In your vehicle’s engine, the timing belt connects the crankshaft to the camshafts, which in turn controls the opening and closing of the engine's valves. A four stroke engine requires that the valves open and close once every other revolution of the crankshaft. The timing belt does this. It has teeth to turn the camshaft(s) synchronized with the crankshaft, and is specifically designed for a particular engine. In some engine designs, the timing belt may also be used to drive other engine components such as the water pump and/or oil pump .

Importance of Service:
The usual failure modes of timing belts are one of two problems:

• Stripped teeth which leave a smooth section of belt where the drive cog will slip or delaminate and unravel the fiber cores.
• Belt breakage is uncommon because of the nature of the high tensile fibers they are constructed with but is also a possible problem.

Correct belt tension is critical - too loose and the belt will whip, too tight and it will whine and put excess strain on the bearings of the cogs. In either case belt life will be drastically shortened.
Aside from the belt itself, also common is a failure of the tensioner, and/or the various gear and idler bearings, causing the belt to derail.

What May Happen if The Service is Not Performed
Failure to replace the belt can result in complete breakdown or catastrophic engine failure. Timing belts must be replaced at the manufacturer's recommended distance and/or time periods. Your vehicles owner’s manual maintenance schedule is the source of timing belt replacement intervals, typically every 60,000 to 90,000 miles. It is common to replace the timing belt tensioner at the same time as the belt is replaced.