Compression Test ? 86 Johnson 150hp

[Pst76]

Looking at a 1986 J 150hp that has been sitting for about 2 yrs. Went to look it over this weekend Cosmetic wise in good shape. Did a compression test after spraying wd-40 into each cyl and spun over a few times. Average reading was 50 to 70 lbs. My guess is that thats pretty low. Guessing it should be closer to 100lbs. Guy that owns motor said he would get it fired up this week on a stand and we could retest. He figures once the oil has lubed up the rings it will be OK. Question I have is would the low compression make this motor a candidate for a overhaul or It what he's saying make sense.<br />He is selling motor as ready to go. Need of overhaul will make a difference on what I would offer him.<br /><br />Thanks for any advise<br />Pst

 

[JB]

Re: Compression Test ? 86 Johnson 150hp

Howdy, PST76.<br /><br />I suppose there is a chance that you will get better (100+ psi) readings on a second test, but the WD-40 should have elevated them the first time. <br /><br />Do not let him spray fogging oil in the cylinders before testing. That would exaggerate the compression readings. Make him crank it up, then test it warm.<br /><br />The low compression could be a sign of bad carbon buildup, which is easy to fix, or worn out rings/cylinders, which is expensive to fix.<br /><br />My instincts say to pass.<br /><br />Good luck.

 

[Pst76]

Re: Compression Test ? 86 Johnson 150hp

Thanks JB I'll keep you posted.

 

[Mufasa]

Re: Compression Test ? 86 Johnson 150hp

If that motor has not been overhauled yet I am sure it is due. Figure about $4,000.00 to recondition the unit. Those compression numbers are beyond "sealing up".