Main Bearings

This procedure covers removal and replacement of the main bearings on the 5.9L Cummins diesel engine, requiring complete engine removal from the vehicle and crankshaft extraction.

Warnings

Tools required

Parts

• Main bearing set (standard or appropriate oversize) × 1 — Use OEM specification or premium aftermarket
• Thrust bearing set × 1 — Use OEM specification
• Main bearing cap bolts (if reuse not permitted) × 1 — Consult factory service manual
• Complete engine gasket set × 1 — Use OEM specification
• Oil pan gasket × 1 — Use OEM specification
• Rear main seal × 1 — Use OEM specification
• Front crankshaft seal × 1 — Use OEM specification
• Oil pump O-rings and seals × 1 — Use OEM specification
• Engine oil filter × 1 — Use OEM specification
• Coolant hoses (replace if deteriorated) × 1 — Inspect and replace as needed
• Valve cover gaskets × 1 — Use OEM specification
• Harmonic balancer bolt × 1 — Use OEM specification - one-time use
• Oil drain plug washer × 1 — Use OEM specification

Fluids

• 15W-40 diesel oil or 5W-40 synthetic — 12 qt
• HOAT coolant 50/50 — 28 qt

Preparation

1. Park vehicle on level surface and engage parking brake
2. Disconnect both battery cables (negative first) and remove batteries
3. Drain engine oil completely and remove oil filter
4. Drain cooling system at radiator petcock and block drain plugs
5. Remove engine cover and air intake system from turbocharger to air filter housing
6. Remove radiator, intercooler, and A/C condenser assembly
7. Remove fan shroud and engine cooling fan
8. Disconnect all electrical connectors from engine (alternator, starter, fuel injection harness, sensors) - photograph and label all connections
9. Relieve fuel system pressure and disconnect fuel supply and return lines at fuel filter housing
10. Disconnect heater hoses and any remaining coolant hoses
11. Remove exhaust system from turbocharger outlet back to catalytic converter
12. Remove turbocharger inlet and outlet piping
13. If equipped with automatic transmission: drain transmission fluid and remove torque converter bolts through starter opening
14. If equipped with manual transmission: remove clutch slave cylinder without disconnecting hydraulic line
15. Support transmission with transmission jack
16. Remove transfer case to transmission mounting bolts and lower transfer case (4WD models)
17. Mark driveshaft positions and remove front and rear driveshafts
18. Disconnect transmission shift linkage, wiring harnesses, and cooler lines (if automatic)
19. Remove transmission crossmember and bellhousing bolts - support transmission securely
20. Attach engine hoist with heavy-duty lifting chains to factory lifting eyes on cylinder head
21. Remove engine mount through-bolts on both sides
22. Clear all connections and carefully lift engine from vehicle - have assistant guide transmission away from engine as it separates
23. Mount engine securely on engine stand using bellhousing bolt holes
24. Prepare clean workspace with adequate lighting for disassembly and inspection

Procedure

1. 1

   Remove external engine components
   With engine on stand, remove remaining external components: alternator, power steering pump (if still attached), fuel injection pump, fuel filter housing, oil cooler, turbocharger assembly, exhaust manifold, intake manifold, valve cover, and front engine accessories. Drain any remaining coolant from water pump housing. Remove starter motor and flywheel/flexplate inspection cover.
2. 2

   Remove flywheel and front accessory drive
   Install flywheel holding tool and remove flywheel/flexplate bolts. Remove flywheel or flexplate and set aside. At front of engine, use harmonic balancer puller to remove crankshaft balancer. Remove front timing cover bolts and carefully pry off timing cover - note position of any alignment dowels. Remove oil slinger from crankshaft snout.
3. 3

   Remove oil pan and oil pump
   Rotate engine on stand to access oil pan from below. Remove all oil pan bolts and carefully separate pan from block - may require gentle prying at designated pry points. Clean gasket surfaces. Remove oil pump mounting bolts and withdraw oil pump and pickup tube assembly. Remove windage tray or oil pan baffle if equipped.
4. 4

   Remove connecting rod caps and pistons
   Rotate crankshaft to position each connecting rod at bottom dead center. Mark each rod and cap with cylinder number and orientation using permanent marker or stamps. Remove rod cap nuts/bolts and carefully remove rod caps - keep caps with corresponding rods. Install rod bolt protectors or pieces of rubber hose over rod bolts. Push each piston/rod assembly up and out through top of cylinder bore. Store piston assemblies in order on padded surface.
5. 5

   Mark and remove main bearing caps
   Carefully examine main bearing caps and engine block for factory alignment marks. Using permanent marker or number stamps, clearly mark each main bearing cap with its position number (front to rear) and orientation arrow pointing toward front of engine. The thrust bearing is typically on the center main journal - note this position. Remove all main bearing cap bolts in progressive pattern, loosening each bolt 1-2 turns at a time working from outer caps toward center to prevent crankshaft binding.
6. 6

   Remove crankshaft and bearing shells
   With all main cap bolts removed, carefully lift off each main bearing cap - caps may be tight and require gentle tapping with soft mallet. Place caps in order on clean work surface. Enlist assistant or use crankshaft support fixture to carefully lift crankshaft straight up and out of engine block - Cummins crankshaft weighs approximately 100-120 lbs. Place crankshaft on padded surface or in V-blocks for inspection. Remove all upper bearing shells from block and lower shells from caps, keeping each bearing set together with its position marked.
7. 7

   Clean and inspect crankshaft and block
   Thoroughly clean crankshaft with solvent, paying special attention to oil passages. Use compressed air to blow out all oil galleries in crankshaft and engine block - ensure passages are completely clear. Clean all main bearing saddles in block and caps with lint-free cloth and solvent. Inspect crankshaft journals for scoring, discoloration, or damage. Using micrometer, measure each main journal diameter at four points (90 degrees apart) and at three positions along journal length to check for out-of-round and taper. Record all measurements. Inspect block main saddles for cracks, scoring, or damage.
8. 8

   Determine bearing size and prepare for installation
   Compare crankshaft journal measurements to factory specifications to determine if standard, 0.010, or 0.020 undersize bearings are needed. If journals show more than 0.001 inch out-of-round or taper, crankshaft must be reground to next undersize. Clean bearing saddles in block one final time with lint-free cloth dampened with oil. Apply light coat of assembly lube to bearing backs. Ensure oil holes in bearings align with oil passages in block.
   ⚠Never file, sand, or machine main bearing caps or saddles. Any material removal will create improper bearing clearance and destroy the engine.
9. 9

   Install upper bearing shells and crankshaft
   Install new upper bearing shells into block saddles, ensuring locating tabs engage properly and oil holes align perfectly with block oil passages. Apply thin coat of assembly lube to bearing surfaces. With assistant or support fixture, carefully lower crankshaft into position, ensuring journals seat properly in bearings. Verify crankshaft rotates freely by hand - if binding occurs, investigate cause immediately before proceeding.
10. 10

    Install lower bearing shells and check clearances with Plastigage
    Install new lower bearing shells into main bearing caps with locating tabs engaged. Place strips of Plastigage across each main journal parallel to crankshaft centerline - do not rotate crankshaft with Plastigage installed. Install main bearing caps in correct positions with orientation marks aligned. Install cap bolts finger-tight, then progressively torque bolts to approximately 50% of final specification in sequence from center cap outward. Do not rotate crankshaft. Remove caps one at a time and measure Plastigage width using scale on Plastigage package. Compare measurements to specification (typically 0.0015-0.0035 inches for mains). Record all clearances.
    ⚠If any bearing clearance exceeds specification, determine cause before proceeding. Excessive clearance will cause low oil pressure and bearing failure.
11. 11

    Final main bearing installation and torque
    Remove Plastigage residue from journals and bearings with lint-free cloth. Apply generous coat of engine assembly lube or manufacturer-specified break-in oil to all bearing surfaces. Install main bearing caps in correct positions with orientation marks properly aligned. Install thrust bearing washers on center main (or designated thrust location) with oil grooves facing outward. Install new main cap bolts if required by specification. Hand-tighten all main cap bolts, then torque in progressive steps following factory torque sequence, starting from center cap and working outward. Note: Since no torque specification is provided in database, consult factory service manual for exact torque value and sequence - Cummins main cap bolts use a multi-stage torque-plus-angle procedure that must be obtained from the factory service manual. After torquing, verify crankshaft rotates smoothly with no binding.
    ⚠️Main bearing cap torque specification is critical and must be obtained from factory service manual. Incorrect torque will cause bearing failure or cap fracture.
12. 12

    Check crankshaft endplay
    Mount dial indicator against crankshaft snout or rear flange with plunger parallel to crankshaft centerline. Using pry bars, carefully move crankshaft fully forward and zero dial indicator. Pry crankshaft fully rearward and note endplay reading on indicator. Specification must be obtained from the factory service manual (typically in the range of approximately 0.003-0.011 inches for the Cummins). If endplay is insufficient, verify thrust bearing washers are installed correctly. If excessive, verify correct thrust bearing size or check for worn thrust surfaces on crankshaft.
13. 13

    Install rear main seal and inspect pistons/rods
    Clean rear main seal housing thoroughly. Lightly oil new rear main seal and carefully drive into position using seal driver or large socket - seal must be flush and square in bore. While crankshaft is accessible, inspect connecting rods and pistons for damage. Check rod bearing clearances using same Plastigage method as mains. Verify ring gaps are within specification before reinstalling pistons. Apply assembly lube to rod bearings and carefully guide piston/rod assemblies into cylinders using ring compressor, ensuring orientation marks face correct direction.
14. 14

    Reassemble engine lower end
    Install rod caps in correct positions with orientation marks aligned. Torque rod cap fasteners to specification per factory service manual in proper sequence. Install oil pump with new O-rings and gaskets, ensuring pickup tube seals properly. Install windage tray if equipped. Apply thin bead of appropriate RTV sealant to oil pan gasket surfaces per service manual instruction, install new oil pan gasket, and install oil pan with all bolts torqued in proper sequence. Install new front crankshaft seal in timing cover. Apply RTV to timing cover gasket surfaces and install timing cover with new gasket.
15. 15

    Complete engine reassembly and installation
    Install crankshaft balancer using new installation bolt torqued to specification. Install flywheel/flexplate with new bolts and flywheel holding tool. Reinstall all external components in reverse order of removal: intake manifold with new gaskets, exhaust manifold, turbocharger, fuel injection components, valve cover with new gasket, all accessories, wiring harnesses, and cooling system components. Remove engine from stand and reverse engine removal procedure to install back into vehicle. Reconnect transmission, driveshafts, transfer case, exhaust system, cooling system, fuel lines, and all electrical connections.

Reassembly

1. Ensure all main bearing caps are oriented correctly with factory marks or your reference marks aligned
2. Verify thrust bearing is installed in correct position (typically center main)
3. Double-check that all oil passages in crankshaft and block are clear before final assembly
4. All main bearing cap bolts must be torqued to exact specification in proper sequence - consult factory service manual
5. Apply assembly lube liberally to all bearing surfaces during final assembly
6. Rotate crankshaft by hand throughout assembly process to verify smooth rotation with no binding
7. Install all external components with new gaskets and seals
8. Refill engine with 12 quarts of 15W-40 diesel oil or 5W-40 synthetic with new oil filter
9. Refill cooling system with 28 quarts of 50/50 HOAT coolant mixture
10. If transmission was removed or drained, refill with appropriate ATF+4 quantity per transmission type

Verification

• Before starting engine, rotate crankshaft by hand at least two complete revolutions to verify no interference or binding
• Prime oil system by cranking engine with fuel system disabled until oil pressure gauge shows pressure
• Start engine and immediately verify oil pressure - should show at least 10 psi at idle within 10-15 seconds
• Listen carefully for any unusual noises - knocking, rattling, or grinding indicates assembly problem requiring immediate shutdown
• Monitor oil pressure at idle and 1500 RPM - should be at least 10 psi at idle and 30+ psi at speed
• Check for oil leaks around pan, timing cover, and rear main seal after initial start
• Verify no coolant or oil mixing - check radiator for oil contamination and oil for coolant contamination
• Allow engine to reach operating temperature and verify cooling system operates properly
• Test drive vehicle and monitor oil pressure under various loads and speeds
• After first 50-100 miles, recheck oil level and inspect for leaks
• Perform oil and filter change after 500-1000 mile break-in period to remove assembly lube and break-in debris

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