11 25 530 Removing and installing/replacing all pistons (S63)

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Special tools required:

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.
Connecting rod and connecting rod 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.
Connecting rod bearings must always be replaced.

Necessary preliminary work:

Remove engine. See REMOVING ENGINE FROM FRONT AXLE (M6, DUAL-CLUTCH TRANSMISSION) or REMOVING ENGINE FROM FRONT AXLE (M6, MANUAL TRANSMISSION) .
Mount engine on ASSEMBLY STAND .
Remove both cylinder heads. See REMOVING LEFT CYLINDER HEAD and REMOVING RIGHT CYLINDER HEAD .
Remove oil sump. See REMOVING LOWER OIL SUMP SECTION and REMOVING UPPER OIL SUMP SECTION .
Remove OIL PUMP .

Unscrew connecting rod bearing cap.

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 connecting rod bearing caps in order.

Fig 1: Identifying Pairing Letters

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NOTE: To install and remove the connecting rods, 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 into connecting rod.

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

Remove connecting rod with piston from cylinder head side.

Fig 2: Pressing Out Connecting Rod And Piston Toward Cylinder Head Side

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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: Lifting Out Circlip

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If necessary, replace connecting rods.

NOTE: The connecting rods 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 Gudgeon Pin Through Bush

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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 Installation Clearance

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

Refer to DIAMETER OF CYLINDER BORE , PISTON INSTALLATION CLEARANCE , and TOTAL PERMISSIBLE WEAR TOLERANCE .

Fig 6: Measuring Cylinder Bore

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

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

Fig 7: Identifying Pistons And Connecting Rods

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

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

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

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

Fig 8: Identifying Connecting Rods Mounted On Piston

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Install retaining ring.

Fig 9: Installing Circlip

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Installation:

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

See Fig 10.

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

Fig 10: Identifying Correct Installation Position Of Piston Circlip

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Insert special tools 11 8 151 and 11 8 152 into connecting rod.

Install connecting rod bearing.

Fig 11: Inserting Special Tools Into Connecting Rod

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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 120° Offset Of Piston Ring Contact Points

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Keep piston rods 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-In Piston Using Finger Force

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

NOTE: Graphics show N63.

Fig 15: Identifying Piston Crown Direction Arrow

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Attach crankshaft journal to connecting rod.

Remove special tools 11 5 440 and 11 8 152 .

Fig 16: Pressing Out Connecting Rod And Piston Toward Cylinder Head Side

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

IMPORTANT: Connecting rods and connecting rod 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 Connecting Rod Pairing Letters

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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 connecting rod bolts.

Fig 18: Identifying Connecting Rod Bolts

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

Tightening torque 11 24 1AZ .

Fig 19: Securing Connecting Rod Bolts Using Special Tool 00 9 120

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Assemble engine.