha,
> I feel your pain. I recently purchased a Themac J45 tool post grinder through ebay and ran into exactly the same problem. Mine required wheels with 1/2" center holes, but I couldn't find grinding wheels for it that would fit between the cheeks of my 3/8" wide journals. I then found a spindle adapter for 1/4" center hole wheels, but then the only wheels I could find with enough diameter to clear the adapter were Cratex-type resin bonded wheels. I wasn't sure these were suitable for what I wanted to do but I decided to give it a try anyway. I ran into the same interference with the tailstock. There was just no way to use it with a tailstock.
> 
> I also have an old Dumore TPG that I acquired through a local estate sale 15 years ago, It's 1/3 hp and doesn't have enough power for anything much larger than the mounted stones you would normally use in Dremel. It has even greater problems with the tailstock. I probably now have some $1k invested in tool post grinders, parts, and wheels for them and still haven't been able to do anything real with them. - Terry



I had the same tailstock interference problem, i solved it through these diamond grinding wheels.
Their are available with diameters from 80 to 150 mm and thicknesses from 10 to 20 mm, the body is aluminum and the internal hole can be reduced or enlarged.
Their removal capacity is higher than normal grinding wheels.


----------



## wthomas

Hi Terry:
     I forgot to tell you if you mount the end of the crank in a four jaw chuck and work between it and a steady rest in the middle of the crank 
you will have a much stronger setup to machine the mains.  You may not be able to do this with the steady rest on the middle main for lack
of space but if you go to the next main and run it in a steady rest with a piece of heavy leather belting as well as the tailstock you should
have lots of support.  If you use an offset hole in a support sleeve on another crank pin in the steady rest  you can machine the pins this way.
The closer to the supported (chucked end) of the crank the stronger the setup and less flexing.  Just think how much stronger your straight
pins are compared to the offset split pins that Buick run on the even fired V6.  The crank blank was 7" in diameter and 24"s long.  When they
turned the ends and added throw blocks they had a WHOLE LOT of unbalanced weight swinging in the lathe between centers.  It would
have been better to do like you are and to mill most of the unbalanced weight off. 
    Also if you are unable to grind the pins and mains consider using a narrow flat belt sander st finish them.
Keep looking and you will find a solution!
                                                 Bill Thomas


----------



## johwen

Hi Guys,
Faced with machining a crank for a 4cylinder Sealion engine I decides to build my own crankshaft grinder from the plans published in Strictly I C mag. I machined up the crankshaft in the normal way after Centre drilling the ends of the material to accommodate the centres of the mains and crank pins. I turned all journals leaving the  .005 oversize. Mounting the shaft in the grinder then it was easy to grind mains all in line and the crankpins all to size. The grinder was relatively easy to make and it's sitting there waiting for the next crank. Making the grinder was a good exercise in engineering practice. Cheers. John


----------



## G54AUST

johwen said:


> Hi Guys,
> Faced with machining a crank for a 4cylinder Sealion engine I decides to build my own crankshaft grinder from the plans published in Strictly I C mag. I machined up the crankshaft in the normal way after Centre drilling the ends of the material to accommodate the centres of the mains and crank pins. I turned all journals leaving the  .005 oversize. Mounting the shaft in the grinder then it was easy to grind mains all in line and the crankpins all to size. The grinder was relatively easy to make and it's sitting there waiting for the next crank. Making the grinder was a good exercise in engineering practice. Cheers. John


 'Afternoon John.

     The SIC plans are from issues 63,  64 and 65 ???


Regards,

Trevor,
Melbourne,  AU


----------



## ICEpeter

petertha said:


> I seem to recall your post ICEpeter. If you could locate your link or find your pics I would certainly appreciate seeing them.
> 
> I created a new post on toolpost grinding. I'll leave it to you guys if you want to carry on discussion there or not. I'm starting to share Terry's sentiment. I had much bigger plans for the TPG compared to what I've been actually able to accomplish thus far. But that could also be lack of experience or good ideas on my part.
> 
> 
> 
> 
> 
> Toolpost (or other) grinding in the lathe
> 
> 
> I thought it might be beneficial to share information & experiences on this subject because it seems to come up often. The typical reason behind grinding in general is to achieve a high degree of accuracy as well as surface finish. Personally, I am interested in what you have achieved with...
> 
> 
> 
> 
> www.homemodelenginemachinist.com





petertha said:


> I seem to recall your post ICEpeter. If you could locate your link or find your pics I would certainly appreciate seeing them.
> 
> I created a new post on toolpost grinding. I'll leave it to you guys if you want to carry on discussion there or not. I'm starting to share Terry's sentiment. I had much bigger plans for the TPG compared to what I've been actually able to accomplish thus far. But that could also be lack of experience or good ideas on my part.
> 
> 
> 
> 
> 
> Toolpost (or other) grinding in the lathe
> 
> 
> I thought it might be beneficial to share information & experiences on this subject because it seems to come up often. The typical reason behind grinding in general is to achieve a high degree of accuracy as well as surface finish. Personally, I am interested in what you have achieved with...
> 
> 
> 
> 
> www.homemodelenginemachinist.com



Hello Petertha,
I sold the cam / crank grinder a while ago and the link to it is SOLD - For sale Camshaft - Crankshaft grinder / accessories
When using the grinder, I had the CBN wheels custom made with a specific width and with corner radius for the crank journals. I picked CBN for the wheels because, supposedly, diamond wheels don't like the carbon in steel and CBN wheels permit dry grinding without coolant.
To see other info about the grinder and other stuff, you could take a look at my list of posts. They give you quite an overview of posts I contributed at HMEM.

Peter J.


----------



## petertha

ICEpeter said:


> Hello Petertha, I sold the cam / crank grinder a while ago and the link to it is SOLD - For sale Camshaft - Crankshaft grinder / accessories
> Peter J.



Ah yes, that's the grinder I recall. Work of art! 
What kind motor did you use? (it has the look of a Sherline?).


----------



## ICEpeter

petertha said:


> Ah yes, that's the grinder I recall. Work of art!
> What kind motor did you use? (it has the look of a Sherline?).



Petertha,
You have good eyes. Yes, it is a Sherline variable speed motor system (as used for their lathe drives) and a Sherline industrial spindle that I used when building the tool post grinder for use in the cam / crank grinder.


----------



## mayhugh1

Even though I decided to scrap the first crankshaft, I finished it up so I'd have a test bed for the remaining setups and operations. I also wanted to be sure there weren't any surprises waiting for me inside the crankcase or with the starter assembly before getting getting too far along with the second one.

Without grinding capability, the Offy's eight inch long crankshaft with its eight half-inch journals is a difficult part to accurately machine. In comparison, the Merlin's crankshaft with its three-quarter inch journals was considerably more rigid and much less troublesome. Even with rod journal packing, .006" deflections could be demonstrated with only modest finger pressure on the center of the Offy's crank. A drawing shows the deflections measured in four different directions with finger pressure on one of the center rod journals with the other three packed. A journal that must be unpacked for machining appeared to be responsible about half of the worst-case deflection. I was able to reduce the .006" deflection shown in the drawing by about half by packing the main journals as well. Even with carefully shimmed packings, tailstock pressure adds its own deflection by distorting the long flimsy workpiece.

The deflections make it difficult to turn a truly round journal to a precise diameter using what is essentially has to be parting tool. They also affect the centerlines of the rod journals' axes and, potentially, their alignment with the main axis. The exact locations of the rod journals' axes isn't a major issue, but they need to be parallel to the main axis to prevent the pistons from binding in their bores.

After semi-roughing a pair of rod journals, I was satisfied with their measured .001" TIR. I continued on and performed the same operations in different setups on the other journals but then discovered the TIR of the first pair had increased to some .010". The subsequent machining operations had apparently changed the workpiece and its reaction to the tailstock. In order to turn the rod journals to their finished diameters, the finishing operation had also to move their axes some .005" in the presence of a .003" workpiece deflection.

Maintaining a consistent tailstock pressure between setups (and throughout an operation in a given setup) can be tricky since the way the workpiece reacts to tailstock pressure changes as material is removed from it. For example, after finishing all the journals, I needed to remove excess material from the nose of the crankshaft so I could trial fit the crankshaft inside the crankcase. This involved turning down a one inch long length to just under a half inch in diameter which I knew would weaken the workpiece and allow it to distort. I watched runout developing in the main journals as more and material was removed from the nose. When finished, the nose ran true, but the TIR of the main journals were now at .005".

Along the way I discovered that centrifugal force on the packed but unbalanced workpiece created an additional deflection. To get around this and its accompanying surface finish problems, the maximum spindle speed was limited to 50 rpm. Some of the final .001" passes on the second crankshaft were actually performed while rotating the spindle by hand.

One of the photos shows the new grooving tool purchased for all journal operations on the second crank. Its style is identical to the one used to machine the first crank's rod journals (as well as the Merlin's), but its narrower .155" width allows it to fit in the narrow space between the cheeks of the Offy's main journals. It was also bifurcated and lapped on a diamond plate until its cutting edge was keen enough to take a consistent .001" depth of cut on a steel test rod. The corners of its chip breaker also had to be lapped flat to reduce the cutter's tendency to dig in during side-to-side cutting. In use, the depth of cut was limited to a maximum .005" (diameter), and the cutting edge was touched up and re-indicated for each journal.

The new workpiece was prepared identically to the first one including the end spigots, reference flats and center-drills. The journals on the main axis were again roughed out on the mill while the workpiece was supported in the vise. Ten-sided polygons instead of six were used this time in order to reduce the trauma to the workpiece during the interrupted cuts. This time I also roughed-in the surfaces for the front and rear ball bearings at the same time.

The workpiece was set up on centers in the lathe and its o.d. immediately skimmed. Left overnight, its TIR creeped up from essentially zero to .0015". All five bearing surfaces on the main axis were then semi-finished to within .030" of their final values using the new tool, and the cheeks were faced to their finished values. The measured TIRs were essentially zero.

The workpiece was returned to the mill where the rod journals were roughed in. After completion, the workpiece was temporarily re-installed in the lathe where I noticed the main journal TIR's had increased by a couple more thousandths. The rod journals were then semi-finished, and their cheeks faced to their final thickness.

On the following day the TIRs were rechecked. The main journals now measured between .005" and .007". The #2 and #3 rod journals were at some .012", and the #1 and #4 rod journals measured .009". All journals were still round to within less than a thousandth and so the entire TIR increase was attributed to workpiece distortion in response to its previous machining.

I allowed the workpiece rest for a couple days in hope that it might self-heal but no joy. The workpiece was moved back to the mill where the final cheek profiles were machined. When the journal TIRs were later remeasured, there didn't appear to be any further changes.

I should add that rod journal TIR's aren't obvious unless they're measured with a dial indicator. Runout created by a journal that's out of round by only a few thousandths will be irritatingly visible to the naked eye, but 10X that amount due to a displaced rod journal axis won't even be noticed. If one could be sure this displacement doesn't also include a skewed axis, its only effect would be just a degree or so change in valve timing and not worth worrying about. - Terry


----------



## gbritnell

Hi Terry,
The only way I could come close to having an accurate crank (.002 overall) was to rough mill the main journals then turn them on the lathe leaving .010-.015 stock for final finishing. Go back to the mill and rough cut the rod journals taking the webs to almost finished width. Remount the crank in my offset blocks and turn the throws to finish size and like you said at a very low rpm. With the throws turned I would rechuck the crank between centers and finish turn the mains. I have had tolerances between .0007 and .002 depending on the size of the crank and journals. I wasn't so much concerned with the total accuracy of the throws, square and parallelism as I was with the mains. I would clamp portions of the crank with hose clamps to try and stiffen the cranks while cutting. At best it's a tenuous job getting a truly accurate crankshaft. 
As a side note I have even had my finished cranks really close and after weeks of sitting around they would then measure off from the original readings. Stress relief, temperature changes, who knows. 
gbritnell


----------



## petertha

You guys are scaring me. I was thinking my next project might be an inline. Would cast iron offer any lower stress relief deflections over SP once machined? Or are there more overriding 'con' issues relating to CI for crankshafts in applications like this?


----------



## gbritnell

I'm not saying that cast iron wouldn't work but I have used stressproof since  I found it worked so well compared to common cold rolled steel. It's not that you can't get very good accuracies it's just that you have to be patient. When I built my 302 V-8 engine I finish ground the crank. I had made a toolpost grinder and I knew a fellow that had a grinding shop so he took a couple of thin (.250 as I remember) grinding wheels and cut the diameter down for me. The grinding was the way to go as it doesn't put much load on the metal like using a bifurcated cut-off tool.


----------



## mayhugh1

Petertha,
I suspect cast iron would warp even more although it would be easier to take finer cuts. Cutting out offset rod journals is a pretty traumatic operation, and even Stressproof reacts badly. One thing that would help would be to make the journal diameters as large as possible - three quarters of an inch would be a lot better than a half inch.

It's logical to machine the crankshaft before machining the crankcase since it will be easier to fit bearings to the crankshaft journals rather than the other way around. Although I realized this when I started the build, I knew from my Merlin experience how hard it was going to be, and so I procrastinated as long as I could.  Like George says, 'you just have to be patient.' - Terry


----------



## mayhugh1

The next step was to turn a ten degree taper and a 3/8-24 thread on the rear of the crankshaft to secure the flywheel. I used a left-hand thread so I'll have the option of drill-starting the engine from its rear. After roughing away most of the spigot and before turning the taper, I was able to nearly zero-out the rear bearing TIR in the setup at the tailstock using a set-true chuck. Finally, the remaining spigot stub was parted off and the rear end center-drilled for contingency.

Attention was then focused on the front of the crankshaft. Its long skinny nose will receive a Loctite'd pinion gear and a hardened sleeve that will engage the starter's sprag clutch. The crankshaft was set up in the lathe with its rear end in a collet chuck and its front-end spigot supported by the tailstock. Taking advantage of the chuck's .0015" runout, I rotated the workpiece in the collet until a location was found that essentially cancelled the TIR of the front ball bearing surface. This allowed me to turn the 1-1/2" long nose to a .281" diameter concentric with the front bearing. After parting away the remaining spigot, the front end was center-drilled and the nose polished for a close sliding fit to the already machined pinion drive gear.

The crankshaft drawing called for a pair of bosses to be integrally machined with the outside cheeks on each end of the the crankshaft to locate it to the crankcase. To simplify the machining a tiny bit, I instead custom ground a separate pair of spacers.

The bronze crankcase bearings were originally bored to .5145" to provide what I felt would be an optimum clearance to a length of .513" drill rod used to verify the bore alignment. With a little oil, the rod was snug but turned uniformly without binding. One of the crankshaft's three main journals ended up out-of-round by a thousandth, and since the crankshaft's TIR measured one to two thousandths depending upon the time of day, the main journals were polished down to .511" to eliminate any chance of binding. With the crankshaft installed, the TIR measured at any of the three main journals was between one and two thousandths and outside the front and rear ball bearings it was less than a thousandth.

The starter sleeve was machined from drill rod and hardened before being Loctite'd to the crankshaft. Since it must carry the engine's full starting torque as well as survive kick-backs, a best possible cure is mandatory. It's important to polish away any oxides remaining in the bore after heat treatment since they will interfere with Loctite's cure. A .002" sliding fit to the crankshaft was close to optimum for Loctite 680.

Before permanently attaching the pinion gear and starter sleeve, the crankshaft was assembled several times with the front cover inside the crankcase halves in order to make sure it's fit was consistent. The final step will be to drill interconnecting oil passages between the rod journals and the main journals. These risky operations will require a proper fixture in order to perform them safely. - Terry


----------



## mayhugh1

The crankshaft's final machining step was to drill the interconnecting oil passages between the main and rod journals. There isn't a lot of safety stock around the drill path, whose angle is a steep 30 degrees. In order to be able to use a reasonably stout bifurcated parting tool to turn the journals, I increased their widths from .375" to .410" by decreasing the thicknesses of the cheeks. This further reduced my working margins for this drilling step and made the accuracy of the angle even more important.

Care was taken to avoid breaking through the inside corner of a cheek or even worse sticking a broken .063" drill. Ron mentioned that this had happened to him when a drill grabbed the edge of its exit hole. Not wanting to spoil a second crankshaft, I spent a few days on a custom drilling fixture.

The initial drilling procedure involved creating a flat area for the drill's entry on the rod journal using a 3/32" end mill. This was followed by a 1/16" v-cutter to spot the hole. The hole was then peck drilled every .050" using a new 134 degree drill that was totally withdrawn after each peck. Compressed air kept the drill free of chips. The entry point for each hole was selected so its exit from the main journal would be in its center directly over the oil groove in the bearing.

The first drilled hole wound up at 27 degrees causing its exit to miss the center of its main journal and the oil groove by .060". After verifying the CAD work and drilling fixture, I began playing with the drilling procedure on the scrapped crankshaft. The same procedure on the same journal of the scrapped crank produced exactly the same result.

After some experimenting, I eventually had a process that drilled the remaining three holes where they belonged. The primary change was using the v-cutter to drill the first 1/8" of the hole rather than just spotting it. I also changed to a 118 degree drill for the first half of the hole's depth and then finished with a 134 degree drill. In separate testing, the 134 degree drill seemed to drill more easily through Stressproof and produce smaller chips that easily cleared a deep hole. Its broader nose, however, didn't seem to like an unsupported angled starting surface even when spotted.

The real test of the drilling process were the oil passages in the #2 and #3 rod journals that shared a common exit hole in the #2 main bearing. The earlier mis-drilled exit hole in the #3 main journal was repaired with a short milled slot which will connect it with the bearing's oil groove. The crankshaft was then moved to the lathe where the journals received their final polishing with 1200g paper. - Terry


----------



## michelko

You are an artist. Awesome work. Thanks for showing


----------



## mayhugh1

The Offy's flywheel was machined from a chunk of 2-3/4" diameter 316 stainless. Compared with the crankshaft machining, the flywheel wasn't much of a challenge. With both ends containing features that need to be concentric, a 4-jaw chuck was used for all the turning operations.

A ten degree internal taper locates the flywheel to a matching o.d. taper on the rear of the crankshaft, and a 3/8-24 left hand nut binds the two together. In order to insure matching angles on both tapers, they were CNC turned on my little Wabeco lathe. I was pretty disappointed when the flywheel wobbled so badly on the crankshaft that was running true. The amount of wobble was different each time the flywheel was mounted and sometimes was as bad as ten thousandths.

Bluing and wringing the parts together was inconclusive, but a tiny bit of 1200g grinding grease brought up a contact pattern showing the two angles didn't quite match. After some head scratching, I remembered the two tapers had been turned using different tools and their contact points may not have been handled properly. Lapping the flywheel to the crankshaft with 600g grease eventually reduced the wobble to a consistent .0015".

Since ten degrees is too steep for a self-locking taper in steel, I wasn't expecting the flywheel to need a puller. After lapping, the flywheel tended to stick tight to the shaft, and when the engine is fully assembled it will be awkward to remove. A pair of 8-32 threaded holes was added on either side of the taper for pulling screws that can also be used to grip the flywheel while wrenching the nut. The nut was machined from drill rod and hardened, and a backup washer (engraved with a warning about the nut's handedness) was machined from a bit of Stressproof.

Ron added tick marks around the entire perimeter as a timing aid to match those on the full-size flywheel. I used my mill's fourth axis to engrave 72 five degree marks around the flywheel's circumference. For this operation a mandrel was turned using the same tool and taper program originally used on the crankshaft. The wobble of the flywheel mounted on the mandrel was under two thousandths indicating that the error before lapping had been the flywheel's taper.

A timing pointer bolted to the rear cover wrapped up the work on the flywheel. When the flywheel is mounted at final assembly, the tick closest to TDC will be colored in with paint. For now, the machining of the rods, pistons, and rings are all that remain. - Terry


----------



## propclock

Left Hand thread? Usually a flywheel going CCW has a right hand thread?
Perhaps I am wrong. 
As always, thanks for you informative posts.


----------



## mayhugh1

propclock said:


> Left Hand thread? Usually a flywheel going CCW has a right hand thread?
> Perhaps I am wrong.
> As always, thanks for you informative posts.


Don't forget this flywheel is at the rear, and so if the engine is started from the rear the nut will have to be cranked counterclockwise. - Terry


----------



## ozzie46

Starting from rear counterclockwise means engine turns clockwise looking from front,no?

Ron


----------



## propclock

I was confused because I marveled at the beautiful starter splines on the front of the crank.
I use 1 way sprag/Torrington  bearings for starters on most of my models. Thanks.


----------



## mayhugh1

ozzie46 said:


> Starting from rear counterclockwise means engine turns clockwise looking from front,no?
> 
> Ron


Correct


----------



## mayhugh1

propclock said:


> I was confused because I marveled at the beautiful starter splines on the front of the crank.
> I use 1 way sprag/Torrington  bearings for starters on most of my models. Thanks.


That spline-looking thing on the front is actually a spur pinion that drives the oil and water pumps and the camshafts. The smooth portion at the very front of the crankshaft is a hardened sleeve that's one-half of a sprag clutch that is built into the front of the engine for starting.  If the front-start system is used, the radiator (if located at  the front of the engine) will need a hole through its core to pass the drill starter. I'm not yet sure I want to do this, and so I put the LH nut on the rear flywheel so I could rear start it with a drill. If I end up doing this, I'll make up drill starter with its own built-in clutch. Thanks for the comment. - Terry


----------



## propclock

Thanks again. I really appreciate all you do for this site/hobby/ obsession.
The tale of 2 cranks was very enlightening. 
 Or depressing , if it is your own bent crank. 
I have the v8 version of the bent one.


----------



## elliot9797

Where do I buy these plans, or the book that you Young Gentleman are using?
Thank you
Elliot


----------



## mayhugh1

See this thread:





						Looking for Ron colonna offy plans
					

I have a copy of the book that I do not need-sell for $40 plus postage. Condition is like new. I am in USA.  Bob  How much for postage to the UK




					www.homemodelenginemachinist.com
				




Ron Colonna designed this engine and sold the plans as a book and more recently on a USB thumb drive. He still might be willing to sell you a copy. - Terry


----------



## elliot9797

Thank you- I sent him funds through PayPal this morning. Hope that they are kind enough to get me a copy. I am 29 years old, and just starting my model engine experience.

thanks again
Elliot


----------



## mayhugh1

The connecting rods were machined from 7075 aluminum. The big ends will be fitted with bronze sleeve bearings, but hardened steel wrist pins will turn directly in the aluminum on the small ends. An oil passage through each rod will connect the two. One of the earliest operations in the workflow, and perhaps most important, was machining the big and small end bores parallel with each other.

Machining began by laying out three workpieces containing two rod/cap pairs each. Each workpiece was made up of a pair of aluminum blocks held together with seven SHCS's. Four of these screws were threaded deep inside the workpiece and held together what would eventually become the rod/cap pairs. These screws will be later replaced by the actual cap screws. The other three screws kept the workpiece halves together while the finished parts were machined free from it.

The rods were laid out along the grain of the metal with the rod/cap seams aligned with the seam between the workpiece halves. The rod machining was done through both sides of the workpiece. A unique pair of letters engraved on the faces of each rod/cap pair will insure no mixups later on. After completing the first side, a Devcon quick-set epoxy was used to retain the parts in their workpiece while they were machined free through the other side. For good measure some reinforcing strips were also added. Heat was used to finally release the finished parts.

Additional material added inside the workpiece to the rears of the caps protected the temporary cap screws from the cutting tools. This extra material will be removed in a later operation with the parts free of their workpieces.

For convenience during machining, the half inch thick workpieces were supported on parallels in a vise. Since the span between the parallels might allow cutting induced vibrations in the thin workpieces to affect the surface finishes, a temporary steel dampener was bolted to the underside of each workpiece during machining. - Terry


----------



## mfrick

gbritnell said:


> Terry,
> While I agree that there is a certain amount of thermosyphoning of the water and therefore while running an engine the radiator does tend to heat up (model T cooling system) the introduction of a pump should assist in the cooling effort. Not having a CNC machine I machine my impellers with straight vanes but offset from the centerline to give the desired flow across the vanes. My pump body has the outlet tangential to the inside bore of the pump. I have made the impeller shaft bore two different ways, one on center with the housing bore and one with an offset center to form what has been referred to as a cutwater. I have never tested the flow rate of these pumps but even after just a few seconds of running an engine I can feel heat circulating through the radiator.
> Your impeller design should work great but I agree with the other posters that you need to make your discharge port tangential to the pump bore.
> Attached is the drawing for the pump on my 4 cylinder engine. This design has somewhat of a cutwater that is simpler to machine without CNC. The pump draws water from the block then pumps it to the radiator.
> gbritnell


Un able to open DWG file I would like to connect via Email 
Mike


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## gbritnell

Hi Mike,
Send me a PM for my email address.
gbritnell


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## propclock

Beautiful work. Just being stupid here, almost all the rods I have seen,
or made, are of the basic tapered I beam construction not round. I know you can make whatever you desire. Were the original Offy  rods round?  roundish?
Just wondering.  Thanks for all your input here.


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## mayhugh1

My rods were made to Ron's drawing with only a few minor changes. I've never actually seen an Offenhauser rod, but I suspect they were probably designed for clearance inside the close-fitting crankcase. Here is a photo I found of one being offered for sale on ebay:


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## mayhugh1

A simple fixture was made up to support the rod caps while their rear ends were finish machined. All went well, but then I discovered the diameters of the previously machined big end bores had all come out different. After retracing my steps I found the bores had been growing by a thousandth or so with each succeeding operation. My first suspicion was built-up edge on the tool, but the surface finishes were great, and the cutting edge looked clean under a microscope. I made another test cut and it too was oversize. Since the grub screws in both the dovetail and toolholder seemed snug, I have some more detective work to do. Although the Offy's rod journals ended up within a thousandth of their target diameter, these bore variations will result in a unique rod on each journal after all.

The bearings were machined from a 932 bronze. After turning an appropriate blank, each was split using a .008" slitting saw so both halves could be used. A zero thickness kerf would produce perfectly round bearings for truly round journals, but my rod journals are out of round by a thousandth, and so I went for a next best solution.

The blank's i.d. was calculated by dividing the sum of the journal's circumference (including a running clearance) plus twice the saw's kerf thickness by pi. The blank's o.d. was then calculated by dividing the sum of the circumference of the rod's bore plus twice the saw kerf by pi.

I've included a scale drawing comparing one of my bearings with a perfectly circular equivalent. There's a .002" difference between the two which for all practical purposes vanishes when the bearing shells are deformed by snapping them into place in the rod halves. With the bearing installed and the rod tightened around a gage pin with zero running clearance, I could see no light passing between the two. The fits are probably as good as anything I could have achieved using more conventional soldered or wasted half fabrication techniques.

The rod bearings were fitted to the crankshaft with a .0015" running clearance. Although I was prepared for a slight bind as an out-of round journal rotated inside one of these compromise bearings, the fits were all uniformly smooth for their entire revolution.

The rods were finished up by drilling an oil passage connecting the bearings on the big and small ends. A fixture designed to reduce risk to the rod was used for this final machining step. A drop of Loctite 290 (wicking grade thread locker) was added behind each cap-side bearing in order to reduce the chances of a spun bearing later on. The Loctite was allowed to cure overnight with the finished rods tightened snugly around gage pins. - Terry


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## propclock

Very informative ,thank you , I like the tie wrap parting fixture
and that method saves a LOT of bronze


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## Steamchick

mayhugh1 said:


> A simple fixture was made up to support the rod caps while their rear ends were finish machined. All went well, but then I discovered the diameters of the previously machined big end bores had all come out different. After retracing my steps I found the bores had been growing by a thousandth or so with each succeeding operation. My first suspicion was built-up edge on the tool, but the surface finishes were great, and the cutting edge looked clean under a microscope. I made another test cut and it too was oversize. Since the grub screws in both the dovetail and toolholder seemed snug, I have some more detective work to do. Although the Offy's rod journals ended up within a thousandth of their target diameter, these bore variations will result in a unique rod on each journal after all.
> 
> The bearings were machined from a 932 bronze. After turning an appropriate blank, each was split using a .008" slitting saw so both halves could be used. A zero thickness kerf would produce perfectly round bearings for truly round journals, but my rod journals are out of round by a thousandth, and so I went for a next best solution.
> 
> The blank's i.d. was calculated by dividing the sum of the journal's circumference (including a running clearance) plus twice the saw's kerf thickness by pi. The blank's o.d. was then calculated by dividing the sum of the circumference of the rod's bore plus twice the saw kerf by pi.
> 
> I've included a scale drawing comparing one of my bearings with a perfectly circular equivalent. There's a .002" difference between the two which for all practical purposes vanishes when the bearing shells are deformed by snapping them into place in the rod halves. With the bearing installed and the rod tightened around a gage pin with zero running clearance, I could see no light passing between the two. The fits are probably as good as anything I could have achieved using more conventional soldered or wasted half fabrication techniques.
> 
> The rod bearings were fitted to the crankshaft with a .0015" running clearance. Although I was prepared for a slight bind as an out-of round journal rotated inside one of these compromise bearings, the fits were all uniformly smooth for their entire revolution.
> 
> The rods were finished up by drilling an oil passage connecting the bearings on the big and small ends. A fixture designed to reduce risk to the rod was used for this final machining step. A drop of Loctite 290 (wicking grade thread locker) was added behind each cap-side bearing in order to reduce the chances of a spun bearing later on. The Loctite was allowed to cure overnight with the finished rods tightened snugly around gage pins. - Terry
> 
> View attachment 120831
> View attachment 120832
> View attachment 120833
> View attachment 120834
> View attachment 120835
> View attachment 120836
> View attachment 120837
> View attachment 120838
> View attachment 120839
> View attachment 120840


Excellent work and engineering explanation. Easy when you know how. Essentially, The same calculations are made by Glacier and Vandervell. I visited both in 1989 to discuss bearing manufacture, with some Japanese experts, who were well impressed. The only extra that you get in a modern engine would be tempted rare metal plating (Indium, etc.) for anti-corrosion. Unlikely the you engine will need that as it is only to extend lifetime by a factor of 5 or more, against corrosion from acids formed in  the oils with age and blow-by gasses.
Incidentally, the mass production uses broaching of pairs of shells to get "perfect" repeatable sized parts - at hundreds of pairs every hour. But "pinch" sizing is the same. Mass production sizing  and grading is measured using  air gauging, to microns! As grinding of cranks, manufacture of journal housings and journals is all 10 times less capable than the design tolerance for perfect fit, all the parts are measured, then graded, and at assembly, the graded bearings are selected to suit the housing and rod diameters. Not something for the one-off engine.
Thanks for the excellent tutorial.
K2


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## johnmcc69

Great work!
 I'm sure you are properly torquing all the mains, rod ends, ETC., to check fits & clearances, but what specs are using & how were they determined?

 John


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## JonnyC

Hi, I'm watching in the background on this beautifully engineered piece of work and admiring the detail you are going to on every part of it.

Looking through the rod, cap and bearing machining you appear to have machined the rods and caps complete as one piece. Did you then split them and re machine the bores? I cant see any photos that show this. Also on the bearings, I see that you did split these but did you only make one true half at a time or do I see that you made one over centre and one under centre piece from each and then mixed these with another set to get two full rounds? Hope I've explained that well enough for you to understand.
Keep up the great work.

Jon


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## mayhugh1

JonnyC said:


> Hi, I'm watching in the background on this beautifully engineered piece of work and admiring the detail you are going to on every part of it.
> 
> Looking through the rod, cap and bearing machining you appear to have machined the rods and caps complete as one piece. Did you then split them and re machine the bores? I cant see any photos that show this. Also on the bearings, I see that you did split these but did you only make one true half at a time or do I see that you made one over centre and one under centre piece from each and then mixed these with another set to get two full rounds? Hope I've explained that well enough for you to understand.
> Keep up the great work.
> 
> Jon


Jon,
The rods and caps were machined together at the same time, but there were two separate pieces of aluminum bolted together with the seam between them being the seam between the rod and cap.
The blanks for the bearings were turned a calculated amount oversize and after parting off, the bearing was slit in half and both halves used.

Sorry the write-up was so unclear.

Terry


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## mayhugh1

As mentioned at the very beginning of this build, in addition to a slight repositioning of some of the head bolts, the diameters of the liners were reduced by .030" to improve the robustness of the head gasket. These changes in turn required changes to the pistons, and a sketch shows their dimensions and clearances inside the liners. The Offy's pistons use two rings and a groove below them with an array of radially drilled holes for oil control. The pistons were machined from 7075 aluminum.

The wrist pins were turned from drill rod and then hardened. Soft aluminum rivets pressed into their ends prevent scoring on the liners. In order to avoid scuffing and/or abnormal ring wear, it's important for the wrist pin bore to be carefully placed on the piston's centerline and truly perpendicular to it.

After attaching the pistons to the rods, I found a cosmetic filet that I'd added on the rods' small ends was nearly in contact with the inside floor of the piston. I created a fixture to allow me to allow the rods' small ends to be manually rotated against an end mill to remove the fillet and return the rod to its stock .013" clearance.

As far as I can tell, only the rings and the radiator currently stand in the way of the engine's final assembly. Of the two, the radiator with its PITA starter clearance hole through its core seems more interesting and will probably be tackled next. - Terry


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## Steamchick

Beautiful workmanship! WELL DONE sir!
I just wonder about the design? - I would have expected a more "traditional" shape of the con-rod section? I.E. - H-section for max strength and stiffness and minimum weight? 
Why the round section? - As you are so capable with the miller, I can't imagine it is because the lathe work is "easier?" than milling the H-section?
I am very impressed by the work and thread.
Thanks!
K2


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## mayhugh1

Steamchick said:


> Beautiful workmanship! WELL DONE sir!
> I just wonder about the design? - I would have expected a more "traditional" shape of the con-rod section? I.E. - H-section for max strength and stiffness and minimum weight?
> Why the round section? - As you are so capable with the miller, I can't imagine it is because the lathe work is "easier?" than milling the H-section?
> I am very impressed by the work and thread.
> Thanks!
> K2


See posts 423 and 424 above ...


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## Steamchick

Thanks Mayhugh1. I had missed that. Picking up threads after hundreds of posts means there are many "answers" already posted that are hard to find. I had guessed it would be for rod stiffness in the available space but it does appear to be a design for a lathe rather than truly optimised.
But your genius s not that you are using someone else's design, but in the way you really understand and explain your approach to such problems as the bronze big-end bearing maching method - and calculations. I am really impressed with your complete approach. I am enjoying learning from you. Well done Sir!
K2


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## Cogsy

Steamchick said:


> I had guessed it would be for rod stiffness in the available space but it does appear to be a design for a lathe rather than truly optimised.


I think you missed the point - look again at post #424 which has a picture of the actual rod from a full-size engine. The rod design is obviously staying as close to true scale as possible. As the full-scale engine was a well refined racing engine, I would say the rod design was optimised for power production, but not necessarily the same parameters as other engines.


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## Steamchick

Thanks Cogsy. I appreciate people trying to accurately copy full sized engines. Beyond my skills and patience. All the workmanship on show on these threads puts my humble work to shame. But I like to know why something has been made the way it is, to learn more of the various designs - and history thereof.
H-section con-rods have been the "optimised" design since late Victorian times, as metals became better controlled, and manufacturing methods allowed parts to become closer to the "Designer's ideal", rather than just "what it is possible to make". Obviously on this racing engine there was some reason to vary from that norm, but the answer isn't here. Possibly drawn aluminium was more "defect free" than forged steel at the time of developing and racing that engine? - or maybe it was a special alloy - tempered for strength - or something? Or perhaps the machined alloy rods were light, stiff enough and minimise stress raisers that start fatigue cracks? - My limited knowledge of racing engines is mostly the British Motorcycle engine developments of the 1940s to 1960s. (I owned a couple of old Triumph racing engines, and I seem to remember the T500C 1955 racing engine having forged aluminium H-section rods....? - But it may have been the 1946 GP engine? - Also, Road Production engines had forged steel rods? - Someone will correct me if I am wrong in my recollection!). The reason for asking about the design is my engine experience of seeing "shapes" used to "maximise strength against minimum material", and these rods deviate from that experience.  - Not always easy in the Home workshop. And not intended as any criticism.
Post 431 is "Rocket science" compared to my humble workshop practice. I'm just an Engineer, not a skilled artisan. I am awed by the skill and workmanship applied here.
K2


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## Cogsy

Steamchick said:


> H-section con-rods have been the "optimised" design since late Victorian times, as metals became better controlled, and manufacturing methods allowed parts to become closer to the "Designer's ideal", rather than just "what it is possible to make".



H-section rods abound and have for a long time but there are still significant deviations in some specialised applications (especially high-level racing). Have a look at the profiles used for top-fueler dragsters for instance. Strength and clearance considerations could easily be the reason these rods are non-traditionally shaped, but I think it's unlikely they were chosen simply for ease of construction.


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## L98fiero

Cogsy said:


> H-section rods abound and have for a long time but there are still significant deviations in some specialised applications (especially high-level racing). Have a look at the profiles used for top-fueler dragsters for instance. Strength and clearance considerations could easily be the reason these rods are non-traditionally shaped, but I think it's unlikely they were chosen simply for ease of construction.


It's pure speculation but I'd imagine that the shape of a top fuel con rod has more to do with column strength, they're running around 6000 psi cylinder pressure and at $1500 for a set of eight rods I doubt changing the forging dies to reduce the weight of a 900 gram rod would be much of an issue if a reduced weight could be achieved and the rod still hold up.
As a matter of interest, AWA composites Arthur Warfield & Associates make top fuel rods from an advanced carbon fibre composite, it reduces the weight to about 640 grams and instead of lasting 4 - 6 runs is projected to last 600 runs and as a side benefit when the rod fails it shatters rather than destroying the block. The downside is a set of rods is $144,000.


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## mayhugh1

The effectiveness of the model engine coolant systems I've had experience with don't seem to scale very well with engine displacement. There are probably some hard-to-fix reasons for this, but there may also be a few things that can be improved with a re-think of the radiator.

The Offy's block and head, which seem better designed for coolant than most, hold only about 1.5 ounces. This works out to be less than half the amount of coolant per cubic inch cylinder displacement than, say, a small block Ford. The first step in removing waste heat from around the combustion chambers is to transfer it to the coolant, and more coolant can mean more removed heat.

Another limitation involves the relatively poor thermal conductivity of brass which, due to its solderability, is a popular material for model engine radiators. This important material property affects the amount of heat absorbed from the coolant circulating through it - the second step in the engine's cooling process. Thermal conductivities for aluminum and copper, the materials used in full-size radiators, are two to four times greater than that of brass.

A third issue is the typically poor air flow through the core of a scaled-down radiator. Automotive radiators are designed to shed their heat to the air flowing through their core which is the final step in the cooling process. Even a well-shrouded model engine fan has difficulty pulling enough air through the tiny passages of a scaled-down core to be of consequence. The use of an electric fan would be a major improvement, but the core isn't being fully utilized with only conduction and radiation.

The Offy's requirement for a radiator with a starter shaft running through it complicates an already troublesome part of the cooling system. And so, I gave up trying to design a traditional radiator for it and instead focused on increasing the amount of coolant in the system. I used the space that would have otherwise been taken up by an underutilized core to hold it. In the worst-case, the engine's runtime should be lengthened by the time it takes to heat up the additional coolant to an unacceptable temperature. In the best case, the reservoir holding it may perform as well as a traditional radiator core sitting in static air.

As shown in the SolidWorks renderings, the reservoir was designed to look like a radiator with an upper and lower tank attached to a faux core. Since the components are aluminum, they'll be bonded with JB Weld rather than soldered.

As a baseline, the Howell V4 radiator uses traditional finned brass tube construction and has an envelope that's roughly 4" x 6" x 1/2" that holds about an ounce of coolant. The total surface area of its finned core is some 200 square inches.

For comparison, the Offy's reservoir measures 7" x 8" x 1-3/4" and will hold about 40 ounces of coolant. Its all aluminum construction should absorb more heat from the circulating coolant. Even with only radiation and conduction heat transfers, its 150 square inch surface area may shed heat as well as a typical finned core. - Terry


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## Ghosty

Terry,
Could you not use radiators like in you Rolls Royce V12 Merlin?(computer coolant rads), Just a question. I have been following along of another fantastic build
Cheers
Andrew


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## mayhugh1

Ghosty said:


> Terry,
> Could you not use radiators like in you Rolls Royce V12 Merlin?(computer coolant rads), Just a question. I have been following along of another fantastic build
> Cheers
> Andrew



Ghosty,
Yes, I could. At first I thought that using a couple of them would be the solution to the starter shaft problem as well. The problem with pc radiators is that their inlet and outlet are on the same end of the core making them awkward to use in a model engine. My earlier Offy coolant pump testing showed I needed the radiator inlet up high and its outlet down low to get all the air out of the engine. I could have put a pair of them inside an enclosure and hid the plumbing to correct the I/O this like I did on the Merlin, but then I realized I was wasting a lot of real estate on non-cooling stuff. Remember, though, the Merlin also had a 25 oz coolant reservoir in addition to the two radiators and electric fans, and it got really warm while the engine was running. This time I thought I'd just go with a bigger reservoir and see what happens. - Terry


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## Ken I

Terry, been following with interest but this is my first comment.
As per usual another mind bogglingly impressive build - I'm in awe.
Re your comments on scalability of radiators etc.
The "fins" on radiators are wrinkled to induce turbulent flow - the difference in heat abstraction ability of the airflow through the radiator is much reduced if it does so in laminar flow mode. Ditto the flow of water inside to a lesser extent.
Flow velocity is also a major influence in turning laminar flow into turbulent flow.
As you said, radiators don't scale well - if you scale down an automotive radiator you will end up with a fragile gossamer thing but that surface area and thin sections densely packed into a small volume is what gives automotive radiators their ability. If you consider your surface area per unit volume of your scaled radiator I think you will find it to be a fraction of the original and laminar flow might halve that again.
I'm not sure how to translate that into helping your model - perhaps a lip on the fins, pierced and flared holes, stippling etc.
A larger reservoir will buy you more run time - but then perhaps that is all you need (or want).
FYI - Regards, Ken


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## mayhugh1

The three parts making up the radiator were machined from 6061 aluminum. Both tanks and the core's exterior were machined on my Tormach, but I did the core's interior manually on my Enco Bridgeport clone. Hogging out the interior required a 3-1/2" cutter stick-out, and so a 3/4" diameter end mill was used to limit the deafening chatter-induced squeal. I felt more comfortable working manually inside the deep narrow cavity where it was difficult to prevent re-cutting some of the huge chips. Without high volume flood cooling, the chips occasionally welded themselves to the cutter which, on the Tormach, would have resulted in a nasty crash. The front and rear faces of the simulated core were grooved using a 60 degree vee cutter.

All three parts were bead-blasted in preparation for paint. After sanity checking the hole locations with a mock-up of the Offy, the parts were bonded together by filling with JB Weld the seams that would have received solder in a full-size radiator. - Terry


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## Skipper

I built Ron‘s Offy engine.  Couldn’t get the head bolts tight enough.  Kept blowing head gaskets.
Skipper


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## Peter Twissell

Nice work, as ever.
When milling an item right through like your core block, I find it useful to start by drilling one or more large-ish holes through.
The holes provide a route fo clear chips, even if it means stopping the cut occasionally to brush chips towards the hole.
A drilled hole also avoids the need to plunge the cutter at each depth of cut.


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## kvom

There's something to be said for plunge milling in a chain for the entire length of the slot followed by a finishing pass.


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## mayhugh1

The radiator was painted with matte black Gun Kote which requires a 300F oven bake-out to cure. In the past I've had trouble with JB Weld out-gassing underneath this paint and creating bubbles in the finish. So, after the epoxy had been allowed to cure for a full day, the radiator received a one hour 300F pre-bake which seemed to solve the problem.

The radiator cap was machined from 303 stainless and then polished. Although it's vented to the atmosphere through a tiny central hole, the cap is sealed to the radiator with an o-ring.

The radiator's inlet and outlet were also fabricated from stainless. The lower outlet tube required a one inch "S-bend" to accommodate an offset between the radiator and the water pump inlet. It took a full day with jury-rigged bending jigs and lots of scrapped tubing to finally get a threaded tube to fit and look acceptable. The top inlet was simply machined from rod stock.

I've never come across a commercial miniature hose clamp that looked at home with the silicone coolant hoses I use on my engines, and so I decided to design my own. Two batches of clamps were machined to handle the hose o.d.'s (3/8" and 7/16" ) that I'm using on the Offy. The clamps' important dimensions are the i.d.'s which I experimentally determined to be optimum at .010" less than the hose o.d.'s. The slot width was .040", and 2-56 SHCS's are used to tighten them around the hose.

Finally, a pair of brackets were fabricated to attach the radiator to the display stand in front of the engine.

Before wrapping up work on the radiator, I'm considering machining a shroud for a pair of electric fans on the rear surface of the radiator's faux core. Although they'd likely be more cosmetic than functional, I found that mounting them a quarter inch off the radiator's grooved surface churns up a lot of turbulent air that might provide a bit of additional cooling. In any event, I have a couple six volt fans that are currently looking for a good home. - Terry


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## dsage

Beautiful work as usual.
Good call on the pre-heat. I hadn't considered it for JB weld. Thanks for that tip.
I do powder coating and it's necessary to pre-heat cast iron or cast aluminum to over the cure temperature of the paint to force the gas out of the casting. Then you let it cool a bit before applying the paint. Then back up to curing temperature. Otherwise, as you have found, you get what looks like rice crispies finish on the surface. A disaster in powder coating because it's near impossible to remove.
Thanks Terry.


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## kuhncw

Terry,  Great work as always.  Thanks for the hose clamp idea.  Is the spring clamp in the photo for damping or something else?

Chuck


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## mayhugh1

kuhncw said:


> Terry,  Great work as always.  Thanks for the hose clamp idea.  Is the spring clamp in the photo for damping or something else?
> 
> Chuck


Chuck,
Yes, the clamp dampened the tall skinny workpiece during cutting. - Terry


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## mayhugh1

A shroud for a pair of 60 mm fans was machined from a block of aluminum and painted to match the radiator. When mounted, the fans stand 3/8" off the rear of the radiator, and the air they draw in around the sides of the shroud is blown over the top of the engine. The 6V fans are powered by the ECM, and their combined 36 cfm results in a surprising amount of felt cooling air flowing over the head.

One last coolant related task - leak testing the block - was something that should have been done long ago. The Offy's block, being separate from the crankcase and head, contains the cylinder liners and a number of oil return tubes. It will be closed up with a pair of gasket'd side covers that are secured by eighty 0-80 SHCS's. The cylinder liners which were close sliding fits inside their bores were sealed with Loctite 620. When filled with hot circulating coolant there'll plenty of opportunities for leaks to the outside of the engine or, even worse, into its oil.

For the leak check, the side covers were temporarily installed and the block filled with isopropyl alcohol. Sure enough, a leak showed up at the bottom of the rear liner. Although a block-to-crankcase gasket will be part of the final assembly, I didn't want to risk a major teardown later on.

Loctite 290 is a wicking grade thread locker that's sometimes used to solve metal porosity problems. A single drop deposited in the bottom corner of each liner quickly wicked around its raised circumference forming a meniscus. A few hours later, the meniscus around the rear liner had been entirely drawn into the gap causing the leak, leaving Loctite on the liner inside the block. After an overnight room temperature cure, the block was moved inside my (130F) welding rod oven for several more hours. The uncured drip inside the block was wiped away and a second drop of Loctite added the rear liner. This time its meniscus was still in place a day later indicating the gap had likely been closed. After several more hours in the oven the uncured surface Loctite was wiped away.

Thread locker was also dropper'd onto the topside of the block around all four liners even though there had been no indication of leaks on the top ends of any of the liners. After an overnight cure at 130F the block was retested, and it passed my alcohol leak test. - Terry


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## dsage

More great tips and tricks to somehow remember.
Thanks Terry


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## mayhugh1

I use George Trimble's method to make my piston rings. The only change I've made to his process is to use a normalization temperature of 975F rather than his originally published 1475F. In addition, I use a 200 lumen flashlight to check the fit of each finished ring inside a cylinder before it's installed on a piston. A ring that has any light leaking between it and its cylinder wall, other than through its running gap, is discarded.

My yields are typically limited by circularity issues that often show up during or after the blank's final machining. I use class 40 gray cast iron from a number of sources that's been laying around in my shop for years. The circularity errors have been as high as eight tenths over portions of the finished blanks. Typically, less than half of any blank passes my acceptance criteria of two tenths, and occasionally an entire blank is scrapped. Once a ring has been removed from a blank, it's nearly impossible to evaluate until it's fully finished and light tested. After slicing candidate rings from the well-behaved portions of the blanks, my yields are typically 80%-90%.

When starting a large batch of rings, I usually prepare several blanks from different sources. Even though only eight rings plus a few spares were needed for the Offy, I prepared three 3" long blanks. The Offy's rings require a finished diameter of 1.002", and so I started with one inch diameter raw material which actually measured 1.080".

All three blanks were turned down to 1.063" so they could be gripped in a standard collet during their final machining. The blanks were then drilled/bored to the rings' final i.d. for a depth of two inches leaving an inch spigot at one end for the collet during final machining. In order to relieve some internal casting stresses, the pre-finished blanks in my last few builds next have next received a 700F heat soak. This heat soak seems to have reduced issues with circularity errors which sometimes show up even days after the blanks' final machining. Rather than my usual five hour soak, an oven programming error soaked these three blanks for some 12 hours.

A few days later, the o.d. of the first blank was finished and polished to its final diameter with 600 grit paper. Quadrature measurements of the blank's diameter recorded continually along every half inch of its length during machining showed (surprisingly) negligible errors over the blank's two inch length. Using a .019" parting tool, I was able to get 25 candidate rings from that single blank, and so I didn't finish the remaining two blanks.

The inside corners of the parted rings were broken using a 1/4" diameter ceramic file. Using 600 grit grinding grease on a glass plate and a simple holding fixture, both flat sides were lapped to obtain a .001" clearance in the piston grooves. During combustion, the rings will seal against the lower walls of the pistons' groove to provide an important component of the combustion chamber's overall seal.

The Trimble article recommends a straight radial break in each ring for proper contact with the spreader dowel in the normalization fixture. Although 'good enough' results might be obtained by simply snapping the rings, I constructed a cleaver several years ago. After lapping and just before heating, each ring was cleaved and the running gap set to .004" with a diamond file. Each gap was verified inside a cylinder using a feeler gage.

The Trimble articles describe the construction of the fixture required to support the rings during their heat treatment. Equations were provided for the dimensions of the mandrel and spreader dowel which are its key components. This fixture isn't difficult to make, but its dimensions are specific to a particular ring diameter. I finally got to reuse one of my earlier made fixtures.

In the past I've sealed the fixture'd rings in an argon-filled stainless bag for protection during heat treatment, but the contents invariably wound up covered in a mysterious brown deposit. Although it wasn't difficult to remove, it was an annoying extra step that I began suspecting is related to the sulphur and lead that are alloyed into the free-machining steels used for the fixtures. This time I didn't cover the fixture, and only minor burnishing with a white Scotch Brite pad cleaned the o.d.'s up nicely.

My light tests yielded a dozen 'perfect' rings and only five that I labeled as rejects. The remainder were a bit off from being perfect, but in all likelihood would be 'good enough'. - Terry


----------



## G54AUST

Bumper issue Terry.   I've printed this one off for Ron;   later ron.   This is now a reference source,  going straight to the pool room library.   (_please refer to Aussie film "The Castle"_)


Kind Regards,

Trevor,
Melbourne,  AU


----------



## Charles Lamont

I forget, does the Trimble method include a final turning stage, after heat-treatment?


----------



## tornitore45

Hi Terry, miss our get together...
That black ring holder,  how does it work?
My question is how you direct the intense light to the ring but blank off the light from the center to blind you.
I suppose is all in keeping the ring holder centered inside the ring ID without blocking light where it needs to go.

Can you sketch the ring holder?


----------



## mayhugh1

Trevor,
It's probably because of the continent I grew up on, but I didn't understand your comment....

Charles,
The Trimble method doesn't include any machining after the heat treatment. The results of his mathematical analysis are that the correct size spreader dowel during heat treatment will result in a circular ring when it's inserted into the cylinder afterward.

Mauro,
I miss our monthly meets as well.
I've included a sketch that should make my light test procedure a little clearer. The ring is actually held inside the bore by its own friction with the cylinder. The pusher block referred to in my previous photo is a close fit to the cylinder bore and insures the ring is properly aligned in the bore for the test. The light source I use provides a ring of light around the ring's perimeter.

Terry


----------



## doug tyler

Have you ever checked the glass plate to see if it has stayed flat?


----------



## mayhugh1

doug tyler said:


> Have you ever checked the glass plate to see if it has stayed flat?


Doug,
I usually discard them after after an hour or so use on each side or when the surfaces become too frosty looking to see through. I've never actually been able to measure any flatness errors across them. Even the ones I discard seem to be better than my surface plate. I bought a stack of 5"x7" glass panes some ten years ago from a local hardware store that was going out of business. The cost was just a few dollars and it looks like they'll last my lifetime. - Terty


----------



## mayhugh1

A number of the Offy's subassemblies including their associated gaskets were built-up and tested earlier as their constituent parts were machined over the past year or so. These included the water and oil pumps, carburetors, gear tower, magneto, head, and camshaft assemblies. The ECM, radiator, and the oil and fuel tanks were also completed and installed on a display/running stand. With all this prep work completed, final assembly should be pretty straightforward.

Before closing up the crankcase, though, I decided to make a last minute change to the upper half. The bearing supports which were integral to Ron's original single piece crankcase were machined away. They serve no useful purpose in the split crankcase and after being removed allow the pistons to be installed or removed with the block attached to the crankcase. After completing this operation, the block was secured to the upper crankcase using fourteen 3-48 SHCS's and a .005" thick Teflon gasket between them.

Oracal 651 adhesive backed sheet vinyl was applied to the upper half crankcase on the surfaces that will mate to those on the lower half. I used this 2.5 mil thick material in a similar gasket'ing application during the Knucklehead build. In this case it will be used to seal the crankcase halves together with a nearly invisible seam. Strips of .0005" shim stock were used to verify the seam will tightly close and not seep oil later.

The crankshaft, rods, and pistons (sans rings) were temporarily installed sometime earlier in order to check for any tight spots before the friction of the rings and rear oil seal hide them. With the rings now installed, the piston assemblies could be installed and the crankcase finally closed up. The crankcase halves, precisely aligned by a pair of dowel pins, were then bolted together with ten SHCS's. A tiny but important -002 o-ring seals an oil passage crossing the seam that will eventually deliver a portion of the oil from the scavenger pump to the engine's top-end. The rod caps and bolts were easily inserted and tightened through the access ports on the sides of the crankcase.

The rear oil seal was pressed into the rear housing which was then attached to the engine and sealed with an o-ring. The crank was spun with an electric drill while oil was injected into the engine's oil inlet with a syringe. Oil eventually showed up on the floor of the sump indicating that the pressure pump seemed to be working. - Terry


----------



## kvom

Custom allen wrench for the win!


----------



## petertha

Hi Terry, just going back to your gaskets. Was the Oracal selected maybe because you could computer cut those smaller fiddly & has self adhesive for positioning or..? Any idea if/how much that material might change in thickness once clamped or do you just allow for the full nominal 2.5 mil thickness?


----------



## mayhugh1

Petertha,
The Oracal gaskets weren't computer cut. Although they certainly could be, the gaskets I've been typically using it for have been too small and separating the backing sheet would have been a hassle. For my gaskets. I removed the backing sheet and then press the pre-cleaned part down against the sticky side of the vinyl. An Xacto knife with a brand new blade was then used to trim the excess away from the part. The vinyl doesn't seem to compress any measurable amount on the surface areas I've been typically using it on, - Terry


----------



## mayhugh1

With the number one piston at TDC and the flywheel rotated so its engraved TDC mark was directly under the rear housing's timing pointer, the flywheel was installed on the rear of the crankshaft. A simple shop-made tool was used to hold the flywheel while the locking tapers were wrenched tightly together with the crankshaft nut. This left-handed nut will provide an alternative rear start for the engine.

The front cover/water pump assembly was installed next with a .010" Teflon gasket between it and the crankcase. This required patience because the shaft on the upper 60 tooth drive gear had to engage its cover bearing simultaneously with the tang on the oil pump shaft engaging the slotted water pump shaft. Since the starter clutch winds up captured between the water pump and front cover, the starter shaft had to be installed on the crankshaft at the same time. Installing the starter support bracket was trivial and completed the front end assembly.

With the crankshaft finally supported by all five bearings, it could be safely drill spun for a more thorough test of the oil pumps. In the process, I discovered the oil passage leading to the top-end was blocked. The -002 o-ring between the crankcase halves used to seal the passage in the seam had been compressed completely closed. After looking back over my notes, I realized the crankcase had actually been machined for a 1x1.5 metric o-ring. I had only to spread the crankcase halves slightly apart in order to replace it, but I had to start over on the just-assembled front end.

I then discovered the gear tower and the head (with its installed camshafts) had to be partially preassembled before either one could be installed on the engine. The front cover's protruding 60 tooth drive gear along with the "Y" shaped tower would otherwise require the camshafts to be removed from the head. Preassembling the pair was easier to do than to describe, but the cam gears still had to be removed from the cams and placed in position inside the gear tower.

My method for securing the head to the block was to use sixteen 5-40 SHCS's threaded up through the top of the block. (The original plans specified long studs running up through the block from the crankcase.) In addition, I repositioned the head bolts slightly to provide a little more head gasket 'meat' around the cylinders. Unfortunately, these new locations with their already limited clearances to the stock intake/exhaust ports allowed a thread depth of only 3 to 4 threads. The ports were later re-designed, and their new shapes provide more clearance, but I forgot to go back and deepen the threads for more engagement. Still not wanting to remove the camshafts, I wrapped the entire head assembly in vinyl tape for chip-proofing while the holes were deepened for an 8 to 9 thread engagement.

Since the head was machined from aluminum and the SHCS's are stainless steel, there is a potential for galvanic corrosion between the two inside the block's wet environment. For some protection against this, the screws were liberally coated with nickel (anti-seize) grease before being installed.

The o-ring cord surrounding the oil passage running up the rear surface of the gear tower eliminated the need for a gasket or sealer between it and the block. Oracal was used on its bottom, however, as a gasket to seal a potential leak around the oil drain back passage surrounding the 60 tooth drive gear. - Terry


----------



## srobovak

It's getting there! Really looking forward to see/hear it running...


----------



## kvom

For deepening threaded holes, how much smaller than minor diameter do you choose for the drill?


----------



## mayhugh1

kvom,
The original tap drill size was .101", and for deepening the holes I used an .096". - Terry


----------



## mayhugh1

While standing in front of the engine the intake valves are on the right, and the exhaust valves are on the left. Both camshafts rotate counterclockwise while the crankshaft rotates clockwise. The camshaft gears accumulate significant backlash from the five meshed gear sets that connect them to the crankshaft. Since the 40 tooth cam gears rotate once for every two crankshaft revolutions, their resolution winds up being 18 crankshaft degrees. In order to reduce this to a more manageable 5 degrees, each cam gear is pinned to its camshaft using a particular hole in a special pattern of holes that was drilled through the cam gear.

In order to realize the resolution offered by what is effectively a vernier, the proper tooth on the cam gear must first be meshed with its driving gear. The correct hole in the vernier pattern will be one that lies directly over (or is very close to) a hole in the camshaft flange. This hole will be among those located in one of the ten possible hole combinations made available by the vernier. Five of these hole combinations have been sketched in a photo. Each is separated from its neighbor by a single cam gear tooth. The sequence of hole combinations repeats every ten gear teeth, and so the probability of randomly selecting the correct tooth is only 10%.

In order to locate the correct hole for the intake cam, for example, the crankshaft was first set to the angle (20 deg BTDC) at which the intake valves should open. (Since the perimeter of the flywheel was previously engraved with five degree tic marks, a degree wheel wasn't required.) The as yet unpinned camshaft was then rotated to the point where the intake valves actually were beginning to open. The (unmeshed) cam gear was then rotated to a candidate position.

However, in order to be rotated and since the camshaft was already installed, its bearing caps had to be loosened so the cam gear could be raised free of its drive gear. With the bearing caps re-installed and the camshaft back into position, a drill was temporarily inserted in the hole with the best looking match. The result was evaluated by rotating the crankshaft and measuring the intake valve opening and closing points so they could be compared with the camshaft specs. A satisfactory result wasn't found with that particular hole (nor any of the others at that particular tooth location), and so the camshaft was again raised so the cam gear could be rotated to another tooth. In practice, it's harder to do than describe. The backlash and valve spring forces tend to rotate the cam while it's raised and make the tooth re-meshing something of a trial and error process. Once the best hole in the best combination was found (four tooth tries later), the drill was replaced with a pin, and the cam gear firmly secured to the camshaft with a nut and wavy washer.

It took several days to fully understand the vernier, wrap my head around the various measurement problems, and to come up a procedure to deal with them. Some upfront preparation turned out to be very important. For example, when machining the camshafts, I included a permanently installed grub screw in each end so they could be easily rotated with a hex key. (The front screws were drilled through for oil passages.) The ability to rotate the camshafts in small controlled increments was invaluable.

Since the lobes on the overhead cams prevent easy access to the followers, indicating the valves is difficult. A shop-made fixture using a needle probe working with a dial indicator was able to access the outside edges of the followers, but the results were inconsistent. I eventually settled on using a strip of .0005" shim stock between the lobes and their followers in order to detect the valves' opening and closing points.

Another issue is that the tiny index pins are nearly impossible to install without special tools, and there's a risk of losing them in the gear tower. One of the photos shows a pair of tools that worked well for me. The insertion tool is a length of .063" magnet-tipped drill rod that slides inside a close-fitting aluminum tube. With the rod fully inserted, the magnetic end of the rod is flush with the end of the tube. Withdrawing the rod slightly, allows the steel pin to be loaded inside the tube and safely held on the end of the rod. After the rod pushes the pin into the cam gear, the tool is swiped sideways leaving the pin in place. For extraction, I used a simple tool made long ago to test Hall devices. It's just an 1/8" diameter magnet pressed into the end of a brass tube.

Even with these tools I quickly realized that it was much easier to deal with the pins while the gears were horizontal rather than vertical. So, I also made a simple wood stand to safely support the engine nose up for some of the steps.

My final valve timing results were:

intake opens: 5 deg BTDC (spec was 20 deg BTDC)
intake closes: 60 deg ABDC (spec was 52 deg ABDC)

exhaust opens: 55 deg BBDC (spec was 48 deg BBDC)
exhaust closes: ATDC (spec was 6 deg ATDC)

I retarded the cams a bit in order to reduce the overlap at TDC so it would be more in line with the other model engines I've built. The higher manifold vacuum that may result might help later with carb synching.

Sanity checks on the valve timing were done simply by holding a thumb over each spark plug well while the engine was spun with a drill. Although the plug wells effectively increase the combustion chamber volume (and decrease its pressure) by some 50%, the pressure pulses felt strong and consistent among all four cylinders.

I was also finally able to thoroughly exercise the oil system. The crankshaft appears to be receiving oil from the pressure pump, and the top end is getting a share of the oil from the scavenger pump which also seems to be able to evacuate the sump. - Terry


----------



## Vixen

Is it possible to publish a drawing showing the angular relationship of all the holes in the cam gear and camshaft?

Thanks

Mike


----------



## mayhugh1

Vixen said:


> Is it possible to publish a drawing showing the angular relationship of all the holes in the cam gear and camshaft?
> 
> Thanks
> 
> Mike


Are you saying you want to see the other 5?


----------



## Vixen

In the bottom centre drawing (position n ) there appear to be a set of eight holes and a second set of four holes. 
Only one of the four holes lines up with the eight. 
Are the eight holes equi spaced = 45* ?
What is the position angles for the four holes?

Thanks

Mike


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## Vixen

Are the four holes angular positions something like 0*, 105* 190* 275*  (5 degree increments)

Mike


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## mayhugh1

See post #222 at:





						270 Offy
					

Here's an online calculator for pretty much any parallel UN thread UN imperial screw thread calculator Should help next time. LaVerne  Thanks!




					www.homemodelenginemachinist.com
				




The four holes in the camshaft flange are equi-spaced at 0, 90,180, and 270 degrees. The 8 holes in the cam gear are the ones with incrementally increasing angles. 
Terry


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## Vixen

Thank you Terry. 
I can see that in the drawing now you have explained it.

Mike


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## propclock

Thank you again for your concise explanation of your experiences . I especially appreciate
your willingness to share the problems encountered and not just showing the things that 
go as planned.   Thanks again!


----------



## Ken I

I remember the old Alfa Romeo Julietta DOHC engines had 19 holes in the cam flange and 20 holes in the chainwheels thus the angular error between the next hole lining up was 360° ÷(20 x 19) = 0.947° per "step".
The Jags had something similar with Vernier wheels.


----------



## mayhugh1

Vixen said:


> Thank you Terry.
> I can see that in the drawing now you have explained it.
> 
> Mike


Mike,
I was so close to the problem that I didn't realize that it wasn't clear in my sketch which holes were drilled where. I set the cam gear to 'transparent' in my CAD tool, and what was going on was much more obvious on my screen than it ended up being on the jpg that was created from it. Thanks for your interest. - Terry


----------



## Vixen

Terry
My interest in the Offy vernier adjustment relates to my 1/3 scale Mercedes Benz W165 engine. It also has vernier adjustment for it's four camshafts.The only design information I have is from these two archive photos. The W165 appears to have 19 holes in *both* the cam flange and cam gear; Both sets of holes line up and there are four bolts holding the gear to the flange, nothing else. Mercedes seem to be using a completely different approach  to the Offy  Mike
.


----------



## Ken I

Vixen - I'm guessing 19 holes in both allows 18.947° per hole while 10 teeth of the 64 tooth gear is 56.25° leaving an an error of 0.592° to the next hole (3 of 19 divisions = 56.84°) to line up. That's a pretty fine adjustment (0.592° per step) - and 4 bolts are close enough to symmetry as to not worry about balance.
In the case of the Alfa engines a single small bolt went through the correctly aligned hole and a central nut on the center did the securing by friction.
I like your (Mercedes) set up better.

Regards, Ken


----------



## Vixen

Ken,
Sometimes, counting teeth and hole spacing, from old photos, is the only way to unravel the detail.
I work it out slightly differently to you. A 64 tooth gear has 5.625* between teeth. The 64T gear can be fitted in any one of 19 angular positions. So 5.625* divided by 19 = 0.2961*. _Now that *is* a fine vernier adjustment._
I think we may have trespassed on Terry's turf for long enough.

Mike


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## geo

Terry excellent explanation on timing as are your thoughts on machining gears for small engines


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## mayhugh1

The cam gear covers were gasket'd with Oracal vinyl before being installed, but the cam box covers were only temporarily set in place for now. There's an oil flow adjustment screw on the front starboard side of the engine which will be finally set while watching the top-end oil delivery with the engine running.

The block and crankcase side covers were installed next with each being sealed with a Teflon gasket. Since it would have been easy to drop one of the 0-80 block cover fasteners inside the crankcase, the crankcase covers were installed first.

The magneto (which is actually a distributor) was then mounted on the front cover bracket. A pair of timing adjustments involving the phasing's of the rotor and trigger magnets completed its installation. Since the ECM was needed for these adjustments, it was time to move the engine to its display/running stand.

With the crankshaft set to TDC in the number one cylinder's compression stroke, the rotor was aligned with the number one high voltage tower. Since the shaft driving the magneto spins at the same speed as the crankshaft, a 2:1 gear reduction inside the magneto drops the rotor speed down to match that of the camshaft. An alignment mark, visible on the top inside surface of the magneto, will be inline with the grub screw located on the rear of the rotor when it's properly positioned. This grub screw locks the rotor in place.

A collar containing the pressed-in trigger magnets was slipped onto the distributor driveshaft during the magneto's installation. Three grub screws lock it to the driveshaft so it spins at the same speed as the crankshaft. The pair of diametrically opposite magnets generate the four trigger pulses required for every two crankshaft revolutions. Before tightening the grub screws, the collar was aligned with the magneto so the CDI is triggered at TDC in the number one cylinder's compression stroke. A lever on the side of the magneto can manually advance the ignition timing up to thirty degrees.

Finally, the carburetor and exhaust subassemblies were added. Each was sealed to the head using one of the nineteen custom Teflon gaskets made earlier for this engine. 

A set of plug wires was made up using repurposed automotive vacuum fittings (Dorman 47411) for plug boots that nicely fit the VR2L spark plugs. Before installing the plugs, they were temporarily fixture'd outside the engine to verify the ignition one last time. After they were installed, the engine had plenty of compression.

A little oil and gas were added and the engine cranked for a few seconds to verify it at least wanted to run before adding the radiator and (messy) coolant. With the four carb screws opened 3/4 turn, the little engine started right up. I shut it down after a few seconds since I really didn't want to run it without coolant.

There's just a few loose ends including the addition of the already completed radiator to finish this build. With no experience with multi-carb set-ups, nor carb design for that matter, tuning promises to be a learning experience. It seems I've elected to put four unknown and untested carburetors on the same engine. - Terry


----------



## ddmckee54

It looks like you are getting dangerously close to the point where you won't be needing to make the Vroom-Vroom noises anymore.  You'll be able to let the Offy speak for itself.  As usual, this has been an interesting and educational ride. 

Don


----------



## nj111

Fascinating seeing how you have made all of the parts. Stunning build (as always).  I know it takes ages to document builds, especially with this much detail,  but I can assure you it is greatly appreciated!  I am a lover of Alfa twin cam motors and you've got me thinking if I could make a model....


----------



## propclock

As much as I enjoy the cnc parts the exhaust manifold is my favorite! 
It just sounds good sitting still.  Thanks for all your work and sharing.


----------



## mayhugh1

propclock said:


> As much as I enjoy the cnc parts the exhaust manifold is my favorite!
> It just sounds good sitting still.  Thanks for all your work and sharing.


Thanks... to tell you the truth, the exhaust is my favorite also ...


----------



## mayhugh1

The radiator was installed along with the engine's rather delicate water outlet pipe. The pipe was bolted down to three tiny flanges on the head through .010" thick Teflon gaskets before filling the system with 1200 mL of coolant. Clear silicone tubing was used for the top radiator hose so coolant flow could be monitored while running. Earlier pump testing showed at least 500 rpm being needed to get any appreciable flow and, with the spark plugs installed, my starter drill can manage only a few hundred cranking rpm.

Texas is currently in the middle of an historic arctic front with near 0F temperatures and some six inches of ice and snow. The trees and vegetation in our area weren't designed to deal with this, and large over-stressed limbs have been falling and creating a lot of havoc for property owners. Almost half our population has been without electricity, and many of those also have no water. My own power was off for some 30 hours while the outside temperatures hovered around 20F.

Although trivial in comparison with all the real problems around me, the weather has limited progress on the Offy. The engine must be run indoors, and I'm currently dealing with a lot of oil smoke. Only brief (less than one minute) runs are possible between necessary half-day fume clearing pauses. On the positive side, the engine is remarkably easy to start and responds well to its throttle while still using my original 'all carb screws open 3/4 turn' guesstimate. 

Oil smoke is a problem though and watching and listening to the exhaust seems to indicate all four cylinders are smoking. My guess is that the issue is a combination of too much oil in the engine and not enough runtime on the rings. As it turns out, the Offy is a tough neighborhood in which piston rings must live.

Ideally, the Offy's 2x scavenging pump should stay ahead of its 1x pressure pump and evacuate the crankcase so there's only a light oil mist remaining for the cylinders. I've learned from experience, however, this is seldom the case. For example, the Hodgson radials are dry sump engines, but their 2x-1x pumps require drip feeding the pressure pump to limit the amount of oil in the engine and prevent flooding the cylinders.

The Offy really doesn't have an actual oil sump but has instead four floor drains situated between the main bearings. The huge mains create enclosed compartments around the crank web pairs that straddle each rod. Unlike the Merlin with its deep open sump and 2x-1x pumps, the Offy's connecting rods whip up much of the oil that would otherwise collect on the floor drains for removal. The resulting oil storms inside those four compartments also fill the bottoms of the cylinders directly above them and challenge the oil rings. The only oil that can be removed by the scavenger pump is that which falls out of suspension on the floors of the drains.

I originally began with 50 mL of 10W-30 in the oil tank with an expectation that the scavenging pump would always leave about 5 mL inside the oil pump, crankshaft, and scavenger return passages. At the end of the run there was some 27 mL still inside the engine. Most of it had likely been in suspension until the engine was shut down. Upon removing one of the crankcase side covers I found the oil levels in all four drain areas well above the connecting rods. This was the oil that was feeding the smoky exhaust.

The solution, of course, is to break-in the rings for the best possible piston oil control. If an unacceptable amount of smoke persists, the amount of oil in the tank can be reduced while carefully watching the oil flows in the oil tank hoses during running. If necessary, oil can be removed from the tank up to the point where the flow in the tank's return line is affected.

Before continuing, I decided to open up the crankcase breathers on the exhaust side to also make them functional. In addition, I milled a groove on the inside faces of the covers to connect the breather ports and make them more available to the two compartments in the middle of the engine. Although crankcase pressure pulses are prominent in the breather hoses while running, there's little to no oil inside them. In order to reduce the indoor smoke during the rings' break-in period, the amount of oil in the tank was reduced to 25 mL. After a number of short runs and nearly four ounces of gasoline, the smoke has been steadily decreasing.

Remarkably, the only engine leak I've found so far has been an exhaust leak. A slight warp in the silver-soldered stainless flange was discovered and ground away. The ports underneath the flange had their own story to tell. All four were equally wet with oil, but the rear three were also sooty. Those three cylinders had obviously been running rich compared with the front cylinder.

A magnetic dipstick made up from couple brass tubes and cylindrical magnets was Loctited to the oil tank lid.

The current plan is to continue with the brief indoor break-in runs until the exhaust is running clean before I begin playing with the carb adjustments. Hopefully my next post will include a video of a well running engine.

In the meantime, ... brrrr ... - Terry


----------



## mayhugh1

I'm not sure if a four carb setup having 8 individual adjustments on a quarter scale engine having a marginal cooling system inside a shop with a 20F fluctuating temperature can ever be fully optimized, but I've reached a point of diminishing returns while trying. Attempting to methodically tune four carburetors by measuring their individual manifold vacuums proved to be inconsistent and inconclusive. I finally obtained results I can live with using the 'seat of my pants'.

The engine starts easily, hot or cold, and idles reliably at 1100 rpm. Although I've not been interested in finding out how fast it will go, I've routinely rev'd it to 5000 rpm. The exhaust is relatively clean except for a puff of oil smoke when the throttle is blipped. At the time this video was made, the engine had accumulated a couple dozen short runs with only a few lasting several minutes. Most wouldn't consider it broken in yet.

The Offy's coolant system could be further improved with a constant displacement pump as suggested by Ron. (Frankly, I'm just glad to have wound up with a coolant system that doesn't leak.) The pump that I designed has kept the surface temperature of the head below 155F during the longest (five minute) run that I've made. The coolant warms up quickly even at idle, but with the huge volume involved, the radiator fans weren't necessary after all.

The only oil leak that's shown up has been at the crankshaft's exit through the front cover. An o-ring used as a shaft seal was supposed to have been installed there, but after several tries, I couldn't keep it in place while the cover was being installed over the crankshaft. I eventually decided to omit it.

My real contribution to the project has been the split crankcase which I highly recommend to anyone who decides to build one of their own. Unfortunately, producing drawings wasn't part of my process since I created and worked solely with SolidWorks 2010 models.

I'd like to thank Ron for sharing his drawings for the Offy. Without actually building one, it's difficult to appreciate the effort that must have gone into producing such a faithful model of the original engine. The amount of error-free complexity is humbling especially considering the primitive 2D CAD tool that was used 20 years ago to produce it. 


And so, this will likely be my last post associated with what has turned out to be an eighteen month build. I'm not yet sure what my next project might be or if there will even be a next one.  The Offy has not only been very challenging but a lot of fun. - Terry


----------



## The_reach

Amazing work as always, I have read this thread from start to finish several times now in readiness to starting my own offy but scaled x2 size. The end product is a beautiful piece of work and this has been the best thread I've read so far. Thank you for the insane detail and lengths you went to and documenting them for us all to read.
Jimmy


----------



## elliot9797

I sure hope you keep building...as a 29yr old, you are an inspiration and someone I look forward to reading and watching the builds


----------



## dsage

Yup. That's the Offy !!. Ive heard Ron's many times at shows. Such a wonderful sound.
Fantastic work Terry. I'll miss all the detailed writings about your work on this one and looking forward to how all the pieces go together.  I've learned a lot of things since the beginning of this build. I'm sure the next one will just as educational.
I'm not sure if it was the Offy but I remember Ron describing how he tuned an engine by removing the exhaust pipes and  looking in each exhaust port where I believe he tuned by the color of the flame (or whatever is to be seen there) and tuning them to all be the same. Rich / lean blue / orange. I'm not sure.

Great stuff (as usual).
Thanks


----------



## Vietti

I've had good luck with commercial oil seals, they go down to 1/4", maybe smaller.


----------



## petertha

Sorry to see the white stuff blanket your area & create so much distress, Terry. Hope you stay safe. 

I sourced some clear silicone tubing to coupling sections of my radial induction pipes & subsequently discovered the tubing can also be had in colors including black just in case you cared for scale-ish appearance. No quarter scale hose clamps though LOL

I'd be interested to hear how you went about multi-carb tuning. I have a feeling my next project will require that knowledge. I've seen a few videos of people tweaking the carbs back & forth at low & high speed, occasionally holding holding a finger over exhaust (oilyness? temp?). These were glow mind you but the process looked mysterious.


----------



## tornitore45

What can I say? Just beautiful!   Must be satisfyingly after so much work seeing run so well.

Terry, are you running the engine in a close shop?  Is 20F out.   Last time I did that I I felt nauseous and headachy.


----------



## minh-thanh

*mayhugh1 !*
I watched your projects, All parts are made perfectly.. You are a master !
You're not making an engine, you're creating a work of art.
Thanks for sharing !!


----------



## kuhncw

Very well done, Terry.  Thanks for another great and educational build log.

Chuck


----------



## Eccentric

Thank you Terry.  It has been a wonderful and humbling experience following along with your build.  I have learn so much from your detailed explanations, photos and CAD models.  I can't tell you how much I appreciate the time and effort you put into the build log in addition to the time actually modeling and building the Offy.  I wish you the best, you are a true artist.


----------



## propclock

You are the master and  I Thank you.


----------



## burkLane

Thank you for the great write ups and pictures of your progress! Some of the best work on the net! 
I understand why my sprutcam post lists you as one of the authors!


----------



## ShopShoe

Terry,

Thank you for another great and inspirational build of another legendary engine.

You have so many skills that I always feel like it's Christmas when I see you have put up another post.

I also thank you for the generous way you respond to the questions you get asked.

Thank You for posting.

--ShopShoe


----------



## stragenmitsuko

Great Terry , another runner . And what a beauty it is ! 

My suggestion for a next build would be the snow engine . 

Pat


----------



## sbdtasos

Piece of art
congrats Terry for this masterpiece


----------



## prophub

stragenmitsuko said:


> Great Terry , another runner . And what a beauty it is !
> 
> My suggestion for a next build would be the snow engine .
> 
> Pat


I would love to see Terry do the snow engine! I'm currently gathering materials for that one.


----------



## oldCB

mayhugh1 said:


> The cam gear covers were gasket'd with Oracal vinyl before being installed, but the cam box covers were only temporarily set in place for now. There's an oil flow adjustment screw on the front starboard side of the engine which will be finally set while watching the top-end oil delivery with the engine running.
> 
> The block and crankcase side covers were installed next with each being sealed with a Teflon gasket. Since it would have been easy to drop one of the 0-80 block cover fasteners inside the crankcase, the crankcase covers were installed first.
> 
> The magneto (which is actually a distributor) was then mounted on the front cover bracket. A pair of timing adjustments involving the phasing's of the rotor and trigger magnets completed its installation. Since the ECM was needed for these adjustments, it was time to move the engine to its display/running stand.
> 
> With the crankshaft set to TDC in the number one cylinder's compression stroke, the rotor was aligned with the number one high voltage tower. Since the shaft driving the magneto spins at the same speed as the crankshaft, a 2:1 gear reduction inside the magneto drops the rotor speed down to match that of the camshaft. An alignment mark, visible on the top inside surface of the magneto, will be inline with the grub screw located on the rear of the rotor when it's properly positioned. This grub screw locks the rotor in place.
> 
> A collar containing the pressed-in trigger magnets was slipped onto the distributor driveshaft during the magneto's installation. Three grub screws lock it to the driveshaft so it spins at the same speed as the crankshaft. The pair of diametrically opposite magnets generate the four trigger pulses required for every two crankshaft revolutions. Before tightening the grub screws, the collar was aligned with the magneto so the CDI is triggered at TDC in the number one cylinder's compression stroke. A lever on the side of the magneto can manually advance the ignition timing up to thirty degrees.
> 
> Finally, the carburetor and exhaust subassemblies were added. Each was sealed to the head using one of the nineteen custom Teflon gaskets made earlier for this engine.
> 
> A set of plug wires was made up using repurposed automotive vacuum fittings (Dorman 47411) for plug boots that nicely fit the VR2L spark plugs. Before installing the plugs, they were temporarily fixture'd outside the engine to verify the ignition one last time. After they were installed, the engine had plenty of compression.
> 
> A little oil and gas were added and the engine cranked for a few seconds to verify it at least wanted to run before adding the radiator and (messy) coolant. With the four carb screws opened 3/4 turn, the little engine started right up. I shut it down after a few seconds since I really didn't want to run it without coolant.
> 
> There's just a few loose ends including the addition of the already completed radiator to finish this build. With no experience with multi-carb set-ups, nor carb design for that matter, tuning promises to be a learning experience. It seems I've elected to put four unknown and untested carburetors on the same engine. - Terry
> 
> View attachment 122867
> View attachment 122868
> View attachment 122869
> View attachment 122870
> View attachment 122871
> View attachment 122872
> View attachment 122873
> View attachment 122874
> View attachment 122875
> View attachment 122876


 Awesome build dude!


----------



## stihl1master

mayhugh1 said:


> The front-end machining on the crankcase includes a bore for the front crankshaft bearing and a pocket for a gear case containing bearing recesses for a pair of driven gears. One of these gears will eventually connect the crankshaft to the gear tower, and the other will drive the water and oil pumps. The Offy uses a dry sump oiling system, and its pressure and scavenger pumps will eventually be located inside the gear case.
> 
> The crankcase was set up in the mill vise and indicated for access to its front end. The location of the bore for the crankshaft bearing was picked up from the test rod running through the three bronze bearings. The rear bearing in the rear housing and the starter bearing in the not-yet-machined front cover each have a bit of 'wiggle' room since they're bolt-ons to the crankcase. The front bearing, though, will be hard fixed to the crankcase and must be on the same axis as the main bearings.
> 
> I was concerned about attempting an interference fit for the front bearing since I was unsure of just how much interference could be tolerated while drawing the crankcase halves closed. If the flat surfaces of the crankcase halves don't completely close against each other, not only will there be an oil leak, but the axis of the front bearing may end up displaced from the axis of the main bearings and create a bind in the crankshaft. On the other hand, too loose of a fit will allow the bearing to spin in its bore and damage it.
> 
> Boring the perfect fit would require more luck than I was willing to risk and couldn't be tested without removing the crankcase from its setup. So, I opted for a one thousandth oversize bore that would provide a clearance that I could later shim out - something that's possible with a split bore. Aluminum foil as thin as .0005" is used by some candy manufacturers on their chocolate treats and can be a sweet source shim stock.
> 
> The remainder of the gear case machining was completed including bores for the two driven gear bearings which were also bored a thousandth over. Although I'd have preferred zero interference fits for these bearings, the front cover will eventually contain a matching pair of bearings, and there's no way to align bore them in pairs. The front cover's wiggle room will likely be taken up by the starter bearing, and unavoidable errors in locating the positions of the two bearing bores will make the cover difficult to assemble unless the bearings have some wiggle room of their own. When assembled, there will most likely be enough friction created by positioning errors to prevent the gear bearings from spinning in their bores.
> 
> A trial assembly of the crankcase halves around the front bearing was successful. I found that adding a thousandth shim around only the upper half of the bore allowed the crankcase to close tightly around the bearing and allow the thousandth-under test rod to freely rotate inside all five bearings.
> 
> One of the things that attracted me to the quarter scale Offy is its faithful adherence to the original engine's great looking appearance. The painstaking detail in many of the model's individual parts will provide a number of interesting mini-projects with their own short term satisfactions that'll help keep me interested in such a long term project.
> 
> The first of these parts is the front cover. It encloses the gear case and contains the starter bearing which will be the sixth crankshaft bearing. Other than rearranging its mounting bolt pattern to accommodate the crankcase split, I duplicated Ron's design. It's finished periphery will provide a template for the later machining the crankcase's lower sloping sides. The magneto mounting bracket was an integral part of the casting for this part in the original engine. Ron attached a separate bracket to the cover with hidden screws and blended the seams with fillets of metal-filled epoxy. I used my Tormach to machine the cover and bracket as a single part. There isn't room for a front shaft seal, but Ron included a groove for a 12 mm x 1mm CS o-ring around the bearing's i.d. that should be effective against oil leaks.
> 
> My first serious mishap in this project occurred while removing the overhanging excess stock from the rear of the cover in preparation for its rear face machining. The large multi-insert facing cutter that I was power feeding in my manual mill grabbed the overhanging lip and pulled the end of the part partially out of the vise. This stalled the cutter until I was able kill power to the spindle. There was no damage to the already machined top surface, but there was a deep gouge on the part's back surface. With all the effort invested so far, I felt there was nothing to lose by trying to salvage the part with a tig-welded repair. The welding created some of its own damage to the topside surface, but the final result was much better than expected with no visible trace of the repair.
> 
> As it turned out, my biggest concern was with the mill itself since I had to hammer the R8 cutter out of the spindle using a long drift in place of the draw bar. The cutter had spun inside the spindle bore and was jammed against what remained of the collet key pin. Fortunately, TIR checks on the spindle bore showed there was no apparent damage, and re-tramming the mill seemed to return things to where they were before the accident.
> 
> With the cover installed on the crankcase, there's still no sign of binding of the test rod, but the friction of the cover's o-ring has added significant drag. - Terry
> 
> View attachment 111127
> View attachment 111128
> View attachment 111129
> View attachment 111130
> View attachment 111131
> View attachment 111132
> View attachment 111133
> View attachment 111134
> View attachment 111135
> View attachment 111136


This is art worked. is it all CNC, or hand work ??


----------



## stihl1master

mayhugh1 said:


> Much of last week was spent modeling the complex gear tower which includes a pair of front and rear halves, end caps, and a tightly integrated take-off block for the magneto. After a lot of frustration, I still don't have an assembly that I trust to begin machining. My wife would say it's because I can't follow instructions, and to an extent she'd be right. I've found a few online screen shots from those that have gone before me to be invaluable.
> 
> I took a break from the tower and returned to removing chips from the crankcase since its modeling had been completed. With the foundational machining done, I felt it was safe to finish up the external profiling that will finally give the crankcase its distinctive shape. Other than several o-ring grooves that are still planned, its bottom and both sides were finish machined. The bottom was milled using a tiny ball cutter in order to create an array of cooling fins with rounded tips and filleted roots.
> 
> The exhaust fan on my bead blasting cabinet is currently out of service, and so the photos show the machined surfaces straight off the mill. Some cleanup will be required, but that will become more obvious after the surfaces are bead blasted for the first time. - Terry
> 
> 
> View attachment 111263
> View attachment 111264
> View attachment 111265
> View attachment 111266
> View attachment 111267
> View attachment 111268
> View attachment 111269
> View attachment 111270
> View attachment 111271
> View attachment 111272





mayhugh1 said:


> The front-end machining on the crankcase includes a bore for the front crankshaft bearing and a pocket for a gear case containing bearing recesses for a pair of driven gears. One of these gears will eventually connect the crankshaft to the gear tower, and the other will drive the water and oil pumps. The Offy uses a dry sump oiling system, and its pressure and scavenger pumps will eventually be located inside the gear case.
> 
> The crankcase was set up in the mill vise and indicated for access to its front end. The location of the bore for the crankshaft bearing was picked up from the test rod running through the three bronze bearings. The rear bearing in the rear housing and the starter bearing in the not-yet-machined front cover each have a bit of 'wiggle' room since they're bolt-ons to the crankcase. The front bearing, though, will be hard fixed to the crankcase and must be on the same axis as the main bearings.
> 
> I was concerned about attempting an interference fit for the front bearing since I was unsure of just how much interference could be tolerated while drawing the crankcase halves closed. If the flat surfaces of the crankcase halves don't completely close against each other, not only will there be an oil leak, but the axis of the front bearing may end up displaced from the axis of the main bearings and create a bind in the crankshaft. On the other hand, too loose of a fit will allow the bearing to spin in its bore and damage it.
> 
> Boring the perfect fit would require more luck than I was willing to risk and couldn't be tested without removing the crankcase from its setup. So, I opted for a one thousandth oversize bore that would provide a clearance that I could later shim out - something that's possible with a split bore. Aluminum foil as thin as .0005" is used by some candy manufacturers on their chocolate treats and can be a sweet source shim stock.
> 
> The remainder of the gear case machining was completed including bores for the two driven gear bearings which were also bored a thousandth over. Although I'd have preferred zero interference fits for these bearings, the front cover will eventually contain a matching pair of bearings, and there's no way to align bore them in pairs. The front cover's wiggle room will likely be taken up by the starter bearing, and unavoidable errors in locating the positions of the two bearing bores will make the cover difficult to assemble unless the bearings have some wiggle room of their own. When assembled, there will most likely be enough friction created by positioning errors to prevent the gear bearings from spinning in their bores.
> 
> A trial assembly of the crankcase halves around the front bearing was successful. I found that adding a thousandth shim around only the upper half of the bore allowed the crankcase to close tightly around the bearing and allow the thousandth-under test rod to freely rotate inside all five bearings.
> 
> One of the things that attracted me to the quarter scale Offy is its faithful adherence to the original engine's great looking appearance. The painstaking detail in many of the model's individual parts will provide a number of interesting mini-projects with their own short term satisfactions that'll help keep me interested in such a long term project.
> 
> The first of these parts is the front cover. It encloses the gear case and contains the starter bearing which will be the sixth crankshaft bearing. Other than rearranging its mounting bolt pattern to accommodate the crankcase split, I duplicated Ron's design. It's finished periphery will provide a template for the later machining the crankcase's lower sloping sides. The magneto mounting bracket was an integral part of the casting for this part in the original engine. Ron attached a separate bracket to the cover with hidden screws and blended the seams with fillets of metal-filled epoxy. I used my Tormach to machine the cover and bracket as a single part. There isn't room for a front shaft seal, but Ron included a groove for a 12 mm x 1mm CS o-ring around the bearing's i.d. that should be effective against oil leaks.
> 
> My first serious mishap in this project occurred while removing the overhanging excess stock from the rear of the cover in preparation for its rear face machining. The large multi-insert facing cutter that I was power feeding in my manual mill grabbed the overhanging lip and pulled the end of the part partially out of the vise. This stalled the cutter until I was able kill power to the spindle. There was no damage to the already machined top surface, but there was a deep gouge on the part's back surface. With all the effort invested so far, I felt there was nothing to lose by trying to salvage the part with a tig-welded repair. The welding created some of its own damage to the topside surface, but the final result was much better than expected with no visible trace of the repair.
> 
> As it turned out, my biggest concern was with the mill itself since I had to hammer the R8 cutter out of the spindle using a long drift in place of the draw bar. The cutter had spun inside the spindle bore and was jammed against what remained of the collet key pin. Fortunately, TIR checks on the spindle bore showed there was no apparent damage, and re-tramming the mill seemed to return things to where they were before the accident.
> 
> With the cover installed on the crankcase, there's still no sign of binding of the test rod, but the friction of the cover's o-ring has added significant drag. - Terry
> 
> View attachment 111127
> View attachment 111128
> View attachment 111129
> View attachment 111130
> View attachment 111131
> View attachment 111132
> View attachment 111133
> View attachment 111134
> View attachment 111135
> View attachment 111136


How long does it take to run the program on a CNC mill ?? great work


----------



## mayhugh1

Thanks everyone for your kind comments. They're very much appreciated. 

Stihl1master:
I'd say the percentage of CNC was around 60%. Often a part like the crankcase or head received both types of machining. To be honest, my experience with CNC (or the way I use it) doesn't always result in a time savings over manual if I'm making just one piece of a particular part. For safety, I tend to take smaller cuts on my Tormach compared with making the same part on my Bridgeport clone. And so, the total machining time is often the same on many parts either way. CNC does let me make 3d cuts that would otherwise have to be accomplished with lots of filing, and that is where a major time savings can be had. Hope that helps. - Terry


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## srobovak

Congrats! Excellent workmanship. And thanks for taking so much time to share all the details with us.
cheers,
Branislav


----------



## johwen

An excellent project, a great engine model and an engine note to complete the package.
Well done John


----------



## mayhugh1

Even though I hadn't planned another Offy post, I thought I'd share a few things I've learned working with it during these past several weeks. Since I usually enjoy making engines more than running them, mine often end up on a display shelf with only an hour or so running time. It seems that once they're running reliably, I'm on to the next project. So far, even after running a liter of gasoline through it, I still enjoying playing with the Offy.

Being obsessive about oil leaks, the Offy was almost my first leak-free engine. There's some seepage around the forward end of the crankshaft due to an o-ring I omitted, but a proper fix would require a new front cover machined for a lip seal. Since it's relatively hidden by the front bracket and doesn't drip, I've decided to live with it. Fortunately, some of this oil seems to be wicking into the starter clutch and lubing it.

I've had doubts about the grease-packed seal inside the water pump I designed, and it started leaking right after a long hard run. In addition to leaking onto the display stand, coolant was also finding its way into the oil. Adding an o-ring shaft seal just ahead of the pump's rear bearing turned out to be easier than expected and eliminated the problem, but several oil changes were required to completely flush out the coolant.

Many cold garage starts and short runs soon caused water (a by-product of combustion) to begin accumulating in the oil. Although the head heats up quickly while running, the crankcase doesn't get hot enough to drive out moisture. Over time, its chocolate color warned that the oil was becoming a corrosive mixture of water and crankcase gasses. I expected to see puke oil inside the clear PCV hoses that had been routed to the oil tank, but they never contained anything but clean condensed water. It didn't make sense to continue piping this into the oil tank, and so I eventually vented the PCV hoses to the atmosphere.

The most frustrating issue I run into was trying to control the oil smoke in the exhaust. The oil holes in the piston groove just below the scraper ring don't seem to be enough to keep oil out of the Offy's combustion chambers. This same oil control scheme has worked well in deep sump engines, but seemed to be overwhelmed by the oil whipped up by the connecting rods inside the Offy's confined crankcase compartments. Testing showed the problem to be worse with straight 30W than with 10W-30, and so 5W-20 might be a worth try. If I were re-making the pistons, I'd mill oil return slots rather than drill holes.

My 'easy fix' to the smoke problem was initially to limit the amount of oil in the crankcase drains by maintaining a minimum amount of oil in the tank. Since I'd originally placed the tank's outlet near the bottom of the tank, this allowed only 10 mL of reserve oil - an amount determined by removing oil from the tank (while maintaining a flow in the pressure pump hose) until the smoke went away. Even with this minimum level, the plugs still showed signs of oil. A new problem created by such a small reserve, though, would be its increased vulnerability to crankcase vapors. To get around this, a new outlet was installed higher up on the tank which allowed me to increase the reserve oil nearly 10x.

During a two minute 3000 rpm run, the upper half of the radiator becomes noticeably warm since about half the gets moved through the engine. A thermometer showed the coolant in the upper part of the radiator to be just over 100F.
The actual flow was measured by temporarily diverting the output of the upper radiator hose into an external container. Coolant flows through the engine at all running speeds, and the flow rates roughly agreed with the measurements made during the water pump development.

However, worrisome air bubbles show up in the coolant at high rpms. There's no oil leaking into the coolant, and the bubbles haven't gotten any worse since the engine's very first run. I've noticed these same bubbles, which are likely due to a head gasket leak, in the Youtube videos of two other Offy builders. And so, before tearing into the engine, I decided to run a compression test to see if I had a major cylinder problem.

Compression tests on model engines are complicated by the small volumes of their combustion chambers. While running a test, the volume of the tester is effectively added to the volume of the combustion chamber which reduces the pressure readings. An additional issue with the Offy is the limited access to its spark plug holes created by the water outlet pipe.

I converted an inexpensive mechanical tire pressure gage purchased from Amazon into a compression tester. The meter and valve body were reused, but the Schrader end was replaced with a custom adapter specially machined for the Offy's 1/4-32 spark plug holes. The tester's internal volume was also determined in order to come up with a correction factor for the Offy's pressure readings. The huge 41% correction factor is an indication of the measurement problem.

My pistons produce a theoretical static compression ratio of 7.85 which by design is less than Ron's high compression pistons. This reduced c.r. should theoretically produce readings of 115 psi. Although I was prepared for one or two dramatically lower readings, all four were within a generally accepted 10% variation. My corrected readings were: #1 = 99 psi, #2 = 107 psi, #3 = 113 psi, and #4 = 99 psi. Although the two outside cylinders are a bit low, I'm enough satisfied with the results that I have no plans for a teardown. To be honest, I'm not sure how I'd improve on the current head gasket.

The engine continues to start easily and after a brief warm-up idles reliably at 1100rpm. The air bleed adjustments had more effect on the idle performance than I expected. There are no hot-start problems and, even without a choke, starting in a 55F garage hasn't been a problem. The stainless steel exhaust gets incredibly hot, and its previously polished chrome-like finish has become a golden yellow. With 25 degrees advance the engine will rev to its top-end of just over 5k rpm. The #1 and #4 carbs seem to be well matched to each other and so are the #2 and #3. There seems to be only an eighth turn adjustment screw difference between the two pairs. The plug insulator colors aren't the ideal tan color that I've been able to achieve on my other engines using TruFuel 4 cycle gasoline, but that might be related to the still excessive oil.

The radiator fan turned out to be more effective than I initially thought. At the end of a run, the engine cools down twice as fast with the fan running, and so the air it's blowing over the head is having more effect on it than on the radiator.

Lastly, our pond fish and turtles survived our infamous week long Texas freeze and power blackout, but it will take months to replace all the landscaping we lost. - Terry


----------



## Vietti

I too made a compression tester and was shocked by the low numbers.  Wonder how you calculated a correction factor?  I still use it but consider the numbers relative.

I  have a two cylinder engine that has oil control issues.  A well respected builder and collector suggested I try heavy (60-70) weight oil, the old Harleys used it.  I tried it and not sure it helped much but I'd be interested in your opinion re oil weight and oil consumption in model engines. 

One of  the best things I did to help control the oil getting past the rings was to go to 0 rings but we won"t go there.  At one time I had 4 ci rings per piston and oil drain holes around the bottom ring with no joy.  Tried three sets of pistons with different ring arrangements, drain holes etc.  Probably, like you, a very low oil level seems the best answer, though is is scary to consider such a low oil level.

Your engine is wonderful so I looked up your previous engines, equally outstanding.  What you do shows what is possible and encourages me to pick up my game.

John


----------



## The_reach

Oil choice for these smaller motors isn't something I had previously considered to make a huge difference, once again I'm surprised


----------



## stragenmitsuko

Commercial compression testers work with a shrader valve from a bicycle tire . 
Valves from a car tyre have a higher opening pressure . 

I found out when I made an adaptor for my tester and used a car tyre valve . 
Compression was abt 1.2 bar lower then with the tester's original valve .
This was consistent and repeatable . 

It was only then that I found out that there are two types of shrader valves . 
The bicycle tyre one has a much weaker spring .

Pat


----------



## mayhugh1

Vietti said:


> I too made a compression tester and was shocked by the low numbers.  Wonder how you calculated a correction factor?  I still use it but consider the numbers relative.
> John



John,
The pressure of a gas is inversely proportional to its volume. So, calculate or measure the volume of your combustion chamber and the internal volume of your tester. Then to correct your reading multiply it by (VOLhead + VOLtester)/(VOLhead). - Terry


----------



## mayhugh1

Pat,
The one I used:


			https://www.amazon.com/gp/product/B08CXLVKLQ/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1
		


has the weaker spring. - Terry


----------



## Vietti

Terry,

Thanks, I ordered one!  Still unclear how to measure the volume of the gauge fill with water somehow?

Are you going to try some 60 weight oil?

John


----------



## mayhugh1

Vietti said:


> Terry,
> 
> Thanks, I ordered one!  Still unclear how to measure the volume of the gauge fill with water somehow?
> 
> Are you going to try some 60 weight oil?
> 
> John


John,
I measured the volume of the meter by droppering in alcohol. The rest of the gage I was able to calculate. I also calculated the head volume. Right now I'm not planning to try any more oils.

By the way, I enjoyed your magneto article in Model Engineer Builder several year ago. - Terry


----------



## The_reach

Terry,

I have just about collected all the material needed to make a 1/2 scale model of this engine. In your opinion what would you change if you were able to do so due to making it on a larger scale? Any suggestions would be appreciated 

Jimmy.


----------



## johwen

When testing compression it is important to have a full open throttle to allow the full compression reading to take place if you are not aware of this. You will not get a top reading if this is the case. John


----------



## stihl1master

mayhugh1 said:


> John,
> I measured the volume of the meter by droppering in alcohol. The rest of the gage I was able to calculate. I also calculated the head volume.


would the use of a digital tester be easier and more accurate ??


----------



## dsage

Terry et.al.
If you have a scope you might want to try one of these. They are low volume, you can measure the peak pressure pulses and no need for a shrader valve. You can put it in place of a sparkplug with the engine running. (short the sparkplug wire to ground to protect your coil).
With a bit of training (Youtube search pressure pulse transducers) you can also diagnose valve sealing issues, valve timing,  blocked exhaust systems etc, etc. They are used in the automotive industry all the time now.









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You'll get best resolution if the sensor is just over the maximum expected in the application. For most work the 200lb version would be suitable.


----------



## Vietti

Dsage,

Great idea but beyond my capabilities.  What would be great is for someone to build one of these and then calibrate the common gauges like Terry recommended.  Then anyone could build one as Terry described and know the correction factor.

Terry, the magneto article and subsequent improvement articles by Don Grimm were kind of a disappointment to me.  I've been to many shows since the articles were published and seen very few, 2-3, magnetos in use.  Too bad, they are relatively simple and cheap to build, and they are within the capability of anyone who can build an engine.  Also more prototypical than a CDI and no batteries or Hall effect sensors etc.  Don Grimm's Red Wing with a low tension magneto is extremely reliable and runs for two days without drama at the shows.  He wrote a great build article in MEB.

The hardest part is winding the coil but that is unnecessary as commercial coils exist and low tension coils are easily wound by hand.  I've continued to work on magneto design such as the oscillating mag on my Red Wing.  I also have a new version of a magneto that uses commercial points and an old Stihl chainsaw coil, very easy to build.  Continue to look for small coils however, all the newer small coils since about the early 70s are made for CDI and don't work in a magneto. Gittig coils are still avaliable as are the Stihl coils, even some cheap ones from China.  If you have a suggestion of a small coil that could be used in a mag I"d love to hear about it.

John


----------



## Art K

Terry,
I have been following along but haven't said much. I just wanted to say that in talking to guys that have built the Offy they know its time to shut it down when they see bubbles in the top coolant line. That is the sign its getting hot. I'm glad that you were able to do a compression test and remove that possibility from the list of potential problems. When you get right down to it the cooling is just a few holes in a block of aluminum, not nearly enough. Great work by the way.
Art


----------



## mayhugh1

The_reach said:


> Terry,
> 
> I have just about collected all the material needed to make a 1/2 scale model of this engine. In your opinion what would you change if you were able to do so due to making it on a larger scale? Any suggestions would be appreciated
> 
> Jimmy.


Half scale is going to be a beast! I hope you do a build thread - it will be really interesting. Cooling would become an even bigger concern, I would think and so Ron's idea of a constant displacement water pump might be worth considering. You'll have some really deep oil and water passages to drill at half scale. If you choose to not split the crankcase but instead assemble through the side covers you'll at least have more room to work. I'm not sure how the gears will work out inside the gear tower - I'can't visualize how they will scale and keep the same ratios, but that's due to my current brain cloud. I can't wait to watch progress. Best of luck. - Terry


----------



## The_reach

mayhugh1 said:


> Half scale is going to be a beast! I hope you do a build thread - it will be really interesting. Cooling would become an even bigger concern, I would think and so Ron's idea of a constant displacement water pump might be worth considering. You'll have some really deep oil and water passages to drill at half scale. If you choose to not split the crankcase but instead assemble through the side covers you'll at least have more room to work. I'm not sure how the gears will work out inside the gear tower - I'can't visualize how they will scale and keep the same ratios, but that's due to my current brain cloud. I can't wait to watch progress. Best of luck. - Terry


I'm hoping that along with the other issues that being scaled up brings that it may be possible to go for the 1 piece head and block construction too though the jury is still out on that one. I've watched many of the build threads on this forum with great interest and looked at several that I would love to attempt "scaled up" but always come back to the offy.
100% there'll be a thread once I get my backside In gear and make a start. It's been a close run thing between the offy and a German designed 3 cylinder inline aero engine


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## tornitore45

> all the newer small coils since about the early 70s are made for CDI and don't work in a magneto.


Let me clarify that.  When a coil is not a coil.
The classic Kettering ignition coil is what a purist would call a 2 winding INDUCTOR. What characterize an inductor is the storage of magnetic energy.  It also act as a  transformer but that is not as fundamental as the fact that the energy for the spark is stored in the magnetic field.  When the contact open much of the energy is coupled to the secondary and goes into the spark, a small amount goes into the point capacitor.

CDI ignition "Coill" are actually  a high ratio pulse transformer, a completely different animal.  The energy is stored in the Capacitor at about 200V.  1/2 uF @ 200V  = 10 mJ   Incidentally, 200V is the same order of magnitude of the primary voltage on a Kettering Coil after the points open and the capacitor across the points charge to its peak.

Transformers change the voltage via the turn ratio, they do not store magnetic energy. They use a small amount of the primary current to create the magnetic field that is at the base of the transfer of energy.  The primary current is the sum of the load current reflected at the primary plus the usually much smaller magnetizing current.  The energy passes through the transformer.   The magnetizing current is something that may be undesirable sometime but is an unavoidable necessity,  since is normally designed to be minimized by assuring a high primary inductance the energy involved is minimal and is never stored to be reused later is just wasted.

Inductors have gapped cores, because the gap is where the energy is stored.  Except rare cases, transformers do not have gapped cores, the lamination are alternated to minimize the gap.

What happens when one try using a CDI coil as a Kettering coil?   The high primary inductance will ramp the current at a much slower rate, that current is technically the magnetizing current of the transformer, is not going to store much energy LxI^2   Big L small I.   When the point open, the small stored energy is barely enough to charge the capacitor across the points. 

The reason that CDI are easier to miniaturize is that Capacitors have a higher volumetric storage than Inductors.
Magnetic storage is limited by saturation, typically a hard limit of about 1 Tesla. On the other hand we have available very good insulators capable to withstand high voltage at extremely small thickness.  On top of that the permeability of the gap is set by nature to about 1, while the dielectric constant of the insulator allow for some manipulation by the material engineer, one can chose paper, Mylar, Teflon, Polypropylene etch.


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