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Scratch with no itch... Thoughts?

Grumpy Bear

Grumpy Bear

Regular Contributor
1974 Merc 50hp 500. See pic. First time the case has been opened in 41 years. Actually didn't realize that a scratch in my cylinder #4 was this significant until I started honing (as odd as that is -- 220# hone, about to finish with 320#). Replaced the piston and rings for this cylinder already before reinstall. Funny thing is, #4 had great compression before disassemble! Anyway, there is a scratch that my fingernail will definitely catch upon but not horribly so (it's the middle scratch that goes down to the port and no further -- the ones to the left and right of it are either barely detectible or not detectible at all with a fingernail or any other pointed utensil). I've invested a couple hundred dollars in this rebuild and don't really want to invest more in a bore/sleeve. Give me your thoughts...

scratches.jpg
 
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Personal I feel that proof is in the pudding. If you have good compression and the motor runs well, you may well get many more years of service out of this motor. I am currently running a Yamaha 50HP that I rebuilt and I know there are aspects of it that aren't perfect, but if I wanted perfection I'd buy a new motor. :) Like all things, I guess there are two main questions: has the cause of the scratching been removed and will it not fixing it cause more damage down the track. My feeling is that if whatever scratched it has been removed, you have honed the depth down a bit and the compression is good, you will probably be fine in a two-stroke. Happy to have those wiser than me convince me otherwise.

Stuart
 
My brother ha a Mark 25 that some knucklehead assembled while leaving a spare needle bearing inside. Ouch! It made a huge scratch (more like a gouge) down the cylinder...and it ran like a raped ape!

Also, I had a Zundap dirt bike engine with a similar problem, and it ran like the gouge wasn't there.

Go for it!

Jeff
 
Interestingly enough, when I went back at these jugs with a careful finishing 320# grit, the snag of the one scratch really subsided. Let's hope, then, that too much materiel wasn't removed for stock sized piston rings.
 
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