converting '05 YZ450F to 5-speed using 426 gears

Hi there,

I wondered if some one here maybe able to help. When i bought this bike i realized it had 5 gears and should have had 4 speed. So previous owner had modified obviously. He used 426 gears, and now i need to replace worn clutch (probably just the friction plates) i noticed the main nut thats holds the clutch boss on is only holding by a few threads. I wonder if he has used the wrong combination of parts. The reason i know they are 426 gears is i recently rebuilt bottom end and checked for worn parts in trans area, i compared them to my friends 426 old gears he had lying around.

Just wondered if anyone could enlighten me to what would allow me to do up the clutch boss nut without having to go back to 4 speed gear set.


Robert  :aussy:  :banghead:


Hi. I got no knowledge about thing you've asked, but it's pretty cool to know that there's possibility of replacing/repairing my old transmission (i got '04 yz450f) with 426 parts :).
I'm inspecting my grabby clutch right now and I wonder if my clutch plates and steel pads are still fine.
I've measured the plates and they are in spec. What made me wonder was the black and deep orange color of my clutch plates. Could you look at my pictures and advice me if they are burnt and should be replaced? Im not sure if the steel pads should have this brown marks on it. (didn't have time to inspect them for any warpage). Thank you!! :D



sosycz: Don't ask a question about your clutch in a topic someone else starts about their gearbox.  It's called "hijacking".  Start another topic with your question.


dattorob: The 426 transmission does not drop into any YZ450.  I only know of one other case of a 426 trans being used in a Gen1 4 speed 450, and that was one of the guys who built Doug Henry's '03 Super Moto bike.  He reported that the operation required a considerable amount of custom fitting and machine work, and that it was "a PITA".  If yours is working, wonderful, as long as no one expects to duplicate the trick just by dropping the 426 parts in.


As to your clutch boss, I would probably have a machinist cut it back at the outside end of the bore, where the nut sits, so that the nut would run on all the way.

You should confirm that the bike or engine is of a 05 YZ450F and not a WR/YZ426F.

...or a 400, for that matter.

hi guys,

Sorry for the delay in posting back. I like your suggestion grayracer on machining the clutch boss outside bore where nuts sits.

I am fairly certain its 450 as it has 480 big bore kit from cylinder works. Also when i google some of the other part numbers around the 

transmission area they came up 450. But yes i guess there is a chance its something else.

Anyways i will follow through and post back with the results. Thank you again.


Robert :)

It would be a little far fetched, I suppose, but it is actually possible to install a 450 cylinder and head (has to be both) on a 426, which means the 480 kit will go on, too.  It's only a 444cc engine if it still has a 426 crank.


And that's something else you can check: measure the stroke using a probe through the plug hole (if the engine is assembled).  The 426 is 60.1mm and the 450 is 63.4mm.


Post a picture of the left side of the engine. 

i'll try and post better picture later, and measure up stroke. Thanks man.  :thumbsup:


Hi mate, 

here is those pictures. I got it to fit in the end had to do small amount 2-3 mm of machining to the clutch to get it to fit. It now bolts up tight and flush but allows hub to spin. So i hope it works out. cheers

450 left side .JPG

450 right side.JPG

FYI, it all worked out and goes very well. I confirmed that it is in fact 450. I got machined 3mm off the basket if anyone was interested. cheers 

Robert  :ride:  :aussy:

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