On most modern cars there is two kinds of belts; timing belts and accessory drive belts. While they are similiar in nature to make up and what they do, they are very different.

Older vehicles use to have timing chains, but newer modern cars have changed to timing belts because they are much lighter, quieter, and more efficient. The timing belt is responsible for making sure the engine's crankshaft, pistons, and valves operating insync or in time. (Hence the term timing belt.)

Accessory drive belts are used to drive all the accessories that run off the front of the engine. The drive belt is responsible for using the engine's revolutions to drive the power steering pump, a/c compressor, alternator, water pump, and other belt driven accessories. For more information concerning each type of belt and when they should be changed click the links below.

Timing Belts

Timing belts are critical compenants to ensuring a reliable running engine. The timing between camshafts, valves, pistons, and the crankshaft are so precise that if it is off even just one degree, the engine may not run or worse cause severe damage. This is why it is so important that the timing belt and tensioner be in good working condition all the time.

Unfortunately, like other rubber componants, timing belts wear out and must be replaced. Most manufacturers recommend that the timing belt be replaced on schedule, as a form of maintenance. This is typically at 90,000 miles, but see our timing belt replacement guide for vehicle-specific information.

If the belt isn't changed it will eventually break. If this occurs the engine will stop running and will not restart. However, on some vehicles the engines are refered to as "interference engines."

In "interference engines", when the timing belt breaks severe internal engine damage can occur. This usually involves open valves becoming bent as they strike the pistons, which results in expensive engine damage. In worst case scenarios, the engine may need to be replaced.

If your vehicle is not an "interference engine" it is known as a "free-running engine". In these engines if the belt breaks the engine will stop running and will prevent internal damage from occuring. While you will still need to be towed to a repair facility, usually a new belt is all that is required to make the car run again.

On most cars with timing belts, the water pump is also driven by the timing belt. While it is not required, it is recommended that the water pump be replaced at the same time as the timing belt because these also wear out over time, and you can save yourself some of the cost of labor by having the two replaced at the same time.

Accessory Drive Belts

Drive belts are another important maintenance item that should be replaced on schedule before they break and leave you stranded. There are two types of drive belts that car manufacturers use. There are V-belts and serpentine belts.

V-belts are typically found on older vehicles. While they do not have the same life span as a serpentine belt, they are not as expensive to be replaced. V-belts should be replaced every three years or 36,000 miles. The incidence of failure rises sharply after three years.

Serpentine belts are what is installed on most new cars. They are more flexible and run cooler than V-belts. This helps them last longer, only needing to be replaced every five years or 50,000 miles. However these added benefits come at a price, because they are about twice as much to replace than V-belts.

What causes belts to fail?

With belts, heat and mileage are the main causes of wear. Every time a belt passes around a pulley, it bends and flexes. This produces heat, which hardens the rubber over time. The wear process is greatly accelerated if the belt is loose and slips.

The additional friction between the belt and the pulley will make the belt run hotter. After millions of journeys around the pulleys, even the best drive belt begins to suffer the effects of age.

Rubber begins to crack and fray and the internal cords become brittle.

You cannot always determine a belts condition by appearances alone. Any belt obviously cracked and frayed should be replaced.

With many of today’s bandless belts, there is no outside cover to peel lose and betray the belt’s deteriorated condition.

A belt may appear to be like new on the outside, yet be on the verge of failure because of weakened separated cords inside.

When a belt is replaced, it is important that the belt be properly tensioned. If too loose, it will slip and wear quickly.

If too tight, it may damage internal cords as well as overload shaft bearings on the accessories that it drives.