How Your Vehicle Works
Belts & Hoses
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Fan belt is the traditional term for what today is called a drive belt. Drive belts are made of reinforced, high-tensile strength cords and synthetic rubber. They connect the engine to front-mounted accessories. Belts come in two different types: The traditional V-belt (cross-section of belts has a V-shape for V-shaped pulleys) and the serpentine belt (also called Poly-V, Poly-Rib, Multi-Rib, and Micro-V belt), which uses multiple Vs for more positive contact with its mating pulleys.
Drive belts provide power to engine-mounted accessories like the power steering pump, air conditioning compressor, mechanical cooling fan, and air injection pump. Serpentine belts are now used on almost all vehicles.
Studies show that the chances of a drive belt failure rises dramatically after four years or 36,000 miles for V-belts, 50,000 miles for serpentine belts. This doesn’t mean that the belts shouldn’t be inspected before then, though. The belts should be checked every time the oil is changed to make sure they’re OK and properly tightened. When checking V-belts, a slipping belt usually has shiny sidewalls (glazing) caused by heat from sliding in the pulleys. The glazing often causes a chattering, slapping or squealing noise. And, because the glazing hardens the belt, it's prone to cracking and early failure. Belt slippage often occurs because of low tension, the wrong belt, or grease or oil. Missing chunks, or separating layers of the belt often hint at a dousing of oil or grease. The source of the oil or grease needs to be corrected before installing a new belt. A V-belt with any of these conditions should be replaced as soon as possible. On serpentine belts, inspect the belt closely for any cracks in the ribbed area. Also check the backside of the belt for grooves, fraying, or splitting. Although random cracks across the ribs are a sign of normal belt wear and don’t mean the belt will fail immediately, it’s a good idea to replace the belt the next time your car is serviced.
With automotive engines as with many aspects of daily life, timing is critical. One vehicle component often overlooked during routine maintenance is the engine timing belt. If it fails, the engine will stop and the car will coast to a stop. The lucky motorist will only have the inconvenience of being stranded on the side of the road until the car can be towed to a repair facility to have the timing belt replaced. On the other hand, the engine might suffer severe, if not catastrophic, damage to its internal components.
This potential disaster can be avoided easily and relatively inexpensively by replacing the timing belt within the required replacement interval.
Timing belts resemble an engine accessory serpentine belt in appearance, only they typically have square teeth on the inside surface. They usually are constructed of rubber reinforced with nylon. 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.
Timing belts usually are protected from foreign objects by a cover, making visual inspection impossible.
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 is a source of timing belt replacement intervals, typically every 60,000 to 90,000 miles.
Timing belt 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.
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