There is nothing wrong with your engine. This is an ABC engine. It has a TAPERED Sleeve and an ringless piston. When new it is very common not to be able to turn the motor over by hand. This is why you use a heat gun to heat the cylinder head up. This eases the pinch at the top of the sleeve and makes it easier to start and makes it easier on the motor too. As the motor breaks in (the piston laps itself into the sleeve while running ) the pinch will start to go away and the motor will also start to run cooler and make more power. This usually takes about a 1/2 to a full gallon of fuel.