Cummins/Onan — Undercutting the Mica Insulation
Repair & overhaul · Commutator
From a Cummins/Onan service manual — check it applies to your exact model before use.
Applies to: Cummins/Onan MCCK
Before you start
- Use extreme care not to draw the undercutting tool into the slip rings.
Procedure
- Center the cutting tool over the mica.
- Draw the tool the length of the commutator with a firm, steady pull.
- Repeat the cutting operation until the mica is removed to approximately 1/32 inch (0.8 mm) below the commutator surface.
- Proceed to the next section until all are equally undercut.
- Remove any burrs with #240 sandpaper against the commutator with a flat piece of wood.
Tools required
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- Mica undercut to approximately 1/32 inch (0.8 mm) below commutator surface
Full service-parts list: Cummins/Onan MCCK →
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.