Piston: Service and Repair

Removal and Installation

(engine removed)

Removal
Removal of pistons is described separately from installation.
Assembly sequence for removal and installation is different.
Mount engine on special tool 00 1 450 and remove both cylinder heads.
Remove lower oil sump section.
Remove oil circuit changeover valve, left and right, refer to Engine Lubrication, Service and Repair.
Remove oil pump.
Remove upper oil sump section.

Caution: 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.





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





Caution: When the pistons are removed and installed, there is a danger that the piston-cooling spray nozzles might be damaged.

If necessary, remove piston-cooling spray nozzles.





Remove connecting-rod cover.





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





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

Lift out retaining ring and press out piston pin.

Installation
Installation of pistons is described separately from removal. The 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.





Prior to 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 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, refer to Engine, Specifications.
Piston installation clearance, refer to Engine, Specifications.
Permissible total wear tolerance, refer to Engine, Specifications.





Caution: The pistons of cylinder banks 1 to 4 and 5 to 8 are different.

Fit the conrod with piston pin to the piston so that the additional weight (1) on the conrod points to the inlet side.

Note: The direction in which the pairing numbers on the conrod point does not affect the function. Install conrod bearing, refer to Connecting Rod Bearings.





Install retaining ring.





Insert special tool 11 3 480 in connecting rod.





Lightly coat pistons and piston rings with oil.
Offset the contact points of the piston rings by approx. 120o to each other but do not position above the piston pin boss.
Press together piston rings using special tool 11 7 180.





Keep piston rings pressed with special tool 11 7 180.
Install pistons with arrows pointing towards camshaft drive.

Caution: 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.





Secure conrod with special tool 00 9 120.
Tightening Torque, refer to Engine, Specifications.





Install piston-cooling spray nozzles, tighten down banjo bolts.
Tightening Torque, refer to Engine, Specifications.