Piston: Service and Repair
11 25 530 - Removing and installing/replacing all pistons (N62TU)
Special tools required:
- 00 9 120 00 9 120 Torque Angle Measuring Dial
- 11 5 430 11 5 430 Piston Ring Pliers
- 11 5 440
- 11 5 450 11 5 450 Mounting Sleeve
Important!
Re-install piston, conrod 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.
Necessary preliminary tasks:
- (engine removed)
- Install engine on assembly stand
- Remove both cylinder heads
- Removing oil pan
- Remove oil pump Service and Repair
In event of heavy oil carbon residue:
Carefully remove oil carbon residue from cylinder wall.
Important!
When removing and installing pistons, make sure piston cooling spray nozzles (1) are not damaged.
Unscrew conrod bearing cover.
Important!
Conrods and conrod bearing caps are denoted with the same pairing letters.
Set down conrod bearing caps in order.
Insert special tool 11 5 440 in conrod.
Screw special tool 11 5 440 into conrod with screw (1).
Remove conrod with piston from cylinder head side.
Important!
Piston and piston pin are matched to each other.
Mixing up the components will result in engine damage.
Lever out circlip with special tool 11 4 492 in direction of arrow and press out piston pin.
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.
Important!
The conrods of cylinder banks 1 to 4 and 5 to 8 are mounted to the pistons differently.
Cylinder bank 1 to 4
Mount conrod on piston in such a way that arrow on piston points upwards and marking on conrod points upwards.
Cylinder bank 5 to 8
Mount conrod on piston in such a way that arrow on piston points downwards and marking on conrod points upwards.
Install conrod bearing Service and Repair.
Install retaining ring.
Offset the contact points (1) of the piston rings by approx. 120° to each other but do not position above the piston pin boss.
Note:
See illustration.
Illustration shows N52.
Installation Note:
B40 and B48:
Insert special tools 11 5 440 in conrod.
Installation Note:
B40:
Prepare piston with rings with special tool 11 5 450 11 5 450 Mounting Sleeve.
B40:
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 in special tool 11 5 450 11 5 450 Mounting Sleeve with piston (1).
Install piston so that arrow points to camshaft drive.
Important!
Danger of piston ring failure.
Press in piston with finger force only.
B48:
Keep piston rings compressed with special tool 11 5 430 11 5 430 Piston Ring Pliers.
Install piston so that arrow points to camshaft drive.
Important!
Danger of piston ring failure.
Press in piston with finger force only.
Attach crankpin to connecting rod.
Remove special tools 11 5 450 11 5 450 Mounting Sleeve.
Note:
For purposes of clarity, the pairing letters (1) are shown on the removed conrod.
Important!
Conrods and conrod bearing caps are denoted with the same pairing letters (1), do not mix them up.
Important!
Conrod of cylinder 1 to 4 is installed in direction of travel, see arrow (1), front.
Conrod of cylinder 5 to 8 is installed in direction of travel, see arrow (1), rear.
Markings on conrod must be situated on the outside (see arrows)
Incorrect assembly will result in engine damage.
Apply light coat of oil to connecting-rod bearing shells.
Fit bearing cap so that pairing letters match up.
Install new conrod bolts.
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.
Assemble engine.