KYMCO Mongoose 50-4T

8. CYLINDER/PISTON
8-3
SERVICE INFORMATION (90cc/70cc/50cc-4T)
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 mm (in)
Ite
m
Standar
d
Service Limit
90cc 47～47.01 (1.88～1.8804) 47.1 (1.884)
70cc 47～47.01 (1.88～1.8804) 47.1 (1.884)
I.D.
50cc-4T 39～39.01 (1.56～1.5604) 39.1 (1.564)
Warpage ⎯ 0.05 (0.002)
Cylindricity ⎯ 0.05 (0.002)
Cylinder
True roundness ⎯ 0.05 (0.002)
Rin
g
-to-
g
roove
Top 0.015～0.055 (0.0006～0.022) 0.09 (0.0036)
clearance
Second 0.015～0.055 (0.0006～0.022) 0.09 (0.0036)
Top 0.15～0.3 (0.006～0.012) 0.5 (0.02)
Ring end gap Second 0.3～0.45 (0.012～0.018) 0.65 (0.026)
Oil ring 0.2～0.7 (0.008～0.028) 0.9 (0.036)
90cc 46.97～46.99 (1.8788～1.8796) 46.9 (1.876)
70cc 46.985～46.995 (1.8794～1.8798) 46.9 (1.876)
Piston O.D.
50cc-4T 38.975～38.99 (1.559～1.5596) 38.9 (1.556)
Piston O.D. measuring
position
4 (0.16) from bottom of skirt ⎯
Piston-to-cylinder clearance 0.01～0.04 (0.004～0.0016) 0.1 (0.004)
Piston, piston ring
Piston pin hole I.D. 13.002～13.008 (0.5208～0.52032) 13.04 (0.5216)
Piston pin O.D 12.994～13 (0.51976～0.52) 12.96 (0.5184)
Piston-to-piston pin clearance 0.002～0.014 (0.00008～0.00056) 0.02 (0.0008)
Connecting rod small end I.D. bore 13.016～13.034 (0.52064～0.52136) 13.06 (0.5224)
Connecting rod-to-piston pin
clearance
0.016～0.04 (0.00064～0.0016) 0.06 (0.0024)