Pistons and Connecting Rods
Pistons And Connecting Rods
Clean and inspect pistons
Use piston ring pliers 998 5424.
Remove piston rings.
Remove all carbon deposits. Clean piston ring grooves by scraping with a special scraping tool or part of an old ring ground to suit.
Inspect pistons for:
- damage
- wear
- cracking
Check piston ring side play
Use new rings.
Upper compression ring 0.060-0.092 mm (0.0024-0.0036 in)
Lower compression ring 0.040-0.072 mm (0.0016-0.0028 in)
Oil scraper ring 0.030-0.065 mm (0.0012-0.0026 in)
Replace piston if play is excessive.
Measure piston ring gap Use feeler gauges.
Place ring in cylinder bore and use inverted piston to locate it in correct position for measurement.
Piston ring gap is measured with crown of inverted piston 15 mm (0.6 in) from bottom of cylinder.
Compression rings 0.30-0.55 mm (0.012-0.022 in)
Oil scraper ring 0.30-0.60 mm (0.012-0.024 in)
Measure piston diameter
Use micrometer 9705 and feeler gauges.
A = 68.7 mm (2.64 in) Total height of piston
B = 39.9 mm (1.57 in)Height from gudgeon pin center to crown
C = 11.0 mm (0.43 in)Piston diameter to be measured at right-angles to gudgeon pin hole, at distance C from edge of skirt
D = Piston diameter
Standard
Pistons marked C* 95.98-95.99 mm (3.7787-3.7791 in)
Pistons marked D 95.99-96.00 mm (3.7791-3.7795 in)
Pistons marked E* 96.00-96.01 mm (3.7795-3.7799 in)
Pistons marked G* 96.02-96.03 mm (3.7803-3.7807 in)
* Production only (non-stocked)
Oversize
Oversize 1 96.28-96.29 mm (3.7906-3.7910 in)
Oversize 2 96.58-96.59 mm (3.8024-3.8028 in)
Max. difference in weight between pistons in same engine 14 g (0.5 oz)
Piston Clearance Measurement:
Calculate piston clearance
Example:
Cylinder bore diameter less piston diameter = Piston clearance
96.02 mm (3.7803 in) - 96.01 mm (3.7799 in) = 0.010 mm (0.0004 in)
Specified piston clearance
Minimum 0.010 mm (0.0004 in)
Maximum 0.030 mm (0.0012 in)
Check con rod/piston side clearance
Use feeler gauges.
Specified con rod/piston axial clearance 0.15-0.45 mm (0.0059-0.0177 in)
Separate con rods and pistons
Before separating, check that each piston and con rod is marked. Mark as required.
Carefully prise out locking circlip with a screwdriver.
Press out gudgeon pin by hand.
Clean and inspect con rods, bearing caps and bolts
Check for:
- damage
- wear
- cracks
Check fit of gudgeon pins in pistons
No play is permissible. Gudgeon pin should slide through hole without play when pressed gently with thumb.
Replace piston if play is present.
Check fit of gudgeon pins in con rods
Gudgeon pin should slide through hole without noticeable play when pressed gently with thumb.
If play is excessive, measure gudgeon pin and fit new con rod bushing, if necessary. Use micrometer 9701.
Specified gudgeon pin diameter 23.994-23.000 mm (0.9053-0.9055 in)
Check big end bearing seats
Inspect bearing shells visually.
If in doubt, measure out-of-round.
Use inside micrometer 9639.
Tighten bearing cap on con rod as indicated by markings.
Bearing seat diameter 52.00-52.01 mm (2.9472-2.9476 in)
Max. permissible out-of-round: 0.03 mm (0.0012 in)
Check con rod in alignment gauge
Check for straightness and twisting.
Important! Ensure that clamping surface of fork is round and free of burrs. Release and tighten expander at big end between each alignment check.
Check length of con rod bearing bolts
Use sliding callipers.
Max. length 55 mm (2.1654 in)
Con rod bushing replacement
Replacing con rod bushing
Press out bushing
Use drift 5309.
Position drift correctly with short end downwards.
Use 2413 as counterhold.
Press in new bushing
Use drift 5309.
Position drift correctly with long end downwards.
Press drift down fully.
Check fit of gudgeon pin in new bushing
Gudgeon pin should slide through hole without noticeable play when pressed gently with thumb.
Adjust bushing as required.