Hi HighPlains and others
On the OS engines I use, a special hardened and tapered washer is supplied/used, against which the prop nut will bear and transfer the nut load to the prop. The washer is of a generous diameter so that the pressure the nut produces is distributed over an area sufficiently large enough to protect the prop from being crushed. The washer is of a sufficient thickness, strength, and hardness, to prevent it from deforming under the action of the nut being torqued. All of this, of course, is my opinion, since I did not design the engines or props. If you do not use the special prop washer I described, you can expect problems. An ordinary mild steel flat washer is absolutely worthless as a replacement for the special washer supplied with the engine. When I wear out or destroy an engine, I always save the special prop washer. I would not be surprised to learn that the prop nut can be torqued sufficiently high enough to shear the crankshaft or prop nut, without damaging an APC prop. Please do not do that.