Cummins/Onan 1B Series — Timing the ignition

Adjustments · Magneto

For the Cummins/Onan 1B Series, from the Cummins/Onan owner's manual.

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Procedure

1. Ensure timing gear marks coincide.
2. Revolve crankshaft clockwise until intake valve opens and closes and piston at top.
3. Remove flywheel and check magneto breaker point gap at 0.020 inch.
4. Loosen backplate screws to shift assembly.
5. Shifting clockwise retards; counterclockwise advances spark timing.
6. Use low voltage series timing light.
7. Light should go out when 25 degree flywheel mark aligns with gear cover mark.
8. Tighten backplate screws and recheck.

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.

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