Piston: Service and Repair
Piston and Connecting Rod Overview
1 Piston Rings
• Offset gaps by 120°.
• Use piston ring pliers for removal and installation.
• "TOP" faces toward the piston crown.
• Checking the ring gap, refer to => [ Piston Ring Gap, Checking ].
• Checking the piston ring groove clearance, Refer to => [ Piston Ring Groove Clearance, Checking ].
2 Piston
• With the combustion chamber.
• Mark the installed position and cylinder allocation.
• Installed position and allocation, piston to cylinder, refer to => [ Piston Installed Position and Piston/Cylinder Allocation ].
• The arrow on the piston face points towards the belt pulley side.
• Install using piston ring compressor.
• Replace if the piston skirt is cracked.
• Checking the piston projection in Top Dead Center (TDC), refer to => [ Piston Projection in TDC, Checking ] Testing and Inspection.
3 Piston Pin
• If difficult to move, heat the piston to 60 °C (140 °F).
• Remove and install using the pilot drift (VW 222).
4 Lock Ring
5 Connecting Rod
• Mark the allocation to the cylinder using a colored mark - A -.
• Installed position: The mark - B - points to the belt pulley side.
• With a cracked bearing cap.
• Separate new connecting rods. Refer to => [ New Connecting Rod, Separating ] Procedures.
6 Bearing Shell
• Note the installed position.
• Note the version: The upper bearing shell (to the piston) is made of a wear resistant material, identification: Black line on the contact surface in the area of the separating point.
• Do not interchange used bearing shells (mark them).
• Insert bearing shells in the center.
• Make sure it they are secure.
• Axial play:
Wear limit: 0.37 mm
• Measure the radial clearance using Plastigage(R):
Wear limit: 0.08 mm
• Do not rotate the crankshaft when checking the radial clearance.
7 Cylinder Block
• Checking the cylinder bore, refer to => [ Cylinder Bore, Checking ].
• Piston and cylinder dimensions, refer to => [ Piston and Cylinder Dimensions ] Piston and Cylinder Dimensions.
8 Connecting Rod Bearing Cap
• Pay attention to the installed position.
• Due to the separation procedure (cracking) of the connecting rod, the cap only fits in one position and only to the corresponding connecting rod.
9 Oil Spray Jet
• For piston cooling
10 Bolt
• 25 Nm
• Install without sealant.
11 Bolt
• 30 Nm + an additional 90° (1/4) turn.
• Always replace.
• Lubricate the threads and contact surface.
• Use a old bolt to measure the radial play.
Piston Ring Gap, Checking
Special tools, testers and auxiliary items required
• Feeler Gauge
- Push the piston ring squarely from above, down to approximately 15 mm from the bottom of the cylinder.
Piston Ring Groove Clearance, Checking
Special tools, testers and auxiliary items required
• Feeler Gauge
- Clean the groove in the ring before checking.
Cylinder Bore, Checking
Special tools, testers and auxiliary items required
• Internal Dial Gauge 50 to 100 mm
• or Inside Micrometer Set 18-100 mm (US1033/S)
- Measure the bore at 3 locations in both directions - A - across the engine and - B - in line with the crankshaft. Deviation from nominal size: Max. 0.10 mm.
• The cylinder bore must not be measured when the cylinder block is mounted on the engine and transmission holder (VAS 6095) because the measurements may be incorrect.
Piston Installed Position and Piston/Cylinder Allocation
The arrow on the piston crown - arrows - faces cylinder 1.
Connecting Rod Bearing Shell Installed Position
The bearing shell - 1 - with the oil bore - arrow - is for the connecting rod.
The bearing shell - 2 - without a oil bore is for the connecting rod cap.
- Place the bearing shells centrally into the connecting rod and connecting rod bearing cap.
Dimension - a - must be the same on the left and right.