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Top End Rebuild (RM250)

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Hey everyone,

After witnessing my mates YZ explode the piston halfway through a day i have decided it would be in my best intrest to be doing the same soon. My RM is a 2000 model and my main question is when i take the top end off, will i get springs and sh!t shoot out everywhere as there seems to be alot of cases with adjustments behind them on the top end?

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nope, no springs will come shooting from your topend! Drain the coolant, and start tearin her down! Dont forget to undo the powervalve actuator arm under the right side cover on the cylinder. Pop in a new top end kit and gaskets and you're good to go

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There is a 8mm bolt at the top of the actuator. pull that out and the linkage will come off the pv shaft.

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Be sure to clean the motor and frame good before you tear it down, and get a manual! It's not hard to do, but a manual is priceless! Any other problems, let us know and we will help.

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remember to label nuts bolt etc..i found that helped alot ..if you come into trouble there is loads a good people on here to give advice

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I have a manual that has been invaluable to me so far as it was not running well at all when i got it. It was a small price to pay to get it running crisp again.

Yes i 'assisted' where i could when my father in law rebuilt his KTM SX250, and picked up what i could so atleast i have someone that can lend a hand close by as well. Im sure i will turn to this site alot in the coming months. Currently it has a wossner piston kit in it. Do most people run a Wiseco piston?

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i run wiseco and have great luck with the pistons...i like ordering the wiseco piston and getting a cometic gasket kit....dont like wisecos gaskets seems like i hafta replace a few throughout the year .....Definatly clean everything up real good get all carbon build up off the Power valve if there is any and make sure to lube where needed when putting back together

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was going to bring up the carbon issue? Do you or anyone run upper engine cleaner through the bike like the subaru seafoam stuff. After a good clean would it be useful to continue running that stuff through it?

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Our bikes are so simple, it's more effective to just clean the inside of the motors by hand rather than use seafoam, but it won't hurt your motor if you decide to run some through it. If you decide to take your PowerValve apart to remove the gunk, please pay close attention to how it is assembled. That will be the most mechanically advanced thing you encounter while doing a top end.

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2 strokes are pretty simple. Just be careful when putting the piston back on, make sure you put some premix on the piston and rings as well as the cylinder to avoid any scratches.

This might help you:

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would there be any noticable advantage to cleaning the power valve?

YES! If it is gummed up now and not working, it will be a night and day difference. If it is working now, it will keep it working!

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ah, well im sure its working now but i might give it a clean anyway it would be a shame not to when its already apart

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