Pre-Assembly Of Pistons And Connecting Rods

Information 

• Ensure even weight distribution when installing new pistons or connecting rods. 
• Only one weight group is permitted per engine. 

Component overview 

1. Connecting rod bolts → Initial tightening: 20 Nm (15 ftlb.) → Torque angle: 80° 
   Fig 1: Identifying Connecting Rod/Piston Components

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Tools: 

1. Retaining device 9778 
2. Inserts that can be used for the appropriate pistons: 9778  includes the insert for 3.4-litre pistons with a diameter of 97 mm. 9778/1  is the insert for 3.8-litre pistons with a diameter of 102 mm.
   Fig 2: Identifying Retaining Device 9778

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Information 

• The parting surface between the connecting rod and connecting rod cap is broken during the manufacturing process. 
• Assign connecting rod cap to the relevant connecting rod immediately after removal. 
• Also check the four-digit matching number. 
• Replace connecting rod bolts. 
• Replace connecting rod bearings. 

1. Allocate connecting rod bearings based on the marking on the crankshaft.
   1. 1.1. Read off the bearing shell color from the series of letters -2-  . The con-rod marking  indicates the con-rod journal. This is read from left to right. The bearings are fitted from the belt side to the flywheel side.
      1. G  - Yellow
      2. B  - Blue
      3. R  - Red
         Fig 3: Identifying Crankshaft Bearing Shell Allocation Marking

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   2. 1.2. Fit new con-rod bearing shells in the connecting rod cap and connecting rod and grease with Optimol Optipit grease (Part No. 000.043.204.17).
   3. 1.3. Check that the new con-rod bearing shells are seated correctly (check locking lugs) -arrow-  .
      Fig 4: Locating Connecting Rod Bearings Locking Lugs

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   4. 1.4. Secure connecting rod cap with relevant connecting rod and new M10 screws by hand.
2. Fit pistons and connecting rods for cylinders 4-6 (the positions of the above-mentioned markings also apply for the pistons and connecting rods for cylinders 1-3).
   Fig 5: Identifying Connecting Rod Matching Number

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   1. 2.1. The matching number -2-  and data matrix code -inset-  on the correctly installed connecting rod must be facing the exhaust side.
   2. 2.2. In contrast, the cone-shaped neck and data matrix code -1-  on the piston must be facing the intake side.
   3. 2.3. The pistons for cylinders 1-3 are pre-fitted without connecting rods.
3. Insert connecting rod with piston -1-  or only the piston into the retaining device 9778  (3.4-litre).
   1. 3.1. For 3.8-litre pistons, pull off the piston receiving element and then attach the piston receiving element 9778/1  .
      Fig 6: Holding Piston/Connecting Rod In Retaining Device 9778

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      WARNING: Preloaded or pressurized components

      • Risk of eye injuries
      • Risk of bruising

      → Wear personal protective gear.

      → Secure components to prevent them from falling off suddenly.

4. First, fit the piston-pin circlip, which must be facing the flywheel side later.
   1. 4.1. Fit the circlip on the side of the piston that does not have an assembly groove for the assembly tool 9776  .
   2. 4.2. Fit the circlip -1-  at the position shown. Use a small screwdriver to do this.
   3. 4.3. Press the circlip in with your thumbs and guide it to its final position with the screwdriver.
      Fig 7: Identifying Circlip Facing Flywheel Side

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      Pistons and connecting rods for cylinders 4-6: 

5. Turn piston and connecting rod by 180° and fit the circlip, which must be facing the belt side later. Use special tool assembly tool 9776  to do this.
   1. 5.1. Coat piston pin with new engine oil and press it into the relevant piston/connecting rod assembly.
   2. 5.2. Turn the groove for the small hook on the tool -2-  towards the observer.
      Fig 8: Pressing Piston-Pin Circlip Into Tool 9776

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   3. 5.3. Slide a new circlip -1-  into the assembly tool and press the edges together.
   4. 5.4. Position small hook facing the groove -arrow-  .
      Fig 9: Locating Hook Groove

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   5. 5.5. Turn the circlip -1-  as required.
      Fig 10: Turning Piston-Pin Circlip In Tool

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   6. 5.6. Pull back and hold push rod in tool. Place the pipe -1-  on a hard surface. Slowly guide the push rod down and press the circlip into installation position. You should hear a distinct click.
      Fig 11: Pressing Circlip Into Installation Position

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6. Assembly tool 9776  must be positioned on the piston in such a way that the small hook is lying in the half-moon-shaped bore -arrow-  .
   Fig 12: Locating Assembly Tool 9776

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   View of piston on the circlip -1-  in the tool.

   Fig 13: Identifying Piston Circlip Position

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   1. 6.1. Hold on firmly to the tube of the tool -1-  and tap the push rod slightly towards the piston with the ball of your hand -arrow-  . The circlip will lock with a clearly audible click.
      Fig 14: Installing Circlip On Piston

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   2. 6.2. The circlip -1-  must be fitted as shown. The hook is at the 9 o'clock position -2-  .
      Fig 15: Identifying Piston Circlip (Viewed From Belt Side)

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7. Remove piston and connecting rod from the retaining device 9778  .
8. If piston rings will be replaced on the re-installed pistons, these can be removed and fitted by hand.
   IMPORTANT: Check installation position and avoid breakage!