Posted by Gordon Maney on Sunday, August 15, 2004 at 2:30PM :
In Reply to: compression anyone??? posted by adam on Sunday, August 15, 2004 at 12:05PM :
If you listen to an engine cranking during a compression test, it will make an audible, rhythmic sound patter as it passes through the operating cycles for that cylinder.
I take no issue with a number, whether it be four or five or six. Having said that, you want to crank the engine the same amount for each cylinder. If you have a cylinder that can produce 110 psi in three compression strokes, and another cylinder that can produce 110 psi in 12 compression strokes, those two cylinders are not equal and should not be regarded as such.
Do your test with the throttle wired wide open, the choke wide open, the ignition system disabled, and all plugs removed. It might seem foolish to say all plugs have to be out, but I have talked to people who did compression tests by removing plugs one at a time.
Different sources cite different variation limits. It would be really nice to see your pressures vary no more than 10 percent, though it may be tolerant of more. A bit part of your decision will stem from how smoothly the engine can be made to run in spite of any variation in compression, and the larger economic situation with regard to the engine and the vehicle.