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i am thinking of buying a 2001 sporttrax 250 that has a blown top end. I know it needs to be bored and a new piston, but i was wondering if i would have to rebuild the valves. I also want to know what would cause a 4 stroke top end to go out.. Thanks for any responces
 

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I did a top end on a 450 es last year. It had been smoking pretty bad for awhile. It fouled a couple of spark plugs. One night it just quit. New plug didn't help, it would not sty running. So it was top end time. It was just excessive wear in the cylinder. The bike had alot of hours on it when he bought it. And I dont thing the last owner did much maintenance like changing the oil and such. Anyways first size over, new piston, rings, valve seals and gasket set from wiseco and the bike has run like a top ever since.

Basically it had smoked itself to death.
 

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i am thinking of buying a 2001 sporttrax 250 that has a blown top end. I know it needs to be bored and a new piston, but i was wondering if i would have to rebuild the valves. I also want to know what would cause a 4 stroke top end to go out.. Thanks for any responces
Welcome to the forums. Concerning the valves, usually you can get by with just replacing the valve stem seals, but you will need to check the valves to make sure they are sealing good and aren't bent when you remove the head.
 

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agreed ^^^^^^..if your gonna tear it down..do it once..and do it right..go over all of the top end..as for why it died to begin with..could be anything..lack of oil from the oil pump going out ?..got it too hot ?..ran it with little or no oil ?..so many things can ruin a motor...check your valves for being bent.
 

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if it's the 250EX they are cake no cam up top to contend with it's a pushrod engine. super simple.
 
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