CHAPTER 3B ENGINE 50cc/80cc ATV SERVICE MANUAL09.0
CHAPTER 3B ENGINE PAGE 3B - 7 -
IN 4.975-4.990 4.9
Valve bar outer diameter
EX 4.955-4.970 4.9
IN 5.0-5.012 5.3 Valve guide pipe inner
diameter
EX 5.0-5.012 5.3
IN 0.010-0.037 0.08 Gap between valve bar and
guide pipe
EX 0.030-0.057 0.10
Inner spring
30.5 26.1
Valve spring
Outer spring
33.5 30.5
Torque Value
Camshaft bolt 20N.m 15 ft .lbs lubricate threads with oil
Valve gap adjusting screw cap 8N. m 6 ft .lbs
Tools:
General tools
Valve spring compressor 45°
IN/EX
Valve seat reamer 24.5mm Plane reamer 30° IN
Valve seat reamer 25mm Plane reamer 32° EX
Valve seat reamer 22mm Plane reamer 60° IN/ EX
Valve seat reamer 26mm
Reamer damping fixture 5mm
Special tools
Valve spring compressor accessories
Valve gap regulatory spanner
Valve guide screwdriver
Valve guide reamer
Trouble diagnosis
●Confirm poor operation of cylinder head by
measuring pressure or by noise produced by
engine upper end.
Slow speed hitch White smoke from exhaust pipe
●too low compression pressure ●wearing of valve guide
●bad valve gap ●broken oil seal
●burning or curving of valve
Abnormal noise
●bad valve timing ●bad valve gap
●broken valve spring ●broken or burning of valve or valve spring
●bad valve seat ●wearing and breaking of camshaft
●leakage of cylinder head gasket ●wearing of inner chain adjusting plate
●cylinder head surface warping or cracking ●wearing of camshaft and valve rocker arm
●bad spark plug
Too high compressed pressure
●too much carbon build-up in combustion
chamber
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