Connecting Rod Bearings

This procedure covers the replacement of connecting rod bearings on the 5.9L Cummins diesel engine, requiring engine removal, complete disassembly of lower end components, and precision measurement during reassembly.

Warnings

Tools required

Parts

• Connecting rod bearing set (standard or oversized) × 1 — Use OEM specification
• Main bearing set (inspect and replace if needed) × 1 — Use OEM specification
• Oil pan gasket × 1 — Use OEM specification
• Valve cover gasket × 1 — Use OEM specification
• Front crankshaft seal × 1 — Use OEM specification
• Rear main seal × 1 — Use OEM specification
• Oil pump pickup tube O-ring × 1 — Use OEM specification
• Engine oil filter × 1 — Use OEM specification
• Coolant filter × 1 — Use OEM specification
• Exhaust manifold gaskets × 1 — Use OEM specification
• Turbocharger mounting gasket × 1 — Use OEM specification
• Engine mount bolts × 4 — Use OEM specification
• Rod bolt set (if torque-to-yield) × 1 — Verify if reusable or replace

Fluids

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

Preparation

1. Park vehicle on level ground and engage parking brake
2. Disconnect both battery cables, negative first
3. Drain engine oil and coolant completely into appropriate containers
4. Remove hood and store safely to provide engine access
5. Relieve fuel system pressure by loosening fuel filter drain valve
6. Support vehicle on jack stands at frame rails with front wheels removed for access
7. Place absorbent material under vehicle to catch residual fluids
8. Label and photograph all electrical connections, vacuum lines, and fuel lines before removal
9. Organize workspace with clean area for precision measurement work

Procedure

1. 1

   Remove engine accessories and peripherals
   Remove air intake system, intercooler piping, and air filter housing. Disconnect all electrical connectors including alternator, starter, sensors, and grid heater. Remove serpentine belt and all belt-driven accessories (alternator, power steering pump, A/C compressor, fan clutch and shroud). Remove turbocharger oil feed and return lines, then unbolt turbocharger from exhaust manifold and set aside with downpipe attached if possible. Remove exhaust manifold and intake manifold. Label all fasteners and brackets for reassembly.
2. 2

   Disconnect fuel and cooling systems
   Disconnect fuel supply and return lines at fuel filter housing and injection pump. Cap all openings immediately to prevent contamination. Remove radiator hoses, heater hoses, and bypass hose. Disconnect transmission cooler lines from radiator if automatic transmission. Remove fan shroud and radiator assembly. Disconnect coolant temperature sensors and drain plugs.
3. 3

   Separate transmission and remove engine
   Support transmission with floor jack and remove transmission-to-engine bellhousing bolts. Mark flexplate/flywheel position if automatic. Unbolt engine mounts from frame brackets. Attach engine hoist with chains to factory lift brackets on engine. Carefully lift engine while guiding it forward to separate from transmission input shaft. Once clear, lift engine completely out of vehicle and mount securely on engine stand using bellhousing bolt holes.
4. 4

   Remove valve cover and front accessories
   With engine on stand, remove valve cover and set aside rocker assemblies carefully to maintain order. Remove fuel injection pump and gear (mark timing position). Remove harmonic balancer using appropriate puller. Remove front timing cover, being careful not to damage sealing surfaces. Remove fuel injection pump drive gear and verify timing marks before removing timing gears.
5. 5

   Remove oil pan and oil pump
   Rotate engine on stand to access oil pan from bottom. Remove all oil pan bolts and carefully separate pan from block using plastic scraper to avoid damaging sealing surfaces. Remove oil pump pickup tube and oil pump assembly. Inspect oil pump pickup screen for debris which may indicate bearing failure.
6. 6

   Remove ridge and inspect cylinders
   Use ridge reamer to carefully remove any ridge at top of each cylinder bore where piston rings have not traveled. This prevents ring breakage during piston removal. Measure cylinder bore diameter at top, middle, and bottom in two directions (parallel and perpendicular to crankshaft) using dial bore gauge. Record all measurements. Maximum taper should not exceed 0.010 inch and out-of-round should not exceed 0.006 inch for bearing replacement without boring.
7. 7

   Mark and remove connecting rod assemblies
   Using parts marking pen, clearly mark each connecting rod cap and rod body with cylinder number (1-6) and orientation (mark should face same direction on both cap and rod). Verify factory identification marks are visible. Remove connecting rod cap bolts or nuts from cylinder #1. Remove cap carefully and push piston/rod assembly up and out through top of cylinder bore. Install rod cap back onto rod immediately to prevent mixing. Repeat for all six cylinders, keeping each assembly separate and organized in order.
8. 8

   Inspect crankshaft journals and measure
   Thoroughly clean all connecting rod journals on crankshaft with parts cleaner and lint-free cloth. Inspect each journal for scoring, heat discoloration, or damage. Using precision outside micrometer, measure diameter of each rod journal in at least two positions rotated 90 degrees apart. Standard rod journal diameter must be verified with the Cummins factory service manual for the 5.9L ISB before selecting bearings. Out-of-round should not exceed 0.001 inch and taper should not exceed 0.001 inch. If journals are scored or out of specification, crankshaft must be ground and oversized bearings used.
9. 9

   Clean and inspect connecting rods
   Remove old bearing shells from rods and caps, keeping each set with its respective rod. Thoroughly clean rod and cap bores with parts cleaner and inspect for cracks, especially around rod bolt holes and in the beam area. Check rod big end bore for roundness using inside micrometer or bore gauge - should be within 0.001 inch of round. Inspect rod bolts for stretching, thread damage, or necking. If bolts show any deformation or are torque-to-yield type, they must be replaced. Verify rod alignment using rod alignment fixture - twisted or bent rods must be replaced.
10. 10

    Select and install new bearings with Plastigage check
    Select appropriate bearing size based on crankshaft journal measurements (standard or oversized). Install upper bearing shell into connecting rod, ensuring oil hole aligns and bearing tang seats in notch. Install lower bearing shell into cap. Place a strip of Plastigage across the crankshaft journal parallel to crankshaft centerline. Install rod cap in correct orientation matching marks made during disassembly. Install rod bolts and torque to manufacturer specification (Cummins 5.9L ISB rod bolts are torque-to-yield: typically 30 ft-lbs, then 60 ft-lbs, then 60 degrees rotation — verify exact values with the factory service manual) WITHOUT rotating crankshaft. Remove cap carefully without rotating crankshaft and measure flattened Plastigage using scale on package. Clearance should be 0.0015-0.0035 inches for connecting rod bearings. If clearance is too tight, verify journal diameter and bearing size. If too loose, crankshaft may need grinding and oversized bearings installed.
11. 11

    Final bearing installation and torque
    Once proper clearance is verified with Plastigage, remove bearings and thoroughly clean all Plastigage residue from bearings and journals using parts cleaner. Install bearing shells in rod and cap, ensuring tangs are properly seated. Lubricate bearings thoroughly with fresh engine oil or assembly lube. Lubricate crankshaft journal with engine oil. Carefully install piston/rod assembly into cylinder bore using ring compressor, ensuring rod orientation mark faces correct direction (typically toward front of engine). Guide rod carefully onto crankshaft journal. Install rod cap with orientation marks aligned. Install rod bolts and lubricate threads if specified. Torque rod bolts to specification in stages (5.9L Cummins ISB: typically 30 ft-lbs, then 60 ft-lbs, then 60 degrees rotation - verify exact procedure in service manual, as this engine uses torque-to-yield rod bolts that must be replaced). Repeat for all six connecting rods. Repeat for all six connecting rods.
12. 12

    Verify crankshaft rotation and install oil system
    After all connecting rods are installed and torqued, manually rotate crankshaft through at least two complete revolutions to verify smooth rotation with no binding or tight spots. If resistance is felt, stop immediately and investigate cause. Install oil pump with new pickup tube O-ring, ensuring pickup sits at proper depth in oil pan. Prime oil pump by filling with fresh engine oil before installation if possible.
13. 13

    Install oil pan and timing components
    Clean oil pan and block sealing surfaces thoroughly. Install new oil pan gasket using appropriate sealant only if specified by gasket manufacturer. Install oil pan and torque bolts in spiral pattern from center outward to specification (verify exact values with factory service manual — Cummins oil pan bolts vary by size, generally in the 7-18 ft-lbs range). Reinstall timing gears with marks aligned per factory specifications. Install timing cover with new gasket, ensuring crankshaft seal is properly seated. Install harmonic balancer / vibration damper bolts to proper specification (5.9L Cummins is typically approximately 92 ft-lbs — verify exact procedure and whether an angle step applies in the factory service manual).
14. 14

    Reassemble cylinder head area and accessories
    Reinstall fuel injection pump drive gear and fuel injection pump, carefully aligning timing marks. Reinstall rocker arm assemblies in original positions, ensuring pushrods seat properly in lifters. Install valve cover with new gasket. Reinstall intake and exhaust manifolds with new gaskets. Install turbocharger with new mounting gasket and reconnect oil feed and return lines with new crush washers.
15. 15

    Install engine and reconnect systems
    Remove engine from stand and carefully lower into engine bay using hoist, aligning with transmission. Guide input shaft into clutch/torque converter and align engine mounts. Install engine mount bolts and torque to specification. Install all bellhousing bolts and torque properly. Reinstall all accessories, belts, hoses, electrical connections, and fuel lines in reverse order of removal, referring to photos and labels. Install new oil filter and fill with specified diesel engine oil (approximately 12 quarts with filter — verify exact capacity in factory service manual). Fill cooling system with proper 50/50 HOAT coolant mixture (verify total capacity in factory service manual, typically around 28 quarts). Reconnect batteries.

Reassembly

1. Double-check all torque specifications before starting engine, particularly rod bolts and main bearing caps
2. Verify all electrical connections are secure and properly routed
3. Confirm all fluid levels are correct: engine oil, coolant, power steering, transmission
4. Ensure all hose clamps are tight and fuel lines are properly secured without leaks
5. Verify serpentine belt is properly routed and tensioned
6. Check that no tools or rags were left in engine compartment or on engine

Verification

• Before starting, turn engine over by hand using crankshaft bolt to verify smooth rotation through several revolutions
• Prime oil system by cranking engine with fuel shut-off solenoid disconnected until oil pressure registers on gauge
• Start engine and immediately verify oil pressure reaches normal range (10+ psi at idle when warm)
• Listen carefully for any unusual noises such as rod knock, excessive valve train noise, or grinding sounds - shut down immediately if heard
• Allow engine to idle and warm to operating temperature while monitoring for leaks (oil, coolant, fuel)
• Check for proper coolant circulation and verify thermostat opens (upper radiator hose becomes hot)
• After reaching operating temperature, perform initial test drive monitoring oil pressure, temperature, and listening for abnormal sounds
• After 20-30 minutes of operation, shut down and allow to cool briefly, then check oil level and inspect for any new leaks
• Re-check all accessible fastener torques after initial run cycle
• Perform first oil change at 500 miles, then follow normal service intervals

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