RM125 weird Cylinder damage

kgmkgm
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kgmkgm
Edited Date/Time 12/4/2018 4:30pm
Hey there, just got this rm125 for free...

Pulled the cylinder off to check for rings vs piston vs bottom end.

Anyway, noticed this weird damage above the power valves. I've heard these bikes can break the cylinder, is this what's happening? Weldable? Replacement cylinder? You can feel it, its a dent or gouge in the cylinder. I'd be afraid a ring will catch it eventually.

Rest of the cylinder feels good, there is a minor scratch in the piston near the exhaust ports.


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sandman768
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sandman768 11/30/2018 12:25pm
11/30/2018 12:25pm
Almost looks like powervalves are dropping down into the piston? Are the valves worn?
kgmkgm
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kgmkgm 11/30/2018 12:38pm
11/30/2018 12:38pm
Not sure how to measure that wear. They don't seem to be coming in, piston looks good but I may have just caught it starting
kb228
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kb228 11/30/2018 12:43pm
11/30/2018 12:43pm
Looks like the plating coming off to me. Millennium technologies can fix it. Id imagine it was caused by Low quality bore plating and a top end with way too many hours on it.
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kgmkgm
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kgmkgm 11/30/2018 12:47pm
11/30/2018 12:47pm
Both things I can see. This was jetted by a hillbilly 10 years ago in leadville. AKA stock pilot, SUPER lean main. Then a friend had it, put a top end in 7 years ago, sold it to another friend, then my lady traded her old DH bike for it since she wants to learn how to ride. I imagine I can find spec on those power valves in a manual. Need to track one down
kgmkgm
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kgmkgm 11/30/2018 1:28pm
11/30/2018 1:28pm
Also how stupid is it to run another piston with damaged plating? I was even considering just re-ringing the piston since it just has some very minor scores on that side, maybe buff it down with scotchbrite. This is a learner bike, and we're not trying to spend a fortune on it. It will spend a good portion of its life laying on its side while the lady tries to pick it up, ha ha
Hondas4Life3
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Hondas4Life3 11/30/2018 3:40pm
11/30/2018 3:40pm
kgmkgm wrote:
Also how stupid is it to run another piston with damaged plating? I was even considering just re-ringing the piston since it just has some very...
Also how stupid is it to run another piston with damaged plating? I was even considering just re-ringing the piston since it just has some very minor scores on that side, maybe buff it down with scotchbrite. This is a learner bike, and we're not trying to spend a fortune on it. It will spend a good portion of its life laying on its side while the lady tries to pick it up, ha ha
It will blow up again in short time..
Rickyisms
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Rickyisms 11/30/2018 3:41pm
11/30/2018 3:41pm
kgmkgm wrote:
Also how stupid is it to run another piston with damaged plating? I was even considering just re-ringing the piston since it just has some very...
Also how stupid is it to run another piston with damaged plating? I was even considering just re-ringing the piston since it just has some very minor scores on that side, maybe buff it down with scotchbrite. This is a learner bike, and we're not trying to spend a fortune on it. It will spend a good portion of its life laying on its side while the lady tries to pick it up, ha ha
I give it less than ten hours for the position to catch that, come apart, and maybe take out your crank and crank bearings possibly. do it right the first time.
Falcon
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Falcon 11/30/2018 3:56pm
11/30/2018 3:56pm
x3 on fixing it now.
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kb228
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kb228 11/30/2018 5:56pm
11/30/2018 5:56pm
Dont even think about running it. Its broken dude it needs replaced. If you have anything other than a perfect bore and nice hatching it needs repaired. Youre just going to blow it up.
NoMuff2Tuff
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NoMuff2Tuff 12/1/2018 2:10am
12/1/2018 2:10am
Yea fix it now, I had Millennium fix a few cylinders and they do good work. If it's deep they will have to weld it back up but no big deal to repair. That is a area that gets really hot and where most of the time the Nikasil will first start flaking. It will only get worse
kgmkgm
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kgmkgm 12/1/2018 8:07am
12/1/2018 8:07am Edited Date/Time 12/1/2018 8:09am
Hmm. It was running fine before hand but I don't like to take any chances. This thing is going to live on the idle screw for a while but I'd hate for it to explode.

NoMuff2Tuff wrote:
"
Yea fix it now, I had Millennium fix a few cylinders and they do good work. If it's deep they will have to weld it back up but no big deal to repair. That is a area that gets really hot and where most of the time the Nikasil will first start flaking. It will only get worse" --
Yeah, last owner overheated it repeatedly in the high country, so that's probably why its flaking, but the PV seems to be extending slightly onthat side, looks like its been ground down once already.
Matt Fisher
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Matt Fisher 12/3/2018 9:47am
12/3/2018 9:47am
Thought I'd ask as I have a 02 cylinder. Btw- according to Eric Gorr's book, your 96 is a one-year only cylinder. 97 was a new engine design, and the earlier ones won't interchange either.
kgmkgm
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kgmkgm 12/4/2018 4:30pm
12/4/2018 4:30pm
Yeah I've gotten a ton of conflicting info on year to year changes. I don't expect any problems from Millenium though, and the rest of the bike is in good shape. Just a learner 125 for the chica and for me to take out on fun laps

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