25.10.3 Grease-Type Bearings Most large horsepower motors have ball bearings lubricated with grease rather than oil. A grease fitting (called a zerk fitting) is installed on top of each bearing, and a removable plug is located at the bottom of each bearing. See Figure 25‑60. An ordinary grease gun is used to pump high- grade, medium grease to the bearings every three months. The bottom plug must be removed before pumping grease into the bearing. If it is not removed, pressure can rupture the diaphragm that holds grease in the bearing. A ruptured diaphragm will permit grease to enter the rotor area, resulting in a dry bearing. Removing the bottom plug prevents any pres- sure on the diaphragm because new grease forces old grease (if any) out the bottom port. Continue pumping until new grease appears at the bottom port. Usually, only two or three pumps on the grease gun are required. If the bearing requires more pumps on the gun, the diaphragm has probably been ruptured, and grease is entering the motor. A ruptured diaphragm is revealed by a grease stain or puddle immediately under the motor. The bottom plug should always be rein- stalled after greasing the bearing. A motor with a ruptured diaphragm must be greased frequently to delay or prevent bearing failure. A primary cause of motor failure is dry bearings, which cause the rotor to drag, lock up, or wear out. Dry bearings also cause excess amperage draw, while worn bearings cause a noisy motor. 25.10.1 Permanently Oiled Bushings Many bearings for fractional horsepower motors are permanently lubricated. The bearing is actually a bushing (sleeve around a shaft) made of porous bronze that is saturated with oil at the factory. The bushing is considered permanently lubricated and is used in fan motors and other low-horsepower applications. No additional lubri- cating of the bearing is required for the life of the motor. 25.10.2 Oil-Type Bearings Oil-type bearings should receive three to six drops of oil in each oil port every six months. Avoid over-oiling, since excess oil may accumulate in the stator and collect dirt. The oil ports are located at each end bell of the motor for direct access to the bearing. See Figure 25‑59. The oil ports are normally capped with rubber or plastic plugs to keep dirt out of the bearing. The plugs are easily removed for adding oil and should always be replaced. Regular 10W30, nondetergent automotive oil is used to oil motor bearings. Oil ports Oil ports Bearing Shaft Motor shaft Goodheart-Willcox Publisher Figure 25‑59. Oil ports are located atop the bearings at each end of the motor. Periodic lubrication is needed to prevent motor damage. Grease (zerk) fitting Diaphragms Bottom plug Goodheart-Willcox Publisher Figure 25‑60. Grease fittings are used to force lubricant under pressure into a bearing. The bottom plug must be removed when adding grease to prevent rupturing the diaphragm and allowing grease to leak out of the bearing. 516 Heating and Cooling Essentials Copyright Goodheart-Willcox Co., Inc.