Another Knucklehead Build

[AdvenJack]

Friends, I wonder if the opening poster and others, who are able to create such wonderful examples
as what we see coming together here, can imagine how a know-nothing like myself admires your skill.
I tip my hat to you who are doing these projects. Keep up the inspiring work!!!

 

[byawor]

here is a picture of the slot cut with edm. Looks worse in the picture and might be able to improve at a finer setting but it would take forever. There has to be a better way!
Bob

 

[mayhugh1]

The perimeters of the cam box and its cover will be machined together at the same time. The cover's inside surface will eventually be pocketed for several bearings that will need to be bored in alignment with their counterparts inside the cam box. The exact locations of some of these aren't yet known because they'll depend upon the gear reduction requirements of the starter motor which hasn't yet been selected. After the peripheries are machined, a rectangular fixture plate will be used to locate and machine the bores in both the cam box and its cover.

I began by temporarily joining two 5/8" surfaced aluminum plates using screws in a pair of their diagonal corners. The top plate will eventually become the cam box cover, and the bottom will become the fixture plate for both the cam box and its cover. The fixture plate's long sides will be machined parallel with the centerline through the dowel holes once they're drilled.

With the plates clamped in the mill vise, and the surface that will become the inside of the cover facing upward, I machined a .025" high contour into the plate that matched the interior cavity of the cam box but was radially reduced by .002". This operation turned out to be a leftover step from a previous iteration of my machining strategy that should have been deleted. Although it serves no real purpose in the current plan, with a bit less offset this boss could be used instead of dowels to locate the cover to the cam box. Dowels offer an additional advantage, though. They'll also perform as guide pins during final assembly when all the shafts inside the cam box must simultaneously engage their cover bearings as the cover is being inserted onto the cam box. (If you've ever changed a clutch and tried to reinstall the transmission while lying on your back under a car, you'll appreciate the usefulness of guide pins.) Clearance holes for the screws that will eventually secure the cover to the box were also drilled through both plates using the hole coordinates taken from the cam box.

The cam box workpiece was next mounted in the vise, and its bored center hole used to establish the reference for the dowel hole drilling operation. The cover/fixture plate combo was temporarily attached to the cam box using long 2-56 screws in most of the cover's mounting holes. Pilot holes for a pair of 3/32" dowels were then drilled through both plates and into the cam box using deep drilling parabolic bits. The long sides of the fixture plate were then machined parallel to the centerline through the dowels before finally being unbolted from the cover.

After reaming the pilot holes, dowels were pressed into the cam box. The pins were left 3/8" high which will place them flush with the top surface of the installed cover while also providing a generous guided gap during assembly so the cam box shafts can be nudged into their cover bearings. Thousandth-over holes in the cover and fixture plate provide snug fits between either of them and the cam box. When only the cover is used with the fixture plate, temporary oversize pins are lightly pressed through both provide a similarly snug fit.

The cam box workpiece was returned to the vise, and its center hole re-indicated. After temporarily installing the cover plate with a couple mounting screws, counterbores for the heads of the mounting screws were bored into the cover again using coordinates taken from the cam box. With the snug-fitting dowels, and no place to grab, it's already difficult to separate the cam box from its cover - something that will only get worse after the bearings and shafts are installed. To aid removal, I converted two of the 2-56 mounting screws, one adjacent to each pin, to 6-32 jackscrews. The cam box's previously tapped holes in those locations were filled with steel screws and milled flush to provide a durable jacking surface.

While the cover was still mounted to the cam box and set up on the mill, a decorative pattern of convex ribs was milled into its outer side. I duplicated Draw-Tech's stunning design which may be a little ambitious for someone without CNC capability. An alternative for a manual machine might be the same pattern but instead with concave ribs milled into the cover using a ball mill.

The last operation on the cover side of the fixture plate was to pocket out some clearance for the ribs just milled on the side of the cover. The cover will eventually be polished, and this clearance may prevent its surface from being marred during the later boring operations.

The fixture plate was finished up by preparing its back side for mounting up to the rear face of the cam box. For convenience, the cam box's center was transferred onto the centerline of the fixture plate's already drilled 3/32" dowel holes where a matching through-hole was bored. A second pair of dowel holes was then drilled and reamed to accept the 1/8" dowels located on the rear of the cam box. Drilled/tapped holes for the cam box's five attaching screws were also added. The fixture plate will not only help locate the positions of the cam box bores, but it will also back up and support its thin rear surface during their machining.

With the fixture plate completed and the machining of the cam box and its cover taken as far as possible with the workpieces still rectangular, it's finally time to machine their perimeters. Unfortunately, I've been noticing that my Tormach's spindle has been running unusually hot during the past several weeks. After the four hour long but very light milling operation on the cover's ribs, the tool and toolholder were so hot that I could barely hold them. The spindle turns smoothly by hand, and there's no abnormal noise under load. The runout, though, is now almost three tenths, and my notes show it was just over a tenth about a year ago. Replacement bearings were ordered last week, and so I hope to rebuild the spindle this weekend before beginning the heavy cutting on the case's large workpieces. Those bearings have logged a lot of machining time including a handful of crashes during the twelve years that I've had the machine, and so I'm really not disappointed that it's time for a rebuild. - Terry

 

[mayhugh1]

Replacing the bearings in my mill's spindle was relatively straight forward even though it took the better part of a day. As it turned out, the hardest part of the rebuild was the very first step which was getting the pulley off the spindle shaft. I did heat the cartridge housing to 300F in our oven before installing the new bearings, and much of the rebuild time was involved with the heating and cooling of this massive chunk of metal. The lower bearings had a slight tinge of color to them, but no signs of spalling. Setting the preload was a bit unsatisfying as it's one of those things that's hard to tell when you've got it just right. But after a couple tries, the runout is back to a tenth and the tooling is running somewhat cooler.

There's a lot of scrap associated with a part like the thick teardrop-shaped cam box sitting in the middle of a rectangular workpiece. My goal was to save some machine time by not turning it all into chips, but in the end it would have been much cheaper to have just chewed it all up.

The periphery of the cam box/cover assembly was machined in two separate operations with each having their own setup. The first was a roughing operation that milled a deep slot around the part's perimeter using a long corncob end mill while the workpiece was clamped securely in the mill vise. In aluminum and without flood coolant this can be a risky operation because with the cutter fully engaged in a deep slot, chip evacuation and built-up edge become major concerns. The operation ended .050" short of cutting completely through the workpiece so a bandsaw could be used to safely separate the part from the surrounding scrap. In addition, .030" safety stock was left completely around the perimeter of the part for the final finishing operation(s).

The reason why my starting workpieces may seem excessively large is because it was necessary to leave room for the end mill to pass safely between the part and the jaws of the vise. The workpieces were originally sized for a long 3/8" diameter cutter that I had planned to purchase just for this project. When I decided instead to use a 1/2" eBay special that I already had on hand, the larger diameter cutter didn't leave quite enough stock to counteract the clamping forces of the vise as the slot depth approached the bottom of the workpiece. As a result, the cutter was momentarily pinched in three places where the material around workpiece collapsed ever so slightly. With the conservative metal removal rate I was running, the machine had enough reserve to power through the pinch points even though its moans were those of an impending crash. If the cutter's flute length hadn't been longer than the depth of cut, the results might have been more spectacular. Fortunately, the gouges left behind in the part didn't exceed the depth of the safety stock.

I expected the finishing operations to be much less eventful, but I managed to make a bad last minute decision that became pretty expensive. For the finishing operations the workpiece for the right half crankcase was clamped in the vise for use as a machining fixture and the crankshaft center hole used to establish the machine's work offset. The cam box was packed with modeling clay wrapped in 'Cling Wrap' to add some dampening mass to maybe help with the quality of the final surface finish. A long($) 3/8" diameter four flute carbide cutter was used for the finishing operation, and the plan was to remove the .030" excess stock in two passes. In order to get a clean bottom corner, these operations were set up to continue .015" beyond the bottom of the part and into the sacrificial stock left on the outer face of the right-half crankcase specifically for this operation.

Before starting the finishing operations, I made a last minute decision to machine away the remnants of the bandsaw scrap still attached to the bottom of the part. This was done to avoid chatter marks in the surface finish that would likely occur when the 2-1/2" long cutter ran into the scrap during the first finishing pass. To cleanly remove the scrap I set up another contouring operation for the finishing tool using the same .030" offset that had been used for roughing. My mistake was that in order to avoid cutting air for most of the operation, I set the operation up to begin just above the layer of scrap.

This was a big problem because my cam box periphery contains two .200" radius'd inside corners. When the CAM software created the profile for the roughing pass it left more than the .030" offset stock in these corners since the cutter diameter was too large to reach their insides. When the profile for my impromptu pass was created, even with the same .030" offset, the 3/8" cutter was able to access the additional corner stock left behind by the roughing pass. And that's exactly what it did just seconds into the operation and with a full 1.9" depth of cut. The machine didn't have enough power to bail me out of this one, and it abruptly crashed just before breaking that very expensive cutter and ruining the collet. Again, the safety stock protected the part from the carnage I created. In the twelve years I've owned the Tormach, I can remember hitting the emergency stop button four times, and now two of those have been involved with these case parts.

After recompiling the operation to start at the top of the part, the remainder of the finishing steps went as planned. I didn't have another 3/8" tool with 2-1/2" long flutes, but I was able to get by with grinding down the lower portion of the shank of a shorter tool. Hoping that I've learned from my mistakes and that my machining process is now debugged, my next step is to do it all over again with the crankcase halves. - Terry

 

[doc1955]

Nice end product I can relate to roughing with a larger end mill then having issue in the corners with a finish cutter. But in the end she looks really nice!! I'm still in the modeling stage and doing some changes here and there.

 

[mayhugh1]

Doc,
Did you have any problems matching up the perimeters of the two crankcase halves and the cam box?
Terry

 

[doc1955]

Doc,
Did you have any problems matching up the perimeters of the two crankcase halves and the cam box?
Terry

Not sure if I did those were modeled up some time back. I do know I have been struggling with the drawings and have changed things to suit me so if I did I'm sure I just changed it so they matched.I have all the externals modeled up starting on the internal stuff. I thinking of building this engine next but I have been modeling up the Hoglet at the same time and may do that one first. If I do the Hoglet I'm going to change it to have a full lower end case. Sitting here I do remember I had to make some changes on the case as they didn't match up. Sorry I don't remember what but I do remember putting the pieces together and then struggling to try and figure it out and then just changing it so they would match up.

 

[kvom]

I had missed this build thread until today and was happy to catch up on another of Terry's builds. As always lots of good machining tips.

The "tyranny of the corner" got you like it has me in the past. A good article by Bob Warfield on "plunge milling" showed me that roughing deep profiles by repeated plunges (similar to chain drilling) is often the best strategy for smaller mills as the Z-axis is almost always more rigid that X or Y, plus there's no side forced on the tool.

The clay packed into the chamber to reduce resonance was new to me. Good tip for making thin walls.

 

[TheHomeMechanic]

Can you actually machine all this on a manual mill? It's very nicely done. I'm new here so i have not much experience yet.

 

[mayhugh1]

My plan to machine the peripheries of both crankcase halves together as an assembly remained unchanged even though their stack-up was going to be greater than that of the cam box and its cover. Since one face of each workpiece still contained some excess stock, my first steps were to remove as much of it as possible in order to minimize the total height. The right-half crankcase workpiece would be on the top of the stack, and its top surface was finish machined first. After facing off the sacrificial stock left behind after the cam box machining, the groove for an o-ring that will eventually seal the crankcase to the cam box was machined.

The location and orientation of each crankcase half inside its workpiece is precisely known. The dowels insure the two halves can be consistently assembled before and after being cut free from their workpieces. The dowel centerlines, which are parallel to the long sides of the workpieces, define the parts' orientations with respect to the fixed jaw of the vise. The crankshaft center hole, bored through both centerlines, provides the machining reference.

Although not necessary, it was convenient to machine the pockets for the crankshaft bearings and the rear shaft seal while the workpieces were still rectangular even though the parts' orientations really aren't important for these particular operations. Light-to-moderate press fits, determined by a few practice pockets on a piece of scrap, were used for all three. Even after twelve years my Tormach can still interpolate a circular pocket that's x-y symmetrical to better than three tenths. Since the bearings are open style, they won't be installed until after all the crankcase machining is completed.

The workpiece for the left-half crankcase will be on the bottom of the stack. Its backside surface also contained some excess stock that was faced off. The two workpieces were then bolted together using the eight crankcase fasteners that will be used to finally assemble them. In this set-up, the bottom workpiece is too short to contact the vise jaws, and although the top workpiece sat higher in the vise than I would have liked, pinching wasn't as much of a risk as it was during the machining of the cam box.

The crankcase fasteners alone wouldn't prevent the crankcase assembly from falling free from the top workpiece once the slot depth reached the seam between them. Rather than add additional fasteners outside the perimeter of the crankcase to keep the assembly intact, I decided to let it to drop. The roughing slot operation would be restarted after removing the carcass of the top workpiece and re-referencing the machine to the crankshaft hole in the bottom workpiece. This effectively cut the slot depth in half and decreased the risk associated with the remainder of the machining.

As before, a 1/2" corncob roughing end mill was used to machine the .030" offset slot around the perimeter of the assembled pair. Admittedly, in this operation, I wasn't using the tool as it was intended to be used since I was essentially cutting only with its tip. With the very shallow depth of cut taken per revolution around the contour, efficiency was very poor. Without flood coolant, though, I was more concerned about re-cutting chips inside the slot and creating a built-up edge on the cutter than I was about tool life. My hope was that the corncob flutes would be better suited for dealing with the re-cutting than those on a conventional end mill.

The periphery machining was compiled to stop short of cutting completely through the bottom workpiece since some additional features were required on the rear surface of the left-half part. Two finishing passes were made on the perimeter of the assembly before completing a bit of additional machining on the mounting arms of the right-half part. I don't normally run two finishing passes, but a lot of insurance stock remained after roughing. It was best removed in two passes with only the final one being an actual finishing pass. When completed, the periphery machining of the right-half crankcase was finished, and it was removed from the mill.

The left-half crankcase periphery machining was also completed, but a few additional operations remained for its rear face. Since performing these would cut the part free from its workpiece before they could be completed, the slot was filled with Devon Five Minute Epoxy to retain and stabilize the part inside its workpiece during these operations. When completed, the workpiece was heated in an oven for a hour at 350F in order to release the epoxy. While wearing oven mitts, the part was easily and cleanly pushed out of its still hot workpiece.

All four case components fit together perfectly with no filing or blending required to match their adjacent surfaces. After machining the bores for mounting the cylinders and oil fittings, the crankcase halves will be bead-blasted to give them a faux casting appearance. The cam box will eventually be finished similarly, but first there is a lot of work to be done on its internals. - Terry

 

[mayhugh1]

More Photos...

 

[doc1955]

They look really nice good job!
I'm working on the Hoglet now redoing the lower end to make it a fully enclosed bottom end and still have the variable timing set up. I'm planning on building the Hoglet first then the Knucklehead if I find the time this winter.
You have done a nice job on the case set up man I hate working with long end mills like that. When I get to that stage (if I ever do) I'm going to try load the pieces on the alignment dowels so I can do one piece at a time (we'll see).
You need to be happy with the way yours look and I must say you take some really nice picture also every time I try to take stills they end up blurry.

 

[mayhugh1]

I hate working with long end mills like that. When I get to that stage (if I ever do) I'm going to try load the pieces on the alignment dowels so I can do one piece at a time (we'll see).

That's probably what I would do if I had it to do over again. What I did was just to see if I could do it. The part I enjoy most about this hobby is planning complicated machining setups, but in this case there were too many steps and too much risky effort that I wouldn't recommend to anyone else. -Terry

 

[mayhugh1]

On long term projects I like to build up subassemblies that I can play with and test along the way. Breaking up a complicated build into a checklist of mini-projects provides some short term satisfaction and incentive that helps keep me going on long term projects. My goal for final assembly is, as much as practicable, to end up integrating a collection of known working blocks rather than fitting and first-time assembling individual parts.

With the cylinders and head assemblies completed, it seemed reasonable to next prepare for the crankshaft build-up since only the cylinder deck machining remained to complete the crankcase. This included the bores for the cylinder skirts as well as the drilled and tapped holes for the cylinder mounting studs and oil fittings. When this was completed, holes for the motor mounts were drilled and tapped into the bottoms of the crankcase mounting ears. The crankshaft halves were later bead blasted and the crankshaft bearings pressed into place. The rear oil seal will be pressed in just before the crankshaft is finally installed.

Some sort of assembly stand will be helpful during the crankshaft build-up, and so I fabricated something simple that I'll use now for assembly but later add to for display. Its uprights were machined from 3/8" x 1" hot rolled steel that were welded onto a 6"x12"x3/8" steel plate. It's a heavy stand that shouldn't move around while the engine is running, but I wanted to allow the engine to freely shake while idling. I machined a pair of motor mounts from a sheet of 1/2" thick rubber that I bonded to the stand's uprights. I don't like machining rubber, and it's really something of a 'stretch' to even call it machining, but after a full frustrating day I had a pair of mounts that I could live with.

The SHCS's for the motor mounts screw in through the bottom of the engine to avoid later conflicts with the starter motor. Holes were drilled through the baseplate directly below them so they could be accessed with a hex wrench. The lengths of the mounting bolts were carefully trimmed so they bottom out in the tapped holes in the crankcase before significantly compressing the rubber. In order to keep the bolts in place, their heads will later be cross-drilled for safety wire.

A hole was also drilled through the baseplate directly below where I plan to add the cam box's oil drain plug. With the engine sitting so low on its stand, there'll be no room between it and the baseplate for a drain pan. Instead, used oil will be drained through the baseplate and into a container held below it.

The stand was finally rattle-can'd with the Rust-Oleum textured paint that I've used on a number of engine stands since it easily hides imperfections in unfinished and welded surfaces. After a couple days of curing, it also seems to be resistant to engine fluids. I usually machine an integral drip tray into the baseplate directly below the engine, but that needed to be done before the stand's uprights were welded in, and I forgot to do it. Hopefully, with all the o-rings I've added to the engine, leaks won't be a problem.

The next step is to begin work on the crankshaft. This should be a real learning experience since the crankshaft construction in the downloaded drawing closely parallels that of the full-size engine with its three piece construction and tapered-ends crankpin. I've been studying Youtube videos dealing with rebuilding Harley crank assemblies, and what's ahead looks pretty hairy. - Terry

 

[kuhncw]

Very nice work, Terry. Thanks for posting the photo showing how you protected the parts for bead blasting.

Chuck

 

[natalefr]

Awesome !

 

[stragenmitsuko]

Is it me or is it just the camera angle ?
Somehow the cilinders seem to be pretty small compared to the crankcase .

I like the bead blaseted look .
What kind of blasting abrasive do you use ?

 

[mayhugh1]

Is it me or is it just the camera angle ?
Somehow the cilinders seem to be pretty small compared to the crankcase .
I like the bead blaseted look .
What kind of blasting abrasive do you use ?

Well, now that you mention it ...
Here's a photo with the heads sitting on the cylinders - much better.
By the way, I just use glass bead media from the local harbor Freight.

 

[stragenmitsuko]

Still ... looking at some pictures on the netthe cilinders seem to be taller then the cranckase .


Please don't consider this as criticism , its just an observation

 

[mayhugh1]

I've owned several motorcycles (all Asian), but in thirty years of riding I've never been inside a crankcase. After studying Draw-Tech's crankshaft drawing, I spent several hours watching Youtube videos to get some background and familiarize myself with Harley crankshafts. I developed a particular fondness for a series of videos (Youtube search 'Tatro Machine Knucklehead') dealing with an actual Knucklehead engine rebuild. Although it ended tragically for the owner, it was apparent that Draw-Tech's crankshaft was very similar to the one in the original full-size engine.

The full-size crank assembly has two shafted flywheels and a crankpin with ends that are tapered and threaded. During assembly, large nuts, tightened to some 100 ft-lbs, draw the pin into matching tapers machined into the inside faces of the flywheels. The assembly is then mounted in an on-centers alignment fixture so the runout's of the two outer shafts can be simultaneously monitored. What seems like a brutal alignment process is actually some intelligent hammering, spreading, and pinching of the two flywheels in just the right places to reduce the typical .010" starting runout to a couple thousandths or less. The connecting rods use roller bearings on their big ends, and so they have be installed on the pin before assembly.

Many of us have machined perfectly adequate crankshafts with simple cylindrical crankpins attached to the crank throws with pinch bolts. Several alignment issues disappear if the crank halves are machined from a single billet, and the crankpin hole is drilled and reamed before sawing the halves apart. Since this technique is time consuming and creates a lot of waste, some builders instead opt for a five piece assembly with separate shafts.

The tapered crankpin is capable of handling the power requirements and allows the rods to be serviced. But it adds significant complication and risk because tapers must be machined in four individual parts, and any imprecision in their machining can create misalignment in the final assembly. In addition, the major diameters of the flywheels' tapers, being non-measurable two dimensional quantities, will determine the depths of the crankpin inside the flywheels and therefore the side clearances of the rods in the final assembly.

These concerns create reasonable arguments for tossing aside what will be a hidden-from-sight scaled-down version of the crank and instead fabricating a more conventional model engine crankshaft. Besides 'wimping out', though, this would require reshaping the crank halves to accommodate the pinch bolts which, in all likelihood, would significantly reduce the rotational inertia of the relatively massive Draw-Tech crank. An alternative would be a conventional crankpin held in place with taper pins, but I was concerned about being able to remove them if the rods ever had to come out.

All engines, big or small, benefit from some amount of rotational inertia to keep them rotating between plug firings at low rpm's. One and two cylinder four-cycle engines benefit the most. (It turns out that Harley flywheels are so effective that some owners reduce their older engine's idle speeds to the point where the oil pump can barely function, just to show off that world famous staccato.)

The Draw-Tech Knucklehead includes an additional external brass flywheel, reminiscent of a steam engine, that adds additional inertia to the engine's rotating mass. I plan to replace this with a faux roller sprocket or a belt drive that will look more at home on a motorcycle engine, but it won't be as an effective flywheel. I don't want to give up the rotational inertia of the Draw-Tech crank assembly, and so I decided to stick closely with its design. I had enough Stressproof on hand for two attempts. The drawing called for a finished crank flywheel diameter of 2.83", but since my material was only 2-3/4", my crankshaft flywheels ended up a bit smaller.

My plan did not include turning the crankshaft between centers as one might expect. The modified cross slide on my Wabeco lathe won't allow a cutting tool to access the tailstock end of a workpiece supported by a conventional dead center. The stock cross slide will allow this, but its lightweight construction greatly limits the lathe's precision and surface finish quality. When using the tailstock, I often have to use an expensive long nose live center that can add up to three tenths of its own runout. At the end of the day, turning between centers can be somewhat counter-productive on this lathe.

Construction began with skimming the workpiece o.d. to a consistent diameter in my Enco lathe where I faced both ends and center-drilled one. The workpiece was then moved to a three-jaw chuck in my little Wabeco where, in conjunction with the tailstock, the o.d. was taken to its finished diameter over as much of its length as I could access including the portion that would eventually become the flywheels. The outer shaft was then turned and fitted to the outboard crankcase bearing. At this point, the o.d.'s of the shaft and the flywheels were concentric, and what will become the outside face of the outer flywheel was normal to their axis. A dial indicator showed all three TIR's were less than two tenths with the tailstock engaged and three tenths with it disengaged.

The chuck, with the workpiece still attached, was then taken to the mill where the crankpin through-hole was drilled and reamed. The flat-back chuck insured the hole ended up parallel to the axis of the bearings and identically drilled through both flywheels. A recess for the crankpin nut was then machined into the face of the outside flywheel, and material required for balancing the assembly was removed. Some practice material in a vise is visible in the photo of this operation. A 3/8" end mill with more than two inches of stick-out was required to work around the shaft, and some fine tuning was required to determine the speed, feed, and doc for minimum chatter.

The workpiece was returned to the Wabeco in a six-jaw set-true chuck so the shaft on the cam box side of the crank could be turned. The workpiece was gripped on the finished flywheel diameter which I was now only able to indicate to what would have to be called +/- three tenths because the TIR reading had picked up a second bump in an opposite direction to the first one. The Wabeco and tailstock center bearings left their runout imprinted on the workpiece when it was turned the first time, and now with the workpiece back in the lathe but oriented differently on the spindle, a second copy of their runout was now being indicated. I tried alternate orientations, but differences between the chucks I was using prevented me from improving it.

The fresh end of the workpiece was then center-drilled for the tailstock center, and the shaft diameters for the crankshaft and cam box bearings were turned and fitted. The measured TIR of the shaft had returned once more to two tenths with the tailstock engaged and three tenths with it disengaged. Although it appeared that the second bump was gone, it really wasn't. A second copy of the Wabeco and tailstock runout was now machined into the workpiece, and both will appear when the runout's on the ends of the two shafts are compared.

The chucked workpiece was returned one last time to the mill where the second nut recess and the balance area were machined on the face of the cam box side flywheel.

I slid a couple ball bearings from my scrap collection onto the two shafts so a TIR baseline measurement could be made with the work in progress sitting on a pair of v-blocks. The result was .001" which included the blended humps in the workpiece TIR as well as the runout's of the two ball bearings. Just for interest, I also measured the three runout's with the workpiece held between centers on my lathe. Since the workpiece hadn't been turned between centers, I wasn't expecting stellar results. However, the TIR of the output shaft measured .002", the cam box shaft measured .001", and the flywheels measured .0025". If this had been an actual Knucklehead crankshaft completed at a Harley assembly plant, it would have actually (although just) passed their QC.

I suspect the first measurement is probably the one that's most important to me. After completing the machining and assembly, my current plan is to compare the runout's of the two flywheels while the shafts are in ball bearings on v-blocks to see how well the machining turned out. - Terry