Common Causes of Electric Motor Bearing Overheating and Failure (Part 1)

Common Causes of Electric Motor Bearing Overheating and Failure (Part 1)

Bearings are one of the most critical components in any electric motor system. They are responsible for supporting the rotor, ensuring it maintains proper radial and axial alignment. A well-functioning bearing system guarantees smooth rotation, reduces friction, and extends the life of the motor. However, when bearings are damaged or improperly assembled, they can overheat, wear prematurely, or even collapse, leading to severe motor failures such as shaft seizure or winding burnout.

Understanding the root causes of bearing overheating and damage is essential for improving motor reliability and performance. 

In this first part of our series, we focus on three major causes:

1. Poor Assembly and Improper Use

Although bearings are manufactured under extremely strict quality controls—especially at leading bearing factories—the same level of precision is not always maintained during motor assembly or in end-use environments. Several issues can arise:

Contamination during assembly: Dust, debris, or even water can enter the bearing if the assembly environment is not clean.

Damaged bearing surfaces: Impacts or improper force during installation can create micro-damage on the raceways.

Improper lubrication: Mixing lubricants or using grease with particles can reduce bearing life drastically.

Environmental factors: Motors operating in damp, dirty, or chemically aggressive environments can cause the bearings to rust or corrode.

Additionally, improper sealing between the inner and outer bearing covers may allow foreign particles to enter the bearing chamber. Poor machining or size deviations in the sealing grooves can also lead to premature failure.

2. Improper Fit Between Shaft, Housing, and Bearing

Every bearing has a defined clearance—initial clearance before installation and operational clearance during use. If the bearing is too tightly clamped, it reduces the working clearance and generates excess heat. On the other hand, if the fit is too loose, it may cause bearing creep (relative rotation between the bearing and its seat).

Common issues include:

Overtight interference fit: This leads to reduced internal clearance and increased frictional heat.

Loose fit: The inner ring may rotate on the shaft (inner ring creep), or the outer ring may rotate in the housing (outer ring creep), both causing severe wear.

Dimensional deviations: If the housing or shaft is out of tolerance, the bearing may not seat properly, accelerating damage.

3. Rotor-Stator Misalignment (Non-Concentric Assembly)

Ideally, the motor rotor and stator should share the same central axis. When they are not concentric, especially in horizontal motors, the rotor may sit at an angle relative to the motor feet. This misalignment puts uneven radial and axial loads on the bearings at both ends.

As the motor runs, the resulting mechanical stress causes the bearing to operate under abnormal conditions, often leading to:

Irregular bearing noise

Increased vibration

Localized overheating

Premature wear or even bearing breakdown

The health of your electric motor largely depends on the integrity of its bearing system. Improper assembly, incorrect fits, and rotor-stator misalignment are all common but preventable issues that lead to overheating and bearing damage. In the next article, we’ll explore additional factors such as load imbalance, vibration, and lubrication failures in more detail.