11 25 530 Removing and installing/replacing all pistons (N57 Diesel)

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Special tools required:

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

Necessary preliminary work

Remove ENGINE .
Remove CYLINDER HEAD .
Remove OIL SUMP .
Remove OIL PUMP WITH VACUUM PUMP .

IMPORTANT: Risk of damage to cylinder barrel.
If pistons, connecting rods and bearing shells are reused, they must be reinstalled in the same places.
Individual connecting rod replacement is not permitted; they are classified by weight class.
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.

Release screws (1).

Tightening torque: 11 00 4 AZ .

Remove reinforcement plate (2).

Fig 1: Identifying Reinforcement Plate Screws

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IMPORTANT: Position crankshaft (1) vertically on piston to be removed.
Proceed with care at the cylinder wall and oil spray nozzles Risk of damage!

Fig 2: Identifying Crankshaft

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Carefully remove piston with connecting rod from cylinder barrel (see arrow).

Fig 3: Identifying Cylinder Barrel

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Risk of damage!

IMPORTANT: Do not release screw (1).
Oil spray nozzles (2) must not be maladjusted or bent.
A bent oil spray nozzle cannot be adjusted and must be replaced.

Fig 4: Identifying Oil Spray Nozzle And Screw

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Undo connecting rod bearing bolts (1).

Remove connecting rod bearing caps (2) and set down in neat order.

Fig 5: Identifying Connecting Rod Bearing Cap And Bolts

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Screw special tool 11 8 860 in at large connecting rod eye.

Installation note:

Pay attention to protective edge.

Remove piston with connecting rod towards bottom.

Fig 6: Identifying Special Tool (11 8 860)

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Position piston (1) with connecting rod on special tool 11 8 831 .

Fig 7: Positioning Piston And Connecting Rod On Special Tool (11 8 831)

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

WARNING: Safety goggles must be worn.

Lever out piston circlip (1) with special tool 11 5 464 in direction of arrow.

IMPORTANT: Piston and gudgeon pin are matched to each other.
They must not be mixed up.

Fig 8: Removing Piston Circlip

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IF NECESSARY, REPLACING CONNECTING RODS .

Installation note:

It must be possible to press gudgeon pin (1) through the bush (small connecting rod eye) and must not display any significant play.

Fig 9: Pressing Gudgeon Pin Through Bush

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Before installation, measure piston installation clearance. Measure piston diameter with micrometer at measuring point A from lower edge of piston and offset at 90° to the axis of the gudgeon pin.

Distance A,

Fig 10: Measuring Piston Diameter Using Micrometer

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Adjust micrometer to cylinder bore of engine block. Set internal measuring device on micrometer to zero. Measure bottom, center and top of cylinder bore in direction of travel and direction of rotation.

Fig 11: Adjusting Micrometer To Cylinder Bore Of Engine Block

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WARNING: Safety goggles must be worn.

Fit gudgeon pin retaining ring (1) in connecting rod at the piston.

Fig 12: Identifying Gudgeon Pin Retaining Ring

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IMPORTANT: Piston and gudgeon pin are matched to each other.
They must not be mixed up.
Install circlip so that opening is opposite recess.

Fig 13: Installing Circlip

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Align contact points of PISTON RINGS (offset at approx. 120°, but do not arrange over gudgeon pin boss).

Oil piston and piston rings.

Prepare piston with piston rings on special tool 11 8 140 .

Screw special tool 11 8 860 on at large connecting rod eye.

Fig 14: Attaching Special Tools

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Insert piston (1) with connecting rod in cylinder.

IMPORTANT: Risk of piston ring breakage .
Risk of damage to oil spray nozzle.
Press in piston with finger force only, do not knock in.

Install piston so that arrow points forward in direction of travel.

Bolt piston (1) with CONNECTING ROD to crankshaft.

Fig 15: Installing Piston

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The gasket thickness must be recalculated when repair work is carried out on the crankshaft drive or pistons.

Measuring the piston protrusion:

Fit dial gauge with measuring fixture special tool 00 2 530 on cleaned engine block sealing surface and set to zero under preload.

Fig 16: Fitting Special Tool (00 2 530) To Cleaned Engine Block Sealing Surface And Setting To Zero Under Preload

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Position piston at TDC.

Clean piston at measuring points (1 and 2).

Fit dial gauge at measuring point (1) on piston and determine highest point by rotating crankshaft.

Measure and note down piston protrusion at measuring points (1 and 2) on all pistons.

Determine thickness of CYLINDER HEAD GASKET .

Fig 17: Measuring Piston Protrusion

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Assemble engine.

Check engine function and check for leak tightness.