1990 Johnson 70 HP Compression

[wcoates1]

I am looking at a 1990 Johnson 70 HP that reportedly has 110 to 115 PSI compression across the cylinders. Anybody have a book that shows what normal compression for this engine would be?

 

[JB]

Re: 1990 Johnson 70 HP Compression

There is no "normal" compression, wcoates. Too many variables can affect the compression numbers. . .gauge, battery, conditions, technique. If all of those things affect measurement on one cylinder they will affect all the same amount and produce close to the same psi for all three unless one has a problem..

What we look for is all cylinders compressing within 10% of each other. The numbers you quote are very close and indicate a healthy engine.

 

[fishfeatures]

Re: 1990 Johnson 70 HP Compression

I am looking at a 1990 Johnson 70 HP that reportedly has 110 to 115 PSI compression across the cylinders. Anybody have a book that shows what normal compression for this engine would be?

My 60hp of the same year has the comp readings and it runs and starts fine , if it dropped below the 100 i'd consider getting something done but until that happens ,i''l keep using it as normal.

As Jb says if all 3 are within 10% then it'll be fine