TL;DR
Misalignment between the motor and the driven equipment creates a knocking or rumbling noise. Check soft foot first, then measure parallel and angular alignment with a dial indicator or laser tool.
What you might see
- rhythmic knocking at running speed
- rumbling under load
- premature coupling element wear
- vibration at 1× and 2× run speed
Likely causes
Coupling alignment shifted after a thermal cycle, foundation movement, or load impact
Worn or damaged coupling element, broken jaws, deformed elastomer spider, scored hubs
Soft foot, uneven motor base mounting causing the housing to flex when bolted down
Bearing wear (covered in the bearing-noise guide on this machine)
Required tools
- Dial indicator with magnetic base, OR laser alignment tool
- Shim stock (pre-cut motor shims)
- Wrench set sized to the foot bolts
- Torque wrench
- LOTO kit
Safety first
- Always replace the coupling guard before re-energizing.
- Lock out the motor disconnect before opening the coupling enclosure.
Procedure
- 1
Lock out the motor disconnect.
- 2
Remove the coupling guard.
- 3
Inspect the coupling for visible damage, broken jaws, deformed spider, scored hubs. Replace any damaged coupling element.
- 4
Check for soft foot: loosen each foot bolt one at a time and watch for the motor housing to lift more than 0.002 inches at any foot. Shim flat as needed.
- 5
Set up a dial indicator or laser alignment tool on the coupling halves.[1]
- 6
Measure parallel offset (radial) and angular offset (face). Both should be within Baldor's specification, typically 0.002 inches parallel maximum and 0.001 inches per inch of coupling diameter angular maximum.[1]
- 7
Adjust the motor position with shims under the feet and horizontal jack screws or pry bars until alignment is in spec.
- 8
Re-torque the foot bolts to spec and re-check alignment, torque-down often shifts the motor by a few thousandths.
- 9
Replace the coupling guard before re-energizing.
Warning: Never run a motor with the coupling guard removed.
Sources
Baldor Reliance Industrial Motor Maintenance Manual, Baldor Electric Company (ABB)
Baldor Industrial Motor Maintenance Manual, coupling alignment specifications (general)
View source
More guides for Baldor Super-E (EM/EJMM)
How to diagnose bearing noise and vibration on a Baldor Super-E motor
Vibration is most often a worn bearing. Listen for grinding, log a vibration reading, and plan a bearing replacement during the next planned outage.
How to diagnose intermittent operation on a Baldor Super-E motor
Intermittent stops or restarts almost always come from loose electrical connections or a worn contactor. Check the contactor first, then torque-test the conduit box terminals.
How to fix overheating and excessive current draw on a Baldor Super-E motor
Overheating with high current is usually mechanical overload or supply phase imbalance. Measure phase currents, check the load, and verify supply voltage balance is within 1%.
How to fix reduced speed on a Baldor Super-E motor running on a VFD
If the motor runs below the commanded speed, check the VFD's frequency reference, slip compensation, and supply voltage. Mechanical load increase can also drag speed down.
Stop fixing the same fault twice.
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