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Why Electric Motor Bearings Turn Brown or Blue (and How to Fix It)

2025-06-19

Bearing discoloration — such as brown, blue, or purple marks — is a serious warning sign in electric motors. Ignore it, and you risk unexpected breakdowns and costly repairs. Here’s what causes it and how to prevent failures.

Top 3 Causes of Bearing Discoloration

1. Lubrication Problems (Most Common)

Too little grease: Starves bearings, causing metal-on-metal friction.
Wrong grease type: Standard grease breaks down under high heat or high-speed operation.
Old or contaminated grease: Dirt or moisture makes grease gritty and ineffective.

Warning Sign: Bearing temperature above 70°C (158°F)

2. Installation Mistakes

Forced fitting: Using hammers or improper tools can damage bearings during installation.
Shaft misalignment: Creates uneven pressure and premature wear.

3. Electrical Damage

Voltage leakage from VFDs or motor windings can cause micro arcing, which burns bearing surfaces and leads to fluting or discoloration.

Simple Prevention Checklist

Risk Area	Action to Take
Lubrication	• Fill bearings ⅓–½ full • Use heat-resistant grease for high-temperature environments • Inspect and replace grease annually
Installation	• Avoid hammering bearings into place • Ensure proper shaft and housing alignment
Electrical	• Install grounding brushes • Use insulated bearings when working with VFDs
Monitoring	• Monitor bearing temperature monthly • Listen for unusual grinding or noise

Prevent early bearing failure with the right design, maintenance, and quality components.

Beining Technology – Dedicated to motor bearing production for more than a decade

With over 10 years of experience in manufacturing electric motor bearings, we provide high-quality, durable solutions for industrial applications worldwide. From deep groove ball bearings to insulated and high-speed models, our products are built to perform reliably under demanding conditions.

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Why Electric Motor Bearings Turn Brown or Blue (and How to Fix It)

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