^... as above, I can immediately think of 2 that have sheared the taper off cranks, both on standard 200 motors. One of these was when a pal bought one of the factory clearance 'plug and play' complete Jet 200 motors that Bedlam cleared out of factory. I told him to watch out for the heavy factory flywheel on weak crank but he decided that if it was good enough for factory production that he would give it a go. A few hundred miles later he is calling me on his mobile from the ring road layby to say... you're not going to believe this.... but...
I had no issue believing him that he had a loose flywheel with the taper and nut still in place. This had happened when driving along a long straight road, not down-changing into a corner or anything else that you would expect to stress the assembly.
My other pal's sheared when pulling away from a petrol station, simply going up through the gears as normal.
It is a shame as they have very reliable ignition and lights... until they go wrong

Adam