Assembling pistons
1. First assemble the three-piece oil scraper ring. To do this, carefully stretch the oil scraper spring by hand at its gap to a point where this can be positioned over the piston in ring groove 3. Carefully force apart a ring in the oil scraper ring by hand and fit it into the third piston ring groove below the oil scraper spring. Fit the second ring in the same way over the oil scraper spring.
2. When fitted, the gap in the oil scraper ring must be offset by exactly 180° with respect to the gap in the oil scraper spring. Make sure that the oil scraper spring is in the middle of the oil scraper ring.
Scheme 296
Note. The two compression rings have different strengths and can only be installed in the appropriate groove. If the piston ring has the inscription TOP, this must point to the piston crown.
3. Insert piston ring into the piston ring pliers. Make sure that, when installed, the designation of the piston rings is pointing in the direction of the piston crown -A-. Spread the piston ring until it just fits over the piston. (Scheme 294)
4. Fit piston rings. Using the piston ring pliers, insert the middle piston ring into the second ring groove in such a way that the inscription TOP is facing the piston crown. Insert the top piston ring into ring groove 1 in such a way that the inscription TOP is facing the piston crown.
5. Check that the piston rings are correctly seated and positioned. Make sure that the oil scraper spring is inside the oil scraper ring. In the case of the piston ring in ring groove 2, the inscription TOP must point to the piston crown. The top piston ring must be installed in such a way that the inscription TOP is facing the piston crown. The gaps in the individual piston rings must always be offset by 120°.
Scheme 297
6. Pre-fit piston-pin circlip in assembly sleeve. To do this, insert the ring in assembly sleeve P 9500/9, so that the ring gap is at 6 o'clock or alternatively 11 o'clock (piston crown on top), the assembly groove of the assembly sleeve pointing towards the piston crown --> Ring gap indicating 11 o'clock. (Scheme 295)
Scheme 298
7. Position the assembly sleeve on an even surface with the groove facing downwards and use the assembly aid P 9500/3 to drive down the circlip into the installation position so that the circlip is under tension and sitting in the correct position -arrow-. (Scheme 296)
Scheme 299
8. Check installation position of piston-pin circlip in the assembly sleeve --> Ring gap here at 6 o'clock. (Scheme 297)
Scheme 300
9. Position the assembly sleeve on the piston so that the assembly groove of the assembly sleeve points to the piston crown --> Assembly sleeve on piston. (Scheme 298)
10. Insert plunger P 9500/8 through the assembly sleeve and fit the piston-pin circlip by tapping it with a hammer into the groove of the piston pin eye.
11. Fix piston on retaining device P 9597 with fitted piston-pin circlip facing downwards --> Piston on retaining device. (Scheme 299)
12. Gap of circlip must point downwards away from the piston crown (analogous to 6 o'clock, alternatively 11 o'clock). Place piston pin and connecting rod in installation position. Align connecting rod with matching number so that the matching numbers point to the exhaust side -A-. Illustration shows direction of travel in this case and connecting rod code on one side. (Scheme 300)
13. Fit oiled piston pin through the piston and connecting-rod eye as far as the circlip. Using a plastic hammer, tap gently on plunger P 9500/8, driving the piston pin into the pre-fitted piston-pin circlip -arrow-. see scheme 47
Scheme 301
14. Fit the second piston-pin circlip using the same procedure. Align gap of circlip so that it points downwards away from the piston crown (analogous to 6 o'clock, alternatively 11 o'clock) -arrow-. see scheme 48
15. Check connecting rod and piston for smooth operation.
Note. The connecting rods are cracked and together with the matching numbers cannot be mixed up! Connecting rod bolts and bearing shells must always be replaced. The identification of the connecting-rod bearings is located on the connecting-rod journal of the crankshaft > Removing and installing crankshaft .
16. Fit connecting-rod bearing shells in connecting-rod big end and connecting-rod bearing cap. The retaining lugs must be positioned in the appropriate grooves and on the same side -B and C-. The matching numbers -A- must be the same and on the same side (when installed they point to the exhaust side). Tighten the connecting rod bolts by hand and position the complete connecting rod ready for assembly. see scheme 49, (Scheme 301).
1. Install piston > 131019 Removing and installing pistons - "Installing" section .
Designation Type Number Explanation Piston ring pliers Gr. 1 commercially available tool NR.58 Retaining device special tool P 9597
1. Remove piston. > 131019 Remove and install piston - Chapter "Removing"
Scheme 302
| Item | Designation | Source | Explanation |
|---|---|---|---|
| A- see scheme 51 | Retaining device P 9597 | See Workshop Equipment Manual, Chapter 2.2.2 | Assembly aid for fixing the piston. The piston/conecting rod joint of the V6 is too long for the tool. In order for the tool to fit, both fastening screws of the bracket for the large connecting-rod eye must be removed and the length adjusted accordingly. |
| B- see scheme 51 | Piston ring pliers Gr. 1 NR.58 | See Workshop Equipment Manual, Chapter 2.4 | For careful assembly of the piston rings |
| No. | Designation | Qty. | Removal | Installation |
|---|---|---|---|---|
| 1- see scheme 52 | Piston rings | 3 | Move the gap through 120°; remove and install using piston ring pliers; TOP marking points toward piston crown | |
| 2- see scheme 52 | Pistons | 1 | Mark installation position with respect to connecting rod and cylinder allocation with a felt-tip pen; place corresponding components aside together. | Installation position according to removal marking; flat side of the piston crown points toward the center of the cylinder block |
| 3- see scheme 52 | Circlip | 2 per piston | ||
| 4- see scheme 52 | Connecting rod | Mark allocation to cylinder and piston with a felt-tip pen, see also -B- see scheme 52 | Replace in sets; install according to removal marking | |
| 5- see scheme 52 | Connecting-rod bearing shells | 2 per piston | Observe installation position; replace bearing shells | Replace bearing shells; bearing shell retaining lugs must be on the same side; press bearing shell retaining lugs firmly into the recesses |
| 6- see scheme 52 | Connecting-rod bearing cover | 1 per piston | Mark allocation to cylinder and piston with a felt-tip pen, see also -B- see scheme 52 | Install according to removal marking; markings must be on same side -B |
| 7- see scheme 52 | Connecting-rod bearing screws | 2 per piston | > pre-tightening torque: 30 (22 ftlb.) Nm --> torque angle: 90 ° | |
| 8- see scheme 52 | Cylinder block | 1 | ||
| 9- see scheme 52 | Piston pin | 1 per piston | Take off circlips and remove piston pin using suitable mandrel | If it is sluggish, heat the piston to 60 °C; install with suitable mandrel |
| CAUTION | Danger of cuts due to sharp-edged components! |
> Wear personal protective gear (gloves, safety goggles).
| WARNING | Danger of injury due to piston pin circlip jumping off! |
> Make sure that the piston pin circlip is secured against jumping off at all times (wear gloves and hold circlip in position with thumb).
Note. Combustion deposits on the piston crown are not to be removed mechanically!
Note. When disassembling the piston/connecting rod unit, note or mark the position, relationship to cylinder and installation position using a waterproof felt tip pen. Some Figures show the piston of the V8 as the work steps are analagous.
1. Fix piston onto retaining device P 9597 --> Retaining device. In order to do this, adapt the tool. Remove both fastening screws of the bracket for the large connecting-rod eye Then adjust tool length accordingly. Position piston with connecting rod. see scheme 53
2. Remove both piston pin circlips using a small screwdriver. To do this, guide the screwdriver through the small cutout and carefully lever out the piston pin circlip --> Removing piston pin circlip. (Scheme 302)
Note. If piston is sluggish, heat to 60 °C and remove and install with mandrel.
3. Insert piston in retaining device P 9597 (leave space below for the piston pins) and drive out piston pin using a suitable mandrel applying force by hand --> Piston pin mandrel. Secure piston pin against falling. see scheme 55
4. Remove connecting rod from the piston and place to one side.
| CAUTION | Over-extension of piston rings due to incorrect assembly! Damage to piston rings. |
> Force apart the piston rings using the piston ring pliers just far enough for it to be possible to remove or install them.
5. Place the piston on a clean surface and look for the gaps in the piston rings.
Note. Compression rings and oil scraper rings are installed and removed differently.
6. Remove the piston rings starting from the piston crown. In order to do this, move the middle point of the piston ring pliers Gr. 1 NR.58 into the gap in the relevant ring. The holding arms of the piston ring pliers should clasp the piston ring from above --> Piston ring pliers. Only open the piston ring as much as is needed to remove the piston ring from the groove. Do not overstretch it! see scheme 56
7. Relieve the piston ring pliers and remove the piston ring from the pliers.
8. Remove the three-piece oil scraper ring as follows: First, remove the upper and lower rings by hand by carefully forcing them away from the piston. Then remove the oil scraper spring carefully in the same way.
1. First fit the three-piece oil scraper ring. To do this, carefully stretch the oil scraper spring by hand at its gap to a point where this can be positioned over the piston into ring groove 3. Carefully force apart a ring of the oil scraper ring by hand and fit it into the third piston ring groove below the oil scraper spring. Fit the second ring in the same way over the oil scraper spring.
2. When fitted, the gap in the oil scraper ring must be offset by exactly 180° with respect to the gap in the oil scraper spring. Make sure that the oil scraper spring is in the middle of the oil scraper ring.
Note. The TOP marking must always face the piston crown.
3. Insert piston ring into the piston ring pliers. Make sure that, when the piston rings are installed, the designation of the piston rings is pointing in the direction of the piston crown --> Piston ring designation. Force the piston ring apart just enough for it to fit over the piston. see scheme 57
4. Fit piston rings. Using the piston ring pliers, insert the middle piston ring into the second ring groove in such a way that the inscription TOP is facing the piston crown. Insert the top piston ring into ring groove 1 in such a way that the inscription TOP is facing the piston crown.
5. Check that the piston rings are correctly seated and positioned. Make sure that the oil scraper spring is inside the oil scraper ring. In the case of the piston ring in ring groove 2, the inscription TOP must point to the piston crown. The top piston ring must be installed in such a way that the inscription TOP is facing the piston crown. The gaps in the individual piston rings must always be offset by 120°.
Scheme 303
Note. The gap of the piston ring may not be located next to the removal recess.
6. Install a piston circlip. In order to do this, insert the piston circlip into the ring groove of the piston pin eye in such a fashion that the ring gap is offset approx. 30° with respect to the piston crown. Press this gap end into the ring groove with your thumb -1-. see scheme 58
Scheme 304
7. Lever the piston circlip into the ring groove using a small screwdriver while continuing to press it down.
Scheme 305
8. If the piston circlip does not slide into the ring groove right away, press the second gap end of the piston circlip into the ring groove. Ensure correct installation seating.
9. Fix piston on retaining device P 9597 with fitted piston pin circlip facing downwards --> Retaining device. (Scheme 303)
10. Place piston pin and connecting rod in installation position. Make sure that the cast lugs on the connecting rod and connecting-rod big end are on the same side as the flat side of the piston crown.
Note. If piston is sluggish, heat to 60 °C and remove and install with mandrel.
11. Fit the greased piston pin through the piston and connecting-rod eye up to the circlip. If necessary, drive the piston pin up to the prefitted piston circlip by lightly tapping a suitable pressure piece with a plastic hammer --> Piston pin mandrel. (Scheme 305)
12. Fit the second piston pin circlip using the same procedure.
13. Check connecting rod and piston for smooth operation.
Note. The connecting-rod bolts must be replaced!
14. Fit connecting-rod bearing shells in connecting-rod big end and connecting-rod bearing cover. The retaining lugs must be positioned in the appropriate grooves and on the same side -B and C-. Cast lugs on the connecting-rod big end and the connecting-rod cover must lie on the same side as the flat side of the piston crown. Tighten the connecting-rod bolts by hand and set down the complete connecting rod ready for assembly. see scheme 64
1. Install pistons. > 131019 Remove and install piston - Chapter "Installing"
1. Remove piston. > 131019 Remove and install piston - Chapter "Removing"