Engine Rebuild

Complete disassembly, inspection, machining, and rebuild of the M275 6.0L V12 BiTurbo engine including crankshaft, pistons, camshafts, timing system, and all internal components.

Warnings

Tools required

Parts

• Complete engine gasket set M275 × 1 — Use OEM specification
• Cylinder head bolts (TTY) × 48 — Use OEM specification
• Main bearing cap bolts (TTY) × 12 — Use OEM specification
• Connecting rod bolts (TTY) × 24 — Use OEM specification
• Crankshaft pulley bolt × 1 — Use OEM specification
• Main bearing set (standard or oversized) × 1 — Use OEM specification
• Rod bearing set (standard or oversized) × 1 — Use OEM specification
• Piston ring sets × 12 — Use OEM specification
• Timing chain kit with guides and tensioners × 1 — Use OEM specification
• Valve stem seals × 48 — Use OEM specification
• Crankshaft front seal × 1 — Use OEM specification
• Crankshaft rear seal × 1 — Use OEM specification
• Camshaft seals × 4 — Use OEM specification
• Oil pump (if worn) × 1 — Use OEM specification
• Water pump × 1 — Use OEM specification
• Thermostat assembly × 2 — Use OEM specification
• Oil filter × 1 — Use OEM specification
• Spark plugs × 12 — Use OEM specification
• Oil drain plug crush washer × 1 — Use OEM specification
• Turbocharger gasket kit × 1 — Use OEM specification
• Engine assembly lube × 1 — Use OEM specification
• Thread locker (medium strength) × 1 — Loctite 243
• RTV silicone sealant × 2 — Use OEM specification
• Anti-seize compound × 1 — Copper-based high temp

Fluids

• Mercedes-Benz 229.5 5W-40 — 8.5 qt
• Mercedes-Benz Coolant (Blue) — 18 qt

Preparation

1. Remove engine from vehicle using proper lifting points and support transmission separately
2. Mount engine securely on heavy-duty engine stand using bellhousing bolt holes
3. Clean exterior of engine thoroughly before disassembly to prevent contamination
4. Disconnect all electrical connectors, sensors, and label for reassembly
5. Remove both turbochargers and all exhaust manifolds
6. Drain all coolant and engine oil completely
7. Photograph engine from multiple angles and label all connections
8. Organize workspace with clean benches for component storage and inspection
9. Prepare measurement tools and calibrate torque wrenches

Procedure

1. 1

   Remove Valve Covers and Timing Covers
   Remove valve covers from both cylinder banks. Remove front timing cover assembly by removing all timing cover bolts in reverse sequence. Remove crankshaft pulley using impact wrench and holder tool. Inspect timing cover for cracks or warping.
   Torque spec

   Cover Bolts22 Nm (16 lb-ft)

   Crankshaft Pulley Bolt180 Nm (133 lb-ft)
2. 2

   Lock Timing and Remove Timing Chains
   Rotate crankshaft to TDC cylinder 1. Install camshaft locking tools on all four camshafts to verify timing alignment. Mark timing chain positions relative to sprockets. Release timing chain tensioners and lock with pins. Remove timing chain guide bolts and guides. Remove timing chains, sprockets, and tensioners as an assembly from each bank. Inspect all components for wear.
   ⚠Do not rotate crankshaft or camshafts once timing chains are removed. This will cause valve-to-piston contact.
   Torque spec

   Timing Chain Guide Bolts12 Nm (9 lb-ft)

   Timing Chain Tensioner Bolt25 Nm (18 lb-ft)
3. 3

   Remove Cylinder Heads
   Remove intake manifolds from both banks. Remove exhaust manifolds if not already removed. Loosen cylinder head bolts in reverse of tightening sequence (outer bolts first, working to center) in multiple passes. Remove cylinder heads and place on clean padded surface. Remove and discard cylinder head bolts. Inspect head gasket failure patterns and document.
   ⚠Cylinder heads weigh approximately 80 lbs each. Use assistance or lifting device when removing.
   Torque spec

   Intake Manifold Bolts25 Nm (18 lb-ft)

   Exhaust Manifold Nuts30 Nm (22 lb-ft)

   Cylinder Head Bolts65 Nm (48 lb-ft)
4. 4

   Disassemble Cylinder Heads
   Using valve spring compressor, remove valve keepers, retainers, springs, and valves from all positions. Keep valves organized by cylinder and position. Remove camshaft bearing cap bolts in reverse sequence from outer caps working inward. Carefully remove camshafts and bearing caps, keeping them matched and in order. Remove valve stem seals. Inspect camshaft lobes, journals, and bearing surfaces for scoring or excessive wear.
   Torque spec

   Camshaft Bearing Cap Bolts14 Nm (10 lb-ft)

   Camshaft Cap Bolts14 Nm (10 lb-ft)
5. 5

   Remove Oil Pan and Oil Pump
   Remove oil pan bolts in sequence and carefully separate pan from block. Remove oil pump pickup tube. Remove oil pump mounting bolts and extract oil pump assembly. Inspect oil pump drive components and pressure relief valve. Remove balance shaft assembly if equipped.
   Torque spec

   Oil Pan Bolts12 Nm (9 lb-ft)

   Oil Pump Bolts12 Nm (9 lb-ft)

   Oil Pump Pickup Tube12 Nm (9 lb-ft)

   Balance Shaft Bolts25 Nm (18 lb-ft)
6. 6

   Remove Pistons and Connecting Rods
   Using ridge reamer, remove any ridge at top of each cylinder bore. Rotate crankshaft to access each connecting rod. Mark connecting rods and caps with cylinder number and orientation before removal. Remove connecting rod bolts and caps. Push piston and rod assemblies out through top of block. Keep all components organized by cylinder number. Inspect cylinder walls for scoring, taper, and out-of-round conditions.
   ⚠Do not allow connecting rods to contact cylinder walls or crankshaft journals during removal to prevent damage.
   Torque spec

   Connecting Rod Bolts45 Nm (33 lb-ft)
7. 7

   Remove Crankshaft and Main Bearings
   Check crankshaft endplay before removal. Remove flywheel/flexplate. Mark main bearing caps with position and orientation. Remove main bearing cap bolts in sequence from outer caps working to center. Carefully remove main bearing caps using puller if necessary. Lift crankshaft from block and place on padded surface. Remove all main and rod bearings, keeping them organized by position for inspection.
   ⚠Crankshaft weighs approximately 100 lbs. Use proper lifting technique or assistance.
   Torque spec

   Main Bearing Cap Bolts75 Nm (55 lb-ft)

   Flywheel Bolts95 Nm (70 lb-ft)
8. 8

   Inspect and Machine Components
   Measure all cylinder bores for taper and out-of-round at three depths. Measure crankshaft main and rod journals for taper, out-of-round, and undersize. Measure piston-to-bore clearance and piston ring end gaps. Inspect connecting rods for bend and twist. Send block for hot tank cleaning, magna-fluxing, and boring/honing if cylinders exceed 0.002 inch taper. Send crankshaft for grinding if journals are scored or out-of-spec. Send cylinder heads for valve job, pressure testing, and surfacing. Replace any components that exceed wear limits per Mercedes-Benz specifications.
   ℹ️All critical measurements must be within Mercedes-Benz specifications. Consult factory service manual for exact tolerances for the M275 engine.
9. 9

   Reassemble Short Block
   Thoroughly clean and inspect block. Install main bearing halves in block and caps with assembly lube, ensuring oil holes align. Lubricate crankshaft journals and carefully install crankshaft. Install rear main seal. Install main bearing caps in correct positions with arrows pointing forward. Install new main bearing cap bolts and torque in sequence from center outward to initial torque, then apply angle torque per specification. Verify crankshaft rotates freely and check endplay. Install new front crankshaft seal.
   ⚠Use Plastigage to verify bearing clearances before final assembly. Main bearing clearance should be 0.0008-0.0028 inches.
   Torque spec

   Main Bearing Cap Bolts75 Nm (55 lb-ft)
10. 10

    Install Pistons and Connecting Rods
    Install new piston rings on pistons with gaps staggered per specification. Lubricate rings, pistons, and cylinder walls with assembly lube. Install rod bearings in rods and caps with assembly lube. Using ring compressor, carefully install each piston/rod assembly with piston orientation correct (marks toward front). Install rod caps in correct orientation with new bolts. Torque connecting rod bolts to specification plus angle. Verify each crankshaft journal rotates freely after each rod is installed.
    ⚠Ensure piston ring gaps are properly staggered and rings are not damaged during installation. Broken rings will cause immediate engine failure.
    Torque spec

    Connecting Rod Bolts45 Nm (33 lb-ft)
11. 11

    Install Oil Pump and Oil Pan
    Install new oil pump or rebuilt unit with new gasket. Prime oil pump by filling with engine oil and rotating by hand. Install oil pump pickup tube with new O-ring. Clean oil pan mating surface thoroughly and apply thin bead of RTV sealant where specified. Install oil pan with new gasket and torque bolts in sequence from center outward. Install new oil drain plug with crush washer.
    Torque spec

    Oil Pump Bolts12 Nm (9 lb-ft)

    Oil Pump Pickup Tube12 Nm (9 lb-ft)

    Oil Pan Bolts12 Nm (9 lb-ft)

    Oil Drain Plug35 Nm (26 lb-ft)
12. 12

    Assemble and Install Cylinder Heads
    Install new valve stem seals on guides using proper installation tool. Install valves with assembly lube on stems. Install valve springs, retainers, and keepers. Verify all valves move freely. Lubricate camshaft journals and lobes with assembly lube. Install camshafts in correct positions. Install camshaft bearing caps in correct order and orientation. Torque camshaft bearing cap bolts in sequence from center outward in three passes. Install new camshaft seals. Clean cylinder head and block surfaces completely. Install new head gaskets with alignment dowels. Carefully position cylinder heads on block.
    ⚠Do not use sealant on head gaskets. Ensure head gasket orientation is correct with all oil and coolant passages aligned.
    Torque spec

    Camshaft Bearing Cap Bolts14 Nm (10 lb-ft)

    Camshaft Cap Bolts14 Nm (10 lb-ft)
13. 13

    Install and Torque Cylinder Head Bolts
    Install new cylinder head bolts and torque in proper sequence starting from center working outward. First torque all bolts to 65 Nm (48 lb-ft), then apply angle torque in sequence per Mercedes-Benz specification (typically 90 degrees plus additional 90 degrees). Verify sequence and angle specifications from factory manual for M275 engine as this is critical.
    ⚠️Head bolt torque sequence and angle specifications are absolutely critical. Incorrect torquing will cause head gasket failure or bolt breakage.
    Torque spec

    Cylinder Head Bolts65 Nm (48 lb-ft)
14. 14

    Install Timing System
    Install timing chain guides and torque bolts. Install crankshaft and camshaft sprockets. Rotate crankshaft to TDC cylinder 1. Install camshaft locking tools to verify all camshafts are in correct position. Install timing chains with marked links aligned to sprocket marks. Install timing chain tensioners in compressed and pinned position. Install timing chain guides and verify chain tension. Remove camshaft locking tools and manually rotate engine two complete revolutions. Reinstall locking tools to verify timing is correct. Install timing cover with new gasket and torque bolts in sequence. Install crankshaft pulley and torque bolt to specification using impact wrench.
    ⚠️Timing must be verified multiple times during assembly. Even one tooth off will cause severe engine damage on startup.
    Torque spec

    Timing Chain Guide Bolts12 Nm (9 lb-ft)

    Timing Chain Tensioner Bolt25 Nm (18 lb-ft)

    Cover Bolts22 Nm (16 lb-ft)

    Crankshaft Pulley Bolt180 Nm (133 lb-ft)
15. 15

    Final Assembly
    Install intake manifolds with new gaskets and torque bolts in sequence. Install exhaust manifolds with new gaskets, apply anti-seize to studs, and torque nuts from center outward. Install valve covers with new gaskets and torque in sequence. Install all sensors, actuators, and electrical connections per documentation. Install water pump, thermostats, and all coolant hoses. Install flywheel with new bolts torqued in star pattern. Install turbochargers with new gaskets. Perform final inspection of all connections and torque specifications.
    Torque spec

    Intake Manifold Bolts25 Nm (18 lb-ft)

    Exhaust Manifold Nuts30 Nm (22 lb-ft)

    Cover Bolts22 Nm (16 lb-ft)

    Flywheel Bolts95 Nm (70 lb-ft)

    Sensor Bolts15 Nm (11 lb-ft)

Reassembly

1. Install engine back into vehicle using reverse of removal procedure
2. Reconnect all electrical connections, fuel lines, coolant hoses, and exhaust system
3. Fill engine with 8.5 quarts Mercedes-Benz 229.5 5W-40 engine oil
4. Fill cooling system with 18 quarts Mercedes-Benz Blue coolant and bleed air from system
5. Reconnect battery and prime fuel system
6. Double-check all fluid levels, connections, and torque specifications before startup

Verification

• Perform initial startup with Star diagnostic tool connected to monitor all parameters
• Check for any fluid leaks from oil pan, valve covers, timing cover, and cylinder heads during first startup
• Verify oil pressure reaches normal range within 10 seconds of startup
• Listen for any abnormal engine noises including knocking, ticking, or rattling
• Allow engine to reach operating temperature and verify cooling system operation
• Check for exhaust leaks at manifolds and turbocharger connections
• Perform cylinder contribution test and compression test to verify all cylinders are operating correctly
• Road test vehicle under light load and verify smooth operation without misfires or loss of power
• Perform break-in procedure per Mercedes-Benz specification: avoid full throttle and high RPM for first 500 miles, vary engine speed
• Change oil and filter after first 100 miles of operation to remove assembly debris
• Re-check all fluid levels and inspect for leaks after 500 mile break-in period

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