Electric Motor Bearing Lubrication: How Much, Which Grease, How Often
Practical guide to greasing electric motor bearings: grease type, volume, drain, interval — and why “greasing a hot motor” often makes overheating worse.
Motors are the most common assets on site. “Motor bearing lubrication” usually hides three questions: which grease, how much, how often. A miss on any of them shows up as a hot end shield and an unplanned swap.
Which grease
Rolling bearings → grease. Sleeve bearings → oil. Do not confuse them.
Priority: motor OEM plate/manual → plant lube map → only then “equivalents” with compatible thickener and viscosity. Typical industrial pick: NLGI 2 (lithium or polyurea depending on OEM). Selection deep-dive: choosing grease. Do not mix grades without a controlled changeover.
How much
Do not fill the free volume to 100%. Working fill is often about 30–50% (confirm with OEM). Excess causes churning: grease fights the rolling elements, temperature rises, seals extrude.
Starter relube dose: Q (g) ≈ D × B × 0.005 — a ceiling, not an order to pump it all. Closed drain or leftover grease → safe dose is lower. Technique: how to grease bearings and grease gun.
How often
Catalogue intervals are lab averages. Real life shortens grease life via shield/ambient temperature, starts, vibration, dust/moisture, vertical shafts, seal quality. Fixed “every month for all motors” almost always means some are over-greased and some are dry — why intervals lie.
Procedure with a grease nipple
Clean nipple → open drain if fitted → small shots → run motor so excess can exit → close drain, wipe, log. If the shield is already hot, the instinct to add grease often worsens churning — diagnose first: why the bearing runs hot.
Common motor mistakes
Closed drain → grease into the winding; extra pumps after the ceiling; mixing warehouse grades; greasing sealed 2Z/2RS lifetime bearings; dirty nipples.
Condition control
Temperature lags. Vibration often catches late-stage defects. Ultrasound sees friction rise earlier — and during greasing shows when to stop. Routes: LUBExpert and grease mode on SDT340.
KEG TRK — supply and training for acoustic motor-fleet lubrication in Kazakhstan. Discuss a rollout.
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