See Figure 1
Accessory drive-belt tension is checked every 6000 to 7500 miles (9662-12,077 km). Loose belts can cause poor engine cooling and diminish alternator or power steering pump output. A belt that is too tight places a severe strain on the water pump, alternator, and power steering pump bearings. A belt will loosen with age and wear. A belt loose enough to slip on its pulleys will make a loud, squealing noise. The noise is usually heard under acceleration or during a sharp turn.
To check drive belt tension, push lightly on the belt midway between the pulleys. Correct deflection of the belt is 3 / 16 - 5 / 16 in. (5-10mm). Longer or shorter belts may have slightly more or less deflection. Remember that too tight is as damaging as too loose. Any belt that is glazed, frayed, or stretched so that it cannot be tightened sufficiently must be replaced.
See Figures 2 and 3
Incorrect belt tension is usually corrected by moving the driven accessory (alternator, power steering pump, etc.) away from or toward the driving pulley. Loosen the mounting and adjusting bolts on the accessory and move it to loosen or tighten the belt. Once the belt tension is correct, retighten the mounting bolts and recheck the tension. Never position a metal prybar on the rear end of the alternator housing or against the power steering pump reservoir; they can be easily deformed.
Some models equipped with air conditioning are equipped with a two-part pulley that is split in halves (like two saucers back-to-back). Instead of a tensioner that removes slack, there are very thin spacer shims of various thicknesses in between the pulley halves. Removing a shim effectively tightens the belt by narrowing the pulley, thereby forcing the belt to ride higher and farther from the center. Adding shims effectively loosens the belt by widening the pulley and allowing the belt to ride in the pulley closer to its center (see photographs). When replacing a belt with a new one, begin with the same number of spacers as originally used, then tighten the pulley fasteners (often six in a hex pattern). Check the tension of the belt, and if necessary, adjust by removing shims until the correct tension is achieved. Belt tension should be within the specifications of an ordinary drive belt, as described in the previous paragraph. The belt should be correctly tensioned before installing the rest of the components necessary to complete the job.
REMOVAL & INSTALLATION
If a belt must be replaced, the driven unit must be loosened and moved to its extreme loosest position, generally by moving it toward the center of the motor. After removing the old belt, check the pulleys for dirt or built-up material which could affect belt contact. Carefully install the new belt, remembering that it is new and unused and it may appear to be just a little too small to fit over the pulley flanges. Fit the belt over the largest pulley (usually the crankshaft pulley at the bottom center of the motor) first, then work on the smaller one(s). Gentle pressure in the direction of rotation is helpful. Some belts run around a third or idler pulley, which acts as an additional pivot in the belt's path. It may be possible to loosen the idler pulley as well as the main component, making your job much easier. Depending on which belt(s) you are changing, it may be necessary to loosen or remove other interfering belts to get at the one(s) you want.
When buying replacement belts, remember that the fit is critical according to the length of the belt (circumference), the width of the belt, the depth of the belt and the angle or profile of the V shape. The belt shape should exactly match the shape of the pulley; belts that are not an exact match can cause noise, slippage and premature failure.
After the new belt is installed, draw tension on it by moving the driven unit away from the motor and tighten its mounting bolts. This is sometimes a three or four-handed job; you may find an assistant helpful. Make sure that all the bolts you loosened get retightened and that any other loosened belts also have the correct tension. A new belt can be expected to stretch a bit after installation, so be prepared to re-adjust your new belt, if needed, within the first 100 miles (161 km) of use.