Piston: Service and Repair

Pistons and conrods, disassembling and assembling
1. Piston ring
^ Offset gaps by 120°
^ Remove and install with piston ring pliers
^ "TOP" faces towards piston crown
^ Checking ring gap see Fig. 1
^ Checking ring to groove clearance see Fig. 2
^ 2 or 3 part oil scraper ring, mixed installations permissible
2. Piston
^ Checking see Fig. 3
^ Mark installation position and cylinder number
^ Arrow on piston crown points to pulley end
^ Install using piston ring clamp
3. Conrad
^ Only replace as a set
^ Mark cylinder number -B-
^ Installation position: Marking A- faces towards pulley end
4. Conrad bearing cap
^ Note installation position
5. 30 Nm + 1/4 turn (90°) further
^ Oil threads and contact surface
^ To measure radial clearance tighten only to 30 Nm and no further
6. Pressure relief valve, 27 Nm
^ Opening pressure: 2.5 to 3.2 bar
7. Oil spray jet
^ For piston cooling
8. Bearing shell
^ Note installation position
^ Do not interchange used bearing shells
^ Ensure retaining tabs fit tightly in recesses
^ Axial clearance New: 0.05 and 0.31 mm, Wear limit: 0.37 mm
^ Check radial clearance with Plastigage: New: 0.01 and 0.06 mm, Wear limit: 0.12 mm
^ Do not rotate crankshaft when checking radial clearance
9. Cylinder block
^ Checking cylinder bores see Fig. 4
^ Piston and cylinder dimensions
10. Conrad bolt
11. Circlip
12. Piston pin
^ If difficult to remove, heat piston to 60° C
^ Remove and install with VW 222a

Special tools and equipment

^ Feeler gauges
^ Internal dial gauge 50 to 100 mm
^ Micrometer 75 to 100 mm





Fig. 1 Checking piston ring gap





- Push ring squarely from above down to approx. 15 mm from bottom end of cylinder.





Fig. 2 Checking ring to groove clearance





- Clean groove before check.





Fig. 3 Checking piston
- Measure pistons approx. 10 mm from lower edge of skirt, at 90° to piston pin axis.
^ Deviation from nominal dimension: max. 0.04 mm





Fig. 4 Checking cylinder bores
- Measure bores at 3 locations in both directions -A- across engine and -B- in line with crankshaft. Use internal dial gauge 50 to 100 mm.
^ Deviation from nominal dimension: max. 0.08 mm

Note: Measuring the cylinder bores must not be done when the cylinder block is mounted on a repair stand with holding fixture VW 540, as incorrect measurements would then be possible.





Piston and cylinder dimensions

1. Dimension without graphite coating (thickness 0.02 mm). The graphite coating wears away.