1995 Nissan truck timing chain

1995 Nissan pick-up mileage: 80,000. On the engine timing chain, how much slack, if any should there be? I have over 1/2 inch flexing/movement when I touch the timing chain with a screwdriver through the oil fill cap at the front of the engine. It flops around nicely. Would that also cause an intermittent loud engine knock / tapping?<