1986 20hp Johnson long shaft low compression

reiddo1

reiddo1

Petty Officer 2nd Class
Joined
Jan 17, 2012
Messages
166
Just freed a new to me weather seized 1986 20 hp Johnson long shaft and ran it at elevated idle with a concentrated mixture of Seafoam. While idling has improved with running, I am getting only 60 psi compression on both cylinders and 120 psi if I pour a teaspoon of oil in each cylinder. The engine starts first pull both cold and warm.
I would rather not disassemble and am wondering if it would be wise to run it under load on my boat as a kicker engine with anticipation that the rings may seat better under load. All comments are welcome and appreciated.
 
R

racerone

Supreme Mariner
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Dec 28, 2013
Messages
38,060
Remove cylinder head and inspect cylinder walls.-----Or perhaps you need a better gauge.
 
T

tphoyt

Lieutenant
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Jun 10, 2010
Messages
1,320
I would try a different gauge just for kicks.
If still the same further inspection would be wise.
 
T

tphoyt

Lieutenant
Joined
Jun 10, 2010
Messages
1,320
The risk of major is high if you do it.
I did it ion a motor I didn’t really care about and it’s still running today but it was pure luck in my eyes. If you truly want to save the motor than as suggested pull the head and see what you got and decide from there where you want to go.
Best
 
reiddo1

reiddo1

Petty Officer 2nd Class
Joined
Jan 17, 2012
Messages
166
tphoyt said:
The risk of major is high if you do it.
I did it ion a motor I didn’t really care about and it’s still running today but it was pure luck in my eyes. If you truly want to save the motor than as suggested pull the head and see what you got and decide from there where you want to go.
Best
Click to expand...
Pulled the head. Lower cylinder seems fine but upper one has a scratch which I am hoping can be repaired by honing. Will also light hone the bottom cylinder as well.
 
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