Cummins/Onan — Undercutting High Mica on Commutator
Repair & overhaul · Generator commutator
From a Cummins/Onan owner's manual — check it applies to your exact model before use.
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Before you start
- High mica causes noisy brushes, excessive sparking and pitting.
Procedure
- Lift each brush high in its guide so its spring presses against its side.
- Remove the end bell and tag leads for correct replacement.
- Under cut the mica with a tool made from a hacksaw blade.
- Under cut to a depth about equal to the distance between bars (about 1/32 in.).
- Remove burrs and free spaces between bars of metallic particles.
Tools required
- Tool fashioned from a hacksaw blade Amazon
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- Mica undercut depth approximately 1/32 in.
Source: Cummins/Onan owner's 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.