Did it dry on each cylinder. Then put a capful of oil into each cylinder and retested. This allows you to determine how much of the reduction in compression is a result of “blowby”–gases escaping past the rings on the cylinder–rather than gas escaping around inlet or exhaust valves, or a blown head gasket.
The results:
Dry
#1 480
#2 400
#3 420
#4 480
Wet
#1 540
#2 580
#3 480
#4 530
This signifies to me that we’re getting some blowby. I don’t yet know how to interpret the absolute numbers.
Update 5/27/11:
The engine has run flawlessly since writing this post, with the exception of air in the fuel lines which is unrelated to the internal condition of the engine. It always starts right up and sounds great. Many people have told me not to worry about the compression numbers if the engine is running well. So I won’t.
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