Yamaha YFZ/YZF engine questions

[kyledvor61]

Just picked up a houser 250r/yzf426 hybrid. I checked the bore and stroke, and its 95mm bore and 63.4mm stroke. The bore is regular, but the stroke is longer. It's a 449cc. I'm assuming its the WR450 or the yzf450 crank? is there any way to tell without getting it out? I'm just curious to know which one it is.

Also, I popped the head, and theres some damage. I need a new one. I'm assuming the yfz,yzf,and the 426 head are all the same? I know on the yfz's they did some updating in 06 or 07. but thats fine its going to be a ported one anyway.

so my question is, are the heads the same? and also what are the differences between the yfz and the 426 motor?

thanks everyone

[Fast350ex]

The 426 head has a hole on the top right near the right exhaust valve for the decompression plunger or lever with an oil seal. You can put a pretty billet decompression plug in it, but you must first eliminate the stock 426 cam and use 1 with an auto decompression.

Did u mean the difference between the 426 & yz450f or yfz450?

The yfz motor has a little more beefier tranny than the 426 being that its made to turn 2 wheels instead of 1.
The 06 up yz450 has 4 dogs on each gear vs. 3 dogs/gear on the 426. By looking at the microfiche some of the 06 yz450 gears are interchangable with the 426 tranny.

I would like to know also if your 426 has the 450 crank in it. I've been debating on doing that along with the 06 yz450 tranny.

Someone please correct me if I'm wrong on any of these statements.

[racerx573]

The 450 cranks will not fit in a 426 without EXTENSIVE machine work and a lot of other modding. It probly has a stroker crank in it.

[kyledvor61]

So if I need a new head, I'm better off buying a 426 head then? or getting mine repaired.

I read somewhere else about the crank too, so it must be a stroker then. I'll check it out tonight.