I had this problem of damaged threads on a couple of Southern Cross crankshafts. I ended up buying a die the same size and thread type as the shaft. Worked a treat!
Often a cheaper option is to buy a hexagonal 'die nut'. With a button die, you really need the appropriate die holder as well. Essential, if its a 'split' adjustable die.
These die nuts are suitable for restoring damaged threads, though not for cutting new ones.
The crankshaft thread size [both ends] for all Victa full crank engines is 1/2"-16tpi BSF.
For the bottom thread on the PowerTorque engine cranks, it's an M14 ISO metric, but I can't find a reference as to what pitch it is. 1.25 or 1.5mm would be most likely.
M14x1.25 is the same as a 14mm spark plug, BTW.
