How often to change PISTON !???

At least every oil change :lol: :lol: :lol:

Nah, until you start blowing smoke from bad rings, or lose serious compression, don't worry about it. When you do this, you could check the nickel coating on the cylinder and the piston for wear. The nickel coating is really tough stuff. Unless your valves decide to occupy the same space as the piston, the coating and piston should last a long long time, especially at those speeds.

-Parsko

In my experience with Husaberg's, the pistons seem to last quite a long time. Don't base piston replacement on time, base it on condition of the piston, IE, clearance with cylinder, piston pin bore wear, piston ring groove clearance, and scratches on piston.

One thing that will help your piston life besides keeping clean oil in the motor, is to make sure that you get all the old oil out of the crank area when you do an oil change. After all the oil has drained out, get the bike as vertical as possible, (normal riding positon), hold down the kill button and kick it through repeatedly so as to blow all the oil below the crank past the little reed. Then, lean it back over to finish the draining process. You'll be surprised at how much more oil comes out.

Usually when I split my cases I have another drain plug installed in the crank area with a magnet to catch any pieces that might end up there.