Rebuild?

[kshields2]

I have a 2009 yz450f and am the original owner it's never been rebuilt. Should I rebuild the top end it runs amazing and has well over 150-200 hours, some people say don't mess with it if it's not broke. I recently shimmed the valves and while I was in there I cleaned the piston from all the black stuff built up from the looks of it looked pretty good but i really don't know. What do you guys think new piston or just leave it alone?

[15thumper]

Rebuild it now instead of when it blows could end up costing more, plus I guarantee once you do you will realize you had power loss

[knuckleduster271]

What kind of riding do you do?

Imo 200 hours really isnt much on one of these motors if it was maintained.

If its not using oil or making any noise id run it for a while longer.

[grayracer513]

I stretched mine out beyond 300 on its original top end.  Then I replaced the piston and rings, honing the original bore, when I did the WR 4/5 swap to the trans.  The bike had no outward signs of needing a top end, but the piston had worn to the point it was dragging on the bore walls between the rings, which area of the piston is not supposed to contact the cylinder.  So, in retrospect, while the whole thing ended well, I really should have gotten the piston in there a bit sooner.

[kshields2]

I ride mostly on trails on trips lasting 4+ hours a day and on the track a handful of times. Now the famous question what do I replace the piston ,rings anything else? And what brand do you guys recommend that is gonna last like my oem? Thanks for the responses!

[kshields2]

What about valves I saw the Top was kind of chipping on one of them I don't know what that means

[kshields2]

I stretched mine out beyond 300 on its original top end. Then I replaced the piston and rings, honing the original bore, when I did the WR 4/5 swap to the trans. The bike had no outward signs of needing a top end, but the piston had worn to the point it was dragging on the bore walls between the rings, which area of the piston is not supposed to contact the cylinder. So, in retrospect, while the whole thing ended well, I really should have gotten the piston in there a bit sooner.

.

Rebuild it now instead of when it blows could end up costing more, plus I guarantee once you do you will realize you had power loss

.

Rebuild it now instead of when it blows could end up costing more, plus I guarantee once you do you will realize you had power loss

.

[KTMfinrider]

Throw a new cam chain while you are digging it.

[kshields2]

Throw a new cam chain while you are digging it.

that I replaced a couple months ago