Compression testing questions

Gamalot

Seaman Apprentice
Joined
Jun 17, 2010
Messages
30
Since this test is probably the best indicator of the motors condition I guess it is time to buy a compression gauge and follow the procedure.

Question 1, should I buy a tester that screws into the spark plug hole or just the rubber push fit type?

Question 2, My 1985 EV, V4 has been sitting for a long time. It was claimed to have been winterized and only has a true 6.7 hours on the meter as the owner and shop that installed the new motor both say the meter was new with the engine.

Some guys tell me to get it fired up and warmed up before doing the C test. Not sure if this is correct or not?

I have sprayed each cylinder with oil and can see the top of each piston with almost no carbon and shiny new. I also replaced the impeller and rebuilt the carbs already.

Any pointers on doing the compression test?
 

2manband

Seaman
Joined
Jul 10, 2011
Messages
62
Re: Compression testing questions

I don't know if you should test the motor warm or not. I always seem to end up doing it with a cold motor. That's because I don't have it running yet and I'm trying to decide if its worth the trouble to get it running. :D
 

emoney

Commander
Joined
Jul 19, 2010
Messages
2,551
Re: Compression testing questions

I'd run the test both ways. Check the #'s now with it being cold. Then, check again after you've started it and let it get to operating temp. The latter test will be the most accurate. And I'm a fan of the "screw-in" type testers. Usually can be picked up for around $10.00 at Harbor Freight or big box stores. That and an Infrared Digital Thermometer are two of the most important things to have in the tooldbox for boat owners. I guess if you throw in a spark tester you'd be complete, but I've gotten away without one of those plenty.
 
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