Front Main Seal

Replace the front crankshaft seal on the 5.9L Cummins diesel engine by removing the harmonic balancer and timing cover to access and install a new seal.

Warnings

Tools required

Parts

• Front crankshaft seal × 1 — Use OEM Cummins or quality aftermarket
• Timing cover gasket × 1 — Use OEM specification
• Oil drain plug crush washer × 1 — Copper or aluminum washer
• Engine oil × 12 — 15W-40 diesel rated
• Oil filter × 1 — Use OEM or quality aftermarket

Fluids

• 15W-40 diesel engine oil — 12 qt

Preparation

1. Park vehicle on level surface and engage parking brake
2. Allow engine to cool completely (minimum 2 hours)
3. Disconnect both battery cables, negative first
4. Raise and support front of vehicle on jack stands
5. Remove engine skid plate if equipped
6. Drain engine oil completely and replace drain plug with new crush washer
7. Remove engine fan shroud bolts and reposition shroud rearward (do not remove fan)
8. Remove serpentine belt(s) by releasing tensioner
9. Drain coolant from radiator if additional access is needed

Procedure

1. 1

   Remove accessory components
   Remove the water pump pulley if it interferes with harmonic balancer access. Remove any accessory brackets or components blocking access to the front timing cover. On 4WD models, verify clearance to the front axle and differential. Label all electrical connectors and vacuum lines before disconnecting.
   Torque spec

   Sensor Mounting Bolts11 Nm (8 lb-ft)
2. 2

   Remove harmonic balancer bolt
   Using a 1/2 inch breaker bar or impact wrench, remove the crankshaft harmonic balancer/vibration damper center bolt. This bolt is extremely tight — consult the factory service manual for the correct Cummins torque value (typically a multi-stage torque plus angle, substantially higher than gasoline-engine specs). You may need to lock the flywheel/ring gear from underneath to prevent crankshaft rotation. Verify whether this is a torque-to-yield bolt; if so, replacement is required.
3. 3

   Remove harmonic balancer
   Install a harmonic balancer puller onto the balancer hub. DO NOT use a jaw-type puller that grips the outer ring as this will damage the balancer. Thread the puller center bolt into the crankshaft and tighten gradually to pull the balancer off the crankshaft snout. Note the position of the Woodruff key in the crankshaft keyway.
   ⚠Never hammer on the crankshaft or use heat on the balancer as this will cause permanent damage to the crankshaft and balancer.
4. 4

   Remove timing cover fasteners
   Remove all timing cover bolts, noting their locations as they are different lengths. There are both 8mm and 10mm bolts around the perimeter. The lower bolts may also secure the oil pan front section. Keep bolts organized by size and location for reassembly.
   Torque spec

   Timing Cover Bolts - 10mm45 Nm (33 lb-ft)

   Timing Cover Bolts - 8mm25 Nm (18 lb-ft)

   Oil Pan Bolt12 Nm (9 lb-ft)
5. 5

   Remove timing cover
   Carefully pry the timing cover away from the engine block using plastic pry tools or a gasket scraper at designated pry points. Work around the perimeter evenly. The cover may be sealed with RTV in addition to the gasket. Once loose, pull the cover straight off to avoid damaging the oil pan gasket surface. The front seal will come out with the cover.
   ⚠Avoid prying against machined aluminum surfaces. Damage to the sealing surface will require resurfacing or replacement.
6. 6

   Remove old front seal from cover
   Using a seal puller, hook tool, or carefully with a screwdriver, extract the old front seal from the timing cover. Work around the seal perimeter and pry evenly to avoid damaging the seal bore in the cover. Clean the seal bore thoroughly with degreaser and inspect for any damage, scoring, or corrosion.
   ℹ️Inspect the crankshaft snout surface where the seal rides. Any grooves or scoring will cause the new seal to leak and require crankshaft repair or replacement.
7. 7

   Clean all gasket surfaces
   Remove all old gasket material from the timing cover and engine block using a gasket scraper. Clean surfaces with degreaser and wipe with clean, lint-free rags. The mating surfaces must be completely clean and dry. Inspect the oil pan front gasket - if damaged, the oil pan will need to be dropped to replace it.
   Torque spec

   Gasket Surface Bolts20 Nm (15 lb-ft)
8. 8

   Install new front seal in cover
   Lightly lubricate the outer diameter of the new seal with engine oil. Position the seal in the timing cover bore with the spring side facing inward (toward the engine). Using a seal installation tool or large socket that matches the seal outer diameter, drive the seal squarely into the bore until it seats flush with the cover surface. Ensure the seal is not cocked or damaged during installation.
   ⚠Do not drive on the seal inner diameter or spring as this will damage the seal lips and cause immediate leakage.
9. 9

   Prepare timing cover for installation
   Install a new timing cover gasket on the cover. Some applications use RTV sealant instead of or in addition to a gasket - consult factory service manual for your specific year. If using RTV, apply a continuous 2-3mm bead around the cover perimeter and at oil pan junction points. Lightly lubricate the front seal inner lip with clean engine oil.
10. 10

    Install timing cover
    Carefully slide the timing cover over the crankshaft snout, being extremely careful not to damage the new seal lip on the crankshaft. Align the cover with dowel pins if equipped. Hand-start all timing cover bolts, ensuring correct bolt lengths in their proper locations. Tighten bolts in a star pattern starting from the center and working outward.
    Torque spec

    Timing Cover Bolts - 10mm45 Nm (33 lb-ft)

    Timing Cover Bolts - 8mm25 Nm (18 lb-ft)

    Oil Pan Bolt12 Nm (9 lb-ft)
11. 11

    Install harmonic balancer
    Clean the crankshaft snout and harmonic balancer bore with degreaser. Verify the Woodruff key is properly seated in the crankshaft keyway. Align the balancer keyway with the key and slide the balancer onto the crankshaft snout. The balancer should slide on with moderate hand pressure - do not hammer it on. If resistance is encountered, verify key alignment. The harmonic balancer/damper must be properly aligned to the crankshaft key and seated squarely. On the 5.9L Cummins the harmonic balancer/damper is not tied to camshaft or injection-pump timing — it mounts to the crankshaft and provides only vibration damping. Damper keyway misalignment does not alter cam or injection timing. Improper installation can cause damper failure and vibration; ensure the key is seated and the damper is fully engaged before torquing the bolt.
    ⚠️Misalignment of the harmonic balancer key and keyway will cause incorrect camshaft timing and severe engine damage. Verify alignment before torquing the bolt.
12. 12

    Install harmonic balancer bolt
    Install the harmonic balancer/damper bolt (new bolt if torque-to-yield). Tighten to the factory-specified Cummins value using a torque wrench — this is typically a multi-stage torque-plus-angle procedure, not a single 133 ft-lb value. You may need to prevent crankshaft rotation using the same method as removal. Verify the balancer is fully seated against the crankshaft snout shoulder before final torquing.
13. 13

    Reinstall accessory components
    Reinstall the water pump pulley, accessory brackets, and any components removed during disassembly. Reconnect all electrical connectors per your labels. Install the serpentine belt ensuring proper routing around all pulleys and tensioner.
    Torque spec

    Sensor Mounting Bolts11 Nm (8 lb-ft)

    Electrical Connector Bolts7 Nm (5 lb-ft)
14. 14

    Refill fluids and final checks
    Install a new oil filter and refill engine with approximately 11 quarts of 15W-40 diesel engine oil, then verify level on the dipstick and top off to the full mark. Refill coolant if drained. Reinstall fan shroud and engine skid plate. Reconnect battery cables (positive first, then negative). Double-check all fasteners and connections before starting.
    Torque spec

    Oil Drain Plug35 Nm (26 lb-ft)

Reassembly

1. Verify all timing cover bolts are torqued in the correct sequence with proper values for their size
2. Ensure harmonic balancer bolt is torqued to specification and balancer is fully seated
3. Confirm serpentine belt is properly routed and tensioned
4. Verify all electrical connections are secure and properly seated

Verification

• Start engine and check for oil leaks around timing cover and front seal immediately
• Allow engine to reach operating temperature and verify no coolant or oil leaks
• Check oil level with dipstick after running and top off if necessary
• Listen for any unusual noises from the front of the engine that could indicate balancer or accessory issues
• After 50-100 miles of driving, re-check timing cover area for any seepage and verify oil level
• Monitor oil level for the first 500 miles to ensure seal is not weeping

More procedures for this vehicle