Compression Test?

[Guest]

I want to do a compression test on a 94 70 H.P. Evin. Should the motor be warmed up before I do the test and how close should the test results for each cylinder be? Any info appreciated.
Thanks

[Ole1855]

I'm no mechanic, but I was having problems with my 60 hp Johnson this spring and when the mechanic did a compression check on mine it was 159# on one and 160# on the other. I would assume the motor should be warmed up, but someone else will probably answer that question.

Ole

[wastewaterguru]

cold or hot...doesn't matter because you're not after accuracy you're after precision.

The difference in compression of all cylinders is what is important to determine if something is wrong with one or more cylinders.

If all read low but equal(within 12 or 15 pounds), the engine is worn evenly, and as long as the compression of each is above 90# or so .....you should be OK.

To get the "actual" compression, the engine should be warmed to operating temp and the gage calibrated (most are not accurate). Throttle wide open so no restrictions and all plugs removed.

[united jigsticker]

Also be sure to wait a few moments, and check for "bleeddown" of the cylinder before removing the compression tester from each cyclinder.

[DTro]

rod holder
I've got than same engine. One cylinder was prone to run lean. I believe the middle. I'm pretty sure the VRO failed on mine(no alarm). Needless to say, I be premixin from now on. Hope ya get good results on that test! If not I had a mech do it on the side for me for around 1500.

[Guest]

Thanks for the replies, hope it tests good also. Will find out this weekend.