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Looseness - Rotating Looseness (Coupling)

Symptoms: Multiple Synchronous Frequencies (1x....nx running speed)

 Motor Coupling Looseness3

Rotating Looseness is differnet to Structural Looseness. This is often caused when limits and fit are out of there designed tolerences. for example when a bearing has worn on the shaft or in the housing, or when a coupling has worn and there is play in the coupling. Also collapsed bearings will give rotating loosenss characterhistics

 Rotating Looseness is characterised by:

Icon Spectrum Spectrum: 


  • Multiple peaks at running speed (up to 10 x)
  • Severe looseness will give 1/2 x and sometime 1/3 x peaks in the spectrum. 
  • Both Horizontal and vertical trends apear the same
  • PeakVue or Demodulation spectra will see the shock value at 1x

 Icon Wav Waveform:


  • The waveform will have impacting at 1x

  • PeakVue or Demodulation waveform will see the shock value at 1x

Icon Phase Phase:

  • Not Used

Severity - Medium

 Icon Guage Orange

This condition is likely to cause failures if levels are allowed to get high. Expect vastly reduced life of the asset and it component parts. bearings will fatigue quickly. - Rectify 

What causes Coupling Looseness

Looseness in coupling is quite common and could be down to fatigue or poor maintenance or misalignment. If you can see through the guards then using ultrasonics you can confirm the looseness is coming form a coupling of from the bearings, Also using a strobescope you can see the actual damge or jitter on the coupling due to limits and fits being out. See the video to see a worn spider coupling example using the strobe method.


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