Maintenance
At the first sign of oil discoloration or contamination, replace with new oil. Rapid discoloration is caused by bearing wear, often from vibration or thrust. Change oil as required to keep clean.
When assembling the bearing, it is possible to foul the rings so that they will not turn freely. Check ring operation by rotating shaft by hand after assembly
Oil Seals
580 frame motors use fixed, labyrinth oil seals to close off the bearing cavity. The 500, 708, 788, and 880 frame motors utilize floating type oil seals to close off the bearing cavity. The primary purposes of the oil seal are:
1.To prevent the entrance of dirt in to the bearing cavity.
2.To retain the oil in the bearing cavity.
3.To provide pressure regulation in the bearing cavity.
To achieve these purposes it is necessary that a specific diametrical clearance of oil seal to shaft be held. The cooling fans of the motor tend to create a suction or a pressure in the bearing cavity, which, if large enough, will push or draw oil out along the shaft. The close fitting oil seal gives a pressure drop across it and minimizes the differential pressure.
| Standard oil seal clearances | |
Frame |
| Diametrical Clearance |
500 |
| 0.008 to 0.015 inches |
580 |
| 0.014 to 0.020 inches |
708 |
| 0.003 to 0.008 inches |
788 |
| 0.003 to 0.008 inches |
880 |
| 0.003 to 0.008 inches |
Besides using close clearances to correct differential pressures, some oil seals are vented to the atmosphere. It is important that the piping and venting for these oil seals be kept clean.
The clearance between the journal and the bearing will permit the journal center to be slightly below the bearing center. With the motor operating, the presence of the oil film between the journal and the bearing will cause the shaft to rise slightly.
NOTE
When a sleeve bearing becomes worn and requires replacement, the labyrinth oil seal should also be replaced.
Bearing Clearance Too Large
Too large a bearing clearance or clogged oil return holes in the bearing will permit excessive oil to seep out the ends of the bearing. This seepage, combined with the rotation of the shaft, will create an oil mist inside the bearing cavity which will tend to leak through the oil seals. Excessive pressure in a force feed lubrication system can also cause an oil mist to build up.
Cavity Pressures
Motors are sensitive to the amount of pressure or vacuum existing in the bearing cavity. The table below shows the maximum allowable oil cavity pressure or vacuum in terms of plus or minus inches of water:
Frame | Drive End | ||
End | |||
|
| ||
500 | ±0.12 | +2.35, | |
580 | ±0.12 | ±0.12 | |
708 | ±0.12 | ±0.50 | |
788 | ±0.12 | ±0.50 | |
880 | ±0.12 | ±0.50 |
For the correction of a high or low reading it is important that:
1.The parts and joints around the bearing cavity and oil seals are sealed.
2.Condensation drains, piping, sight gauges and breathers are functioning properly.
3.Auxiliary equipment extending into the motor must be sealed to prevent a transfer of air from inside to outside the motor.
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