Bearings: Types, Symptoms & Failure Clues

Plain-English Summary

Bearings support motion. They allow shafts, rollers, wheels, pulleys, gears, cams, slides, and machine elements to move while carrying load and controlling position. A failed bearing is often the visible symptom, not the full root cause.

Why It Matters

Bearings fail for reasons: contamination, poor lubrication, wrong fit, misalignment, overload, heat, electrical damage, vibration, improper installation, wrong bearing type, bad sealing, or poor operating conditions. Replacing the bearing without correcting the cause may only restart the failure clock.

Field Rule of Thumb

Do not only ask, “Which bearing failed?” Ask: What made this bearing fail? A good replacement includes inspection of fit, alignment, lubrication, sealing, load, environment, installation method, and related machine condition.

Core Concept

Rolling element bearings use balls or rollers to carry load with rolling contact. Plain bearings and bushings use sliding contact. Thrust bearings carry axial load along the shaft direction. Each type has different load, speed, lubrication, alignment, and installation needs.

Worked Example

A conveyor roller bearing fails repeatedly. The bearing is replaced twice, but it runs hot again within a week. Inspection finds a slightly bent roller shaft, the mounted bearing forced out of alignment, a damaged seal from washdown spray, and contaminated grease. The bearing was the part that complained first; the root cause was the system condition around it.

Common Mistakes

• Replacing the bearing without checking the shaft or housing.
• Assuming grease solves every bearing problem.
• Ignoring contamination from water, dust, chips, product, chemicals, or washdown spray.
• Pressing through the wrong race during installation.
• Ignoring alignment, belt tension, coupling load, or base distortion.
• Treating noise as the only failure clue.

First Checks / Troubleshooting Flow

1. Confirm the machine is safe to inspect.
2. Identify the bearing location and function.
3. Listen for noise changes and check for heat.
4. Check vibration, looseness, or rough rotation.
5. Inspect seals, shields, grease, and contamination.
6. Check shaft fit, housing fit, mounting condition, and alignment.
7. Check load, belt or chain tension, coupling condition, and process changes.
8. Verify the bearing type and replacement history.
9. Replace only after likely causes have been considered.