11 25 530 Removing and installing/replacing all pistons (N52T)

Special tools required:

WARNING: Danger of injury!
Carry out work on piston pin circlip wearing protective goggles only.

IMPORTANT: If piston, connecting rod, big end bearing cap and connecting rod bearing shell are to be reused, they must be installed in the same position.
Individual replacement of a connecting rod is not permitted. Connecting rods are classified by weight categories and are only available as a set for all cylinders.
Connecting rod and big end bearing cap are marked with identical pairing letters and must not be mixed up.
Danger of engine damage!
Piston and gudgeon pins are paired and must not be fitted individually.

Necessary preliminary work:

Remove ENGINE .
Mount engine on ASSEMBLY STAND .
Remove intake PLENUM .
Remove CYLINDER HEAD .
Remove OIL SUMP .
Remove OIL PUMP .

NOTE: Carefully remove heavy oil carbon residues from the cylinder wall (arrow).

IMPORTANT: Do not use any metal-cutting tools.

Fig 1: Locating Carbon Residue On Cylinder Wall

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IMPORTANT: Oil spray nozzle (2) must not be maladjusted or bent.
Risk of damage!

Do not release screw (1) of oil spray nozzle (2).

If necessary, readjust OIL SPRAY NOZZLE (2).

Fig 2: Identifying Oil Spray Nozzle And Screw

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Release connecting rod bolts (1).

Tightening torque: 11 24 1AZ .

Installation note:

Replace screws.

Remove connecting rod bearing cap (2) in direction of arrow.

IMPORTANT: Connecting rod and big end bearing cap (2) are marked with identical pairing letters and must not be mixed up.
Danger of engine damage!

Fig 3: Removing Connecting Rod Bearing Cap

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Attach special tool 11 8 330 to connecting rod.

Press out connecting rod and piston with special tool 11 8 330 towards cylinder head side.

NOTE: Special tool 11 8 330 also serves to prevent connecting rod and piston from falling down.

IMPORTANT: Do not touch the oil spray nozzle when removing the components.
Risk of damage!

Fig 4: Attaching Special Tool (11 8 330) To Connecting Rod

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Preliminary work:

Clamp special tool 11 4 491 in vice.

Secure piston (1) with connecting rod to special tool 11 4 491 .

Fig 5: Securing Piston With Connecting Rod

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WARNING: Danger of injury!
Carry out work on piston pin circlip wearing protective goggles only.

WARNING: Safety goggles must be worn.

Lever out circlip for gudgeon pin with special tool 11 4 492 in direction of arrow.

Fig 6: Removing Gudgeon Pin Circlip

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If necessary, replace connecting rods.

IMPORTANT: Individual replacement of a connecting rod is not permitted. Connecting rods are classified by weight categories and are only available as a set for all cylinders.
Existing and new connecting rods must not be installed in mixed combinations.

Installation note:

It must be possible for the piston pin to be pressed with minimal force by hand through the small end bushing. There must be no noticeable play.

Fig 7: Pressing Connecting Rod Pin

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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.

Piston diameter . See PISTONS WITH RINGS AND PINS (N52T) at measuring point "A".

Fig 8: Measuring Piston Diameter Using Micrometer

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Adjust micrometer to cylinder bore of crankcase. 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. See ENGINE BLOCK, CYLINDER CRANKCASE (N52T) .

Piston installation clearance. See ENGINE IN GENERAL (N52T) .

Total permissible wear tolerance. See PISTONS WITH RINGS AND PINS (N52T) .

If necessary, replace piston.

Fig 9: Adjusting Micrometer To Cylinder Bore Of Crankcase

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WARNING: Safety goggles must be worn.

Insert gudgeon pin circlip (2) into groove (1) of special tool 11 4 493 .

Move piston pin circlip (2) into installation position.

Fig 10: Inserting Gudgeon Pin Circlip Into Special Tool (11 4 493) Groove

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WARNING: Safety goggles must be worn.

Guide lug and aperture on special tool 11 4 493 must point to piston crown. Only then can special tool 11 4 494 be correctly fitted.

When special tools 11 4 493 and 11 4 494 are correctly positioned, the circlip for gudgeon pin must be driven in with a plastic hammer in the direction of the arrow.

Fig 11: Positioning Special Tool (11 4 493)

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NOTE: For vehicles with B30 engine.

Install all PISTON RINGS .

Install all CONNECTING ROD BEARING SHELLS .

Coat piston (2) and piston rings with oil.

Pre-install piston (2) in special tool 11 6 261 .

Attach special tool 11 8 330 to connecting rod (1).

Installation note:

11 8 330 Check protective lugs on special tool for correct position and damage.

Fig 12: Installing Piston In Special Tool (11 6 261)

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NOTE: For vehicles with B25 engine.

Install all PISTON RINGS .

Install all CONNECTING ROD BEARING SHELLS .

Coat piston (2) and piston rings with oil.

Pre-install piston (2) in special tool 11 6 241 .

Attach special tool 11 8 330 to connecting rod (1).

Installation note:

11 8 330 Check protective lugs on special tool for correct position and damage.

Fig 13: Installing Piston In Special Tool (11 6 241)

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Insert piston (1) with connecting rod in cylinder.

IMPORTANT: Do not touch the oil spray nozzle when installing the components.
Risk of damage!
Risk of breakage of piston rings.

Press in piston (1) at marked points (see arrows) with finger pressure only, do not drive in.

Insert piston (1) so that arrow (2) on piston crown points to camshaft drive.

Press in piston (1) with special tool 11 6 261 /11 6 241 .

Fig 14: Pressing Piston

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IMPORTANT: Connecting rod and big end bearing cap are marked with identical pairing letters (1) and must not be mixed up.
Mixing them up or incorrectly fitting the big end bearing cap on the connecting rod will result in engine damage .

Fig 15: Identifying Connecting Rod And Bearing Cap Marked Pairing Letters

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Apply a light coat of oil to connecting rod bearing journal.

Join connecting rod and connecting rod bearing journal.

Detach special tool 11 8 330 .

Fig 16: Detaching Special Tool (11 8 330) To Connecting Rod

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Fit big end bearing caps (2) so that pairing letters match up.

Installation note:

Replace screws.

Install new connecting rod bolts (1).

IMPORTANT: Jointing torque and angle of rotation must be observed without fail.
Risk of damage!

Tightening torque: 11 24 1AZ .

Fig 17: Identifying Connecting Rod Bearing Cap And Bolts

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If necessary, tighten connecting rod bolts to angle of rotation with special tool 00 9 120 .

Tightening torque: 11 24 1AZ .

Fig 18: Identifying Special Tool (00 9 120)

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Assemble engine.