Harmonic Balancer

Complete procedure to remove and replace the harmonic balancer (crankshaft pulley/damper) on a 2009 Aston Martin DB9 6.0L V12, including accessory belt removal, pulley extraction, and reinstallation with proper torque specifications.

Warnings

Tools required

Parts

• Harmonic balancer/crankshaft pulley damper × 1 — Use OEM Aston Martin specification
• Crankshaft pulley bolt (TTY - replace if indicated) × 1 — Use OEM specification, verify TTY requirement
• Serpentine belt (if worn or damaged) × 1 — Use OEM specification for 6.0L V12

Preparation

1. Park vehicle on level surface, engage parking brake, and place wheel chocks behind rear wheels.
2. Disconnect negative battery terminal and secure cable away from battery post to prevent accidental reconnection during work.
3. Allow engine to cool completely (minimum 2 hours) to avoid coolant burns if radiator or hoses require manipulation.
4. Photograph serpentine belt routing from multiple angles for reinstallation reference. Pay special attention to tensioner arm position and idler pulley engagement.
5. Raise front of vehicle using hydraulic jack at designated jacking points (refer to owner's manual), and support securely on jack stands rated for vehicle weight. Do not rely solely on jack.
6. Remove engine undertray by locating and removing fasteners (typically Torx or 10mm bolts at multiple points along undertray perimeter). Set aside carefully to avoid damage to clips.

Procedure

1. 1

   Remove Serpentine Belt
   Locate the serpentine belt tensioner on the front of the engine (typically on the driver's side of the V12). Using a breaker bar or 1/2 inch ratchet, insert into the tensioner pulley square drive socket and rotate counterclockwise to relieve belt tension. Slide the serpentine belt off the pulleys, starting with the alternator or tensioner pulley. Carefully release tensioner back to rest position. Remove belt completely from engine bay. Inspect belt for cracks, glazing, or rib separation—replace if any defects are present.
2. 2

   Assess Access and Remove Obstructions
   Evaluate clearance between the harmonic balancer and radiator/fan assembly. On the DB9, clearance between the balancer and the radiator/fan assembly is tight and may be insufficient for harmonic balancer puller operation; verify actual clearance against your tooling before proceeding. If clearance is inadequate, remove the upper radiator hose at the engine connection (loosen hose clamp with flathead screwdriver or pliers, twist and pull hose off). If further access is needed, drain approximately 2 quarts of coolant from radiator petcock into drain pan, then remove upper radiator mounting brackets (typically 2-3 bolts per side, likely 10mm or Torx) and tilt radiator forward slightly. Secure radiator with tie-down strap or bungee cord to prevent stress on lower hose. Note: On the DB9, clearance between the harmonic balancer and the radiator/fan assembly is limited and may be insufficient for harmonic balancer puller operation — assess actual clearance against your puller before proceeding. Note: Harmonic balancer puller (3-jaw style or Aston Martin-specific tool — verify correct tool and engagement points against the AM service manual)
3. 3

   Lock Crankshaft for Bolt Removal
   Prevent crankshaft rotation by installing a flywheel locking tool through the bell housing inspection cover (remove cover by removing 3-4 Torx or 10mm bolts around perimeter). Alternatively, if bell housing access is restricted, have an assistant hold the crankshaft pulley with a strap wrench or insert a pry bar between pulley spokes and frame (use caution to avoid damaging pulley). For shops with factory Aston Martin tooling, use the OEM crankshaft/flywheel locking tool at the location and method specified in the Aston Martin service manual (verify the access point and any cover/bolt that must be removed). Note: For shops with factory Aston Martin tooling, use the OEM crankshaft locking method and tool as specified in the Aston Martin workshop manual; confirm the correct access point and procedure from the official documentation before inserting any locking pin. Note: For shops with factory Aston Martin tooling, use the OEM crankshaft locking tool installed per the service manual procedure (verify the exact access location and any fasteners that must be removed to access it). Note: Aston Martin provides OEM crankshaft/flywheel locking tooling — confirm the exact tool part number, access point, and procedure directly from the Aston Martin workshop manual.
4. 4

   Remove Crankshaft Pulley Bolt
   Using the correct socket size for this bolt (confirm the exact head size from the Aston Martin workshop manual before starting) and a breaker bar or impact wrench, remove the crankshaft pulley bolt by turning counterclockwise. The bolt torque is high and must be verified against the Aston Martin service manual (do NOT assume a value); large V12 crank bolts are commonly torque-to-yield with an initial torque followed by an angle, and the bolt may have thread locker compound. An impact wrench is highly recommended to break the bolt free without disturbing the crankshaft locking tool. Once loose, remove bolt completely by hand and set aside. Inspect bolt threads and underside of bolt head for damage, stretching (necking), or deformation—if bolt is TTY or shows any damage, discard and use new OEM bolt for reinstallation. Note: The bolt torque and reuse specification must be verified against the Aston Martin workshop manual for this V12 (do not rely on a generic value) and the bolt may have thread locker compound. Note: The crankshaft pulley bolt torque is unverified for this engine and must be confirmed against the Aston Martin service manual before removal; it may have thread locker compound. Note: Using the correct size socket (verify size against the Aston Martin service manual for your specific bolt) and breaker bar or impact wrench, remove the crankshaft pulley bolt by turning counterclockwise. Note: Socket size unverified — confirm the exact crankshaft pulley bolt head size against the Aston Martin workshop manual for your specific bolt before starting. Note: Bolt is likely TTY based on modern engine practice, but the initial torque and rotation angle must be obtained directly from the Aston Martin workshop manual — do not use any assumed value.
   Torque spec

   Crankshaft Pulley Bolt180 Nm (133 lb-ft)
5. 5

   Install Harmonic Balancer Puller
   Thread the center bolt of the harmonic balancer puller into the crankshaft bolt threads (verify thread engagement of at least 15mm to prevent stripping). Position the puller arms (typically 3-jaw style) behind the outer rim of the harmonic balancer, ensuring jaws engage the back edge of the pulley, NOT the rubber damper section. Confirm that the puller center bolt is centered on the crankshaft snout and does not contact at an angle. If using an Aston Martin-specific puller, align the tool according to manufacturer instructions to engage the inner hub rather than outer ring. Note: Verify the correct puller type and engagement points against the Aston Martin service manual before applying load, as the proper tool interface (inner hub vs. outer rim) must match the specific balancer design.
6. 6

   Extract Harmonic Balancer
   Using a wrench or socket on the puller center bolt, tighten slowly while monitoring the harmonic balancer for even movement. The balancer should pull straight off the crankshaft snout without tilting. Apply steady pressure—do not impact the puller bolt as this can damage the crankshaft or balancer. If resistance is extreme, apply penetrating oil around the crankshaft snout/balancer interface and allow 15-30 minutes to penetrate, then resume pulling. Once the balancer breaks free from the crankshaft (you will feel a sudden release of tension), continue turning puller bolt until balancer is completely off. Remove puller and balancer together, then separate.
7. 7

   Inspect Crankshaft Snout and Keyway
   Examine the crankshaft snout (the protruding shaft) for scoring, grooves, or surface damage. Light surface rust is acceptable and should be cleaned with fine emery cloth or Scotch-Brite pad. Inspect the Woodruff key or keyway slot for wear, cracking, or deformation—the key should sit flush in its slot with no vertical play. If key is damaged, remove with small punch and hammer (tap upward from bottom), then install new key (OEM part) ensuring it seats fully in keyway slot. Wipe crankshaft snout clean with lint-free cloth and apply a thin film of clean engine oil to the snout surface.
8. 8

   Inspect and Prepare New Harmonic Balancer
   Verify new harmonic balancer part number matches OEM specification for 2009 DB9 6.0L V12. Inspect the inner bore of the balancer for burrs, machining debris, or damage. Check that the keyway slot in the balancer aligns properly with the Woodruff key installed on the crankshaft. Confirm the rubber damper element (the layer between inner hub and outer ring) shows no signs of separation, cracking, or oil saturation—if old balancer is being reused, reject it if any rubber degradation is visible. Apply a thin coat of clean engine oil to the inner bore of the new balancer.
9. 9

   Install Harmonic Balancer onto Crankshaft
   Align the keyway slot in the harmonic balancer with the Woodruff key on the crankshaft snout. Slide the balancer onto the crankshaft by hand as far as possible—engagement depth before resistance increases will vary; do NOT force it beyond hand pressure. Do NOT hammer or pry the balancer into position. Using a harmonic balancer installation tool (threaded rod with thrust bearing and plate) or a large socket that matches the crankshaft snout diameter (NOT the outer pulley diameter), press the balancer fully onto the crankshaft. Thread the installation tool into the crankshaft bolt threads and tighten progressively, checking alignment every few turns. The balancer is fully seated when the front face is flush with the crankshaft snout end and the bolt holes align perfectly. Note: Slide the balancer onto the crankshaft by hand as far as it will go before resistance from the interference fit increases.
10. 10

    Install and Torque Crankshaft Pulley Bolt
    If using a new TTY bolt, verify it is the correct OEM part. If reusing the original bolt, confirm no thread damage or stretching is present. Apply thread preparation (clean oil or thread locker) only as specified by the Aston Martin service manual for this bolt — do not add thread locker unless the OEM procedure explicitly calls for it, as it alters the torque/clamp-load relationship. Thread bolt into crankshaft by hand until finger-tight. With crankshaft still locked (flywheel tool or strap wrench), torque the crankshaft pulley bolt to the exact value specified in the Aston Martin workshop manual using a calibrated torque wrench — DO NOT use an assumed value. This bolt is almost certainly torque-to-yield requiring an initial torque followed by a specified rotation angle; obtain both the initial torque and the angle figure directly from the OEM service documentation before proceeding. Verify bolt is fully seated and torque wrench clicked at specified value. Remove crankshaft locking tool. Note: With crankshaft still locked (flywheel tool or strap wrench), torque the crankshaft pulley bolt to the exact value specified in the Aston Martin workshop manual using a calibrated torque wrench. If the bolt is TTY, follow the OEM torque-plus-angle sequence exactly as published (initial torque value followed by the specified rotation angle)—do not use generic estimates. Note: With crankshaft still locked (flywheel tool or strap wrench), torque the crankshaft pulley bolt to the exact value specified in the Aston Martin service manual using a calibrated torque wrench. If the bolt is TTY, follow the OEM torque-plus-angle specification exactly (initial torque value followed by the specified angle), as published in the service manual — do not use estimated values.
    ⚠️Verify whether the crankshaft bolt is torque-to-yield (TTY) by consulting the Aston Martin service manual. TTY bolts MUST be replaced and follow torque-plus-angle specification. Reusing a TTY bolt can result in bolt failure and catastrophic engine damage.
    Torque spec

    Crankshaft Pulley Bolt180 Nm (133 lb-ft)
11. 11

    Reinstall Serpentine Belt
    Referring to the routing diagram photographed during removal, thread the serpentine belt around all pulleys EXCEPT the tensioner pulley or one easily accessible pulley (typically alternator). Using a breaker bar or ratchet on the tensioner, rotate counterclockwise to relieve tension and create slack. Slide the belt onto the final pulley, ensuring it is properly seated in all pulley grooves (V-ribs must align with pulley grooves, not ride on top of ribs). Slowly release the tensioner to apply proper belt tension. Visually verify belt alignment on all pulleys—misalignment will cause rapid belt wear and noise.
12. 12

    Reinstall Radiator and Hoses (if removed)
    If radiator was tilted or moved, return it to original position and secure with upper mounting brackets and bolts. Torque radiator mounting bracket fasteners to the Aston Martin specification obtained from the workshop manual — do not use an assumed value. Reconnect upper radiator hose to engine-side connection, slide hose fully onto nipple, and tighten hose clamp securely (clamp should be positioned 10-15mm from hose end). If coolant was drained, refill cooling system with the Aston Martin-specified coolant mixed to the correct ratio through the radiator cap or expansion tank to the manufacturer's fill mark, adding the quantity needed to replace what was drained. Burp cooling system by running engine to operating temperature with heater on full, then topping off coolant level as needed. Note: If coolant was drained, refill the cooling system with the Aston Martin-specified coolant mixed to the correct ratio, through the expansion tank, filling to the level mark indicated in the owner's manual. Verify coolant type and capacity against OEM specification. Note: If coolant was drained, refill the cooling system with the coolant type specified by Aston Martin for this vehicle (mixed per spec) through the radiator cap or expansion tank to the 'COLD FULL' mark, adding the quantity that was drained.
13. 13

    Reinstall Engine Undertray and Lower Vehicle
    Position engine undertray beneath vehicle and align all mounting points. Install all undertray fasteners (Torx or 10mm bolts) and tighten in a cross pattern to ensure even seating. Verify no tools or parts have been left in engine bay or under vehicle. Carefully raise vehicle slightly with jack, remove jack stands, and lower vehicle completely to ground. Reconnect negative battery terminal and tighten terminal bolt securely to the Aston Martin specification (clamp-style terminals should be snug without overtightening).
14. 14

    Perform Final Checks and Test Run
    With vehicle on level ground, start engine and allow to idle. Listen for abnormal noises from the front of the engine (squealing, grinding, or knocking may indicate improper belt routing or loose harmonic balancer). Observe the harmonic balancer for wobble or eccentric rotation—any visible wobble indicates improper installation or defective part. Check for coolant leaks around radiator hose connections if cooling system was disturbed. Rev engine gently to 2000-2500 RPM and observe balancer again—rotation should be smooth and concentric. If any abnormalities are noted, shut down engine immediately and re-inspect installation.

Reassembly

1. Reinstall all components in reverse order of removal, ensuring serpentine belt routing matches the photographed diagram exactly.
2. If coolant was drained, burp the cooling system after the first test run by allowing the engine to reach operating temperature with the radiator cap or expansion tank cap removed, then top off coolant level to the 'COLD FULL' mark.
3. Monitor coolant level and check for leaks over the next 100 miles of driving, topping off as necessary until system stabilizes.
4. Inspect serpentine belt tension and alignment after 50-100 miles of operation to ensure belt has not slipped or misaligned.

Verification

• Start engine and confirm no abnormal noises (squealing, grinding, knocking) from the front accessory drive area.
• Visually observe the harmonic balancer while engine is running—confirm smooth, concentric rotation with no wobble or eccentricity.
• Rev engine to 3000 RPM briefly and listen for any vibration or harmonic resonance that was not present before the repair.
• Check serpentine belt alignment on all pulleys—belt should track centered in all pulley grooves without riding on pulley edges.
• Verify no coolant leaks around radiator hose connections if cooling system was disturbed during the repair.
• Test drive vehicle and confirm normal engine operation, smooth acceleration, and no vibration felt through the steering wheel or chassis at idle or under load.

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