M52 B25/B28 S52 M52TU B25/B28 M54 B25/B30 M56

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

Fig 1: Identifying Injection Nozzles

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Installation:

Screw threads are coated with screw securing adhesive (Loctite).

Replace screws.

IMPORTANT: Observe grinding stage of crankshaft. Refer to ENGINE - TECHNICAL DATA .

Fig 2: Identifying Grinding Stage Of Crankshaft

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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.

Fig 3: Inserting Bearing Shells

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NOTE:

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

Fig 4: Identifying Bearing Shells
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NOTE: The axial guide on the crankshaft is fitted to bearing point 6. Insert pilot bearing shell in the engine block.

Fig 5: Inserting Pilot Bearing Shell In Engine Block

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Install crankshaft.

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

Fig 6: Locating Crankshaft Marks

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Installation:

The bearing shell classification for the bearing cover is marked on the crankshaft in yellow, green or white paint.

Fig 7: Identifying Bearing Cover Mark

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Insert main bearing shells with same crankshaft color coding in main bearing caps.

The bearing shells are marked with yellow, green or white paint.

Bearing shell
Guide bearing

Fig 8: Identifying Bearing Shells Marks
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Observe grinding stage of main bearing journals. Refer to ENGINE - TECHNICAL DATA .

NOTE: Bearing caps 1 to 5 are marked on exhaust side.
Bearing caps 6 and 7 are not designated.
Bearing cap 6 is a thrust bearing.

Fig 9: View Of Bearing Cap Mark

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Check clearance on main crankshaft bearing.

Fig 10: Checking Clearance

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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 on one side. Align main bearing cap flush with side of bearing seat.

Fig 11: Installing Main Bearing Cap

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Installation:

To check main bearing clearance, use the old main bearing screws. There must be no oil in the blind holes (risk of cracking).

Tighten down main bearing screws with jointing torque.
Tighten down main bearing bolts with special tool 00 9 120 to angle of rotation.

Fig 12: Tightening Down Main Bearing Bolts

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Tightening torque, 11 11 1AZ. Refer to ENGINE - TIGHTENING TORQUES .

Remove main bearing cap and read off bearing clearance at width of pinched plastic thread on measuring scale.

Fig 13: Reading Off Bearing Clearance

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Radial crankshaft bearing clearance, refer to ENGINE - TECHNICAL DATA .

If necessary, to correct bearing clearance, fit new bearing shells with a different color coding.

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 on one side.

Fig 14: Installing Main Bearing Cap

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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.

Fig 15: View Of Reinforcement Plate

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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:

Tighten all screws on main bearing cover with jointing torque.
Unfasten screws on main bearing cover 6.
Strike back and front of crankshaft with plastic hammer to center thrust bearing (do not damage crankshaft).
Tighten screws of main bearing cover 6 with jointing torque.
Tighten down all screws of main bearing caps with special tool 11 2 110 or with special tool 00 9 120 to torsion angle.

Fig 16: Tightening Down Main Bearing Cover

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Tightening torque, 11 11 1AZ. Refer to ENGINE - TIGHTENING TORQUES .

Check axial play. If permitted end float is exceeded, check crankshaft, guide bearing shells and engine block, replacing if necessary.

Fig 17: Checking Axial Clearance

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End float, refer to ENGINE - TECHNICAL DATA .