The Foundation of Motor Vibration Identification, Part 2

April 22, 2014
One common cause of motor vibration is a warped mounting foot.

In our previous issue, we said that failures in how the motor is mounted are often apparent. So, what should you look for?

Assuming it’s not a c-face motor, look at the motor feet. One common cause of motor vibration is a warped mounting foot. That’s caused by improper tightening.

Always use new bolts, lockwashers, and nuts when fastening a motor in place. Why new? Because once you tighten a threaded steel fastener to its recommended torque, you permanently deform it. The loss of clamping power is typically 50%, so don’t re-use.

Make sure you use the size, hardness, and type (e.g., lubricated) bolt recommended by the motor manufacturer and assemble to the recommended torque.

It’s great if you verified the motor’s properly fastened to its base. But is the base stout enough? If the base is deflecting in response to torque from the motor, you’ll get vibration. You can use dial indicators to measure this deflection. Also look for loose fasteners and any physical deformities (e.g., cracks or broken welds). Inspect the pedestal, the same way.

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