Quarter Scale Merlin V-12

[petertha]

Wow. It looks menacing just standing there!

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

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

 

[mayhugh1]

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

 

[Ken I]

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

Regards,
Ken

 

[DICKEYBIRD]

They do use sealant - typically "Hylomar"

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

 

[ICEpeter]

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

I intend to give it a try.

Peter J.

 

[mayhugh1]

Good tip ... Thanks - Terry

 

[DICKEYBIRD]

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

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

 

[maybach_man]

FYI Section d4 gives the specs

 

[10K Pete]

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

Pete

 

[Vixen]

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

Simples

Mike

 

[Ca-g]

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

 

[10K Pete]

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

Pete

 

[mayhugh1]

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

 

[deboom_j]

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

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

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

John

 

[mayhugh1]

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

 

[mayhugh1]

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

 

[RonC9876]

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

 

[mayhugh1]

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

 

[mayhugh1]

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

 

[mayhugh1]

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