Cummins/Onan 4MCCK / 605MCCK — Ignition Timing
Adjustments · Ignition system
For the Cummins/Onan 4MCCK / 605MCCK, from the Cummins/Onan service manual.
Applies to: Cummins/Onan 605MCCK, Cummins/Onan MCCK, Cummins/Onan MCCK engine
Before you start
- The 4-volt coils can be tested on a 6-volt tester; a 12-volt tester will destroy the coil in a few seconds.
Procedure
- Remove the cover from the breaker box.
- Attain an approximate setting by loosening the mounting screws and shifting the breaker box to align the witness marks.
- Crank the engine slowly by hand in the direction of crankshaft rotation until the flywheel witness mark and the TC mark are in line.
- Adjust the ignition breaker point gap width to 0.020 inches at full separation.
- Turn the flywheel until the timing mark is about two inches past the 25 degree mark on the gear cover.
- Turn the flywheel slowly to the right and note if the points just separate when the mark aligns with the 25 degree mark.
- Shift the breaker box slightly right to retard or left to advance the timing, then tighten the mounting screws.
Tools required
- timing light or continuity test lamp Amazon
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- Spark advance is 25 degrees before top center
- Breaker point gap 0.020 in at full separation
Full service-parts list: Cummins/Onan 605MCCK →, Cummins/Onan MCCK →
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.