5 main differences :

1) Frame with round tubes for 400, square tubes for the 500 :

2) Front brakes:

One disk Inboard for the 400cc	Double disk on the 500cc

Inboard means that the calier is inside the disk, like on the Buell.

3) On the engine, the timing is made by a single chain on the 400cc and a duplex chain on the 500.

So, the crankshaft has 2 gears on the 400cc	and 4 gears on the 500cc

4) Water circuit goes through the frame on the 400cc and outside of the frame on the 500cc.

	500

5) Front fairing fitt on the fork for the 400, on the frame for the 500.