I want to be able to reach the threads left undamaged deeper in the crank bore. I could try to get a bolt about 20mm (5/8") longer. I could try having a machine shop bore a recess into the stock washer so the stock bolt sits a bit closer to the harmonic balancer, but that doesn't get me 20mm.

I reckon that the stock bolt probably isn't harder than grade 8, as any harder might risk breaking the crank snout instead of snapping itself. It would be pretty straightforward to find a longer bolt in grade 8, but the head design wouldn't be the same.

Decisions.

John B.