Cummins/Onan 6.5NH - 3CR / 6000 A — Undercutting the Mica Insulation
Repair & overhaul · Commutator
For the Cummins/Onan 6.5NH - 3CR / 6000 A, from the Cummins/Onan service manual.
Applies to: Cummins/Onan NH engine
Before you start
- Be careful not to draw the undercutting tool into the slip rings.
Procedure
- Center the cutting tool over the mica.
- With a firm, steady pull draw the tool the length of the commutator.
- Repeat the cutting operation until the mica is about 1/32 inch below the commutator surface.
- Cut each section equally and remove any burrs along the bar edges.
- Blow or brush all mica dust and metallic particles from the commutator grooves and surface.
- Install new brushes after servicing slip rings and commutator.
Tools required
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- Mica undercut about 1/32 inch below surface
Source: Cummins/Onan service manual. Steps and values are as documented; always cross-check against the official manual and any later revisions for your exact serial number before servicing.