Crankshaft Main Bearing: Service and Repair
11 21 531 Replacing all main crankshaft bearing shells (N74)Special tools required:
Important!
Risk of injury from sharp crankcase edges.
Necessary preliminary tasks:
^ Remove crankshaft
Note:
Main bearing caps 1 to 5 are marked with punched numbers.
The letters denote the bearing shell classification for the relevant bearing position from 1 to 7 (main bearing cap).
The first letter on the left applies to the first bearing position at the front on the timing chain drive.
Colour coding on crankshaft 1 to 57
Y= yellow
G= green
V= violet
The letters denote the bearing shell classification for the relevant bearing position from 1 to 7 crankcase.
The letters are located on the transmission end in the V-chamber.
The first letter on the left applies to the first bearing position at the front on the timing chain drive.
Colour assignment in crankcase 1 to 7.
Y= yellow
G= green
V= violet
Installation:
Install main bearing shells (1) with lubrication groove in crankcase.
Install main bearing shells (2) without lubrication groove in the main bearing caps.
Note:
Main bearing cap number 4 can be identified by the surfaces (1) for the thrust washers discs of the thrust bearing.
Unscrew thread support bushings in main bearing caps.
Checking main bearing clearance:
To check crankshaft bearing clearance, use the existing main bearing screws.
Important!
Risk of cracking!
No oil is permitted in the blind bores.
Do not twist crankshaft.
Place special tool 00 2 590 (Plastigage type PG 1) on oil-free crankshaft (see arrow).
Tighten down all collar bolts (M11) of main bearing caps in sequence 1 to 7 to jointing torque.
Tightening torque 11 11 1AZ.
Tighten down all collar bolts (M11) of main bearing caps with special tool 00 9 120 with angle of rotation.
Remove main bearing cap.
Read off main bearing play at width of flattened plastic thread with assistance of measurement scale.
Main bearing play.
- Remove plastic thread
- Apply a coat of oil to new bearing shells and crankshaft
Note:
Always replace bolts in main bearing caps with new bolts.
Do not wash off bolt coating.
Important!
Risk of cracking!
No oil is permitted in the blind bores.
Install crankshaft.
Carefully strike back and front of crankshaft (1) with a plastic hammer to centre guide bearing (do not damage crankshaft).
Secure special tool 11 6 252 with magnetic foot on crankcase.
Position special tool 11 6 251.
Tightening specifications for main bearing:
Check guide bearing shell of crankshaft and crankcase.
Check axial play.
Assemble engine.
