When it comes to motor failures, bearing related incidences are the cause of nearly half of the failures. These types of problems are generally due to the bearing itself wearing down over time, leading to a rough rotation and extra friction which will pull the excess load, or the housing that the bearings sit in has begun to wear down and allows play for the bearing.
Continuous use of a motor drawing excessive load will lead to the winding potentially burning up or the bearing itself may seize up and essentially lock up the rotor, preventing it from being used and requiring repair or replacement. Encoder failure can also occur, stemming from extra vibration being allowed from an out-of-roundness in the housing.
There are a couple of tests that can be done to verify the integrity of a bearing housing. The first is to physically use a bearing. This requires the motor to be disassembled and often will require a new bearing to be installed if the old one is removed. Due to this, we generally do not recommend this check to be done on-site unless the user is certain they can piece it back together properly. The other option is using a bore gauge to check the tolerance of the housing to make sure it is within spec, generally under 5 microns of tolerance.
These issues usually are some of the first signs that the motor is starting to be damaged so if an audible sound difference begins to occur while running, it may be a good time to pull that motor out and inspect it to make sure it will not lead to a larger catastrophe.
Here at Precision Zone, we closely inspect the bearings and housings on all motor work performed and if needed, offer a sleeve installed within a freshly bored housing to allow a clean, snug fit and proper seating of the bearing.