Topic: Reliability of compression tests on non running bikes

[Prospect]

I tend to do a compression test on potential bikes that I'm thinking of buying.  Some of them have set for a long time and I'm beginning to wander if the results I'm getting are reliable.  A compression test should be done on a warm engine so that's never an option.  Gauge error and other factors come into play.  I think a test will give you a very rough idea of the state of the engine.   Obviously if you get zero psi then you know what to expect but otherwise I don't usually use it as a predictable benchmark.  Usually also the pressure comes up once I get the bike running.

[Old Scrambler]

On post-60's bikes I like to see 75 to 90 lbs. and evenly across multis.  If not, I suspect a tear-down will be needed.  On motors out of the frame, I like to check the intake and exhaust ports for rust. I agree about the compression improving once running.