Is it crankcase oil or gearbox oil?

If it is gearbox oil, then the bore will probably be ok.

I am convinced that old bikes work for as long as they do due to the fact that oil drips out of everywhere, so you have to keep topping them up with fresh oil!!!

Hi Patrick, definitely engine oil, the gearbox oil level hasn't changed, where the oil tank needs a good litre.

Anyone in Australia know where I can source a new cylinder liner? I have a spare cylinder but it's at 84mm.

email (option): spacemonkeym@gmail.com

Matty
Pretty sure David has them at Modak
Cheers Darren,

email (option): Darrenacartwright@yahoo.com.au

Before tearing your engine down check that the crankcase breather is functioning correctly...
Personally, I have never seen or heard of cylinder wear that is so bad it causes the effects you describe and I would have thought you would have very little compression if such a condition was present......
I'd also consider fitting a different oil pump to confirm that wear in the pump isn't reducing oil return capacity....Ian

email (option): ian@wright52.plus.com

Thanks Darren but I try to avoid Modak.

Ian, thanks for your input, I have removed the breather and it appears to be working properly but I'll swap it for a spare I have. Don't have a spare pump at the moment but will pull it out and check it over before I open up the top end.
Cheers.

email (option): spacemonkeym@gmail.com

Hi Matty...Check that the ball is moving freely in the pickup tube in the base of the oil pump and that everything there is clean and unobstructed...A problem there might restrict crankcase scavenging...Ian

email (option): ian@wright52.plus.com

Matty,
Good check on the pump is to take it for a good run check for the oil return is working then immeditely take the sump drain plug out and see how much oil is in the sump. There will not me much, if this is the case then the pump is working fine.
M20 cylinders take some wearing out but it could always be a stuck ring, but as Ian says it would be down on compression, but as i said its not a big job to remove the cylinder but you will need a new head gasket unless you have a soild copper one. At least you will know what the top end is like.
Years ago i used to use my M for daily transport and ride it hard, the piston used to get a hard time round the valve side and a build up of hard carbon used to mark the piston above the top ring. When this happened the top ring used to get cooked.

Tim W

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

I have plenty of barrels Im in Nth Qld postage might be a bit much though.
gflash11@hotmail.com

As a last resort, check that the spacer behind the engine sprocket is a very close fit to your driveside bearing boss.If not then make one.

It would seem that excessive crankcase pressure would also cause considerable oil loss out the breather, which has not mentioned as a problem.

There are two small holes in the left crankcase between the two drive-side crankshaft bearings that are provided to drain oil back to the sump before it can accumulate in the cavity.

It seems unlikely to occur, but if these drain holes were restricted in some way, oil would continually puddle, trapped in the cavity between the drive bearings. Normal crankcase pressure would force the oil build-up through the outer bearing and into the primary case.

There would be no sign of wet-slumping, no excessive breather oil, no excessive crankcase pressure.

email (option): teladelujo@ msn.com

Thanks folks for the suggestions, I'll check them all on the weekend.

John E, You're correct that there is no noticeable oil leaking from the breather and the blocked drain holes sounds plausible just hoping that it's something else.

Tim, The stuck ring idea could be a possibility, on the very odd occasion with a cold engine when finding TDC for kick starting there can be a lack of compression. The engine will start, then after stopping the engine, will find compression has returned.

Terry thanks for the offer but I think a new liner will be cheaper than postage from Nth QLD.

email (option): spacemonkeym@gmail.com

What grade of oil are you using?

Jeff, 20W50.

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I've swapped the breather valve and inspected the pump, doesn't seem to be any problems there.
Here's a short video of oil returning to the tank.

http://s66.photobucket.com/user/motorbator/media/oil%20tank/20130915_140110-1.mp4.html

I'll keep an eye on it for now

email (option): spacemonkeym@gmail.com

I run a 50/grade oil in my wm20 ,as a m21 is similar it might be worth a try

Return oil flow looks lovely; can't imagine that there is a problem with the pump or excessive amounts of oil collecting in the crankcase.

One other consideration, highly unlikely; is the oil tank breather open? If the tank breather were restricted, it can cause the oil tank to become pressurized during operation which would inhibit oil returning to the tank.....again, a very unlikely scenario, as most oil tank filler caps don't seal well anyway, making the breather outlet redundant.

email (option): teladelujo@ msn.com

John, will check the tank venting, that hadn't crossed my mind at all.

Jeff, where can I get 50 grade oil in Australia? I've searched for it here in Melbourne with no luck.

email (option): spacemonkeym@gmail.com

Clutching at straws, re- oil grade. As soon as it gets hot it will leak just the same.

Penrite make a 4 stroke motorcycle HD oil [for pre 1984 ] it`s really a 50-70 sae oil that I use in my WM20, check out penrite site, I ordered it through supercheap they say to use it where a straight 50 sae is recommended,I run a 1961 G80TCS matchless Typhoon [600cc competition single] on the penrite HPR 50 which is a 40-70 sae oil,they also make other low detegent oils for classic bikes etc.Penrite`s head office is in Wantirna South Victoria, check out their web site

You should be able to get 50w oil from any Harley dealer it was the staple oil of older Harley's and it has the added advantage of being specifically designed for roller big ends in what are basically inefficient engines. Usually it is quite cheap too which for HD is quite surprising!

email (option): davmax@ntlworld.com