Cummins/Onan — JC Ignition Timing, Engine Stopped
Adjustments · Distributor
From a Cummins/Onan service manual covering: 10.0JC, 12.5JC, 15.0JC, 4.0JB, 5.0JB, 6.0JB, 6.1JB, 7.5JB, 7.6JB. Check it applies to your exact model before use.
Applies to: Cummins/Onan 10.0JC, Cummins/Onan 12.5JC, Cummins/Onan 15.0JC, Cummins/Onan 5.0JB, Cummins/Onan 6.0JB, Cummins/Onan JB engine, Cummins/Onan JC engine
Before you start
- Advance 10 degrees more for gas fuel.
Procedure
- Disconnect low voltage distributor lead and connect test lamp and battery so lamp lights with points closed.
- Remove number 1 spark plug and rotate flywheel clockwise until air is forced from the plug hole.
- Continue rotating slowly until lamp goes out; check TC mark alignment with timing pointer.
- To adjust, align TC mark with pointer, loosen distributor body and rotate clockwise if early, counterclockwise if late, until light goes out; tighten.
Tools required
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- Breaker point gap .018 to .022 in.
- Timing 25 BTC of each compression stroke
Full service-parts list: Cummins/Onan 10.0JC →, Cummins/Onan 12.5JC →, Cummins/Onan 15.0JC →, Cummins/Onan 5.0JB →, Cummins/Onan 6.0JB →
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.