98 yz 400f with a wr400 bottom end

I picked up a YZ 400f and the bottom end needs a rebuild. I found a 99 wr400 bottom end with very low hours. Can I use my top end from my 98 YZ on the WR case? I know the piston kits are different. Not sure how compatible these are. Thanks guys.

The piston kits are interchangeable.  Yamaha lists both engines as using the same piston, rings, clips, and pin, showing old part numbers for each.  The two lower ends/top ends are also interchangeable, and apart from the transmission gear set and the magneto assembly, they are almost completely identical.

Thanks for the clarification! Do you recommend I swap anything from the yz 400 and put in the WR? The case and the crank are no good in the yz400. Everything else is there.

It will have more power using the YZ cams, head and carb.

Hey grayracer,do you know what other model kickstarts would fit my 99yz400f?

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