Short Block Replacement

Complete replacement of the short block assembly on a 5.9L Cummins diesel engine, including removal of cylinder head, oil pan, timing components, and all internal rotating assembly.

Warnings

Tools required

Parts

• Short block assembly (5.9L Cummins) × 1 — Use OEM or verified remanufactured unit
• Head gasket set × 1 — Use OEM specification
• Connecting rod bolts (if reusing rods) × 12 — TTY - replace with OEM
• Main bearing cap bolts × 14 — TTY - replace with OEM
• Oil pan gasket × 1 — Use OEM specification
• Front cover gasket × 1 — Use OEM specification
• Rear main seal × 1 — Use OEM specification
• Front crankshaft seal × 1 — Use OEM specification
• Oil pump (if not included) × 1 — Use OEM specification
• Timing gear set (if not included) × 1 — Use OEM specification
• Oil filter × 1 — Use OEM specification
• Fuel filter × 1 — Use OEM specification
• Oil drain plug crush washer × 1 — Use OEM specification
• Flywheel bolts (if TTY) × 8 — Verify TTY requirement
• RTV gasket maker (high-temp) × 2 — Use OEM approved sealant

Fluids

• 15W-40 diesel engine oil — 12 qt
• Ethylene glycol 50/50 coolant — 28 qt

Preparation

1. Park vehicle on level surface, engage parking brake, and place wheel chocks behind rear wheels
2. Disconnect negative battery cable, then positive battery cable
3. Drain engine oil completely and remove oil filter
4. Drain cooling system from radiator petcock and block drain plugs
5. Remove hood and store in safe location (mark hinge positions for reinstallation)
6. Remove radiator shroud, radiator, intercooler, and all cooling system hoses
7. Relieve fuel system pressure and disconnect fuel supply and return lines
8. Remove air intake system from turbocharger to air filter housing
9. Label and disconnect all electrical connectors from engine (alternator, starter, sensors, injectors, grid heater)
10. Disconnect exhaust system at turbocharger outlet and downpipe
11. Remove drive belts and accessories (alternator, A/C compressor, power steering pump, fan)
12. Support transmission with transmission jack
13. Remove transmission-to-engine bellhousing bolts
14. Attach engine hoist to lifting eyes on cylinder head with appropriate chains or straps
15. Verify all connections are disconnected before attempting engine removal

Procedure

1. 1

   Remove engine from vehicle
   Carefully lift engine while guiding it forward to clear transmission input shaft. Use load leveler to maintain proper angle. Once clear of transmission, lift engine completely out of engine bay. Transfer engine to engine stand and secure at bellhousing mounting points. Rotate engine to convenient working position.
2. 2

   Remove cylinder head assembly
   Remove valve cover and all fuel injector lines. Remove rocker arm assemblies (and pushrods on 12-valve engines; 24-valve SOHC engines have no pushrods). Keep all valvetrain components in order for inspection. Remove cylinder head bolts in reverse of tightening sequence (outside to inside pattern). Carefully lift cylinder head off block using lifting eyes. Inspect head gasket and mating surfaces for damage or warping. Store cylinder head on clean surface with combustion chambers facing up.
3. 3

   Remove front timing cover and components
   Remove crankshaft pulley bolt using impact wrench or flywheel holding tool to prevent rotation. Use harmonic balancer puller to remove crankshaft pulley. Remove timing cover bolts in sequence and carefully pry cover off block. Remove camshaft thrust plate bolts. Verify timing marks are aligned before removal. Remove camshaft gear bolt and use gear puller to remove the timing gears. On 12-valve engines, remove tappets/lifters or secure them before withdrawing the in-block camshaft straight out, supporting it to prevent bearing damage. Follow the correct procedure for your specific 12-valve or 24-valve configuration.
   Torque spec

   Crankshaft Pulley Bolt180 Nm (133 lb-ft)

   Timing Cover Bolts - 8mm25 Nm (18 lb-ft)
4. 4

   Remove oil pan and oil pump
   Remove oil pan bolts in crisscross pattern starting from ends working toward center. Carefully break oil pan gasket seal using rubber mallet or soft pry tool. Lower oil pan and remove from engine. Remove oil pump mounting bolts and withdraw oil pump assembly from block. Remove oil pump pickup tube.
   Torque spec

   Oil Pan Bolt12 Nm (9 lb-ft)

   Oil Pump Bolts12 Nm (9 lb-ft)
5. 5

   Remove connecting rod and piston assemblies
   Rotate crankshaft to position piston at bottom dead center. Mark connecting rod caps and rods with cylinder number and orientation. Remove connecting rod cap bolts (these are TTY and must be replaced). Remove rod caps and push piston/rod assembly up and out of cylinder bore. Store assemblies in order. Repeat for all six cylinders. Inspect pistons, rings, and rod bearings for wear patterns.
   Torque spec

   Connecting Rod Bolts45 Nm (33 lb-ft)
6. 6

   Remove flywheel and rear main seal housing
   Use flywheel holding tool to prevent rotation. Remove flywheel bolts in star pattern (these may be TTY - replace if specified). Remove flywheel and starter ring gear. Remove rear main seal housing bolts and carefully pry housing off block. Remove old rear main seal from housing.
   Torque spec

   Flywheel Bolts95 Nm (70 lb-ft)
7. 7

   Remove main bearing caps and crankshaft
   Mark all main bearing caps with position and directional orientation. Remove main bearing cap bolts (these are TTY and must be replaced). Carefully remove main bearing caps and set aside in order. Verify upper bearing shells are not damaged. Carefully lift crankshaft straight up out of block. Inspect all main and rod journals for scoring, discoloration, or out-of-round condition. Store crankshaft on padded supports.
   Torque spec

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

   Prepare and inspect new short block
   Thoroughly clean new short block assembly. Inspect all machined surfaces for damage. Verify main bearing clearances using Plastigage if bearings are not pre-installed. Check crankshaft endplay with dial indicator (specification 0.003-0.010 inches). Verify cylinder bore finish and measurements. Check deck surface flatness. Ensure all oil passages are clear and plugs are properly installed.
   ⚠If short block does not include rotating assembly, all bearing clearances must be verified before final assembly. Incorrect clearances will cause immediate engine failure.
9. 9

   Install crankshaft and main bearing caps
   Lubricate main bearing surfaces with assembly lube or clean engine oil. Carefully lower crankshaft into block, ensuring it seats properly in all bearings. Install main bearing caps in correct position and orientation. Install NEW main bearing cap bolts and hand-tighten. Torque main cap bolts in stages per the factory Cummins specification (verify exact values for your engine year, typically a multi-stage sequence ending with a torque-angle step) in sequence from center outward. Do NOT rely on a single generic torque value. Verify crankshaft rotates freely after torquing.
   ⚠Main bearing cap bolts are TTY and require torque-plus-angle tightening. Use torque angle gauge for accurate angle measurement. Over-torquing will stretch bolts beyond yield point.
   Torque spec

   Main Bearing Cap Bolts75 Nm (55 lb-ft)
10. 10

    Install piston and connecting rod assemblies
    Install piston ring compressor on first piston. Lubricate cylinder wall, piston, and rings with engine oil. Position piston with orientation marks facing front of engine. Carefully tap piston into cylinder bore using wooden hammer handle. Rotate crankshaft to position rod journal at bottom. Lubricate rod bearing and journal. Install rod cap in correct orientation with NEW connecting rod bolts. Torque rod bolts per the factory Cummins specification for your specific engine (verify exact torque and angle values, which differ between 12-valve and 24-valve engines). Repeat for all cylinders. Verify crankshaft rotates smoothly.
    ⚠Connecting rod bolts are TTY and must be replaced. Follow torque-plus-angle procedure exactly. Ensure rod cap orientation is correct to prevent bearing failure.
    Torque spec

    Connecting Rod Bolts45 Nm (33 lb-ft)
11. 11

    Install camshaft and timing components
    Lubricate camshaft lobes and bearings with assembly lube. Carefully slide camshaft into block, supporting weight to prevent bearing damage. Install camshaft thrust plate with bolts torqued to specification. Install crankshaft timing gear with keyway aligned. Install camshaft timing gear with keyway aligned. Verify timing marks on both gears are aligned properly (typically marks facing each other at 6 o'clock position). Install camshaft gear bolt. Check camshaft endplay with dial indicator (specification typically 0.006-0.010 inches).
    ⚠️Incorrect timing gear alignment will cause catastrophic engine damage on first startup. Double-check timing marks before proceeding.
12. 12

    Install oil pump and oil pan
    Install oil pump pickup tube and torque bolts. Prime oil pump with clean engine oil. Install oil pump assembly and torque mounting bolts to 12 Nm (9 ft-lb). Rotate pump to verify smooth operation. Clean oil pan and block mating surfaces thoroughly. Apply thin bead of RTV sealant to oil pan rail or install new gasket per manufacturer instructions. Install oil pan and torque bolts to 12 Nm (9 ft-lb) in crisscross pattern from center outward. Allow RTV to cure per manufacturer instructions before filling with oil.
    Torque spec

    Oil Pump Bolts12 Nm (9 lb-ft)

    Oil Pan Bolt12 Nm (9 lb-ft)
13. 13

    Install front timing cover and seal
    Install new front crankshaft seal in timing cover using seal driver. Clean timing cover and block mating surfaces. Apply RTV sealant to cover gasket or install new gasket. Position timing cover on block, carefully sliding over crankshaft snout. Install timing cover bolts and torque 8mm bolts to 25 Nm (18 ft-lb) in sequence. Install crankshaft pulley using installation tool. Install pulley bolt and torque to the factory Cummins specification (verify exact value and any torque-angle step for your engine year). Verify pulley is seated flush against timing gear.
    Torque spec

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

    Crankshaft Pulley Bolt180 Nm (133 lb-ft)
14. 14

    Install rear main seal and flywheel
    Install new rear main seal in housing using seal driver. Clean housing and block mating surfaces. Apply RTV sealant to housing mating surface. Install housing and torque bolts evenly. Clean flywheel and crankshaft flange thoroughly. Position flywheel on crankshaft with alignment dowel. Install flywheel bolts and torque to the factory Cummins specification (typically around 101 ft-lb — verify for your specific application) in star pattern. Use flywheel holding tool to prevent rotation during torquing.
    ℹ️Verify whether flywheel bolts are TTY for your specific year. Some applications require replacement bolts.
    Torque spec

    Flywheel Bolts95 Nm (70 lb-ft)
15. 15

    Install cylinder head assembly
    Clean block deck surface thoroughly with gasket scraper. Verify surface is flat and free of debris. Position new head gasket on block with orientation marks visible and facing up. Carefully lower cylinder head onto block, aligning dowel pins. Install head bolts with light oil on threads. Torque head bolts in the factory Cummins sequence and stages for your specific engine (12-valve: staged to spec; 24-valve: TTY torque-plus-angle procedure). Follow the exact factory pattern and values. Install pushrods in original positions. Install pushrods (12-valve only) and rocker arm assemblies, then adjust valve lash per the specification for your specific 12-valve or 24-valve engine. Install valve cover with new gasket.
    ⚠Cylinder head bolt torque sequence is critical. Follow factory torque sequence exactly to prevent head gasket failure. Some bolts may be TTY requiring replacement.
    Torque spec

    Gasket Surface Bolts20 Nm (15 lb-ft)
16. 16

    Reinstall engine in vehicle
    Attach engine hoist to engine on stand. Remove engine from stand. Carefully lower engine into engine bay while aligning with transmission. Use load leveler to maintain proper angle. Guide engine onto transmission input shaft and align bellhousing. Install transmission-to-engine bolts and torque to 55 Nm (41 ft-lb). Remove engine hoist. Reconnect all previously disconnected components in reverse order of removal.
    Torque spec

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

Reassembly

1. Reinstall all accessories (alternator, A/C compressor, power steering pump) with mounting bolts torqued to 47 Nm (35 ft-lb) for critical mounts
2. Reconnect all electrical connectors, ensuring proper seating and locking clips engaged
3. Reconnect fuel supply and return lines with new O-rings
4. Install new fuel filter and prime fuel system
5. Reinstall exhaust system to turbocharger outlet
6. Install all cooling system components (radiator, intercooler, hoses, shroud)
7. Reinstall air intake system from turbocharger to air filter
8. Install drive belts and adjust tension properly
9. Install new oil filter and fill with 12 quarts of 15W-40 diesel engine oil
10. Fill cooling system with 28 quarts of appropriate coolant mixture
11. Install oil drain plug with new crush washer, torqued to 35 Nm (26 ft-lb)
12. Reinstall hood, aligning with previously marked positions
13. Reconnect battery cables (positive first, then negative)

Verification

• Verify all fluid levels are correct (engine oil, coolant, power steering, transmission)
• Double-check all electrical connectors are properly seated
• Verify all hoses and lines are connected with no leaks
• Check that all bolts are torqued to specification and none are missing
• Perform initial engine start: prime fuel system, verify oil pressure within 15 seconds of startup
• Check for fuel, oil, and coolant leaks during initial run
• Allow engine to reach operating temperature and verify proper cooling system operation
• Check for unusual noises, vibrations, or smoke during initial break-in
• Verify charging system operation (14+ volts at idle)
• Perform valve lash adjustment after initial warm-up cycle if required
• Recheck all fluid levels after test drive
• Retorque cylinder head bolts after 500 miles if specified by manufacturer
• Change engine oil and filter after 500-1000 mile break-in period

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