These kx450 are pretty reliable , the only thing I heard was a owner put a oil filter back to front and seized it , but took about a hour to do it. if it a fault with the bike ,kawi should come to the party, I recall once that Honda allow 1 in every 1000 machines to be a lemon, and what I see crf break more than any other brand ,having 2 separate oil compartments ,were people forget to change oil, and the d**n valves that would wear out in no time especially if the air filter was neglected as well as the to light of a transmission that would slip in no time at all, gears to weak ,they upgraded these parts as well because they new there was a problem, all bikes have troubles ,I sure there a good reason behind this failure.