Cummins/Onan B43 / B48 — Ignition Timing Test
Testing & diagnosis · Ignition system
For the Cummins/Onan B43 / B48, from the Cummins/Onan owner's manual.
Applies to: Cummins/Onan B48, Cummins/Onan B43M engine, Cummins/Onan B48M engine
Before you start
- If timing is early (advanced) the point gap is too large. If timing is late (retarded) the point gap is too small.
Procedure
- Adjust the breaker points.
- Remove the blower housing to expose timing marks on top of the gearcase cover and flywheel.
- Rotate the flywheel clockwise until the timing mark aligns with the 21 degrees BTDC mark on the gearcase cover.
- Connect an ohmmeter or continuity test lamp across the ignition breaker points; touch one prod to the coil lead terminal (screw B).
- Touch the other test prod to a good ground on the engine.
- Turn the crankshaft counterclockwise until the points close, then slowly turn clockwise.
- The lamp should go out or continuity be lost just as the points break, which is where ignition occurs; adjust point gap accordingly.
Tools required
- Ohmmeter or continuity test lamp Amazon
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- 21 degrees BTDC
- Point gap 0.021 in (0.53 mm)
Full service-parts list: Cummins/Onan B48 →
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.