Sym FIDDLE 125 Service Manual page 80

7. CYLINDER/PISTON
PRECAUTIONS IN OPERATION
General Information
Both cylinder and piston service cannot be carried out when engine mounted on frame.
Specification
Cylinder
Piston/
Piston ring
OD of piston pin
Clearance between piston and piston pin
ID of connecting rod small-end
TROUBLE DIAGNOSIS
Low Or Unstable Compression Pressure
Cylinder or piston ring worn out.
Compress pressure to high.
Too much carbon deposited in combustion
chamber and piston.
Knock or Noise
Cylinder or piston ring worn out.
Carbon deposits on cylinder head top-side.
Piston pin hole and piston pin wear out.
7-2
Item
ID
Bend/wrap age
Roundness
Cylindrical
Clearance between
piston rings
Ring-end gap
OD of piston
Piston OD measurement position
Clearance between piston and
cylinder
ID of piston pin hole
Standard
58.50
0.005
0.005
Top ring 0.025~0.060
nd
2 ring 0.015~0.050
Top ring 0.200~0.400
nd
2 ring 0.250~0.400
Oil ring
0.200~0.700
52.370~52.390
Lower-end up 7mm
of piston skirt
0.010~0.040
15.002~15.008
14.994~15.000
0.002~0.014
15.005~15.020
Smoking in Exhaust Pipe
Piston or piston ring worn out.
Piston ring installation improperly.
Cylinder or piston damage.
Engine Overheat
Carbon deposits on cylinder head top side.
unit: mm
Limit
58.2~58.5
－
0.050
0.050
0.050
0.090
0.090
0.500
0.650
52.300
0.100
15.040
14.980
0.060
15.060
SYM
－
－