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A timing belt, timing chain, or cambelt is a part of an internal combustion engine that synchronizes the rotation of the crankshaft and the camshaft so that the engine's valves open and close at the correct times during each cylinder's intake and exhaust strokes.

The timing belt is connected to the camshaft and the crankshaft, so if the timing belt snaps the turning momentum of the crankshaft that the pistons are attached to will hit the valves in the cylinder head and seriously damage your engine. Put another way, if the timing belt fails to properly function, the valves and pistons in your car will begin to collide repeatedly, more than a hundred times a minute, smashing into one another, causing irreversible damage to the engine. This is why it’s so important to have the belt changed at the manufacturer’s recommended intervals.

On most timing belt changes, pulleys and tensioners should be replaced at the same time. If the timing belt drives a water pump it is also recommended to replace the water pump.