Haemorrhaging oil from transmission side - possible causes?

[owain]

My BSA A10 (plunger) sidecar outfit is haemorrhaging an embarrassing amount of oil and I'm having difficulties fixing it. It is leaking an incredible amount of oil from the behind the clutch and is covering the rear tyre in oil. In my desperation I installed a bunn valve system as shown in this video (https://www.youtube.com/watch?v=P1gGEYJd-A0) but this has not resolved the issue at all and there appears to be no oil being collected in the bottle that is attached to the crankcase breather.

The joint between transmission and transmission case cover has a silicon gasket (Wynns black gasket maker) and I cannot detect any leaks from this joint. There is an old oil seal between the clutch and gearbox sprocket although it appears to be doing absolutely nothing due to the volume of the oil that appears to going past it. Is there much oil traffic behind the clutch usually?. Finally there is a weld repair behind the clutch where it appears that part of the transmission casing broke off. This does seem to relatively well repaired but is it worth perhaps trying to cover this area in some type of epoxy to eliminate any tiny leaks?

Could anyone please help shed some light on some probable causes for this big oil leak. Would the newly installed crankcase bunn valve breather system eliminate the need of the oil pressure release valve? Could a dysfunctional oil pressure release valve cause high oil pressures despite a rankcase bunn valve breather system? Could a crappy old oil seal really allow this much oil pass from this location?

[Swarfcut]

  Three sources of leaks on an unmodified engine.....Damaged/split castings. Gearbox oilseal. Primary case oilseal behind the clutch.  Empty bottle shows no oil or vapour is coming out of the breather. Is the breather actually working? Try it with a tappet cover off. If crankcase pressure can't escape it will vent through the weakest join, be it a duff seal, gasket or crack. You need to identify whether it is engine, primary chaincase or gearbox oil.

 Oil pressure within the pump and bearings is not influenced by the breather system. The oil pressure relief valve controls the maximum oil pressure and has no effect on the breather system used, original or modified.

  Are the Bunn valves fitted to give air in and vapour out? Check oil levels as a quick guide to where the oil is coming from.

 Swarfy

[owain]

I can confirm that it is definitely not coming from the gearbox and the leak is certainly originating from behind the clutch.

I've just checked if the bunn valve breather system is working and I'm getting a nice rythmic pulse of air from the outlet when the engine is running. I just tested it by placing my thumb over the outlet. An afterthought is whether there should also be a way for the air to escape the oil collection bottle? At the moment. Air is just getting pumped into an air tight bottle, so at some point the pressure in the bottle would equal the same pressure as the engine and the system would stop working as intended? or am I just talking a load of hot air?

The bunn valve system is set up with an air inlet through the inlet tappet cover and outlet through the crankcase breather hole next to the gearbox sprocket.

I have a feeling that the oil pressure is getting too high in the engine (I have no way of accurately measuring it) but the motorcycle is always under heavy load due to the sidecar. I thought a new oil valve release valve from SRM might relieve the issue but I think that'd just be throwing money at the problem without knowing if it is the actual cause.

I'll double check that the bunn valves are correctly orientated. Do you think I should remove the outlet tappet cover and let the motorcycle run at idle for a long time to see if any leaks develop?

[Triton Thrasher]

The air from the breather has to be allowed out to the atmosphere.  Do you still have the original BSA breather?

I don’t see why you think you have high oil pressure.

I don’t see how high oil pressure in the oil pump, oil drillings and crankshaft could make oil leak from the drive side of the engine.

Is oil draining down from the oil tank and filling the crankcase while the bike is parked?

[Minto]

With where you say the leak is, I would take a close look at the oil seal behind the clutch and the gearbox oil seal. Unfortunately neither are an easy fix on a semi unit motor/box.
How much oil is in the primary case? It doesn’t need much.
Have you tried the old ATF in the primary instead of oil, this helps identify whether what’s leaking is engine oil or from the primary.

[owain]

@TritonThrasher I've installed a 'modified' BSA breather into the timing side. Essentially it's been cut in half to remove the timed breathing. I also have the intact original BSA breather as a spare.

I have a anti-wet sump valve in between the oil tank and crankcase, so wet sumping the crankcase isn't possible unless I forget to close the valve.

Good idea @Minto, I'm running the standard 20/50w classic engine oil in all parts of the motorcycle at the moment. I poured a pint of oil into the transmission side yesterday after putting everything back together again. The thinking was that it is better to have too much oil than too little. Although I should also mention that this oil leak has been persistant for months now without topping up the transmission side oil.

I've got a new oil seal for the clutch on the way. I hope I can install it by just removing the clutch and not having to remove the entire gearbox! :/

[muskrat]

G'day owain.
To change the primary/mainshaft seal the motor and g/box must be removed from the frame and then the g/box removed from the motor.
I use three different oils in my plunger. 20/50 in motor,ATF in primary and 90wt gearbox oil in the box. That way I know where the leak is.
Yes the catch bottle must be vented. I see your using the same system as my cafe (modified breather top hat).
Cheers

[owain]

haha ok, a pint is too much. I'll make sure I use less next time. Approx 200ml isn't it?

Ah bugger, was hoping it'd be a nice simple clutch removal to insert the oil seal.  Is it possible to removal a plunger gearbox with the engine still mounted in the frame or is an entire engine removal required for this oil seal?

[Rex]

haha ok, a pint is too much. I'll make sure I use less next time. Approx 200ml isn't it?

Ah bugger, was hoping it'd be a nice simple clutch removal to insert the oil seal.  Is it possible to removal a plunger gearbox with the engine still mounted in the frame or is an entire engine removal required for this oil seal?

Nope, you've got to remove the whole unit and then strip out the clutch and remove the gearbox. Well, strip out the clutch before removing the lump.
Then (if it's still original) you have to drill out the rivets holding the old seal in place.

[orabanda]

Is the engine wet sumping?
How much oil flow is returning back to the tank?

[chaterlea25]

Hi All
A couple of points
In my opinion the size of the oil drains at the base of the cylinder are very small for a breather (Bunn) system
if one of the pipes is attached to a rocker cover.
Piping the breather as in the YouTube video back to the oil tank is not a good idea, an awful lot of water vapour
exits the breather and will condense in the oil tank. I have seen this happen 

Owain needs to clean the bike and then see where the oil is coming from
Excess oil in the primary or gearbox will cause problems,
I can hardly believe he fed the breather into a sealed bottle

John

[Minto]

Hey there Owain, as a starting point I would drain the oil from the primary case, and the gearbox, get it all cleaned up then refill the box with the correct amount of oil, and just slowly add ATF to the primary until you can see it flicking past the filling hole with the engine ticking over.
Go for a ride and see what colour the leaky stuff is. ATF in the primary is red, gearbox oil will be nice n clean, engine oil will likely be less clean.
I’ve got a very similar issue with my plunger that I’m trying to sort out, but I’m 90% sure it’s the gearbox oil seal on mine.
Good luck.

[owain]

Thanks @Minto, that makes sense. The gearbox oil seal is the original oil seal from 1950, needless to say I think it may be time for a change.

Took the primary cover off this morning and saw fine metal dust in the oil and some scoring marks on the casing. See photos. There seems to be marks on behind the shock absorber and the clutch basket. There were some marks behind the shock absorber when I bought the bike but due to the metal dust and fresh looking scoring, I think this is a recent thing.

There also seems to be abit of wear on the gearbox mainshaft (i.e. where the collets sit behind the clutch). Wondering whether this wear could be causing the primary chain to rub against the casings? Any ideas on how to remedy this? My first thought is it buy new shims for the shock absorber and perhaps try to source a NOS gearbox mainshaft?

[owain]

I believe the chain is correct, it's not an x-ring or o-ring chain and I don't believe I had this issue before I reassembled the motorcycle a few days ago (although there was som evidence of the chain rubbing when I first took the engine apart after buying it as a basketcase.

Can confirm that split link was secure when I removed the transmission cover. Could this be caused if the gearbox mainshaft nut was not torqued tightly enough? I couldn't find a torque specification in the BSA A10 maintenance handbook..

The cush-drive/shock absorber side appears to have good clearence for the chain when I place. So the score marks in this area may be from the PO but the score marks behind the clutch basket are certainly new...

Will add a picture of the primary chain in a moment! 

[owain]

et voila