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Here's how... (archive)
[ Follow Ups ] [ M5 (E28) Message Board ] [ Msg. Board FAQ ]
Posted by JamesM on February 01, 2002 at 08:23:11:

In Reply to: COMPRESSION TEST posted by Sean on February 01, 2002 at 08:08:58:

Compression should be done on a warm engine. Remove the main relay in the glove box to disable the ignition and fuel systems. Remove the plug wires and blow holes out with compressed air to keep dirt from getting in. Remove one spark plug and thread compression tester in. Hold throttles wide open and crank engine over 8-10 times. Compression should be between 170-210psi, and all 6 should be within 20 psi of each other. If any cylinder registers low, squirt some motor oil into the cylinder and retest. If the compression comes up, you have worn piston rings. If the compression only comes up a little, you have burned valves/seats, most likely on the exhaust side.

Check valve clearance yearly to avoid burned exhaust valves. The clearance tightens--not loosens--over time!

JamesM

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