11 21 531 Replacing all crankshaft main bearings (N52)

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.

The end faces of aluminium screws/bolts are painted blue for the purposes of reliable identification.

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.

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

For tightening torque refer to 11 11 5AZ in 11 11 ENGINE BLOCK (N52) .

NOTE: See Fig 1.

Fig 1: Identifying Special Tool (11 4 251) And (11 4 252)

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Remove bearing shells (2) and (3).

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

Observe Bearing Classification.

Fig 2: Identifying Bearing Shells And Crankshaft

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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 3: Identifying Bearing Shell With And Without Lubricant Groove

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Surface (1) for identification.

Seven-digit part number (2).

Bearing classification (3) of crankshaft as per table (values 1 to 3).

Reworking (4) as per table (main bearing).

B= build date 1 (-0.25mm).

B= build date 2 (-0.50mm).

Reworking (5) as per table (lift bearing).

B= construction stage 1 (-0.25mm).

C = construction stage 2 (-0.50mm)

Fig 4: Identifying Bearing Classification Tag

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Bearing classification (1) in crankcase as per table (values of A/B/C).

Installation:

When all the letters and number code have been determined, the bearing shell colour must be allocated, see BEARING SPECIFICATION table.

Fig 5: Identifying Bearing Classification In Crankcase

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IMPORTANT: Engine damage will result if a small bearing play is determined.

The colour combination Yellow and Red must not be fitted.

Possible colour combinations, see BEARING SPECIFICATION .

BEARING 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

Insert all bearing shells (2 and 3).

IMPORTANT: Clean sealing surfaces.

Do not clean sealing faces with a metal-cutting tool.

Clean sealing faces with special tool 11 4 470 only.

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 Bedplate with bearing shells.

Fig 6: Identifying Bearing Shells And Crankshaft

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Remove bedplate.

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 7: Identifying Crankshaft Bearing Clearance Radial

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Install Bedplate .

Assemble engine.