Layshaft Bearing Depth

Add my name to the list of those who have had layshaft bearing failures this year. Mine happened while leaving the parking lot at work on Tuesday afternoon. I consider myself blessed that it didn't happen that morning on my way to work, a crowded 17 mile, 70+ mph urban interstate commute. Got the familiar bump on the back of the leg from the K/S, looked down & saw the K/S at 6 O'clock, so I pulled over immediately, shut it down, & pushed it back to the motorcycle parking lot to retrieve later with my truck.

Disassembled my gearbox in situ to find a disintegrated Portuguese FAG 6203, balls & pieces of brass cage strewn about the bearing cavity & the sump. Looks like I lucked out (again) because there was no other damage to gears or shafts, the layshaft bearing outer race was still snug in the case, and no sign of a crack in the case radiating out from the layshaft bearing counterbore.

There was some damage in the layshaft bearing counterbore. Evidently when the cage let go a couple of the balls exited the race towards the bottom of the counterbore (towards the clutch) and were wedged outward between the case & the bearing outer race. This actually pushed the race about 1/3 out of it's bore, and the balls rolling around in that gap mashed some of the case into the bearing land area. I was able to modify a 2" sanding disk to fit in the counterbore, mount it in a long-nosed die grinder, and sand down the mashed aluminum to restore the land.

My question is how deep should the layshaft bearing counterbore be in the case? I presume it should be equal to the width of the layshaft bearing, but a sanity check depth measurement would be very helpful. Anyone have an undamaged gearbox apart that could take a quick measurement for me?

Thanks for your time,

Mine's apart, measures .4650" depth

Thanks Concourse for the quick response & dimension!

I am a little unsure, but this topic has caused me to wonder about whether this depth is critical since the layshaft typically gets shimmed at the outer end. If it is the difference of a few thousandths then I wonder if you should just be planning on doing a thorough job of shimming at the (right) outer end of the shaft?

Russ

Yes, layshaft shimming will be required since I will be installing the superblend-type roller bearing. I just wanted to ensure that the bore was properly reworked so the race will be seated fully prior to installing the race.

I find this shimming stuff a real bitch and have a good quality ball bearing in place.

That being said, i may in the future go back to a roller type(superblend) bearing, but I will go through the process of shimming the outer race in the case rather than putting rear iso shims that need to be relieved and cause problem, as far as i am concerned, with the kickstart.

Yes, this will be some what of a hassle, but it will be proper, IMHO.

There are two gaskets in the tranny that are totally unneeded for anything but gasket sales so can remove one or both instead of shiming to get nice lay shaft support and ks rachet function.

hobot said:

There are two gaskets in the tranny that are totally unneeded for anything but gasket sales so can remove one or both instead of shiming to get nice lay shaft support and ks rachet function.

Click to expand...

Yes, I agree. This is a good precautionary statement to take in account for the gasket thickness between the inner cover and shell when shimming.

pvisseriii said:

I find this shimming stuff a real bitch and have a good quality ball bearing in place.

That being said, i may in the future go back to a roller type(superblend) bearing, but I will go through the process of shimming the outer race in the case rather than putting rear iso shims that need to be relieved and cause problem, as far as i am concerned, with the kickstart.

Yes, this will be some what of a hassle, but it will be proper, IMHO.

Click to expand...

The shimming of the shaft is a no brainer and worth it as far as using a better bearing in a place known for failures of ball bearings.
The shims don't move at all until one kicks the engine over and then they stay put behind the kicker shaft.
You need a dial indicator and a Dremel tool or round file to open the ID of the shim.
Don't put the balls back in, roll with the times.
So simple even a caveman can do it!

Guido said:

pvisseriii said:

I find this shimming stuff a real bitch and have a good quality ball bearing in place.

That being said, i may in the future go back to a roller type(superblend) bearing, but I will go through the process of shimming the outer race in the case rather than putting rear iso shims that need to be relieved and cause problem, as far as i am concerned, with the kickstart.

Yes, this will be some what of a hassle, but it will be proper, IMHO.

Click to expand...

The shimming of the shaft is a no brainer and worth it as far as using a better bearing in a place known for failures of ball bearings.
The shims don't move at all until one kicks the engine over and then they stay put behind the kicker shaft.
You need a dial indicator and a Dremel tool or round file to open the ID of the shim.
Don't put the balls back in, roll with the times.
So simple even a caveman can do it!

Click to expand...

I hear ya, guido. Been there done that. Got all the tools and have done it a few times. Results vary. I simply just don't like or prefer that particular process. As i said, although a bit more detailed, I believe there is a better way. If a roller is a more permanent solution, then a shimming process should match it.
As with shimming mains in the cases, so should the layshaft superblend.

When it come down to it, it's not a big deal to put the layshaft stack in place, the inner cover with the kickshaft and take the reading. The real trick is taklng a good educated guess on how much shim to start with. Pulling and pushing in the outer race should of course be limited, but is it not the point of the superblend layshaft bearing in the first place to not have to go back in there?