Second oppinion on rebuild

[REN_IBOAT]

Hi all. I am rebuilding a 1985 Merc 60HP 3 Cyl.
so far I have been positively surprised that nothing is mangled beyond repair inside, as I bought the engine with a toasted cylinder 1, and it had run for quite some time with that, according to the seller.

Well, my question is: The cylinders look fine, I even think it will run std. after a clean-up, but the head has a problem that I am not sure what to do about.
It would seem that some sort of pitting happened in the far corner of cyl 1?s combustion chamber. weather if it where there before the piston went up in smoke, I don't know, but I am a little concerned that it will cause a hot spot, and fry my new piston if left untouched. Should I grind it down and risk disturbing combustion, or should I just ignore it?

As to what caused the problem i don't know, but my prelim theory is failure to retard ignition during load. The wiring harness is banged up.
Can anybody give some opinions on this piston damage?

last question: The pistons read: 744-9188 for parts number, I just cant find it in my EPC, does anybody know what these pistons are? Std. 0.15 etc.?

Best regards
Rasmus

Edited due to obscene language

 

[REN_IBOAT]

Re: Second oppinion on rebuild

Not to be the nagging type, but no one care to chip in with some thoughts? I really would like to start the honing job Monday.

Also in absence of a decent workshop service manual I really could use some info on cylinder wear limit for std. size pistons, anybody?

R

 

[shearpin]

Re: Second oppinion on rebuild

the trouble is going to be getting to that rough spot to smooth out the chamber or at least remove the bur's. there is a goood chance that the engine will work fine if you can do that. you will be working blind, unless you can get a 6 inch carbe shaft, and a die grinder. If it was me I would contact a machaine shop that deal with porting and polishing cylinder heads and ask them where you can get the 6 inch carbi bits. if you can get lucky last I new harbor freight offered an electric die grinder for porting and polishing but every time I tried to order one It was in back order. As for the numbers unless you see .010, .015, .020 ect. under the word "up" stamped on the piston treat it as a standard piston.

 

[CharlieB]

Re: Second oppinion on rebuild

Forget the #'s on the piston, get a mic and read the cyl bores.

As for the combustion chamber, steel shot bead blast the surface prior to boring /honing, you are looking to develope a uniformly surface, relatively smooth as possible. Even new, these chambers were 'as cast' finished. No sharp edges or projections that could heat and pre-ignite the fuel mixture.

As part of your rebuild ALWAYS install BOTH a new fuel pump/kit and water pump/kit. And clean/rebuild carbs.