11 24 571 Replacing all connecting rod bearings (N51)

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Special tools required:

00 2 590
00 9 120

IMPORTANT: Aluminium-magnesium materials.

No steel screws/bolts may be used due to the threat of electrochemical corrosion.

A magnesium crankcase requires aluminium screws/bolts exclusively.

Aluminium screws/bolts must be replaced each time they are released .

Aluminium screws/bolts are permitted with and without color coding (blue).

For reliable identification:

Aluminium screws/bolts are not magnetic .

Jointing torque and angle of rotation must be observed without fail (risk of damage).

Necessary preliminary tasks:

Remove Oil Pan

IMPORTANT: All crankshaft crank pins are classified.

Possible classifications per connecting rod at top and bottom:

r: Red
b: Blue

Only one color may be fitted per big end bearing cap and connecting rod.

In direction of arrow from (1 to 2) crank pin (1 to 6).

Example:

Possible classification: rbbrrb

Cylinder Classification Red / Red
Cylinder Classification Blue / Blue
Cylinder Classification Blue / Blue
Cylinder Classification Red / Red
Cylinder Classification Red / Red
Cylinder Classification Blue / Blue

Fig 1: Big End Bearing Cap Mark

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Release conrod bolts (1).

Remove connecting rod bearing cap (2).

Fig 2: Connecting Rod Bearing Cap And Conrod Bolts

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IMPORTANT: Risk of damage to cylinder wall and to crankshaft.

Gently release connecting rod from crankshaft.

Remove connecting rod bearing shells (1 and 2).

Install new conrod bearing shells.

Installation:

Pay attention to guide lugs during installation.

IMPORTANT: All crankshaft crank pins are classified.

Fig 3: Connecting Rod Bearing Shells And Connecting Rod

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In each case insert only one color of connecting rod bearing shell (1 and 2) for each connecting rod.

Check conrod bearing clearance.

Piston in BDC position.

Determine bearing clearance, ensure that bearing points are free from oil and grease.

Fit special tool 00 2 590 (Plastigage Type PG 1) to the oil-free crankshaft.

Fit conrod bearing cap so that pairing letters match up.

Fig 4: Locating Bearing Cap

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IMPORTANT: Do not distort conrods or crankshaft.

Use the old conrod bolts to check conrod clearance.

Tighten down conrod bolts with special tool 00 9 120.

For tightening torque refer to 11 24 1AZ in 11 24 CONNECTING RODS AND BEARINGS .

Fig 5: Special Tool (00 9 120)

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Remove bearing cap. Read off bearing clearance at width of crushed plastic thread (Plastigage) with aid of measuring scale.

Conrod Bearing Clearance .

Remove Plastigage
Coat crankshaft and connecting rod bearing shells with oil
Install new conrod bolts and tighten down with special tool 00 9 120.

For tightening torque refer to 11 24 1AZ in 11 24 CONNECTING RODS AND BEARINGS .

Fig 6: Checking Bearing Play

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Assemble engine.