Gear oil leak (1965 B40F)

[Phil C]

I have a slight leak of gear oil, but am not sure where it's coming from. Is there any chance it could be coming from anywhere on the timing (RH) side?  Phil.

[Mike40M]

Of course it can leak anywhere. Usually seals. not mating surfaces, bypassing screws and even through bad castings. Are you certain that it's gearbox oil? Had a hard to find leak on my B40 from a faulty inlet oil rubber pipe. Dripping from footrest bracket.
Two of my eight British bikes don't leak. A Norton twin not finished restoring, no oil in it to leak and a Manx with a Molnar engine. Just lying, after a full race season one drop of oil from the rev counter drive.
Wife don't understand why oven trays disappear.

[Phil C]

Pretty sure there is a slight leak of gear oil. I put some red dye in it, and I think the leak drip has that colour. Trouble is, I'm colour blind!  So it's not simple. But then not much is.  Phil.

[Phil C]

Something for you to ponder as you toast your toes by the fire this evening. Sooner or later, maybe when the weather is not quite so cold, I'll revisit this. When I had a look a few weeks ago it looked like it might be coming from the bottom of the outer timing side cover. How might gear oil get into there?  Phil

[Phil C]

I'm guessing from a shaft oil seal or the inner casing joint?
Phil

[PeteRae]

Hi Phil,
On my B40, one of the many leaks was gear oil running along the threads of the lowermost Timing casing bolt. This bolt, though not apparently designated as a drain, went through both the outer and inner casings. Unfortunately a PO had graunched a metric bolt into the alloy which had subsequently stripped allowing oil to run along what was left of the threads, even though they had used half a tube of Hylomar to try to seal it.
Also had some oil running along the gearchange shaft. Think that was mainly coz there was too much oil in it.
Rebuilding the engine at the mo, helicoiling and welding as I go!
Pete

[Blackthou]

Just reading the posts again. Re the bottom of the timing cover. As you say it should be dry. I did have a recent weep from there and investigated it. There's a tiny drain hole as per photo which had become blocked either with muck or sealants over the years. It prevented the collected "waste" oil from returning. I got a small twist dril and cleared it out by hand, then I straightened a paper clip to its last joint and puggled away until there were no restrictions. The hole seemed to be 2-3" deep. Hasn't wept from the timing side since.

Hope that helps

[Phil C]

So the oil drsins away into the crankcase. But where would it have come from to get inside the outer timing case? Phil

[Blackthou]

It appeared to be coming tracking through the clutch operating arm hole /shaft. There is nowhere else I could see plus it was moist around that area. Guess the oil gets flung on to the shaft and works its way along?

[Pete A10]

The B40 has a timed crankcase breather (next to the the cam pinion locknut) which exits into the outer timing case. This allows pressure and oil mist to enter the timing case. This is the source of the oil in the timing case and is the reason that there is a drain hole. Later B40s had a breather hole at the rear of the outer timing cover.

[Phil C]

Is that it at top right on the above photo? Just to the right of the nut?   Phil

[Pete A10]

Yes

[Pete A10]

If you look at the left hand side of the photo there is a small notch in the face of the inner timing case just below the rearmost case screw. This is the breather hole when the outer case is fitted

[Phil C]

Very interesting - thanks very much Pete. I guess I might need to get a paper clip ready. I think I'd want to be very careful sticking a tiny drill bit in there in case it snapped below the surface.  Phil

[Phil C]

Is it necessary to check if the top right breather hole from the crankcase  is clear? If so, how? Presumably there is something at the other side rather than it just being a plain hole?  Phil