Piston: Service and Repair
11 25 530 - Removing and installing or replacing all pistons (M52/S52/M52TU/M54/M56)
Special tools required:
- 00 9 120 00 9 120 Torque Angle Measuring Dial
- 11 2 110
- 11 2 260 11 2 260 Piston Ring Compressor
- 11 2 470 11 2 470 Guide mandrel (2)
- 11 3 480 11 3 480 Guide Mandrel (2)
- 11 8 141 11 8 140 Assembly Sleeves
(engine removed)
Remove cylinder head.
Removal:
Removal of pistons is described separately from installation. Assembly sequence for removal and installation is different.
Important!
Re-install piston, connecting rod and bearing shells back in the same position and in the same installation location.
Connecting rods and bearing covers are designated with the same pair number: do not mix them.
Remove oil pump Service and Repair.
If oil pump and oil scraper are two parts:
Remove oil scraper.
Note:
Figure shows crankshaft removed.
On engines with spray nozzles for piston cooling on cylinder underside:
Important!
When removing and installing pistons, make sure the piston cooling spray nozzles are not damaged.
Installation Note:
Screw threads are coated with screw securing adhesive (Loctite). Replace screws.
In event of heavy oil carbon residue:
Carefully remove oil carbon residue from cylinder wall.
Unscrew conrod bearing cover.
Insert special tool 11 3 480 11 3 480 Guide Mandrel (2) in conrod.
Remove conrod 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. The assembly sequence differs between removal and installation.
The piston 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 distance A from the underside of the piston and at offset angle of 90° to piston pin axis.
Measurement 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.
Replace conrod bearing shells Removal and Replacement.
Important!
Piston and piston pin are paired and must not be fitted individually.
Fit conrod with piston pin to piston in such a way that both of the visible pair numbers on the installation direction arrow on the piston point to the right.
Install snap ring so that opening is opposite recess.
Insert special tool 11 2 470 11 2 470 Guide mandrel (2) in conrod.
Lightly coat pistons and piston rings with oil.
Align contact points on piston rings (offset at approx. 120°, but do not arrange over piston pin lug).
Note:
Piston diameter 84 mm:
Use special tool 11 8 141 11 8 140 Assembly Sleeves.
Piston diameter 80 mm:
Press together piston rings with special tool 11 2 260 11 2 260 Piston Ring Compressor.
Install piston so that arrow points to camshaft drive.
Entire circumference of tightening strap must rest firmly on engine block.
Important!
Danger of piston ring failure.
Press in piston only with finger force (do not knock in!).
Attach crankpin to connecting rod.
Apply light coat of oil to connecting-rod bearing shells.
Fit bearing caps so that pair numbers match up.
Install new conrod bolts.
Tighten down conrod bolts with special tool 00 9 120 00 9 120 Torque Angle Measuring Dial or special tool 11 2 110.
Tightening torque 11 24 1AZ 11 24 Connecting Rods and Bearings.
Install oil pump Service and Repair.
If oil pump and oil scraper are two parts:
Fit oil scraper.
Assemble engine.