Cummins/Onan GS-107-AC — Timing the magneto to the engine
Adjustments
For the Cummins/Onan GS-107-AC, from the Cummins/Onan service manual.
Applies to: Hol-Gar GS-107-AC, Cummins/Onan J120-S/967F engine
Before you start
- Do not disassemble magneto unless witness marks are made for correct reassembly
Procedure
- Remove No. 1 spark plug; turn flywheel until pressure builds.
- Continue turning until the 25 degree mark aligns with timing pointer.
- Turn magneto until white mark on rotor is visible in window.
- Mount magneto on studs with gasket; mesh gears.
- Run engine and use timing light for exact timing.
- Tighten magneto mounting securely.
Tools required
- Timing light Amazon
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- Ignition timing 25 degrees BTC
Full service-parts list: Hol-Gar GS-107-AC →
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.