Disassembling and Assembling Pistons
Disassembling and assembling pistonsTools
Preliminary work
1. Remove piston.
Special tools
Disassembling pistons
ATTENTION 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 analogous.
1. Fix piston onto retaining device 9597. 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.
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.
Note: If piston is sluggish, heat to 60°C and remove and install with mandrel.
3. Insert piston in retaining device 9597 (leave space below for the piston pins) and drive out piston pin using a suitable mandrel applying force by hand.
4. Remove connecting rod from the piston and place to one side.
ATTENTION 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. Only open the piston ring as much as is needed to remove the piston ring from the groove. Do not overstretch it!
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.
Assembling pistons
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. Force the piston ring apart just enough for it to fit over the piston.
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°.
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-.
7. Lever the piston circlip into the ring groove using a small screwdriver while continuing to press it down.
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 9597 with fitted piston pin circlip facing downwards.
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.
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.
Subsequent work
1. Install pistons.