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Massive oil consumption/leaks problem

Well I've done over 400 miles since I restored the M20 and am enjoying riding her. I have such confidence in her that we did my first ever bike camping weekend with the BSAOC last weekend. Over 140 miles and the only problem was a rear brake torqure arm bolt going AWOL.

But she has been developing a significant oil leek issue. After riding her she will drop guite a puddle of oil on the floor which stops after a short while. Before the camping weekend I had checked the crankcase drain and sump plate bolts.

The lower rear chainguard and framework in the area are plastered in oil which I am suspecting is coming from the breather. I also suspect a slight leak from the valve lifter.

I have checked the breather and it is working fine.

I have not checked for a smoky exhaust.

I reckon she used about 1 pint of oil over the 140 miles!

I am suspecting piston ring blow-by pressurising the crank cases. Does this sound feasible or are there othetr more likely explanations?

I had a new liner and the cylinder bored to standard and new rings but looking back I may have been over generous when filing the ring ends to gap them.

Your advice would be really appreciated.

Cheers
Dean

Re: Massive oil consumption/leaks problem

Hi Dean

First, you were really lucky with the rear brake torque arm. I lost the nut from the hub end and it smashed my racking to bits and bent the rear sub frame. Make sure it has the correct castelled nut and a good split pin!

My guess is that it is wet sumping and just chucking oil out wherever it can, but mainly out of the breather.

Regards

Pat

email (option): sacombsashtrees@hotmail.com

Re: Massive oil consumption/leaks problem

Dean,
is your oil-return working properly ?
Do you have a oilfilter or something on the return ?
It sounds like the crankcase is indeed full of oil.

If you cilinder liner etc is good, I don't think the piston ring gap can cause such problems (unless the gap is very big!)

Re: Massive oil consumption/leaks problem

Thanks for your reply guys.

I will check the oil return although it looked alright with the filter top off but perhaps the in-tank filter is restricting it...a long shot.

The reason I was wandering about crankcase pressure is that their is abit of a weep from the exhaust lifter mechanism and I was told this could indicate high crankcas pressure resulting from worn rings.

I have fitted a new ball and spring in the anti wet sumping valve but I'll let her stand overnight and see how much oil drains out of the case when I remove the drain plug.

Re: Massive oil consumption/leaks problem

Hi Dean

Leaving it overnight is probably not long enough.

Leave it standing for as long as you usually leave it (for a lot of people this can be a week or longer), drain the oil from the sump into a bowl and measure.

Regards

Pat

email (option): sacombsashtrees@hotmail.com

Re: Massive oil consumption/leaks problem

Hi Pat
I understand what you are saying, Indeed it is my belief that all BSA's wet sumped but we did not notice when using them everyday!
However my problem is it leaking after a long ride ie after enough time for the pump to return any excess to the tank. The oil pool under the bike occurs within minutes of the bike being stopped after a ride! It then stops. Maybe a gradual leak is pooling in the sump guard and it is this emptying that leaves the pool.

But why is it chucking oil out of every orifice? Must be excess crankcase pressure???

Re: Massive oil consumption/leaks problem

Although the term 'wet-sumping' is used for the draining down of the oil tank contents whilst standing, techincally, that is not actually what it is. The term was originally used to indicate a failure to scavenge the sump contents whilst running, particularly at high revs. Some models of Norton Commando were particularly prone to it as the factory repositioned the return pick-up location and apparently failed to realise that the symptoms were being disguised by the amount of oil going up the breather pipe (which runs to the oil tank on those machines).

I don't know the BSA bottom end, but there are various possible causes of scavenge failure - blocked oilways, whether by gasket or goo, or air leaks internal to the pump or on the return side spring to mind.

If your sump constantly contains more than the proverbial teacupfull, some of the oil will find its way up the bore and old-fashioned oil rings will not cope with it.

It would be a good idea to drain the sump after a fast run and measure how much comes out - just to rule out this aspect if nothing else.

Re: Massive oil consumption/leaks problem

I think you are thinking too much into this, It won't wet sump when you are riding it, and it won't wet sump in a hour after running it. Unless something is severely wrong with your pump, and if it was it would have shown up on your trip. What i would do is wash the crankcase and oiled areas down in with spirit, go for a short ride and leave it ticking over and look where the oil is coming from. Most likely the breather or the back of the chain case. If it is wet sumping it will usually take well over a week to empty the tank and this must be a bad case of wet sumping if it is doing this. You may well have a bit of blow back and oil consumption past the rings with a new bore, but it will soon get better when things bed in. My newly bored cylinder used a little oil till things had bedded in ok took about 1000 miles and does not use much oil at all now.
I am sure any big problem would have shown up on your trip, leaks from the valve lifter are common as it has not got any kind of seal on its shaft.

Tim W

email (option): t.j.walker@btinternet.com

Re: Massive oil consumption/leaks problem

Hi Dean.

My BSA always drip oil after I top the gearbox oil, drive and stop.
Mainly if I use a side stand.
Your oil may be dripping from the gearbox, not engine. worth checking.

Another point I would check,
Is the primary chaincase, if you run it oiled.

Good luck,
Noam.

Re: Massive oil consumption/leaks problem

Thanks Tim and Noam for your helpful input.

I think I do have a big problem as shown in the 'long' trip....over 1 pint of oil used in about 140 miles!
The bike used to just drip after a ride and I can live with that as it proves there's oil in her (:wink: ) but recently this has become a 'pool'.

I have enough to do at the moment fixing the Super Rocket and getting the Three Wheeler ready for France so I'll just keep the drip tray and oil can to hand. If I have a spare moment I may convert the sump guard to a catch can so I can reuse the oil!

Re: Massive oil consumption/leaks problem

G'day Dean,

I had a similar issue with my M21. It had good oil return to the tank but was dumping a lot of oil out of the breather valve when running and like you, everything aft of the clutch would be coated in oil. Turned out to be a broken compression ring.

Re: Massive oil consumption/leaks problem

I had a similar problem recently and was pulling my hair out trying to find the cause of the leak! I thought it was the chaincase seal leaking, so I stripped it all down, replaced the cork seals, re-sealed the lot and carefully screwed it all back together... Still leaking! So I felt underneath and the oil seemed to be coming from the gearbox, so, thinking the seals were gone in the box, I pulled that out, opened it up, fitted new seals, replaced it and ran the bike... Nope, STILL leaking oil! :-/ I then though it was the rings being worn out or broken, so, just before I pulled the head off, I looked at the breather pipe & noticed it was sitting on TOP of the chaincase, instead of being neatly tucked inside... It turned out that it was THAT which was blowing oil onto the back of the chaincase, making it look like I had a big oil leak! I tucked the pipe back where it belonged and the oil leak now seeks to have been cured to an occasional drip.
Food for thought...
Good luck
Ian

email (option): fozzie001@hotmail.com

Re: Massive oil consumption/leaks problem

Not quite sure what Ian is saying? The breather pipe should be open to atmosphere! ie pointing at the road or the rear chain in some cases. Not tucked inside the chain case, where any undo heavy breathing would result in over oiling of the chain case/clutch.

Any excessive oil coming from the breather pipe, needs addressing from the engine end.

I can't really think what seals you might replace in an M20 gearbox? Ron

email (option): ronpier@talk21.com

Re: Massive oil consumption/leaks problem

This morning I've checked the oil tank breather and the oil return with the engine running. Return looks fine with the few air bubbles to indicate that the return is correctly shifting more oil than the feed.

I've cleaned the oil stains from the engine and rear frame so hopefully new stains willbe evident when I take here for a run tomorrow night (club night).

I am going to try running with the oil tank filter removed to se if that's creating resistance to the oil return. I noticed how quickly the filter filled up when I was running the engine with the filter cap removed.

Re: Massive oil consumption/leaks problem

Ron Pier
Not quite sure what Ian is saying? The breather pipe should be open to atmosphere! ie pointing at the road or the rear chain in some cases. Not tucked inside the chain case, where any undo heavy breathing would result in over oiling of the chain case/clutch.

Any excessive oil coming from the breather pipe, needs addressing from the engine end.

I can't really think what seals you might replace in an M20 gearbox? Ron
I meant that I tucked in so it blew oil onto the chain as opposed to blowing it onto the back of the chaincase, thus "showing" a leaking chaincase/gearbox.

The "oil puddle" itself, seemed to stop once I re-positioned the pipe.

For "seals" replace with "gaskets"... (to be pedantic, a gasket is a seal) ;-)

Hope that cleared that up?

email (option): fozzie001@hotmail.com

Re: Massive oil consumption/leaks problem

Well it's your bike Ian, and you can deal with it however you want, but to my understanding, you haven't fixed the problem, just made it so that it's less noticeable.

The main culprit for gearbox leaks is the large 'open' drive end bearing (especially prone to leak when leaning on the field stand). The solution is to fit a modern bearing with double lipped seals (I remove the inner seal....Some guys don't) Ron

email (option): ronpier@talk21.com

Re: Massive oil consumption/leaks problem

Yo're not simply overfilling the oil tanks are you?

email (option): jeremy@clogmaker.co.uk

Re: Massive oil consumption/leaks problem

I don't think so Jeremy. I top up to about 1.5 inches below the return pipe holes.

I am starting to think about wet sumpng again. I drained 200ml from the sump yesterday having left it overnight, admittedly I have not done a drain and remeasure test yet.

Re: Massive oil consumption/leaks problem

Hi Dean

You do top up after the pump has had time to scavenge any sump oil back into the tank?

I am sure that you do.

Regards

Pat

email (option): sacombsashtrees@hotmail.com

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