I just bought a used 2007 yz250f that looked to be in great shape. Since its my first 4 stroke, I really wanted to check valve clearances just be safe. I have replaced the timing chain as well with an OEM one. 2 of my intake valves and both of my exhaust valves were kinda tight.. about .001" too tight. Nothing major, but I want them to be back towards the middle of the spec range. When I measured the shims, the exhaust shims were .075" and the intake shims were a bit bigger, more like .080". Since I needed more clearance, I got some sandpaper and went to work sanding the .001" I need off every shim. I sanded for at least an hour and am missing a few fingernails and my fingers are down to nubs, but the shims didnt seem to measure much different. Frustrated, I decided to just throw it back together and measure my clearances to see if anything changed. I decided to do this without the cam chain on, I was planning to put the exhaust/intake cams back in, and then put the chain on as thats how the manual instructs. Exhaust cam goes in, torque it down with my new cheapo harbor freight wrench, turns over smooth as glass by hand until the lobes hit the lifter buckets of course. Then I go to try the intake cam.. torque it down (evenly as the manual suggests) and it turns by hand, but with quite a bit of resistance. Doesnt feel anywhere near the other side, and I dont feel like this is normal. Undo everything, clean it all, reinstall, do this about 3 more times to no avail. Tried a few different methods.. seating cam into cap first then installing, then tried seating cam into head first, then fitting cap.. no change. Even with the bolts finger tight, it still doesnt turn great. What is going on here? I did notice when installing it, I feel like one (or more) of the valves is being compressed a little bit, but why would this happen and what could cause it? Could my shims I "made" cause it? First thing Im trying is going to a dealer and buying new shims (correct way) and lightly sanding the journals with 2000 grit sandpaper. Any other suggestions??