Crankshaft Main Bearing: Service and Repair
Replacing All Crankshaft Main Bearing Shells
(Engine Dismantled)
M52 B20 / M52TU B20
M54 M22
Note: Injection nozzles for cooling the pistons are installed in the bores of bearing seats 2 to 7.
Design of injection nozzles:
1. Nozzle housing
2. Nozzle
3. Spring
4. Ball
M52 B25/B28
S52
M52TU B25/B28
M54 B25/B30
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: Check grinding size of crankshaft, refer to Specifications, Mechanical.
Installation:
When replacing the bearing shells (also for replacement crankshaft), classification for bearing shell arrangement in engine block is waived.
Insert bearing shells with yellow color coding in 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 on 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
Check ground size of main bearing journals.
Note:
Bearing caps 1 to 5 are designated on exhaust side.
Bearing caps 6 and 7 are not designated.
Bearing cap 6 is a thrust bearing.
Check clearance on main crankshaft bearing.
Install crankshaft and place special tool 00 2 590 (Plastigage Type PG1) on oil-free crankshaft.
Do not twist crankshaft.
Install main bearing cap so that grooves in main bearing shell guide are one one side.
Align main bearing cap flush with side of bearing seat.
Installation:
To check main bearing clearance, use the old main bearing screws.
There must be no oil in the blind holes (risk of cracking).
1. Tighten down main bearing screws with jointing torque.
2. Tighten down main bearing bolts with special tool 00 9120 to angle of rotation.
Tightening torque, refer to Specifications, Mechanical.
Remove main bearing cover and read off bearing clearance on width of squashed plastic thread using the measuring scale.
Radial crankshaft bearing clearance.
If necessary, fit new bearing shells with a different color code to correct bearing clearance.
Remove plastic thread.
Coat main bearing shells and crankshaft with engine oil.
Install main bearing cap so that grooves in main bearing shell guide are one one side.
Align main bearing cap flush with side of bearing seat.
Installation:
Always replace bolts of main bearing cap with new bolts
There must be no oil in the blind holes (risk of cracking]
Note: The reinforcement plates are not fitted on engines with gray cast iron engine blocks or on engines with oil pumps integrated in oil scrapers.
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 down all screws of main bearing caps with special tool 11 2 110 or with special tool 00 9 120 to torsion angle.
Tightening torque, refer to Specifications, Mechanical.
Check axial play.
If permitted end float is exceeded, check crankshaft, guide bearing shells and engine block, replacing if necessary, end float.