Timing Belt Problems: Symptoms, Causes, & How to Fix Them

Timing belts play a critical role in the operation of precision machinery, ensuring the seamless coordination of components within a belt drive system. Despite their seemingly simple design, polyurethane timing belts can experience issues that lead to failure and cause disruptions or costly damage.  

The good news is that the vast majority of timing belt failures are fixable, or even avoidable! In this guide, we’ve outlined some of the most common timing belt problems, potential causes, and what you can do to fix them.

Timing belt problems at a glance:

• Timing belt problems can happen for several reasons, including improper installation or belt drive design, poor handling, incompatible equipment, and environmental factors.
• Some of the most common timing belt problems include tooth shear, snapped belts, accelerated wear, excessive vibration, or belt cracking and degradation.  
• To avoid timing belt issues, make sure your belts are properly tensioned, your pulleys are aligned, and that all your equipment is compatible with each other, the environment, and the required load.  

7 common timing belt problems and how to fix each one

Timing belt problems present themselves in several ways, but the most common include:

• Snapped timing belts or broken teeth
• Uneven or excessive wear on belt teeth or edges
• Degradation or cracks in timing belt or backing
• Tooth jumping/skipping
• Overheating
• Loss of synchronization

Let’s take a closer look at each of these timing belt issues in detail so you can identify how to fix them.

1. Broken or snapped timing belt / broken belt teeth

Issue: Timing belt has snapped, teeth have broken off, tension members are sticking out  ‍

Potential causes: Overloading, shock loads, improper tension, incompatible components improper pulley size, misalignment, exposures and debris

Broken timing belts can appear in several ways. In some cases, the belt teeth completely break off from the belt base. In others, a timing belt might snap completely in half. Here are a few common types of timing belt failures:

• Tooth shear: Usually found in power transmission applications, the belt’s teeth fall off the belt, which can be the result of excessive torque, improper pretensioning or overloading the belt. While less common, tooth shear can occur because of over-worn pulleys, debris entering the drive, or extreme chemical and temperature exposures.  

• Tensile failure: This happens when the tension members inside of the belt snap, usually from being overloaded. You’ll know it’s tensile failure by how the belt looks – it'll have an angled, ragged tear. Tensile failure is commonly caused by overloading or incorrect pretension.

• Fatigue failure: Presenting as a clean, straight tear, fatigue failure is typically the result of a belt crimping or flexing sharply because of small pulley diameters, a foreign object entering the system, or mishandling.  

• Weld zone failure: Commonly appears when a spliced and welded belt is used instead of a truly endless belt in high-load applications. Spliced and welded belts have half of the tensile strength of truly endless ones, meaning they can’t withstand the same conditions.

• Tensile fatigue: When tension members within a belt break or become damaged, they can start to poke out of the sides of the belt. Overtensioning is a common cause of tensile fatigue, but misaligned pulleys, shock loading, or using pulleys that don’t meet the minimum pulley diameter requirements can also be the culprit.

Potential solutions

• Check and adjust belt tension using the SM5 Tension Meter.
• Verify that components are aligned properly.
• Confirm that the belt type, width, and tooth pitch match and meet your load requirements.
• Confirm you are using properly sized belts for your load requirements and that pulleys that meet minimum diameter requirements.  
• Handle belts with care and store them in suitable conditions.
• Keep your system free of debris and contamination.

2. Uneven or excessive belt wear

Issue: Belt teeth show irregular or accelerated wear patterns, belt edges appear frayed or unevenly worn

Potential causes: Misalignment, improper tracking, damaged pulleys, or debris and obstructions  

While timing belts will show signs of wear and tear as they age, excessive damage on belt edges or teeth can indicate an external issue. Left unchecked, severe wear can impact precision performance and even lead to total failure.

Uneven or excessive timing belt tooth wear often indicates that the belt isn’t distributing loads evenly across its width, usually because of misalignment or improper tension. Though less likely, tooth wear can be a sign that there’s an issue with your pulleys or contamination.  

Accelerated edge wear can also be a problem that impacts performance, eventually causing the belt to wander side to side. In some cases, worn edges can expose the tension members within the belt, which can cause corrosion and other damage that reduces the belt’s ability to handle loads evenly. Misalignment, worn flanges, or the belt running against an obstruction can cause damage to the belt edges.

Potential solutions:  

• Check pulley alignment and ensure proper tracking.  
• Inspect pulleys and flanges for damage or uneven wear.
• Identify and remove any obstructions or debris.
• Consider using a self-tracking timing belt and pulley system to prevent lateral belt movement.
• Confirm pulley and belt materials are compatible with your environment.  
• Check belt pretension.

3. Degraded or cracked timing belts and backings

Issue: Signs of degradation and/or cracks are forming on polyurethane belt or belt backing

Potential causes: Temperature extremes, improper storage, undersized pulleys, exposure to incompatible chemicals

Belt cracking is easy to spot and prevent. Belt cracking is often the result of operating belts below their rated temperature, or it can indicate that your pulleys don’t meet the proper minimum diameter requirements for the belt, backing, or backing thickness you’re using. Another often overlooked cause is improperly storing spare belts by tightly bending them, which leads to stress. Other forms of degradation can be a sign of chemical contamination.  

Potential solutions:

• Check that your pulleys meet the proper minimum diameter requirements.  
• Consider using a type of polyurethane better suited to low ambient temperatures, like TPU-KF2.
• Follow proper belt storing practices and avoid sharp bending.
• Identify potential contamination using our chemical compatibility chart.

4. Timing belt tooth skipping or jumping

Issue: Timing belt teeth are disengaging with pulley grooves

Potential causes: Under tensioned belt, worn components, debris in belt drive, mismatched components

If you notice performance or precision issues with your timing belt, it could mean that it’s ratcheting or “jumping teeth”. Under tensioning is the most common cause of tooth skipping, as it prevents the belt’s teeth from meshing properly with the pulley’s grooves. Tooth skipping can also be the result of worn out or low-quality belts or pulleys, debris contamination within the drive. In some cases, timing belt ratcheting occurs when the pitches of the belt and the pulley don’t match.  

Potential solutions:

• Ensure that timing belts are properly tensioned.
• Verify that timing belts and pulleys have the same pitch and tooth shape.
• Inspect components for signs of wear and aging to determine if replacements are necessary.
• Clear components of debris and identify ways to minimize future contamination.  

5. Timing belts are running hot

Issue: Timing belts are getting hot in ambient temperature environment

Potential causes: Misaligned drive, improper pretension, incompatible components, friction

Timing belts that run hot can experience failure quicker, so it's important to inspect your belt drive right when you notice that your timing belts are getting hotter than expected. Misalignment is the most common cause, but improper pretension, and friction can also lead to overheating. Sometimes, timing belts run hot because the tooth side of the belt is not meshing with something that it's meeting at high speed, like a flat idler.  

Potential solutions:

• Make sure pulleys are aligned.  
• Check that the belt is properly pretensioned.  
• Consider getting belts with low-friction tooth-side nylon coatings to help minimize heat produced by friction.
• Potentially switch from a flat idler to a toothed idler.

6. Excessive vibration

Issue: Timing belt is vibrating under normal operating conditions

Potential causes: Misalignment, weak drive structure, pulley imbalance

Vibration in a belt drive can be very serious if left unchecked. When you notice unusual levels of vibration, check that your pulleys are aligned, your belt is tracking properly, and that your drive structure is secure. It may be a sign that your pulleys are imbalanced, meaning that one side of the pulley is heavier than another.  

Potential solutions:

• Ensure pulleys are aligned and that belts are tracking properly.
• Inspect drive structure components for loose or worn parts.  
• Check that pulleys are properly balanced and replace or reweight them if necessary.
• Consider using equipment optimized for extra-smooth performance, like the BRECOflex BAT(K) series or self-tracking belts and pulleys.  

7. Loss of synchronization

Issue: Timing belts are not moving components together in the correct time

Potential cause: Tooth skipping, poor tensioning, worn components, misalignment, excessive backlash, improper components

Loss of synchronization happens when the belt can't keep the driven components in the right positional timing. It can manifest in a few ways, like reduced motion accuracy or your products not being positioned properly.

When this happens, it's usually because the belt is skipping teeth, the belt isn't tensioned correctly, or the components are worn out. You may need to switch to a higher stiffness belt or upgrade to high-precision pulleys for better accuracy.

Potential solutions:

• Verify and adjust belt tension.
• Inspect and replace worn parts.
• Clear drive of debris.
• Check pulley alignment.
• Upgrade to a timing belt with higher stiffness.

What are the top causes of timing belt problems?

Issues with timing belts can result from several things, but here are five of the most common causes of timing belt problems:  

• Misalignment: One of the most common causes of timing belt problems is misalignment, where the pulleys aren’t on the same plane. Misalignment can cause a slew of issues, and it’s usually the first thing you should check if you notice a problem with your belt drive.  ‍
• Tensioning and pre-tensioning issues: Both over- and under-tensioning timing belts can cause issues, putting stress on all components of your system and potentially resulting in total failure. Using tools like the SM5 Belt Tension Meter can help keep your system properly tensioned, prevent future problems, and keep your belts lasting as long as possible.  ‍
• Excessive loads: Timing belts that are overloaded degrade faster and are more likely to break, which can cause major delays, extended downtime, and even permanent damage to your equipment.  ‍
• Wrong equipment: Sometimes, you aren’t using the right components. This can mean the pulleys and timing belt pitches are mismatched, pulleys or belts aren’t correctly sized, the wrong type of timing belt is used, or different pulley or belt materials are needed.  

Although these are the most common timing belt issues, that doesn’t mean they have to be what’s causing you problems. The exact causes and solutions are unique to your application.

Preventing future timing belt problems

While accidents are bound to happen once in a while, you can easily prevent many of the timing belt problems discussed above. Regular maintenance and inspections are critical to keeping your timing belts running smoothly, as you’ll become aware as soon as issues start, instead of waiting until things break. Also, making sure your team is properly trained for handling, installing, and identifying parts of timing belt systems can minimize future errors in set up and replacements.  

One of the best ways to protect yourself against timing belt problems is by using high-quality parts. BRECOflex is the leader in polyurethane timing belts, and we pride ourselves in offering the highest quality belts and pulleys in the industry. If you want to maximize your uptime and prevent timing belt problems, contact BRECOflex today.  

Frequently Asked Questions (FAQs)