J15RCRM has different pistons. Is this a big deal?

[Bullie]

This is a 1984 15hp Johnson I picked up sometime back. It would start I was told but didn't run well. I should have checked it a bit better as it had 110/75 compression readings. I removed the power head and the head and noticed the pistons looked a little different on top. I then pulled the bypass cover and saw that the pistons are definitely different. One looks "normal" and the other has a lot of circumferential grooves around it. The cylinders looked good and smooth with no scoring. There was some blow by on #2 that I could see on the head gasket, explaining the skewed compression numbers I assume.

 

[Bullie]

This is as deep as I have been in my outboard tinkering and though I want to know how to really repair these things...breaking it down any further makes me a bit nervous. What would you guys do?

 

[flyingscott]

That looks odd I have never seen a piston like that take a picture of the piston top and bore

 

[racerone]

??????-------No big deal here and it looks like it might have an after market piston installed.---Happens all the time !!!

 

[Chinewalker]

The pistons being different isn't that big of a deal, but the compression being off certainly is. Which cylinder had the higher reading?

 

[Bullie]

The pistons being different isn't that big of a deal, but the compression being off certainly is. Which cylinder had the higher reading?

#1 had the higher pressure. Which is the cylinder on the left (grooved piston) in the picture. The leaking from the head gasket was at the very bottom ( 6 o'clock) of #2. I didn't take a picture but there was a small area where it was fairly obvious.

From the responses I think I will clean up and lightly sand the head to check to see if it is warped, replace the gaskets and check the upper water grommet to make sure nothing is blocked. Is there anything else you guys would recommend?

There is no scoring in the cylinders that I could feel or see and everything else looks pretty good.

 

[racerone]

Every head that I look at is warped.-----Just the nature of aluminum castings that are not stress relieved during the original manufacturing process.