The screw element bearings are reaching end of life. You can hear it coming: grinding, rumbling, or increased vibration. Bearing life is about 40,000 running hours.

What you'll see

A new noise that wasn't there before: grinding, rumbling, or a metallic scraping sound from the airend area. The noise may change with load (louder during loading or unloading). Vibration levels increase. In advanced stages, the motor current rises as the bearings create more friction.
Before you assume this is the problem

Verify the noise is from the airend, not the motor, coupling, or belt. Put your ear (or a stethoscope) close to each component to isolate the source. See: Motor Bearing Failure, Belt Problems, Coupling Wear.

See all causes of unusual noise →

How to diagnose

  1. Isolate the noise source

    Use a mechanic's stethoscope or even a long screwdriver (handle to your ear, tip touching the component) to pinpoint whether the noise is from the airend, motor, or coupling. Bearing noise is typically a constant rumble or grind that changes with speed.

    Result: Noise from airend = bearing wear.

  2. Check running hours

    Airend bearings typically last about 40,000 hours. If you're approaching or past this, bearing wear is expected. Check the compressor's hour meter.

    Result: Near or past 40,000 hours = expected wear.

  3. SPM (Shock Pulse Method) vibration measurements

    Perform SPM measurements if the airend is equipped with the necessary measuring points. Although absolute values are useful, it is more important to look at the trend over time. So start measuring SPM values at every service interval and compare them over time.

How to fix it

  1. Plan an airend overhaul

    Don't wait for seizure. Schedule a bearing replacement / airend overhaul. New bearings, seals, and inspection of the rotors. This is expensive but far cheaper than replacing a seized airend and possibly the motor.

Common mistakes

Running a compressor with noisy bearings 'until it breaks' turns a bearing replacement into a full airend replacement. The rotor surfaces get damaged when bearings fail, and then the element is scrap.

Parts & tools

Airend bearing kit and seals. This is specialist work: usually done by the compressor service company.

Review safety precautions before starting →

Safety

Don't ignore bearing noise. A failing bearing will eventually seize, destroying the rotors and possibly the motor. The earlier you catch it, the cheaper the repair.

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