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11 25 530 Removing and installing/replacing all pistons (N52)

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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: 

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
G09920610Courtesy of BMW OF NORTH AMERICA, INC.
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
G09920611Courtesy of BMW OF NORTH AMERICA, INC.

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
G09920612Courtesy of BMW OF NORTH AMERICA, INC.

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
G09920613Courtesy of BMW OF NORTH AMERICA, INC.

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 And Connecting Rod To Special Tool (11 4 491)
G09920614Courtesy of BMW OF NORTH AMERICA, INC.
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
G09920615Courtesy of BMW OF NORTH AMERICA, INC.

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: Identifying Gudgeon Pin
G09920616Courtesy of BMW OF NORTH AMERICA, INC.

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 PISTONS WITH RINGS AND PINS - N52 ENGINE .

Fig 8: Measuring Piston Diameter Using Micrometer
G09920617Courtesy of BMW OF NORTH AMERICA, INC.

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.

Refer to:

DIAMETER OF CYLINDER BORE .

TOTAL PERMISSIBLE WEAR TOLERANCE .

If necessary, replace piston.

Fig 9: Adjusting Micrometer To Cylinder Bore Of Engine Block
G09920618Courtesy of BMW OF NORTH AMERICA, INC.
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 Groove Of Special Tool (11 4 493)
G09920619Courtesy of BMW OF NORTH AMERICA, INC.
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 Tools
G09920620Courtesy of BMW OF NORTH AMERICA, INC.
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 12: Installing Piston
G09920621Courtesy of BMW OF NORTH AMERICA, INC.

Installation note: 

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 13: Installing Piston In Special Tool (11 6 241) And Attaching Special Tool (11 8 330) To Connecting Rod
G09920622Courtesy of BMW OF NORTH AMERICA, INC.

Installation note: 

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! 
Risk of breakage of piston rings.

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

Fig 14: Pressing-In Piston
G09920623Courtesy of BMW OF NORTH AMERICA, INC.

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 15: Identifying Pairing Letters For Connecting Rod And Bearing Cap
G09920624Courtesy of BMW OF NORTH AMERICA, INC.

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: Attaching Special Tool (11 8 330) To Connecting Rod
G09920625Courtesy of BMW OF NORTH AMERICA, INC.

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

Installation note: 

Replace screws  .

Install new connecting rod bolts (1).

IMPORTANT: Joining torque and angle of rotation must be observed without fail.
Risk of damage! 
Fig 17: Identifying Connecting Rod Bearing Cap And Bolts
G09920626Courtesy of BMW OF NORTH AMERICA, INC.

Tightening torque 11 24 1AZ .

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

Tightening torque 11 24 1AZ .

Fig 18: Tightening Connecting Rod Bolts Using Special Tool (00 9 120)
G09920627Courtesy of BMW OF NORTH AMERICA, INC.

Assemble engine.

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