Bwahahaha - "unless" Did he grow up on a 2t Mike? If so, he will be on the rev limiter like white is on rice. I put a vid of Monkey-Boy up here on his first 4t - rev limiter, here we come.I have to check the manual but I believe that it's piston, rings, valve, cam chain and guide that get replaced at 50hrs. Though I can't see it being much different than your kx. You are probably right on the amount of time and with him I would go 60 hrs unless he starts bouncing it off the rev limiter.