Cylinder/Piston (4-Stroke) - KYMCO VITALITY 50 Manual

7. CYLINDER HEAD (2-STROKE)/
CYLINDER/PISTON
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
I.D.
Warpage
Cylinder
Cylindricity
True roundness
Ring-to-groove Top
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.
Compression too low or uneven
compression
• Worn, stuck or broken piston rings
• Worn or damaged cylinder and piston
Compression too high
• Excessive carbon build-up in combustion
chamber or on piston head
Second
Top
Second
Oil ring
If white smoke is found, it means that the piston rings are worn, stuck or broken.
Standard (mm)
39.00 39.01



0.015 0.055
0.015 0.055
0.15 0.3
0.3 0.45
0.2 0.7
38.975 38.99
4.5mm from bottom of skirt
0.010 0.040
13.002 13.008
12.994 13.000
0.002 0.014
13.016 13.034
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
VITALITY 50
Service Limit (mm)
39.1
0.05
0.05
0.05
0.09
0.09
0.5
0.65
0.9
38.9

0.1
13.04
12.96
0.02
13.06
7-4