I have a 1955 B31 rebored, new big end, new valves and guides, in fact a complete engine rebuild.

It is now run in and performing perfectly, except a lot of oil is being expelled from the engine breather whist being ridden, the breather is standard and the clack valve is free and operating correctly, I have tried making a sleeve cover to prevent oil being thrown straight into the hole near the top of the tube, this made the problem worse, I suspect that the oil level inside the timing case is rising too high and reaching the breather hole, the hole between the timing case and the crank case is clear, my thoughts are to enlarge this hole.

Any advice on how to cure this problem would be appreciated.

Thanks.

How good is your oil pump?
If the oil level in the crankcase is too high, maybe the scavenge pump is not doing its job.
Not sure about B 31 but on A models a sticky ball in the scavenge pipe can cause this problem. I have also seen it happen on a B44.
Trev.

Hi Trev

Thanks for your reply, the oil pump is good, the oil level in the crank case is fine, I just feel that possibly the timing case is retaining too much oil, IE not draining into the crank case fast enough.

The B series use a different system to the A and the pump is located in the bottom of the crank case.

The bike is not wet sumping the scavenge pump is clearing the sump as it should.

Regards
Dennis

It may not help but I seem to remember someone saying that turning the pipe so that the hole is not in the direct line of oil flying off the various rotating bits in the timing case can help. I.e. have the hole facing the outer cover or the like.
Cheers
Pete

Did you replace the two rubber seals for the cam quills in the timing cover ?
if these are not a good fit then oil will squirt every where including into the breather.

Pete, thanks for your advice, I have tried altering the direction of the hole to no avail.

Trevor, the seals where new when I rebuilt the bike, but with pattern parts anything can happen, I will take another close look at them, thanks for you help.

Hi Trevor

I had a look at the seals and found that the pattern replacements are slightly thinner than original, I have placed an extra washer behind both the quill bolts and the situation is much improved, however it is still loosing more oil than I would like.

Thanks for the pointer, a big help.
Regards Dennis.

Get your torch out and have a good look at the drain hole back into the sump.
It is a pretty big hole but there might be an obstruction in there.
Have a close look at the cover and the gasket.
Make sure that there are no leaks

No leaks the oil is only coming out the breather, the drain is clear, I had considered enlarging the drain hole but the size it is should easily clear any excess oil.

My B32 which is essentially the same engine is almost ready for the road, so I will soon see if it looses a similar amount of oil from the breather as a comparison, perhaps I am being too pedantic about the oil.

Revband
I had this drama with my M20 same set up as yours ...I tried every bloody thing.

Bsa did have a service sheet talking about this and it siad that the hole must be "facing the cover and slightly backwards" to avoid excessive oil...it was obviuosly a known problem.

In the end I just gave up (for now) and have put a clear plastic pipe on the breather tube exiting by the number plate ...at least that keeps the oil off the tyre....if anyone makes a snide remark about it i just say "Bill *****er a well known legend of BSA racing told me to do that"....there is instant silence as they dont want to critice Bill...

If you do find a solution I would love to hear it.

Hell I even made a "mushroom cap" covering the hole so the oil had to go up hill but it didnt make a blind bit of diffrence.

I guess the only thing left to try is the return line is clear of any build ups of crap slowing the return.

keep us posted.

Hi Ignoramus

I have tried the extended tube over the rear wheel, but as it was the tube filled with oil and blocked the breather causing crankcase pressure with the result that the pressure tried to get out in any way it could mostly through the left main bearing into the primary this then escaped past the gearbox main shaft, result, oil all down the other side of the rear tyre, like you I made and fitted a cap to cover the top of the tube so the oil had to go upwards, this made it worse.

Now the oil escape has been reduced with Trevor's help I will realign the breather as you advise and try the tube again.

Thanks
Dennis

Dennis...its BSA service sheet number 603 that talks about the breather. I cant find the link to it but I found it with google search of "bsa service sheet 603" its on the net somewhere quite intresting.

Ignoramus

Thanks again, I found the sheet here, along with loads of other useful Info.

http://www.classicrider.dk/english/technic/ServiceSheets.php

hi,I had the same problem with my B33goldie replica that i built many moons ago,
after a lot of head scratching i cured the problem by replacing the pressure release ball valve (located in the bottom of the timing chest).
when i removed and examined the origonal ball I couldn't see any signs of wear,until I used used a powerful magnafying glass.
Got a replacement ball used a copper drift and hammer to seat it and it hasent leaked since.(ten years)
and as stated already the tho rubber washers need to be a tight fit to both the acorn bolts and their recess in the timing cover
hope this may be of some help .
best regards ..Ronnierockets..

Thanks Ronnierockets

The ball and spring were replaced and reseated when I rebuilt the engine.

Hi all

Thanks to everyone who offered help with this problem.

It seems that two things were adding together to cause the trouble, 1/ the pattern rubber oil seals on the cam feeds being too thin, 2/ the position of the breather hole, it needs to be pointing outwards towards the cover and slightly to the rear.

Cool Revband

glad to know realigning the hole made a diffrence....

Also pleased to learn that the pattern rubber oil seals were partly to blame.

PS. Hope you had a trouble free ride home from the Manchester Branch Camp at Dent.

Beezageezauk.

Very Intresting
I had the same fault and the only way to describe it was that the timing case was filling up above the level of the breather, I tried everything above and more. including various different timing covers. I then bought another B31 Running perfectly so I took the timing cover off and tried it on my problem bike, Guess what Cured WHY not sure but I think it is the quil going into the crank if this is worn oil can pass back filling the timing case or the end of the crank has a internal taper and the quil to match, question, do these need to be set up witn mimimum clearence to stop oil leaking,
FOOD FOR THOUGHT

PAUL