Compression test help!!!!

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PULLNIT

Seaman Apprentice
Joined
Dec 15, 2001
Messages
31
I am looking to purchase an older boat and motor.I want to do a compression test.What is the procedure to do this and what compression should a good motor hold?I am debateing two motors,A 1989 Johnson 150 OR A 1986 Mercury 150. :confused:
 
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rloper

Cadet
Joined
Nov 17, 2001
Messages
23
Re: Compression test help!!!!

Pullnit, what I usually do is pull the plugs on all cyclinders. Then squirt a light mist of wd-40 in all the holes (if the motor has not been run), then crank over till you get the highest reading. Repeat on all cyclinders, should all read within 12psi. If the motor is still warm from running the wd-40 is not needed. As long as it is over 105 or so, all I look for is being close to the same. Also ask the owner to let you pull the bottom lower unit drain plug to see what the oil looks like, if milky beware. Loper ;) A bad day fishing is better than a good day at work
 
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