What You Should Know About Greasing Your Air Compressor Motor

Oct 12, 2020 by Brad Taylor

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Ever wonder how much motor grease is enough when pumping it into a motor? Or what type of grease is the best? We wondered the same so we invited in John Wojdyla from Timken, to educate us on bearing greasing. We took our previous knowledge and combined it with what he taught us to produce the below information.

The challenge we face as an air compressor service company, is that we maintain many different brands of compressors that use different brands of motors, some of which are domestic and many that are European and Asian. To add to the confusion, some manufactures use shielded bearings or even sealed bearings, but then still add a grease zerk to the bearing cavity! Adding grease to a motor with shields or seals will implode and damage the bearing. So is there a standard amount of grease that is enough?

As we all know, there are variables to when trying to figure out how much grease to put in, such as heat, motor RPM, grease type, and much more. Upon review of these many applications, we realized that a few things need to be determined before a motor should have any grease added to it.

1. Is the bearing an open greaseable type bearing?
2. What is the size of the bearing?
3. What type of grease is currently being used?
4. How much grease is currently in it?
5. Are the bearing casing cavities full?
6. What is the RPM of the motor?
7. How many hours does it run?
8. What is its environment?

Once this info is gathered, a baseline of how much grease is currently in the motor needs to be determined. For motors with a drain port, this is easily completed by removing the port plug and pumping in grease until fresh grease is purged out of this port. Once completed, start the motor and run the bearing up to temperature to allow any extra grease to purge from the bearing cavity. You do not want to over-grease and cause a churning effect.

What is grease churning?

Over-greasing a bearing causes the machine to work extra hard by ‘pushing’ or ‘plowing’ the excess lubricant around the bearing, resulting in an increase of energy usage, operating temperatures, and a reduction of the lubricant quality because of oxidation. So instead of just providing a steady film of lubrication on the bearing race, the excess lubrication is constantly forced in front of the rotating bearing elements, thus causing a churning effect and not allowing the machine to operate at optimum conditions.

Once we know the grease level in the bearing, you need to determine how much, and at what frequency that grease should be pumped into the bearing. We have created a chart as a guide to assist in how much grease is acceptable. This does not replace what’s recommended by the manufacturer, but rather just gives you a general guide to start with. Always refer to the manufacturer’s guide for proper greasing methods whenever possible.

Think you need grease and don’t have time to do it? Call us today!

How do I know how much one pump of grease is from my gun?

First, get the technical specifications from the manufacturer that details how much is in one pump from your gun. Then you need to make sure that you are getting the full volume from each pump. If you are only getting partial volume with each pump of grease, the manufacturer’s specifications for a full pump will not match with what you are actually getting.

What type of grease? Is there a universal type? What happens if there is an incompatibility?

The best way to determine what type of grease to use for your bearing is to utilize this chart from Timken. This resource allows you to determine which greases are the compatible with each other. If you are unsure what type of grease is in your bearing and you have little or no way to find out, Polyurea Shear Stable grease is the one of the most universal types of grease, meaning it is compatible with most other types of greases. It is important to not run into a situation where you have incompatible greases because this could lead to de-gelling and oil separation within the bearing.

Can a thermal imaging gun be used to measure grease levels?

First, a baseline needs to be recorded in order to determine normal operating temperatures with the proper amount of grease. Then, a thermal imaging gun will let you know if you are within manufacturer’s temperature specifications. This measurement can be used as a reference point to determine if temperatures are in range in the future.

What are automatic lubricators?

Automatic lubricators are used for hard-to-access greasing ports, where the motors themselves are inaccessible, and/or if maintenance personnel are not always on site or available to perform this necessary task. See Timken and Machinery Lubrication for more information on automatic lubricators.

Other Resource: For more about grease guns see Machinery Lubrication

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