Causes of Engine Bearing Failure and How to Fix It
Posted on May 27, 2025
Engines are complex machines, and like any mechanical system, their parts can wear out over time. One of the most critical components is the engine bearing, which helps reduce friction and keep everything running smoothly.
But when an engine bearing fails, it can lead to severe damage, costly repairs, or even complete engine failure. So, what causes engine bearing failure, and more importantly, how can you prevent it?
In this guide, we’ll explore the main causes of bearing failure and provide expert insights on how to catch the warning signs early. Plus, we’ll share essential maintenance tips on how to prevent it and keep your engine running at peak performance for years to come.
What is a Rod Bearing?
A rod bearing is a crucial component in your engine that helps the crankshaft and connecting rod work smoothly together. It’s designed as a split sleeve, meaning it has two halves that fit around the crankshaft. This design allows the crankshaft to rotate freely while staying securely in place with the connecting rod.
To keep everything running smoothly, the rod bearing features a small pinhole that helps distribute lubrication. This oil reduces friction and prevents the crankshaft from overheating as it spins.
Every piston and connecting rod in your engine relies on a rod bearing to function properly, making it an essential part of the engine's operation.
Differences Between Rod Bearings and Main Bearings
Rod bearings and main bearings are essential for the crankshaft's operation, but they serve different purposes and are positioned differently in the engine. Here's a simple breakdown of how they differ:
1. Location
Rod bearings sit between the connecting rods and the crankshaft, allowing the rods to rotate smoothly. Main bearings, on the other hand, are positioned between the crankshaft and the engine block, supporting the crankshaft's rotation.
2. Attachment
A rod bearing’s top half is attached to the larger end of the connecting rod, while the bottom half connects to the rod bearing cap. In contrast, the main bearing’s top half is mounted to the engine block, and its bottom half is secured by the main bearing cap.
3. Oil Flow
Oil flows through the main bearings first, lubricating them before reaching the rod bearings to keep the crankshaft and connecting rods functioning smoothly.
4. Material
Both rod and main bearings are typically made from durable, nonferrous metals like aluminum or bronze to withstand wear and tear.
5. Quantity
The number of rod bearings in an engine depends on the number of cylinders, as each piston requires a rod bearing. Main bearings are fewer, with at least two located at each end of the crankshaft, and additional bearings can be added for extra stability.
6. Purpose
Rod bearings are precisely shaped to fit in the large end of each connecting rod, providing a replaceable wear surface. They work with lube oil pumped under pressure to prevent grinding and damage between the crankshaft and bearings.
Main bearings serve a similar function but focus on supporting the crankshaft's overall rotation within the engine.
25 Most Causes of Rod Bearing Failure and How to Fix Them
Rod bearing failure is often preventable with proper maintenance and care. Let’s take a closer look at some of the most common causes and how to address them.
1. Lack of Lubrication
Insufficient lubrication is one of the main culprits behind rod bearing failure. Without enough oil, the bearing surfaces experience excessive friction and heat, which can lead to wear and damage.
To fix this, ensure your engine has the correct oil level and regularly check for leaks or clogs in the oil system. Routine oil changes are essential to maintain proper lubrication.
2. Misassemble
Improper assembly during engine repairs or manufacturing can misalign rod bearings, causing uneven wear or failure.
To avoid this, follow the manufacturer’s specifications during installation and use precision tools to ensure all components are properly aligned. If you suspect a misassembled rod bearing, consult a professional mechanic for reassembly.
3. Using Sub-Par Oil
Low-quality or incorrect oil can fail to provide the necessary protection for rod bearings. Cheap oils may not have the right additives to reduce friction and prevent heat buildup.
Always use the oil recommended by your engine manufacturer and choose high-quality brands that meet the required specifications. Switching to a better-grade oil can improve bearing performance and longevity.
4. Dirt Build-Up
Contaminants like dirt, debris, and sludge can accumulate in the oil, damaging rod bearings over time. These particles can scratch and wear the bearing surface, leading to premature failure.
Regularly replace your oil filter, use clean oil, and keep the engine environment free of dust and debris to minimize contamination.
5. Contamination
Contamination happens when foreign particles, like dirt, dust, metal shavings, or grit, enter the bearing's lubricant or cleaning solution. This can come from unclean tools, work areas, or even dirty hands, leading to wear and damage over time.
6. Cage Damage
Cage damage can occur for various reasons, often leading to compromised bearing performance. Common causes include:
- excessive vibration,
- operating at speeds beyond the bearing's design limits
- natural wear and tear over time
- blockages that disrupt smooth operation
Identifying and addressing these factors early is crucial to maintaining the bearing's integrity and preventing further damage.
7. Electric Arcing
Also referred to as "Electric Arc Erosion," electric arcing occurs when an electrical current flows through the bearing, breaking at the contact points between the races and rolling elements.
This process generates high temperatures at localized spots, leading to damage. Over time, the heat can create pits on the raceways and rolling elements, compromising the bearing's integrity and performance.
8. Poor Fitting
Proper installation and sizing of the bearing on the shaft are critical to its performance. An incorrect fit can cause two major issues:
- Too Tight Fit: If the shaft is oversized or expands, the bearing will become too tight, reducing its internal clearance. This can lead to increased friction and premature wear.
- Too Loose Fit: If the shaft is undersized or the fit is too loose, the bearing may shift or "creep" on the shaft. This movement can cause excessive wear, generate heat, and eventually lead to vibration and runout problems.
Making sure the shaft and bearing are properly matched in size is essential to prevent these issues and ensure smooth, efficient operation.
9. Brinelling
Brinelling occurs when excessive loads push the bearing material beyond its elastic limit, leaving permanent indentations in the raceways. These indentations can result in increased vibration and reduce the bearing’s efficiency.
Brinelling is classified into two types:
- True Brinelling: This happens when the bearing is subjected to loads that exceed the material’s elastic limit, causing permanent indentations in the raceways.
- False Brinelling: This type is caused by vibration or movement between the rolling elements and the raceways, leading to shallow depressions around the race. False brinelling doesn’t involve excessive load but rather the effects of oscillation or swaying.
Both types of brinelling can lead to significant performance issues, but recognizing them early can help prevent further damage.
10. Misalignment
Misalignment can cause excessive vibration and put extra stress on bearings. While some bearings can tolerate minor misalignments, it’s best to avoid them. Common causes of misalignment include:
- bent shafts
- dirt or burrs on the shaft or housing surfaces
- uneven threads
- locking nuts that aren’t square to the threads
To prevent misalignment, regularly inspect shafts and housing, use high-quality locknuts, and shim the housing when necessary.
11. Path Patterns
To understand how a bearing is performed during operation, it's helpful to examine the wear pattern on a bearing that's already been used.
By analyzing these wear patterns through failure testing, you can determine whether the bearing operated under normal or abnormal conditions. This helps in assessing if the bearing was used in the ideal environment.
12. Seal Selection & Maintenance
Properly selected and maintained seals are essential for protecting bearings from contamination and preserving the integrity of lubrication. Effective seals prevent dirt, dust, and moisture from entering, ensuring the lubricant stays intact and the bearing operates smoothly for longer.
13. Overload
Excessive load on a bearing is a frequent cause of failure. When a bearing is subjected to more stress than it’s designed to handle, it can wear out quickly or even break down completely.
To prevent overload, reduce the load on the bearing or consider upgrading to a bearing with a higher capacity to better handle the demands of your engine.
14. Improper Handling & Storage
Improper storage of bearings can lead to problems down the line. When bearings are exposed to moisture, dust, or extreme temperatures, it can cause damage.
Handling also becomes an issue when boxes are opened, or packaging is torn too early, allowing dirt and contaminants to get to the bearings, which can lead to corrosion. To avoid this, store bearings in a clean, dry place and only remove packaging when ready to use them.
15. Inadequate Internal Clearance
When there isn’t enough clearance inside the bearing, it can lead to excessive friction and heat buildup. This affects the bearing’s ability to handle loads and shortens its lifespan.
As we’ve seen, high temperatures are harmful to bearings and can cause issues like poor lubrication and increased internal friction, which only worsen the problem.
16. Overlay Fatigue
Overlay fatigue occurs when the aluminum lining of a rod bearing becomes damaged, leading to cracks and distress on the bearing surface. This can result in the loss of aluminum material, impacting the bearing's performance.
Appearance:
You’ll notice cracks, craters, and an overall distressed bearing surface where the aluminum lining has worn away.
Possible Causes:
- Incorrect bearing material choice
- Increased engine power beyond its original design
- Excessive clearance between parts
- Fuel detonation or advanced ignition timing
- Defects in part geometry that cause uneven load on the bearing
Corrective Actions:
- Choose a bearing material that can handle higher loads
- Ensure proper clearances and check part geometry
- Retard the ignition timing or use fuel with a higher octane rating
- Repair or replace any distorted parts to restore function
Taking these corrective actions can prevent overlay fatigue and extend the life of your rod bearings.
17. Surface Wear
Surface wear happens when the bearing material slowly degrades due to friction and heat. This can lead to the bearing’s surface becoming rough and uneven, ultimately causing failure.
To prevent surface wear, make sure the oil is changed regularly to reduce friction and keep the bearings properly lubricated.
18. Edge Wear Due to Distorted Connecting Rod
When a connecting rod becomes distorted, it can cause the edges of the rod bearings to wear unevenly. This often occurs when the rod is misaligned, leading to excessive load on the bearing edges.
To fix this, inspect the connecting rod for any distortion or misalignment. If necessary, replace or repair the rod and make sure the bearings are seated properly to prevent further edge wear.
19. Imperfect Journal Geometry
Imperfect journal geometry refers to irregularities in the crankshaft journals that cause uneven contact with the rod bearings. These imperfections can lead to excessive wear or even bearing failure. To correct this, measure the crankshaft journals to ensure they meet the manufacturer’s specifications.
If there are any deviations, have the journals repaired or replaced to restore proper alignment and prevent bearing damage.
20. Cavitation Erosion
Cavitation erosion occurs when bubbles form in the oil due to rapid changes in pressure and subsequently collapse, causing tiny but damaging pitting on the bearing surface. This can weaken the bearing over time.
To reduce cavitation erosion, ensure the oil flow is consistent, and the oil pump is functioning correctly. Maintaining the right oil pressure and quality will also help minimize cavitation.
21. Spinning of the Bearing in the Housing
A spun bearing occurs when the rod bearing loses its secure fit within the housing, leading to excessive friction, engine damage, and potential failure.
Appearance:
When the bearing spins within its housing, it creates a highly polished area on the back of the bearing, which can lead to failure.
Possible Causes:
- Insufficient crush height
- Oil starvation or lugging the engine, causing seizure
- Housing diameter being too large
Corrective Actions:
- Use bearings with an adequate crush height for your application
- Address the cause of engine seizure
- Check the housing diameter for proper size and roundness
- Tighten bolts to the manufacturer’s specified torque value
22. Moisture
Moisture from outdoor or humid environments can seep into your bearings, setting the stage for rust and corrosion that eventually leads to bearing failure. To prevent this, store your engine in a dry, controlled environment, and regularly check for signs of moisture or corrosion.
23. High Temperatures
Operating your engine at temperatures higher than recommended can affect both the lubricant and the bearing itself. Overheating can cause the lubricant to break down and reduce the hardness of the bearing, leading to cracks.
Always refer to the manufacturer’s operating guide to ensure the engine temperature and lubrication requirements are met. Use the correct lubricant for the conditions to avoid overheating.
24. Incorrect Installation
Improper installation is a common cause of bearing failure. Misalignment, imbalance, or excessive shaft run-out can all contribute to premature wear and failure. Make sure to follow correct installation procedures, ensuring proper alignment, balancing, and mounting of the bearing.
25. Electrical Damage
Electrical currents passing through the bearing can lead to electrical erosion or arcing, which damages the bearing surfaces and degrades the lubricant. This can result in pitting, excessive wear, and eventual failure.
To prevent electrical damage, consider using insulated bearings or check for electrical issues in your engine system that could be affecting the bearings.
How to Avoid an Engine-Bearing Failure
Preventing engine-bearing failure requires a proactive approach to maintenance, proper part selection, and diligent monitoring of the engine's performance. Here are some essential steps to avoid bearing failure and keep your engine running smoothly.
1. Adequate Lubrication
Proper lubrication is crucial for preventing bearing failure. Without enough lubrication, friction increases, leading to wear and overheating. Always ensure that the engine oil level is sufficient and that the oil is of the correct viscosity.
Regular oil changes and checks for oil contamination can also help maintain proper lubrication, reducing the risk of bearing damage.
2. Dealing with Material Fatigue
Bearing materials can wear out over time due to constant stress and pressure. To prevent material fatigue, ensure the bearings are made of high-quality, durable materials that can withstand engine loads.
Regular inspection of the bearings for signs of wear, such as cracks or surface distress, can help detect fatigue early, allowing for replacement before failure occurs.
3. Selecting the Right Bearing
Choosing the correct bearing for your engine is critical for performance and longevity. Select a bearing material that matches the engine’s power, load, and temperature requirements.
An ill-fitting bearing may not provide the necessary support, leading to premature wear. Consult your manufacturer’s specifications to ensure you're using the right bearing for your engine type.
4. Installing the Bearing Properly
Improper installation is a common cause of bearing failure. Misalignment, incorrect mounting, and imbalanced installation can cause excessive load on the bearings.
Be sure to follow installation guidelines carefully, ensuring the bearings are properly aligned, seated, and securely fastened. This will reduce stress on the bearings and prevent damage from installation errors.
5. Lubricating the Bearing According to the Manufacturer's Guidelines
Always follow the manufacturer’s guidelines when lubricating bearings. The type of lubricant, the frequency of lubrication, and the amount used all play a role in the bearing’s performance.
Using the wrong type of lubricant or failing to follow guidelines can lead to inadequate lubrication, increasing the chances of bearing failure.
6. Temperature Monitoring
Excessive heat is one of the biggest enemies of engine bearings. Consistently high temperatures can degrade the bearing material and reduce lubrication effectiveness.
Regularly monitor engine temperature and ensure the cooling system is working efficiently. If the engine is running too hot, address the cause before it leads to bearing damage.
7. Winding Analysis
Winding analysis involves monitoring the electric motor’s winding condition, which can impact bearing health, especially in electric-driven engines.
Using sensors to analyze vibrations and detect abnormalities can help identify potential bearing issues before they lead to failure. Early detection of electrical problems can prevent damage to the bearings.
8. Motion Amplification Monitoring
Motion amplification is a technique used to monitor vibrations in machinery that might indicate impending bearing failure. By using advanced cameras and software, you can detect small vibrations that are not visible to the naked eye but may signal problems with the bearing.
Regular motion amplification monitoring can help identify misalignments or issues with bearing performance early on, reducing the likelihood of catastrophic failure.
Engine Bearing Preventative Maintenance Program
An effective preventative maintenance program is key to extending the life of your engine bearings and avoiding unexpected failures. By focusing on proper care and regular checks, you can keep your engine running smoothly for the long haul.
1. Routine Inspections
Frequent inspections are essential for catching potential bearing problems early. Check for signs of wear, such as unusual noises, vibrations, or oil contamination.
Look for damage on the bearing surface, including cracks or uneven wear patterns. Regularly monitoring your engine's condition helps address minor issues before they turn into major problems.
2. Proper Storage and Handling
Improper storage or handling can damage bearings before they are even installed. Always store bearings in clean, dry environments to prevent rust and contamination. When handling them, avoid dropping or mishandling bearings, as this can create dents or scratches that lead to premature failure.
3. Using Quality Components
High-quality bearings and associated components are critical for long-term reliability. Subpar or counterfeit parts may save money upfront but can lead to costly failures down the line.
Always source bearings from reputable suppliers and ensure they meet the specifications of your engine. Investing in quality components pays off by improving engine performance and reducing downtime.
Prevent Costly Engine Repairs with Proactive Maintenance
Engine-bearing failure is a preventable issue that, if ignored, can lead to severe engine damage and expensive repairs. Understanding what causes bearing failure—from poor lubrication to material wear—allows you to take proactive steps to extend the life of your vehicle.
Routine maintenance, high-quality parts, and expert service are key to keeping your engine and bearings in peak condition. At CarHub, our team of professionals is here to help with trusted automotive expertise and top-tier service.
For more expert insights on how to keep your car performing at its best, explore the CarHub Blog. Need hands-on assistance? Book a service appointment today and let our experts keep your vehicle running smoothly for years to come!