Serpentine Belt Service By Ken Buie The downsizing of automobiles has caused many changes. Even though cars are smaller, it seems there is more packed under the hood every year. One change in car design that first seemed like a nightmare is the serpentine belt. At first glance, some serpentine belt setups look quite complicated, but in reality most serpentine belts are easy to replace. A serpentine belt is a balance between the traditional V-belt and a flat belt. A V-belt drives the accessories by wedging into the pulley groove. A flat belt depends on friction to transmit power and can use both sides of the belt for surface contact. When you visit museums you see flat belts driving all sorts of machinery. A serpentine belt is wider and thinner than the traditional V-belt and is sometimes called a V-ribbed belt. The first application of a serpentine belt was on the 1979 Ford Mustang. Since then, serpentine belts are found on almost every domestic and import car. There are many advantages of a serpen- tine belt system over a V-belt system. Some advantages are: ¢ Power transmission provided by both sides of the belt. *Only one driver belt needed to power all accessories. ¢ Spring-loaded belt tensioners can be used to maintain proper belt tension at all times. ¢ Increased belt flexibility allows the use of smaller diameter pulleys. * More belt to pulley contact surface than a V-belt system. A slight disadvantage of a serpentine belt system is the occasional need for special tools to move the spring-loaded belt tensioner. One thing that can quickly ruin your day is to remove a serpentine belt and forget how it was wrapped around the pulleys. Most vehicles (except the one you’re working on) have a decal under the hood with a diagram of the belt routing. The Gates Rubber Company has an excellent installation guide for serpentine belts. The booklet, part no. 28-1795, gives you installation tips and vehicle belt routing diagrams. Belt Installation. There are some simple rules that apply to all serpentine belt installations. The V-grooved side of the belt always meshes with the pulley grooves. The smooth backside of the belt only contacts the smooth pulley surfaces. Always be sure the belt and the pulley have the same amount of grooves. Usually there is only one pulley that can be threaded incorrectly. That pulley is always the smooth pulley near the center of the pulley group. When installing a serpentine belt, begin by encircling the pulley group (Figure 1, Step 1). Then, loop the smooth side of the belt around the smooth pulleys (Figure 1, Step 2). If the belt appears to be too long or too short, it is usually threaded wrong. Refer to Figure 2. Most serpentine belt systems use a spring-loaded belt tensioner. This makes for easy installation and no periodic retensioning. For vehicles not using a spring-loaded tensioner, a belt tension gauge should be used for accurate belt tension. Belt tension gauges come in a variety of shapes and sizes. Many times there is hardly enough room for the belt, let alone a belt tension gauge. But, prac- tice using a tension gauge on belts that provide enough room so you can get a feel for proper belt tension. Refer to the operating instructions for your particu- lar type of tensioning gauge. Use the above chart as a guideline for proper belt tension on belts not using a spring-loaded tensioner. A belt is considered “used” once it has been “run-in.” The amount of time it takes to “run-in” varies from five to 15 minutes. I prefer to let the car idle for 15 to 20 minutes with a full acces- sory load—air conditioning on high, headlights on, etc. Then I recheck the belt tension. Belt Replacement Cycle. Serpentine belt systems should follow a four-year replacement cycle, regardless of appear- ance. Random cracks in the ribs are considered normal in the later stages of belt life. When three or more rib cracks appear in a three-inch span, 80 percent of the belt’s life is depleted. It is now time to replace the belt. Anytime you see parts of the ribs missing, the belt should be replaced immediately. It’s also a good idea to give the customer the old belt to keep as a spare. When replacing belts that use a spring-loaded tensioner, pay close atten- tion to the operation of the tensioner. When you move the tensioner to replace the belt, the tensioner should not bind or hang up. The General Motors 2.0L and 2.5L engines seem to have a higher than normal failure rate with their belt ten- sioners. Use caution when quoting prices for belt or alternator replacement. When you loosen the tensioner to remove the belt for alternator or belt replacement and the tensioner breaks, you and your customer could be in for a surprise. Some tensioners can be expen- sive as well as labor intensive to replace. Since many serpentine belt systems use only one belt to drive all of the accessories, belt inspection is becoming very important. Rather than gamble with vehicle safety or the risk of engine damage, recommend a