11 25 530 Removing and installing or replacing all pistons (N16)

Special tools required:

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

IMPORTANT: If pistons, connecting rods and bearing shells are reused, they must be reinstalled in the same places.
Connecting rods and connecting rod bearing caps are denoted with the same pairing letters; mixing them up will result in engine damage.
Piston and gudgeon pins are paired and must not be fitted individually.

Necessary preliminary tasks:

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

NOTE: In event of heavy oil carbon residue:

Carefully remove oil carbon residue from cylinder wall.

NOTE: Illustration shows N46.

Fig 1: Locating Oil Carbon Residue On Cylinder Wall

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NOTE: Mark all pistons and connecting rods with a pen prior to removing.

Example N14:

Direction of arrow (1) points to camshaft drive.

Cylinder allocation (2) per cylinder.

Fig 2: Identifying Camshaft Drive Direction And Cylinder Allocation

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NOTE: Mark all pistons and connecting rods with a pen prior to removing.

Example:

Mark cylinder assignment (1) for the respective cylinder.

Direction of arrow (2) points to timing chain drive.

Fig 3: Identifying Timing Chain Drive Direction And Cylinder Identification Markings

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Release connecting rod bolts (1).

Tightening torque, 11 24 1AZ .

Remove connecting rod bearing cap.

IMPORTANT: Connecting rods and connecting rod bearing caps are denoted with the same pairing letters; mixing them up will result in engine damage.

Fig 4: Identifying Connecting Rod Bolts

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Attach special tool 11 9 620 in connecting rod big end.

Press out connecting rod and piston to cylinder head side.

Fig 5: Attaching Special Tool (11 9 620) In Connecting Rods Big End

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WARNING: Safety goggles must be worn for the next operation.

WARNING: Safety goggles must be worn.

IMPORTANT: Piston and gudgeon pins are paired and must not be fitted individually.

Fig 6: Removing Piston Pin Circlip Using Screwdriver

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Lever out piston pin circlip with a screwdriver in direction of arrow.

If necessary, replace connecting rods.

Installation note:

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 7: Installing Gudgeon 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 (refer to TECHNICAL DATA ).

Fig 8: Measuring Piston Diameter Using Micrometer

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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.

For diameter of cylinder bore, piston installation clearance, and total permissible wear tolerance: see technical data for ENGINE BLOCK/CYLINDER CRANKCASE and PISTONS/RINGS/PINS .

If necessary, replace piston.

Fig 9: Checking Cylinder Bore Diameter

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Install all PISTON RINGS .

Install all BEARING SHELLS .

Coat piston and piston rings with oil.

Pre-install piston in special tool 11 9 670 .

Screw special tool 11 9 620 into connecting rod.

Installation note:

Check protective lugs on special tool 11 9 620 for correct position and damage.

Fig 10: Identifying Special Tools (11 9 620 And 11 9 670)

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Insert piston with connecting rod in cylinder.

IMPORTANT: Risk of breakage of piston rings.
Press in piston with finger pressure only, do not drive in (see arrows).

Fig 11: Pressing In Piston With Special Tool (11 9 670)

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

If reusing the pistons, assign cylinder allocation (2) to correct cylinder.

Press in piston with special tool 11 9 670 .

IMPORTANT: Point of fracture (1) on connecting rod.
Connecting rod and connecting rod bearing cap are identified with pairing letters (2) and must not be mixed up.
Mixing them up or incorrectly fitting the connecting rod bearing cap on the big end will result in engine damage .

Both pairing letters (2) must be together on one side.

Fig 12: Identifying Connecting Rod Pairing Letters

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Apply a light coat of oil to crankshaft journals.

Attach connecting rod to crankshaft journal.

Remove special tool 11 9 620 .

Fig 13: Attaching Special Tool (11 9 620) In Connecting Rods Big End

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

Check cylinder identification markings (1).

Direction of arrow (2) points to timing chain drive.

Fig 14: Identifying Timing Chain Drive Direction And Cylinder Identification Markings

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Install new connecting rod bolts (1).

00 9 120 Carry out torsion angle tightening of connecting rods with special tool.

Tightening torque: 11 24 1AZ

Fig 15: Identifying Connecting Rod Bolts

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Assemble engine.