Oil leak

[AWJDThumper]

There should be a greased felt washer on the bush that projects to the left of the gearbox sprocket - it's there to keep muck off the clutch seal. The gearbox seal bears on the gearbox sprocket journal on the RHS of the sprocket. Unfortunately, this doesn't have the benefit of a greased felt washer protecting it and the journal can pit under the seal causing the leak. It's always best to replace seals especially after you've gone to the trouble of dismantling the engine to get at them.

[Phil C]

So is this right: there should a felt washer showing on the photo attached; and to look at at the gearbox seal I need to remove the nut and sprocket shown on the photo?

[AWJDThumper]

Exactly right. The felt washer is about 1/4 thick and needs to be greased before use.

However, can you remind me whether the clutch seal bears on the clutch shaft or the sleeve bush projecting from the gearbox? In other words, does the seal fit tightly around the shaft or the bush?

If the former then one possible source of the leak is between the bush and the shaft. For this to happen the bush would need to be very worn, in which case, there should be a lot of freeplay between shaft and bush which is worth checking.

After you have removed the sprocket, check for pitting on the journal under where the gearbox seal touches. If there is pitting, you'll need to replace the sprocket and the seal. Also check the condition of the sprocket teeth for excessive wear.

[Phil C]

Thanks AWJDT.

The clutch seal slides on very easily but I don't feel any play. Regarding whether it slides on to the clutch shaft or a sleeve bush, please see photos (one without seal, one with.) I think it may be a sleeve bush?

Anyway I guess I now need to remove the gearbox sprocket in order to look at the oil seal underneath?  But I don't know what I can use to undo the big nut (about an inch and a half across flats)?

Also, will I need to remove the rear chain before taking the sprocket off?

Phil.

[JulianS]

The groove on the outside of the bush extension is where the oil seal bears on it and wears it, it is the fit of the seal on that bit of the bush which is important.

[Phil C]

Thanks very much, Julian, I didn't realise that was where it sat. I've just been and tried it there - still don't feel any play other than the give in the rubber.

[JulianS]

If it was my bike, being it is the middle of summer with lots of riding time available, I would consider putting it back together and using it. If the leak is too bad then you could strip the bike at your leisure when autumn comes.

[Phil C]

When you park the bike on its sidestand, there's a drip every few seconds at first, so I assume it's losing oil when being ridden, so I guess it's not wise to ride it. I've got a 2011 Bonneville I can go for a ride on, so think I'll carry on with this.  It's a learning experience for me. A bit like an apprenticeship by correspondence (not really - no offence to people who did a real apprenticeship, back in the day.)

The gear sprocket nut I think is 7/8" BSW, so I could get a socket on ebay. If I take the sprocket off, will I see the oil seal underneath and be able to remove the seal without any special tools (I haven't got any) to see if it's okay?

Also, to get the sprocket off, do I need first to remove the rear chain?

I do wonder why the leak appeared so suddenly, after I changed the oils (co-incidence?), but anyway, got to find the source.

Phil.

[JulianS]

You will need to remove the chain after loosening the retaining nut. You will see the seal when you pull the sprocket off. The seal should just lever out.

[Phil C]

Split the chain?

[JulianS]

There will be a split link in it.

[AWJDThumper]

Phil. You've done most of the hard work by taking the clutch off. Removing the gearbox sprocket is relatively easy. It's best to use a socket but it can be taken off with a large adjustable wrench if you have one. With everything taken apart and both seals remove, it should then be possible to work out what was leaking.

[Phil C]

I've ordered a socket from ebay to fit it (hopefully!): 7/8" BSW. It's a bit frustrating having to wait for things like this but of course once I've got them...

[Phil C]

Nothing in life is simple. Well, not when it comes to me and my BSA! To try to locate the source of my oil leak, I am going to take off the gearbox sprocket. To do that, I need to take off the rear chain. To do that, I guess I need to take off the chain guard. The front attachment bolt for that is very tricky to get at, and I think I might need to remove the panel which straddles the air filter hose in front of the battery. One of the fastenings for that (RH side, near the oil tank) is hard to get at and I think might mean removing the seat.  No, surely it's not that difficult to get the chainguard off. Any tips please?   Phil.

[AdrianS]

Do you have to take off the rear chain??
Never removed a sprocket whilst on the bike on my previous C15 or B40 but I would have thought if the rear wheel is pushed to the front of the swing arm cut outs there may be enough slack in the chain to pull the chain off with the sprocket.
Another possibility is to split the chain at the sprocket or just under it and put a cable tie or a bit of wire to hold the ends together to save having to feed it through the chain guard.