2000 426 gears

does anyone know if a 03 450s tranny guts will fit into a 426?

Won't fit.

You might be able to make it fit, since the opposite swap has been done. It was not a bolt-in by any means, and required quite a bit of custom fitting and machine work.

does anyone know if a 03 450s tranny guts will fit into a 426?

I know that the gears from a WR426 will fit, as long as you get them all in pairs. The only tricky one would be first gear as that requires replacing one of the shafts, but everything else is a direct swap.

im just concerned with 4tha nnd 5th to be honest...that and maybe like the shift drums(?) or forks(?) just was lookin at ebay and saw parts to a 450 and wondered if i coulda used those parts for whenever i break into my motor

Bear in mind that the '03-'05 YZ450 models were 4 speeds in the first place.

The '06+ 5 speed is 12mm wider and will not fit.

im just concerned with 4tha nnd 5th to be honest...that and maybe like the shift drums(?) or forks(?) just was lookin at ebay and saw parts to a 450 and wondered if i coulda used those parts for whenever i break into my motor

If you need to replace 4th then you probably need to replace third gear as well, as 3rd and 4th mesh on the driven side and replacing one may not cure your problem. When I had my 426 trans on the bench I noticed that if one was worn there were corresponding marks on the mating gear, and the shift fork had marks on it as well. These gears aren't that expensive, you could replace all of the offending parts for less than $500, IIRC, including forks. This also gives you a chance to modify your ratios to better suit your riding style. As long as you buy gears in sets, you can easily swap between WR and YZ gears from 2nd through 5th, but as I said before replacing 1st gear requires replacing one of the shafts which will get a bit spendy.

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