426 repair options; cylinder

i have a 2001 wr426 with a scored cylinder. i'm looking at options and trying to learn.

what 450 top ends would fit? are the quad 450s the same as bike 450s?

You could always go big bore? There are serveral kits available.

Next size up is the 444, there is also a 446/449 and the daddy 473.

As to wheather the quad wil be the same? probably? but not 100% sure.

I would go the big bore route, unless you already got a quad 450 sourced.

I'm pretty sure the 450 cylinder will not fit. Millenium will repair yours and re-niklseal it. I think it's around $200.


i have found that 03-09 yzf and yfz and wrf 450 all take the same cylinder.

also read that 450 cylinder will work on 426 but the head is needed, too; the 426 head doesnt fit the 450 cylinder. can anyone confirm that?

For sure you cannot use the 06 and newer yz cylinder/head or the 07 and newer WR cyl\head as they have internal oiling instead of the external piping used on earlier models. Also if you go with a 450 cyl\head you may have some cam timing issues if you use the 450 cams. The have a smaller pitch circle than the 426 cams. You can get away with one cam as many have done with the autodecomp upgrade. I'm not sure there is enough travel in the tensioner to compensate for two. Might be pretty sketchy. Why do you want to go with the 450? Why not just replate and go big bore if you want more displacement?

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