Sym JOYMAX 250 User Manual

7. Cylinder / Piston
7-2
Precautions in Operation
General Information
 Both cylinder and piston service cannot be carried out when engine mounted on frame.
Specification Unit：mm
Item
Standard
Limit
Cylinder
ID
70.995~71.015
71.100
Bend
-
0.050
Piston/
Piston ring
Clearance between piston
rings
Top ring
0.015~0.050
0.090
2
nd
ring
0.015~0.050
0.090
Ring-end gap
Top ring
0.150~0.300
0.500
2
nd
ring
0.300~0.450
0.650
Oil ring side rail
0.200~0.700
-
OD of piston (2
nd
)
70.430~70.480
70.380
Clearance between piston and cylinder
0.010~0.040
0.100
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
 Cylinder or piston ring worn out
Knock or Noise
 Cylinder or piston ring worn out
 Carbon deposits on cylinder head top-side
 Piston pin hole and piston pin wear out
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
 Cooling pipe clogged or not enough in coolant
flow
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Sym JOYMAX 250 Specifications

General

Brand	Sym
Model	JOYMAX 250
Category	Scooter
Language	English