Installing Pistons - Cylinders 3-4

Information 

• Some of the illustrations show the 6-cylinder engine variant as an example. 
• But this does not affect the procedure or the steps to be carried out. 

Preliminary work: New bearing shells installed, crankshaft inserted in crankcase half 3-4, connecting rods with pistons prefitted. 

1. Secure the crankshaft to the main bearing in the middle using > 9779 - holding bridge-1-  .
   1. 1.1 Tighten two fastening screws -2-  hand-tight.

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   Holding bridge 9779 for crankshaft (view of 6-cylinder engine)

2. Tighten three M8 screws -2-  securing the vibration damper to the crankshaft flange hand-tight.
   1. 2.1 Turn the crankshaft using > 9773 - turning device  so that the con-rod journal is at bottom dead center position.

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   Turning crankshaft (without vibration damper)

   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. 
3. Check that the new con-rod bearing shells are seated correctly (check retaining lugs) -Arrow-  .

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   Retaining lugs for connecting-rod bearings

   1. 3.1 Check allocation of connecting rod to connecting rod cap (matching number -1-  and data matrix code).

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   Connecting rod on crankshaft

   Information 

   • If pistons are to be replaced, only one weight group is permitted for all pistons. 
4. Install piston 3 with connecting rod.
   1. 4.1 For re-installation, fit the relevant piston into the related cylinder bore according to the inscription.
   2. 4.2 Check installation position of pistons. Data matrix code on the piston must be facing the intake side. In contrast, the matching number and data matrix code on the connecting rod must be facing the exhaust side.

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      Matching number on connecting rod

      1. Data matrix code on piston
      2. Matching number and data matrix code on connecting rod
   3. 4.3 Align piston rings. Offset the ring gaps by 120°. Check the twist lock -Arrow-  at the second ring groove.

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      Twist lock on second piston ring

   4. 4.4 Coat pistons and tools with new engine oil.
   5. 4.5 Insert piston as far as required into the relevant assembly funnel until the lower edge of the piston is flush with the surface of the tool.

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      Lower edge of piston flush with contact surface of assembly funnel

      1. Piston
      2. >9784/2 - Funnel  or > 9784/4 - funnel 
      3. Piston-pin circlip
   6. 4.6 Guide connecting rod and piston -1-  into the cylinder bore and position assembly funnel -2-  on the crankcase -Arrow-  .

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      Inserting piston into cylinder bore (view of 6-cylinder engine)

   7. 4.7 Press the piston into the cylinder bore immediately using the handle of a hammer -2-  and hold assembly funnel -1-  firmly while doing this.

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      Pressing in piston (shown on 6-cylinder engine as an example)

   8. 4.8 Remove assembly funnel.
   9. 4.9 Fit the correct connecting rod cap with new screws.
   10. 4.10 Repeat these steps for piston 4.
       IMPORTANT: Con-rod journal for piston/connecting rod 4 must be at bottom dead center!
5. Pre-fit connecting rods 1-2 with new bearings and the relevant connecting rod caps and new screws on the crankshaft.
   1. 5.1 The matching number -1-  and data matrix code are facing the exhaust side.

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   Connecting rod on crankshaft

6. Fit rubber sleeves on connecting rods 1-2 to protect the cylinder lining (> 9795 - assembly aid  ).
7. Tighten all connecting rod caps according to tightening specifications.

   Step 1: > Initial tightening 5 Nm (3.5 ftlb.) 

   Step 2: > Subsequent tightening torque 16 Nm (12 ftlb.) 

   Step 3: > Tightening torque 20 Nm (15 ftlb.) 

   Step 4: > Tightening angle 80° 

   Step 5: > Loosen screws - 360° 

   Step 6: > Initial tightening 5 Nm (3.5 ftlb.) 

   Step 7: > Subsequent tightening torque 16 Nm (12 ftlb.) 

   Step 8: > Tightening torque 20 Nm (15 ftlb.) 

   Step 9: > Final tightening angle 80° +/- 3° 

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   Connecting rod cap screws