cylinder scoring

Snowbird11 · Oct 23, 2012

I'm about 150-200 miles into a fresh aftermarket rebuild and noticed some lite scoring on the intake side cylinder walls about where the ring gaps are. so far i can only see three striations through the cross hatch, one on mags side and two on pto side. they are only felt by the finger nail and not otherwise noticeable by touch. I'm nervous that this is a sign of things to come.

would you run it without question or tear it down further and inspect.

mtncat1 · Oct 23, 2012

is that a single ring piston, looks like where the gap is on the ring

AKSNOWRIDER · Oct 23, 2012

if you can feel them with a fingernail...i would pull it down and have a look....

lonerider1 · Oct 23, 2012

Disassemble and measure ring end gap. It might be to tight. If it is file it to the correct gap. Also check ring pins. Make sure rings compress far enough into ring groove for expansion. Time to measure everything again.

Snowbird11 · Oct 23, 2012

mtncat1 said:
is that a single ring piston, looks like where the gap is on the ring

double ring forged piston.

I can actually see the ring gap in the reflection of the cylinder for the top ring. the score is a few mils off of that gap but lines up perfectly with the corner of the port.

I guess since i'm this far in it, i might as well tear it down and have a look. I'm pretty bummed because everything was within spec and measured twice. the cylinder had no scoring before it was re-honed either.

AKSNOWRIDER · Oct 23, 2012

check the ring end gaps..might be they closed up and butted..which if they did, they leave marks just like that...inspect the ends real close, if they touched you should be able to see it, if they didnt, recheck bore clearence(might need to be a thou or two looser) or it could be the port edge didnt get chamfered good enough...

Snowbird11 · Oct 24, 2012

Looks like they may be a little tight. first one i pulled was .017 the rest were .020

i as just informed that .019-.028 is where to run them. i may have measured them too high in the cylinder before. this time i dropped it down an inch. i will try to set them all at .022

i'm thinking i may need to do a lite rehone and possibly new rings to fix this thing up. any thoughts?

also, upon tear down i noticed a familiar mark on the exhaust side mag piston...
the left side of the photo shows it. that's not just a reflection but at least its not gouging.

jim9006 · Oct 24, 2012

just one comment... better take a zero out of your numbers

Snowbird11 · Oct 24, 2012

jim9006 said:
just one comment... better take a zero out of your numbers

copy, move decimal point. i guess that would make the clearance tight.

jim9006 · Oct 24, 2012

lol..... Oh, are you using the MTK kit on that? I installed the fix kit last year and I'm a believer.

Snowbird11 · Oct 24, 2012

jim9006 said:
lol..... Oh, are you using the MTK kit on that? I installed the fix kit last year and I'm a believer.

yes, i think it will hold up. i just need to do it right this time around. after seeing a couple other lite scores on the cylinder not associated with the rings, i'll be tearing it down again after another 5-600miles to inspect.

i do want to point out that mtn tek has been helpful and always willing to give me good advice along the way. I would use them again.

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cylinder scoring

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