Thanks. As per other reply - fault down to valve clearances - exhaust valve staying slightly open on compression stroke. Not sure how did eventually start and why compression would improve when warm. Compression wasnt checked with wide open throttle either so may have had some impact. Once shims have been replaced and everything back to spec I'll check compression again as even when warm there may have been leakage. Just hoping that valve seat hasnt suffered.
and just to clarify - engine still started evomonster? (take note @West Cork Paul ) Controversial (yet again) but closing clearance nothing like as crucial for running as opener because you have a "helper" spring.
While checking the clearances, with the opening shim removed, able to pressurise the cylinder as the exhaust helped closed with the spring but with the opening shim in place it was opeining the valve ever so slightly and leaking into the exhaust. Also not sure how it ever fired with such low compression or why it should improve once war. I guess the valve should be helped closed by the ignition and explosion within the cylinder but would have been inclined to expect the situation to have been worse when things were warm with things expanding. Anyhow - it looks like I have got to the root of the problem and just need to get the correct shims and get things back to spec. Many thanks for everyones input and comments.
yes, not sure why you are telling me the above - the helper spring assists the closing shim if a gap outside tolerance occurs. What i wanted to confirm is that engine still started with low readings.
Yes. Engine did start. Needed to hold it around 4000rpm for a few minutes before it would idle without stalling.
Zero clearance on opening rocker shim (the one that pushes the valve open) so in fact valve propped slightly open when should be closed - even with the help of the closing spring. I understand closing rocker should be 0.00 - 0.05mm clearance and it was more like 0.15 so relying on the spring to get fully closed - but as I say effectively propped open by the opening rocker. Hope that makes some kind of sense.
Had exactly the same problem with an R1. When I finally got round to it the seats and valve were in poor condition so it was a head off job.
Fingers crossed its not got to that stage. Will know once things are back to spec and I can do another compression test.
it's that invisible ink thing again isn't it? It's entirely normal for the shims to reduce like this on an air-cooled 2 valve
