May 2004 Articles & Features
By Karl Seyfert | May 2004
This year-long series offers timely advice designed to help you understand the potential rewards a good preventive maintenance program offers you and your customers.
Can you tell the difference between the two drive belts in the photo on this page? Which is still good, and which is ready for replacement? Would you believe the top belt has already given over 100,000 miles of service, while the other hasn't been installed yet? The "old" belt is showing a few small cracks, but still looks like it has more miles left in it.
But how many more? The first indication of a faulty belt or other problems may be a squeaking noise coming from the engine compartment. However, not all worn belts will squeak. Therefore, belts should be inspected whenever a vehicle comes in for service. If a belt exhibits any of the following signs of wear, it should be replaced.
Small cracks normally occur along the length of a rib or ribs. This type of wear typically occurs after more than 50,000 miles of service or under extreme operating conditions. Excessive cracking may occur if the belt is exposed to a period of severely cold weather of -20�F or below.
Friction, caused by a loose belt slipping in the pulley, gives the belt sidewalls a glazed, or slick and shiny appearance. If the belt is slipping, cracking and chunking also will accelerate.
If belt material has sheared from the ribs, it builds up in the belt grooves. The grooved surface becomes uneven, which causes vibration, belt noise and belt slip. In severe cases, the debris may cause the belt to "walk off" the drive.
Grease, oil, coolant and other engine fluids can soak the belt sidewalls, resulting in a glazed belt that slips and makes noise. Prolonged contact with petroleum products can also cause premature belt failure. Before installing a replacement belt, identify and repair the source of the fluid leak or leaks that damaged the original.
High-mileage belts may "chunk-out" as pieces or chunks of rubber material break away from the belt. A belt with this much wear can fail at any moment, and should be replaced immediately.
In addition to normal wear, belts may be damaged or their service life shortened by a variety of other factors. An incorrectly installed belt may show ribs that have begun separating from the joined strands. The belt also may have been accidentally cut during other repair work.
Various mechanical problems also can cause accelerated belt wear or failure. If the back side of a belt appears shiny or glazed, look for an object such as a flange or bolt in its path that may be making contact. A seized idler bearing may cause the belt to stop turning for a time.
Look for a melted or glazed section. V-belts may twist out of the upright position and turn over due to pulley misalignment, excessive belt span vibration or excessive pulley or belt wear.
In addition to signaling belt wear, belt noise may also alert you to underlying damage to tensioners, bearings, pulleys and other components. The two major causes of belt noise are improper tension and misalignment.
Improper tension allows the belt to slip. This causes the sidewalls to wear smooth, and the belt eventually hardens and becomes glazed. The more glazed the belt surface becomes, the more likely it is to be noisy and lack the ability to transmit power.
Tension levels will decrease over time, which is why new belts are typically installed tighter than used belts. A belt's properties are designed to provide minimal tension loss with a decay rate that is gradual and predictable. A new or used belt that's overtightened may not cause noise, but the excessive hub loads can shorten pulley bearing life. Too much tension can also result in accelerated wear, increased temperatures and premature failure.
Parallel belt misalignment refers to pulleys that are outside the plane of other pulleys in the drive system but whose shafts remain parallel with the other components. Angular misalignment refers to pulleys that are within the drive system plane but are tilted because their shafts are not parallel. Both misalignment conditions can cause belt tracking problems, excessive wear, noise and belt stability problems. Just a few degrees of misalignment can increase belt operating temperature by 30*F, reducing belt life by as much as 50%
Misalignment belt noise is generally loudest at idle speed and diminishes with increasing engine rpm. High humidity (or a damp belt) often increases misalignment noise. To diagnose belt noises caused by misalignment and/or improper tension, use a spray bottle filled with water to spray the belt with a light mist while the engine is running.
If the noise increases right after you mist the belt and does not become louder, incorrect tension may be to blame. The belt may also be worn or misrouted. If the noise decreases for a few seconds, then returns even louder, the problem is likely due to misalignment.
A noise caused by belt misalignment will not be corrected by increasing tension or simply replacing the belt. All pulleys and tensioner assemblies should be checked for proper installation and alignment to correct the problem.