Sym Orbit 125 Service Manual page 78

7. CYLINDER/PISTON
PRECAUTIONS IN OPERATION
General Information
Both cylinder and piston service cannot be carried out when engine mounted on frame.
Specification
ID
Bend/wrap age
Cylinder
Roundness
Cylindrical
Clearance between
piston rings
Ring-end gap
Piston/
Piston ring
OD of piston
Piston OD measurement position
Clearance between piston and
cylinder
ID of piston pin hole
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 Standard
39.00
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
38.970~38.990
Lower-end up 5mm
of piston skirt
0.025~0.040
13.002~13.008
13.000
0.002~0.014
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
0.050
－
0.050
0.030
0.090
0.090
0.500
0.650
0.100
13.040
12.994~13.000
0.020
13 13.005~13.020
SYM
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