My Kawi dealer recommended annual top end changes on the 2-strokes whether I needed it or not. I pushed my luck since I really don't think that I ride hard and got a year and a half before breaking a piston. The bike was bought used but the previous owner took better care of it than I do. I have learned my lesson, and the damage could have been a lot worse. Bottom line, you don't necessarily need to change it as often as the manual says, but make sure that you don't wait too long. I never lost any compression, my bike alway started within 3 kicks when cold, and I don't feel any more power increase with the new top end, so the tried and true method of doing a top end when it feels like the compression has dropped will not suffice.