Piston: Service and Repair

(engine removed)

Removal
Removal of pistons is described separately from installation.
Assembly sequence for removal and installation is different.
Removing cylinder head, refer to Cylinder Head Assembly, Service and Repair.
Removing oil pan, refer to Engine Lubrication.

Caution:
Re-install piston, connecting rod and bearing shells back in the same position and in the same installation location.
Connecting rods and bearing covers are designated with the same pair number: do not mix them.





Caution:
Injection nozzles for cooling the pistons are installed on the underside of the cylinder between the bearing seats.
Be careful not to damage the spray nozzles for cooling the pistons when removing the pistons.
In order to avoid the possibility of injury from the piston or connecting rod, the location of spray nozzles is equipped with special tool 11 7 320.





Unscrew conrod bearing cover.





Insert special tool 11 3 480 in conrod.
Remove conrod with piston from cylinder head side.





Lift out retaining ring and press out piston pin.

Caution: Piston and piston pin are paired and must not be fitted individually.

Installation
Installation of pistons is described separately from removal.
Assembly sequence for removal and installation is different.





If necessary, replace connecting rods.
Spare connecting rods can only be obtained in complete sets.
It should be possible to press piston pin into bush by hand using only slight pressure. Clearance should then be minimal.





Before installation, 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 piston pin.
Measuring point A, refer to Engine, Specifications





Adjust micrometer on cylinder bore of engine block and set plug gauge on micrometer to zero. Measure bottom, centre and top of cylinder bore in direction of travel and direction of engine rotation.
Diameter of the cylinder bore, refer to Engine, Specifications
Piston installation clearance, refer to Engine, Specifications
Max. permissible total wear clearance, refer to Engine, Specifications





Install conrod bearing, refer to 11 24 571

Caution: Piston and piston pin are paired and must not be fitted individually.

Fit connecting rod with piston pin to piston in such a way that both of the visible pair numbers on the installation direction arrow on the piston point to the right.





Install retaining ring.





Insert special tool 11 3 480 in conrod.





Lightly coat pistons and piston rings with oil.
Align contact points of piston rings (offset at approx. 120°, but not over piston pin lug).
Press together piston rings with special tool 11 2 260.





Install pistons with arrows pointing towards camshaft drive.
The tightening strap must locate firmly right around circumference of engine block.

Caution:
Danger of piston ring failure.
Press in piston only with finger force (do not knock in!).





Caution: Be careful not to damage the spray nozzles for cooling the pistons when installing the pistons.

Attach crankpin to connecting rod.





Apply light coat of oil to connecting-rod bearing shells.
Place bearing caps in position, making sure that matching numbers are paired. Install new conrod bolts.





Tighten down conrod bearing with special tool 00 9 120 or with special tool 11 2 110.
Tightening torque, refer to Engine, Specifications.





Check the setting of the spray nozzles.
Attach special tool 11 7 320 to the intake side in the receiving bore hole in the engine block.





The spray nozzles must fit into the guide of special tool 11 7 320.
If necessary, loosen the spray nozzles and adjust and tighten them using special tool 11 7 320.
Tightening torque, refer to Engine, Specifications.
Assemble engine.