Harmonic balancer 340

Buy a new bolt... no need to muck the internal threads in the crank any more than they are. It ought to be a grade 8. (IMO.... your mechanic is a knothead for running this in with an impact wrench. Impact wrenches can turn minor problems into major ones.)

A 2" bolt ought to go all the way in with the damper. If not, then the threads in the crank may be damaged. If so, then you can get a new set of bolt: a 2.5" long one to start the damper onto the crank snout and pull it down at least 1", and then a 2" (and a 1.5" if the threads are damaged deep in the hole) to finally pull it into place. Once the damper is down snug where it should be, then the short bolt should be fine to achieve the final torque of 135 fl-lbs, even if it only has 1/2"-3/4" of the threads engaged. The interference fit of the damper on the crank really does the work.

BTW, very good pix, KK.