Connecting Rod Bearings

Replace connecting rod bearings on the AMC 390ci V8 engine, requiring removal of pistons from below to access and install new bearing shells.

Warnings

Tools required

Parts

• Connecting rod bearing set (std or appropriate oversize) × 1 — Use OEM specification or matching crankshaft journal size
• Engine oil × 1 — 10W-30 or 10W-40 conventional motor oil
• Oil filter × 1 — Use OEM specification
• Connecting rod bolts (if replacement required) × 1 — AMC 390 V8 rod bolt set
• Oil pan gasket × 1 — AMC 390 V8
• Valve cover gaskets × 2 — AMC 390 V8
• Intake manifold gasket set × 1 — AMC 390 V8
• Exhaust manifold gaskets × 2 — AMC 390 V8
• Oil pump pickup tube O-ring × 1 — Use OEM specification

Fluids

• Engine oil (10W-30 or 10W-40) — 5 qt

Preparation

1. Disconnect negative battery cable
2. Drain engine oil completely into suitable container
3. Remove hood for better access (mark hinge positions)
4. Remove air cleaner assembly and carburetor linkage
5. Label and disconnect all vacuum lines, fuel lines, and electrical connections from engine
6. Remove radiator hoses and transmission cooler lines if equipped
7. Remove radiator and fan shroud
8. Remove alternator, power steering pump, and A/C compressor (if equipped), securing aside without disconnecting hoses
9. Remove distributor (mark position before removal)
10. Remove valve covers
11. Remove intake manifold assembly
12. Remove exhaust manifolds
13. Raise vehicle and support securely on jack stands
14. Remove starter motor
15. Tag all spark plug wires and remove spark plugs

Procedure

1. 1

   Remove oil pan
   Remove oil pan bolts and carefully lower oil pan. You may need to raise engine slightly using engine hoist to gain clearance. Clean all gasket surfaces thoroughly on both oil pan and engine block.
2. 2

   Remove oil pump
   Remove oil pump mounting bolts and lower oil pump assembly with pickup tube. Inspect pump for debris or damage that may indicate bearing failure severity.
3. 3

   Remove cylinder ridge
   Rotate crankshaft to position pistons at bottom dead center. Use ridge reamer to carefully remove ridge at top of each cylinder bore. Follow ridge reamer instructions carefully to avoid gouging cylinder wall. Clean all cuttings from cylinder and crankcase.
4. 4

   Mark connecting rods and caps
   Using number stamps or permanent marker, clearly mark each connecting rod and cap with cylinder number (1-8, front to rear) and orientation (which side faces forward). AMC rods may have factory markings on one side that should face camshaft. Verify all eight rod/cap pairs are marked before proceeding.
5. 5

   Remove connecting rod caps
   Starting with cylinder 1, remove connecting rod cap bolts. Gently tap cap with rubber mallet to break it free if needed, keeping cap with its matching rod. Inspect rod bolt threads for damage or stretching. Place cap bolts back into cap to prevent mixing. Repeat for all eight cylinders, keeping each cap with its rod.
6. 6

   Remove pistons and rods
   Using wooden hammer handle or similar tool, gently push each piston and rod assembly up and out through top of cylinder bore. Protect crankshaft journals by installing short pieces of rubber hose over rod bolts. Remove old bearing shells from rods and caps, noting any unusual wear patterns that indicate alignment or lubrication problems.
7. 7

   Inspect crankshaft journals
   Thoroughly clean all eight connecting rod journals on crankshaft with solvent and lint-free cloths. Inspect each journal for scoring, heat discoloration, or out-of-round condition. Measure each journal with micrometer in multiple locations. Standard journal diameter is 2.7474-2.7489 inches. If journals are tapered, out-of-round more than 0.001", or scored, crankshaft must be removed and reground.
8. 8

   Inspect connecting rods
   Clean all rod and cap bearing surfaces thoroughly. Inspect big end bores for scoring, cracks, or damage. Check small end (piston pin) bushings for wear. Examine rod bolts for thread damage, necking, or stretching. Replace rod bolts if any damage is evident or if this is second use of torque-to-yield bolts.
9. 9

   Install new bearing shells
   Wipe rod and cap bearing seats clean with lint-free cloth. Install new bearing shells (upper and lower halves) into rods and caps, ensuring tang on bearing engages slot in rod or cap. Do not file, scrape, or alter bearings. Install bearings dry for clearance checking. Ensure oil holes in bearing align with oil passages in rod.
10. 10

    Check bearing clearances with Plastigage
    Place strip of Plastigage lengthwise on crankshaft journal parallel to crankshaft centerline. Install rod cap in correct orientation, install bolts, and torque to 30-35 ft-lbs (typical specification for AMC 390, verify with factory manual). Do not rotate crankshaft with Plastigage installed. Remove cap and measure width of flattened Plastigage using scale on package. Clearance should be 0.001-0.003 inches. Record clearance for each rod. If clearance is excessive, next oversize bearings may be required.
11. 11

    Prepare for final assembly
    Remove Plastigage completely from journals and bearings. Clean journals and bearings again with lint-free cloth. Lubricate all eight crankshaft journals liberally with assembly lube or fresh engine oil. Coat new bearing shells with engine oil on both back (shell contact surface) and inside (journal contact surface).
12. 12

    Install pistons and rods
    Install rubber hose protectors over rod bolts. Apply engine oil to piston rings, piston skirts, and cylinder walls. Using piston ring compressor, carefully guide each piston and rod assembly down into its original cylinder bore from top. Ensure any directional markings on piston (often notch or arrow) face front of engine. Guide rod carefully onto crankshaft journal, avoiding contact between rod bolt and journal.
13. 13

    Install and torque connecting rod caps
    Remove rubber hose protectors from rod bolts. Position rod cap on rod in correct orientation (matching marks made during disassembly). Install rod bolts and hand tighten. Torque rod bolts in two stages: first to 30-35 ft-lbs, then final torque to 40-45 ft-lbs. Typical AMC 390 specification is 40-45 ft-lbs final, but verify with factory service manual. After torquing, check that rod has slight side clearance on journal (0.004-0.014 inches typical) using feeler gauge.
14. 14

    Verify crankshaft rotation
    After all eight rods are installed and torqued, manually rotate crankshaft two complete revolutions using breaker bar on crankshaft bolt. Rotation should be smooth without binding or tight spots. Any resistance indicates misalignment, insufficient clearance, or improper assembly requiring immediate investigation.
15. 15

    Reinstall oil pump and pan
    Install new O-ring on oil pump pickup tube. Reinstall oil pump assembly and torque mounting bolts. Clean oil pan and engine block mating surfaces completely. Install new oil pan gasket using light coat of gasket sealer if recommended by gasket manufacturer. Install oil pan and torque bolts in circular pattern from center outward to 15-18 ft-lbs (typical for AMC).

Reassembly

1. Reinstall exhaust manifolds with new gaskets
2. Reinstall intake manifold with new gaskets, torquing in proper sequence from center outward
3. Reinstall distributor in original position, aligning rotor with mark made during removal
4. Reinstall valve covers with new gaskets
5. Reinstall alternator, power steering pump, and A/C compressor
6. Reinstall starter motor
7. Lower vehicle from jack stands
8. Reinstall radiator, fan shroud, and all hoses
9. Reinstall all vacuum lines, fuel lines, and electrical connections per labels
10. Reinstall carburetor linkage and air cleaner
11. Reinstall hood, aligning with marks made during removal
12. Install new oil filter
13. Fill engine with fresh oil to proper level (5 quarts typically)
14. Reconnect negative battery cable

Verification

• Before starting engine, remove all spark plugs and disable ignition. Crank engine with starter for 10-15 seconds to prime oil system and verify oil pressure
• Reinstall spark plugs and reconnect ignition
• Start engine and immediately verify oil pressure on gauge. Pressure should register within 3-5 seconds
• Listen carefully for any unusual knocking, ticking, or rattling sounds that could indicate bearing issues
• Allow engine to reach operating temperature while monitoring for leaks around oil pan and other reassembled components
• Check oil level after engine reaches operating temperature and add if necessary
• Test drive vehicle and monitor oil pressure under various loads and RPM ranges
• After 50-100 miles, recheck oil level and inspect for any leaks. Change oil and filter after 500 miles of break-in period

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