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FlashGordon

2001 YZ426F Intake Cam binding

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Anyone experienced this before? Picked up a 2001 426 that had the top end disassembled. Previous owner planned to do a new top end, but never finished. Sat around for years.

On re-assembly, i noted some scoring on the center bearing surface of the intake cam, head, and cap. I was able to clean it up, but found something is out of whack with the camshaft cap. Camshaft will not rotate when cap is bolted in place. With both out of the engine, it will get stuck just by pressing it firmly into the cap assy. I used plastigauge, the the end bearing has .001" clearance, and the center one in question is .002" on the top, and .003" on the bottom; so should be plenty loose. I confirmed it is the center one binding. I looked at it under magnification, and on the head without the camshaft, and can't see anything obvious.

Seems like the only option is to try to get a replacement, which is not sold separately at MrCycle, or Bike Bandit.

Since that area was scored, I am surmising this problem was there before the engine came apart. Also found the cam chain guide on the exhaust side (front) was beat to crap; all the edges gone. I replaced it and the cam chain when I ordered all my parts. It is probably all related.

Suggestions welcomed,

Ron

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This is fairly common, and nearly always brought on by improperly torquing the caps. They fit very snugly on the cams (.0008 - .0021"), and are very easily distorted by incorrect assembly. They have to be seated by hand, torqued in steps in the correct pattern and to the correct spec (or less; I use 75 in/lb).

Check the clearance near 9:00 o'clock in the bores. Also check the runout on the cam. If the head's distorted, a good shop like Engine Dynamics can correct it economically. The caps are line bored on the head as main bearing caps on an engine block are, and can't be sold separately.

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