AGCO Auto has as great article, When Should I Replace My Timing Belt?
At MY Automotive we have a lot of questions and concerns about timing belts, sounds, smells, and what a customer needs to do to fix their issues.
The timing belt is a point of confusion for lots of people. The first point of confusion is that not ever engine has a timing belt. Engines which do have timing belts require replacement at certain mileage or time intervals. Like any piece of rubber, a timing belt deteriorates over time. To figure out if your engine has a timing belt, refer to your owner’s manual or ask to a trusted professional.
Typical Timing Belt
Broken Timing Belt
A Timing Belt and a Serpentine Belt are Not the Same Thing
Some vehicles also have exterior belts and serpentine belts. Sometimes these are confused and think replacing the outside belts is the same as the timing belt. The timing belt is inside the motor. If your vehicle is older than seven years, check to see if it has a timing belt. If so, make sure the timing belt has been replaced. Often times, this can save your motor.