Crankshaft Main Bearing: Service and Repair

(engine dismantled)





Note: Injection nozzles for cooling the pistons are installed on the underside of the cylinder between the bearing seats.

Installation:
Screw threads are coated with screw securing adhesive (Loctite). Replace screws.





Caution: Note grinding stage of crankshaft, refer to Engine Specifications.





Installation:
When replacing the bearing shells (also for replacement crankshaft), classification for bearing shell arrangement in engine block is waived. Only install yellow bearing shells in the engine block.





Note:
1. Install bearing shells with continuous lubricant groove and one retaining lug in engine block.
2. Fit bearing shells without continuous lubricant groove and two retaining lugs in bearing cover.





Note:
^ The axial guide on the crankshaft is fitted to bearing point 6.
^ Insert pilot bearing shell in the engine block.





Install crankshaft.

Note: The crankshaft is marked with yellow, green or white paint according to the tolerance of the main journal.





Installation:
The bearing shell classification for the bearing cover is marked or the crankshaft in yellow, green or white paint.
Place main bearing shells with same color code as that of crankshaft in main bearing caps.





The bearing shells are marked with yellow, green or white paint.
1. Bearing shell
2. Guide bearing
Note grinding stage of main bearing journal, refer to Engine, Specifications.





Note:
^ The bearing covers 1 ... 5 are designated on the exhaust end.
^ Bearing covers 6 and 7 are not designated.
^ Bearing cover 6 is a thrust bearing.





Check clearance on main crankshaft bearing.
Install crankshaft and place special tool 00 2 590 (Plastigage Type PG1) on the oil-free crankshaft. Do not twist crankshaft.





Install main bearing cover with grooves in main bearing shell mount on one side.
Align main bearing cap flush with side of bearing seat.

Installation:
To check main bearing clearance, use the old main bearing screws.
No oil is permitted in the blind bores (danger of cracking).

Note: On engines with aluminum engine block, do not wash off screw coating. On engines with cast iron engine block, wash and oil screws.





1. Tighten down main bearing screws with jointing torque.
2. Tighten down main bearing screws using special tool 9 120 and torsion angle.
Tightening Torque, refer to Engine Specifications.





Remove main bearing cover and read off bearing clearance on width of squashed plastic thread using the measuring scale.
Radial runout on crankshaft bearing, refer to Engine Specifications.
If necessary, fit new bearing shells with a different color code to correct bearing clearance.





Color code for shaft diameter/bearing size:
1. Crankshaft
Ge = yellow
Gn = green
Ws = white
2. Bearing clearance
3. Bearing shells: yellow, green or white
4. Bearing cover





Note:
^ Remove plastic thread.
^ Coat main bearing shells and crankshaft with engine oil.
^ Install main bearing cover with grooves in main bearing shell mount on one side.
^ Align main bearing cap flush with side of bearing seat.

Installation:
Always replace the screws on the main bearing cover with new ones.
No oil is permitted in the blind bores (danger of cracking).

Note:
^ On engines with aluminum engine block, do not wash off screw coating.
^ On engines with cast iron engine block, wash and oil screws.





M52 with aluminum engine block only:
Installation:
Install reinforcement plates and fit screws with zero backlash.
Install main bearing shells and abut firmly.
Tighten down screw connection on reinforcement plates.





Tightening specifications for main bearing:
1. Tighten all screws on main bearing cover with jointing torque.
2. Unfasten screws on main bearing cover 6.
3. Strike back and front of crankshaft with plastic hammer to center thrust bearing (do not damage crankshaft).
4. Tighten screws of main bearing cover 6 with jointing torque.
5. Tighten all screws of main bearing cover with special tool 11 2 110 or special tool 00 9 120 with torsion angle.
Tightening Torque, refer to Engine Specification.





Check end float.
If the permitted end float is exceeded, check crankshaft, pilot bearing shells and engine block and replace where necessary.
Axial clearance, refer to Engine Specifications.