Piston: Service and Repair

Piston Removal and Installation

(engine removed)

Removal
Removal of pistons is described separately from installation.
Assembly sequence for removal and installation is different.
Remove both cylinder heads.
Remove upper section of oil pan.
Remove oil pump.

Important:
Re-install piston, connecting rod and bearing shells back in the same position and in the same installation location.

Conrod and conrod bearing cover are designated with same pair number: do not interchange / confuse.





Important:
When removing and installing the pistons, there is a risk of the spray nozzles becoming damaged.

Unfasten screw and remove spray nozzle.





Remove connecting-rod cover.





Insert special tool 11 2 470 in conrod.
Remove connecting rod with piston from cylinder-head side.




Lift out retaining ring and press out piston pin.

Important:
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.

Note: The conrods can also be replaced individually.

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 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. Connecting Rod Bearing

Important:
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, with the pair number visible, the installation direction arrow on the piston points to the right.





Install retaining ring.





Install special tool 11 2 470 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 using 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.

Important:
Danger of piston ring failure.

Only press pistons into place with finger force - do not knock in!





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 connecting-rod screws.





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





Install spray nozzle and tighten down screw.