Frequency of oil changes will dictate the usable life of a timing chain as well. The chain wears much faster with infrequent oil changes.

If you leave it in service too long it will make a mess of the sprockets as well. Stretch must be checked periodically.

That is also the only way to tell usually if it has been changed before as most these cars come to us with little or no history. The other reason to check is the tweaked odometers on these cars. Most total indicated miles on the majority of them are not accurate. So it is really unwise to go by indicated milage.