September 13, 2018

Too Much Grease (a “liquid” unbalance!)

By Stan Riddle

Too much grease feat. image

We recently published a blog about using the Fixturlaser SMC as a lubrication tool.

Ironically, just a couple of weeks later I received some photos from a new SMC customer.  He got a report from his SMC stating that a chilled water pump was experiencing motor unbalance.  He took the motor apart to inspect it, and said he thought two tubes of grease fell out!  There was so much grease packed into the bearing cavities, into the windings, and even in the rotor, that it was unbalanced, and they decided to simply replace the entire motor.


For many years, when mechanics followed a PM (preventive maintenance) task to grease the motor, the PM typically didn’t say how much to grease the bearing – just grease it!

This brings to light several important considerations about PM’s , such as having a good “checks and balances” test for maintenance tasks.

The SMC is a great tool for knowing when bearings have enough grease (click on the blog link above for more information).

But it’s not the only method.

  • A relief plug on a grease fitting is a good way to prevent over-greasing.  When internal pressure in the bearing cavity is created, the relief plug will allow extra grease to escape.
  • If the machine has a grease purge plug, allow some extra grease to purge out of the bearing cavity.
  • Use a mechanic’s stethoscope, or an ultrasonic tool. These will allow you to “hear” when grease contacts an under-lubricated bearing.
  • Have an understanding how much grease per stroke is actually being delivered.

It’s common knowledge that over-greasing bearings may be more common than under-greasing bearings, so it is a best practice to grease only when needed.  And a good way to know when a bearing needs grease is not a PM, but “asking” the bearing when it needs grease.