Bad timing chain ?

could have jumped a tooth maybe. If its that old, i wouldnt even wait to change it. My 72, and afaik 73s as well had NYLON tooth timing gears. Which yes, is very stupid, is also very annoying once the chain 'goes'. My chain 'went' and i just bought a new oil pump pickup because of all the nylon chunks that were sucked up in it, so if its a concern and its still running? Pull that thing out, or you'll be pulling the pan and picking nylon chips out for days whenever the chain goes.

just my .02cents