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Timing Belt Tooth Shear

A common timing belt failure resulting from insufficient timing belt installation tension is referred to as tooth rotation. Timing belt tooth rotation can occur as timing belt teeth climb out of their respective timing belt pulley grooves (self tensioning) and drive loads are no longer applied at their roots. Drive loads applied further down the timing belt tooth flanks cause the timing belt teeth to bend (like a diving board) and “rotate.” Timing belt tooth rotation can result in timing belt material tearing at the base of the timing belt teeth along the tensile member. As the tearing continues, timing belt teeth often begin to separate from the timing belt in strips. Failures due to excessive tooth rotation may resemble failures caused by insufficient rubber adhesion to the tensile cords. Unlike tooth rotation failures, failures from insufficient rubber adhesion leave the exposed tensile members clean where the timing belt teeth were once located.

Probable Cause:

  • Excessive shock load

Corrective Action:

  • Check horsepower rating
  • Redesign drive

Probable Cause:

  • Less than six (6) timing belt teeth in mesh

Corrective Action:

  • Check horsepower rating
  • Redesign drive

Probable Cause:

  • Extreme timing belt pulley run-out

Corrective Action:

  • Replace timing belt pulley

Probable Cause:

  • Worn timing belt pulley

Corrective Action:

  • Replace timing belt pulley

Probable Cause:

  • Sub-minimal timing belt pulley diameter

Corrective Action:

  • Use correct timing belt pulley diameter

Probable Cause:

  • Backside idler

Corrective Action:

  • Use inside idler

Probable Cause:

  • Incorrect timing belt tooth profile for the timing belt pulley

Corrective Action:

  • Check timing belt / timing belt pulley compatibility

Probable Cause:

  • Misaligned drive

Corrective Action:

  • Check parallel and angular alignment  of the pulleys

Probable Cause:

  • Timing belt tension too low

Corrective Action:

  • Adjust tension to recommended value

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