11 12 100 Removing And Installing/Sealing Cylinder Head (N51)

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Special tools required:

For the following special tools, refer to ENGINE - SPECIAL TOOLS (N51) .

11 0 320
11 4 420
11 4 430
11 4 471
11 4 47
11 5 190
11 8 580

IMPORTANT: Aluminum-magnesium materials. No steel screws/bolts may be used due to the threat of electrochemical corrosion. A magnesium crankcase requires aluminum screws/bolts exclusively. Aluminum screws/bolts must be replaced each time they are released . Aluminum screws/bolts are permitted with and without color coding (blue). For reliable identification: Aluminum screws/bolts are not magnetic . Jointing torque and angle of rotation must be observed without fail (risk of damage) .

Necessary preliminary tasks:

Remove exhaust system. See 18 00 020 REMOVING AND INSTALLING/REPLACING COMPLETE EXHAUST SYSTEM (N52/N52K/N51) .
Drain coolant . See 17 11 000 REMOVING AND INSTALLING RADIATOR (N51, S65) .
Drain engine oil .
Remove both exhaust manifolds . See 18 40 050 REMOVING AND INSTALLING/REPLACING FRONT EXHAUST MANIFOLD (N53/N52/N52K/N51) or 18 40 060 REMOVING AND INSTALLING/REPLACING REAR EXHAUST MANIFOLD (N53/N52/N52K/N51) .
Remove intake air manifold . See 11 61 050 REMOVING AND INSTALLING INTAKE AIR MANIFOLD (N51) .
Detach coolant hoses from cylinder head.
Remove cylinder head cover . See 11 12 000 REMOVING AND INSTALLING OR SEALING CYLINDER HEAD COVER (N51) .
Remove inlet and exhaust adjustment unit . See 11 36 046 REMOVING AND INSTALLING/REPLACING INLET AND EXHAUST ADJUSTMENT UNITS (N51) .

IMPORTANT: Fit new cylinder head screws. Do not wash off bolt coating. There must not be any coolant, water or oil present in the pocket holes (risk of corrosion and cracking) .

Release screws (1).

Unclip timing chain module (2) at junction (3) and remove towards top.

Do not allow timing chain to drop down.

Installation:

Only during assembly is the timing chain lifted out with a hook.

Fig 1: Identifying Timing Chain Module And Screws

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Release screws (2).

Remove eccentric shaft sensor (1) towards front.

Fig 2: Removing Eccentric Shaft Sensor

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Release screw (1).

Remove magnet wheel (2) towards front.

IMPORTANT: Magnet wheel (2) is extremely magnetic.

Fig 3: Removing Magnet Wheel

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IMPORTANT: After removing, pack magnet wheel (1) away immediately in a plastic bag (2) for safety reasons.
Magnet wheel must be protected against metal chips.

Fig 4: Identifying Pack Magnet Wheel

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Pretension eccentric shaft (1) upwards in direction of arrow.

Remove min stop screw between 1st and 2nd cylinders.

Tightening torque. See 11 37 6AZ in 11 37 VARIABLE VALVE GEAR .

Fig 5: Identifying Eccentric Shaft

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Release screws (1).

Tightening torque. See 11 12 3AZ in CYLINDER HEAD WITH COVER .

Screw (2) can only be released when the chain module is pressed forward slightly.

IMPORTANT: Secure screw (2) with a gripper against falling out and remove.

Installation:

Replace aluminum screws .

Fig 6: Identifying Screws

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IMPORTANT: Different screw heads

M10 screw (1) is released with special tool 11 8 580. See Fig 7.

M9 screw (2) is released with special tool 11 4 420. See Fig 7

NOTE: Illustration shows camshaft removed.

Fig 7: Identifying Special Tools

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Release screws (1 and 3) with special tool 11 4 420.

Tightening torque, see 11 12 2AZ in CYLINDER HEAD WITH COVER .

Release screws (2) with special tool 11 8 580 from outside inwards.

Tightening torque. See in 11 12 1AZ CYLINDER HEAD WITH COVER .

IMPORTANT: All screws must be replaced.
Jointing torque and angle of rotation must be observed without fail (risk of damage) .

Fig 8: Identifying Screws

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Secure special tool 11 0 320 with old cylinder head cover bolts (1).

Tightening torque, see 11 12 4AZ in CYLINDER HEAD WITH COVER .

IMPORTANT: Weight of cylinder head with add-on parts is approx. 40 kg.

Remove and install cylinder head with two persons.

Do not set cylinder head down on sealing face, risk of damage to engine valves.

Fig 9: Identifying Cylinder Head With Persons

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Insert special tool 11 4 430 into bores. See Fig 10.

Fig 10: Identifying Special Tool (11 4 430)

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Use special tool 11 4 471 to remove coarse gasket remnants from sealing faces of cylinder head and crankcase. See Fig 11.

IMPORTANT: Do not use any metal-cutting tools.

Fig 11: Identifying Special Tool (11 4 471)

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Remove fine gasket remnants with special tool 11 4 472. See Fig 12.

IMPORTANT: Do not use any metal-cutting tools.

Fig 12: Identifying Special Tool (11 4 472)

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There must not be any coolant, water or oil present in the pocket holes (risk of corrosion and cracking) .

Clean all threaded holes.

Fig 13: Identifying Threaded Hole

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Replace cylinder head gasket . See 11 12 101 REPLACING CYLINDER HEAD GASKET (N51) .

IMPORTANT: Observe tightening sequence.

Fit new cylinder head screws.

Insert screws (1 to 10) with special tool 11 5 190.

Tightening torque. See 11 12 1AZ in CYLINDER HEAD WITH COVER .

Insert screws (11 to 14) with special tool 11 4 420.

Tightening torque. See 11 12 2AZ in CYLINDER HEAD WITH COVER .

NOTE: Illustration shows camshafts removed.

Fig 14: Cylinder Head Bolts Tightening/Loosening Sequence

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Observe tightening sequence .

Installation:

Jointing torque: Screws 1 to 14 / 1x 30 Nm

Angle of rotation: Screws 1 to 14 / 1x 90°
Angle of rotation: Screws 1 to 10 / 1x 90°
Angle of rotation: Screws 1 to 14 / 1x 45°

Replace screws (1).

Tightening torque. See 11 12 3AZ in CYLINDER HEAD WITH COVER .

IMPORTANT: Secure screw (2) with a gripper against falling out.

Installation:

Replace aluminum screws .

Fig 15: Identifying Screw With Gripper

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Assemble engine.