ORIGINAL: jonlowe

The stock crank can and will break at the rear of the intake port window from a sharp machining edge. I radiused the sharp corner with a Dremel and polished it. I had three break in one year using an APC 18.1x10W. All three had exactly the same failure, and the pieces were so matched they would almost intechange with each other. I started radiusing the port after that, and stopped using that prop at the same time, and had no further failures. The 18.1x10W is a heavy prop, which I think exacerbated the problem. The 17x12W turns out to be a better match for the engine anyway.