1986 johnson 150 (high or low compression?)

[david lacey]

I have been told by a boat mechanic that my engine serial number J150TLCDC has a high compression rating so my 70-80 per cyclinder average is so low I need a new engine. Whereas if my engine was a low compression rating I would not be far off. How do I find out rather than just his say so? It doesn't seem to have much power. I just got it and am trying to make due rather than spend a ton. Thanks David

 

[steelespike]

Re: 1986 johnson 150 (high or low compression?)

imo Your 70-80 psi would be low for either one. 100 psi is considered minimum for
for typical outboards.Your 150 should be signifigantly higher. My hand cranked 57 30 hp was a little over 100 psi. would run pretty good on 60 psi.
You'll get more specific answers in the Evinrude/Johnson section.This is props.

 

[Dhadley]

Re: 1986 johnson 150 (high or low compression?)

Yep, it's shot and cannot ever be fixed. As a favor I'll let you send it to me.

Or....you could switch mechanics and find someone who knows what he's talking about. Static compression is just a guideline. A lot depends on what heads are on it, if it has standard head gaskets or thick gaskets, was it turning over slowly when tested, were the rings coked up or starting to coke up, and on and on. That's why the folks who designed it and built it never published numbers for a static compression test.

I'm interested to know where he found these "ratings" he mentioned.