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Electric Motor Upkeep: An Overview Of Mechanical Inspections

Electric Motor Upkeep: An Overview Of Mechanical Inspections

Preventative maintenance is all about nipping motor issues in the bud before they can cause a breakdown and warrant an untimely call to the repair shop for their electric motor overhauling services. This ongoing effort all starts with conducting regular inspections. Still, while the motor’s electric components certainly require much attention, its mechanical aspects are just as important, starting with the critical fits.

Critical fits and their significance to motor performance

One of the mundane yet integral aspects that keep electric motors running efficiently and reliably are their mechanical fits and tolerances. Thus, a thorough inspection always includes carefully dismantling the motor and measuring its critical fits, which covers:

  • Bearing fits
  • Seal fits
  • Journal fits
  • Keyway
  • Housing
  • Shaft extension size

When the dimensions of these fits are no longer in line with the manufacturer’s tolerances, an electric motor will eventually encounter an issue sooner than later. For instance, if a shaft bearing’s inner diameter is not within the recommended tolerance threshold for the rotor shaft it supports, the latter may become misaligned and damage the stator as the rotor starts to rub against it. On top of that, the bearing may experience uneven wear and tear and fail prematurely.

Poor fits can also cause significant vibration issues, including those identified through vibrational analysis, that could wreck other parts of the motor. If a mechanical part no longer fits within the manufacturer’s set tolerance, any extra space–no matter how small–allows for excess displacement and, ultimately, potential vibrations that the motor was not designed to handle.

Seal fits that go beyond the acceptable tolerances pose another problem since they inevitably lead to leaking. The same thing happens when lubrication like motor grease or mineral oil transformer is not properly sealed, causing it to leak out and negatively affect the temperature and friction of the parts that are making physical contact. Worst of all, contaminants like moisture and dirt can gradually get mixed with the lubricant, further increasing friction and temperature and causing surface damage.

Performing mechanical inspections on electric motors

Now that we have established the importance of mechanical inspections, let us proceed with how they occur.

Critical parameters

The mechanical inspection of an electric motor includes monitoring the measurements of certain parameters in shafts, seals, and bearings, such as:

  • Mechanical Seal Fit Clearance
  • Bearing Outer Diameter to Housing Inner Diameter
  • Bearing Inner Diameter to Shaft Outer Diameter
  • Coupling Inner Diameter to Shaft Outer Diameter
  • Runouts

Essential equipment for mechanical inspections

There are key instruments required to perform the measurements above, including:

  • Digital calipers – these are used to measure lengths as well as inner and outer diameters if necessary
  • Outside and inside micrometers – for measuring external and internal dimensions
  • Lathe – typically combined with a dial indicator to measure runouts.
  • Dial bore gauge – a tool for measuring small bearings that have been spun, cast and finished.

Typical measurement process

It is not enough to take a single measurement of a bearing’s diameter and call it a day. When measuring sleeve bearings, for instance, their inner and outer diameters should be measured at the same, multiple points along the length of the bearing using an inside and outside micrometre but at different orientations. This approach ensures a full set of data points for the bearing’s inner and outer diameter that, when combined, allows for calculating clearances to verify whether they remain within appropriate tolerances.

Visual inspection

A mechanical inspection is never complete without performing a visual inspection. For example, take sleeve bearings, which often have oil rings or oil ring keepers that require a quick check every now and then to evaluate their condition and see if the babbit material remains secured to the bearing’s interior. Technicians also look for indicators of surface wear on mechanical components, such as abrasions, scuff marks, pitting, and gauges. This visual check is also key when it comes to the insulation of insulated bearings.


While the electrical functionality of a motor takes top priority, inspecting its mechanical aspect should never be neglected as it also largely dictates its performance. Consulting with a reputable electrical engineering company in Singapore can prove helpful in improving this area of your motor maintenance regimen.