Piston: Service and Repair
11 25 530 Removing and installing/replacing all pistons (N52)
Special tools required:
* 00 9 120
* 11 4 491
* 11 4 492
* 11 4 493
* 11 4 494
* 11 6 241
* 11 6 261
* 11 8 330
Warning!
Protective goggles must be worn when working on the gudgeon pin circlip.
Important!
If pistons, connecting rods and bearing shells are reused, they must be reinstalled in the same places.
Individual connecting rod replacement is not permitted; they are classified by weight group.
Connecting rods and connecting rod bearing caps are denoted with the same pairing letters; mixing them up will result in engine damage.
Piston and gudgeon pins are paired and must not be fitted individually.
Necessary preliminary tasks:
* Remove engine.
* Mount engine on assembly stand.
* Remove intake air manifold.
* Remove cylinder head.
* Remove engine oil sump.
* Remove oil pump.
Note:
In event of heavy oil carbon residue:
Carefully remove oil carbon residue from cylinder wall.
Note:
Illustrations show N46.
Do not release screw (1).
Oil spray nozzle (2) must not be maladjusted or bent.
If necessary, readjust(risk of damage).
Release connecting rod bolts (1).
Tightening torque, 11 24 1AZ.
Remove connecting rod bearing cap (2) in direction of arrow.
Important!
Connecting rods and connecting rod bearing caps are denoted with the same pairing letters; mixing them up will result in engine damage.
11 8 330 Attach special tool in conrod big end.
Press out connecting rod and piston to cylinder head side.
Important!
Risk of damage to oil spray nozzle.
Preliminary work:
Secure special tool 11 4 491 in vice.
Secure piston (1) with connecting rod to special tool 11 4 491.
Warning!
Safety goggles must be worn for the next operation.
Warning!
Safety goggles must be worn.
Lever out piston circlip with special tool 11 4 492 in direction of arrow.
If necessary, replace connecting rods.
Important!
Connecting rods are divided into weight classes and are only available as a set.
Old and new connecting rods must not be installed in mixed combinations.
Installation:
The gudgeon pin must be able to be pressed through the liner by hand with little force and must not display any significant play.
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 gudgeon pin.
Piston diameter at measuring point A.
Adjust micrometer to cylinder bore of engine block. Set internal calliper 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.
Piston installation clearance.
Total permissible wear tolerance.
If necessary, replace piston.
Warning!
Safety goggles must be worn.
Insert piston circlip (2) into groove (1) of special tool 11 4 493.
Bring piston circlip into assembly position.
Warning!
Safety goggles must be worn.
Guide lug and opening on special tool 11 4 493 must point to piston crown; only then can special tool 11 4 494 be fitted correctly.
If special tools 11 4 493 and 11 4 494 are correctly positioned, the piston the circlip for gudgeon pin must be driven in with a plastic hammer in the direction of the arrow.
Note:
See graphic.
Note:
B 30.
Install all piston rings.
Install all bearing shells.
Coat piston and piston rings with oil.
Pre-install piston (2) in special tool 11 6 261.
Slip special tool 11 8 330 in connecting rod (2).
Installation:
Make sure protective lugs (1) on special tool 11 8 330 are positioned correctly and check for damage.
Note:
B 25.
Install all piston rings.
Install all bearing shells.
Coat piston and piston rings with oil.
Pre-install piston (2) in special tool 11 6 241.
Slip special tool 11 8 330 in connecting rod (2).
Installation:
Make sure protective lugs (1) on special tool 11 8 330 are positioned correctly and check for damage.
Insert piston with connecting rod in cylinder.
Important!
Risk of damage to oil spray nozzle.
Danger of piston ring failure.
Press in piston with finger pressure only, do not drive in (see arrows).
Insert piston (1) so that arrow (2) on piston crown points to camshaft drive.
Press in piston (1) with special tool 11 6 261/11 6 241.
Important!
connecting rod and connecting rod bearing cap are identified with pairing letters (1) and must not be mixed up.
Mixing them up or incorrectly fitting the connecting rod bearing cap on the big end will result in engine damage.
Apply a light coat of oil to crank pin.
Assemble connecting rod and crankshaft journal.
Detach special tool 11 8 330.
Fit bearing caps (2) so that pairing letters match up.
Install new connecting rod bolts (1).
Tightening torque: 11 24 1AZ
Adjust torsion angle of connecting rod with special tool 00 9 120 (see illustration).
Tightening torque: 11 24 1AZ
Assemble engine.
