I think I'm missing a nut.

Hi, I use this thread to ask.
I needed to remove damper as I am going to change timing chain.

I bought retaining bolt forehand so I can install damper back. Bolt is 3/4-16 , but it only goes in few millimeters to crank and then jams.
Just want to be sure that there is no other threads used except 3/4-16 bolt size? If so, I think somebody or something has broke threads inside crank. It is hard to see inside crank.. I trien lubricating and turning bolt back and forth, but no success.

What options I have left to install damper? Should I bought thread tap and try to clean threads or is it possible to tap damper to place using rubber hammer or so? Or will it damage crankshaft?

Engine is slant six 170, car is valiant V100 -64.