A timing belt, or otherwise called a timing chain, is a flexible toothed belt that connects the engine crankshaft to the camshaft. The timing belt synchronizes the camshaft to the crankshaft position, so the valves will open and close at the proper time in relation to the position of the pistons. The camshaft rotates once for every two rotations on the crankshaft.
The automobile engine uses a metal timing chain, or a flexible toothed timing belt to rotate the camshaft. The timing chain/belt is driven by the crankshaft. The timing chain, or timing belt is used to "time" the opening and closing of the valves. The camshaft rotates once for every two rotations of the crankshaft. If the timing belt or timing chain is not properly installed and adjusted, the valves on the engine won't open and close at appropriate times. This will result in poor running, valve clatter, and loss of power. A broken timing belt or timing chain can cause an engine to stop running or cause the valves to crash to the pistons.
You may wonder why most people use a timing belt rather than a timing chain. For one, a timing chain is much noisier, less efficient, and more expensive than a timing belt. Though a timing chain may last longer than a rubber-built timing belt, the latter has specific requirements for specific intervals.
Usually, timing belts or timing chains must be replaced on recommended intervals, often ranging from 60,000 miles to 105,000 miles. A replacement timing belt should be put if the old one already has signs of damages like cracks, cuts or excessive wear. If not replaced in time, chances are, it may break causing serious engine damage. The engine will stall because of the damages in the valves and pistons and destroyed cylinder head. Having a replacement timing belt is not a cheap job but it is far less costly than the alternative.