I heard noise under the valve cover, after.

I heard noise under the valve cover, after removing it I found my intake rocker arms very loose, what causes this? Also afterwards I had the car towed to a repair shop, the mechanic put a wrench on the camshaft sprocket bolt and when he tried to loosen it I heard a cracking sound, he wiggled the timing chain and said "look this is also bad"how do I know if I have to replace it?