A timing belt is a device inside your engine that serves to synchronize all of the moving internal parts. Like a conductor of an orchestra, the timing belt makes sure that all of the components are in the right place at the right time.
The belt itself is a toothed or ribbed rubber belt that wraps around the engine crankshaft and the camshaft(s). As the crankshaft rotates (as a result of being “pedaled” by the pistons), a pulley moves the timing belt. The timing belt, in turn, rotates one or more camshafts to open and close the intake and exhaust valves at just the right moment - in time with ignition.
Some engines feature a timing chain rather than a timing belt. They do the same job, but a chain is more durable than a belt. It is also more expensive to produce, replace, and repair.
Timing belt replacement is quite an involved procedure that requires a good deal of tools and training. To replace the timing belt on your vehicle, a technician needs to gain access to the front of the engine. This usually requires safely lifting and supporting the vehicle off of the ground, removing shields, guards, covers, ducts and the serpentine drive belt. The radiator might also need to be removed, depending on the orientation of your engine.
With those items out of the way, a typical timing belt replacement (the procedure differs from one vehicle make and model to the next) involves the following general steps: