Connecting Rod: Service and Repair

Pistons And Connecting Rods, Disassembling And Assembling





1 - Piston ring
^ Offset gaps by 120°
^ Remove and install with piston ring pliers
^ "Top" marking faces toward piston crown
^ Checking ring gap - Fig. 1
^ Checking ring/groove clearance - Fig. 2

2 - Piston
^ Checking - Fig. 3
^ Mark installation position and cylinder number
^ Arrow on piston crown points toward pulley end
^ Install only with piston ring compressor
^ Dimensions - Fig. 4

3 - Connecting rod
^ With oil supply hole for piston pin lubrication
^ Replace only as complete set
^ Installation position: marking
-A- points toward pulley end
^ Make matching marks
-B- for cylinder number

4 - Connecting rod bearing cap
^ Note installation position

5 - 30 Nm (22 ft lb) plus additional 1/4-turn (90°)
^ Oil threads and contact surface
^ Measuring radial clearance: tighten to 30 Nm (22 ft lb) only, NOT additional 1/4-turn (90°)

CAUTION!
DO NOT turn crankshaft while measuring radial clearance.

6 - Pressure relief valve
^ Tightening torque: 27 Nm (20 ft lb)
^ Opening pressure: 2.5-3.2 bar (36-46 psi)

7 - Oil spray jet
^ For piston cooling

8 - Bearing shell
^ Note installation position
^ Shells with oil hole are installed in connecting rod -3-, face toward piston pin
^ Do not interchange worn bearing shells
^ Check to make sure holding tabs seat correctly
Axial clearance:
^ New: 0.05-0.31 mm (0.0020-0.0122 in.)
^ Wear limit: 0.37 mm (0.0146 in.)
Radial clearance:
^ Measure with plastigage
^ New: 0.01-0.06 mm (0.0004-0.0024)
^ Wear limit: 0.12 mm (0.0047)

CAUTION!
DO NOT turn crankshaft while measuring radial clearance.

9 - Cylinder block
^ Checking cylinder bore diameter - Fig. 5
^ Piston and cylinder dimensions - see table.

10 - Connecting rod bolt

11 - Circlip

12 - Piston pin
^ If difficult to remove, warm piston to 60°C (140°F)
^ Remove and install with drift VW 222a

Special tools, testers and auxiliary items
^ Feeler gauges
^ Internal dial gauge 50-100 mm
^ Micrometer 75-100 mm

Fig. 1 Checking piston ring gap








- Squarely insert piston ring into cylinder from above, to approx. 15 mm (5/8 in.) from bottom of cylinder.

Fig. 2 Checking piston ring/groove clearance








- Clean ring groove before measuring.

Fig. 3 Checking piston wear





- Measure approx. 10 mm (0.4 in.) from lower edge of piston skirt at right angle (90°) to piston pin.

^ Maximum deviation from nominal diameter: 0.04 mm (0.0016 in.)

Fig. 4 Piston dimensions





Note:
Only pistons and piston rings of the same type and pistons of the same weight class may be installed.

Fig. 5 Cylinder bore, checking





- Use 50-100 mm internal micrometer.

- Measure in direction -A- perpendicular to crankshaft, and direction -B- parallel to crankshaft.

- Measure in three places as shown.
1 - 10 mm (0.39 in.) from top
2 - Center
3 - 10 mm (0.39 in.) from bottom

Max. deviation from nominal diameter: 0.08 mm (0.0015 in.)

CAUTION!
DO NOT measure cylinder bore when cylinder block is mounted in engine stand VW 540. Measurement accuracy can be affected by cylinder block distortion as it hangs down from the engine stand.




Piston and Cylinder Dimensions