Cummins/Onan 1B Series / 1B Series Plant — Timing the ignition

Adjustments · ignition system

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

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Procedure

1. Revolve crankshaft clockwise until intake valve opens and closes and piston is at extreme top of cylinder.
2. Remove flywheel and check magneto breaker point gap. Adjust to .020 inch by loosening two screws holding stationary point bracket and sliding bracket up or down.
3. Slightly loosen two screws holding magneto backplate assembly to gear cover to permit shifting. Shifting clockwise retards spark; counterclockwise advances spark.
4. Use a low voltage series timing light to obtain exact timing. Connect one lead to stop wire and other lead to good ground on engine.
5. Place flywheel loosely on crankshaft and rotate clockwise. Light will go out when points separate; this is when spark occurs.
6. If light goes out before 25° timing mark on flywheel aligns with mark on gear cover, shift backplate clockwise to retard. If after, shift counterclockwise to advance.
7. Tighten backplate screws and recheck. Replace coil lead and tighten screw. Replace flywheel, lockwasher, and nut; tighten nut 35 to 40 lbs. ft.

Source: Cummins/Onan operator'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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