Valve Seals

Replace valve stem seals on the 5.9L Cummins I6 diesel engine to address oil consumption or smoking issues without removing the cylinder head.

Warnings

Tools required

Parts

• Valve stem seal kit (12 seals) × 1 — Use OEM Cummins specification
• Valve cover gasket × 1 — Use OEM specification
• Intake horn gasket × 1 — Use OEM specification
• Rocker housing gasket kit × 1 — Use OEM specification
• Oil drain plug washer × 1 — Use OEM specification
• Engine oil filter × 1 — Use OEM specification

Fluids

• 15W-40 diesel oil or 5W-40 synthetic — 12 qt

Preparation

1. Park vehicle on level surface and engage parking brake
2. Disconnect both negative and positive battery cables
3. Allow engine to cool completely (minimum 3 hours)
4. Drain engine oil completely and replace drain plug with new washer
5. Remove intake horn and air filter housing assembly
6. Remove intercooler tubes if they obstruct access to valve cover
7. Label all electrical connectors and vacuum lines before disconnection
8. Take photos of rocker arm assembly and pushrod arrangement for reference

Procedure

1. 1

   Remove valve cover and rocker assembly
   Disconnect fuel injector harness connectors and set aside. Remove valve cover bolts in reverse of tightening sequence (from ends toward center). Carefully lift valve cover away. Remove rocker shaft assembly bolts evenly in stages to prevent warping. Lift off entire rocker arm assembly as a unit. Keep pushrods in order using a numbered holder or cardboard template - they must be reinstalled in their original positions.
2. 2

   Identify cylinder firing order and prepare for TDC location
   The 5.9L Cummins firing order is 1-5-3-6-2-4. Cylinder 1 is at the front (accessory end). You will need to bring each cylinder to TDC on its compression stroke individually. Mark the harmonic balancer with a reference line aligned with the TDC mark on the timing cover for easier identification.
3. 3

   Bring cylinder 1 to TDC on compression stroke
   Relieve high-pressure fuel rail pressure per Cummins procedure, disconnect and cap the high-pressure line, then remove the injector hold-down and injector from cylinder 1 using appropriate tools. Locate TDC using the engine's timing pin/damper marks rather than probing the injector bore. Rotate engine by hand using the appropriate socket on the crankshaft damper bolt (verify correct size for your engine — typically 1-1/2") until piston 1 reaches TDC and both valves are closed (both rocker arms should have clearance). Verify TDC timing marks align. Install air line adapter into injector hole and apply 90-100 PSI of shop air pressure to hold valves in place. Leave air connected throughout the valve seal replacement for this cylinder.
4. 4

   Compress valve springs and remove keepers for cylinder 1
   Position heavy-duty valve spring compressor on the first valve. Compress the spring slowly and evenly until keepers are fully exposed. Use a magnetic keeper removal tool to carefully extract both keepers. Place keepers in a labeled container. Slowly release spring compressor and remove. Remove valve spring retainer and valve spring. Remove old valve stem seal by carefully pulling upward or using seal removal pliers. Inspect valve stem for damage or scoring. Repeat for second valve on cylinder 1.
5. 5

   Install new valve seals for cylinder 1
   Lightly oil the valve stem with clean engine oil. Place protective plastic sleeve (usually included in seal kit) over valve keeper grooves to prevent seal damage during installation. Slide new valve seal down over the stem and onto the valve guide. Use the appropriate seal installation tool or deep socket to gently tap the seal into place until it seats on the valve guide. Remove protective sleeve. Ensure seal is fully seated and square on the guide. Repeat for second valve.
6. 6

   Reinstall valve springs and keepers for cylinder 1
   Install valve spring over the valve stem with the correct orientation (tighter wound coils typically face the head). Install valve spring retainer. Compress spring with compressor tool. Apply small amount of grease to keepers to hold them in position. Carefully install both keepers into the keeper grooves, ensuring they seat properly. Slowly release spring compressor while verifying keepers remain fully engaged. Once released, tap valve stem tip gently with plastic mallet to ensure keepers are fully seated. Remove air pressure and verify valve moves freely. Repeat for second valve, then remove air adapter.
7. 7

   Repeat process for remaining cylinders in sequence
   Reinstall injector in cylinder 1. Following firing order (1-5-3-6-2-4), bring cylinder 5 to TDC on compression stroke by rotating engine clockwise. Each cylinder will be 120 degrees of crankshaft rotation apart (this is an inline 6-cylinder). Repeat steps 3 through 6 for cylinder 5, then continue with cylinders 3, 6, 2, and 4 in sequence. Maintain meticulous cleanliness and organization throughout the process.
8. 8

   Clean and inspect rocker arm assembly
   Thoroughly clean rocker arms, rocker shafts, and pushrods with solvent. Inspect rocker arm tips, pushrod seats, and valve stem contact surfaces for wear, pitting, or scoring. Check rocker shaft bearing surfaces for scoring. Replace any worn components. Verify all rocker shaft oil holes are clear and unobstructed.
9. 9

   Reinstall pushrods and rocker assembly
   Apply clean engine oil to all pushrod ends. Install each pushrod into its original position, ensuring the bottom end seats properly in the lifter. Apply engine oil to rocker arm contact points. Carefully position rocker arm assembly over pushrods, guiding each rocker arm onto its corresponding pushrod and valve stem. Install rocker shaft bolts finger-tight initially.
10. 10

    Torque rocker shaft assembly
    Tighten rocker shaft assembly bolts evenly in stages working from center outward. Torque the rocker shaft/pedestal bolts to the factory Cummins specification (approximately 27 ft-lbs / 36 Nm — verify against current service data) in stages, evenly from center outward. Ensure assembly sits flat and even on the head. Rotate engine two complete revolutions by hand to verify no interference or binding.
11. 11

    Adjust valve lash
    The 5.9L Cummins requires specific valve lash settings. Set intake valves to 0.010 inch and exhaust valves to 0.026 inch cold (verify against current Cummins service data for your engine). Adjust valves using the firing order method: with cylinder at TDC compression, adjust both valves for that cylinder. Loosen adjuster locknut, turn adjusting screw to achieve proper feeler gauge drag, hold adjuster and tighten locknut. Recheck clearance after tightening. Proceed through all cylinders in firing order.
12. 12

    Reinstall valve cover
    Clean valve cover and cylinder head mating surfaces thoroughly with gasket scraper and solvent. Install new valve cover gasket - verify it seats properly in the valve cover groove. Apply small dabs of RTV silicone at the corners where gasket meets (if applicable per gasket instructions). Position valve cover carefully to avoid disturbing gasket. Install bolts finger-tight, then torque in sequence from center outward. Torque the valve cover bolts to the factory Cummins specification (approximately 18 in-lbs / 2 Nm — verify against current service data), being careful not to overtighten and distort the cover.
13. 13

    Reinstall remaining components
    Reconnect all fuel injector harness connectors in their original positions. Reinstall intake horn with new gasket. Reinstall intercooler tubes if removed. Reconnect all vacuum lines and electrical connectors per photos taken during disassembly. Install new oil filter and fill engine with approximately 11 quarts of 15W-40 diesel oil or 5W-40 synthetic (verify exact capacity for your engine).
14. 14

    Prime engine and initial startup
    Reconnect both battery cables. Turn ignition to run position without cranking to allow fuel system to prime (wait for lift pump to complete cycle). Cycle key 3-4 times to ensure fuel system is fully primed. Start engine and immediately check for oil pressure on gauge. Monitor for oil leaks around valve cover and injectors. Allow engine to idle for 2-3 minutes while checking for unusual noises or smoke.

Reassembly

1. Valve lash must be adjusted to specification after rocker assembly installation
2. All pushrods must be returned to their original positions
3. Verify valve spring keepers are fully seated before releasing spring compressor pressure
4. Ensure all injectors are properly torqued and sealed to prevent combustion gas leakage
5. Double-check that no tools or debris remain in the engine before valve cover installation

Verification

• Start engine and verify oil pressure reaches normal range within 10 seconds
• Listen for any valve train noise indicating improper adjustment or assembly
• Monitor exhaust for blue smoke during warm-up and after reaching operating temperature - should significantly reduce or eliminate if seals were the issue
• Check for oil leaks around valve cover, injectors, and rocker housing after 15 minutes of running
• Road test vehicle and monitor oil consumption over next 500 miles to verify repair success
• Recheck valve lash after first 500 miles and adjust if necessary

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