Solving low-compression problems
My old Nash was not driven for several years and ran OK when I started it, but a compression test showed 105, 115, 30 and 40 PSI. Adding an ounce of oil to each cylinder did not change the numbers much.
Believing the head gasket was blown between cylinders 3 and 4, I removed the head but found no trace of a problem on either side of the gasket, nor were there cracks in the head or block.
A local machine shop surfaced the head and ground the valves. After I assembled everything we never did find a problem and compression is now excellent in all holes. What happened?
It is not uncommon for an engine that has been stored for a long time to have uneven compression when you start it up. Experienced mechanics recommend you warm the engine up and then shut it off and torque the head prior to a compression test. Even then, the valves can stick and the rings might not be seating as well as they should be at first. Once they get fresh oil to them and everything expands to normal operating temperatures a few times, they usually seat in nicely.