I know that you need to pull the spark plugs and connect compression tester there. But how long do turn the engine over, how do you record compresson, and what are acceptable #'s. Thanks in advance!!! graemlins/beers.gif

Numbers will vary depending compression ratio,cam,etc. but the numbers should all be within 10% of each other. Cranking 4-5 complete revolutions should work,just make sure its exactly the same on each cylinder.

Originally posted by Rapid Robert:
Numbers will vary depending compression ratio,cam,etc. but the numbers should all be within 10% of each other. Cranking 4-5 complete revolutions should work,just make sure its exactly the same on each cylinder. Ditto!

when it cranks over those 4-5 times what # do you read? The last # that the needle goes to or do you add them up? The motor is between 9.0:1 to a 9.5:1 compression motor(pretty sure 9.2:1), what would be acceptable compression?

The last number...the cam affects cylinder pressure,so its hard to say what kind of number you'll come up with,,, 150psi maybe???

sounds good...so whatever number the needle lands on last after I am done cranking it over 4-5 times is the number I record? Thanks for all the help!

I always cranked the engine over until the needle stops rising. 4-5 revloutions are usually enough. Be sure to wire the carb wide open. The engine should be hot but by the time you get to the later cylinders it will have cooled a bunch. After doing the test dry, you can dribble some oil into the cylinders and do the test again (wet test). If the readings rise significantly, the rings are showing wear. You should do the wet test on any cylinders that are 10% lower than the rest. That will show if the cylinder is leaking at the rings or valves.

how come you wire the carb wide open?

To get free flowing air into the cylinder. The carb closed will restrict air flow and produce low readings.

O, makes sense now thanks for the help! graemlins/beers.gif

Turn the engine over untill the guage stops climbing. The carb. butterflies realy don't matter.

Cant forget to pull the coil wire either. Dont want to get the s**t scared out of me when the engine pops off. :D graemlins/thumbsup.gif

LOL, good point!