Cylinder/Piston; Service Information; Troubleshooting - KYMCO YUP 250 Manual

7

. CYLINDER/PISTON

SERVICE INFORMATION

GENERAL INSTRUCTIONS
• The cylinder and piston can be serviced with the engine installed in the frame.
• When installing the cylinder, use a new cylinder gasket and make sure that the dowel pins are
correctly installed.
• After disassembly, clean the removed parts and dry them with compressed air before inspection.
SPECIFICATIONS
I.D.
Warpage
Cylinder
Cylindricity
True roundness
Ring-to-groove
clearance
Piston, Ring end gap
piston ring
Piston O.D.
Piston O.D. measuring position
. Piston-to-cylinder clearance
Piston pin hole I.D.
Piston pin O.D
Piston-to-piston pin clearance
Connecting rod small end I.D. bore

TROUBLESHOOTING

• When hard starting or poor performance at low speed occurs, check the crankcase breather for
white smoke. If white smoke is found, it means that the piston rings are worn, stuck or broken.
Compression too low or uneven
compression
• Worn or damaged cylinder and piston rings
• Worn, stuck or broken piston rings
Compression too high
• Excessive carbon build-up in combustion
chamber or on piston head
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Item
top
Second
top
Second
Oil side rail
Standard (mm)
SH50AA
SH25CA
72.7500_ 72.7015
0.01
0.01
0.01
0.01
0.01
0.01
0.2
0.015_ 0.050
0.015_ 0.050
0.1_ 0.25
0.15_ 0.30
0.15_ 0.30
0.15_ 0.30
0.25_ 0.7
0.2_ 0.9
72.67_ 72.69
9mm from bottom of skirt 52.370_ 52.390
0.010_ 0.040
0.010_ 0.040
17.002_ 17.008
15.002_ 15.008
16.994_ 17.000
14.994_ 15.000
0.002_ 0.014
0.002_ 0.014
17.016_ 17.034
15.016_ 15.034
Excessive smoke from exhaust muffler
• Worn or damaged piston rings
• Worn or damaged cylinder and piston
Abnormal noisy piston
• Worn cylinder, piston and piston rings
• Worn piston pin hole and piston pin
• Incorrectly installed piston
YUP 250
Service Limit (mm)
SH50AA
SH25CA
72.80
52.50
0.05
0.05
0.05
0.05
0.05
0.05
0.09
0.09
0.09
0.09
0.50
0.50
0.50
0.50 1.0
æ
72.6
9mm from bottom of skirt 52.30
0.1
0.01
17.04
15.04
16.96
14.96
0.02
0.02
17.06
15.06
7-2