How much is acceptable

[rollcaster]

"I have a '74 Johnson 25hp

"I have a '74 Johnson 25hp outboard that lost power on me one day, and upon inspection,I found it to be a blow head gasket. Minor fix, but I disassembled the block and noticed scuffing on the piston skirts. The bores on both cylinders are perfect. No scars, no ring grooves,nothing. You can still see the original hone marks on the walls. How much scoring and scuffing is acceptable on the pistons? I had plans of installing new rings, but do I need new pistons also? Thanks for your replies. Rollcaster..........."

 

[outboard_doctor]

"A small amount of scuffing on

"A small amount of scuffing on your motor is acceptable, I would recommend facing the cyclinder head to ensure it is flat. Use a steel ruler and check it for straightness, use feeler gauges to check if it is warped...upto 4 thou would be acceptable.

Check that there is no cylinder delamination between the steel liner and the alloy.

Cheers
from Australia"

 

[a_leonard]

"Ditto Jamie's advice but

"Ditto Jamie's advice but I would add a caveat. Yes a small amount of scuffing is acceptable, but what is a small amount? Your small amount may be much different than mine. This is a call based on experience. A picture would certainly help. As for checking for delamination between the sleeve and block, thats a new one to me, and I don't know how you would do it. Maybe Jamie could explain."

 

[david_r]

"allan, i think he is wanting

"allan, i think he is wanting him to make sure the sleeves in the cyls havent slipped and all the ports are still aligned.........it happens more than you would think."

 

[a_leonard]

"Oh yes, quite different from

"Oh yes, quite different from delamination wouldn't you say. In my limited 40+ years of experience I would say that its #1 highly unlikely and #2 very uncommon. But that just been my experience. Unless you have done some resleeving and maybe some racing. Then all bets are off.

"