Preliminary work

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Clamp special tool 11 4 491 in vice.

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

Fig 1: Securing Piston With Connecting Rod To Special Tool (11 4 491)

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WARNING: Risk 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 2: Removing Gudgeon Pin Circlip Using 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.

Fig 3: Installing Gudgeon Pin

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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.

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 N52K/B30 or PISTONS WITH RINGS AND PINS N52K/B25 at measuring point "A".

Fig 4: Measuring Piston Diameter Using Micrometer

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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 ENGINE BLOCK, CYLINDER CRANKCASE N52K/B30 ; ENGINE BLOCK, CYLINDER CRANKCASE N52K/B25 ; ENGINE IN GENERAL N52K/B30 ; ENGINE IN GENERAL N52K/B25 ; PISTONS WITH RINGS AND PINS N52K/B30 ; PISTONS WITH RINGS AND PINS N52K/B25 ; PISTONS WITH RINGS AND PINS N52K/B30 or PISTONS WITH RINGS AND PINS N52K/B25 .

If necessary, replace piston.

Fig 5: Checking Cylinder Bore

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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 6: Inserting Gudgeon Pin Circlip Into Groove Of Special Tool (11 4 493)

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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 7: Installing Circlip For Gudgeon Pin

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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).

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

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Installation:

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

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).

Fig 9: Attaching Special Tool (11 8 330) To Connecting Rod

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Installation:

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

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.

Fig 10: Pressing Piston

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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.

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 11: Identifying Pairing Letters On Connecting Rod Bearing Cap