Layshaft bearing replacement reality check

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Jun 14, 2007
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Next project for my Commando is layshaft bearing replacement - just as a precaution, as no bad symptoms yet. And for all I know, the PO may have done the job already, but unless I check, I'll never know - and if I'm going in there, I'm darned well putting in a new one.

I've got to research the job a bit more, to be sure, but a couple of very preliminary questions:

- Does the primary HAVE to come off? Just been there, done that (to replace sprockets/chain and alternator/rotor), and would sure like to avoid doing it again so soon....

- Does the gearbox HAVE to come off - I am hoping I can use a blind-hole bearing puller and avoid taking the gearbox off. I'll freeze the bearing to shrink it a bit and drift it in, carefully, with an appropriate socket.

Such is the hope, anyway. Thanks folks - B
Not really the answer that you want to hear here Brian. To do the job properly, you really do need to remove the box.

It can be done but as far as I am concerned the only safe way to drop the new bearing in is to warm the case in an oven and let the bearing seat with a clonk. The area of case is so thin and the risk of a bearing subsequently spinning is great if the housing is damaged.

If the PO has replaced the bearing, there is a good chance that he has used a roller and this can be checked by removing the layshaft without disturbing the primary drive. With a bit of luck you can just reassemble. If you do need to remove the box though you will find that it would have been easier to dismantle the primary while the box was still in one piece.

To be perfectly honest, I would probably plan on replacing all the bushes (including the layshaft bush in the kickstart) while the box is apart, just for peace of mind.
This is one of those jobs that when you look at you think it would be simple to do with the box in the bike. Trust me, you'll spend more time farting around than just pulling the box. It makes it much easier to clean the inside of the box anyway.

The primary doesn't really take that long to pull. And as 79X100 says, might as well check the bushes while your in there. Then you can button the whole thing up and go riding knowing that the gearbox is right!
Also check the kickstart shaft for cracks. On my 850 box it was cracked where it's machined back for the pawl, right at the bottom of the V. My machinist said it's pretty common.

Pulling the box is another example of a little extra work up front making the overall job much easier. Just do it. Heck, after pulling the primary a few more times you'll be able to do it in your sleep! :lol:

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