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Home›Repair guides›Commutator Brush Fitting and Seating

Cummins/Onan — Commutator Brush Fitting and Seating

For these Cummins/Onan models: GS-107-AC, J120-8/967F, J120-S/967F.

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Before you start

  • New brushes that have not been seated may spark
  • Never reuse flint paper from one application to another unless characteristics are similar

Procedure

  1. Slip a piece of grade OO flint paper between contact surface with flint surface facing the brush
  2. Ensure the paper is the same width as the contact surface
  3. Move the paper in one direction only
  4. Lift and return until the proper brush surface is obtained
  5. Repeat process until all brushes have been seated
  6. If sparking occurs, operate the generator set at a light load to wear brushes

Tools required

  • Grade OO flint paper

Specs & torque values

  • Total effective brush length: 11/16 inch
  • Minimum limit: 3/8 inch

Source: manual:HOL-GAR GS-107-AC.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.