Bill
I had two of the 40s like yours that broke the shaft just like yours. In fact the broken crank pieces were almost interchangeable between the 2 cranks. I was using mine in rat racing on Missile Mist when they broke. I also lost more than one crank in a K&B 35 green head when trying to use them in a 100 mile rat race. I again was using Fox Missile Mist fuel back then. All my shaft problems went away when I switched to the K&B 40 series 64 rear rotor.