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Cummins/Onan — Fan Drive Belt Adjustment

A Cummins/Onan service procedure — check it applies to your exact model before use.

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Before you start

  • Do not adjust to full tension with adjusting screw, this would result in overtightening
  • Self tensioning backside idler on certain engines requires no adjustment

Procedure

  1. Loosen large locking nut on fan hub shaft or capscrews securing fan hub shaft
  2. Turn adjusting screw to increase belt tension
  3. Tighten locknut or capscrews until fan hub is straight
  4. Belt tension should read as indicated on applicable gauge
  5. Tighten appropriate fasteners per engine model specifications
  6. Recheck belt tension
  7. Back out adjusting screw one-half turn to prevent breakage

Tools required

  • Adjusting screw
  • Socket wrench
  • Belt tension gauge

Specs & torque values

  • NH/NT Engines locknut: 400 to 450 ft-lbs (then back off 1/2 turn)
  • NTC-350 FFC: 75 to 85 ft-lbs
  • V-903 Engines: 75 ft-lbs or 450 ft-lbs

Source: manual:CUMMMINS_OPERATIONS_MAINTENANCE_1978.pdf. Figures and steps are as documented; always cross-check against the official manual and any later revisions for your exact serial number before servicing.