Remove and replace the harmonic balancer (crankshaft damper) on the 390ci V8 engine to eliminate vibration and prevent crankshaft damage.

Warnings

Tools required

Parts

• Harmonic balancer × 1 — Use OEM specification for 390ci V8
• Harmonic balancer bolt × 1 — Recommend replacement - one-time torque fastener
• Crankshaft seal (front) × 1 — Recommended replacement during service
• Radiator hose (lower) if damaged × 1 — Inspect before ordering

Fluids

• Engine coolant — 2 qt

Preparation

1. Park vehicle on level surface and engage parking brake
2. Disconnect negative battery cable
3. Allow engine to cool completely if recently operated
4. Raise front of vehicle and secure on jack stands
5. Remove driver side wheel for improved access if necessary
6. Place drain pan under radiator and drain approximately 2 quarts of coolant from petcock
7. Remove radiator shroud bolts and position shroud toward engine for clearance
8. Remove drive belts by loosening alternator and power steering pump mounting bolts
9. Remove all accessory pulleys if they obstruct access to harmonic balancer bolt

Procedure

1. 1

   Remove radiator hoses and fan
   Disconnect upper and lower radiator hoses from radiator using hose clamp pliers. Remove fan clutch and fan assembly by loosening the four bolts attaching the fan to the water pump pulley. Note that fan clutch threads may be left-hand thread on this application - turn clockwise to loosen.
2. 2

   Access harmonic balancer bolt
   Locate the large bolt in the center of the harmonic balancer at the front of the crankshaft. Clean area around bolt with wire brush and apply penetrating oil. Allow to soak for 10-15 minutes if bolt shows corrosion.
3. 3

   Prevent crankshaft rotation
   Use a crankshaft holding tool or strap wrench around the harmonic balancer to prevent crankshaft rotation. Alternatively, have an assistant place transmission in gear and apply brakes firmly, or use a breaker bar against a frame member through the flywheel inspection cover. Do not use starter motor bump method.
4. 4

   Remove harmonic balancer bolt
   Using a breaker bar and appropriate socket, remove the harmonic balancer center bolt by turning counterclockwise. This bolt is typically very tight (100+ ft-lbs). Remove bolt completely and set aside if reusable, otherwise discard.
5. 5

   Install harmonic balancer puller
   Thread the harmonic balancer puller bolts into the threaded holes in the balancer hub (not the outer ring). Ensure the puller center screw contacts the crankshaft nose squarely. Verify puller is positioned correctly with even pressure distribution.
6. 6

   Remove harmonic balancer
   Gradually tighten the puller center bolt, alternating pressure evenly if using multi-bolt puller. The balancer will resist initially then release from the crankshaft. Continue pulling until balancer is completely free from crankshaft snout. Remove puller and balancer together.
7. 7

   Inspect crankshaft and timing cover
   Examine crankshaft snout for scoring, burrs, or damage. Check Woodruff key slot and key for wear. Inspect front crankshaft seal for leakage. If seal shows any seepage or damage, pry out carefully and install new seal using seal driver. Clean crankshaft snout thoroughly with solvent and rag.
8. 8

   Inspect new harmonic balancer
   Verify new harmonic balancer matches original in diameter, width, and timing mark position. Check that balancer keyway aligns properly. Inspect rubber isolation ring for any defects. Ensure balancer bolt threads are clean and undamaged.
9. 9

   Prepare for installation
   Apply light coat of clean engine oil to crankshaft snout and inside bore of harmonic balancer. Ensure Woodruff key is properly seated in crankshaft keyway. Align balancer keyway with Woodruff key on crankshaft.
10. 10

    Install harmonic balancer
    Position harmonic balancer onto crankshaft snout, aligning keyway with key. Use harmonic balancer installation tool (threaded installer) to draw balancer onto crankshaft. Never hammer or drive balancer onto crankshaft as this will damage the balancer and crankshaft thrust bearings. Thread installer into crankshaft and tighten gradually until balancer is fully seated against the timing cover boss.
11. 11

    Install and torque balancer bolt
    Install new or reusable harmonic balancer bolt with any supplied washer. Hand thread bolt to avoid cross-threading. Using crankshaft holding method from step 3, torque bolt to manufacturer specification. Without factory specification, torque to 100-110 ft-lbs for this 390ci AMC engine application. Apply in 50 ft-lb increments.
12. 12

    Reinstall accessories and pulleys
    Reinstall any accessory pulleys removed during disassembly. Install and tension drive belts to proper specification (typically 1/2 inch deflection under moderate thumb pressure at longest belt span). Reinstall fan and fan clutch assembly with proper rotation direction.
13. 13

    Complete cooling system reassembly
    Reconnect upper and lower radiator hoses with new clamps if originals are damaged. Reposition radiator shroud and secure with mounting bolts. Refill cooling system with appropriate coolant mixture to proper level.

Reassembly

1. Reinstall driver side wheel if removed and torque lug nuts to specification
2. Lower vehicle from jack stands
3. Reconnect negative battery cable
4. Double-check all belt tensions and cooling system connections
5. Start engine and verify no coolant leaks from hoses or water pump
6. Allow engine to reach operating temperature and verify cooling fan operation
7. Check belt alignment and listen for unusual vibrations or noises from front of engine

Verification

• Verify harmonic balancer runs true with no wobble at idle by visual inspection
• Check that timing marks on balancer align properly with timing tab
• Confirm no abnormal vibrations from engine at idle or under acceleration
• Inspect for coolant leaks around all radiator hose connections after initial warm-up cycle
• Verify all drive belts are tracking properly on pulleys without slipping or squealing
• Use timing light to verify timing marks are visible and stable if timing was previously set
• Recheck harmonic balancer bolt torque after first 50-100 miles of operation

More procedures for this vehicle