Oh, a small amount of "end play" is normal for many engines. Just be careful that if you push on the prop shaft and turn, you don't feel resistance or hear anything. Sometimes it's possible for the crank to rub the backplate. It's not a problem when the engine is running with a normal prop, as it will be pulled forwards, but you can shave off bits if you crank away with an electric starter. Pusher props are right out.