Cummins/Onan — Valve Tappet Adjustment
Adjustments · Valve system
From a Cummins/Onan service manual — check it applies to your exact model before use.
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Procedure
- Remove all parts that block access to the valve tappets.
- Remove the spark plugs to make turning the engine easier.
- Rotate the crankshaft clockwise until the left intake valve opens and closes, then align the TC marks.
- Verify the left intake and exhaust valves are closed and lifters are unloaded.
- Check each valve with a feeler gauge between valve stem and tappet.
- Turn the self-locking adjusting screw to correct clearance.
- Turn the engine one revolution, align TC marks, and adjust the right cylinder.
- Replace all parts removed and tighten all screws securely.
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 (0.330 mm)
- Engine at ambient temperature
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.