I'd like to get this oil leak sorted at some stage, maybe when the summer is over. But I'm not sure how I'll go about it. Stopping a leak is one thing. But finding where it's coming from is clearly not always easy. And I guess it's hard to stop it if you don't know the source, and not knowing the source is frustrating. I just took the bike (1965 B40F) out for about two miles, and took this photo when I got back. You can see there is an oil leak from somewhere. I have been thinking it might be coming from the alternator wires grommet in the primary chaincase, but am not sure. Maybe, maybe not. I think I'll need to buy a mirror on a stick to perhaps get a better look (been thinking of getting one for a while now.) Maybe it's from the primary chaincase gasket (gasket has been replaced and the allen bolts are done up very tight, but I'm not sure if they should have to be so tight.) It doesn't appear to be coming from the sump plate - that looks fine. And maybe not from the gearbox plug, but not certain. Any advice please on how to locate the source of an oil leak? And any ideas on where my leak is? Phil
It's always difficult to find the source of this type of oil leak. What would narrow it down is if you can tell whether it is engine oil or gearbox oil. One of the classic sources of oil leaks in this area is from the seal around the drive sprocket which becomes especially noticeable when you leave the bike on its sidestand.
I think I probably replaced that seal some time ago when, with much guidance from, I think, you and others on this forum, I went in search of the leak and ended up doing quite a bit of work inside the primary chaincase, eg taking the clutch off. This was, I guess, a couple of years ago. I learnt a lot, but still have a leak. Is there a way of telling which oil it is? Phil
Checking back to summer 2018 on this forum, I replaced the seals behind the clutch and at the gearbox sprocket. Is that the one you mean, AWJDThumper? Phil
I think I might do something which I think you suggested back then: drain the primary chaincase and take the bike for a run, and see if the leak is still evident. Would doing that cause any damage, for example to the clutch? Phil
That test would be worth doing. The oil is mainly there to lubricate the primary chain but I don't think going for a shortish ride will cause any harm. In order to determine whether it is chaincase oil or gearbox oil, I would be tempted to add a dye to one of them:
https://www.demon-tweeks.com/ring-uv-dyes-250947/?sku=RINRLD4&istCompanyId=a2904180-3a7d-4e56-b876-cf81c9512180&istFeedId=6fbc4b04-fd28-4ce1-8513-835c8f118690&istItemId=wptrtapap&istBid=t&gclid=CjwKCAjwxqX4BRBhEiwAYtJX7ZFuCvbAJGgCyyv-IRsrFyIEnfRCBm8NiXzyzdwTX_WOhNLg0zmdYRoCeg8QAvD_BwE&gclsrc=aw.ds
Thanks AWJDThumper. I had thought a dye would be useful, but didn't know they existed. Anybody used this dye?
In the meantime, I'll drain the primary chaincase and go for a short ride.
Phil
I believe the dye is designed for this purpose and is therefore harmless to engine. If you add it to the chaincase oil for the test then it is easy enough to drain and change the small amount of oil afterwards. Slightly more involved if you need to test whether it's gearbox oil versus engine oil!
I know when I took a previous bike for an MoT it had a leak. The guy doing the test used powdered chalk.
Totally clean the area of the leak then dust the area with powdered chalk over it. Take it for a run and then as well as seeing where the oil is dripping from you should be able to see track through the chalk back to the actual leak position.
Obviously you need to have eyes on the whole area which will mean a mirror or lying in the mud under the bike.
You would have thought that chalk powder would do the trick but the problem sometimes is that you get so much spread of oil from the leak that it doesn't generate a clear track. This is likely to be particularly true if the leak is around a rotating part as is probably the case here and also when it happens when the bike is being used rather than when it is parked up. I've used the technique on a cylinder head leak and it was impossible to see where it had originated from the oil soaked chalk powder due to slipstream spreading - in the end I had to replace the engine! That all said, it certainly does no harm to try the technique - it might work in a particular case.
Interesting. Drained the primary chaincase oil. Went for a ride - just about a mile or so. Had a look when I got back. No evidence of the leak. So, that they d progress. It looks like it was coming from the primary chaincase. Just need to establish exactly where from. I did find, when I took off the footrest, the chain oiler Allen screw was a bit loose, so I've tightened that ( some time ago I replaced the oiler with a nut and fibre washer.) I'll now put some oil in again and see what happens. Maybe I'll use some dye, as a double-check. Trouble is I'm colour-blind! Haha. Seriously, I am. But colour blindness does not necessarily mean unable to see any colours, so the dye might be useful. Phil
You could try using ATF oil. Already red. Though there are conflicting opinions on using it in primaries.
I thought I had just posted an update on this, a few minutes ago, but it seems to have disappeared. So here goes again. Refilled the primary chaincase (pc) with 1/4 pint of oil, went for a spin down the road and back, and had a look. Sure enough, there were a couple of dribbles of oil running down the inboard external wall of the pc. That supports the theory that the leak is coming from the pc, but I need to know where exactly. I noticed the Allen screw which used to hold the chain oiler ( now has a nut and fibre washer instead) was loose, despite having been tightened earlier today. Presumably the vibration of the ride had done that. So I need to think about how to stop that happening. Could it be the source of the leak, I ask myself. The oil didn't appear to be coming from the gasket area. But could it be working its way along the thread, past the fibre washer and nut, and creeping out that way? Hmmm... I wonder. The oil looks to be a bit too spread out for that, but I'm not sure. Need to look again. I guess. Any thoughts much appreciated. Phil
Your original picture showed oil on the bottom of the gearbox - it's hard to see how chaincase oil could have found its way across while at the same time not leaving similar evidence on the bottom of the chaincase?
When I took the original picture there would have been oil on the bottom of the chaincase as well. But after cleaning it off and a short ride today it was on the inboard face of the pc but not on the underside of it. Not enough of it produced on such a short ride, I guess. Anyway, I think the ex- chain oiler bolt is no longer a prime suspect. I've just been looking again, and the vertical dribbles on the pc wall are too far forward for that. They are about in line with the clutch. I see them running down where the bottom half of the circular plate is, but the upper half of the circular plate looks clean ( I think). So I'm now thinking it might be coming from the clutch/ shaft area. I had the clutch off two years ago ( hardly any miles since then, and the leak's been there for ages.) I replaced what I thought needed replacing, but can't recall exactly what. A seal was one thing, and a fibre washer which I think was missing. I seem to recall the felt washer was loose, and am now wondering if that is an issue. Do you think pc oil could be leaking via the clutch/shaft to the outside? Phil
The felt washer is there to stop crud getting to the seal but is a pretty crude way of achieving this. It sounds as though the clutch seal is the main culprit and needs to be examined more closely. It might be worth checking the seal has been inserted the correct way around.
Phil,
Could it be there's simply too much oil in the PC? I know you added 1/4 pint but did you use the level screw? I've seen scenarios like this before when it was either too much oil per se, or just enough over to work its way out on a run.
Well, I drained it through the drain hole and then put in 1/4 pint. I confess I was surprised when I drained it to find there was 1/2 pint in there rather than just 1/4 pint. Phil
Hi Phil,
Was there a happy ending to this? Did the 1/4 pint of oil resolve it? I ask as I took my C15 out on its maiden run today (well for me after 6 months of ownership and fettling). The engine was beautiful, the brakes weren't bad unless braking into a corner then it squirrelled a bit. Ran well and sounded awesome.
I did 25 miles and checked her over when I got back. There was sign of oil on the top of the cranckcase which I deduced to be a weep from a rocker banjo (I had annealed the new washers) that had blown about and an oil leak on the pc wall just as your pictures and description. I'd put the amount of oil in as per manual but can't remember the volume.
Good morning Rick, This conversation was continued in another conversation thread that was ongoing at the time, entitled "Clutch oil seal and sleeve gear bush". You might want to read that.
I still have some slight leak(s). I'm considering taking the clutch off again.
Please let us know how you get on with this. We might have the same problem. Phil
Hi Phil,
Thanks for the update. Sorry for the time lag but haven't had chance to log on lately. I remember the other post and revisit it. I'm also wondering if I put too much oil in the PC. I only put in as it said but from posts there seems to be a debate between 500cc and 750cc. If I've put 750cc in, it could be the problem.
Isn't that an awful lot of oil for the primary chaincase? I put in 1/4 pint, which I believe is about 142cc? Could be different for your bike of course. Mine's a 1965 B40F. Phil
Possibly Phil, I was talking from "memory". After I posted I remembered there's a level screw so that will my first port of call. Also, after the initial loss on returning from the ride, there hasn't been any since - while parked. Is yours like that?
I'm a bit confused about my oil leak(s). To answer your question, Rick, yes, I think anything leaking from my pc is only when the engine is running. The vertical dribble lines on the inside of the pc are only there when I've been for a ride.
I think I also have a very slight leak of gear oil (evident because I put dye in the gear oil), maybe from a seal, but I've not yet begun properly exploring that. It's only very slight so I guess I could live with it, but I might try to fix it.
Please let us know how you get on. Good luck! Phil
If it is only when it is running then it must be something quite high up in the PC. When standing all the oil sits in the bottom of the case. When it is running, oil gets thrown around inside the case and can leak out from higher up.
In that case there are three possible sources.
The central oil seal on the clutch shaft.
The perimeter of the sealing plate which gives access to the socket.
I also seem to remember that the set screws holding this plate on were not in blind holes but threaded right through. It is possible that oil can leak out through the threaded holes when it get hot. Resolve it with a bit of threadlock.
Hope this helps.
Otherwise accept that it is BSA. At least you know that you have oil in your PC!!
Sorry the second item should read sprocket not socket