Cummins/Onan — Spark Plug Maintenance and Replacement
Maintenance
From a Cummins/Onan operator's manual covering: 2.0 EGHAM, 2.5 EGHAA, 3.5 EGHEM, 4.0 EGHAB, 4.0 EGHEB, 5.0 EGHAB, 5.0 EGHEB, 5.0 EGHEM, 6.0 EGHEB. Check it applies to your exact model before use.
Applies to: Cummins/Onan 2.5 EGHAA, Cummins/Onan 4.0 EGHAB, Cummins/Onan 5.0 EGHAB, Cummins/Onan 5.0 EGHEB, Cummins/Onan 6.0 EGHEB, Cummins/Onan Elite E140H engine, Cummins/Onan GH170 engine
Before you start
- Shut the fuel valve and handle the fuel tank carefully to prevent fuel leakage when raising the fuel tank.
Procedure
- Remove the spark plug and clean carbon and other deposits off with a wire brush.
- Inspect and measure the plug gap. Replace the plug if it is discolored or badly fouled.
- Thread the spark plug in by hand until it seats to prevent cross-threading.
- If reusing the spark plug, turn it with a wrench an additional 1/4 turn.
- If the spark plug is new, turn it an additional 3/8 to 1/2 turn; or torque to 20 lbs-ft (26 N-m).
- If needed, the fuel tank can be raised for easier service access after reducing fuel level and closing the fuel shutoff valve.
Tools required
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- Torque: 20 lbs-ft (26 N-m)
- Reused plug: additional 1/4 turn
- New plug: additional 3/8 to 1/2 turn
Source: Cummins/Onan operator'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.