Cummins/Onan — Undercutting Mica Between Commutator Bars
Repair & overhaul
From a Cummins/Onan owner's manual covering: 1.5UF-232S, 10.0UF-150S, 12.0UF-3S, 12.0UF-4S, 15.0UB-150S, 15.0UF-3S/104, 2.0UF-125S, 2.0UF-232S/32, 2.0UG-1S/135, 2.5UF-1S, 2.SUD-IS, 2.SUD-IS/ID…. Check it applies to your exact model before use.
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Before you start
- Do not scratch the surface of any bar while undercutting.
Procedure
- Remove the end bell only, tagging all disconnected leads.
- Remove each spring and brush from its guide.
- Pull the end bell off carefully.
- Fashion an undercutting tool from a hack saw blade ground to the mica thickness.
- Cut the mica down to 1/32 inch below the bar surface.
- Remove any burrs along the edges of the bars.
Tools required
- hack saw blade (undercutting tool) Amazon
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- Mica cut down to 1/32 inch below surface
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.