All motors, including alternating current (AC) fan motors, have bearings fitted between the armature and the motor housing. The bearings allow the armature to rotate freely without causing friction. There are usually two bearings on the front of the motor and two bearings on the rear. Inevitably, they do wear, meaning that the armature is loose, so you need to replace them. You can usually recognize the presence of worn bearings because the motor makes a rattling sound.
Confirm that the power supply is off. Never attempt to replace bearings on an AC motor if the power supply is connected.
Locate the screws on the AC fan motor housing; there are usually four to six, equally spaced. The screws hold the two halves of the casing together. Use a screwdriver to remove the screws. Gently slide a flathead screwdriver between the two halves of the motor housing, then gently twist the screwdriver so the halves start to separate. You may need to do this in several places.
Lift off the top half of the motor housing and turn it over so the inside is facing you, then place it next to the other half. Lift off the armature from the bottom and place it to one side.
Remove the bearings. Each half has two bearings--one at the front and one at the back. Use a screwdriver and gently pry the bearings out from the motor housing seals. Do this carefully and don't scratch the seals. Lift the bearings from the housing with your fingers, once the bearings are loose.
Use a clean cloth and rub the seals to remove any dirt. Very lightly grease the seals with a little motor oil.
Put the replacement bearings into the seals. Push them in place with your fingers. Lightly grease the bearings with oil.
Replace the armature and set it on the bearings on the bottom half of the motor housing. Replace the top half of the motor housing onto the bottom half. Push the two half together, gently ensuring that the screw holes line up.
Replace the screws into the holes. Tighten the screws firmly, using a screwdriver.
Using your hand, rotate the fan backward and forward. This helps bed-in the bearings. The fan turns smoothly, but it will appear rather stiff at first. Turn on the AC fan motor and let it run for a few minutes, then turn it off for a while. You may get a smell of oil initially, but this stops after a while. Use the motor as normal after you complete the bedding.