Hey guys, I'm considering buying an 07 yz450f that the owner "claims" has 20 hours on it. I'm not new to bikes, and if i go look at it, i'll be able to tell if it really only has 20 hours. Anyway, i'm curious as to what your maintenance intervals are. I do all sorts of riding, but if i get the bike i'm going to do an AWRCS race that is 3 hours long. The regular maintenance i would do is clean the air filter every 2 or 3 rides and change the oil every 4-6 hours and change the oil filter every other oil change. If i do this, how long should i expect a piston to last and how often should i be expected to shim valves? sorry about the long post, thanks!