short and sweet: Bike is a 2000 model YZ426, steel valves. WR426 heavy flywheel and stator (for lights). bought the '03 YZ450 auto decomp cam new from the dealer a year ago, never installed it. Rebuilt my motor 4 months ago myself, all new bearings (all new everything). Tried installing the 450 cam then, following the "PDF" etc, no luck. Dropped my 426 cam in, fired off 3rd kick from a fresh rebuild. Rode it like that for 4 months. Tore bike down to install another shock, decided to give the 450cam another shot. Removed valve cover, set piston to TDC. Ziptied IN cam at the 12 mark to the chain. Verified Timing again. Used a scribe to mark the angle of the tops of the cam lobes on the right side of the cam caps (with the CCT still installed). Counted 12 PINS between stock 12:00 marks on IN and EX cams. = Try 1========= Installed 450 cam with 12 pins between 12:00 marks, installed tensioner (CCT). Checked scribed marks. EX lobe sits point at a HIGHER angle on top. EX valves with 450cam have .033mm and .035mm of gap. Stock range is between .025 and .030. I'm too loose by .003 and .005mm respectively. Buttoned it all up, no go, as expected. = Try 2========= Installed 450 cam with 13 pins between 12:00 marks, installed CCT. Checked Scribed marks. 450 EX lobe sits DEAD ON to the marks from the stock EX lobe. Same valve gaps. Buttoned it all up, no go. SUPRISED. = Try 3========= Installed 450 cam with 14 pins between 12:00 marks, as called for by "THE PDF", installed CCT. Checked Scribed marks. 450 EX lobe sits LOWER than the stock EX lobe at TDC. Same valve gaps. Buttoned all up, no go, as expected. = Try 4========= Same as above. 14 pins between 12 marks. Re-gapped the valves to be .029 and .030mm tolerance, within factory spec. NO GO. = Try 5========= Haven't tried it yet. Very frustrated. Gaps set within factory specs, going to go back to 13pins between 12" marks. ============================= Cylinder reads 426 c3. back of cylinder or cases (can't remember) says Y - Z (assuming this indicates that indeed it IS a YZ motor not a WR). I've both timed this bike a half dozen times with the stock cams and its run perfectly every time, same with the valve clearances. I've built this motor from the ground up, head and bearings and everything. There was not ONE part left in the cases during this process. Although i feel like a complete idiot trying to do this mod, i just can't accept that I am, but believe more that i'm missing some key piece of information. Is it possible that i have a WR head and WR cams? or maybe this is a stock 400 head and 400 cams? Would i not have found problems while ordering all new valves, springs, keepers, cam chain, etc for the head when i rebuilt it? What other possibilities are there that I'm ignorant of? PLEASE HELP. I"M PULLING MY HAIR OUT!