I have got to do a compression test, and don't know how. Any help would be great. I have the tester and the engine is a '73 460
Anthony
Disconnect the coil, remove a spark plug(document which one and the results.) and turn the key-you may be able to do it by hand(removing all plugs will be easier). If you use the starter, dont turn the key for too long, just a couple rotations per cylinder are necessary, if your starter is tired already, this could kill it. Easier than turning over by hand though...
I've been told that you should hold the throttle wide open when doing the test as well.
Yes, remove ALL the plugs, and YES hold the carb open. I've never done it by hand, always about three pumps per hole with the starter. You're not really looking for a target number, but for equality. All cylinders should be within 5-8 percent accross the board. A low reading (weak) cylinder can be further tested by squirting a little oil in it and re testing. If it comes up, the rings are weak, if not the valves are the problem. Volumetric air pressure at sea level is 14.7 PSI. So, a reading of 147# would be close to 10:1 CR. However, this testing is not absolute, only a guide and should be used as such..........Moneypitt
Originally posted by Moneypitt
=Volumetric air pressure at sea level is 14.7 PSI. So, a reading of 147# would be close to 10:1 CR.
Is that how you determine the compression ratio of a motor?
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