Like RCI said remove the prop adapter and see what the end of the crank looks like. OR Open the throttle all the way and shine a light inside and look at the rod. If it is aluminum its got a A&M crank, if its a bronze/cooper looking rod then its a Sachs rod and a MUCH better engine.
The A&M crank had the wrong metal harding, wrong fit, wrong balance and used the cheapest bearings that could be bought.