Connecting Rod: Service and Repair
Pistons, Connecting Rods, Piston Rings And Cylinder Bores
Pistons and connecting rods - remove
1. Remove cylinder head(s).
2. Remove big-end bearings.
3. Remove carbon ridge from top of each cylinder bore.
4. Suitably identify each piston to its respective cylinder bore.
5. Push connecting rod and piston assembly to top of cylinder bore and withdraw assembly.
6. Repeat above procedure for remaining pistons.
CAUTION: Big-end bearing shells must be replaced whenever they are removed.
Piston rings - remove
1. Using a suitable piston ring expander, remove and discard piston rings.
2. Remove carbon from piston ring grooves.
NOTE: Use an old broken piston ring with a squared off end.
CAUTION: Do not use a wire brush.
Piston rings - inspection
1. Temporarily fit new compression rings to piston.
NOTE: The ring marked 'TOP' must be fitted, with marking uppermost, into second groove. The chrome ring fits into top groove and can be fitted either war round.
2. Check compression ring to groove clearance:
Top compression ring A = 0.05 to 0.10 mm (0.002 to 0.004 in)
2nd compression ring B = 0.05 to 0.10 mm (0.002 to 0.004 in)
3. Insert piston ring into its relevant cylinder bore, held square to bore with piston and check ring gaps.
Top compression ring = 0.44 to 0.57 mm (0.02 to 0.22 in)
2nd compression ring = 0.44 to 0.57 mm(0.02 to 0.22 in)
Oil control ring rails = 0.38 to 1.40 mm (0.14 to 0.05 in)
Pistons - remove
1. Clamp hexagon body of LRT-12-013 in vice.
2. Screw large nut back until flush with end of centre screw.
3. Push centre screw forward until nut contacts thrust race.
4. Locate piston adapter LRT-12-014 with its long spigot inside bore of hexagon body.
5. Locate piston and connecting rod assembly on centre screw and up to adapter LRT-12-014.
6. Fit remover/replacer bush of LRT-12-014 on centre screw with flanged end away from gudgeon pin.
7. Screw stop nut on to centre screw.
8. Lock the stop nut securely with lockscrew.
9. Push connecting rod to right to locate end of gudgeon pin in adapter LRT-12-014.
10. Ensure remover/replacer is located in gudgeon pin bore of piston.
11. Screw large nut up to LRT-12-013.
12. Hold lockscrew and turn large nut until gudgeon pin is withdrawn from piston.
13. Dismantle tool and remove piston, connecting rod and gudgeon pin.
NOTE: Keep each piston and gudgeon pin with their respective connecting rod.
14. Repeat above operation for remaining pistons.
Pistons and connecting rods - inspection
1. Clean carbon from pistons.
2. Inspect pistons for distortion and cracks.
3. Measure piston diameter at 90 ° to gudgeon pin axis and 10 mm (0.4 in) from bottom of skirt. The piston must be 0.02 mm to 0.045 mm (0.001 to 0.002 in) smaller than cylinder bore.
4. Check gudgeon pin bore in piston for signs of overheating.
5. Check connecting rods for alignment.
Gudgeon pins - inspection
NOTE: Gudgeon pins are only supplied as an assembly with replacement pistons.
1. Check gudgeon pins for signs of wear and overheating.
2. Check clearance of gudgeon pin in piston:
Gudgeon pin to piston clearance = 0.006 to 0.015 mm (0.0002 to 0.0006 in)
3. Check overall dimensions of gudgeon pin:
Overall length = 72.67 to 72.79 mm (2.85 to 2.86 in)
Diameter - measured at each end and centre of pin = 22.215 to 22.220 mm (0.87 to 0.871 in).
Cylinder liner bore - inspection
1. Measure cylinder bore wear in two axis 40 to 50 mm (1.5 to 1.9 in) from top of bore:
Cylinder bore diameter - standard:
3.5 litre = 88.90 mm (3.5 in)
3.9 litre = 94.00 mm (3.7 in)
4.2 litre = 94.00 mm (3.7 in)
Maximum ovality = 0.013 mm (0.0005 in)
2. Compare cylinder bore diameter with piston diameter and calculate piston to cylinder bore clearance.
Piston to cylinder bore clearance = 0.002 to 0.045 mm (0.001 to 0.002 in)
NOTE: Pistons are available in service standard size and 0.508 mm (0.02 in) oversize. Service standard size pistons are supplied 0.0254 mm (0.01 in) oversize. When fitting new service standard size pistons, check for correct piston to bore clearance, rebore or hone bore if necessary.
CAUTION: The temperature of piston and &, cylinder block must be the same to ensure accurate measurement. When reboring cylinder block, the crankshaft main bearing caps must be fitted and bolts tightened to: Initial torque - all bearing caps -13 Nm (10 ft. lbs.) Numbers 1 to 4 bearing caps - 70 Nm (52 ft. lbs.). Rear bearing cap - 90 Nm (66 ft. lbs.).
3. If only new piston rings are to be fitted, break cylinder bore glazing using a fine grit, to produce a 60 ° cross-hatch finish.
CAUTION: Ensure all traces of grit are ill removed after above operation. If dipstick tube has been removed, coat portion of tube below collar with Loctite 572 prior to refitting.
Pistons - refit
CAUTION: On later 4.2L engines the piston ill has a 0.5 mm (0.02 in) offset gudgeon pin which can be identified by an arrow mark on the piston crown. This arrow MUST always point to the front of the engine.
1. 4.2L engine only: Assemble pistons to connecting rods with arrow on piston pointing towards domed shaped boss on connecting rod for RH bank of cylinders, and arrow pointing away from dome shaped boss for LH bank of cylinders.
2. Clamp hexagon body of LRT-12-013 in vice.
3. Slacken large nut and pull the centre screw 50 mm (1.9 in) out of hexagon body.
4. Locate piston adapter LRT-12-014 with its long spigot inside bore of hexagon body.
5. Fit parallel sleeve, grooved end last, up to shoulder on centre screw.
6. Lubricate gudgeon pin and bores of connecting rod and piston with graphited oil.
7. Locate connecting rod and piston to centre screw with connecting rod entered on sleeve up to groove.
8. Fit gudgeon pin on to centre screw and into piston bore up to connecting rod.
9. Fit remover/replacer bush with flanged end towards gudgeon pin.
10. Screw the stop nut on to centre screw and position piston against face of adapter LRT-12-014.
11. Lubricate centre screw threads and thrust race with graphited oil, screw large nut up to thrust race.
12. Lock the stop nut securely with lockscrew.
13. Set torque wrench to 16 Nm (12 ft. lbs.), and using a socket on large nut, pull gudgeon pin in until flange of remover/replacer bush is distance A from face of piston.
Distance A = 0.4 mm (0.02 in)
14. If correct torque figure is not achieved during above operation, fit of gudgeon pin to connecting rod is not acceptable and necessitates renewal of components.
CAUTION: The centre screw and thrust Lb race must be kept well lubricated throughout operation. Flange of remover/replacer must not be allowed to contact piston.
15. Dismantle tool, remove piston, check no damage has occurred during pressing and piston moves freely on gudgeon pin.
16. Repeat above operation for remaining pistons.
Piston to cylinder bore clearance - checking
1. Starting with number 1 piston, invert piston and with arrow on piston crown pointing towards REAR of cylinder block, insert piston in cylinder liner.
2. Position piston with bottom of skirt 30 mm (1.2 in) from top of cylinder block.
3. Using feeler gauges, measure and record clearance between piston and left hand side of cylinder block:
Piston to bore clearance = 0.02 to 0.045 mm (0.001 to 0.002 in)
4. Repeat above procedures for remaining pistons.
Pistons and connecting rods - refit
1. Fit oil control ring rails and expander, ensuring ends butt and not overlap.
2. Fit ring marked 'TOP' with marking uppermost into second groove.
3. Fit top compression ring into groove either way round.
4. Position oil control expander ring joint and ring rail gaps all at one side, between gudgeon pin and away from left hand side of piston - viewed from front of piston. Space gaps in ring rails approximately 25 mm (1.0 in) each side of expander ring joint.
5. Position compression rings with ring gaps on opposite sides of piston between gudgeon pin and right hand side of piston - viewed from front of piston.
6. Thoroughly clean cylinder bores.
7. Lubricate piston rings and gudgeon pin with engine oil.
8. Lubricate cylinder bores with engine oil.
9. Fit ring clamp to piston and compress piston rings.
10. Insert connecting rod and piston assembly into respective cylinder bore ensuring domed shaped boss on connecting rod faces towards front of engine on RH bank of cylinders, and towards rear on LH bank of cylinders.
NOTE: When both connecting rods are fitted to each journal, bosses will face towards each other.
11. Fit big-end bearing caps and bearing shells.
12. Fit cylinder head(s).