An electric motor generally runs maintenance-free for many years. It has only one moving part, the armature, which has one or more wire windings wound around the central section. The end spindles on the armature are seated between bearings, which enable the motor to rotate smoothly and quietly. However, electric motor bearings do wear, or get exceptionally dry over time. Typical indications of worn bearings include the motor vibrating, whereas a loud squealing noise coming from the front or back of the motor is usually indicative that the bearings require oiling.
Look on the front or back of the electric motor, where the armature spindle extends from the motor. This is the area the squealing noise is coming from.
Check to find a small oil container. It is very close to the armature on the casing of the motor and has a small cap on top. It often has a small symbol, like a teardrop, indicating it's the oil container.
Remove the oil container cap. If it's rubber, then pry it off using your fingers; if it's a metal cap, then use a screwdriver to unscrew the cap.
Check if there is also a drain plug; some motors have a plug that allows you to drain old oil, others don't. The drain plug is on the underside of the motor armature. If there is a drain plug, then remove it using a screwdriver or wrench. Make sure you have a small container underneath ready to catch any oil.
Flush the system through using SAE10 or 20 grade oil until the oil flowing from the drain hole is clean. Replace the drain plug and tighten using the screwdriver or wrench once the oil has drained.
Pour SAE 10 or 20 grade oil carefully into the oil container. Let it fill to near the top. Leave the oil to settle and then top up again. Replace the cap.
Rotate the armature manually using your hands. Do this several times. This lets the oil travel to the areas that need lubricating without putting stress on the bearings and armature.
Turn on the electric motor. You may find it makes an initial squealing noise, but this stops very quickly as the bearings and armature lubricate.