11 21 531 Replacing All Crankshaft Main Bearings (N51)

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Special tools required:

For the following special tools, refer to MAINTENANCE AND GENERAL INFORMATION - SPECIAL TOOLS -- 128I .

00 2 590

For the following special tools, refer to ENGINE - SPECIAL TOOLS (N51) .

11 4 251
11 4 252
11 4 470

IMPORTANT: Aluminum-magnesium materials. No steel screws/bolts may be used due to the threat of electrochemical corrosion. A magnesium crankcase requires aluminum screws/bolts exclusively. Aluminum screws/bolts must be replaced each time they are released . Aluminum screws/bolts are permitted with and without color coding (blue). For reliable identification: Aluminum screws/bolts are not magnetic . Jointing torque and angle of rotation must be observed without fail (risk of damage) .

Necessary preliminary tasks:

Remove crankshaft . See 11 21 500 REPLACING CRANKSHAFT (N51) .

Check setting of oil spray nozzles, adjusting if necessary:

Attach special tool 11 4 251 to screw connection on main bearing.

Special tool 11 4 252 must be pre-installed at the seventh main bearing block.

Tightening torque. See 11 11 5AZ in 11 11 ENGINE BLOCK .

Fig 1: Attaching Special Tool To Screw Connection On Main Bearing

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Remove crankshaft (1).

Fig 2: Removing Crankshaft

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NOTE: Pilot bearing shell (1) at the fourth bearing block is a thrust bearing.

Fig 3: Identifying Pilot Bearing Shell

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Remove bearing shells (1).

Fig 4: Identifying Bearing Shells

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Installation:

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).

Fig 5: Identifying Bearing Shells

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Bearing classification (1) on crankcase lower section (values from 1 to 3).

Bearing classification (2) of connecting rod bearings (b/r). See 11 24 571 REPLACING ALL CONNECTING ROD BEARINGS (N51) .

Fig 6: Identifying Bearing Classifications

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Bearing classification (1) in crankcase upper section as per table (values of A/B/C).

Installation:

When all the letters and numbers have been determined, the bearing shell color must be allocated, see table.

IMPORTANT: Engine damage will result if a small bearing play is determined. The color combination Yellow and Red must not be fitted. Possible color combinations, see BEARING CLASSIFICATION .

Fig 7: Identifying Bearing Classification Of Crankcase Upper Section

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BEARING CLASSIFICATION

(A1) Bedplate / Yellow	(B1) Bedplate / Yellow	(C1) Bedplate / Green
(A1) Crankcase / Yellow	(B1) Crankcase / Green	(C1) Crankcase / Green
(A2) Bedplate / Green	(B2) Bedplate / Green	(C2) Bedplate / Green
(A2) Crankcase / Yellow	(B2) Crankcase / Green	(C2) Crankcase / Red
(A3) Bedplate / Green	(B3) Bedplate / Red	(C3) Bedplate / Red
(A3) Crankcase / Green	(B3) Crankcase / Green	(C3) Crankcase / Red

Clean sealing faces (1).

IMPORTANT: Do not clean sealing faces with a metal-cutting tool.

Clean sealing faces (1) with special tool 11 4 470.

Fig 8: Identifying Sealing Faces

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Insert all bearing shells (2 and 3).

NOTE: Bearing shell at the fourth bearing block is a thrust bearing.

Fig 9: Identifying Bearing Shells

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Determine bearing play with special tool 00 2 590.

Installation:

All measuring points must be free from oil and grease.

Use used screws to determine bearing play.

Set up crankcase lower section with bearing shells. See 11 21 500 REPLACING CRANKSHAFT (N51) .

Fig 10: Removing Crankshaft

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Remove lower crankcase.

Read off bearing play at width of flattened plastic thread and measurement scale.

Crankshaft bearing clearance radial.

Installation:

Remove plastic thread.

Apply a light coat of oil to bearing shells and crankshaft.

Fig 11: Locating Measurement Scale

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Install crankcase lower section . See 11 21 500 REPLACING CRANKSHAFT (N51) .

Assemble engine.