vibration damper removal?

i have a 94 s-10 blazer 4.3L im trying to change my timing chain and gears but i cannot hold the vibration damper still to get the center bolt out any suggestions? Im using a breaker bar to get the center bolt out but i just keeps cranking over the engine.

put a couple of spark plugs back in and use the compression . unless you removed a lot of stuff, radiator etc, you probably don't have room for a hammer driven impact driver . assuming you don't have air tools available. It may be reverse thread , can't remember , good luck