Cummins/Onan — Valve Tappet (Clearance) Adjustment
Adjustments · Valve tappets
From a Cummins/Onan service manual — check it applies to your exact model before use.
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Before you start
- Adjust valve clearance only when engine is at ambient temperature
Procedure
- Remove parts necessary to gain access to valve tappets; remove spark plugs.
- Rotate crankshaft clockwise until left intake valve opens and closes.
- Align TC mark on flywheel with TC mark on gear cover.
- Verify left intake and exhaust valves are closed and tappets unloaded.
- Check clearance with feeler gauge; intake 0.005 in, exhaust 0.013 in.
- Turn self-locking adjusting screw as needed for correct clearance.
- Turn engine one revolution and adjust right cylinder the same way.
- Replace all parts removed and torque manifold bolts.
Tools required
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- Intake 0.005 in (0.127 mm)
- Exhaust 0.013 in (0.33 mm)
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.