Will a YZ426 complete clutch swap to a YZ400?

I've done a search and some suggest it will not work. The cases are the same. Is the shaft a different size or drive gears different making the 426 clutch not fit?

There seems to be some debate about that. It may fit the engine assembly, but I don't think it will fit under the YZ400 right side case covers.

The covers do have different part numbers from 1998 although the 2000 WR400 cover is the same number as the 2000 YZ426 cover even though the clutches are different.

I happen to have a spare 2000 WR400 bottom end that has the smaller clutch and comparing the side covers to my 1998 yz400, the 2000 is slightly larger in diameter in the clutch area. It looks like they adjusted the casting to make the larger diameter clutch fit. I should be able to use the 426 clutch with the newer side cover.

Please let us know if it works. I have been wanting to do the same thing but was told it wouldnt work.

The 426 part numbers begin with 5JG and the 400 begin with 5BE. My spare 2000 WR400 right side case and clutch cover has the 5JG in the casting. Yamaha must have started using the larger housing in 2000 even in the WR400 which came with the smaller clutch. The difference in size is not real obvious until you get a tape measure out to compare or look closely at the other areas of the casting with the cases side by side. Only then can you see the clutch cover is closer to other cast areas like the kick starter shaft hole and water pump. I'm still gathering all the bits for my '98 YZ400 to WR426 conversion. I'm going to use the newer style 2001-2002 426 crankshaft as it's actually cheaper new than the 2000 style with the keyed gear.

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