Crankshaft Main Bearing: Service and Repair

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





Special tools required:
- 00 2 590 00 2 590 Measurement Aid
- 11 4 251
- 11 4 252
- 11 4 470 11 4 470 Tool






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

colour 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 Service and Repair





Checking position of oil spray nozzles:

Insert special tool 11 4 251 11 4 250 Gauge with Adapter Plate in screw connection of main bearing.

Note:
Special tool 11 4 252 11 4 250 Gauge with Adapter Plate 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 11 4 250 Gauge with Adapter Plate.

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

Tightening torque 11 11 5AZ. Specifications





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

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

Observe bearing classification.





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!
It is not possible to remachine the crankshaft.

Surface (1) for marking.

Seven-digit part number (2).

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





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

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

Important!
Excessively small bearing play will result in engine damage.

The colour combination Yellow and Red must not be fitted.

Possible colour combinations (see table).









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 only.

Determine bearing play with special tool 00 2 590.

Installation Note:
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 Service and Repair 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.





Install bedplate Service and Repair.

Assemble engine.