Main Bearings

Complete replacement of main bearings on the 5.9L Cummins diesel engine, requiring engine removal or cab lift and extensive disassembly.

Warnings

Tools required

Parts

• Main bearing set (standard or appropriate undersize) × 1 — Use OEM specification
• Thrust bearing set × 1 — Use OEM specification
• Main bearing cap bolts (torque-to-yield) × 14 — Use OEM specification
• Oil pan gasket × 1 — Use OEM specification
• Front cover gasket × 1 — Use OEM specification
• Rear main seal × 1 — Use OEM specification
• Oil pump pickup tube O-ring × 1 — Use OEM specification
• Oil drain plug crush washer × 1 — Use OEM specification
• Engine oil filter × 1 — Use OEM specification
• RTV silicone sealant (Mopar or equivalent) × 1 — Use OEM specification

Fluids

• 15W-40 diesel engine oil — 12 qt
• Mopar ATF+4 (if transmission removed) — 14 qt
• Ethylene glycol 50/50 coolant — 28 qt

Preparation

1. Park vehicle on level surface and engage parking brake
2. Disconnect both battery cables, negative first
3. Drain engine oil completely and remove oil filter
4. Drain cooling system at radiator petcock and lower hose
5. Remove hood and mark hinge locations for reinstallation
6. Remove air intake system from air filter housing to turbocharger inlet
7. Label and disconnect all wiring harnesses from engine
8. Remove coolant hoses from engine including radiator hoses and heater hoses
9. Disconnect fuel supply and return lines at fuel filter housing
10. Remove radiator, fan shroud, and cooling fan assembly
11. Discharge AC system and disconnect AC lines from compressor
12. Disconnect exhaust downpipe from turbocharger outlet
13. Remove transmission inspection cover and mark flexplate-to-torque converter relationship
14. Support transmission with transmission jack
15. Remove bellhousing-to-engine bolts and separate transmission slightly
16. Remove front driveshaft and mark yoke orientation
17. Attach engine hoist with proper lifting chains to engine lift brackets
18. Remove engine mount bolts and verify all connections are disconnected

Procedure

1. 1

   Remove Engine from Vehicle
   With engine hoist properly attached and transmission supported, carefully lift engine while tilting slightly to clear transmission input shaft. Once clear of frame mounts, lift engine high enough to clear radiator support and carefully move forward out of engine bay. Use load leveler to maintain balance during removal.
2. 2

   Mount Engine on Stand
   Lower engine onto engine stand and secure using bellhousing bolt holes. Ensure engine is securely mounted before releasing hoist. Position engine vertically with oil pan facing up for easier disassembly.
3. 3

   Remove Oil Pan and Pickup Tube
   Remove all oil pan bolts in reverse of tightening sequence. Carefully separate oil pan from block using gasket scraper if necessary. Remove oil pump pickup tube mounting bolts and extract pickup tube with O-ring. Inspect pickup screen for debris.
   Torque spec

   Oil Pan Bolt12 Nm (9 lb-ft)

   Oil Pump Pickup Tube12 Nm (9 lb-ft)
4. 4

   Remove Timing Cover and Accessories
   Remove harmonic balancer using puller tool. Remove timing cover bolts and carefully pry cover away from block. Remove oil pump drive gear. Mark timing gear positions before removal. This provides access to front main bearing cap.
   ⚠Do not use impact tools on harmonic balancer bolt as this can damage crankshaft threads or keyway.
5. 5

   Remove Flywheel or Flexplate
   If not already removed, mark flywheel/flexplate position relative to crankshaft flange. Remove all flywheel bolts in star pattern. Use flywheel holder or have assistant hold crankshaft to prevent rotation. Lift flywheel off crankshaft flange.
   Torque spec

   Flywheel Bolts95 Nm (70 lb-ft)
6. 6

   Inspect and Mark Bearing Caps
   Verify all main bearing caps are numbered from front (1) to rear (7). Note orientation arrows on caps - they must face forward. Check for any existing markings indicating cap-to-block relationship. Photograph or document existing positions before removal.
   ⚠️Main bearing caps are line-bored as a matched set with the block. Installing caps in wrong position or orientation will cause immediate engine seizure.
7. 7

   Remove Main Bearing Cap Bolts
   Working from front to rear, loosen main bearing cap bolts gradually in multiple passes. Start with outer caps (1 and 7), then work toward center. Loosen each cap 1/4 turn at a time to avoid distorting crankshaft. Once all bolts are loose, remove them completely. These are torque-to-angle bolts; verify Cummins reuse policy before reinstalling.
   ⚠Do not loosen cap bolts unevenly as this can bend the crankshaft or cause binding.
   Torque spec

   Main Bearing Cap Bolts75 Nm (55 lb-ft)
8. 8

   Remove Main Bearing Caps
   Carefully lift each main bearing cap straight up. Some caps may require light tapping with rubber mallet. Keep caps in order on workbench. Do not allow caps to fall or be dropped as this damages machined surfaces. Note position of thrust bearing on center main cap (#4).
9. 9

   Remove Crankshaft
   With all caps removed, carefully lift crankshaft straight out of block. This requires two people due to weight (approximately 130 lbs). Place crankshaft on padded surface or crankshaft stand. Do not drag crankshaft across block surface.
   ⚠️Crankshaft is extremely heavy. Use proper lifting technique and have adequate assistance to avoid injury.
10. 10

    Remove Old Bearings and Clean Surfaces
    Remove upper bearing shells from block saddles and lower shells from caps. Note position of bearing tangs in locating slots. Clean all bearing surfaces in block and caps thoroughly with brake cleaner. Inspect for scoring, discoloration, or damage. Clean crankshaft journals with brake cleaner and inspect for scoring, taper, or out-of-round condition.
11. 11

    Measure Crankshaft Journals
    Using micrometer, measure each main bearing journal diameter at multiple points (90-degree intervals and along journal length). Record all measurements. Compare to service specifications (verify standard main journal diameter against Cummins service manual). Check for taper (difference in diameter along journal) and out-of-round (difference around journal). Maximum acceptable variation is 0.0005 inch. If journals are worn beyond specification, crankshaft requires grinding and undersize bearings.
    ⚠Crankshaft with scored or out-of-specification journals will cause immediate bearing failure even with new bearings.
12. 12

    Measure Bearing Bores
    Install bearing caps in correct positions without bearings and torque bolts to specification using old bolts (new TTY bolts will be used for final assembly). Using dial bore gauge, measure each main bearing bore diameter. Record measurements. Bores should be within 0.001 inch of each other. Remove caps after measuring.
    Torque spec

    Main Bearing Cap Bolts75 Nm (55 lb-ft)
13. 13

    Install Upper Bearing Shells
    Apply thin coat of assembly lube to bearing backs. Install upper bearing shells (with oil holes) into block saddles, ensuring bearing tang engages locating slot. Do not force bearings. Wipe assembly lube from bearing surface and apply fresh lube to bearing face. Install all seven upper bearings. Install thrust bearing halves on center main (#4) with oil grooves facing out.
14. 14

    Install Crankshaft and Check Clearances
    Carefully lower crankshaft into block, aligning journals with bearing shells. Install lower bearing shells (without oil holes) into main caps with assembly lube on backs and faces. Place Plastigage strips across each crankshaft journal parallel to crankshaft centerline. Install bearing caps in correct order and orientation. Install new main cap bolts finger-tight, then torque to the Cummins-specified initial value in sequence from center outward (verify torque spec against Cummins service manual). Do NOT rotate crankshaft with Plastigage installed.
    ⚠Do not apply final torque angle at this stage - this is only for clearance checking.
    Torque spec

    Main Bearing Cap Bolts75 Nm (55 lb-ft)
15. 15

    Measure Bearing Clearances
    Carefully remove main caps without rotating crankshaft. Check Plastigage width on each journal using scale on Plastigage envelope. Specification per Cummins service manual (verify main bearing clearance values against Cummins documentation). Record all clearances. If clearances are too tight, check for debris or incorrect bearing selection. If too loose, verify crankshaft journal diameter or select different bearing size. Remove all Plastigage material completely.
    ⚠️Bearing clearances outside specification will cause bearing failure and engine damage. Do not proceed without correct clearances.
16. 16

    Check Crankshaft Endplay
    With clearances verified, reinstall main caps with new assembly lube on bearing faces. Install new main bearing cap bolts. Torque to the Cummins-specified initial value in sequence from center outward, then apply the specified torque angle in same sequence (verify torque and angle against Cummins service manual). Using dial indicator on crankshaft snout, pry crankshaft fully forward and zero indicator. Pry crankshaft fully rearward and read endplay. Specification per Cummins service manual (verify crankshaft endplay range against Cummins documentation). Adjust with different thickness thrust bearings if needed.
    Torque spec

    Main Bearing Cap Bolts75 Nm (55 lb-ft)
17. 17

    Final Main Bearing Installation
    If endplay adjustment was needed, remove caps, replace thrust bearings, and repeat clearance check. Once all measurements are within specification, perform final installation. Apply fresh assembly lube to all bearing surfaces. Install crankshaft, install caps in correct order with new bolts. Torque main cap bolts to the Cummins-specified initial value in sequence from center (#4) outward to ends, then apply the specified torque angle in same sequence (verify torque and angle against Cummins service manual). Verify crankshaft rotates freely by hand.
    Torque spec

    Main Bearing Cap Bolts75 Nm (55 lb-ft)
18. 18

    Install Rear Main Seal
    Install new rear main seal in housing using seal driver or appropriate socket. Seal lip should face engine interior. Apply small amount of RTV sealant to outer edge of seal housing where it meets block. Torque seal housing bolts evenly.
19. 19

    Reinstall Timing Components
    Install oil pump drive gear ensuring proper timing marks alignment. Install new timing cover gasket with RTV sealant at block-to-oil pan junctions. Install timing cover and torque cover bolts to specification. Install harmonic balancer ensuring keyway alignment. Torque balancer bolt to specification.
20. 20

    Reinstall Oil Pickup and Pan
    Install new O-ring on oil pump pickup tube. Install pickup tube and torque mounting bolts to specification. Clean oil pan thoroughly and install new gasket. Apply thin bead of RTV at block corners where timing cover and rear seal housing meet. Install oil pan and torque bolts in sequence from center outward.
    Torque spec

    Oil Pump Pickup Tube12 Nm (9 lb-ft)

    Oil Pan Bolt12 Nm (9 lb-ft)
21. 21

    Install Flywheel
    Clean flywheel mounting surface and crankshaft flange. Align flywheel with marks made during disassembly. Install new flywheel bolts (if TTY type) and torque in star pattern to specification. Apply thread locker if specified by manufacturer.
    Torque spec

    Flywheel Bolts95 Nm (70 lb-ft)
22. 22

    Reinstall Engine
    Remove engine from stand and attach to hoist. Carefully lower engine into vehicle, aligning engine mounts and transmission input shaft. Install transmission-to-engine bolts and torque to specification. Install engine mount bolts. Reconnect all previously disconnected components in reverse order of removal including exhaust, cooling system, fuel lines, wiring, and accessories.
    Torque spec

    Transmission-to-Engine Bolts55 Nm (41 lb-ft)

    Sensor Mounting Bolts11 Nm (8 lb-ft)
23. 23

    Fill Fluids and Prime Oil System
    Install new oil filter. Fill engine with 12 quarts of 15W-40 diesel engine oil. Fill cooling system with 28 quarts of appropriate coolant mixture. Before starting engine, prime oil system by cranking engine with fueling disabled (disconnect fuel shut-off solenoid on 1994-1998 engines, or use the appropriate fuel-disable method for VP44/common-rail engines) until oil pressure registers on gauge. Reconnect fuel solenoid.

Reassembly

1. Torque specifications are critical - use calibrated torque wrench and angle gauge
2. Main bearing cap bolts are torque-to-yield and must be replaced with new bolts
3. Follow torque sequences carefully, especially for main caps (center outward)
4. Verify crankshaft rotates freely by hand before reinstalling oil pan
5. Double-check all clearances before final assembly - corrections after installation require complete disassembly
6. Use only specified assembly lube on bearings - do not use engine oil or grease

Verification

• Verify oil pressure reaches normal operating pressure (10 psi per 1000 RPM minimum) within 15 seconds of startup
• Listen for abnormal engine noises during initial startup - any knocking indicates bearing problem
• Monitor oil pressure gauge during initial 20-minute break-in period at varying RPM
• Check for oil leaks at pan gasket, timing cover, and rear main seal
• Verify no coolant leaks at all connection points
• Check that all electrical connectors and sensors are properly connected and functioning
• After initial startup and warm-up, shut down and recheck oil level - add as needed
• Perform test drive and monitor oil pressure under load
• After 500 miles, change engine oil and filter and inspect for metal particles indicating bearing wear

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