Sym MB10A7-A series Service Manual page 111

7. Cylinder Head / Valve
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Valve stem inspection
Check if valve stems are bent, cracked or
burnt.
Check the operation condition of valve stem in
valve guide, and measure the valve stem
outer diameter
Service limit：In. valve
Ex. valve 4.90mm
Valve guide inspection
Caution
Clean all the carbon deposit with reamer
before measuring the valve guides
Special tool: Valve guide reamer 5.0mm
Measure and record each valve guide inner
diameters.
Service Limit：5.10mm
The difference that the inner diameter of valve
guide deducts the outer diameter of valve
stem is the clearance value between the valve
stem and valve guide.
Service Limit：
Intake: 0.08mm
Exhaust: 0.10mm
Caution
If clearance is over service limit, check if
only replaces new valve guide will fix the
clearance into service limit or not. If yes,
replace valve guide only.
Fix the guides with reamer after replacement.
If clearance still exceeds service limit after
replacing valve guides, please also replace
valve stem too.
Caution
Fix the valve seat after replacing valve
guides.
7-10
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4.90mm
Valve guide reamer 5.0mm
Valve guide reamer 5.0mm