Hitchcocks Forum

Can anyone advise me on how to cure an oil leak from around the gearbox sprocket? This is on a 2001 iron barrelled 350 bullet.


For the avoidance of doubt, I'm not talking about the sprocket that drives the final drive chain, between the rear wheel and the gearbox.


6 months ago I replaced this sprocket to up the number of teeth and modify the gearing. Now, when I crawl under the bike and shine a torch, I can see lots of gloopy oil dribbling all the way down to the side stand. I might have mucked something up when I changed it. Hitchcocks parts book shows what looks like a rubber o-ring between the sprocket and the gearbox, but when I click on it it says "no parts available". Any advice please?

Hi Dave it could be coming from either the gearbox mainseal or the primary case seal, my guess if it is dribbling down to the sidestand I'm guessing the primary case mainshaft seal. I'm guessing you didn't replace it when you had it apart

I have the same problem with my 1960 Clipper and wasn't sure if the leak is from the gearbox or the primary chaincase. After investigation, I'm sure my leak is from the gearbox as I've been monitoring the oil levels in the gearbox and the chaincase. If the oil stops dribbling out the chaincase level screw on checking it means it's the seal on the chaincase. If the oil stops coming from the gearbox level plug, then the oil must be leaking from the gearbox. After running the engine a few times with the oil sloshing around you need to wait until the oil settles in the gearbox and chaincase before checking the levels again. I've put new seals in both the chaincase and the gearbox without curing the problem. What the cure is, I've yet to establish.

O dear, I see I made a typo in my original explanation. I meant to say, I AM talking about the sprocket that drives the final drive chain, to the rear wheel. So this is nothing to do with the primary chain case.



Sorry to see that others have had similar tricky problems.

Ok so if is coming out of the gearbox then fit a sealed bearing in the drive side and fit a new seal