Valve Adjustment

This procedure adjusts the valve lash on the 5.9L Cummins I6 diesel engine to maintain proper valve train operation and prevent premature wear.

Warnings

Tools required

Parts

• Valve cover gasket × 1 — Cummins 3943982 or equivalent
• Valve cover gasket bolt grommets/seals × 1 — Use OEM specification
• Degreaser/brake cleaner × 1 — Standard automotive

Preparation

1. Ensure engine is completely cold (ideally sit overnight)
2. Park vehicle on level surface and engage parking brake
3. Disconnect both negative battery cables to prevent accidental starting
4. Remove engine cover if equipped
5. Clean area around valve cover to prevent debris from entering engine

Procedure

1. 1

   Remove valve cover
   Disconnect any wiring harnesses or breather hoses attached to the valve cover. Remove the valve cover bolts in a crisscross pattern. Carefully lift the valve cover off the cylinder head. If stuck, gently tap with a rubber mallet - do not pry between mating surfaces.
2. 2

   Clean valve cover mating surfaces
   Thoroughly clean the valve cover and cylinder head mating surfaces using a plastic scraper. Remove all old gasket material without gouging the aluminum surfaces. Wipe clean with a rag and brake cleaner. Inspect for any cracks or warping.
3. 3

   Rotate engine to TDC for cylinder 1
   Using a breaker bar on the crankshaft pulley bolt (front of engine), rotate the engine clockwise until the timing mark on the harmonic balancer aligns with the TDC mark on the timing cover. Verify cylinder 1 is on compression stroke by confirming both rocker arms on cylinder 1 are loose (valves closed) with the TDC mark aligned; cross-check against the Cummins service manual valve-set diagram before adjusting.
4. 4

   Adjust valves for cylinders 1, 2, and 3
   With engine at TDC for cylinder 1, adjust the following valves per the Cummins ISB firing order (1-5-3-6-2-4): with cylinder 1 at TDC compression, adjust intake and exhaust valves as specified in the service manual valve-set chart for the first crank position. For each valve, loosen the rocker arm adjusting screw locknut (verify wrench size per Cummins service manual) while holding the adjusting screw. Insert the appropriate feeler gauge between the rocker arm and crosshead. Intake valves use 0.010" clearance, exhaust valves use 0.020" clearance. Identify intake versus exhaust valves by tracing the intake and exhaust manifold runners to each valve rather than assuming a fixed side. Adjust the screw until there is light drag on the feeler gauge. Hold the adjuster and torque the locknut to the Cummins service manual specification (approximately 18 ft-lbs / 24 Nm), then recheck clearance. Recheck clearance after tightening.
   ℹ️Intake valves use 0.010" clearance, exhaust valves use 0.020" clearance. Intake valves are on the driver side, exhaust on passenger side.
5. 5

   Rotate engine 360 degrees
   Rotate the crankshaft clockwise exactly one complete revolution (360 degrees) until the timing mark returns to TDC. This positions cylinder 6 at TDC compression stroke.
6. 6

   Adjust valves for cylinders 4, 5, and 6
   With engine at TDC for cylinder 6, adjust the remaining intake and exhaust valves specified in the Cummins service manual valve-set chart for the second crank position. Follow the same procedure as step 4: loosen locknut, insert appropriate feeler gauge (intake: 0.010", exhaust: 0.020"), adjust until light drag is felt, torque locknut to 18 ft-lbs, and recheck clearance.
7. 7

   Verify all valve adjustments
   Double-check each valve adjustment by rotating the engine through two complete revolutions and rechecking all 12 valve clearances with feeler gauges. Adjust any that are not within specification. All intake valves should have 0.010" clearance and all exhaust valves should have 0.020" clearance with light drag on the feeler gauge.
8. 8

   Install new valve cover gasket
   Position the new valve cover gasket on the cylinder head, ensuring it seats properly in the gasket groove. Replace any damaged bolt grommets or seals. Ensure the gasket is aligned with all bolt holes and breather/wiring passages.
9. 9

   Install valve cover
   Carefully position the valve cover onto the cylinder head, aligning all bolt holes. Install all valve cover bolts with grommets. Tighten bolts in a crisscross pattern starting from the center and working outward to the Cummins specification (approximately 18 in-lbs / 2 ft-lbs); do not overtighten. Do not overtighten as this can distort the cover and cause leaks.
10. 10

    Reconnect components and verify
    Reconnect all breather hoses and wiring harnesses to the valve cover. Reinstall engine cover if equipped. Reconnect both battery negative cables. Start the engine and listen for any unusual valve train noise. A properly adjusted valve train should be noticeably quieter.

Reassembly

1. Ensure all valve cover bolts are torqued to specification in proper sequence to prevent oil leaks
2. Verify all breather hoses and electrical connections are secure
3. Check for oil leaks around valve cover after initial startup

Verification

• Start engine and allow to idle - valve train noise should be minimal and consistent
• Listen for any ticking or tapping noises that may indicate improper adjustment
• Check for oil leaks around valve cover gasket
• Test drive vehicle and verify normal engine operation and performance
• Recheck valve cover for leaks after vehicle reaches operating temperature

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