Yesterday I had my engine apart, again. Sure enough, there is excessive axial play in the crank. Almost one millimeter. There is no movement of the bearings when I push the crank back and forth. They still seat tightly. I believe there is too much play between the rear counter weight and the rear bearing allowing the crank to shift. I suspect, when the motor gets warmed up it loosens up, allowing the crank to move backward when the throttle is cut back to idle in flight. The prop is acting like a brake when the airplane slows down. I wonder if I could place a thin washer where the back end of the crank slides into the rear bearing, acting as a shim? What is your opinion, pe reiver?