If everything is free to move then i would just say that there was a fault (crack) in the crankshaft. Like i said the loadings on the shaft are large. I didnt realise it was the pin that was broken, the forces on this are different but again large.

There is no reason why that should happen on a good crank shaft, you would have to give it some hell of abuse! I would certainly say its a manufacturing fault...IMO

Cheers,
David