Mismatched, Worn

or Stretched Belts

multiples of belt frequency (B). 2B usually strongest

radial in line with belts

may be unsteady beating if the 2B is near speed of either shaft

B is always less than 1X

Eccentric and/or

Unbalanced Sheaves

1X shaft

radial

steady

Easily confused with imbalance

Drive Belt or Sheave

Face Misalignment

1X driver

axial

steady

Confirm with strobe light

Drive Belt

Resonance

varies

radial

may be unsteady

Belt resonance with no relationship to rotational speed.

Improper Belt

Tension

Can produce belt resonance

(see above) Can increase bearing wear