What makes things shake?

Misalignment-couplings/bearings and bent shafts; why do motor bearings fail? Which one fails first?

  • Bad bearings
  • Eccentric journals-think of it as being off-center
  • Bad gears or shafts, bent or chipped teeth, normal wear and more
  • Mechanical looseness
  • Bad drive belts; when replacing one gear on chain drive, always replace both (same for sheave)

The mark on the belt; with unit properly locked out, place a chalk mark across multiple V belts, and rotate the unit by hand; observe what happens to the marks as the belts rotate at different rpm's


  • Rotor not round
  • Eccentric armature journals
  • Rotor and stator misalignment - unequal air gap
  • Elliptical stator bore - egg - shaped barrel
  • Open or shorted windings
Aerodynamic or Hydrolic Forces
  • Blade pass - in water or air
  • Why fan housings vibrate opposite the rotating blades
  • Reciprocating forces/pistons/engines
  • Back and forth, stop and go the other way
  • Everything runs smoothly until the second dryer is started
  • A machine's "natural" beat
  • A great way to bring down the Golden Gate Bridge
  • By the way...is air a liquid, solid, or gas?


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