Clearance for main bearings

[olddaze]

Working on a `42 WLA. Installed new main races on both sides. I'm set-up ready to Line lap and size the bearings. Manual says .0005-.001 clearance for the sprocket side and .0008-.0012 clearance for the pinion side.
OK? Now how do you measure that? I'm using the TM 9-1879 military manual and most things it explains really well, this it don't.
My flywheels are still apart so using the sprocket shaft and pinion shafts as gauges is easy.
Only way I can figure is micrometer to measure bearing OD with shaft in and bore gauge to measure race.

Or, am I over thinking it and the numbers are arbitrary and it's more of a "feel" thing.

[koanes]

Measure the shaft diameter, bearing size times 2, and add your desired clearance for your race ID. Example: Shaft size .875, bearings .250 x 2 = .500, + clearance of .0007 gives you a race ID of 1.3757

[Steve Slocombe]

Harley probably did it in the factory by fitting up the machined races and shafts dry with different sized rollers. First you need to find the plug fit, where the rollers just jam in but there is no running clearance. Suppose you find this with +0.0006" rollers. Then fitting +0.0002" rollers gives 0.0008" running clearance, twice the difference between the plug fit rollers and the ones chosen. Even today you'll be struggling to measure within one two tenths of a thou with digital micrometers. Harley were helped by having factory rollers to plus 0.0010" and minus 0.0010" in tenths of a thou increments, when today we have just standard rollers and two tenths increment oversizes. Respect those guys from long ago!

[Paps]

Kyle and Steve provided the answers. If you have a tough time feeling with mics, go Steve's way. If you got a decent feel with mics, go Kyle's way. I always felt I had a really good feel with mics but for insurance purposes, I do my math fitting as Kyle explained but I try my first fit with one roller size larger than my math. If those all go in with little effort, try the next size up. keep going up in size until the last one will not fit into the race with the rest of the rollers. Drop down a roller size and settle with those rollers. You will have a .0006" to .0008" clearance fit then. 100 miles later, they will lap themselves in to .0008 to .0010". Paps

[olddaze]

Thanks guys. I'm in spec now.
Now it's time to assemble the flywheels and size the cam bushings.
Anyone have a 41-R-2265 ream for the cam bushings they wanna part with?

[Steve Slocombe]

Those cam bushing reamers are still out there nos. Have you tried www.jwboon.com or his US operation in Ohio at www.nosparts.com?

[koanes]

The only thing wrong with the o/s bearing fitting method is that without accurately measuring the hole, you have no idea about taper or bell mouth. It is very difficult to lap a race without enlarging the outer portion of the race, inside and out. When you think you have the fit you want, use a dial bore gauge to check for this condition. A tenth or two will not cause a problem.

[Paps]

The only thing wrong with the o/s bearing fitting method is that without accurately measuring the hole, you have no idea about taper or bell mouth. It is very difficult to lap a race without enlarging the outer portion of the race, inside and out. When you think you have the fit you want, use a dial bore gauge to check for this condition. A tenth or two will not cause a problem.

I agree...It is critical to have a true bore. I also agree with a few tenths will be ok. Anymore than that and the rollers will walk towards one side of the race, while running, and create excessive force and wear on the thrust surfaces. Tapers will ack like threads. They will deliver directional movement. Finish will do the same. Thus the real reasoning behind the cross hatch finish. Cross hatching delivers a two directional movement which helps to keep the rollers self centered within the race. Paps

[T. Cotten]

I strongly suggest obtaining a ground piece of rod stock that is the same size as the mainshafts, and long enough to extend through both races with the cases torqued.

Then use o-rings to space your rollers and cages upon it to simulate your entire crank assembly.

Although your individual races may be to spec'd clearances, any of the distortions that Kyle cited, or any misalignment of of the races themselves (frome welding or whatever), can cause bind or screwing thrust in one direction or the other.

You will not be able to determine this until you have cleaned the cases and attempt to install the crank.

A trial shaft such as I describe, however, can save a lot of tail-chasing.


....Cotten
PS: Lapps were a crude attempt at a "field repair" apparatus, and should be considered historical novelties only. Get thee to a Sunnen!

[Paps]

Great piece of advice Cotten !