Sym RV 250i - Precautions in Operation; Troubleshooting

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
LM25W5 LM30W
Item Standard Limit Standard Limit
I.D. 70.995~71.015 71.100 72.995~73.015 73.100
Out of round - 0.050 - 0.050
Taper - 0.050 - 0.050
Cylinder
Warpage - 0.050 - 0.050
Top 0.015~0.050 0.090 0.015~0.050 0.090 Clearance
between
piston ring and
ring groove
2
nd
0.015~0.050 0.090 0.015~0.050 0.090
Too 0.150~0.300 0.500 0.150~0.300 0.500
2
nd
0.300~0.450 0.650 0.300~0.450 0.650
Piston ring end
gap
Oil
(side rail)
0.200~0.700 - 0.200~0.700 -
Piston O.D. (2
nd
) 70.430~70.480 70.380 72.430~72.480 72.380
Clearance between piston
and cylinder
0.010~0.040 0.100 0.010~0.040 0.100
Piston/
Piston
ring
ID of piston pin boss 17.002~17.008 17.020 17.002~17.008 17.020
Piston pin O.D. 16.994~17.000 16.960 16.994~17.000 16.960
Clearance between piston and piston pin 0.002~0.014 0.020 0.002~0.014 0.020
Connecting rod small end I.D. 17.016~17.034 17.064 17.016~17.034 17.064
Troubleshooting
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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