How to Grease Electric Motor Bearings

Maintaining a proper greasing schedule and technique are crucial to maximize the life of the bearings in an electric motor. But do all motors need to be greased? No. Many motors have shielded or sealed bearings that cannot take grease. (Shielded bearings can pull in grease when running, but are difficult to re-grease properly). Attempting to grease these will cause more harm than good. Grease will build up inside the motor which will reduce air flow, leading to eventual motor winding failure.

Determine if motor has re-greasable bearings

The first step is to determine if the motor has re-greasable bearings. If the motor has not been repaired, then this is as simple as looking for the grease zerk fitting nipple on each end of the motor. See photo below. Then follow the remaining steps below. If the motor has been repaired, then, short of prior-hand knowledge , there no good way to know if the bearings are re-greasable without tearing down the motor to have a look. Many motor shops will label the motor with something like "Do Not Grease" if the bearings were replaced with non-greasable types.

Clean the area around the grease zerk fitting on top and grease purge valve on bottom, then remove the grease purge or plug on bottom of the end bell.
Attach grease gun to top of zerk fitting, or screw fitting into grease inlet port. Slowly pump grease into the end bell. After a few strokes, 3-5, you should see old grease start to come out of the bottom grease drain. Continue until the new grease is visible, then stop. If no grease flows after 10 or more strokes, stop the procedure.
Re-install any removed grease plugs.