I have only checked my valves once on my 2000 WR400f. I have raced the piss out of it, revved it to the moon, and generally road it like a race bike should. I always change the oil and filter and the only problem ever was 3rd and 4th gears let go at a WORCS race. Had the bottom end fixed up and slapped a new set of rings on it. Other then that it has been bulletproof, I keep reading posts about people messing with the valves after 10-20 hours on the bike and it makes me feel guilty, like I am slacking on the maintence, then I read the occasional post that says the valves are good to go for long periods of time. Their was a pretty good one on the YZ side recently. So whats the real deal on Valves, is their a diff between my 2000 and 2004, can I treat the 04 like the 00?????