Remember when cars used to have at least several rubber belts under the hood? Called "fan" belts or drive belts, they've been replaced on most late model vehicles with a single, "serpentine" drive belt. Another belt under the hood of most cars is hidden under a cover at the front of the engine. It's the timing belt, often overlooked during routine maintenance.
On the majority of vehicles if the timing belt fails the engine will quit, unharmed. The lucky motorist will have only the inconvenience of being stranded on the side of the road. The car can then be towed to a repair facility to have the timing belt replaced. On some engines, however, a broken timing belt can cause major damage to internal components. This potential disaster can be avoided easily and relatively inexpensively by replacing the timing belt as recommended in the owner's manual.
Timing belts resemble an engine accessory serpentine belt in appearance, only they typically have square teeth on the inside surface. They're usually constructed of rubber reinforced with nylon. Simply put, the timing belt transfers the rotation of the crankshaft to the camshaft. The rotating camshaft activates the valves, which provide air and fuel to the cylinders and expel combustion gases to the exhaust system.
The valves and pistons are constantly moving up and down at very high speeds. When the pistons are down, the valves are open; when the piston is at the top of its travel, the valves are closed. Some engines don't allow clearance between a valve at its lowest point and a piston at its highest. The timing belt, therefore, is the critical link to ensure that these components don't collide. If collision occurs, damage to the valves, pistons, cylinder head, and cylinder walls can result. This can be an expensive repair.
Many domestic vehicles built within the last several years and the majority of imports are equipped with a timing belt. Other engines rely on a timing chain rather than a belt. Refer to your owner's manual or take your car to a repair facility if you are unsure. The owner's manual maintenance schedule shows timing belt replacement intervals, typically every 60,000 to 90,000 miles.
Timing belts usually are protected from foreign objects by a cover, making visual inspection impossible. Replacement usually requires removal of the engine drive belt that operates the alternator, water pump, power steering pump, and air conditioner. Consider replacing this belt, or multiple belts, when having a new timing belt installed.