I bought a brand new 07 YZ450 a couple months ago and have put 8 hours on it and decided to check the valves yesterday. After reading all the posts in this forum about how hardly anyone has had to adjust them, I was very surprised to find that my exhaust valves were out of spec to the tight side, they measured .17mm to be exact. I reshimmed to within spec and will check the clearance again in another 8 or 10 hours. Hopefully they will still be in spec. Not sure why I am one of the few that has had to adjust the valve clearance. I changed the oil and filter right after break-in and then again after 3 hours. This is the first yamaha i've owned in about 5 years. I've had 4 different CRF450s and have never had to adjust the valves on any of them(except for 1 tight exhaust valve after the break-in on an 06) . Other than the valves I really love the YZ. Power is great and handling is so much better than the crf IMO. I can throw it around so much easier and it doesn't tire me out as fast as the crf did. As long as I don't experience any valve issues I will be very happy with the switch I made.