Piston: Service and Repair
11 25 530 - Removing and installing/replacing all pistons (N62)
Special tools required:
- 00 9 120 00 9 120 Torque Angle Measuring Dial
- 11 8 141 11 8 140 Assembly Sleeves
- 11 8 151
- 11 8 152
- 11 9 500 11 9 500 Pliers
(engine removed)
Removal
Removal of pistons is described separately from installation. Assembly sequence for removal and installation is different.
Mount engine on assembly stand.
Remove both cylinder heads.
Unscrew oil sump.
Remove oil pump.
Caution!
Re-install piston, connecting rod and bearing shells back in the same position and in the same installation location.
Conrods and conrod bearing caps are denoted with the same pairing letters, do not mix them up.
In event of heavy oil carbon residue:
Carefully remove oil carbon residue from cylinder wall.
Caution!
When removing and installing pistons, make sure piston cooling spray nozzles (1) are not damaged.
Remove connecting-rod cover.
Note:
Conrods and conrod bearing caps are denoted with the same pairing letters.
Set down conrod bearing caps in order.
Insert special tools 11 8 151 and 11 8 152 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.
The piston pin must be able to be pressed through the liner by hand with little force and must not display any significant play.
Prior to installation, measure piston installation clearance: Measure piston diameter with micrometer at measuring point A from lower edge of piston and offset by 90° to piston pin axis.
Measuring point A.
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.
Piston installation clearance.
Total permissible wear tolerance.
Note:
The pistons and conrods of cylinders 1 to 8 are identical.
Caution!
The conrods of cylinder banks 1 to 4 and 5 to 8 are mounted to the pistons differently.
Cylinder bank 1 to 4
Fit conrod with piston pin to piston in such a way that arrow on piston points to front and flat end of conrod points to rear.
Cylinder bank 5 to 8
Fit conrod with piston pin to piston in such a way that arrow on piston points to front and flat end of conrod points to rear.
Install conrod bearing Service and Repair.
Install retaining ring.
Insert special tools 11 8 151 and 11 8 152 in conrod.
N62 B44
Lightly coat pistons and piston rings with oil.
Offset the contact points of the piston rings by approx. 120° to each other but do not position above the piston pin boss.
Compress piston rings with special tool 11 9 500 11 9 500 Pliers.
N62 B44
Keep piston rings compressed with special tool 11 9 500 11 9 500 Pliers.
Install piston so that arrow points to camshaft drive.
Caution!
Danger of piston ring failure.
Only press pistons into place with finger force - do not knock in!
N62 B36
Lightly coat pistons and piston rings with oil. Offset the contact points of the piston rings by approx. 120° to each other but do not position above the piston pin boss.
Slide special tool 11 8 141 11 8 140 Assembly Sleeves over piston (1).
Install piston so that arrow points to 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.
Remove special tools 11 8 151 and 11 8 152.
Note:
For purposes of clarity, the pairing letters (1) are shown on the removed conrod.
Caution!
Conrods and conrod bearing caps are denoted with the same pairing letters (1), do not mix them up.
Apply light coat of oil to connecting-rod bearing shells.
Fit bearing cap so that pairing letters match up.
Install new connecting-rod screws.
Secure conrod with special tool 00 9 120 00 9 120 Torque Angle Measuring Dial.
Tightening torque 11 24 1AZ 11 24 Connecting Rods and Bearings.