Piston: Service and Repair
Pistons and Connecting Rod Assembly Overview
• Oil spray nozzle and pressure relief valve.
1 Bolt
• Replace
• 30 Nm plus an additional 90° turn
• Lubricate the threads and contact surface
2 Connecting Rod Bearing Cap
• Due to the separation procedure (cracking) of the connecting rod, the connecting rod bearing cap only fits in one position and only to the corresponding connecting rod.
• Mark allocation to cylinder with paint - B -
• Installed position: markings - A - face the pulley side
3 Bearing Shell
• Installed location
• Replace any worn bearing shells
• Note the version: the upper bearing shell (to piston) is made of wear-resistant material. How to recognize new bearing shells: there is a black line on the contact surface near the separating point.
• Ensure seated tightly
4 Connecting Rod
• Only replace as set
• With a cracked connecting rod bearing cap
• Separate new connecting rod
• Mark allocation to cylinder with paint - B -
• Installation position: markings - A - face the pulley side
• Axial play wear limit: 0.37 mm
• Radial clearance, measuring, refer to => [ Connecting Rod, Measuring Radial Clearance ] Testing and Inspection
5 Circlip
• Replace
6 Piston Pin
• If tight, heat piston to 60 °C (95 °F)
• Removing and installing using a pilot drift (VW 222 A)
7 Piston
• With combustion chamber
• Mark the installation position and cylinder allocation
• Checking
• Install with piston ring compressor
• Piston and cylinder dimensions, refer to => [ Piston and Cylinder Dimensions ] [1][2]Piston, Engine
• Measuring cylinder bore
• Measure the piston projection at TDC, refer to => [ Piston Projection, Measuring at TDC ] Testing and Inspection
8 Piston Rings
• Compression rings
• Offset gaps by 120°
• Use piston ring pliers for removal and installation
• Installed position: TOP marking or side with writing faces the piston crown.
• Gap, measuring
• Measuring side clearance
9 Piston Ring
• Oil scraping ring
• Offset gaps by 120° on the lower compression ring
• Use piston ring pliers for removal and installation
• Gap, measuring
• Measuring side clearance
Measuring the Piston Ring Gap
- Push the piston ring squarely from above down to approximately 15 mm from the bottom end of the cylinder.
- Use a piston without a piston ring for sliding in.
Measuring the Ring to Groove Clearance
- Clean the piston ring groove before checking.
Pistons, Checking
- Measure approximately 15 mm from the lower edge at a 90° angle to the piston pin axis using a 75 to 100 mm external micrometer.
• Maximum deviation from the specified dimension: 0.04 mm.
Nominal dimension, refer to => [ Piston and Cylinder Dimensions ] [1][2]Piston, Engine.
• A piston must be replaced if there are cracks on the piston shaft.
Piston Installed Location and Allocation, Piston to Cylinder
• Arrow on the piston crown - arrows - facing the pulley side.
Measuring Cylinder Bore
- Using a cylinder gauge (VAS 6078) measure diagonally at 3 positions transversely - A - and longitudinally - B -.
• Maximum deviation from the specified dimension: 0.10 mm.
Nominal dimension, refer to => [ Piston and Cylinder Dimensions ] [1][2]Piston, Engine.
Bearing Shell Installation Position in the Connecting Rods
- Install the bearing shells into the center of the connecting rod and into the connecting rod bearing cap.
• Dimension - a - = 2.5 mm.
Separating the New Connecting Rod
New connecting rods may not be separated at the location where they should be. If it difficult to remove the connecting rod bearing cap by hand, do the following:
- Clamp the connecting rod in a vise, which has protectors over the grips to prevent damage.
• Clamp the connecting rod below the dotted line.
- Remove the bolts - arrows - approximately 5 turns.
- Carefully tap the connecting rod bearing cap with a plastic hammer - arrow - until it comes loose.
Oil Spray Jet and Pressure Relief Valve
1. Bolt with pressure relief valve - 27 Nm
2. Oil spray jet (for piston cooling)
• Installation position: the guiding edge of the oil spray jet to the machined surface of the cylinder block.
• Do not bend the oil spray nozzles.
• Replace the oil spry nozzles if they are bent.