Engine Rebuild

Complete disassembly, inspection, machining, and rebuild of the AMC 390ci V8 engine including removal and reinstallation in the vehicle.

Warnings

Tools required

Parts

• Complete engine gasket set (AMC 390) × 1 — Use OEM specification
• Piston and ring set (std or oversized as measured) × 1 — Use OEM specification
• Main bearing set (std or oversized as measured) × 1 — Use OEM specification
• Rod bearing set (std or oversized as measured) × 1 — Use OEM specification
• Camshaft bearing set (AMC 390) × 1 — Use OEM specification
• Timing chain and gear set (AMC V8) × 1 — Use OEM specification
• Oil pump (AMC 390) × 1 — Use OEM specification
• Valve stem seals (intake and exhaust) × 16 — Use OEM specification
• Camshaft (if worn beyond specification) × 1 — Use OEM specification
• Lifter set (if replacing camshaft) × 1 — Use OEM specification
• Freeze plugs (core plugs) complete set × 1 — Use OEM specification
• Oil filter × 1 — Use OEM specification
• Harmonic balancer bolt × 1 — Use OEM specification
• Head bolts (if reusing shows any stretching) × 16 — Use OEM specification
• Main bearing cap bolts (if damaged) × 10 — Use OEM specification
• Rod bolts (if damaged or stretched) × 16 — Use OEM specification
• Engine assembly lube × 1 — Use OEM specification
• Thread sealant (for freeze plugs and bolts) × 1 — Use OEM specification
• RTV silicone gasket maker × 1 — Use OEM specification

Fluids

• Engine oil (10W-30 or 10W-40) — 5 qt
• Engine coolant (50/50 mix) — 16 qt

Preparation

1. Disconnect negative battery cable and remove battery
2. Drain all engine coolant from radiator and block into appropriate containers
3. Drain all engine oil into appropriate container
4. Remove hood and set aside safely (mark hinge locations for reinstallation)
5. Remove air cleaner assembly and carburetor linkage
6. Disconnect all electrical connections from engine (alternator, starter, temperature sender, oil pressure sender)
7. Disconnect fuel line at fuel pump and plug line
8. Remove radiator, fan shroud, fan, and water pump drive belt
9. Remove power steering pump and bracket (if equipped) and secure aside without disconnecting hoses
10. Remove exhaust manifolds from cylinder heads
11. Label and disconnect all vacuum lines
12. Remove bellhousing-to-engine bolts and separate transmission from engine (support transmission with jack)
13. Position engine hoist and attach lifting chain to engine lift brackets
14. Remove motor mount bolts from frame brackets
15. Clear workspace around vehicle for engine stand and disassembly area

Procedure

1. 1

   Remove engine from vehicle
   Verify all connections are disconnected. Carefully lift engine forward and upward to clear transmission input shaft, then lift engine out of vehicle. Immediately mount engine to engine stand using bellhousing bolt holes. Secure engine stand in stable position.
2. 2

   External component removal and documentation
   Remove all external components: intake manifold, carburetor, distributor (mark position before removal), fuel pump, water pump, thermostat housing, cylinder heads, valve train components (pushrods and lifters in order), oil pan, oil pump and pickup, timing chain cover, harmonic balancer using puller, timing chain and gears (note alignment marks). Photograph and label everything for reference during reassembly.
3. 3

   Cylinder head disassembly and measurement
   Use valve spring compressor to remove valve springs, keepers, retainers, and valves from both heads. Keep valves in order by cylinder. Measure valve stem diameter, valve length, and valve guide wear. Check head surface for warpage using straight edge and feeler gauge (maximum warpage 0.007 inches). Measure combustion chamber volume if performance rebuild. Send heads to machine shop for valve job, guide work if needed, and surface milling if warped.
4. 4

   Block disassembly and inspection
   Remove ridge at top of cylinders using ridge reamer if cylinders will be reused. Remove piston and rod assemblies by removing rod cap bolts and pushing pistons out top of block (keep rods and caps matched and numbered). Remove main bearing caps (mark orientation and position). Remove crankshaft. Remove camshaft carefully by threading long bolts into cam to use as handle. Remove all freeze plugs using appropriate puller or punch method. Remove cam bearings using cam bearing removal/installation tool.
   ⚠Camshaft must be removed carefully to avoid damaging cam bearings or cam lobes on block edges.
5. 5

   Component measurement and machine shop preparation
   Measure all cylinder bores at top, middle, and bottom in two directions for taper and out-of-round (maximum taper 0.010 inches, maximum out-of-round 0.005 inches). Measure crankshaft main and rod journals with micrometer for wear and out-of-round (maximum out-of-round 0.001 inches). Check crankshaft runout with dial indicator (maximum 0.002 inches TIR). Measure camshaft lobe lift and journal diameter. Inspect all components for cracks, scoring, or damage. Create list of required machine work: cylinder boring/honing (specify oversize), crankshaft grinding (specify undersize), deck surface milling, align honing if needed.
6. 6

   Block cleaning and preparation
   After return from machine shop, thoroughly clean block in hot tank or with degreaser. Clean all oil galleries using oil galley brushes and compressed air. Flush block multiple times with hot soapy water, then rinse and dry immediately with compressed air. Install new cam bearings using cam bearing installation tool, ensuring oil holes align with block oil passages. Install new freeze plugs using freeze plug installer and appropriate sealant. Tap in evenly until seated. Chase all threads with tap set. Final wipe down all machined surfaces with lint-free cloth and light oil.
   ⚠Cam bearing oil holes MUST align with block oil passages or engine will fail immediately. Verify alignment before final seating.
7. 7

   Crankshaft installation and main bearing clearance check
   Liberally coat all main bearing surfaces with engine assembly lube. Install upper main bearings in block (without bearing tabs in oil grooves). Install lower main bearings in caps. Place crankshaft in block. Install Plastigage on each main journal. Install main caps in correct orientation and location. Torque main cap bolts to specification (consult AMC service manual: typically 100 ft-lb for 390). Remove caps and measure Plastigage (clearance should be 0.001-0.003 inches). If clearance correct, remove Plastigage residue, reapply assembly lube, reinstall caps and torque to specification. Check crankshaft endplay with dial indicator (specification 0.003-0.008 inches).
   ℹ️Do NOT rotate crankshaft with Plastigage installed or measurement will be invalid.
8. 8

   Camshaft and timing gear installation
   Coat all camshaft lobes and journals liberally with engine assembly lube or dedicated cam break-in lube. Carefully slide camshaft into block, rotating slowly to avoid damaging bearings. Install camshaft thrust plate if equipped. Install crankshaft timing gear using press or installation tool (heat gear to 250°F for easier installation). Install camshaft timing gear, aligning timing marks per AMC specification (mark on cam gear aligns with mark on crank gear). Install timing chain with slack on right side. Verify timing marks align correctly. Install new lifters (if replacing camshaft, new lifters are mandatory), coating with assembly lube.
   ⚠New camshaft requires new lifters and specific break-in procedure or premature failure will occur.
9. 9

   Piston and connecting rod assembly
   Install new piston rings on pistons using ring expander tool. Position ring end gaps 120 degrees apart, never aligned with piston pin or thrust surfaces. Install rod bearings in rods and caps (match numbered sets). Liberally coat piston, rings, rod bearings, and cylinder walls with assembly lube. Install ring compressor on piston. Orient piston notch or marking toward front of engine. Insert rod and piston assembly into correct cylinder, tapping piston through ring compressor with wooden hammer handle. Guide rod onto crankshaft journal. Install rod cap in correct orientation (numbers must match and face same direction). Install Plastigage on rod journal, install cap, torque to specification (consult AMC service manual: typically 45-50 ft-lb). Check clearance (0.001-0.003 inches). If correct, remove Plastigage, reapply lube, reinstall and torque. Repeat for all eight cylinders.
10. 10

    Oil system installation
    Install new oil pump with pickup tube, ensuring pickup is correct distance from oil pan floor (typically 1/4 to 3/8 inch clearance). Prime oil pump by filling with petroleum jelly or assembly lube and rotating pump shaft. Install oil pan gasket using appropriate gasket sealer or RTV as specified. Install oil pan and torque bolts in spiral pattern from center outward to specification. Install harmonic balancer using installation tool (never hammer onto crankshaft). Install new balancer bolt with thread sealant and torque to specification (consult AMC service manual: typically 80-90 ft-lb). Install timing chain cover with new gasket and seal.
11. 11

    Cylinder head installation
    Install new head gaskets on block, ensuring correct orientation and alignment with dowel pins. Carefully position cylinder heads on block. Install head bolts with light oil on threads and under bolt heads. Following AMC 390 bolt tightening sequence (consult service manual - typical pattern starts center and works outward), torque head bolts in three progressive steps to final specification (consult AMC service manual: typically 95-105 ft-lb). Allow to sit 30 minutes, then re-torque in sequence. Install pushrods in original locations, coat with assembly lube. Install rocker arms and shafts assembly, torque to specification.
    ⚠Head bolt torque sequence and multi-step torquing is critical to prevent head gasket failure and head warping.
12. 12

    Valve train adjustment and external component installation
    Adjust valve lash according to AMC specification (for hydraulic lifters, typically zero lash plus 1/2 to 1 turn). Install intake manifold with new gaskets and appropriate sealant at end rails, torque in proper sequence to specification. Install exhaust manifolds with new gaskets. Install distributor in marked position, ensuring oil pump drive engages. Install fuel pump with new gasket. Install water pump with new gasket. Install all remaining external components: alternator, power steering pump, brackets, accessory drive belts.
13. 13

    Engine installation into vehicle
    Attach lifting chain to engine lift brackets. Carefully lower engine into engine bay, guiding onto motor mounts and aligning with transmission. Install motor mount bolts finger-tight. Align engine to transmission bellhousing, carefully engaging input shaft with clutch disc or torque converter. Install bellhousing bolts and torque to specification. Torque motor mount bolts to specification. Remove lifting chain and engine hoist.
14. 14

    Reconnection of all systems
    Reconnect exhaust manifolds to exhaust system. Reconnect all electrical connections: alternator, starter, temperature sender, oil pressure sender, distributor. Reconnect fuel line to fuel pump. Install power steering pump and adjust belt tension. Install radiator, connect hoses, install fan and fan shroud. Reconnect all vacuum lines per labels. Install carburetor linkage. Install air cleaner assembly. Reinstall battery and connect cables.
15. 15

    Initial startup and break-in procedure
    Fill engine with break-in oil (or specified oil with ZDDP additive for flat tappet cam) and new oil filter. Fill cooling system with 50/50 coolant mix. Verify all connections secure. Prime oil system by disconnecting coil wire and cranking engine until oil pressure registers. Reconnect coil wire. Start engine and immediately bring to 2000-2500 RPM. If new camshaft installed, maintain 2000-2500 RPM for 20-30 minutes for cam break-in. Monitor oil pressure, coolant temperature, and check for leaks. After break-in period, allow to idle and recheck all systems. Perform initial timing adjustment. Road test vehicle under light load, avoiding full throttle for first 500 miles. Change oil and filter at 500 miles.
    ⚠️New camshaft break-in requires immediate startup and sustained 2000-2500 RPM for 20-30 minutes or cam failure will occur. Have fire extinguisher ready.
    ⚠Monitor temperature gauge closely during initial startup. Shut down immediately if overheating occurs.

Reassembly

1. Hood reinstallation should use marked hinge positions for proper alignment
2. All gaskets must be replaced with new components - never reuse head gaskets, intake gaskets, or oil pan gaskets
3. Torque all fasteners to AMC factory specifications using proper sequence where applicable
4. Adjust drive belt tension to proper specification (typically 1/2 inch deflection with moderate pressure)
5. Bleed cooling system of air pockets by running engine to operating temperature with radiator cap off, then top off coolant

Verification

• Oil pressure should register 40-60 PSI at 2000 RPM when warm with proper grade oil
• Coolant temperature should stabilize at 180-195°F with thermostat functioning properly
• No oil, coolant, or fuel leaks present after 30-minute break-in run
• Engine should idle smoothly at 600-800 RPM after warm-up with no unusual noises
• Exhaust smoke should be minimal (slight haze normal during first few minutes with new rings)
• All cylinder compression readings should be within 10% of each other and meet AMC specification (typically 140-160 PSI)
• Vacuum reading at idle should be steady at 17-21 inches Hg
• After 500-mile break-in period and oil change, re-inspect for leaks and verify all fluid levels

More procedures for this vehicle