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2005 KX 125 Tech Question

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I bought this bike and the previous owner replaced top end along with new cylinder and since put 10 hrs. on bike. The cylinder was replaced because it had a 144 kit on it and it failed damaging cylinder. My mechanic riped the top end down to inspect after we found antifreeze in tranny due to water pump seal failure, but also from head. While apart, we found that the piston was trashed on the exhaust side, damage to exhaust bridge and some detonation. He also foundthat the power valve is the one which was cut for 144 kit. He said that we need to machine the head replace top end, clean up cylinder which he said shouldn't be a problem and replace power valve. Is replacing power valve necessary. I dont want to challenge him but I dont see how that would cause a problem. The power valve itself is $100 bucks. I am pissed, because this is a xmas gift for my son and we didn't even put a minute on this thing yet.:bonk:

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If the plan is to bring back to a 125, then yes you have to replace the PV. It will not run correctly having the extra clearance ( about 2mm). If you keep it 144 and need a new PV, then it needs to be machined for the bigger bore. No one makes a 144 PV out of the box. No good builder will machine a PV without have the entire engine to test fit PV for proper clearance. UNLESS, it's a Pro Circuit, RPM or Eric Gorr motor, they know their exact specs.

Check ebay, I found a complete PV setup for our 03, for $45. 04-05's are more plentiful than 03.

Unfortunately since it's already a 2mm overbore, Millenium won't do an exchange. Not sure about US chrome or LA sleeve though.

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Thanks, I am bringing back to 125 and it was done by Millenium. I guess I could sell the power valve that has been shaved for someone doing a 144. I looked on ebay but could not find one. Thanks for info SAPPERS.

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In the new issue of Motocross Action, they blew up an '06 YZ250. Their cylinder and head were sent to Millenium to have repaired. The head looked like it had confetti dumped on it, from the piston parts grinding into it, in the before picture. It was looking brand new when returned. I figured I would let you know about the head because I didn't know Millenium did head work. I can vouch for their cylinder work though.

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they're doing alot of different things now. A few friends are having their V8 engine blocks done. They coat the cylinder bores with their special coating just like our bike cylinders. I just seen one of them honed to his pistons. MAN!!! it is so sweet. 1500hp on alky.

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In the new issue of Motocross Action, they blew up an '06 YZ250. Their cylinder and head were sent to Millenium to have repaired. The head looked like it had confetti dumped on it, from the piston parts grinding into it, in the before picture. It was looking brand new when returned. I figured I would let you know about the head because I didn't know Millenium did head work. I can vouch for their cylinder work though.

the head works easy for them if it's not cracked, they can just run a bead over it and stick it in the lathe

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