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

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Special tools required:

WARNING: Safety 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.
Pistons and gudgeon pins 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 tasks:

Fully remove front axle together with engine.
Remove engine from front axle. See applicable procedure for drivetrain configuration: 11 00 598 REMOVING AND INSTALLING ENGINE ON FRONT AXLE (N63O1) WITH GA8HP70Z TRANSMISSION , 11 00 598 REMOVING AND INSTALLING ENGINE ON FRONT AXLE (N63O1) WITH GA8HP70Z ALL-WHEEL DRIVE VEHICLE TRANSMISSION , 11 00 598 REMOVING AND INSTALLING ENGINE ON FRONT AXLE (N63O1) WITH GA6HP26Z ALL-WHEEL DRIVE VEHICLE TRANSMISSION or 11 00 598 REMOVING AND INSTALLING ENGINE ON FRONT AXLE (N63O1) WITH MANUAL GEARBOX .
Install engine on assembly stand. See 11 00 MOUNTING ENGINE ON ASSEMBLY STAND (N63) .
Remove both cylinder heads. See 11 12 105 REMOVING AND INSTALLING LEFT CYLINDER HEAD (N63) and 11 12 106 REMOVING AND INSTALLING RIGHT CYLINDER HEAD (N63) .
Removing oil pan. See 11 13 020 REMOVING AND INSTALLING/REPLACING LOWER OIL SUMP SECTION (N63) and 11 13 010 REMOVING AND INSTALLING/REPLACING UPPER OIL SUMP SECTION (N63) .
Remove OIL PUMP

Unscrew connecting rod bearing cap.

NOTE: Connecting rods and connecting rod bearing caps are denoted with the same pairing letters.
The production dates are always arranged in opposite directions.
Set down connecting rod bearing caps in order.

Fig 1: Locating Connecting Rods Pairing Letters

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NOTE: For installation and dismantling of 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: Pistons and gudgeon pins are paired and must not be fitted individually.

Lift out circlip and press out piston pin.

Fig 3: Removing Circlip From Piston

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If necessary, replace connecting rods.

NOTE: The connecting rod can also be replaced individually.

The gudgeon pin must be able to be pressed through the bush 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 at 90° to the axis of the gudgeon pin.

MEASURING POINT A .

Fig 5: Measuring Piston Installation Clearance

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

DIAMETER OF CYLINDER BORE .

PISTON INSTALLATION CLEARANCE .

TOTAL PERMISSIBLE WEAR CLEARANCE .

Fig 6: Measuring Cylinder Bore Diameter

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

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

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, screw connection on connecting rod points at an angle to left.

Fig 7: Identifying Piston And Connecting Rod Assembly Cylinders 1 to 4 And 5 to 8

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

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

Fig 8: Identifying Piston And Connecting Rod Assembly

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Install circlip.

Fig 9: Installing Piston Pin Circlip

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Installation note:

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

See Fig 10.

It must still be possible for the gudgeon pin to be 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.

Fig 11: Inserting Special Tools Onto Connecting Rod

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Lightly coat pistons and piston rings with oil.

INSTALL CONNECTING ROD BEARING .

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

NOTE: Illustration shows S85.

Fig 12: Identifying 120° Offset Of Piston Ring Contact Points

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Keep piston rings compressed with special tool 11 7 280 .

Install piston so that arrow points to camshaft drive.

IMPORTANT: Risk of breakage of piston rings.

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

Fig 13: Compressing Piston Rings Using Special Tool (11 7 280)

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IMPORTANT: Risk of breakage of piston rings.

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

Fig 14: Pressing Piston Using Minimal 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 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 1 AZ .

Fig 19: Tightening Connecting Rod Bolts Using Special Tool (00 9 120)

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Assemble engine.