Preliminary work

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Clamp special tool 11 4 491 in a vice.

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

Fig 1: Identifying Piston And Special Tool (11 4 491)

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WARNING: Protective goggles must be worn for the next work step.

WARNING: Protective goggles must be worn.

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

Fig 2: Removing Piston Circlip Using Special Tool (11 4 492)

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If necessary, replace connecting rods.

IMPORTANT: Connecting rods are divided into weight categories and are only available as a set.
Old and new connecting rods must not be installed in mixed combinations.

Installation:

The piston pin must be able to be pressed through the liner by hand with little force and must not display any significant play.

Fig 3: Installing Gudgeon Pin

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Measure piston installation clearance:

Measure piston diameter with micrometer at measuring point A from bottom edge of piston and offset at 90° to the axis of the piston pin.

Piston diameter at measuring point A.

Fig 4: Measuring Piston Diameter

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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.

Diameter of cylinder bore.

Piston installation clearance.

Total permissible wear tolerance see 1121-N51-03B1S1 CRANKSHAFT AND BEARINGS .

If necessary, replace piston.

Fig 5: Measuring Diameter Of Cylinder Bore

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WARNING: Protective goggles must be worn.
Insert piston circlip (2) into groove (1) of special tool 11 4 493 PLIERS .
Bring piston circlip into assembly position.

Fig 6: Identifying Piston Circlip And Groove Of Special Tool

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WARNING: Protective goggles must be worn.

Guide lug and cutout on special tool 11 4 493 PLIERS must point to the piston crown; only then can special tool 11 4 494 MANDREL be correctly fitted.

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

NOTE: See Fig 7.

Fig 7: Driving Piston Pin Using Plastic Hammer

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NOTE: B 30.

Install all PISTON RINGS .

Install all BEARING SHELLS .

Coat piston and piston rings with oil.

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

Attach special tool 11 8 330 ASSEMBLY TOOL in conrod (2).

Installation:

Check protective lugs (1) on special tool 11 8 330 ASSEMBLY TOOL for correct position and damage.

Fig 8: Attaching Special Tool In Connecting Rod

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Insert piston with conrod in cylinder.

IMPORTANT: Risk of damage to oil spray nozzle.
Danger of piston ring failure.
Press in piston with finger pressure only, do not drive in (see arrows).

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

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

Fig 9: Inserting Piston On Piston Crown Points

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

Fig 10: Identification Pairing Letters On Conrod Bearing Cap