Piston: Service and Repair
WM 131020 Removing and installing pistons (with cylinder sleeve)
Preliminary Work
1. Remove engine.
2. Remove transmission.
3. Disassemble engine down to the crankcase.
Removing pistons
Caution
Risk of damage due to particles of dirt.
^ Danger of material damage due to blocked oil bores/oil ducts.
- Absolute cleanliness is essential when working on the engine.
- Lay removed engine parts on a clean base and make sure to cover them.
- Use the cover for dust protection when fitting the engine NR.165 on the engine assembly support.
Component overview:
Component overview of pistons and cylinders
Removal for cylinder bank 1-3:
1. Mark pistons in installation position with a paint marker (do not scratch piston crown).
Marking pistons
2. Mark cylinder housing with a paint marker and lift it carefully up and off the pistons.
Slide hose pieces or aluminium sleeves over the threaded bolts to protect the pistons and piston rings.
3. Turn engine clockwise at the crankshaft pulley until piston 1 is at the top dead center.
Notice
Loose parts in crankcase
^ Risk of engine damage
- Cover crankcase bores with a clean cloth.
4. Cover crankcase bores behind the pistons with a clean cloth so that parts cannot fall into the crankcase.
5. Remove piston-pin circlip on piston 1 on the inside (towards piston 2) using a small screwdriver.
Piston-pin circlip
6. Slide piston pin out with your hand. Carefully tap it out using a plastic or aluminium mandrel if necessary. Remove piston and place it on a clean surface.
7. Turn engine clockwise at the crankshaft pulley until piston 3 is at the top dead center.
8. Remove piston-pin circlip on piston 3 on the inside (towards piston 2) using a small screwdriver.
9. Slide piston pin out with your hand. Carefully tap it out using a plastic or aluminium mandrel if necessary. Remove piston and place it on a clean surface.
10. Turn engine clockwise at the crankshaft pulley until piston 2 is at the top dead center.
11. Remove piston-pin circlip on piston 2 on any side using a small screwdriver.
12. Slide piston pin out with your hand. Carefully tap it out using a plastic or aluminium mandrel if necessary. Remove piston and place it on a clean surface.
View of piston pins on outer pistons
13. Check piston shank for wear.
14. Tap cylinder sleeves out of the cylinder housing. To do this, insert the pressure piece of the pushing device 9660 at the base of the cylinder sleeve and drive the cylinder sleeve out with a plastic hammer.
Driving out cylinder sleeve
15. Remove O-rings from the cylinder housing and O-rings from the cylinder sleeves and dispose of them. Mark cylinder sleeves with a paint marker and assign them to the corresponding pistons.
16. Complete the same steps to remove pistons for cylinder bank 4-6.
17. To make the assembly markings (engraved arrow and letter -E-) Removing visible on the piston crown, the combustion residues must be removed using an ultrasound bath or with a brass brush with solvent naphtha.
The arrow in the center of the piston crown is a colored stamp and is only visible on new pistons.
Piston installation marking
Installing pistons
Caution
Risk of damage due to particles of dirt.
^ Danger of material damage due to blocked oil bores/oil ducts.
- Absolute cleanliness is essential when working on the engine.
- Lay removed engine parts on a clean base and make sure to cover them.
- Use the cover for dust protection when fitting the engine NR.165 on the engine assembly support.
Installation for cylinder bank 1-3:
Information
^ Observe installation sequence.
^ The central pistons of cylinders 2 and 5 are fitted onto the connecting rod without a cylinder sleeve.
^ The pistons for the outer cylinders 1, 3, 4 and 6 are preassembled in the cylinder housing.
1. Fit individual pistons.
1.1. Align the gaps of the piston rings offset by 120° with respect to the middle piston ring (gap at the straight pin).
Caution
Risk of damage by tightening the piston restraining strap.
^ Risk of material damage.
- Pay close attention to the oil scraper rings when tightening the restraining strap.
2. Coat pistons generously with new engine oil. Fit commercially available restraining strap. Restraining strap 9659 must be fitted at the piston (piston junk).
Piston restraining strap with assembly aid 9659/9
3. Align restraining strap. The restraining strap lock should be aligned between the inlet valve recesses.
Aligning restraining strap for piston rings
Information
^ The assembly sleeve is used to position the restraining strap.
^ Work quickly when positioning the strap so that the piston rings are not damaged.
4. Insert the piston inverted into the assembly aid 967. Quickly press the piston downwards and press the restraining strap downwards at the same time with your other hand.
Piston in assembly sleeve
5. Slide hose pieces or aluminium sleeves over the threaded bolts to protect the pistons and piston rings.
6. Turn crankshaft pulley clockwise until the connecting rods of cylinders 2 and 5 are positioned at top dead center.
Notice
Loose parts in crankcase
^ Risk of engine damage
- Cover crankcase bores with a clean cloth.
Information
^ It is advisable to get a second person to assist in fitting the circlip on the piston.
^ Check that the piston-pin circlips are seated correctly.
7. Fit pistons 2 and 5 on the connecting rod. Pay attention to direction of installation.
7.1. Piston must be fitted so that the engraved arrow marking always points in the direction of the flywheel. In addition, the intake side is identified by an engraved E.
Piston installation marking
7.2. Cover crankcase bores with a clean cloth.
7.3. Coat piston pin with fresh engine oil and slide it in as far as it will go.
Piston pins for middle pistons
8. Fit piston-pin circlip -1- on the piston by hand.
Fitting circlip on piston
9. Fit circlip by pressing it with a slotted screwdriver (approx. 5 mm wide) while at the same time sliding it towards the hook groove -arrow- until it engages in the ring groove. Check again that the circlip is seated correctly.
Fitting piston-pin circlip
Installation position of piston-pin circlip
10. Turn the crankshaft at the pulley so that the middle piston is flush with the sealing edge of the crankcase bore.
11. Prepare the cylinder housing, outer cylinder sleeves and pistons for installation.
12. Insert new O-rings into the cylinders. Coat the O-ring area with a generous amount of special grease (Part No. 000.043.205.10).
Inserting new O-rings into cylinder housing
13. Fit new O-rings onto the cylinder sleeves. Coat the O-ring area with a generous amount of special grease (Part No. 000.043.205.10).
Greasing O-rings on the cylinder sleeve
14. Fit outer cylinder sleeves in the cylinders. Align the cylinder sleeves in the cylinder. The flattened areas must face towards the other cylinder sleeves in the longitudinal direction.
Fitting cylinder sleeves in cylinder housing
15. The recesses on the cylinder sleeve must align with the bores of the studs.
Installation position of cylinder sleeve
16. Fit the outer cylinder sleeves using the pushing device 9660.
Pushing device 9660
Using pushing device
17. The outer cylinder sleeves can also be pushed in using a hydraulic press.
Pressing in cylinder sleeve using a hydraulic press
18. Oil the piston shank and fit a commercially available piston restraining strap. Slide the piston into the cylinder sleeve while pressing the piston restraining strap down at the same time.
Fitting outer pistons in cylinder sleeve
Piston installation marking
19. Check the position of the pistons. The engraved arrow must point to the flywheel side while the letter -E- must point to the intake side when in installation position. Turn the pistons in the cylinder sleeve if necessary. Pull the pistons far enough out so that the piston pins can just be inserted.
Visual inspection of the installation position of the outer pistons
Outer pistons in cylinder housing
20. Fit the piston pins into the associated pistons from the inside. The piston pin should only be inserted so far that the connecting rod can still be fitted.
View of piston pins on outer pistons
21. Detach aluminium sleeves or hoses from the threaded bolts.
22. Fit cylinder base seal above the studs. The "TOP" marking must be facing the observer.
23. Spacers 9651 must be placed on the outer studs.
Spacers 9651
24. Slide preassembled cylinder housing onto the threaded bolt.
Fitting preassembled cylinder housing
Notice
Loose parts in crankcase
^ Risk of engine damage
- Cover crankcase bores with a clean cloth.
25. Fit the piston pin and the piston-pin circlip for the outer pistons from the inside (through the middle cylinder bore).
Piston pins for outer pistons
26. Remove the cloth at the crankcase bores.
27. Once you have fitted the piston-pin circlips, slide the cylinder housing as far as the spacers 9651 and fix in place using two threaded sleeves from the special tool set of retaining nuts P140.
28. Prepare middle cylinder sleeve. Fit new O-ring and apply a generous amount of special grease (Part No. 000.043.205.10).
Greasing O-rings on the cylinder sleeve
29. Position the cylinder sleeve on the studs. Pay attention to the flattened areas on the cylinder sleeve -arrows-.
Inserting middle cylinder sleeve
30. Pushing device 9660 must be fitted on the stud. Lay a plastic washer on the cylinder sleeve and press the cylinder sleeve into place on the piston (piston junk) by turning the shifting wheel.
Pushing device 9660
Fitting middle cylinder sleeve using pushing device 9660
31. Slowly turn the crankshaft clockwise at the pulley until the middle piston can no longer be seen in the gap between the cylinder housing and crankcase. Then press the cylinder sleeve into place with the pushing device until the restraining strap detaches from the piston shank.
32. Open the restraining strap lock using two screwdrivers and guide the restraining strap out between the crankcase and cylinder sleeve.
Removing piston restraining strap
33. Subsequently press in the middle cylinder sleeve as far as it will go using the handwheel.
Fitting middle cylinder sleeve
34. Loosen the threaded sleeves (set of retaining nuts P140) on the studs until the spacers 9651 between the crankcase and cylinder housing can be removed.
35. Slide the cylinder housing towards the crankcase.
36. To prevent the cylinder housing from sliding out when you turn the crankshaft, secure the position using threaded sleeves from the set of retaining nuts P140.
37. Complete the same steps for cylinder bank 1-3 to fit pistons for cylinder bank 4-6.
38. When the pistons have been completely fitted in both cylinder housings, turn the crankshaft twice in a clockwise direction at the pulley. The crank drive must not become jammed.
Subsequent Work
1. Assemble engine.
2. Refit the transmission.
3. Install engine.