Sym HD 125 - Precautions in Operation; Trouble Diagnosis

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.
Specification Unit：mm
LH12W & LH18W
Item Standard Limit
ID ( LA18W not included) 56.995~57.015 57.016
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 ( LA18W not included) 56.985~57.005 56.900
Clearance between piston and cylinder 0.010~0.040 0.100
Piston/
Piston ring
ID of piston pin boss 15.002~15.008 15.040
OD of piston pin 14.960~15.000 14.930
Clearance between piston and piston pin 0.002~0.014 0.020
ID of connecting rod small-end 15.016~15.034 15.060
LH18W
Item Standard Limit
Cylinder ID 60.995~61.015 61.016
Piston OD of piston 60.985~61.005 60.900
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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