Valve Adjustment

Adjust valve lash on the AMC 390ci V8 engine to proper specifications using feeler gauges to ensure optimal valve train performance and engine longevity.

Warnings

Tools required

Parts

• Valve cover gaskets × 2 — Use OEM specification or cork/rubber composite
• Valve cover bolt grommets × 12 — Use OEM specification
• Gasket sealer (non-hardening) × 1 — Permatex Aviation Form-A-Gasket or equivalent

Preparation

1. Ensure engine is completely cold (preferably overnight)
2. Disconnect negative battery cable
3. Remove air cleaner assembly and set aside
4. Disconnect any vacuum lines, breather hoses, or wiring attached to valve covers
5. Label and disconnect spark plug wires from both banks
6. Mark firing order and cylinder numbers for reference if needed

Procedure

1. 1

   Remove valve covers
   Remove the valve cover retaining bolts from both valve covers. Carefully lift valve covers off the cylinder heads. If covers are stuck, gently tap with a rubber mallet. Remove old gaskets and grommets from valve covers and clean all mating surfaces thoroughly with gasket scraper and solvent. Inspect valve covers for damage or warping.
2. 2

   Inspect valve train components
   Visually inspect all rocker arms, pushrods, and valve tips for wear, scoring, or damage. Check that all rocker arm pivot balls are secure and not excessively worn. Look for any broken valve springs or bent pushrods. Replace any damaged components before proceeding with adjustment.
3. 3

   Position crankshaft for cylinder #1 TDC compression
   Rotate the engine clockwise using a socket on the crankshaft bolt until the timing mark on the harmonic balancer aligns with the TDC mark on the timing cover. Verify cylinder #1 is on compression stroke by checking that both intake and exhaust rocker arms have clearance (both valves closed). If not, rotate engine one complete revolution (360 degrees) to achieve TDC compression on cylinder #1.
4. 4

   Adjust valves for cylinder #1
   With cylinder #1 at TDC compression, locate the intake and exhaust rocker arms for cylinder #1 (front of right bank). Loosen the rocker arm adjusting nut while holding the pushrod to prevent it from turning. Slowly tighten the adjusting nut while rotating the pushrod with your fingers until you feel resistance (zero lash). Once zero lash is achieved, tighten the adjusting nut an additional 1/2 to 1 full turn (per AMC specification for hydraulic lifter preload). This compresses the lifter plunger to the proper operating position. Repeat for both intake and exhaust valves on cylinder #1.
5. 5

   Follow firing order sequence for remaining cylinders
   The AMC 390 V8 firing order is 1-8-4-3-6-5-7-2. Rotate the crankshaft clockwise 90 degrees (1/4 turn) at a time, following the firing order sequence. After each 90-degree rotation, adjust the valves for the next cylinder in the firing order that reaches TDC compression. Continue pattern: after cylinder #1, rotate 90° and adjust cylinder #8, rotate 90° and adjust cylinder #4, and so on through the complete firing order until all 16 valves are adjusted.
6. 6

   Verify all adjustments
   After completing all valve adjustments, rotate the engine two complete revolutions and recheck several random valve adjustments to ensure they maintained proper lash. Verify all rocker arm adjusting nuts are secure and no pushrods are loose or binding. Check that all rocker arms move smoothly through their full travel range.
7. 7

   Prepare valve covers for reinstallation
   Install new valve cover gaskets onto the valve covers. Install new grommets on all valve cover bolts. Apply a thin bead of non-hardening gasket sealer to the cylinder head corners where the intake manifold meets the head (common leak points on AMC V8 engines). Do not use excessive sealer as it can squeeze into the engine.
8. 8

   Install valve covers
   Carefully position valve covers onto cylinder heads, ensuring gaskets remain properly seated. Install all valve cover bolts with grommets finger-tight first to ensure even gasket compression. Tighten bolts in a cross-pattern sequence starting from the center and working outward. Torque valve cover bolts to 35-45 in-lbs (approximately 3-4 ft-lbs) - do not overtighten as this can distort covers and cause leaks.

Reassembly

1. Reconnect all vacuum lines, breather hoses, and wiring to valve covers
2. Reinstall spark plug wires in correct firing order sequence
3. Reinstall air cleaner assembly with all connections
4. Reconnect negative battery cable

Verification

• Start engine and listen for abnormal valve train noise such as ticking, clicking, or tapping
• Allow engine to reach normal operating temperature and verify no oil leaks from valve covers
• Engine should idle smoothly without excessive valve train noise
• Recheck valve cover bolt tightness after initial heat cycle if any seepage is observed
• Test drive vehicle and verify normal engine performance across RPM range

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