The bike in question is a '03 YZF 450. I raced a full season of enduros here in Colorado last season, and a few motos as well. This season I am broke and have just been riding. I bought the bike new and have not adjusted the valves, but have religiously changed the oil, oil filter, and cleaned the air filter. Despite being a hack mechanic at best, I have been reading the service manual intensely, and have decided to dig in. The bike is not starting any differently than when new, but I am beginning to get paranoid, and would rather take the time for preventative maintenance, than have the motor grenade, subsequently shredding my wallet. If the valves need to be replaced, should I opt for stainless valves for the sake of longevity? As long as I am "digging in" should I replace the piston and rings? Any words of wisdom, with the exception of, "you're a dumb-ass, take it to a shop!" would be greatly appreciated. Thanks, Geoff