Timing Belts are reinforced rubber bands or sometimes chains that are used to coordinate the turnings of the crankshafts and camshafts in internal combustion engines. There are teeth situated in the inner part of some timing belts and these will correspond to the gears of a specific engine design.
In older vehicles, the timing belts were only used to synchronize camshafts and crankshafts. But nowadays with our modern engines, they are often used to drive the water pumps as well.
It is important that the timing belts keep the valves and the pistons working in a precise order. Each valve and piston combination must push down on the individual cams on a camshaft at just the right time. This works the same way as pedaling a bicycle, where the pedal must reach the top before you can push it down again. If you tried to push the pedal too soon, your foot will either fall through or just break the pedal right off. Timing belts work to prevent the pistons and the valves from pushing on the camshaft before it has reached a full cycle.
Timing belts are supposed to last at least 60,000 miles. But some of the newer designs will last the whole life of the engine. As a vehicle owner you should replace your timing belts according to the vehicle manufacturer's recommendations.
If the timing belt happens to fail completely, the engine will just grind to a halt and the vehicle won't be able to function. What could also happen is that the valves and pistons can drive themselves into the camshaft, thus causing them to just bend and brake. You may often find that if the timing belt is to fail, there is usually very little warning that it is about to happen. So it is suggested that a timely timing belt replacement may be the best prevention.
Replacing timing belts is definitely a job for the professionals. The reason for this is because a lot of peripheral parts, like the distributor and may be the water pump, have to be removed for it to become accessible. The new timing belts have to match the old ones exactly and this could be a very time consuming custom order. Broken timing belts will require the vehicle to be towed into the shop, it will not be able to be driven. When the timing belt has been replace, the mechanic has to synchronize the camshaft and the crankshaft with a special kind of strobe light. This job of repairing the broken timing belt could take several hours.
When the mechanic replaces the timing belt in your car, he may also suggest that the water pump be changed at the same time, as it will probably be worth your while in the long run. The reason for this is because just about all the work is done to replace the water pump when the timing belt is being changed. So it won't require any extra labor. Whereas, if the water pump has to fail at a later stage, all that work would have to be repeated and the mechanic would then charge again for the labor.