KYMCO Vitality 50, Manual, Page: 110 / 275

7. CYLINDER HEAD (2-STROKE)/
CYLINDER/PISTON
7-4
VITALITY 50
SERVICE INFORMATION (4-STROKE)
GENERAL INSTRUCTIONS
•
The cylinder and piston can be serviced with the engine installed in the frame.
• Before disassembly, clean the engine to prevent dust from entering the engine.
• Remove all gasket material from the mating surfaces.
• Do not use a driver to pry between the cylinder and cylinder head, cylinder and crankcase.
• Do not damage the cylinder inside and the piston surface.
•
After disassembly, clean the removed parts before inspection. When assembling, apply the
specified engine oil to movable parts.
SPECIFICATIONS
Standard (mm) Service Limit (mm)
I.D. 39.00 39.01 39.1
Warpage

0.05
Cylindricity  0.05
True roundness

0.05
Ring-to-groove Top 0.015 0.055 0.09
clearance Second 0.015 0.055 0.09
Top 0.15 0.3 0.5
Piston, Ring end gap Second 0.3 0.45 0.65
piston ring Oil ring 0.2 0.7 0.9
Piston O.D. 38.975 38.99 38.9
Piston O.D. measuring position
4.5mm from bottom of skirt

. Piston-to-cylinder clearance 0.010 0.040 0.1
Piston pin hole I.D. 13.002 13.008 13.04
Piston pin O.D 12.994 13.000 12.96
Piston-to-piston pin clearance 0.002 0.014 0.02
Connecting rod small end I.D. bore 13.016 13.034 13.06
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
Excessive smoke from exhaust muffler
• Worn, stuck or broken piston rings • Worn or damaged piston rings
• Worn or damaged cylinder and piston • Worn or damaged cylinder and piston
Compression too high Abnormal noisy piston
•
Excessive carbon build-up in combustion
•
Worn cylinder, piston and piston rings
chamber or on piston head
•
Worn piston pin hole and piston pin
Cylinder