SANYANG INDUSTRY CO. SYM, Service Manual

Page: 70 / 176

SYM 6. CYLINDER HEAD/VALVE
6-9
Valve stem
Check if valve stems are bend, crack or burn.
Check the operation condition of valve stem
in valve guide, and measure & record the
valve stem outer diameter.
Service Limit: IN
→
4.900mm
EX
→
4.900mm
Valve guide
Caution
Special Service Tool: 5.0mm valve guide
reamer
Measure and record each valve guide inner
diameters.
Service limit: 5.300mm
The difference that the inner diameter of
valve guide deducts the outer diameter of
valve stem is the clearance between the
valve stem and valve guide.
Service Limit: IN
→
0.08mm
EX
→
0.10mm
Caution
Correct it with reamer after replacement.
If clearance still exceeds service limit after
replaced valve guide, replace valve stem too.
Caution
Valve guide replacement
Heat up cylinder head to 100~150
℃
with
heated plate or toaster.
Caution
Before measuring the valve guide, clean
carbon deposits with reamer.
If clearance between valve stem and valve
guide exceeded service limit, check whether
the new clearance that only replaces new
valve guide is within service limit or not. If
so, replace valve guide.
It must correct valve seat when replacing
valve guide.
y
Do not let torch heat cylinder head directly.
Otherwise, the cylinder head may be
deformed as heating it.
y
Wear on a pair of glove to protect your
hands when operating.
5.0mm valve guide reamer
Valve guide driver
5.0mm