Cummins/Onan 6.3 NHEL / 6.5 NH — Tappet Adjustment (Valve Clearance)
Adjustments · Valve tappets
For the Cummins/Onan 6.3 NHEL / 6.5 NH, from the Cummins/Onan service manual.
Applies to: Cummins/Onan NHEL
Before you start
- Adjust the valve clearance only when engine is at ambient temperature.
Procedure
- Remove all parts necessary to gain access to valve tappets.
- Remove spark plugs to make turning the engine easier.
- Rotate crankshaft clockwise until left intake valve opens and closes; continue until TC mark on flywheel lines up with TC mark on gear cover (left piston #1 at top of compression stroke).
- Verify left intake and exhaust valves are closed and there is no pressure on valve lifters.
- For each valve, the gauge should just pass between the valve stem and valve tappet.
- Turn the self-locking adjusting screw as needed to obtain the right clearance.
- To adjust right cylinder valves, turn engine one complete revolution and realign the marks, then repeat.
- Replace all parts removed; tighten all screws securely 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 valve lash 0.005 in. (0.127 mm)
- Exhaust valve lash 0.013 in. (0.330 mm)
Full service-parts list: Cummins/Onan NHEL →
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.