I rebuilt an engine and the compression is zero. I aligned the cam and crank marks. Lapped the valves and they seem to be closed at top dead center. Put some compressed air thru the spark plug hole and it appears to be leaking out of the exhaust valve a little. You would think I could get a little compression. What am I missing?
First make sure you are on TDC compression when doing the leakdown air test. If you are still getting valve leakage, then time to investigate why. Not lapped properly, improper valve clearances, It doesn't take much air leakage to really drop the compression, especially if an engine has compression release, not saying your does, but it is possible.
You adjust the valve clearances by filing off or grinding off the end of the valve stem to set the clearances. If your didn't do that that explains the compression issues. You are floating the valves, which could include the intake also.
Now they tell me. Grinding the shank to get .005 clearance is a joke. The human hair thickness is about the same. Not to mention if its hardened you just destroyed that. So I grinded it down the best I could and its seated so we will see what the compression will be now.
I like to see more than that, but without knowing the compression ratio, that may be the normal compression for that engine. a 7.5:1 engine will produce less compression than a 10:1 compression engine.
