Crankshaft Main Bearing: Service and Repair
11 21 531 - Replacing all crankshaft main bearings (N52)
Special tools required:
- 00 2 590
- 11 4 251 11 4 250 Gauge with Adapter Plate
- 11 4 252 11 4 250 Gauge with Adapter Plate
- 11 4 470 11 4 470 Cleaning Kit
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 Service and Repair.
Check setting of oil spray nozzles, adjusting if necessary:
Attach special tool 11 4 251 11 4 250 Gauge with Adapter Plate to screw connection on main bearing.
Special tool 11 4 252 11 4 250 Gauge with Adapter Plate must be pre-installed at the seventh main bearing block.
Tightening torque: 11 11 5AZ 11 11 Engine Block.
Note:
See illustration.
Remove bearing shells (2) and (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 upper section.
Bearing shell (2) without lubricant groove must be fitted in crankcase lower section (bedplate).
Important!
Allocation of bearing points:
Bearing point 1 is at the front on the timing chain drive in the direction of travel.
Surface (1) for identification on crankshaft web 1.
Seven-digit part number (2).
Main bearing classification (3) for crankcase lower half (bedplate), code numbers 1 2 3, see table.
Note:
Code letters (4 and 5) are exclusively required for a machined crankshaft.
Code letter (4) as per table, main bearing.
B= build date 1 (B 1 2 3 -0.25 mm).
B= build date 2 (C 1 2 3 -0.50 mm).
Code letter (5) as per table, lift bearing.
B= construction stage 1 (-0.25mm).
C = construction stage 2 (-0.50 mm)
Observe bearing classification.
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.
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.
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).
Bearing 2: - A and 2 colors Yellow and Green.
Bearing 3: - B and 2 colors Green and Green.
Bearing 4: - C and 2 colors Red and Green.
Bearing 5: - B and 1 colors Green and Yellow.
Bearing 6: - C and 3 colors Red and Red.
Bearing 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.
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 11 4 470 Cleaning Kit 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.
The existing screws must be used 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.
Crankshaft bearing clearance radial.
Installation Note:
Remove plastic thread.
Apply a light coat of oil to bearing shells and crankshaft.
Install bedplate Service and Repair.
Assemble engine.