Just replaced the piston on my 04 KDX220. Had the cylinder honed and just cleaned the head up as it was in very good shape. Used a stock Wiseco piston and ring set and replaced the rod bearing. Probobly went a little over board but went as far as to check ring gap and skirt clearance and it is within the tolerances allowed in the Kawasaki manual. Fired it up and went thru three heat cycles. Rode it thru the gears slowly up and down the street, let it cool down and did the same two more times. I am running heavy on the premix for breakin. Next time down the road I went about 1/3 throttle and went thru the gears clearing it out. I did this four or five times and it felt strong. What I did notice is alot more vibration. It diffenently is assemlbly vibration. :bang: To be safe I grabbed another head gasket and pulled the jug to make sure a clip had not backed out and the pin was walking back and forth. The pin, rings, piston looked perfect. I put it all back together this afternoon and took off. Same thing. Im sure there is a weight difference from the stock to the wiseco and I am feeling a difference in the balance of the rotating assembly. I didnt go as far as to weigh the pistons but i am assuming this is what is happening. Has anyone else run into this? :ride: