Got back into MX about 2 years ago after 20+ years off the dirt. Bought a new '09 YZ450F. Just turned 100 hours. I've checked the valves twice and they've been fine. Bike still runs super strong, starts first kick. I'm old and slow (and 240lbs)...so I rarely see the rev-limiter. Oil + Filter has been changed every 3-5 hours, and I've never had any shaving on my magnetic drain plug. The bike has been a dream to own. Absolutely trouble free. I did buy some new clutch plates this week, so I am going to swap those out this weekend, even though the clutch isn't real bad. So...should I just go ahead and do a top end, timing chain and ???? I want to keep this bike another 100 hours (since I have thousands invested in suspension/aftermarket goodies)...how do I get there?