Harmonic Balancer

This procedure covers removal and replacement of the harmonic balancer (crankshaft damper) on the M275 6.0L BiTurbo V12 engine, including accessory drive component removal and proper torque sequence.

Warnings

Tools required

Parts

• Harmonic balancer/crankshaft damper × 1 — Use OEM Mercedes-Benz specification
• Harmonic balancer bolt (if TTY) × 1 — Use OEM Mercedes-Benz specification
• Serpentine belt × 1 — 6PK2380 or equivalent
• Lower engine cover fasteners (if damaged) × 1 — Use OEM specification

Preparation

1. Park vehicle on level surface and engage parking brake
2. Disconnect negative battery terminal and wait 10 minutes for SRS system to discharge
3. Raise front of vehicle and support securely on jack stands at manufacturer lift points
4. Remove front wheels if additional access is needed
5. Remove lower engine splash shields and belly pans using appropriate socket
6. Allow engine to cool completely if recently operated (minimum 2 hours)
7. Document serpentine belt routing with photo or diagram before removal
8. Place oil drain pan beneath work area to catch any residual fluids

Procedure

1. 1

   Remove serpentine accessory belt
   Locate the belt tensioner on the right side of the engine. Using a 17mm wrench or belt tensioner tool, rotate the tensioner clockwise to release tension. Slip the belt off the pulleys while maintaining tension, then slowly release the tensioner. Remove the belt from the engine bay and inspect for wear or damage.
2. 2

   Remove crankshaft pulley
   Remove the multiple bolts securing the crankshaft pulley to the harmonic balancer. These are typically 6-8 bolts arranged in a circular pattern. Keep these bolts organized as they will be reused. Remove the pulley and set aside. Inspect the pulley for cracks or elongated bolt holes.
   ℹ️Some S65 AMG variants may have the pulley integrated with the balancer. Verify your specific configuration before proceeding.
   Torque spec

   Crankshaft Pulley Bolt180 Nm (133 lb-ft)
3. 3

   Lock crankshaft rotation
   Install a flywheel locking tool through the starter motor opening or bellhousing access hole to prevent crankshaft rotation. Alternatively, place the transmission in gear (manual) or use a crankshaft holding tool at the front. Verify the crankshaft cannot rotate before attempting to remove the center bolt.
   ⚠️Never attempt to hold the crankshaft by jamming a screwdriver or wedging the flywheel teeth. This can cause severe transmission or flywheel damage.
4. 4

   Remove harmonic balancer center bolt
   Using a 1/2-inch impact wrench with appropriate socket (typically 21mm or 22mm), remove the harmonic balancer center bolt. This bolt is torqued to 180 Nm and requires significant force. If using a breaker bar instead of impact, ensure the crankshaft is securely locked. Remove the bolt completely and inspect threads for damage. If this is a TTY bolt, discard it and use a new bolt during installation.
   ⚠If the bolt is extremely difficult to remove or shows signs of thread damage, stop and verify you are turning counter-clockwise (standard right-hand thread).
   Torque spec

   Harmonic Balancer Bolt180 Nm (133 lb-ft)
5. 5

   Remove harmonic balancer from crankshaft
   Thread a harmonic balancer puller onto the balancer hub using the center bolt threads. Ensure the puller jaws grip only the inner hub, not the outer inertia ring. Tighten the puller center screw gradually while supporting the balancer. The balancer will release from the crankshaft taper with a distinct pop. Remove the puller and balancer together, then separate them on the workbench.
   ⚠️Never use a puller that contacts the outer ring of the harmonic balancer. The outer ring is bonded to the hub with rubber dampening material that will be destroyed by puller pressure.
6. 6

   Inspect crankshaft snout and keyway
   Thoroughly clean the crankshaft snout, keyway, and front seal surface with a clean rag and appropriate solvent. Inspect for scoring, burrs, or damage to the tapered surface. Check that the woodruff key is present and properly seated in the keyway. Inspect the front main seal for leakage or damage. If the seal shows wear, this is the ideal time to replace it.
   ⚠Any burrs or damage on the crankshaft taper will prevent proper harmonic balancer seating and may cause vibration or balancer failure.
7. 7

   Prepare new harmonic balancer
   Unbox the new harmonic balancer and verify it matches the original in dimensions, keyway position, and bolt hole pattern. Clean the inner bore of the balancer thoroughly. Apply a thin coat of clean engine oil or anti-seize to the crankshaft taper (not the keyway). Do NOT apply sealant or excessive lubricant.
8. 8

   Install harmonic balancer
   Align the keyway in the harmonic balancer with the woodruff key on the crankshaft. Slide the balancer onto the snout by hand as far as it will go. Install the harmonic balancer installation tool or use a large socket that fits the inner hub (never contact the outer ring). Thread the center bolt partially and use it to draw the balancer onto the crankshaft taper. Tighten gradually, checking alignment frequently. The balancer should seat flush against the crankshaft timing gear or shoulder.
   ⚠Do not hammer the harmonic balancer onto the crankshaft. It must be drawn on using the center bolt to preserve the taper fit and internal dampening.
9. 9

   Torque harmonic balancer center bolt
   Ensure the crankshaft is still locked in position. Clean the threads of the harmonic balancer bolt and apply medium-strength thread locker if specified (check service manual). Install the bolt (use new TTY bolt if applicable) and torque to 180 Nm (133 lb-ft) using a calibrated torque wrench. If specified as TTY, perform the additional angle rotation specified in the service manual (typically 90 degrees additional). Verify the torque specification sequence in the factory service manual before final tightening.
   ⚠️Incorrect torque or reusing a TTY bolt can result in bolt failure during operation, causing immediate loss of accessory drive and potential catastrophic engine damage.
   Torque spec

   Harmonic Balancer Bolt180 Nm (133 lb-ft)
10. 10

    Reinstall crankshaft pulley
    Position the crankshaft pulley onto the harmonic balancer, aligning all bolt holes. Install the pulley bolts hand-tight in a star pattern. Torque the pulley bolts to specification (verify in service manual, typically 180 Nm for these bolts or lower if separate from main bolt) in a cross-pattern sequence. Remove the flywheel locking tool or crankshaft holding device.
    Torque spec

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

    Reinstall serpentine belt
    Route the new or inspected serpentine belt around all pulleys according to the routing diagram documented during removal. Rotate the belt tensioner clockwise with the tensioner tool and slip the belt onto the final pulley (typically the tensioner pulley itself). Slowly release the tensioner to apply proper belt tension. Verify the belt is properly seated in all pulley grooves.
12. 12

    Reinstall lower covers and wheels
    Reinstall all lower engine splash shields and belly pans, torquing fasteners to 22 Nm if specified or hand-tight plus 1/4 turn for plastic fasteners. Reinstall front wheels if removed and torque to manufacturer specification (typically 150 Nm). Lower vehicle from jack stands.
    Torque spec

    Cover Bolts22 Nm (16 lb-ft)

Reassembly

1. Reconnect negative battery terminal and torque to specification
2. Perform idle relearn procedure using Star Diagnosis tool if necessary
3. Clear any fault codes related to battery disconnection
4. Verify all tools and parts have been removed from engine bay

Verification

• Start engine and verify smooth idle with no abnormal vibration (compare to baseline before repair)
• Observe harmonic balancer during idle for any wobble or eccentric rotation
• Rev engine to 2000-2500 RPM and verify no unusual vibration or noise
• Verify all accessory components are operating correctly (alternator, power steering, A/C compressor)
• Inspect for any fluid leaks around front main seal area
• Take vehicle for short test drive and monitor for vibrations at various RPM ranges, particularly 1500-2500 RPM
• Re-inspect harmonic balancer bolt torque after 50-100 miles of driving (warm engine, verify still at specification)

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