The drive belts are used to transfer power from the crankshaft at the bottom of the engine to another component which needs to be turned. The belts are generally made of rubber and fabric layers and are subject to deterioration from wear, heat, and chemicals.
To inspect the belts, make sure the engine is off and the key removed from the ignition. (This eliminates any chance of surprises while you've got your hands on potentially moving parts). Select a long section of a belt and examine it closely. There should be no signs of fraying, cracking or chunking on either the top surface or the working faces.
Continue checking all the belts in the same fashion. If you're checking the longest sections, you're seeing a representative section of the belt. If you wish, start the engine and shut it off again; the belts will come to rest in another position and other sections may be viewed.
Considering the speed at which the belts turn, and the importance of what they drive (alternator, water pump, power steering, etc..), any flaw found in a belt should be viewed as a potential for failure. Replace the belt before it chooses to break on a cold, rainy night.
CHECKING TENSION AND ADJUSTMENT
See Figures 1 through 5
The belt tension on most driven components is adjusted by moving the component (alternator, power steering pump, etc..) within the range of a slotted bracket. Some late model air conditioner compressor drive belts are adjusted by varying the number of discs between the halves of the crankshaft pulley.
Check the belt tension every 6 months or 10,000 miles. Push in on the drive belt about midway between the crankshaft pulley and the driven component. If the belt deflects more than 9/16 inch or less than 3/8 inch, adjustment is required.
- Loosen the adjustment nut and bolt in the slotted bracket. Slightly loosen the pivot bolt(s).
- Pull (don't pry) the component outward (away from the engine) to increase tension. Push inward to reduce tension. Tighten the adjusting nut and bolt and the pivot bolt.
- Components such as the power steering pump and some air conditioner compressors, may be mounted with a double slotted adjusting bracket using a threaded bolt or bolts and locknuts to adjust and maintain tension. Loosen the locknut(s) and slightly loosen the bolt(s) in the slotted groove(s), turn the threaded adjustment bolt(s) in or out to gain correct tension. Tighten locknuts and slotted bracket bolts.
- Recheck the drive belt tension, readjust if necessary.
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 engine. 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 - 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 engine) 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 (diameter), 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 hundred miles of use.