1985 Johnson 175 Compression?

[Mugsey]

I just got this motor so I'm asking lots of questions until my shop manual shows up. I did a compression check and all the cylinders were within 5 lbs of each other but the readings were all in the 65 to 70 psi range. Motor runs good just wondering if this was within the acceptable limits or is this too low? Thanks

 

[ezeke]

Re: 1985 Johnson 175 Compression?

The fact that the range is close is a good reason to redo the test with a different gauge and, to be sure to do it with all of the spark plugs removed and the engine warmed up if possible. The battery should be fully charged.

If you can't warm it up, at least spray some fogging oil on the pistons.

 

[JB]

Re: 1985 Johnson 175 Compression?

Could be that it would benefit from a decarb, but I agree with ezeke.

 

[Mugsey]

Re: 1985 Johnson 175 Compression?

I did the test with the plugs out and the engine warm. The compression gauge is new. If I redo the test and the readings remain low is that going to be a reason for concern? If so what would good compression be?

 

[ezeke]

Re: 1985 Johnson 175 Compression?

If you feel that the engine was well lubricated and that the engine was turning as fast as possible, a thorough de-carbon treatment may help you to get higher readings: http://forums.iboats.com/showthread.php?t=158076

The rings may be stuck a little if the engine has not been run for awhile. The readings are not what you would expect from a recently rebuilt clean engine with newer rings, but it should run OK.