11 25 530 Removing and installing/replacing all pistons (N12)

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

Special tools required:

00 9 120
11 9 620
11 9 670

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 air manifold
Remove cylinder head
Remove engine oil pan
Remove oil pump

NOTE: In event of heavy oil carbon residue:
Carefully remove oil carbon residue from cylinder wall.

NOTE: Illustrations show N46.

Fig 1: Locating Oil Carbon On Cylinder Wall

Courtesy of BMW OF NORTH AMERICA, INC.

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

Example N14:

Direction of arrow (1) points to camshaft drive.

Cylinder allocation (2) per cylinder.

Fig 2: Direction Of Arrow (1) Points To Camshaft Drive

Courtesy of BMW OF NORTH AMERICA, INC.

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

Example:

Mark cylinder allocation (1) per cylinder.

Direction of arrow (2) points to camshaft drive.

Fig 3: Direction Of Arrow (2) Points To Camshaft Drive

Courtesy of BMW OF NORTH AMERICA, INC.

Release connecting rod bolts (1).

Tightening torque 11 24 1AZ

Remove conrod 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

Courtesy of BMW OF NORTH AMERICA, INC.

Attach special tool 11 9 620 in conrod big end.

Press out connecting rod and piston to cylinder head side.

Fig 5: Identifying Special Tool (11 9 620)

Courtesy of BMW OF NORTH AMERICA, INC.

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

WARNING: Protective goggles must be worn.

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

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

Fig 6: Removing Piston Pin Circlip With Screwdriver

Courtesy of BMW OF NORTH AMERICA, INC.

If necessary, replace connecting rods.

Installation:

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

Courtesy of BMW OF NORTH AMERICA, INC.

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 gudgeon pin.

Piston diameter at measuring point A.

Fig 8: Checking Piston Diameter

Courtesy of BMW OF NORTH AMERICA, INC.

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.

If necessary, replace piston.

Fig 9: Checking Diameter Of Cylinder Bore

Courtesy of BMW OF NORTH AMERICA, INC.

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 conrod.

Installation:

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)

Courtesy of BMW OF NORTH AMERICA, INC.

Insert piston with connecting rod in cylinder.

IMPORTANT: Danger of piston ring failure.
Press in piston with finger pressure only, do not drive in (see arrow in illustration).

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.

Fig 11: Inserting Piston

Courtesy of BMW OF NORTH AMERICA, INC.

IMPORTANT: Point of fracture (1) on conrod.
Conrod and conrod bearing cap are identified with pairing letters (2) 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.

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

Fig 12: Point Of Fracture (1) On Conrod; Conrod And Conrod Bearing Cap Are Identified With Pairing Letters (2)

Courtesy of BMW OF NORTH AMERICA, INC.

Apply a light coat of oil to crank pin.

Assemble connecting rod and crank pin.

Remove special tool 11 9 620.

Fig 13: Identifying Special Tool (11 9 620)

Courtesy of BMW OF NORTH AMERICA, INC.

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

Check cylinder identification markings (1).

Direction of arrow (2) points to camshaft drive.

Fig 14: Identifying Camshaft Drive Mark And Cylinder Allocation

Courtesy of BMW OF NORTH AMERICA, INC.

Install new connecting rod bolts (1).

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

Tightening torque 11 24 1AZ

Fig 15: Identifying Connecting Rod Bolts

Courtesy of BMW OF NORTH AMERICA, INC.

Assemble engine.