Loose layshaft bearing

Bobolink · Mar 21, 2010

I have eventually stripped my gearbox down for a re-build. The kick start was moving around under hard accaleration in 1991, so, after numerous thousands of miles including 2 up to italy & back with camping gear as well, I thought it was about time to have a look.

Everything is a little worn but not too bad, except the old layshaft bearing has been spinning in the case & now is about 0.010" loose.

Will a good grade of locktite hold the new bearing in or should I try to get a strip of shim steel in as well?

Regards

Bob.

Danno · Mar 21, 2010

I don't know if there's room to mill out the bearing pocket and re-size it properly or use an oversize bearing. Shimming the bearing assumes the pocket is worn perfectly concentric to the laysaft centerline (not likely, but possible if you're lucky) I would take the box to a machine shop to have that checked and possibly trued up before adding a shim or an oversize bearing. If you just shim it and it's slightly off-center, it could lead to other parts wearing unevenly at best and catastrophic failure at worst.

L.A.B. · Mar 21, 2010

Mick Hemmings recommends Loctite 638 but as Danno has said the bearing could end up slightly off centre.
http://www.bearingshopuk.co.uk/index.as ... 2Aod5yCMgA

It's also available in a 3 ml size tube, which is probably all you'd need.

rvich · Mar 21, 2010

If you use the Loctite and get it completely wrong on the alignment, we are talking about ten-thousandths of an inch, or probably in reality 5-thousdandths of error. Over the length of that shaft that is a very small percentage, or change in angle. I gotta wonder if the original specs where tighter than that.

If you have a machine shop true it for you, I wonder if they could guarantee results better than that. Any of you machinests out there think this is within tolerances?

Flo · Mar 22, 2010

Loctite will fail.
It will probably be that the bore is downwards from the mainshaft, as the force is downwards.
Putting shim around the bearing might work, the bearing plus the shim to be .001 to .002" bigger than the bore. Wrap the shim around the bearing & cut it to leave a small gap, deburr it, put it inside the casing, heat the shit out of the casing (gas ring on the oven works well), then push the bearing in. Best of luck!
Normally the best method would be to bore it out & insert a bronze sleeve, but the wall thickness is too weak in these gearboxes to do this.
I would be inclined to get a new casing.

Danno · Mar 22, 2010

Flo said:
Loctite will fail.
It will probably be that the bore is downwards from the mainshaft, as the force is downwards.
Putting shim around the bearing might work, the bearing plus the shim to be .001 to .002" bigger than the bore. Wrap the shim around the bearing & cut it to leave a small gap, deburr it, put it inside the casing, heat the shit out of the casing (gas ring on the oven works well), then push the bearing in. Best of luck!
Normally the best method would be to bore it out & insert a bronze sleeve, but the wall thickness is too weak in these gearboxes to do this.
I would be inclined to get a new casing.

I guess if you put it all back together without investing a lot of $ in new parts, the worst that could happen is a failure that would likely take out a few more usable parts + what you would need to replace the case and overhaul the box, so give it a try. That way, if it goes to hell, you haven't lost much.

Loose layshaft bearing

Bobolink

Danno

L.A.B.

Moderator

rvich

Flo

Danno

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