Carefully inspect new bearings upon arrival for any obvious damage that may have occurred during shipping, storage or manufacture. Inspect bearings to determine if all parts are present. Bearings have been known to ship from the factory missing roller elements and other parts. Also, check for factory lubricant. Lack of lubricant from factory can cause rust.

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From the book "The Practical Handbook of Machinery Lubrication":

In general, the important parameters influencing bearing wear are contaminant particle size, concentration, hardness and lubricant film thickness. Increases in all of these parameters except film thickness will increase bearing wear.

Increasing lubricant viscosity will reduce bearing wear for a given contamination level.

Bearings operating in a contaminated lubricant exhibit a higher initial rate of wear than those not running in a contaminated lubricant. But with no further contaminant ingress, this wear rate quickly diminishes as the contamination particles are reduced in size as they pass through the bearing contact area during normal operation.

More information about "The Practical Handbook of Machinery Lubrication"

"We recently switched electric motor rebuild shops. Since switching, a number of bearings have failed, typically just a few months after putting the motor back into service. For the most part, these failures have been attributable to inadequate lubrication. On closer inspection, the grease appeared to have thinned-out to almost a liquid consistency. We suspected that the rebuild shop was using a grease inferior to our electric motor grease, but they assure us they're using a premium-quality synthetic grease. What is your opinion?"

Without more details, it's hard to attribute an exact root cause. However with greases, one of the most commonly encountered problems is incompatibility between different types of grease made from different thickeners.

For electric motors, the most commonly used greases are made either from a lithium complex soap thickener or polyurea material. While both polyurea and Li complex-based greases can be used in this application, the two are usually considered to be incompatible with each other and should not be mixed unless proper compatibility testing has been performed.

To avoid these types of problems, it is advisable to request that the rebuild shop use the same grease that you plan to use to regrease the bearings, or at the very least, indicate the exact type and brand of grease being used, so that you can determine if there are any serious compatibility issues between the two greases.

It is often advisable to provide a tube of grease to the rebuild shop whenever a motor is sent to rebuild to avoid these issues.

Mark Barnes, Noria Corporation

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