A leakdown rate of 5% indicates a top end in excellent condition. The compression test doesn't add any engine condition information to that, except to tell you that you've got a lower compression engine configuration for some reason, maybe different pistons or a base plate on the cylinders or something.
I've had Britbike and Jap engines with a leakdown rate of 30% that still
ran well, though they were a bit hard to start and didn't idle very good. But an engine can be very leaky and still pull well at high RPMS where there's no time for leaks to affect things....
Lannis
Greg Bender wrote:
Okay, the leak-down tester arrived today and I headed out to the garage right after work. Here is what I found both for compression and leak-down:
Compression values (taken with the engine fully warmed up the other day before I destroyed my breather box): Left: 130 Right: 130
Leak-down values (taken with the engine stone cold. yes, I know they should be taken with the engine warm, but I don't have a breather box just yet. I would suspect these values will increase with a warm engine due to an expansion of materials AND the associated ring gap???): Left: 5-6% Right: 5-6%
I could not detect any air escaping from either the intake or the exhaust on either cylinder. This is in line with what I would suspect given the head work that I had done. I could not detect any air escaping
from either the base gasket or the head gasket. I did detect air escaping from the crankcase via the oil fill hole. This indicates ring/piston/cylinder wear to me.
But, everything I've read indicates that 5-6% leakage is not bad. Am I misinformed? Do I just need to be patient and re-run the test when I have my breather box back installed?