11 21 531 Replacing all crankshaft main bearings (N51)

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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

Check setting of oil spray nozzles, adjusting if necessary:

Attach special tool 11 4 251 to screw connection on main bearing.

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

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 crankshaft (1).

Fig 2: Bearing Shells And Guide Bearing Shell

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NOTE: Pilot bearing shell (1) at the fourth bearing block is a thrust bearing.

Fig 3: Pilot Bearing Shell

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Remove bearing shells (1).

Fig 4: Bearing Shells

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Installation:

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

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

Fig 5: Bearing Shells With And Without Lubricant Groove

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IMPORTANT: Bearing classification (1) on crankcase lower section (values from 1 to 3).

Bearing classification (2) of connecting rod bearings (b/r).

Fig 6: Connecting Rod 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: Engine damage will result if a small bearing play is determined.

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

Fig 7: 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

Clean sealing faces (1).

IMPORTANT: Do not use any metal-cutting tools.

Clean sealing faces with special tool 11 4 470 only.

Fig 8: Sealing Surfaces

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Insert all bearing shells (2 and 3).

NOTE: Bearing shell at the fourth bearing block is a thrust bearing.

Fig 9: Bearing Shells

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Determine bearing play with special tool 00 2 590.

Installation:

All measuring points must be free from oil and grease.

Use used screws to determine bearing play.

Set up Crankcase Lower Section with bearing shells.

Fig 10: Bearing Shells And Guide Bearing Shell

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Remove lower crankcase.

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

Crankshaft bearing clearance radial.

Installation:

Remove plastic thread.

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

Fig 11: Checking Bearing Play

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Install Crankcase Lower Section.

Assemble engine.