400 head on 426?

4 replies to this topic
  • kounkel321

Posted April 16, 2007 - 12:45 PM


anyone knnow if a head off a yz400f will fit on my 02 yz426? just wondering if anythng is different or something.

  • kounkel321

Posted April 16, 2007 - 01:07 PM


oops i mean a WR400 head on a yz426??

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  • Birdy426

Posted April 17, 2007 - 05:41 PM


Yup. It will fit. The earlier heads have a vacuum port at the base of the intake that you have to either cap off or plug, but other than that, they work fine. Need to be sure you get the right combination of valve train parts, though. The 98-00 bikes used stainless valves and appropriate springs, clips, and retainers. The 01 and up bikes use Ti valves with much lighter springs. Either way, be sure you use the right springs with the valves. Early springs will beat the snot out of Ti valves and later springs will allow the heavier SS valves to float and do some real damage. Be sure the guides are in good shape (mic them and replace as necessary), and always use a fresh cut on the seats with new valves.

I have a YZ400 head on my 426 (YZ and WR heads are the same), and it works great.

  • kounkel321

Posted April 18, 2007 - 01:21 PM


awesome yea i bought my 426 with the head blown apart so i found one off a 400 complete valves and everything...

  • Birdy426

Posted April 18, 2007 - 09:10 PM


Kewl. I would at least pull the valves out and inspect them, clean it all up, put it back together and do a solvent leak test before I put it on the bike...just to be sure...

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