Cummins/Onan — Magneto Service and Timing
Repair & overhaul
From a Cummins/Onan service manual — check it applies to your exact model before use.
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Before you start
- Do not damage flywheel or fins.
Procedure
- Remove air housings and blower wheel on Vacu-Flo units or blower housing on pressure cooled units.
- Loosen flywheel bolt a few turns. While pulling outward on flywheel, strike flywheel bolt sharp blow to loosen.
- Remove flywheel bolt and pull flywheel off.
- Examine breaker contact points. Dress slightly burned points with stone; replace badly burned points.
- Adjust gap at full separation per Table of Clearances. Replace defective condenser.
- Check magneto pole shoe air gap .010-.015 inch.
- To time, install flywheel loosely with key.
- Turn flywheel to position where mark aligns with proper degree mark on gear cover.
- Points should just separate. If not, loosen magneto backplate screws.
- Shift backplate counterclockwise if points separate too late, clockwise if too soon.
- Retighten and recheck.
Tools required
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- point gap .022 inch
- pole shoe air gap .010-.015 inch
- timing 25° BTC 3000/3600 rpm, 19° BTC 1800 rpm
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.