Johnson 9.9 compression question

[Island-life]

Hello

Couple weeks ago the head gasket on my 75 9.9 seahorse decided to go on me so when I got it home I tested the compression on both cylinders which read 90 psi on the top and 88 on the bottom.
I knew it was the head gasket that went due to the top spark plug being "steam cleaned" and of course it running on 1 cylinder.. So my question is at those compression ratings is it worth replacing the head gasket without a rebuild?
Not certain what acceptable compression is on these engines. I managed to pull the head off and aside from heavy carbon build up on the cylinder crowns the walls looked pretty clean. no heavy scoring where I can fit a finger nail in.
model # 10R75C have had the engine for 2 seasons

 

[Crosbyman]

most of my oldies don't reach those compression numbers and run fine so why not just change the gasket … remeasure and try it out


in any event you indicate having taken those measurements ...with the bad head basket in place ??? so unless I read this wrong the numbers mean nothing .


change the gasket ..go fishing

 

[Island-life]

Thanks for the response!

Yes I took the measurements shortly after I got it home with the bad gasket still in place.
I'm fairly certain the head gasket failure was due to overheating because the thermostat was in pretty rough shape..
engine was running great on the lake and then it bogged way down to 50% power and sounded like it was runnin on one
when I got it out of the water i noticed a sludge coming out the water hole. when I got home is when I tested compression and checked plugs. I also found it odd that both cylinders had near same compression. I'm guessing it must of blew in an odd way. i'll order a gasket and clean everything up and see what the compression is at and see how she runs!

 

[RCO]

A compression test really isn't a valid test for piston/ring condition with a known bad head gasket. Resurface the head, replace the gasket, then recheck the compression.

 

[raczekp1]

on ebay com is a oversize piston kit for 40$.
you need 2 x piston kit and 2 x upper con rod bearing

 

[Crosbyman]

on ebay com is a oversize piston kit for 40$.
you need 2 x piston kit and 2 x upper con rod bearing

:faint2ersonably I would invest in a gasket before spending bucks on expensive parts and cracking open an oldy

 

[Island-life]

Thanks everyone for the input I appreciate it.
Going to clean it up and put a fresh gasket on it and see what happens. I'll report back with some accurate compression numbers