compression test

[big ken]

hi i am going to possibly buy a boat this sat. it has a 1994 johnson 88 hp on it. im going to do a compression check on it. what would be decent numbers? also would i just take out all plugs then open throttle and crank to get the #s thanks ken

 

[Tacklewasher]

Re: compression test

Ground all 4 plug wires to the block.

Make sure you have a good battery.

Use a screw-in type compression gauge.

Full throttle and crank until the needle stop going higher. 5-6 turns of the motor should do it.

Don't worry too much about the actual numbers, but they should be within 10% of each other.

 

[big ken]

Re: compression test

Ground all 4 plug wires to the block.

Make sure you have a good battery.

Use a screw-in type compression gauge.

Full throttle and crank until the needle stop going higher. 5-6 turns of the motor should do it.

Don't worry too much about the actual numbers, but they should be within 10% of each other.

stupid question
how do you ground the sparkplugs to block? thanks ken

 

[Elbo]

Re: compression test

A compression check has nothing to do with the plugs grounded.As a matter of fact the spark plug is not there.You will be testing the comp. of the cylinder.The tester is in the plug hole.What you are looking for is worn out rings ect.

 

[SKEETR]

Re: compression test

If you have a kill switch or lanyard just pull that. It will shut down the spark but still crank over.

 

[Elbo]

Re: compression test

JUst pull ur plug wires off and test one at a time

 

[kenmyfam]

Re: compression test

If you have a kill switch or lanyard just pull that. It will shut down the spark but still crank over.

Easy way to do it.

 

[big ken]

Re: compression test

tested motor today, all 4 cylinders were 120 real happy, bought boat brought it home, later this night realized i forgot to open carbs up while doing check[dam] will that make much difference? thanks ken

 

[Dhadley]

Re: compression test

Nope, you're fine. Don't over think the process. You're looking for consistancy, which you found. As long as all were checked the same (which they were) you're good to go.

 

[trendsetter240]

Re: compression test

A compression check has nothing to do with the plugs grounded.As a matter of fact the spark plug is not there.You will be testing the comp. of the cylinder.The tester is in the plug hole.What you are looking for is worn out rings ect.

The point of grounding the spark plug leads is to prevent the ignition system from trying to throw a spark to the block. I always just pull the kill switch.

 

[JB]

Re: compression test

It is almost always helpful to check the stickys and the FAQs on topics that suffer from so much mythology and disagreement, Ken.

Check this one out: http://forums.iboats.com/showthread.php?t=313884