Did you know that 2% of motor failures are due to the shaft coupling?

Here are the reasons why:

1. Misalignment

  • A coupling that is badly aligned suffers unusual load stresses and can lead to failure.
  • Ensure the coupling is aligned parallel to the shafts.

Tips: Check all 3 types of alignment of your motor

Mechanical alignment: Experience has shown that any base-mounted assembly of motor and driven load, no matter how rugged or deep in section, may twist out of alignment during shipping or moving, and that alignment by eye is ineffective. Proper alignment of direct-coupled drives can be accomplished by a dial-indicator, laser, or computerised instrumentation.

Parallel misalignment: This is the offset between the centrelines of the two shafts. This can be determined by mounting a dial indicator on one coupling half with the indicator probe bearing radially on the other coupling half, and then rotating both shafts together through 360 degrees.

Angular misalignment: This is the amount by which the faces of the two coupling halves are out of parallel. This may be determined by mounting a dial indicator on one coupling hall with the indicator probe on the face of the other half, and then rotating both shafts together through 360 degrees to determine any variation in reading. During this check, you must keep the shaft of a motor with endplay against its thrust shoulder and the shaft of a driven load with endplay against its thrust shoulder to prevent false readings due to shaft movements in the axial direction.


What is the best way to ensure my coupling is aligned correctly?

Laser alignment is the best way to ensure accurate alignment. Contact your coupling manufacturer for the alignment tolerances for your coupling.

2. Bad installation

  • The biggest cause of coupling failure is due to incorrect mounting.
  • Research and use appropriate fitting techniques for your motor.

There are two main types of couplings available:

  • Rigid couplings – for use when shafts are coaxially aligned.
  • Flexible or compensating couplings – for use when shafts alignment cannot be guaranteed or there is expected distortion or movement that could be transmitted through the shaft


  • When installing a shaft coupling, ensure that you are using the correct coupling type.
  • If there is a degree of distortion or shock expected through the shaft, then a flexible coupling should be used.


Can rigid couplings be used on misaligned shafts?

Rigid couplings should not be used on misaligned shafts. Misalignment could generate lateral forces which could lead to premature failure of the shaft, bearings or couplings from wear and metal fatigue.

Do you know what are the other reasons for motor failure? Our 60 Minute Guide to Motor Maintenance is designed to give you, the engineer, all the information you need in industrial electric motor maintenance in a format that is concise, easy to understand and is a point of reference for now and the future. Visit our website and request your Free Guide: 

We provide 24/7 Technical Support to engineers, our dedicated Support line is available 8am – 5pm every day, manned by one of our fully qualified engineers.

If you need further assistance on how to prevent your motor from failing, call us, day or night, on 0330 9000 247.