Shibaura ST318, Workshop Manual

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35
2) Cylinder head ass’y
Disassembly
(1) Using a valve spring replacer, compress the valve
spring to remove the valve cotter, retainer, spring and
valve.
(2) Remove the valve guide seal.
1. Valve guide seal 4. Valve
2. Spring 5. Valve cotter
3. Retainer
T109
Inspection and service
(1) Distortion of cylinder head bottom surface Apply a
straight edge to the bottom surface of the cylinder head,
and insert a thickness gauge at 6 points from A to F in
the right figure and measure distortion. If the distortion
exceeds the repair value, correct with surface grinder or
the like.
Distortion at cylinder head bottom surface (mm)
Standard assembling value Repair value
Less than 0.05 More than 0.12
(2) Valve guide and valve stem
➀
Check the head and stem of each valve and replace
if burnout, wear or deformation is remarkable.
➁ Measure the outside diameter at the position I, II,
and III on the valve stem with a micrometer and
replace if the result is less than the service limit.
➂ Replace a valve if its head thickness is less than
service limit.
T110
Wear of valve stem (mm)
Intake valve Exhaust valve
Standard
assembling
value
Service
limit
Standard
assembling
value
Service
limit
6.955 – 6.97 6.89 6.94 – 6.955 6.84
T111
Valve head thickness (mm)
Standard assembling value Service limit
0.775 – 1.075 Less than 0.5
T112