Piston: Service and Repair

11 25 530 - Removing and installing/replacing all pistons (S65)

Special tools required:
- 00 9 120 00 9 120 Torque Angle Measuring Dial
- 11 4 492
- 11 5 250
- 11 5 341
- 11 5 342
- 11 5 343
- 11 5 344
- 11 9 500
- 12 2 100

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.

Piston and piston pin are matched to each other and can only be replaced as a pair.

Connecting rod and connecting rod bearing cap are cracked.

Identification is effected by means of identical pairing letters on the connecting rod big end.

Mixing up the components will result in engine damage.

Setting of special tool 11 5 343 must not be altered.

Necessary preliminary tasks:
- Remove engine Removing and Installing Engine.
- Mount engine on assembly stand 11 00 ... Mounting Engine on Assembly Stand.
- Remove intake air manifold Service and Repair.
- Remove cylinder head on left and right.
- Remove engine oil sump Service and Repair.
- Remove oil pump 11 41 000 Removing and Installing/Replacing Oil Pump.
- Remove oil suction pump Removing and Installing/Replacing Oil Suction Pump.

Do not bend oil nozzle (2) at outlets.

It is not possible to adjust the nozzles.

Oil nozzle (2) must be replaced if it is maladjusted or bent.

Remove crankshaft Service and Repair.

Release connecting rod bolts (1) with special tool 12 2 100.

Remove connecting rod bearing cap with bearing shell.

Special tool 11 5 250 without locating rod must be screwed in on the connecting rod at the bottom.

Special tool 11 5 250 with locating rod must be screwed in on the connecting rod at the top.

Rotate crankshaft (1) in direction of arrow, risk of damage to special tool 11 5 250.

Remove piston with connecting rod and special tool 11 5 250.

Depiction of function on cylinders 1-4.

Important!
Risk of damage to oil nozzle.

Clamp special tool 11 5 341 in a vice.

Note:
Piston and piston pin are optimized to each other.

There are two different inside diameters on the piston pin.

Screw matching special tool 11 5 342 into special tool 11 5 341.

Secure piston (1) with connecting rod to special tool 11 5 341.

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.

If necessary, replace connecting rods.

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

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.

Adjust micrometer to cylinder bore of engine block. Set internal calliper on micrometer to zero. Measure bottom, centre 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.

Important!
The connecting rods are not symmetrical.

Pay attention to elevation to direction of travel arrow.

Make sure the connecting rod is in the correct installation position during preliminary installation.

On cylinders 6-10 the elevation (2) must point forwards with the arrow.

On cylinders 1-4 the elevation (1) must point rearwards against the arrow.

Valve pockets (E) point to inlet side.

Arrow direction is identical to direction of travel.

On cylinders 5-8 the elevation must point forwards with the arrow.

On cylinders 1-4 the elevation (1) must point rearwards against the arrow.

Important!
No elevations on the connecting rod big end are permitted to point to each other during installation, risk of damage to connecting rod.

Installation Note:
When installed, the two lugs on connecting rods (1 and 2) must point outwards.

Secure piston (1) with connecting rod to special tool 11 5 341.

Warning!
Protective goggles must be worn.

Important!
Setting of special tool 11 5 343 must not be altered.

Installation Note:
Insert piston circlip (2) so that opening points to window.

Insert piston circlip (2) into groove (1) of special tool 11 5 343.

Note:
Illustration shows N52.

Position special tool 11 5 343 with window to opening on piston (see arrow).

Warning!
Protective goggles must be worn.

Guide lug and cutout on special tool 11 5 343 must point to piston crown.

When special tools 11 5 343 and 11 5 344 are correctly positioned, the piston circlip must be driven in with a plastic hammer in the direction of the arrow.

Note:
See illustration.

Installation Note:
Piston circlip (1) is correctly installed when the opening points upwards.

See illustration.

It must still be possible for piston pin to moved easily.

Install all piston rings Service and Repair.

Install all bearing shells Service and Repair.

Screw special tool 11 5 250 into conrod.

Always screw in special tool 11 5 250 with rod to exhaust side.

Preinstall piston with piston rings in special tool 11 9 500.

Insert piston with connecting rod in cylinder.

Important!
Risk of damage to oil spray nozzle.

Danger of piston ring failure.

Insert piston so that arrow (direction of travel pointing forwards) on piston crown points to camshaft drive.

Piston cyl. 1-4 right side, cyl. 5-8 left side.

Press in piston with special tool 11 9 500.

Arrow on piston crown must point to camshaft drive (direction of travel towards front).

Important!
connecting rod and connecting rod 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.

Important!
Risk of damage to oil nozzle.

Rotate crankshaft (1) in direction of arrow, risk of damage to special tool 11 5 250.

Insert piston with connecting rod and special tool 11 5 250.

Moisten conrod bearing shell and crank pin slightly with engine oil.

Assemble connecting rod and crank pin.

Remove special tool 11 5 250.

Install connecting rod bearing cap with bearing shell.

Secure connecting rod bolts (1) with special tools 12 2 100 and 00 9 120.

Tightening torque: 11 24 1AZ. Mechanical Specifications

Assemble engine.