I just adjusted the valves for the first time ever on an XR650 and I would rather shim any current 4 stroke motocross bike any day of the week then have to deal with the limited space on the 650. I can remove the cam assembly, shim and put back togehter in about 30 minutes on my 450... the 650 took me that long to just get top dead center looking through that little peep hole with a mirror while kicking it over, I finally got it close enough then put it in gear and rocked the tire back and forth until it was dead nuts. Talk about a PIA. I tried taking my side case cover off but the skidplate was in the way and that is as much a PIA to re-install as was the exhaust valves to adjust! I am going to keep the valve checks on the pig at the current interval...1500 miles! I would rather split the case or change 30 tires then deal with that again!