Overhaul
WM 131037 Disassembling and assembling pistons
Tools
Preliminary work
1. Remove piston. -> 131020 Removing and installing pistons Removal and Replacement
Disassembling pistons
CAUTION
Engine damage if piston rings overstretched!
-> Do not overstretch piston rings with piston ring pliers. Spread the piston ring until it just fits over the piston.
Information
- If reusing a piston, do not remove combustion residues on the piston crown are mechanically!
Piston, connecting rod
Connecting-rod assembly, bearing shells
Piston classification, turbo engine
Information
- When disassembling the piston/connecting rod unit, note or mark the position, relationship to cylinder and installation position using a waterproof felt tip pen.
1. Secure piston on retaining device 9597 ( => Piston on retaining device ).
Piston on retaining device
2. Remove both piston-pin circlips using a small screwdriver. To do this, guide the screwdriver through the small cut-out and carefully lever out the piston-pin circlip => Levering out piston-pin circlips with a small screwdriver.
Levering out piston-pin circlips with a small screwdriver
3. Insert piston into the retaining device 9597 (leave space below for the piston pins) and drive out piston pins using a suitable pressure piece. => Piston pin with plunger
Piston pin with plunger
4. Remove connecting rod from the piston and place to one side.
Information
- Compression rings and oil scraper rings are installed and removed differently.
5. Remove piston rings.
5.1. Place the piston on a clean surface and look for the gaps in the piston rings.
5.2. Remove the piston rings, starting at the piston crown. To do this, move the middle point of 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 on piston ring. Only open the piston ring as much as is needed to remove the piston ring from the groove. Do not overstretch it!
Piston ring pliers on piston ring
5.3. Relieve the piston ring pliers and remove the piston ring from the pliers.
5.4. Remove the two-piece oil scraper ring as follows: First, remove the outer ring by hand by carefully prying it away from the piston. Then remove the inner oil scraper spring in the same way.
Assembling pistons
Information
- 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 marking on the connecting rod bearings is located on the flywheel or drive plate flange of the crankshaft. -> 134819 Removing and installing crankshaft Service and Repair
Information
- The tightening specifications for the basic engine are stored centrally. -> 1001IN Tightening torques, tightening sequences, assembly overviews [1][2]Specifications. Tightening torques and assembly instructions for other assemblies (e.g. chassis, electrics, transmission or body) or for peripheral engine equipment can be found in the corresponding documents.
Piston, connecting rod
Connecting-rod assembly, bearing shells
Piston classification, turbo engine
1. First fit the two-piece oil scraper ring. To do this, insert the oil scraper spring into ring groove 3. Carefully force the oil scraper ring (TOP marking facing up towards the piston crown -A- ) apart with your hand and fit it into the third piston ring groove above the oil scraper spring.
Piston ring marking
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.
CAUTION
Engine damage if piston rings overstretched!
-> Do not overstretch piston rings with piston ring pliers. Spread the piston ring until it just fits over the piston.
Information
- 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 marking on the piston rings is pointing in the direction of the piston crown -A-. Spread the piston ring until it fits across the piston. => Piston ring pliers on piston ring
Piston ring pliers on piston ring
Piston ring designation
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°.
6. Fit a piston-pin circlip. To do this, insert the piston-pin circlip into the ring groove of the piston pin eye so that the ring gap is offset with respect to the piston crown (6 or 11 o'clock position). Press this end into the ring groove with your thumb -1-.
Piston circlip
7. Lever the piston circlip into the ring groove using a small screwdriver while continuing to press it down.
Inserting the piston circlip
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.
Pressing the piston circlip into the ring groove
9. Secure piston with fitted piston-pin circlip facing downwards and connecting rod on retaining device 9597 ( => Retaining device ).
Retaining device
10. Place piston pin and connecting rod in installation position. Ensure that the connecting rod marking is facing the exhaust side and the combustion chamber recess is facing the centre of the engine during assembly. Direction of travel arrow on the piston must be in direction of travel.
11. Slide the oiled piston pin through the piston pin eye and through the connecting rod eye. Tap in carefully with a rubber hammer if necessary.
12. Fit the second piston-pin circlip using the same procedure. Align the ring gap so that it is facing downwards, away from the piston crown (6 o'clock position, 11'o'clock position optional).
13. Check connecting rod and piston for smooth operation.
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-. The matching numbers -A- must be the same and must be on the same side (pointing to the exhaust side when installed). Tighten the connecting-rod bolts by hand and position the complete connecting rod ready for assembly.
Position of bearing shells
Surface with connecting rod number marking (exhaust side)
Subsequent work
1. Install piston. -> 131020 Removing and installing pistons Removal and Replacement