Excessive motor vibration is caused by

Excessive motor vibration is caused by

Right Answer is:

Worn bearings


Machine Vibration Causes

Almost all machine vibration is due to one or more of these causes 

  1. Repeating forces
  2. Looseness
  3. Resonance

Repeating forces

Repeating forces in machines are mostly due to the rotation of imbalanced, misaligned, worn, or improperly driven machine components.

  1. Imbalance machine components:- Imbalance machine components contain “heavy spots,” which, when rotating, exert a repeating force on the machine. Imbalance is often caused by machining errors, nonuniform material density, variations in bolt sizes, air cavities in cast parts, missing balance weights, incorrect balancing, uneven electric motor windings, and broken, deformed, corroded or dirty fan blades or dirt that has dropped from a fan blade, suddenly creating a big imbalance.
  2. Misaligned machine components:- It creates “bending moments,” which, when rotated, exert c repeating force on the machine. Misalignment is often caused by inaccurate assembly uneven floors, thermal expansion, distortions due to fastening torque, and improper mounting of couplings.
  3. Worn machine:- Worn components exert a repeating force on the machine because of the rubbing of uneven worn surfaces. The wear in roller bearings, gears, and belts is often due to improper mounting, poor lubrication, manufacturing defects, and overloading.
  4. Improperly driven machine components exert a repeating force on the machine because of intermittent power use. Examples include pumps receiving air in pulses, internal combustion engines with misfiring cylinders, and intermittent brush-commutator contact in DC motors.


  • The looseness of machine parts causes a machine to vibrate. If parts become loose, the vibration that is normally at tolerable levels may become unrestrained and excessive. Looseness can cause vibration in both rotating and non-rotating machinery. Looseness is often due to excessive bearing clearances, loose mounting bolts, mismatched parts, corrosion, and cracked structure.


  • Resonance is a state of operation wherein an excitation frequency is close to a natural frequency of the machine structure, at this frequency, the damping of the vibration is very low and the result is resonance. When resonance occurs, the resulting vibration levels can be very high and can cause damage very quickly.
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