Installing Pistons

Information 

• Connecting rod bolts and bearing shells must always be replaced. 
• The marking on the main bearings and connecting rod bearings is located on the flywheel flange of the crankshaft. 

Information 

• The pistons must already be pre-fitted (pistons, piston rings, connecting rods and fastening material) before performing the next step. 
• Fit the number on the connecting rod -A- facing the exhaust side. 
• When installing the piston in the crankcase, the direction of travel arrow on the piston crown must point in the direction of travel. 
• The code on the connecting-rod big end and connecting rod cap must be on the same side -A-  .
  Fig 1: Identifying Cylinder Number Marking

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• The direction of travel arrow is on the same side as the connecting rod code -A- on the piston shown. Fit the number on the connecting rod -A- facing the exhaust side. 
  Fig 2: Identifying Connecting Rod Code On Piston

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• The direction of travel arrow must be pointing forwards (in direction of travel) when installed -inset-  . The combustion chamber recess -1- on the DFI piston is facing the inner V (center of the engine) when installed -Up arrow-  .
  Fig 3: Installing DFI Piston In Crankcase

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Information 

• The piston connecting rods are cracked and only fit in one position (in conjunction with the matching numbers). 
• Install con-rod code towards exhaust side -A-  .
  Fig 4: Identifying Cylinder Number Marking

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Information 

The tightening specifications for the basic engine are stored centrally (→ 1001IN TIGHTENING TORQUES, TIGHTENING SEQUENCES, ASSEMBLY OVERVIEWS ).

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.

1. Turn the engine in the engine support so that the crankshaft lies at the bottom.
2. Install the piston. To do this, turn the crankshaft with a wrench (a/f 27) until the corresponding crank pin is pointing vertically downwards.
3. Lightly oil the cylinder, piston and funnel 9784/1  (-1-  ).
   1. Oil the inside of the funnel
   2. Piston and connecting rod ready for installation
      Fig 5: Oiling Piston Funnel

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4. Align piston ring gaps (offset by 120°) and clamp the piston rings together using the funnel 9784/1  . Ensure that all piston rings are correctly tensioned by the special tool and check that they are not jammed. When doing this, slide the piston with connecting rod fitted into the funnel -2-  . The collar of the funnel must be facing the crankcase -1-  . Slide the piston into the funnel until the piston shank protrudes approx. one centimeter down out of the funnel. → Piston inserted in piston funnel 
   Fig 6: Inserting Piston Into Piston Funnel

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   Fig 7: Locating Piston Funnel

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5. Place the piston onto the cylinder from above and slide it into the cylinder using the handle of a hammer if necessary. When doing so, make sure that the direction of travel arrow is pointing forwards. If you are using the funnel 9784/1  , position it flush on the crankcase -3-  . Check the position of the combustion chamber recess -1-  and the direction of travel arrow when doing this.
   Fig 8: Identifying Fitting Piston

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6. Push the piston down until the connecting rod bearing is sitting on the lift pin. Push it down further using the handle of a hammer if necessary -see Fig 9. Do not use force. If the piston is jammed in the tool, oil the tool again if necessary or carefully loosen and turn the piston.
   Fig 9: Installing Piston

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7. Oil connecting-rod bearing shells and crank pins.
8. Then fit the connecting rod cap with bearing shell (twist lock together) → Retaining lugs for connecting rod bearings -B and C-  . The connecting rod numbers must be facing each other → View of matching numbers -A-  . Fit connecting rod bolts by hand.
   Fig 10: Identifying Retaining Lugs For Connecting Rod Bearings

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   Fig 11: Identifying Connecting Rod Matching Numbers

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9. Fit the opposite piston (cylinders 1 and 4).
10. Fit other pistons using the procedure described above.
11. Turn crankcase on the assembly support until the crankshaft is on top.
12. Tighten connecting rod bolts that have been replaced. Turn the crankshaft until the corresponding crank pin is pointing straight upwards.
13. Once all pistons have been correctly fitted and secured, turn the crankshaft in a clockwise direction to check it using a ring wrench (a/f 27). When doing so, watch out for stiffness and irregularities. If the crankshaft cannot be turned or if it is very stiff, check whether the installation direction (arrow) of the pistons, the pistons and the cylinders (markings) and the connecting rod caps and connecting-rod big end all match.