Oil leaks - next plan, compression testing

[ChrisE]

So on my never ending quest to try and establish why I am leaking so much oil, out of every orifice (as it were), I’m now thinking that there is too much pressure in the crank case. In my previous thread, I used an oil manometer to measure the pressure while the engine was running and it proved to be about 580mm high of oil in a manometer which my maths equates to about 1.5PSI of positive pressure. The good people of this forum are suggesting that it should be a negative pressure, created by the flapper-valve on the breather that allows gas out but non-return. I’m pretty sure that the valve is working well (if I blow/suck it seems to work fine) before I bolt it back onto the engine.

So the next thing is to compression test the pistons. This again is all new to me and a learning curve.
At cold, I took the plugs out and turned over the engine. I looked in the plug hole and can see oil in the chamber, maybe a teaspoonful that sloshes up, like a wave, when the piston goes to compression. I’ve tried to catch it on the camera but it’s hard to pike a torch and a camera in through a tiny hole.









Then I compression tested using a gauge, with the engine cold, and turning it over with the electric start, accelerator fully open. Trying to test by hand-crank just didn’t put in enough effort to get much of a reading. Results;

Near side 45PSI
Off side 35PSI




I then started the engine, got it fully warmed up and repeated the whole thing. This tiem results;

Near side 60PSI
Off side 49PSI




Now this is where I need help! Where am I on the ‘this is fine’ to ‘this is worn out’ scale? Anybody know anything to help us? I’m hoping to make it to the ex-employees day this weekend so speak now before I badger you there!
Chris

[Keith Clements]

The accuracy and reliability of the compression test that you did is affected by many factors. The expected value depends on the compression ratio which is the ratio of the swept volume and the combustion chamber volume. If the cylinder bore and the valves and your gauge have no leaks then the pressure reached should not be affected by the speed of cranking, but invariably it is. So when warm the crank speed is faster and the bores will have a better seal because of an oil covering. You need to get a consistent reading on each cylinder before drawing any conclusions and even then that conclusion is not reliable, just an indication.
I aim for a maximum difference between cylinders of 10 psi with a compression of 150 psi on a Javelin cylinder but that has a higher CR.