Allowable slack in timing chain?

It's going back together with a new timing set. I've been doing some troubleshooting because the engine won't run right. The timing chain is something I suspected may be causing at least some of the trouble. Had the chain been tight all around with no slack, I may have ruled it out. Since there is significant slack, I suspect this may be part of the problem. I just needed to know if that 1/2 inch of slack was normal or excessive. Thank you all for the replies.