Re: checking compression on a Model A

Posted by Bob Bidonde on November 19, 1997 at 08:41:32

In Reply to: Re: checking compression on a Model A
posted by Jack Richard on November 18, 1997 at 20:46:05

: :I would like to check the compression on my Model A.Is there a particular kind of compression gauge that will best fit the large spark plug hole?What should compression readings be?Are they checked with the engine warm?Any other suggestions ?
Jack Richard has the right answer, but the throttle should be wide open & the engine should be at room temperature when readings are taken. The difference between cylinders should not exceed 5%. Engines with cylinders at 50 psi or less are tired and in need of rebuilding. If a cylinder is very low, squirt oil into it through the spark plug hole and recheck the compression. An increase in pressure with oil indicates pressure leakage past the piston rings. Generally, the oil will not increase the pressure when the leakage is through the valves. Leakage pastvalves usually leaves a black stain on the valve stems that can be seen in the valve chamber.

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