Can I bore a 01' RM 125 cylinder?

dkgoodrich

Member
Sep 9, 2007
33
0
Can I bore a 01' RM 125 cylinder?


I bought this bike it had no compression, I tore it down, half of the middle O ring on the head was missing. So I'm guessing coolant leaked off into the cylinder it over heated and caused cylinder scaring. I mic'd the piston at it looks to be 1mm over sized. This baffles me because I thought the cylinders on most of the newer bikes could not be bored. I just want to know before I take the jug to get it bored and buy a matching piston.

Please help, I finally got my yz up and going for me and now I have a ktm that has no power and a blown up rm. I need a running dirtbike from my little brother. No one will help me on the ktm so here I am looking for help on the rm.

Thanks for your time

dk
 

RM_guy

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Damn Yankees
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Nov 21, 2000
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A stock cylinder is plated and can be bored out only if it is re-plated. Someone may have put a sleeve in the cylinder and in that case it can be bored out without having to re-plate it. You can verify by seeing if a magnet sticks to the inside of the cylinder. If it sticks then it's a sleeve and if not then it's plated.

In your case of a scored cylinder, if it's sleeved you need to bore it out to the next size (if it's possible--there may not be enough sleeve material left). If it's plated you can get it repaired at US Chrome. They can weld up any gouges and re-plate to fit a 55 mm piston.
 

dkgoodrich

Member
Sep 9, 2007
33
0
Thanks for your reply man. I did not know the magnet trick and I will try that when I get back to the shop.

I'm curious why people have us chrome to replate the cylinders. I think the last time I checked they were more expensive to replate than it was to just re sleeve it. Please correct me if I am wrong and I will look into pricing more.

Thanks again for your time
dk
 

RM_guy

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Damn Yankees
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Re-sleeveing may initially be a bit cheaper but you are left with a iron bore that wears a lot faster than plating and you'll end up spending more money in the long run on bore jobs and eventually you won't be able to bore it anymore and will need a new sleeve.

Also a sleeve Will not transfer heat as well as plating and your performance will be hurt. Granted not a lot but it will. Sleeves also have to be lined up perfectly with the existing ports and any mismatched means lost power. It can be significant if done wrong.
 

_JOE_

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May 10, 2007
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If you are one of those "don't fix it if it ain't broke" guys, sleeve it so it can be bored out when it grenades on you. If you plan on taking proper care of it, the plating will last pretty much forever. U.S. uses a thick coating, so you won't have to worry about it wearing through.
 
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