1969 Johnson 55 Compression ??

[zurowski]

Just wondering if anyone may have any idea of what the compression per cylinder should be for a 1969 Johnson 55hp. I have found one for a deal and would like to know what to look for before I go over and a take a look to buy it. Thanks for your time.

 

[Tim Frank]

Re: 1969 Johnson 55 Compression ??

Just wondering if anyone may have any idea of what the compression per cylinder should be for a 1969 Johnson 55hp. I have found one for a deal and would like to know what to look for before I go over and a take a look to buy it. Thanks for your time.

Spend your time checking out the ignition system on that one.
It was the weak spot.

 

[itsaboattime]

Re: 1969 Johnson 55 Compression ??

100 to 120 psi is very good compression for an outboard of that vintage. They will run just fine with numbers between 90 to 100 psi. Any lower than 90 and you start to get into gas consumption and power issues.
All the cylinders should be within 10% of each other.
A decarb can bring comperssion up several PSI.

 

[JB]

Re: 1969 Johnson 55 Compression ??

Psi is irrelevant in compression testing outboards. Different people using different guages under different conditions and using different technique can get differences of 50psi or more on the same engine.

What matters is that all cylinders, measured in exactly the same manner, show psi within 10-15% of each other.

 

[zurowski]

Re: 1969 Johnson 55 Compression ??

Very good, thank you guys. And any major or obvious things with the ignition system I should be looking at or for? Thanks again.

 

[Tim Frank]

Re: 1969 Johnson 55 Compression ??

Good physical inspection of under the hood wiring with particular attention to plug-wiring condition and insulation condition.
Check spark with a spark tester....and make sure that you get to try starting it cold, not if it has "just been running since someone else came to look at it".