Crankshaft R&R

Complete removal and reinstallation of the crankshaft, requiring engine removal from vehicle and full disassembly of rotating assembly.

Warnings

Tools required

Parts

• Crankshaft main bearing set (standard or oversized as needed) × 1 — Use OEM specification or equivalent
• Connecting rod bearing set (standard or oversized as needed) × 1 — Use OEM specification or equivalent
• Rear main seal × 1 — Use OEM specification
• Front main seal × 1 — Use OEM specification
• Oil pan gasket × 1 — Use OEM specification
• Timing cover gasket × 1 — Use OEM specification
• Intake manifold gasket set × 1 — Use OEM specification
• Exhaust manifold gaskets × 2 — Use OEM specification
• Head gasket set × 1 — Use OEM specification if heads removed
• Main bearing cap bolts × 1 — Use OEM specification
• Rod bearing cap bolts × 1 — Use OEM specification if replacing
• Engine oil × 1 — 5W-30 or 10W-30
• Oil filter × 1 — Use OEM specification
• Coolant × 1 — Ethylene glycol antifreeze

Fluids

• Engine oil (5W-30 or 10W-30) — 5 qt
• Engine coolant (ethylene glycol antifreeze) — 16 qt

Preparation

1. Disconnect negative battery cable and remove battery from vehicle
2. Drain engine oil completely and remove oil filter
3. Drain cooling system at radiator petcock and engine block drain plugs
4. Remove hood and set aside on padded surface
5. Remove air cleaner assembly and disconnect all vacuum lines, labeling for reassembly
6. Disconnect throttle linkage, kickdown linkage, and return springs from carburetor
7. Disconnect fuel line at fuel pump and plug line to prevent spillage
8. Remove radiator hoses, heater hoses, and transmission cooler lines
9. Remove radiator and shroud assembly
10. Disconnect all electrical connections from engine including alternator, starter, temperature sender, and oil pressure sender
11. Mark and disconnect spark plug wires, then remove distributor cap and distributor
12. Raise vehicle on lift or support safely on jack stands
13. Disconnect exhaust pipes at manifolds
14. Remove starter motor
15. Mark flexplate to torque converter relationship, remove converter bolts, and push converter back into transmission
16. Remove transmission bellhousing to engine block bolts
17. Support transmission with jack and remove transmission mount if necessary
18. Remove motor mount bolts from frame brackets
19. Attach engine hoist with chains to intake manifold lifting points, taking up slack but not lifting
20. Verify all connections, hoses, and wiring are disconnected from engine

Procedure

1. 1

   Remove engine from vehicle
   Carefully lift engine forward and upward to separate from transmission. Guide engine clear of radiator support and engine bay. Once clear, lower onto engine stand and secure at bellhousing bolt holes. Remove lifting chains and rotate engine to convenient working position.
2. 2

   Remove external components
   Remove intake manifold, carburetor, exhaust manifolds, alternator brackets, power steering pump and brackets, fuel pump, water pump, harmonic balancer using puller, and timing cover. Remove oil pan and oil pump assembly. Mark and remove all accessory drive components.
3. 3

   Inspect cylinder bores and remove ridge
   Rotate engine so cylinders are accessible. Check for ridge at top of cylinder bores. If ridge is present, use ridge reamer to remove carefully, ensuring no metal shavings fall into crankcase. Stuff clean rags into cylinders during reaming. Remove rags and clean thoroughly before proceeding.
4. 4

   Mark and remove connecting rods
   Rotate crankshaft to position each connecting rod at bottom dead center. Using permanent marker or punch, mark each rod and cap with cylinder number (1-8) and orientation. Remove rod cap bolts and carefully remove caps, keeping caps matched with their rods. Push pistons up into cylinders using wooden hammer handle. Install rod caps back on rods loosely to prevent mixing.
5. 5

   Remove main bearing caps
   Mark each main bearing cap with its position number (1-5, front to rear) and orientation arrow pointing toward front of engine. Remove main bearing cap bolts in sequence from outer caps working toward center. Note that cap #5 (rear) retains rear main seal. Carefully remove all main bearing caps and keep in order.
6. 6

   Remove crankshaft
   With all main caps removed, carefully lift crankshaft straight up and out of block. Use assistance as 390 crankshaft weighs approximately 60-70 lbs. Place crankshaft on clean padded surface or in crankshaft support stand. Remove upper main bearings from block by rotating bearing tabs out of block saddles.
7. 7

   Inspect and measure crankshaft
   Thoroughly clean all journals with solvent and lint-free cloth. Inspect all main and rod journals for scoring, discoloration, or damage. Using micrometer, measure all main journals and rod journals in multiple positions (90 degrees apart) and locations to check for taper and out-of-round. Standard main journal diameter is 2.7474-2.7489 inches. Standard rod journal diameter is 2.0934-2.0955 inches. Measure crankshaft endplay surfaces. If journals are more than 0.001 inch out-of-round or tapered, crankshaft requires machining.
8. 8

   Inspect block bearing saddles
   Clean all main bearing saddles thoroughly in block and caps. Inspect for damage, scoring, or cracks. Measure main bearing saddle bores with inside micrometers or bore gauge to ensure proper dimensions. Check block deck for warping if heads were removed. Main bearing bore should measure 2.9989-3.0005 inches with caps installed and torqued.
9. 9

   Install upper main bearings and prepare block
   Install new upper main bearings into block saddles, ensuring bearing tabs engage notches in block. Bearings should be installed dry for initial fitment. Do not force bearings. Ensure oil holes in bearings align with oil passages in block. Verify all bearing surfaces are completely clean and free of debris.
10. 10

    Check bearing clearances with Plastigage
    Place strip of Plastigage on each main journal parallel to crankshaft centerline. Carefully lower crankshaft into position on upper bearings. Install lower bearing shells (dry) into main caps. Install main caps in correct positions with arrows pointing forward. Install and torque main cap bolts to manufacturer specification (typically 90-100 ft-lbs for 390 AMC, consult service manual). Do NOT rotate crankshaft with Plastigage installed. Remove main caps and measure width of flattened Plastigage using gauge on package. Proper clearance is 0.001-0.003 inches. Record all measurements.
11. 11

    Install crankshaft with lubricated bearings
    Remove Plastigage completely from all journals. Remove all bearings and apply assembly lubricant or engine oil generously to all bearing surfaces. Reinstall upper bearings in block. Coat crankshaft journals with assembly lube. Carefully install crankshaft into block, supporting evenly. Install lubricated lower bearings into caps. Apply thread sealer to main cap bolts if specified. Install main caps in correct order and orientation.
12. 12

    Torque main bearing caps and check endplay
    Torque main bearing cap bolts to specification in proper sequence, typically from center outward (cap 3, then 2 and 4, then 1 and 5). Without specification, use 90-100 ft-lbs and verify with service manual. Rotate crankshaft to ensure it turns freely without binding. Install dial indicator against crankshaft end. Pry crankshaft fully forward and zero indicator. Pry crankshaft rearward and read endplay. Specification is typically 0.004-0.008 inches. If excessive, check thrust bearing (usually center main #3).
13. 13

    Install connecting rod and piston assemblies
    Lubricate cylinder walls with engine oil. Compress piston rings with ring compressor. Orient pistons with valve reliefs toward intake side (if directional). Guide connecting rod through bottom of cylinder, installing piston into cylinder with ring compressor seated against block deck. Tap piston gently with wooden hammer handle until it enters bore. Guide connecting rod onto crankshaft journal. Install lubricated rod bearings and caps in correct orientation matching numbered markings. Torque rod bolts to specification (typically 45-50 ft-lbs). Repeat for all cylinders.
14. 14

    Install rear main seal
    Install upper rear main seal half into block groove, ensuring seal lip faces forward toward front of engine. Apply small amount of RTV sealant to corners where seal meets block. Install lower seal half into rear main cap groove. Apply thin bead of RTV to cap mating surface. Ensure seal is properly seated before installing cap.
15. 15

    Reinstall timing components and external parts
    Install timing chain and gears ensuring timing marks align per factory specification. Install timing cover with new gasket. Install harmonic balancer using installation tool, not by hammering. Install oil pump and prime oiling system using primer tool and drill. Install oil pan with new gasket. Reinstall all external components in reverse order of removal. Install new front main seal in timing cover.

Reassembly

1. Reinstall engine into vehicle by reversing removal procedure, ensuring motor mounts align properly
2. Reconnect transmission to engine and torque bellhousing bolts to specification
3. Align torque converter marks and install converter bolts
4. Reconnect exhaust pipes using new gaskets
5. Reinstall starter motor and all electrical connections
6. Reconnect all vacuum lines, fuel lines, throttle linkage per preparation labels
7. Install radiator, hoses, and refill cooling system with fresh coolant
8. Fill engine with fresh oil and new oil filter
9. Reinstall distributor in original position and reconnect spark plug wires in firing order (1-8-4-3-6-5-7-2)
10. Reinstall air cleaner assembly and hood

Verification

• Prime oil system by removing distributor and using oil pump primer tool until oil pressure registers on gauge
• Verify all fluid levels are correct including oil and coolant
• Double-check all electrical connections, vacuum lines, and throttle linkage operation
• Start engine and monitor oil pressure immediately - should register within 5 seconds
• Listen for abnormal noises including knocking, ticking, or grinding which may indicate bearing problems
• Allow engine to warm to operating temperature and check for leaks at all gasket surfaces
• Monitor oil pressure at idle (should be minimum 10 psi) and at 2000 rpm (should be 35-60 psi)
• Verify proper ignition timing and adjust as necessary
• Road test vehicle under light load initially, gradually increasing load while monitoring for unusual noises or vibrations
• Change oil and filter after 500 miles of break-in period

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