Complete replacement of a single piston in the AMC 390ci V8 engine, requiring engine disassembly including cylinder head removal, connecting rod removal, and installation of new piston assembly.

Warnings

Tools required

Parts

• Piston assembly with rings and wrist pin × 1 — Use OEM specification for 390ci V8
• Connecting rod bearings (pair) × 1 — Standard or appropriate oversize
• Cylinder head gasket × 1 — Use OEM specification
• Intake manifold gasket set × 1 — Use OEM specification
• Exhaust manifold gaskets × 1 — Use OEM specification
• Valve cover gasket × 1 — Use OEM specification
• Timing cover gasket × 1 — Use OEM specification
• Oil pan gasket × 1 — Use OEM specification
• Harmonic balancer seal × 1 — Front crankshaft seal
• Connecting rod bolts × 2 — Replace if stretched or per manufacturer
• Head bolts set × 1 — Use OEM specification

Fluids

• SAE 10W-40 engine oil — 5 qt
• Engine coolant (50/50 mix ethylene glycol) — 16 qt

Preparation

1. Position vehicle on level surface and engage parking brake
2. Disconnect negative battery cable
3. Drain engine coolant into appropriate container
4. Drain engine oil and remove oil filter
5. Remove hood for improved access to engine compartment
6. Remove air cleaner assembly and carburetor linkage
7. Label and disconnect all vacuum lines, electrical connections, and coolant hoses
8. Remove alternator, power steering pump, and accessories as needed for access
9. Remove distributor after marking position for reassembly
10. Identify which cylinder requires piston replacement and determine if it is on the left or right bank

Procedure

1. 1

   Remove intake and exhaust manifolds
   Disconnect fuel line and carburetor. Remove intake manifold bolts in reverse of tightening sequence (from ends working toward center). Remove exhaust manifold from the cylinder bank requiring service. Keep all bolts organized by location.
2. 2

   Remove valve cover and rocker assembly
   Remove valve cover from the affected cylinder bank. Remove rocker arm shaft assembly bolts evenly to prevent warping. Lift off rocker arm assembly as a complete unit. Remove pushrods and store in order for reinstallation in same locations.
3. 3

   Remove cylinder head
   Remove cylinder head bolts in reverse of tightening sequence (from ends working toward center). Use a hoist or assistant to carefully lift cylinder head off the block. Place head on wood blocks with combustion chambers facing up. Inspect head gasket for failure pattern to confirm piston damage cause.
4. 4

   Prepare for piston removal
   Rotate crankshaft to bring the affected piston to top dead center. Use ridge reamer to carefully remove any cylinder wall ridge at the top of the bore. Remove ridge completely but avoid removing parent cylinder wall material. Clean any debris from cylinder.
5. 5

   Remove oil pan for connecting rod access
   Support engine with hoist or fixture. Remove engine mount bolts and raise engine approximately 2-3 inches. Remove oil pan bolts and carefully separate oil pan from block using gasket scraper if needed. Remove oil pump pickup tube if it obstructs access to connecting rod.
6. 6

   Remove connecting rod and piston assembly
   Mark connecting rod and cap with cylinder number using punch marks on non-bearing surface. Remove connecting rod cap nuts or bolts. Remove cap and lower bearing shell, keeping them together. Install short lengths of rubber hose over rod bolts to protect crankshaft journal. Push piston and rod assembly up and out through top of cylinder bore. Keep rod cap and bearings with the removed assembly.
7. 7

   Inspect and measure cylinder bore
   Clean cylinder bore thoroughly with solvent and lint-free cloth. Use telescoping bore gauge or inside micrometer to measure cylinder diameter at top, middle, and bottom in two directions (parallel and perpendicular to crankshaft). Record measurements. Compare to AMC 390 specification of 4.165 inch standard bore. If wear exceeds 0.003 inch taper or 0.002 inch out-of-round, cylinder requires honing or boring.
8. 8

   Inspect crankshaft journal
   Clean connecting rod journal on crankshaft with solvent. Inspect for scoring, heat discoloration, or damage. Measure journal diameter with outside micrometer. Standard diameter is 2.7485-2.7495 inches. If journal is damaged or out of specification, crankshaft requires machining and undersize bearings.
9. 9

   Prepare new piston assembly
   If reusing connecting rod, thoroughly clean and inspect for cracks using magnetic particle inspection or dye penetrant. Install new piston on connecting rod with wrist pin, ensuring pin retainers are fully seated. Orient piston notch or mark toward front of engine. Verify piston-to-bore clearance using measurements: subtract piston skirt diameter from cylinder bore diameter. Clearance should be 0.0010-0.0018 inch for AMC 390.
10. 10

    Install and gap piston rings
    Clean ring grooves thoroughly using ring groove cleaner. Install rings starting with oil control ring (bottom), then lower compression ring, then upper compression ring. Gap each ring by placing it in cylinder bore 1 inch from top and measuring gap with feeler gauge. File ring ends as needed to achieve 0.010-0.020 inch gap for compression rings and 0.015-0.055 inch for oil rings. Stagger ring gaps 120 degrees apart.
11. 11

    Install piston and connecting rod assembly
    Lubricate piston rings, piston skirt, and cylinder bore with engine assembly lube. Ensure ring gaps are properly staggered. Install rubber hose over rod bolts. Compress piston rings using ring compressor, ensuring all rings are fully compressed. Orient piston notch toward front of engine. Gently tap piston into bore using wooden hammer handle while supporting connecting rod. Guide rod carefully onto crankshaft journal without contacting cylinder wall.
12. 12

    Install connecting rod bearings and cap
    Wipe crankshaft journal clean and dry. Install new upper bearing shell in connecting rod, ensuring tang engages slot. Lubricate bearing with engine assembly lube. Install lower bearing shell in rod cap. Place Plastigage strip across full width of journal. Install rod cap in correct orientation matching punch marks. Install new rod bolts or nuts and tighten to 35 ft-lb initially (final torque will be verified).
13. 13

    Check bearing clearance
    Remove connecting rod cap carefully without rotating crankshaft. Measure Plastigage width at widest point using scale on Plastigage envelope. Clearance should be 0.0010-0.0025 inch for AMC 390. If clearance is incorrect, determine cause before proceeding. Remove Plastigage material completely from bearing and journal.
14. 14

    Final connecting rod installation
    Relubricate bearing with engine assembly lube. Install rod cap in correct orientation. Install rod bolts and tighten in stages: first to 15 ft-lb, then 30 ft-lb, then final specification of 45-50 ft-lb in multiple passes. If using torque-to-yield bolts, follow AMC specification for angle tightening. Verify crankshaft rotates freely by hand after installation.
15. 15

    Reinstall oil pan and cylinder head
    Clean all gasket surfaces thoroughly. Install new oil pan gasket and reinstall oil pan, tightening bolts to 10-12 ft-lb in cross pattern. Lower engine onto motor mounts and reinstall mount bolts. Clean cylinder head and block surfaces. Install new head gasket with marking facing up. Position cylinder head and install new head bolts finger tight. Torque head bolts in proper sequence (center outward) in three stages: 50 ft-lb, 75 ft-lb, then final torque of 100-105 ft-lb.

Reassembly

1. Install pushrods in original locations, ensuring they seat properly in lifters
2. Install rocker arm assembly and torque bolts evenly to 19-21 ft-lb
3. Adjust valves to specification: 0.012 inch intake and 0.016 inch exhaust (cold)
4. Install valve cover with new gasket, tightening bolts to 4-5 ft-lb
5. Install intake and exhaust manifolds with new gaskets using proper torque sequence
6. Reinstall distributor in marked position and set initial timing to 5 degrees BTDC
7. Reconnect all vacuum lines, electrical connections, coolant hoses, and linkages
8. Install all accessories including alternator, power steering pump, and belts
9. Install new oil filter and fill engine with specified oil to proper level
10. Fill cooling system with proper coolant mixture
11. Reinstall air cleaner assembly and reconnect battery

Verification

• Perform initial engine start and allow to idle, monitoring for unusual noises or oil pressure issues
• Check for oil leaks at pan gasket and coolant leaks at head gasket and manifolds
• Allow engine to reach operating temperature and verify cooling system function
• Recheck valve adjustment after engine reaches operating temperature
• Perform compression test on all cylinders; repaired cylinder should read within 10% of others (typically 140-160 PSI)
• Road test vehicle under light load initially, gradually increasing load over first 100 miles
• After 500 miles, retorque cylinder head bolts to specification with engine cold
• Change engine oil and filter after 500 mile break-in period

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