Gearbox leaks oil into primary drive

[clanger9]

While sorting out the primary drive, I've noticed a quite significant oil weep from the gearbox sleeve gear bush:


It's leaking from the bush between the input shaft and the output sleeve gear (there's no leak from the main seal around the gear). The leak is big enough to leave a puddle of oil, so it needs sorting. There doesn't appear to be any sort of oil seal between the shaft and sleeve gear, so presumably it just relies on a close fitting bushes to stop any oil getting past? Mine appears to be worn (there is visible play between the input shaft and sleeve gear), but the bushes (041275) aren't listed by the spares scheme.

Has anyone tried replacing these bushes? Paul, I noticed on one of your photos you've fitted a green o-ring here. Was that to control oil weep here? And more importantly, did it work?

Alternatively, I've got another gearbox lying around here, so if the sleeve gears are identical (041273?) and the bushes are good, I could try swapping them over...

[Ozmadman]

You should be able to get the bushes at either Russell Motors, Andrew engineering, AMC Classic Spares etc. I changed my ones when I did my gearbox just to be sure but as you say, you can use another gear as they are all the same. Unfortunately you will need to strip down the gearbox completely to replace the gear as it is removed from the inside. You should also have a felt seal in that circular tin housing where the shaft comes through to stop dirt getting into the primary housing and to stop any oil getting out as it splashes around in there. It is a bugger to fit though as it is twice as thick as the space it squeezes into. The o ring was just an idea to seal the end just in case but in reality there is nothing pushing against the o ring so was removed as a bad idea that wouldn't work.

[clanger9]

Thanks, Paul. Good advice as ever!

My gearbox seems to work fine and (unusually) doesn't have any other leaks, so I'll probably suffer it for now.
There is a felt seal in there, but the weep seems to saturate it and then it drips down both sides of the primary case and onto the output sprocket. Oh well, at least it keeps the chain nice & oiled...

[Ozmadman]

Will have a look at my spare box and try to think how you can reduce the leak without stripping the box?

[clanger9]

Thanks, Paul.

I'm toying with this idea at the moment:


It's nothing more than a 20mm electrical grommet, but it happens to be exactly the right size to seal the gap and gently butt up against the clutch centre to keep it in place.
Maybe a complete waste of time, maybe it'll just disintegrate, but I think there's a chance it might limit the leak to a manageable rate...

[Ozmadman]

That looks like a good idea and if it works but disintegrates after a while then maybe a proper seal of the same size will do the trick, anything that is deep enough to be kept in place by the clutch may do. The problem is that both parts rotate unlike the normal situation where you would use a seal when only one part rotates. Whatever you do don't try to compensate by reducing the oil in the gearbox, these need to be kept as full as possible to prevent gearbox wear due to all the gears being near the top of the box, simple but not exactly a brilliant design. Also, use the centre stand, don't leave it on the side stand if you have one. Maybe if they had designed it differently, reducing the bush length and leaving enough room for a small seal in there that would have been better?