altune

I have a wierd engine knock towaed the back of the block.
I had removed the pan and replaced the rod bearings ( they had wear but not too bad ) and restarted the engine. Knock was still there, no difference.
I started the car on the rack and listened from the bottom, sound was not any louder from the bottom, it soundes like it is coming from the top of the engine.

I killed it and a friend suggested I make sure the torque converter bolts were all ok, they were but when turning over the engine to check them, I felt a small gap in the crank between forward and reverse ( I know you are not supposed to turn them back wards ). The gap is maybe a 1/4 on an inch when I pull on it.

I am wondering if this could be the timing chain or possibly a burnt piston pin bearing , need some expert help on this one.
Please help.
Al