7. CYLINDER/PISTON
7-2
Precautions in Operation
General Information
y Both cylinder and piston service cannot be carried out when engine mounted on frame.
UA25A
Specification Unit：mm
Item Standard Limit
ID 74.995~75.015 75.100
Cylinder
Bend - 0.050
Top ring 0.015~0.050 0.090
Clearance between piston
rings
2
nd
ring 0.015~0.050 0.090
Top ring 0.150~0.300 0.500
2
nd
ring 0.300~0.450 0.650
Ring-end gap
Oil ring side rail 0.200~0.700 -
OD of piston (2
nd
) 74.430~75.480 75.380
Clearance between piston and cylinder 0.010~0.040 0.100
Piston/
Piston ring
ID of piston pin boss 17.002~17.008 17.020
OD of piston pin 16.994~17.000 16.960
Clearance between piston and piston pin 0.002~0.014 0.020
ID of connecting rod small-end 17.016~17.034 17.064
Trouble Diagnosis
Low or Unstable Compression Pressure
y Cylinder or piston ring worn out
Knock or Noise
y Cylinder or piston ring worn out
y Carbon deposits on cylinder head top-side
y Piston pin hole and piston pin wear out
Smoking in Exhaust Pipe
y Piston or piston ring worn out
y Piston ring installation improperly
y Cylinder or piston damage
Engine Overheat
y Carbon deposits on cylinder head top side
y Cooling pipe clogged or not enough in coolant
flow
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