Cummins/Onan — Spark Plugs - Removal and Installation
Repair & overhaul · Ignition system
From a Cummins/Onan service manual covering: GNH-250, GNH-XI0, GNHC4, GNVH450, GV12, GV12 series, GV12-525. Check it applies to your exact model before use.
Applies to: Cummins/Onan GV12
Before you start
- Remove transformer cover with care; transformer assembly is spring loaded.
Procedure
- Remove ignition harness wire from transformer terminal.
- Remove screws securing transformer cover, retainer, spring, ground wire; lift off cover.
- Lift transformer, spring, retainer, cover from spark plug adapter tube.
- Use 13/16 inch deep-well rubber insert socket; remove spark plug and gasket.
- Check spark plug gap; should be 0.018 inch.
- Clean adapter seating area; position new gasket; tighten spark plug to 28 to 30 foot-pounds.
- Insert transformer spring and retainer; secure cover and ground wire.
- Connect ignition harness lead to transformer terminal.
Tools required
- 13/16 inch deep-well rubber insert spark-plug socket Amazon
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- spark plug gap 0.018 inch
- spark plug torque 28 to 30 foot-pounds
Full service-parts list: Cummins/Onan GV12 →
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.