i heard something about that you have to put a new piston in every 15 hrs? is this true?

 

if the bike is raced maybe and rode very hard but for a every day rider i doubt it keep oil changed at right times and should be fine.

 

This is a recommendation that they give you if you have the '06 HRC kit installed for tip/top race conditions. The HRC kit is what they call their race kit. I believe they give the same spec for a stock crf450r dirt bike. They are basing it off of 15 hours of racing and it is a spec that, for most casual riders and racers, they will go far beyond. If you divide out 15 hours of hardcore racing on say a motocross track that is actually alot of races. Most weekend riders will put over a hundred hours on theirs (even w/HRC kit) before they change. I am pretty sure that most top racers rebuild their motor every race for top performance and to make sure nothing goes wrong over 60-80 foot doubles and to protect against DNF's. Don't stress it, just pay attention to your general maintenance in your service manual.

 

thanks for your reply

 

well i was told by the guy that does the work on mine 450R needs the top end rebuild just like 2 strokes reconmended every 40 hours, i just had mine rebuilt u dont need a pistion just rings and new gaskets ur lookin at 60 doller make i think the top end gasket kit is like 40 dollers

 

That same talk was going around about the 450R when they first came out. I bought my 450R in February of 2004 and haven't touched the top end.
I don't race but I ride a lot of trails and dunes.
I'f you're not a hard core racer it will last a long time. I don't think you'll have to redo your top end just like on t 2 stroke.