Compression on a 1979 Johnson- known issues?

[marcusknight]

I have 1979 Johnson 70 HP. My dad was talking to some outboard mechanic today who indicated checking the compression on this type of engine is important because piston ring damage can lead to other more complicated issues. I was not exactly sure what he was talking about. Is there any merit to this, particularly on this type of engine? Any known flaws on this model? It seems to running fine ever since I bought it five years ago.

 

[curtis4769]

Re: Compression on a 1979 Johnson- known issues?

If it has been running fine for 5 years I wouldn't worry about it.

 

[orbanp]

Re: Compression on a 1979 Johnson- known issues?

Compression on those engines is anywhere between 100 - 150psi, depending on the condition of the engine. The individual ratios should be within 10% tolerance to each other.
Low compression at any of the cylinders is an indication of piston/cylinder/ring damage or head gasket failure.

Peter