1978 115 Johnson

[JRegier]

Alright so we've finally got the motor in pieces and I've melted away all the aluminum in the cylinder... What should my cylinder bore be (pistons are already .020)? And with new rings what should my ring gap be?

I know, "Get a factory service manual", I just can't find a reasonably priced one anywhere and I don't feel like spending $140 on a manual for a motor I paid $200 for!

 

[racerone]

Your cylinders were bored out to 3.520 / 3.521 or so.--------Ring gap in the order of 0.015 / 0.020 " is OK

 

[emdsapmgr]

If you replace one or more factory pistons in kind, it will be a .020 over piston. Part # 5006703. Last time I purchased oversize factory pistons, they came with a correctly over-sized ringset in the piston box. Standard bore is 3.5" X 2 19/32 stroke.

 

[racerone]

What do you mean by " melted away all the aluminum " in the bore,---Any pictures of the damaged pistons ?------Not sure if 0.020" O/S pistons are now available from factory.

 

[gm280]

Yes I'm interested in that "melted away all the aluminum" as well. Was one piston melted to the cylinder? If you really seriously like your engine, there are after market pistons you could buy. But make sure that you seriously want to rebuild that engine because once you start buying after market new pistons, prices can skyrocket quickly!

 

[emdsapmgr]

When purchasing replacement pistons, make sure they are all from the same original manufacturer. (Don't mix different piston manufacturers in one engine.)