[rotorwrench]

With 40 psi readings it indicates the engine is getting a little tired. To check the rings, a person can squirt some oil in each cylinder and retest. If compression improves then it indicates the rings are getting worn. Leak down testing will check valves and rings for leakage. More average readings for model As with some miles on them would be between 55 and 65 PSI. At least the old engine has consistent readings between cylinders. They can still run at 40 psi but they wont have as much power.

Those that have high compression heads may get higher readings than average but we aren't talking about a very large change in compression ratio between 4:1 and 5 or 6:1. It will make a difference though.

Valve timing can be checked while the manifolds are off in case it does have a timing gear problem. The intake will start to open just after TDC on the beginning of the intake stroke and the exhaust should be opening at the beginning of the exhaust stroke. A check for sticky exhaust valves can also be done since a person can see all the exhaust valves through the ports. Both valves should be closed on the compression stroke.