After talking to a friend who was doing his yearly piston replacement on a CRF bike, I started wondering about the XR600. When is it time to replace the piston? I've been into my engine a couple of times and the piston has always measured as new even though it has a lot of hours on it. I've been riding it 60 or more times a year and it still has the same piston as when I got it in 2000. It's not the stock one that it had in 93, so it is at least seven years old and maybe more. Do theses pistons ever break off a skirt? Is it time for a new one before metal fatigue causes the skirt to break? How many hours is too many?