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Greasing Your Compressor Motor – What You Need to Know

Have you ever thought about how much grease is enough when pumping it into a motor or what particular type is appropriate?


As an air compressor service company, we do maintain a variety of compressors that make use of different motor brands (some are domestic and others are either Asian or European).  There are some who use shielded or even sealed bearings but still add grease to the bearing cavity! Doing so to a motor with seals or shields will only cause damage to the bearing.


So the question is… is there a standard amount of grease that is actually enough?


There are various factors to be considered when figuring out the amount of grease to put in, including motor RPM heat, and grease type, among others. Also, here are some things you need to determine before you add any grease to your motor:

  • What size is the bearing?
  • Is it an open and grease-ready type of bearing?
  • What type of grease are you currently using?
  • How much grease is in it right now?
  • What is the motor’s RPM?
  • How long does it run in a day?
  • What kind of environment does it have?
  • Are the bearing cavities full?


Once you have the necessary information, you have to determine at least a baseline of how much grease is actually in the motor right now. For compressor motors with a drain port, you can complete this by simply removing the port plug and pumping in grease until you get fresh grease out of this port. When this is done, start the motor and run the bearing and allow extra grease to purge from the cavity. You want to avoid over-greasing and a churning effect.


Grease Churning

When you over-grease a bearing, it causes the machine to work harder because it has to push or plow all excess lubricant around the bearing. This results to not only an increase in energy usage, but also in a reduction of the quality of the lubricant due to oxidation. Instead of providing a steady flow of lubrication on the bearing race, all the excess lubrication is forced in front of the rotating bearings, which causes a churning effect and affects the overall operation of the machine.


Now that you know the grease level in the bearing, next you have to determine how much grease and at what frequency it should be pumped into the bearing. To be sure, you should always refer to the manufacturer’s guide that came with the product for the proper greasing methods.

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