1986 20hp Johnson long shaft low compression

[reiddo1]

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.

 

[racerone]

Remove cylinder head and inspect cylinder walls.-----Or perhaps you need a better gauge.

 

[tphoyt]

I would try a different gauge just for kicks.
If still the same further inspection would be wise.

 

[reiddo1]

Remove cylinder head and inspect cylinder walls.-----Or perhaps you need a better gauge.

Tied a second gauge with no difference.

 

[racerone]

Remove cylinder head.----Followed by inspection.

 

[reiddo1]

Remove cylinder head.----Followed by inspection.

Is there any chance that the rings may seat better after loading up the engine?

 

[racerone]

Wishful thinking on your part.-----But good luck and do what you like.

 

[reiddo1]

Wishful thinking on your part.-----But good luck and do what you like.

Thank you!

 

[tphoyt]

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

 

[Dave1027]

Why not try soaking the pistons and rings with powertune?

 

[reiddo1]

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

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.

 

[racerone]

Motor needs to come apart !-----Piston / rings are damaged.

 

[reiddo1]

Motor needs to come apart !-----Piston / rings are damaged.

Ran the motor under load for about 15 minutes. Both cylinders now above 95 psi. Seems like loading it up worked.

 

[racerone]

Piston / rings are still damaged.

 

[reiddo1]

Piston / rings are still damaged.

Small scratch on the upper cylinder with nothing showing; no scratches on lower cylinder whatsoever. I will run it as is.