Timing Belt

Timing belts—also known as synchronous or cog belts—are intended to keep multiple moving parts rotating in tandem. Any slippage can mean missed timings on important components and decreased equipment effectiveness. This is especially important when they’re used in mobile equipment (trucks, forklifts, tractors, etc.), which is their most common application.

Shelf Life

A timing belt’s shelf life is approximately eight years as long as it’s stored in the right conditions. After that point, its service life will begin to gradually decrease.


Timing belts should be kept in a cool, dry environment away from sunlight and moisture. Humidity below 70% is recommended.


The ideal temperature for timing belts is 30°C (85°F). For every 15°F above the recommended temperature, timing belt shelf life decreases by half. Temperatures beyond 45°C (115°F) should be avoided.


As with other types of belts, timing belts should be kept out of direct sunlight since it could diminish both its shelf life and overall service life, resulting in a premature failure.


Timing belts must be kept out of high ozone environments, such as those created by transformers and motors.


Evaporating solvents and other chemicals that give off airborne fumes should be kept well away from timing belts.


Crimping and excess bending should be avoided, as should nesting belts inside one another. Nesting timing belts can damage the tensile components of the belts. In addition, timing belts are best kept on shelves, not pegs, and should be off the floor unless a designated container is used.

How to Read the Date Codes on Belts

Belts come with various markings, including a date code. Often, this code is four numbers. The first two are the week in which it was manufactured, and the last two are the year. For instance:

Example: 0415

A belt marked with 0415 was manufactured in the fourth week of 2015.

Example: 2518

A timing belt marked with the digits 2518 was manufactured in the 25th week of 2018.

Example: 4512

A belt marked with 4512 was made in the 45th week (towards the end) of 2012. It’s probably on its way out.

Keep in mind that different original equipment manufacturers may use different marking systems, and it’s especially important to make sure you don’t confuse the date code with the measurement code on the belt. The measurement code will usually have letters mixed in.

Signs Your Belts Are Deteriorating

If a belt has been on your shelf for an extended period of time, it may show some signs of cracking. However, you usually won’t see wear until it has been in use for a while. Signs of belt deterioration include:

  • Cracking in the rubber
  • Delamination (the exterior rubber starts peeling off)
  • Unraveling of internal fibers
  • Twisting
  • Missing cogs or teeth
  • Missed timings and slippage in the machine
  • Buildup of black residue on sheaves and pulleys from belt wear

One of the best ways to keep track of the age of your belts is to keep careful records through your CMMS. With MRO order and inventory tracking, you can more easily determine whether a belt on your shelf is too old to be put into use.

The Dangers of Forced Deterioration of Belts

Belt deterioration due to poor storage or mishandling—also called forced deterioration—can be problematic in many ways. Some of the dangers of forced belt deterioration include the following.

  • Lost production time
  • Inefficient operation of assets as more power goes into running the machine
  • Failure on startup
  • Drive cog slippage and missed timings

It’s rare for belts to completely break while on a machine. Typically, you’ll have wear and tear that decreases the efficiency of the system, driving up the cost of both operations and maintenance. That said, there’s always a safety risk when it comes to working on equipment. If a belt wears out too quickly, it creates more opportunities for injury to those who have to shut down the equipment and replace worn components.

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