Most fractional-horsepower single-phase motors have sleeve bearings. The bearings are lubricated with oil-impregnated wicking, which lasts for the life of the motor. Most of these motors have no allowance for lubrication, but can be taken apart to apply oil directly into the oil reservoir. Holes for oiling can be drilled into the bearing cap or the end frame. These motors are usually replaced instead of repaired.
Larger motors with sleeve bearings have an oil ring and an oil reservoir.
(The volume of oil needed for large bearings can’t be supplied with a wick.) The oil ring rides directly on the shaft, with about one-third of the ring submerged in oil. As the shaft turns, the ring turns with it, carrying oil to the bearing. Oil lubricates all parts of the bearing by flowing through slots along the length of it, and back to the reservoir.
Sleeve bearings in large high-speed motors should be well oiled before they are test-run with no load. This prevents them from being destroyed (wiped) before the oil ring supplies oil.
It’s normal to have about 1/2 inch of endplay in larger sleeve bearing motors. When the motor runs, the rotor will seek its magnetic center. (The shaft shoulder shouldn’t ride against the bearing.)
The oil level should be checked once a month, and the oil changed once a year. If contaminants or high temperatures exist, the lubrication schedule should be altered accordingly.
Unlike single-phase motors, three-phase motors with worn sleeve bearing don’t show signs of the problem (by becoming noisy). To check for wear, move the shaft back and forth in the direction of the load. There should be no lateral shaft movement.