Timing Belt Replacement
Four-cycle internal combustion engines use a camshaft to open and close the intake and exhaust valves. This shaft has an egg-shaped cam for each valve that pushes open the intake and exhaust valves in the proper sequence.
The camshaft is timed or synchronized with the crankshaft (what the pistons are attached to). In completing the four cycles there are two revolutions of the crankshaft for every revolution of the camshaft. No matter how fast or slow the engine goes, this ratio stays the same. The timing belt governs that ratio. It has rounded "teeth" that engage with sprockets on both the crankshaft and the camshaft.
Replacing the timing belt is not especially difficult although there is usually quite a bit of disassembly to gain access to it. MWI suggests replacing the outer drive belts and water pump at the same time as the timing belt because water pumps are driven by the timing belt and the outer belts must be removed anyway. It is in the car owner’s best interest to replace these items together as it represents the best use of your repair dollar. Since this function is critical to the life and operation of the engine, we strongly recommend using only original parts.