11 25 530 Removing and installing/replacing all pistons (N52K)

WARNING: This page is about a different variant/trim than selected.

Special tools required:

00 9 120 TORQUE ANGLE MEASURING DIAL
11 4 491
11 4 492
11 4 493
11 4 494
11 6 241
11 6 261
11 8 330

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 piston pins are paired and must not be fitted individually.

Necessary preliminary tasks:

Remove engine
Mount engine on assembly stand, see Mounting engine on assembly stand (N52K) .
Remove intake air manifold
Remove cylinder head, see 11 12 100 Removing and installing cylinder head (N52K) .
Remove oil sump
Remove oil pump, see 11 41 000 Removing and installing/replacing oil pump (N52K)

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

IMPORTANT: Do not use any metal-cutting tools.

Fig 1: Locating 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), see 11 21 531 Replacing all main crankshaft bearing shells (N52K) .

Fig 2: Spray Nozzle And Screw

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Release conrod bolts (1).

Tightening torque: 11 24 1AZ, see 11 24 CONNECTING RODS AND BEARINGS .

Installation:

Replace screws.

Remove conrod 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 Conrod 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 to cylinder head side.

NOTE: Special tool 11 8 330 simultaneously 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: Special Tool (11 8 330)

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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 To Special Tool (11 4 491)

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WARNING: Danger of injury!

Carry out work on piston pin circlip wearing protective goggles only.

WARNING: Protective goggles must be worn.

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

Fig 6: Removing Piston Pin Circlip With Special Tool (11 4 492)

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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:

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: Installing Piston Pin Into Small End Bushing

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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 at measuring point "A", see 11 25 PISTONS WITH RINGS AND PINS N52K B25 .

Fig 8: Measuring Piston Diameter

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Adjust micrometer to cylinder bore of crankcase. Set internal caliper 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.

Piston installation clearance.

Total permissible wear tolerance, see 11 25 PISTONS WITH RINGS AND PINS N52K B25

If necessary, replace piston.

Fig 9: Measuring Diameter Of Cylinder Bore

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WARNING: Protective goggles must be worn.

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

Move piston pin circlip (2) into installation position.

Fig 10: Piston Pin Circlip And Groove

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WARNING: Protective goggles must be worn.

Guide lug and cutout 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 piston pin circlip must be driven in with a plastic hammer in the direction of the arrow.

Fig 11: Installing Piston Pin Circlip

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NOTE: For vehicles with B30 engines.

Install all piston rings, see 11 25 671 Replacing piston rings on all pistons (N52K) .

Install all connecting rod bearing shells, see 11 24 571 Replacing all connecting rod bearing shells (N52K) .

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:

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

Fig 12: Connecting Rod, Piston And Special Tools (11 8 330) And (11 6 261)

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NOTE: For vehicles with B25 engines.

Install all piston rings, see 11 25 671 Replacing piston rings on all pistons (N52K) .

Install all connecting rod bearing shells, see 11 24 571 Replacing all connecting rod bearing shells (N52K) .

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:

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

Fig 13: Connecting Rod, Piston And Special Tools (11 8 330) And (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!
Danger of piston ring failure.

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 tools 11 6 261 / 11 6 241 .

Fig 14: Pressing Piston With Special Tools (11 6 261)

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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: Connecting Rod Identical 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: Special Tool (11 8 330)

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

Installation:

Replace screws.

Install new conrod bolts (1).

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

Tightening torque: 11 24 1AZ, see 11 24 CONNECTING RODS AND BEARINGS .

Fig 17: Conrod Bolts And Connecting Rod Bearing Cap

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

Tightening torque: 11 24 1AZ, see 11 24 CONNECTING RODS AND BEARINGS .

Fig 18: Special Tool (00 9 120)

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Assemble engine.