What makes a timing chain gear on a 1995 Olds 3800 engine with 60000 miles breakdown?

The timing chain can fail because of poor maintenance , insufficient oil changes. Lots of long periods sitting with dry starts. Dry starts are murder on engine internals.

Take a picture of it and post it. Never have seen one unless it was a defective part. Most likely you got shafted by you mechanic. My 3800 has 294000.00 miles on it.