I am in the process of rebuilding my friends 2001 WR426 and have run into a problem. It almost seems like the cam chain is too short to fit over both of the cams. The crank cases were replaced, crank, cylinder, piston, rings, cam chain, and all the bearings. The chain is riding on the geared section of the crank and everything is put together as the book says to do it. The part number on the cam chain bag was double checked and is the correct one. I have both cams out of the head, angled forward to ease getting the chain on, but no luck. One cam will seat back into the head, but the other one is too tight to fit into its slot. I rebuilt my 450 and never had this problem. All the parts were bought through Thumpertalk oem parts, is there any chance Yamaha put the wrong part into the wrong wrapper???? longshot.