426 head on 400

will a yz426 complete cylinder head fit on a yz400 bottom end and cylinder.

Ya, for sure....... Nah actually I dont have a clue.

The 400 has a nipple on the intake side (that part of the octapus connects to) that the 426 doesn't. The boss is there on the 426 head, just not drilled out with a nipple pressed in.

I put a 400 head on my 426 with no issues (just plugged up that little hole). The casting numbers are even the same.

Yes it will work. I have a 98' YZ400F and I used a 2000 WR head. Just had to drill a hole for the Hot start. Works fine. I believe that that the valve to piston clearance is the same as well, but you might double check just to be sure.

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