Front Main Seal

Replace the front crankshaft seal on the M275 6.0L V12 BiTurbo engine by removing the front accessory drive components, harmonic balancer, and timing cover to access and install a new seal.

Warnings

Tools required

Parts

• Front crankshaft seal (M275) × 1 — Use OEM specification
• Timing cover gasket × 1 — Use OEM specification
• Oil drain plug crush washer × 1 — Use OEM specification
• Engine oil filter × 1 — Use OEM specification
• Serpentine belt × 1 — Use OEM specification
• Coolant hose clamps × 2 — As needed for disturbed connections
• Oil pan gasket (front section) × 1 — Use OEM specification if damaged

Fluids

• Mercedes-Benz 229.5 5W-40 — 8.5 qt
• Mercedes-Benz Coolant (Blue) — 3 qt

Preparation

1. Disconnect negative battery terminal and wait 15 minutes for system capacitors to discharge
2. Raise vehicle on lift or jack stands to access underside components
3. Remove engine cover and intake air ducting
4. Drain engine oil completely and remove oil filter
5. Drain coolant from radiator and lower coolant hoses that interfere with front engine access
6. Remove front underbody panels and splash shields for access to crankshaft pulley
7. Install engine support fixture across engine bay or attach hoist to certified lifting points
8. Document all electrical connector positions and coolant hose routing with photos

Procedure

1. 1

   Remove serpentine belt and accessories
   Use serpentine belt routing diagram (located on radiator support) to document belt path. Release belt tensioner and remove serpentine belt. Remove power steering pump mounting bolts and secure pump aside without disconnecting hoses. Remove alternator mounting bolts and position alternator clear of work area while maintaining electrical connections if possible.
   Torque spec

   Mounting Bolts64 Nm (47 lb-ft)
2. 2

   Remove front motor mount
   Support engine weight with fixture or hoist to unload front motor mount. Remove the front motor mount bolts and carefully lower or raise engine approximately 2-3 inches to create clearance for harmonic balancer removal. Verify engine is stable and secure before proceeding.
   ⚠️Engine must be fully supported before removing motor mount. Failure to properly support can cause engine to shift suddenly.
   Torque spec

   Mounting Bolts64 Nm (47 lb-ft)
3. 3

   Remove crankshaft pulley and harmonic balancer
   Remove crankshaft pulley bolts using appropriate socket. Using impact wrench, remove the harmonic balancer center bolt (this is a torque-to-yield bolt rotating clockwise to loosen). Install Mercedes-Benz harmonic balancer puller tool onto balancer and turn forcing screw to extract balancer from crankshaft snout. Do not use jaw-type pullers as they will damage the balancer.
   ⚠️Only use impact wrench for harmonic balancer bolt removal. Manual removal can result in tool slippage and serious injury due to extreme torque.
   ⚠Mark harmonic balancer orientation to crankshaft before removal for correct reinstallation alignment.
   Torque spec

   Harmonic Balancer Bolt180 Nm (133 lb-ft)
4. 4

   Remove timing cover bolts
   Remove all timing cover bolts, noting the different lengths and positions. The M275 timing cover uses both 8mm and 10mm bolts in specific locations. Remove upper timing cover bolts first, then lower bolts. Some bolts may thread into oil pan flange at the bottom. Keep bolts organized by size and position for reassembly.
   ℹ️Timing cover bolts are different lengths. Label or organize bolts by position to ensure correct reinstallation.
   Torque spec

   Cover Bolts22 Nm (16 lb-ft)
5. 5

   Remove timing cover
   Carefully pry timing cover away from engine block using plastic pry tools at designated pry points. Work around perimeter gradually to break RTV seal. Once loose, pull cover straight off to avoid damaging timing chain or guides. Inspect timing cover mating surface and remove all old gasket material and RTV sealant using plastic scraper.
6. 6

   Remove front crankshaft seal
   Using seal removal tool or carefully with pick and pry bar, extract old front crankshaft seal from timing cover bore. Work seal out evenly to avoid damaging timing cover seal bore. Thoroughly clean seal bore with brake cleaner and lint-free cloth. Inspect bore for damage, scoring, or wear that could compromise new seal.
   ⚠Do not damage timing cover seal bore during old seal removal. Gouges or scratches will cause new seal to leak.
7. 7

   Install new front crankshaft seal
   Lubricate new seal lip with clean engine oil. Using proper size seal installation tool (must match seal outer diameter), drive new seal squarely into timing cover bore until fully seated and flush with cover surface. Ensure seal is not cocked or damaged during installation. Verify seal is seated evenly around entire circumference.
   ⚠Seal must be driven in perfectly square. Cocked installation will cause immediate oil leak and require seal replacement.
8. 8

   Prepare timing cover for installation
   Clean all mating surfaces on engine block and timing cover with brake cleaner. Ensure surfaces are completely free of old RTV, gasket material, and oil. Install new timing cover gasket if equipped, or apply thin bead of Mercedes-Benz approved RTV sealant to timing cover mating surface and oil pan junction areas. Apply RTV to both sides of gasket at oil pan split line.
   ℹ️RTV requires 10-15 minute setup time before assembly. Follow RTV manufacturer instructions for cure time before adding oil.
9. 9

   Install timing cover
   Carefully align timing cover onto engine block, ensuring timing chain and guides are not disturbed. Guide cover over crankshaft snout, being careful not to damage new seal lip. Install all timing cover bolts hand-tight first. Following Mercedes-Benz tightening sequence (typically center out, alternating sides), torque 10mm bolts to specification first, then 8mm bolts. Tighten in multiple passes.
   ⚠Must follow proper tightening sequence to prevent timing cover warping and oil leaks. Tighten gradually in stages.
   Torque spec

   Cover Bolts22 Nm (16 lb-ft)
10. 10

    Install harmonic balancer and crankshaft pulley
    Clean crankshaft snout and harmonic balancer bore thoroughly. Lightly oil crankshaft snout. Align harmonic balancer to crankshaft using alignment marks made during removal. Slide balancer onto crankshaft carefully to avoid damaging seal. Install new harmonic balancer bolt (torque-to-yield, do not reuse old bolt). Using impact wrench, torque bolt to specification. Install crankshaft pulley and torque pulley bolts to specification.
    ⚠Harmonic balancer bolt is torque-to-yield. Must use new bolt for proper clamping force and engine safety.
    Torque spec

    Harmonic Balancer Bolt180 Nm (133 lb-ft)

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

    Reinstall front motor mount and accessories
    Raise or lower engine back to original position and reinstall front motor mount with mounting bolts torqued to specification. Reinstall alternator and power steering pump with their respective mounting bolts torqued properly. Route new serpentine belt according to routing diagram and verify belt is properly seated on all pulleys.
    Torque spec

    Mounting Bolts64 Nm (47 lb-ft)
12. 12

    Refill fluids and final checks
    Install new oil filter and drain plug with new crush washer, torquing drain plug to specification. Refill engine with 8.5 quarts Mercedes-Benz 229.5 5W-40 oil. Reconnect any coolant hoses removed and refill cooling system with approximately 3 quarts coolant (or amount drained). Reinstall all underbody panels, splash shields, and engine covers. Reconnect battery negative terminal.
    Torque spec

    Oil Drain Plug35 Nm (26 lb-ft)

Reassembly

1. Ensure all timing cover bolts are torqued in proper sequence to prevent oil leaks
2. Verify harmonic balancer is fully seated on crankshaft before torquing bolt
3. Double-check all electrical connectors, coolant hoses, and accessory mounting bolts are secure
4. Allow RTV sealant to cure per manufacturer specifications before starting engine (typically 1-2 hours)
5. Serpentine belt must be properly routed and seated on all pulleys before starting engine

Verification

• Start engine and verify no oil leaks from timing cover, particularly around crankshaft seal area
• Check for proper oil pressure on instrument cluster immediately upon startup
• Monitor engine for unusual noises, vibrations, or accessory belt misalignment during initial run
• Allow engine to reach operating temperature and recheck for leaks around entire timing cover perimeter
• Verify coolant level is correct after engine reaches operating temperature and system is burped
• Check oil level after 5-minute run and top off to proper level on dipstick
• Road test vehicle and verify no warning lights, normal engine operation, and no oil consumption after 50-100 miles

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