I have about 75 hours on my bike (2008 RMZ250) right now, about 30 or so is of hard riding. The motor is all stock, and I do oil changes every 6 hours and filter changes every 12 hours. I've been checking the valve clearances about every 20 hours and they haven't moved yet. I clean the air filter whenever there is a couple of dirt spots on there (around the sides and bottom of it is where it builds up.) My bike still starts on the 3rd kick every time, or sooner; I'm doing it like the manual says: two slow kicks and then a third to start it. I'm starting to really race now and I'm getting relatively much faster than I was. I'm revving it out before I shift, and am on the limiter right before I land from jumps especially when I race. I'm just wondering what all stuff I should be replacing in the engine, and when; and I'm on a really tight budget. My question is should I replace stuff when: 1. My bike is hard to start 2. The valves go out of spec 3. After I've adjusted my valves several times 4. After a set number of hours 5. After the compression gets too low 6. Or other? By "stuff" I mean piston, valves, crank, clutch, etcetera. I know these things wear out, and I'm just wondering when you guys think I will be needing to start replacing things... Thanks!