I have a 2006 yz450f with about 90 Hours. I change the oil every three hours and keep the air filter very clean. The bike runs great. I have only had to adjust the valves one time. And even then only one valve was barely out of spec. THe bike starts first kick, usually, sometimes takes two or three. It uses no more oil now that it did was it was new. It still make great power. Should I be thinking about replacing the piston anytime soon?