11 25 530 Removing and installing/replacing all pistons (N63) up to 3/2011

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Special tools required:

00 9 120
11 5 440
11 7 280
11 8 151
11 8 152

See MAINTENANCE AND GENERAL INFORMATION - SPECIAL TOOLS .

See ENGINE - SPECIAL TOOLS (N54, N63) .

WARNING: Protective goggles must be worn when working on the gudgeon pin circlip.

IMPORTANT: If pistons and connecting rods are reused, they must be reinstalled in the same places.

Piston and piston pin are matched to each other and can only be replaced as a pair.

Conrod and conrod bearing cap are cracked.

Identification is effected by means of identical pairing letters on the connecting rod big end.

Mixing up the components will result in engine damage.

Conrod bearings must always be replaced.

Necessary preliminary tasks:

Remove engine
Mount engine on assembly stand .
Remove both left cylinder head and right cylinder head .
Remove oil sump .
Remove oil pump .

Unscrew conrod bearing cover.

NOTE: Connecting rods and connecting rod bearing caps are denoted with the same pairing letters.

The stamped dates are always arranged in opposite directions.

Set down conrod bearing caps in order.

Fig 1: Identifying Stamped Dates On Connecting Rod Bearing Caps

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NOTE: To install and remove the conrods, it is essential for the crankshaft to be exactly in alignment with the cylinder bore (see dashed line).

Position crankshaft at central bolt.

Insert special tool 11 8 152 in conrod.

Screw special tool 11 5 440 into conrod with bolt (1).

Remove conrod with piston from cylinder head side.

Fig 2: Positioning Crankshaft Central Bolt

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IMPORTANT: Piston and piston bolts are paired and must not be fitted individually.

Lift out retaining ring and press out piston pin.

Fig 3: Pressing Piston Snap Ring

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If necessary, replace connecting rods.

NOTE: The conrods can also be replaced individually.

The gudgeon pin must be able to be pressed through the liner by hand with little force and must not display any significant play.

Fig 4: Pressing Out Piston Pin

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Prior to installation, measure piston installation clearance:

Measure piston diameter with micrometer at measuring point A from lower edge of piston and offset by 90° to piston pin axis.

Measuring point A .

Fig 5: Measuring Piston Diameter

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Adjust micrometer to cylinder bore of engine block. Set internal calliper on micrometer to zero. Measure bottom, center and top of cylinder bore in direction of travel and direction of engine rotation.

Diameter of cylinder bore . See ENGINE - TECHNICAL DATA (N63) .

Piston installation clearance . See ENGINE - TECHNICAL DATA (N63) .

Total permissible wear tolerance . See ENGINE - TECHNICAL DATA (N63) .

Fig 6: Adjusting Micrometer To Cylinder Bore Of Engine Block

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IMPORTANT: The conrods of cylinder banks 1 to 4 and 5 to 8 are mounted to the pistons differently.

NOTE: The pistons and conrods of cylinders 1 to 8 are identical.

Fig 7: Identifying Piston Mark

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Arrow on piston crown (cyl. 1 to 4) points upwards, bolt connection on conrod points at an angle to right.

Arrow on piston crown (cyl. 5 to 8) points upwards, bolt connection on conrod points at an angle to left.

NOTE: For purposes of clarity, pistons are shown removed.

The conrods are correctly mounted on the piston when the bolt connections on the conrods are parallel to each other (see arrow).

Fig 8: Identifying Bolt Connections On Conrods

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Install retaining ring.

Fig 9: Installing Retaining Ring

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Installation:

Piston circlip (1) is correctly installed when the opening points upwards.

See illustration.

It must still be possible for the piston pin to moved easily.

Fig 10: Identifying Piston Circlip

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Insert special tools 11 8 151 and 11 8 152 in conrod.

Install conrod bearing .

Fig 11: Installing Conrod Bearing

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Lightly coat pistons and piston rings with oil.

Offset the contact points of the piston rings by approx. 120° to each other but do not position above the piston pin boss.

NOTE: Picture shows S85.

Fig 12: Identifying Piston Rings Position

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Keep piston rings compressed with special tool 11 7 280.

Install piston so that arrow points to camshaft drive.

IMPORTANT: Danger of piston ring failure.

Press in piston only with finger force (do not knock in!).

Fig 13: Identifying Special Tool (11 7 280)

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IMPORTANT: Danger of piston ring failure.

Press in piston (1) only with finger force (do not knock in!).

Fig 14: Pressing Piston With Finger Force

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The direction arrow on the piston crown must point to the camshaft drive (direction of travel towards front).

Fig 15: Identifying Piston Mark

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Attach crankpin to connecting rod.

Remove special tools 11 5 440 and 11 8 152.

Fig 16: Positioning Crankshaft Central Bolt

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NOTE: For purposes of clarity, the pairing letters (1) are shown on the removed conrod.

IMPORTANT: Conrods and conrod bearing caps are denoted with the same pairing letters (1), do not mix them up.

Fit bearing cap so that pairing letters match up.

Fig 17: Identifying Bearing Cap Mark

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Apply light coat of oil to connecting-rod bearing shells.

Fit bearing cap so that pairing letters match up.

Install new conrod bolts.

Fig 18: Identifying Connecting-Rod Bearing Bolts

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Tighten down conrod bolts (1) with special tool 00 9 120.

Tightening torque 11 24 1AZ .11 24 CONNECTING RODS AND BEARINGS

Fig 19: Tightening Connecting-Rod Bearing Cap Bolt

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Assemble engine.