Cummins/Onan — Spark Plug Service
Maintenance
From a Cummins/Onan service manual — check it applies to your exact model before use.
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Before you start
- Spark plug and muffler will be very hot if engine has been running; be careful not to touch.
- Improperly tightened spark plug could damage engine.
- Never use spark plugs which have an improper heat range. Use only recommended spark plugs or equivalent.
Procedure
- Turn off generator.
- Remove spark plug cap.
- Clean dirt from around spark plug base.
- Use wrench supplied in tool kit to remove spark plug.
- Inspect spark plug; discard if insulator cracked or chipped. Clean with wire brush if reused.
- Measure plug gap with feeler gauge and correct by bending side electrode.
- Check spark plug washer and thread spark plug in by hand.
- Tighten with spark plug wrench to compress washer.
Tools required
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- Spark plug gap: 0.70-0.80 mm (0.028-0.031 in)
- Spark plug torque: 20-25 FridayParts $42.95 N·m
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.