Oil blowing out of oil vent pipe

[keishis]

Thanks for the advice, Mr SPRIDDLER.
I thought I checked it when I assembled it, but I may have assembled it incorrectly. I don't think there is any white smoke, but the plugs are indeed blackened with oil. I will disassemble the top of the engine and check the orientation and angle of the piston rings again. Thank you all for your help.

[clive]

Spriddler i am confused. The piston gap was quoted as 0.12mm or approx 5 thou. I take it this was the clearance of the piston in the bore. The ring gap was 0.64mm or 25 thou which puts it coming up to condemn according to your army figures (although I have run with much worse).
You make a good point though about the top marking on some rings needing to be observed.

[SPRIDDLER]

The ring gap was 0.64mm or 25 thou which puts it coming up to condemn according to your army figures (although I have run with much worse).

I must admit I was having a bit ( a lot) of trouble getting my head around the mix of metric and Imperial measurements but Keishis amended his ring gap measurement from the initial 0.64mm to a current 0.012" (12 thou).
He originally wrote:........

The engine has not been run much since the rebuild and the piston gap is 0.12mm and the ring gap is 0.64mm.

Which he later amended to:.......

By the way, the piston ring gap is less than half of what it used to be (it seems to be 0.012in).

Another stray thought re plug oiling was that the inlet valve lubricating screw may be open too far........although that has no relevance to excessive oil in the crankcase.

[Chazzyb]

The roller bearing big end on a single doesn't need a lot of oil nor any pressure, unlike a white metal shell bearing. The return (in my experience) will always be poor, as not a lot of oil goes in. I've yet to experience a hot oil tank on my 18S. I expect Clive has, as he thrashes his bikes HARD .