What the other guys said on the motor. There are just a lot more parts to wear in a 4 stroke. I've bought a couple of used motors but only for combat or trainer planes. Keep this in mind when you find a used motor. If it is as good as the seller says it is why is he selling it. RC'ers are notorious pack rats. We will store the only recognizable piece from our last crash on the oft chance we may need it in the next ____ years.(fill in any number)