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Hi all. I have posted several times seeking advice re: persistent smoking and oil use from a rebuilt '81 100RS motor which runs beautifully other than a smoke issue at low revs, taking off from the lights,etc. Bores, guides, carburetors (dellortos) have been checked, adjusted, rechecked, readjusted......I'm pretty over it and was nearly prepared to live with it. But...... I have noticed that it is only the left hand plug that oils up and have recently noticed a noise like an air leak, hard to hear over the engine noise at idle..... but definately there. Just couldn't track it down. Plug tight, exhaust nut tight, valve clearances correct .......but a bit of liquid oil seemingly pooling between the fins just above the spark plug (towards the crankcase)ALWAYS JUST OVERLOOKED IT AS A BIT OF GUNK. Anyway, cleaned it out with a thin screwdriver and a bit of cloth, until no gunk remained. After a long 200 km ride the oil has returned!!! What the......?!!! Could the head be porous or cracked? Could oil be getting sucked into the combustion chamber from the rocker box (and between the fins) and be being burnt? How could I dertermine this? Is it a long shot? Oil is definately being consumed according to the dipstick...... Your opinions appreciated. Hools.

If there was any hairline crack or pours that could suck in oil, there would be a black or brown stain around it where the combustion gasses have blown out.

Thanks Garnet. But if oil was 'leaking' from rocker area into the head it would present similar symptoms as a crook valve guide? Ok. It wouldn't be getting straight into the combustion chamber.....through a valve........you know what I mean.........Hools

....and have recently noticed a noise like an air leak.

Thinking about air leaks and how they affect the engine breather. If air can get in it's likely to pump oil out through the breather. To function correctly and pump down the crankcase there has to be no air leaks anywhere including breather valve, dipstick and valve covers.

Hi,

If you're worried about a leak into the combustion chamber via a crack, porous casting, bad gasket... whatever. a leakdown test is the best way to set your mind at rest... or not.

It will prove whether there is a compression issue and an audible indication of where the leak is occuring.

Rob

Thanks Rob. How do we perform a leakdown test? I'm pretty confident that there is some issue like those posed that is contributing to this problem.....just a matter of sorting out what the problem is!! Thanks, Hools.