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The VFD Answer Man, Volume 3: Over Greasing Bearing Failure

December 20, 2015 |By: Terry M. Smith

Over greasing a motor will destroy it. Most people who service motors think they know the proper procedure, but the fact is that 50% of bearing failures at electric motor shops are from over greasing. If anyone has a customer with early bearing failures they may want to reconsider their method for lubrication.

1. Regreasable motors should have plugs on both the fill side and the relief side of the bearing.

2. Zerk fittings should be carried clean by the service tech and inserted to the input side after removal of the plug and ensuring there is not dirt anywhere in the fill side.

3. The relief plug should then be removed and a small wire brush should be used to break out the lube in the relief plug (lithium grease will get hard).

4. Grease should be pumped into the bearing until clean grease is seen leaving the discharge port.

5. With the discharge port open the motor should be turned on and run for 5-10 minutes to allow the bearing to come up to temperature. More grease should be seen leaving the relief port.

6. If the grease coming out remains clean the motor can be shut down and the relief port plug installed. The Zerk should be removed and replaced.

Pressure-Relief Vent Fittings
These fittings are intended to work as pressure-relief valves. Anytime the pressure rises above the designed limit, the unit will open, venting pressure. After pressure is relieved, the fitting will close to form a seal.

Cold grease will expand and blow out the bearing seal. This will put grease into the motor. The eventual resulting short circuit will be catastrophic. Note that the picture has an arrow pointing to the failed ball cage. You should look at the windings. They are burnt black. This is a result of a combination of the bearing seizing up and the short between rotor and stator. The resulting fireball was probably pretty spectacular. We would prefer to avoid spectacular.

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