If the rope in the combustion chamber can stop the piston on the upstroke sufficiently to loosen the pulley bolt, it would also stop the piston on the upstroke when you cranked it. Stopping the piston enough to impair the piston rod from turning on the crank means something in the stroke train has to give. Take your pick - bearing, bent rod, bent skirt. It's possible that the top of the piston was compromised.

Suggestion - drain the oil, see if any metal parts show up.

Once the rope escapes the chamber, most likely into the exhaust valve, you're still left with a wrinkled part.

The thud/thunk you're describing is consistent with a rod knocking. Any of those wrinkled parts would lose linear strength, and it's just a matter of time before it breaks.

A bent valve would not seat properly and would likely be evident in performance, especially an exhaust valve - significant decrease in compression.