Valve Adjustment

Adjust valve lash on the 5.9L Cummins diesel engine to ensure proper valve train clearance and optimal engine performance.

Warnings

Tools required

Parts

• Valve cover gasket × 1 — Use OEM specification
• Valve cover bolt grommets (if equipped) × 1 — Use OEM specification

Preparation

1. Ensure engine is completely cold (preferably overnight)
2. Disconnect both negative battery cables
3. Remove engine cover if equipped
4. Clean area around valve cover to prevent debris from entering engine

Procedure

1. 1

   Remove valve cover
   Disconnect electrical connectors from valve cover or nearby components. Remove valve cover bolts in reverse of tightening sequence (work from outside toward center). Carefully lift valve cover off, noting gasket condition. Clean old gasket material from both valve cover and cylinder head mating surfaces using plastic scraper.
2. 2

   Rotate engine to TDC cylinder 1
   Using breaker bar and socket on crankshaft bolt, rotate engine clockwise (viewed from front) until timing mark on vibration damper aligns with TDC mark on timing indicator. Verify cylinder 1 is on compression stroke by confirming both intake and exhaust rockers on cylinder 1 have clearance (loose). If not, rotate engine one additional full revolution.
3. 3

   Adjust valves for cylinders 1, 2, and 3
   With engine at TDC on cylinder 1, adjust the following valves: Cylinder 1 intake and exhaust, Cylinder 2 intake, Cylinder 3 exhaust. For each valve, loosen adjusting screw locknut, insert feeler gauge between rocker arm and valve stem crosshead using the correct spec: intake 0.010 inch, exhaust 0.020 inch (verify against your model year service manual). Adjust screw until slight drag is felt on feeler gauge. Hold adjusting screw with wrench and tighten locknut to specification. Recheck clearance after tightening.
   ⚠Feeler gauge should slide with slight drag. Too tight or too loose indicates incorrect adjustment.
   Torque spec

   Valve Lash Adjusting Screw Lock Nut20 Nm (15 lb-ft)
4. 4

   Rotate engine 360 degrees
   Using breaker bar on crankshaft bolt, rotate engine clockwise exactly one full revolution (360 degrees) until timing mark returns to TDC. This positions cylinder 6 on compression stroke.
5. 5

   Adjust valves for cylinders 4, 5, and 6
   With engine rotated 360 degrees from initial position, adjust the following valves: Cylinder 2 exhaust, Cylinder 3 intake, Cylinder 4 intake and exhaust, Cylinder 5 intake and exhaust, Cylinder 6 intake and exhaust. Use same procedure as step 3: loosen locknut, adjust screw for the correct clearance (intake 0.010 inch, exhaust 0.020 inch — verify against your model year service manual) with slight drag on feeler gauge, hold screw and tighten locknut to specification, then recheck clearance.
   ⚠Double-check that all 12 valves have been adjusted before proceeding to reassembly.
   Torque spec

   Valve Lash Adjusting Screw Lock Nut20 Nm (15 lb-ft)
6. 6

   Verify all adjustments
   Go back through all valves and verify clearance is correct (intake 0.010 inch, exhaust 0.020 inch — verify count and specs against your model year: 12-valve engines have 12 valves, 24-valve engines have 24). Check that all locknuts are tight. Rotate engine by hand through two complete revolutions and recheck several random valves to ensure adjustments held.
7. 7

   Install new valve cover gasket
   Ensure both gasket surfaces are completely clean and dry. Position new valve cover gasket onto cylinder head, ensuring proper alignment with all bolt holes. If gasket has locating tabs or grommets, ensure they are properly seated.
   ℹ️Do not apply sealant unless specified by gasket manufacturer. Most gaskets are dry-install type.
8. 8

   Install valve cover
   Carefully position valve cover onto cylinder head, ensuring gasket stays in place. Install all valve cover bolts with grommets if equipped. Tighten bolts in sequence from center outward to specification. Use multiple passes, gradually increasing torque to final value.
   Torque spec

   Valve Cover Bolts10 Nm (7 lb-ft)
9. 9

   Reconnect electrical components
   Reconnect any electrical connectors that were removed from valve cover area. Ensure connections are fully seated and secured.

Reassembly

1. Reconnect both negative battery cables
2. Reinstall engine cover if equipped
3. Clear any diagnostic trouble codes that may have set from battery disconnect

Verification

• Start engine and verify no oil leaks from valve cover
• Listen for proper valve train operation - should be quieter than before if adjustment was needed
• Check for unusual valve train noise - clicking or tapping may indicate incorrect adjustment
• Allow engine to reach operating temperature and recheck for leaks
• Test drive vehicle to verify normal performance

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