11 21 531 Replacing all main crankshaft bearing shells (N52K)

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Special tools required:

00 2 590
11 4 251
11 4 252
11 4 470

IMPORTANT: Aluminium-magnesium materials.

No steel screws/bolts may be used due to the threat of electrochemical corrosion.

A magnesium crankcase requires aluminium screws/bolts exclusively.

Aluminium screws/bolts must be replaced each time they are released .

Aluminium screws/bolts are permitted with and without color coding (blue).

For reliable identification:

Aluminium screws/bolts are not magnetic .

Jointing torque and angle of rotation must be observed without fail (risk of damage).

Necessary preliminary tasks:

Remove Crankshaft

Checking position of oil spray nozzles:

Insert special tool 11 4 251 in screw connection of main bearing.

NOTE: Special tool 11 4 252 must be pre-installed at the seventh main bearing.

Check position of oil spray nozzle (2) according to position (1) on special tool 11 4 251.

If necessary, adjust and secure oil spray nozzle (2).

For tightening torque refer to 5AZ in 11 11 CRANKCASE .

Fig 1: Special Tools (11 4 252), (11 4 251), Spray Nozzle And Position

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Remove bearing shells (2) and guide bearing shell (3).

NOTE: Guide bearing shell (3) is a thrust bearing.

Observe Bearing Classification .

Fig 2: Bearing Shells And Guide Bearing Shell

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Installation:

Bearing shell (1) with lubricant groove must be fitted in crankcase.

Bearing shell (2) without lubricant groove must be fitted in bedplate.

Fig 3: Bearing Shells With And Without Lubricant Groove

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IMPORTANT: It is not possible to re-machine the crankshaft.

Surface (1) for marking.

Seven-digit part number (2).

Bearing classification (3) on bedplate (see table : values of 1/2/3).

Fig 4: Crankshaft Surface, Seven-Digit Number And Bearing Classification

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Bearing classification (1) on crankcase (see table : values of A/B/C).

Installation:

When all the letters and number code have been determined, the color of the bearing shells must be allocated (see table ).

IMPORTANT: Excessively small bearing play will result in engine damage.

The color combination Yellow and Red must not be fitted. Possible color combinations (see table ).

Fig 5: Bearing Classification

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BEDPLATE SPECIFICATION

(A1) Bedplate / Yellow	(B1) Bedplate / Yellow	(C1) Bedplate / Green
(A1) Crankcase / Yellow	(B1) Crankcase / Green	(C1) Crankcase / Green
(A2) Bedplate / Green	(B2) Bedplate / Green	(C2) Bedplate / Green
(A2) Crankcase / Yellow	(B2) Crankcase / Green	(C2) Crankcase / Red
(A3) Bedplate / Green	(B3) Bedplate / Red	(C3) Bedplate / Red
(A3) Crankcase / Green	(B3) Crankcase / Green	(C3) Crankcase / Red

Install bearing shells (2) and guide bearing shell (3).

Installation:

Clean all sealing surfaces.

IMPORTANT: Do not use any metal-cutting tools.

Clean sealing faces with special tool 11 4 470 only.

Determine bearing play with special tool 00 2 590.

Fig 6: Bearing Shells And Guide Bearing Shell

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Installation:

All measuring points must be clean and free from oil and grease. If necessary, clean all measuring points.

Use the existing screws to determine the bearing play.

Set up bedplate with bearing shells.

Remove bedplate.

Read off bearing play at width of flattened plastic thread and measurement scale.

Installation:

Remove plastic thread.

Apply a light coat of oil to bearing shells and crankshaft.

Fig 7: Checking Bearing Play

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Install Bedplate.

Assemble engine.