Pistons
Removing and installing pistons
Removing pistons, preliminary work
1. Disassemble engine to 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.
Information
^ Fix the gear carrier for removing the pistons with two auxiliary screws to crankcase half 1-3.
Information
^ Mark pistons in installation position before removal. Combustion residues (carbon deposits) can be removed with a brass brush.
^ Hard to remove residues can be removed in the ultrasound bath following disassembly.
1. Unscrew inner Torx screws with O-ring (M9 x 94 inside and M9 x 84 outside) for gear carrier -arrows- on crankcase half 1-3.
Additional screws for gear carrier, side 1-3
2. Unscrew inner Torx screw with O-ring M9 x 140 for gear carrier -arrow- on crankcase half 4-6.
Additional screw for gear carrier, side 4-6
3. Turn crankcase at assembly support until crankcase half 4-6 stands vertically upwards.
4. Unscrew four coated M6 x 35 Torx screws -1- on crankcase half 4-6 on flywheel side. Replace screws during assembly.
Coated screws for cross bolt connection
5. Unscrew 20 remaining M6 x 35 Torx screws in the crankcase cross bolt connection.
6. Unscrew the star screw that fixes crankcase half 4-6 to the engine support -arrow-.
Mount for crankcase half 4-6 on engine support
7. Tap the crankcase halves gently with a plastic hammer. Carefully lever the various cast lugs with a screwdriver to separate the crankcase halves from one another.
Separating the crankcase half
Caution
Crankcase half 4-6 incorrectly levered off
^ Damage to pistons, piston rings
-> Lever off crankcase half 4-6 only with the help of a second person.
8. Carefully lever off crankcase half 4-6 with the help of a second person to avoid damaging the pistons (e.g. by tilting). Remove old shaft seals.
Levering off crankcase half 4-6
9. For the following steps, fasten the gear carrier to crankcase housing half 1-3 with two cylinder-head screws using spacer sleeves 9613. -> Tightening torque: 15 ftlb.
Auxiliary screws for securing gear carrier
Removing pistons, side 4-6
10. Lever off the front piston-pin circlips of marked pistons 4-6 (from the viewpoint of the drive belt side) using a small screwdriver, push out the piston pin -arrow- and remove the pistons one by one. Assign the piston pins again to the appropriate pistons.
Removing piston pins
Removing pistons and connecting rods, side 1-3
11. Remove marked pistons 1-3, including connecting rods. To do this, turn the crankshaft on the belt pulley/vibration balancer until the respective connecting rod bearing cap stands upwards. Undo and remove the connecting rod bolts (twelve-edged socket wrench insert a/f 14), remove connecting rod bearing cap.
Connecting rod bolts
Information
^ Join connecting rod and connecting rod bearing cap together again immediately after removal.
^ Connecting rod bolts must be replaced.
12. Carefully press connecting rod and pistons downwards out of crankcase half 1-3 using a shop-made plastic mandrel. Allocate a connecting rod cap immediately to the relevant connecting rod and screw on loosely. Pay attention to the bearing shells.
Removing connecting rod using plastic mandrel (shop-made)
13. Unscrew fastening screw for belt pulley/vibration balancer and remove washer or damper. In the case of the vibration balancer, pay attention to the friction plate.
14. To remove connecting rod 4-6, remove the gear carrier.
Disassembling pistons/connecting rods, cylinder 1-3
Information
When removing pistons, the piston-pin circlip always remains in the piston, which is installed opposite the large assembly bore (no chamfer) for the piston pin.
1. Remove piston/connecting rod unit. To do this, clamp the connecting rod to a vice with aluminum jaws, for example.
Caution
Over-extension of piston rings
^ Damage or breakage
-> Using the piston ring pliers, spread open the piston rings only far enough so that the rings can be installed or removed (without scratching the piston).
2. Remove piston ring groove 1 and groove 2 separately using a piston ring pliers Gr. 1 NR.58. Remove piston ring groove 1 first. The piston rings must not be overstretched.
Removing/installing piston rings
3. The three-piece oil scraper ring can be removed by hand. First, carefully remove both rings, then remove the springs.
4. Insert piston/connecting rod unit into the retaining device 9597 in such a way that the twist lock in the second piston ring groove faces the observer.
Piston assembly device 9597
5. Carefully press out piston-pin circlip with a screwdriver; while doing so, place a cloth over the piston so that the circlip does not pop out.
Removing piston pin circlip
6. Turn piston/connecting rod unit through 180° on the assembly device and press out piston pin with the plunger special tool assembly tool 9500.
Pressing out piston pin
7. Repeat steps for removing pistons/connecting rods on cylinders 2 and 3.
Assembling pistons/connecting rods, cylinder 1-3
Information
When removing pistons, the piston-pin circlip always remains in the piston, which is installed opposite the large assembly bore (no chamfer) for the piston pin.
Information
The lug of the piston-pin circlip must always be touching the contact surface facing the oil piston shank.
Special tool retaining device 9597 with spacer ring 9597/1.
Piston assembly device 9597
1. Insert the piston (without piston rings) into retaining device 9597 so that the deep assembly bore for the piston pin in the piston is facing the observer and the remaining circlip is located underneath (check: twist lock of piston ring, second groove, is also pointing towards the observer -arrow-, arrow opposite piston crown).
Piston pin assembly bore
2. Place connecting rod in piston so that the twist lock of the connecting rod bearing shell is pointing downwards in the connecting rod (i.e. in the direction of the arrow on the piston crown).
3. Coat piston pin with new engine oil and press it in manually or using the plunger special tool assembly tool 9500.
Pressing in piston pin
4. Insert new piston-pin circlip in the taper of the assembly aid 9603/1. Position the cylindrical part on the assembly tube of the special tool assembly tool 9602/1.
Assembly sequence for piston-pin circlip
5. Press circlip into assembly tube using the assembly aid 9500/3.
Application of tool 9500/3
6. Position assembly tube on piston eye and press piston-pin circlip into the ring groove using the pressure pin assembly tool 9602/1. The circlip must audibly engage.
Assembling piston pin circlip
7. Check installation position and secure fit of circlip. The lug of the circlip must always be touching the contact surface running in the direction of the oil piston shank opposite the piston ring grooves.
Installation position of circlip
8. Repeat steps for pistons/connecting rods on cylinders 2 and 3.
Piston markings
Markings on piston crown: Replacement pistons are available from dimensional group 'X' and in two weight groups '+' and '-'. The weight groups are listed in the table.
Piston marking
^ Marking X appears as a large colored stamp in the middle of the piston crown, small as an engraved feature -1-.
^ Marking + or - appears appears as a large colored stamp in the middle of the piston crown, small as an engraved feature -2-.
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.
Information
^ If the piston, piston pin or piston-pin circlip are incorrectly assembled, the corresponding piston can be pulled out of the cylinder as follows. Degrease center of piston crown with acetone. Coat suitable plastic mandrel with instant adhesive, allow adhesive to cure, pull out piston, remove plastic mandrel immediately.
Information
^ All O-rings and seals (shaft seals), micro-encapsulated, coated screws or lock nuts must be replaced.
Information
^ Replace M9 x 1.25 connecting rod bolts and the piston-pin circlips that have been removed.
Information
^ With the help of a second person, carefully place crankcase half 4-6 in position on crankcase half 1-3.
Piston/connecting rod assembly, cylinder 1-3:
1. Install gear carrier in crankcase half 1-3.
2. Screw on belt pulley/vibration balancer with fastening screw. Turn the crankcase at the assembly support so that cylinders 1, 2 and 3 stand vertically upwards.
3. Turn crankshaft on belt pulley/vibration balancer until the connecting-rod bearing from cylinder 1 stands vertically upwards. In doing so, the bore marked 'U4' can be fixed with the bore in the crankcase using the fixing pin 9595/1.
Information
^ Observe information on aligning piston ring gaps at all times.
4. Prepare pre-assembled piston/connecting rod unit of cylinder 1 for installation. To do this, clamp the connecting rod to a vice with aluminum jaws, for example. Align the gaps in the piston rings as follows:
4.1. Align the second groove on the piston ring with the twist lock -arrow-.
4.2. Turn gap of piston ring, groove 1, through 180°.
4.3. Turn the gaps of the oil scraper ring so that the gaps are located at the oil piston shank area. When doing so, the gaps of both rings and the springs should not be on top of one another (they should be slightly offset with respect to one another).
Twist lock of piston ring, second groove
5. Coat piston and piston rings with plenty of new engine oil.
6. Insert connecting rod bearing in connecting rod and connecting rod cap. Coat sliding surface with Optimol Optipit.
7. Position clamping tool universal piston ring restraining strap, 75-125 mm NR.55 on the piston; when doing so, ensure that the piston rings are positioned correctly. Adjust restraining strap to piston diameter, use tensioning lever -1- and tensioning screw -2- to fine-tune the adjustments.
Piston with restraining strap
8. Coat cylinder bores 1-3 with plenty of new engine oil.
9. Insert piston, together with connecting rod, into cylinder bore 1, universal piston ring restraining strap, 75-125 mm NR.55 must lie evenly on cylinder surface.
Piston in cylinder bore
10. Pay attention to direction of assembly: arrow on piston crown always points to flywheel side
Piston - installation position in crankcase
Caution
Incorrect and careless assembly of pistons.
^ Component damage (pistons, piston rings, cylinder line)
-> Assemble pistons carefully and gently.
-> Stop process immediately if there is increased resistance during assembly; eliminate the cause of the problem.
11. Hold the piston ring restraining strap firmly and press piston in a cable into the cylinder bore using a plastic mandrel.
Pressing piston into cylinder bore
12. Check installation position of connecting rod: In the installation position, the recesses of the twist lock in the connecting rod bearing point towards the oil pan.
13. Turn crankcase through 180° on assembly support, position marked connecting rod cap with new, greased bearing shell and screw in two new connecting rod bolts.
Connecting rod bolts
14. First, screw in connecting rod bolts to the required torque and tighten to the specified torque angle. Then loosen the bolts again. The final tightening is performed again with an initial tightening per the torque and the concluding tightening is performed with the torque angle wrench. -> Initial tightening: 15 ftlb.; -> Final tightening - torque angle: 110°
15. Repeat steps 3-14 for the pistons/connecting rods on cylinders 2 and 3. For the assembly of cylinder 2, bore 'U5' will be fixed with the fixing pin after the crankshaft is turned on the belt pulley/vibration balancer; for the assembly of cylinder 3, bore 'U6' will be fixed.
16. Remove the cylinder-head screw from crankcase 1-3 using the spacer sleeve 9613.
Only the following sealants may be used to seal the engine:
^ Loctite 5900
^ Drei Bond or Loctite 1209 (optional)
17. Prepare crankcase half 4-6 to fit it onto crankcase half 1-3. Carefully grease sealing faces of both halves with acetone. Align connecting rods 4-6 vertically upwards and fold timing chain.
Aligning timing chain and connecting rod
18. Apply sealant to the sealing face of crankcase half 4-6.
Application of sealant and tightening sequence for crankcase
19. With the help of a second person, place crankcase half 4-6 in position on crankcase half 1-3. Knock gently on crankcase half 4-6 using a plastic hammer. Pull timing chain out through chain space using a bent welding wire.
20. Position four new, coated M6 x 35 Torx screws -1- on flywheel side.
Coated screws for cross bolt connection
21. Position seven M6 x 35 Torx screws on belt pulley side -1-; then fit special tool centering mandrel 9645 for the intermediate shaft. Position centering mandrel on the mounting point of the oil pump and turn the star knob clockwise until it is braced in the crankcase.
Cross bolt connection on belt side
22. Position the remaining 13 M6 x 35 Torx screws on the crankcase. Tighten all screws in the cross bolt connection to the required torque in accordance with the specified tightening sequence. -> Tightening torque: 9.5 ftlb.
Tightening sequence for crankcase
23. Carefully remove any remaining sealant on crankcase (particularly around the oil pan, intermediate-shaft bearing and crankshaft sealing rings).
24. Fit inner Torx screw with O-ring M9 x 140 for gear carrier -arrow- on crankcase half 4-6. -> Tightening torque: 16 ftlb.
Additional screw for gear carrier, side 4-6
25. Tighten third star screw for crankcase half 4-6 on engine support.
Mount for crankcase half 4-6 on engine support
26. Remove belt pulley/vibration balancer.
27. Fit crankshaft sealing ring on belt pulley side.
28. Only position belt pulley/vibration balancer with fastening screw (to turn the crankshaft).
29. Check the position of the crankshaft using the measuring mandrel 9699/1.
Measuring mandrel 9699/1
30. Fit crankshaft sealing ring on flywheel side. Use the insertion device 9699 for the assembly.
Piston assembly, cylinder side 4-6:
31. Turn the crankcase at the assembly support so that cylinder bank 4-6 stands upwards.
32. Move crankshaft of cylinder 6 to TDC by turning it on the belt pulley/vibration balancer (in a clockwise direction). Bore U6 on the belt pulley/vibration balancer must be aligned with the fixing bore on the crankcase. Fix the crankshaft using a fixing pin 9595/1.
33. Secure special tool centering aid 9602/5 to the crankcase using two countersunk crosshead screws.
Guide for piston pin assembly
Information
^ Observe information on aligning piston ring gaps at all times.
34. Prepare pistons for installation in the same way as cylinder bank 1-3 (piston rings, oiling, piston ring tensioning clamp).
Information
^ Leave the centering mandrel in the eye of the connecting rod until the relevant piston (4-6) contacts the centering mandrel during assembly.
35. Align connecting rod using the centering mandrel 9608
Aligning connecting rod
36. Coat cylinder bore with new engine oil. Place piston 6 on cylinder bore 6 using the universal piston ring restraining strap, 75-125 mm NR.55.
Piston in cylinder bore
37. Pay attention to direction of assembly: arrow on piston crown always points to flywheel side
Piston - installation position in crankcase
Caution
Incorrect and careless assembly of pistons.
^ Component damage (pistons, piston rings, cylinder line)
-> Assemble pistons carefully and gently.
-> Stop process immediately if there is increased resistance during assembly; eliminate the cause of the problem.
38. Hold the piston ring restraining strap firmly and press piston in one move into the cylinder bore using a plastic mandrel until the piston touches the centering mandrel
Pressing piston into cylinder bore
39. Check installation position of connecting rod: In the installation position, the recesses of the twist lock in the connecting rod bearing point towards the oil pan.
40. Align piston and connecting rod again using the centering mandrel 9608 before fitting the piston pins.
Align piston connecting rod using the centering mandrel.
41. Insert piston-pin circlip into the assembly tube of the special tool assembly tool 9602/1. Insert the lug of the circlip so that it is aligned to the right in the groove.
Inserting piston-pin circlip into assembly tube
42. Insert pressure pin -1- carefully into assembly tube -2-, ensuring that the circlip does not pop out.
Pressure pin in assembly tool
43. Oil piston pin -3- with new engine oil and place it in an upright position on a clean surface on the workbench. Position assembly tube with circlip -1- and pressure pin on piston pin.
Assembly tool on piston pin
44. Press piston-pin circlip with pressure pin -1- onto piston pin; while doing so, press assembly tube -2- firmly onto piston pin. This will move the piston-pin circlip into the correct installation position.
Moving piston-pin circlip into installation position
45. Check installation position of piston-pin circlip in assembly tube.
Installation position of piston-pin circlip in assembly tube
46. Insert assembly tool 9602/1 with piston pin circlip and piston pin through the centering aid 9602/5 into the crankcase. Press piston pin into assembly bore of piston/connecting rod eye.
Piston pin and circlip on assembly tool 9602/1
47. Groove in assembly tube must sit on dowel pin of centering aid 9602/5.
Position of assembly tube on centering aid 9602/5
48. Push the piston pin circlip to its installation position by briefly and forcefully striking the palm of your hand against the star knob of the pressure pin.
Inserting piston-pin circlip in cylinder 6
49. Using a mirror, check that the piston-pin circlip is seated correctly.
Seating of piston-pin circlip
Caution
Incorrect and careless assembly of pistons.
^ Component damage (pistons, piston rings, cylinder line)
-> Assemble pistons carefully and gently.
-> Stop process immediately if there is increased resistance during assembly; eliminate the cause of the problem.
50. Repeat steps 35-49 carefully to assemble pistons 5 and 4. During this process, the crankshaft is fixed to the crankcase through bore U5 for cylinder 5 and through bore U4 to the belt pulley/vibration balancer. Convert the assembly tool 9602/1 as described below.
51. Push a spacer sleeve onto the assembly tube for the assembly of pistons pins and circlip on cylinder 5.
Spacer sleeve for cylinder 5
52. Fit the piston-pin circlip for cylinder 5 using a sleeve.
Inserting piston-pin circlip for cylinder 5
53. Push two spacer sleeve onto the assembly tube for the assembly of pistons pins and circlip on cylinder 4.
Spacer sleeves for cylinder 4
54. Fit the piston-pin circlip for cylinder 4 using two sleeves.
Inserting piston-pin circlip in cylinder 4
55. Once the pistons have been installed, seal the bore for the piston pin and circlip assembly on the crankcase using the aluminum screw plug and new sealing ring. -> Tightening torque: 59 ftlb.
Screw plug for assembly bore in crankcase
Installing pistons, touching up
1. Assemble engine.