11 21 531 Replacing all crankshaft main bearing shells (N52T)

Special tools required:

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 work:

Remove CRANKSHAFT

Checking position of oil spray nozzles:

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

NOTE: Special tool 11 4 252 must be preinstalled 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).

Tightening torque: 11 11 5AZ .

Fig 1: Checking Position Of Oil Spray Nozzles

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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. See CRANKSHAFT AND BEARINGS (N52T) .

Fig 2: Identifying Bearing Shells

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Installation note:

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

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

IMPORTANT: Allocation of bearing points:
Bearing point 1 is at the front on the timing chain drive in the direction of travel.

Fig 3: Identifying Bearing Shell With And Without Lubricating Groove

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IMPORTANT: All crankshaft crank pins are classified.
The identification (2) is located on the first crankshaft web.

Optional classifications (2) per connecting rod

On the connecting rod and connecting rod bearing cap:

r. connecting rod = yellow

Connecting rod bearing cap = red

b. Connecting rod = violet

Connecting rod bearing cap= blue

Observe bearing classification. See CRANKSHAFT AND BEARINGS (N52T) .

Fig 4: Identifying Main Bearing Classification ID Codes

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Example:

Possible classification: b r r r r r

Cylinder 1: Classification b

Violet (connecting rod)/\Blue (connecting rod bearing cap)

Cylinder 2: Classification r

Yellow (connecting rod)/Red (connecting rod bearing cap)

Cylinder 3: Classification r

Yellow (connecting rod)/Red (connecting rod bearing cap)

Cylinder 4: Classification r

Yellow (connecting rod)/Red (connecting rod bearing cap)

Cylinder 5: Classification r

Yellow (connecting rod)/Red (connecting rod bearing cap)

Cylinder 6: Classification r

Yellow (connecting rod)/Red (connecting rod bearing cap)

Main bearing classification (1) in crankcase, code letters A/B or C, see table.

Installation note:

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

Fig 5: Identifying Main Bearing Classification In Crankcase

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Installation note:

The letter/number combination produces a bearing shell pairing.

Identification by different colors.

IMPORTANT: First bearing point is on the timing drive.
The color combination Yellow and Red must not be fitted.
Engine damage will result if excessively small bearing play is determined.

Code letters on crankcase:

Code letter A = bearing shell (1) color Yellow.

Code letter B = bearing shell (1) color Green.

Code letter C = bearing shell (1) color Red.

Code numbers on crankshaft:

Code number 1 = bearing shell (2) Yellow.

Code number 2 = bearing shell (2) Green.

Code number 3 = bearing shell (2) Red.

Fig 6: Identifying Bearing Shell With And Without Lubricating Groove

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IMPORTANT: The color combination Yellow and Red must not be fitted; the bearing colors Green/Green must be selected for this color combination, see table.

Installation example:

For bearing 1 with code letter A on the crankcase and code number 1 on the crankshaft bearing shell (1) with the color Yellow is required for the crankcase and bearing shell (2) with the color Yellow for the crankcase lower half (bedplate).

Lager 2: A and 2 colors Yellow and Green.

Lager 3: B and 2 colors Green and Green.

Lager 4: C and 2 colors Red and Green.

Lager 5: B and 1 colors Green and Yellow.

Lager 6: C and 3 colors Red and Red.

Fig 7: Identifying Bearing Shell With And Without Lubricating Groove

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Lager 7: C and 1 colors Green and Green.

The color combination Yellow and Red must not be fitted.

Installation note:

Possible color combinations for mounting the crankshaft in the crankcase.

(A 1) Crankcase/Yellow	(B 1) Crankcase/Green	(C 1) Crankcase/Green
(A 1) Crankcase lower half/Yellow	(B 1) Crankcase lower half/Yellow	(C 1) Crankcase lower half/Green
(A 2) Crankcase/Yellow	(B 2) Crankcase/Green	(C 2) Crankcase/Red
(A 2) Crankcase lower half/Green	(B 2) Crankcase lower half/Green	(C 2) Crankcase lower half/Green
(A 3) Crankcase/Green	(B 3) Crankcase/Green	(C 3) Crankcase/Red
(A 3) Crankcase lower half/Green	(B 3) Crankcase lower half/Red	(C 3) Crankcase lower half/Red

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

Installation note:

Clean all sealing surfaces.

IMPORTANT: Do not use any metal-cutting tools.

Clean sealing faces with special tool 11 4 470 .

Determine bearing play with special tool 00 2 590 .

Installation note:

Fig 8: Identifying Bearing Shells

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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 note:

Remove plastic thread.

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

Fig 9: Measuring Radial Clearance Using Flattened Plastigage And Scale

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Install BEDPLATE .

Assemble engine.