The timing belt on your car has a very important and specific job. It controls the timing of your engine's valves. Some older cars used timing chains and some other designs utilise timing gears, but most contemporary auto designs use a timing belt with teeth that integrates the rotary motion of the cam shaft with the alternate motion of the pistons and gears. If a timing belt fails on some engines, it can cause severe damage to the engine, so it is best to pay very close attention to maintenance of this part. Unfortunately, there are very few signs of wear when it comes to your timing belt, but there are a few tips to consider.
Read Your Manual
Read the owner's manual that came with your car. There should be a recommendation for when to have the timing belt replaced that falls somewhere between 60,000 and 105,000 miles. If you don't have an owner's manual, contact the manufacturer for a replacement or a recommendation on when to change your timing belt.
Replace the Belt
Whatever the recommended mileage is in your owner's manual, have your timing belt replaced. If you have the skill, replace it yourself before you have a problem. There are virtually no signs or symptoms indicating a belt failure is immanent.
Some cars have what is called a "serpentine belt" rather than a specific timing belt. The serpentine belt controls several different tasks in the engine including the timing of the cam shaft and valves, making this part equally important to replace according to the manufacturer's recommendation. Your owner's manual should have a recommendation as to when this should be replaced as well.