Playing the percentages

In 1906, Italian economist Vilfredo Pareto created a mathematical formula to describe the unequal distribution of wealth in his native Italy. He observed that 20 percent of the people owned 80 percent of the wealth. Pareto’s theory of predictable imbalance has since been applied to almost every aspect of modern life.

In the manufacturing industry, production managers say 20 percent of the defects cause 80 percent of the problems. Warehouse managers know 20 percent of the merchandise takes up 80 percent of the stockroom space. Similarly, maintenance managers agree 20 percent of the work consumes 80 percent of their time and resources.

Proper tension will increase belt service life. Electronic
tension testers are available from most belt manufacturers.

Application engineers at companies that make power transmission belts agree with the Pareto Principle. They say 20 percent of a plant’s mechanical drive systems typically cause 80 percent of the maintenance problems.

Learning to recognize and then focus on that 20 percent is the key to reducing downtime and day-to-day operational costs. Neglecting any of these areas of concern will result in a belt drive system that does not function properly and in which the belts can fail – in days, hours or even minutes.

By troubleshooting the six most common sources of premature belt failure, and making periodic inspections, plant and maintenance managers can eliminate 90 percent of all unnecessary belt failures.

If belt slippage is a problem on high-torque drives, such as
HVAC units, switch to joined belts or convert the drive to
maintenance-free synchronous belts.

Other than normal wear and use, the most common sources of belt drive problems are:

1) Improper drive maintenance: Belts require very little maintenance. However, you can take some simple steps to help prevent unexpected problems:

  • Periodically retension belts.

  • Tighten loose drive components, nuts and bolts, idler arms, motor mounts, drive guards and pulley bolts.

  • Check for pulley misalignment, pulley groove wear, bearing misalignment and unusual belt wear.

  • Keep drive guards clear for proper ventilation, and clean pulley grooves to remove the buildup of dust, grime, rust or other foreign materials.

  • If V-belt slippage and roller chain lubrication are constant and nagging problems, convert the drives to a maintenance-free and clean-running synchronous belt and sprocket system.

2) Environmental factors: Consider certain environmental factors when drive performance does not meet expectations. These include: high or low temperature extremes, dust and grime, chemical vapors and oil. Harsh weather, high humidity and sunlight exposure also can decrease drive performance.

3) Improper belt or pulley installation: When troubleshooting, be sure to check for: pulley alignment, correct belt size and cross-section, proper installation tension, and contamination of the belts with oil, grease or belt dressing. Never force a belt onto the sheave by prying it over the sheave edges. Use drive center distance adjustment to slip the belt onto the sheaves without prying. If necessary, remove one of the pulleys to install the belt. When installing pulleys, make sure you align them correctly. Tighten bolts evenly to proper torque levels. Be sure to use the correct bushing hardware. Remove paint, rust and dirt from the grooves before installing.

4) Poor drive design: Drives must be properly designed and built to last. In addition to determining the best size and number of belts to use, the plant engineer must consider other drive-design factors. For example, pulleys must be made according to industry-accepted tolerances. Belt guards must be designed for adequate drive protection, yet provide ventilation. Structural members of the drive, including framework, motor mounts and machine pads, must be heavy-duty components. Drives must be designed for minimal vibration and also for ease of maintenance and inspection.

During routine maintenance, check
drive alignment with a straight edge.

5) Improper belt storage or handling: This problem is easy to avoid. Store belts in a cool, dark area, preferably in their original shipping cartons. Or, hang them on properly designed belt racks or hooks. Belts can be damaged by coiling them too tightly or by bending them sharply. Don’t allow them to become contaminated by oil, grease or other chemicals. And, don’t allow them to become wet or exposed to high temperatures or sunlight.

6) Defective drive components: This is rarely the cause of a drive problem. If you eliminated other possible causes and feel you do have a defective part, contact your belt or pulley supplier to verify your concern and correct the problem.


If you are replacing an existing drive which has been less than satisfactory, make every effort to determine why and how the original drive failed. First, verify that the drive was properly sized. Then, examine the failed belt. Look for these telltale signs:

Problem Cause
Belt sidewalls glazed and hard Belt slipped due to inadequate tension
Belt soft and gummy Chemical attacking belt
Belt fabric punctured Belt damaged during installation

Belt sidewalls worn
Misaligned or worn pulleys, or abrasive environment
Belt has cracks in bottom Belt bending around small-diameter pulleys
Belt split at cord line Belt running on sheaves too small in diameter
Belt broken Clean break caused by shock load
Belt broken Ruptured cords may indicate too little tension
Belt stretched Belt overloaded or overtensioned
Problem Cause
Uneven wear across tooth face Belt not properly aligned
Wear on driving side of belt tooth Belt overloaded or overtensioned
Wear on backside of belt tooth Belt undertensioned
Wear between belt teeth Belt overtensioned
Wear at root of belt tooth Belt overloaded
Wear on side of belt Damaged pulley flanges or belt contacting guard
Teeth sheared from belt Excessive loads or lack of belt tension
Ruptured tensile cords Excessive load or shock load
Belt soft and gummy Chemical attacking belt

The ability to anticipate these types of problems in belt drive systems is useful in maintaining serviceable equipment.

Although any belt will wear out eventually, an effective preventive maintenance program that includes inspecting and replacing belts and faulty drive components before they fail can reduce costly downtime and production delays.

Don’t allow 20 percent of your drives to eat up 80 percent of your maintenance budget.

This article provided by the power transmission product application department at Gates Corporation. Gates has a belt drive preventive maintenance and safety program that includes a free on-site seminar and a 48-page manual containing detailed information on failure modes and their causes, as well as general guidelines for proper belt drive maintenance. To learn more, go to www.gates.com/beltpm.

How to get top performance from your V-belt drives
V-belt drives are the most efficient, trouble-free means of transmitting power. If properly designed and correctly installed, they require very little maintenance. Occasionally, as with any other type of machinery, a V-belt drive may accidentally be damaged or knocked out of adjustment. Also, a change in operating or environmental conditions may require corrective measures. The following guide is designed to help you keep your V-belt drives operating at top efficiency, thus reducing machine downtime and labor costs to a minimum.
Belt stretch beyond takeup
Belts stretch unequally Misaligned drive; unequal work done by belts
Belt tensile member broken from improper installation
Realign and retension drive
Replace all belts with new matched set, properly installed
All belts stretch equally Insufficient takeup allowance
Greatly overloaded or undertensioned drive
Check takeup and follow allowance recommended by belt supplier
Redesign drive; consult with belt supplier
Short belt life
Rapid belt failure with no apparent cause Tensile members damaged through improper installation
Worn sheave grooves
Underdesigned drive
Replace with new matched set, properly installed
Replace sheaves
Redesign drive; consult with belt supplier
Belt sidewalls are soft and sticky; low adhesion between cover plies; cross-section swollen Oil or grease contamination of the belt or sheave Remove source of oil or grease; clean belts and sheave grooves with cloth moistened with non-flammable, non-toxic degreasing agent or commercial detergent and water
Belt sidewalls dry and hard; low adhesion between cover plies; bottom of belt cracked High-temperature environment Remove source of heat; ventilate drive
Deterioration of belt’s rubber compounds Belt dressing Never use dressing on rubber V-belts; clean belts and sheave grooves with cloth moistened with non-flammable, non-toxic degreasing agent or commercial detergent and water; tension drive properly to prevent slip
Extreme cover wear Belts rub against belt guard or other obstruction Remove obstruction or align drive to provide proper clearance
Spin-burns on belt Belts slip on starting or stalling load Retension drive until slipping stops
Bottom of belt cracked Sheaves are too small Redesign drive for larger sheaves; consult with belt supplier
Broken belts Object falling into or hitting drive Replace with new matched set of belts; provide shield for drive
Belt turnover
  Excess lateral belt whip Use joined belt
  Foreign material in sheave grooves Remove material; shield drive
  Misaligned drive Realign drive
  Worn sheave grooves Replace sheave
Tensile member broken from improper installation
Replace with new matched set, properly installed
  Incorrectly placed flat idler pulley Carefully align flat idler on slack side of drive as close as possible to driver sheave
Belt noise
  Belt slip Retension drive until slipping stops
Improper driven speed
Incorrect driver-driven ratio Design error Use correct sheave sizes
Spin-burns on belt Belt slip Retension drive
Hot bearings
Drive overtensioned Worn grooves; belts bottoming out and will not transmit power until overtensioned
Improper tension
Replace sheaves; tension drive properly
Retension drive
Sheaves too small Motor/belt manufacturer’s sheave diameters not followed Redesign drive; consult with belt supplier
Bearing wear Underdesigned bearings or poor bearing maintenance Observe recommended bearing design and maintenance
Drive undertensioned Belts slipping and causing heat buildup Retension drive
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