The pressure at kick back is very high since it can undo the tightened prop nuts and even break prop blades in a hurry. This prop blade sheared off during a kickback caused by me having the timing set 40 degrees BTDC instead 35 as I had intended. When you think about that kind of pressure and the number of square inches inside the cylinder that the pressure had available to act on, you can see that happening. This is the second time this 1.50 has sheard off a prop blade during a kick back. It one of the first 1.50s manufactured and had in the neighborhood of 12.56 to 1 compression ration.