05 yz450 piston in 09 wr450 need help

Bought a wr bike that needed work and a buddy has a moose racing 13:5:1 piston for a yz450f, it says 03-05 yz450f but what would make this not work in the wr 450.  Any input would be great.  The wr is a 09

I think only the 2006-09 YZ pistons will fit ?

I'm pretty sure that there is a difference in the compression height (the distance from the wrist pin bore center to the top edge of the piston crown).  Don't think they're interchangeable.

So basically I need to stick wr piston. I read the wr year changes and from 06-11 there was no engine piston changes except:

New engine and balancer. New cases/head. Crank/trans 2mm wider. Cams, piston, clutch, kickstart shaft, shift detent assy, water pump cover. starter drive carried over from 2006.


From what I understand the crank was just made 2mm wider and new head.

Also seen on je website one of the pistons fit 05-09 or 05-2015

You don't need to use a WR piston, just a piston from the right generation of YZ450's.  The '03-'05 YZ450 is a Gen1 engine, your '09 is a Gen2, same as '06-'09 YZ450's are.


There is also no piston that could possibly fit any year from '09 or earlier AND any year from '10 upward, because the '10 and later models have a 2mm larger bore, and are 4 valve engines instead of 5.

Okay I see, so the last thing is the crank which is a 2011 wr crank.  Do i gotta dump it or can i roll with it.  I understand everything you guys have said about the pistons and if this crank is a nogo then i'll have to find another.  Thanks guys

The '11 crank will interchange with any of the '07-'11 models. 

I know the earlier wr piston are higher compression than later models, so does this pertain to the wr pistons too.  My buddies have all these parts at my disposal except for the later model yz pistons, so the yz is out the question.  We have a new oem 04 wr piston and an 05 and if neither of these can be used then um gonna have to wait and order a later model piston then.

Neither of them will fit right.  The '04 and '05 were Gen1 engines, while your '09 is a Gen2 ('07-current)

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