5. Inspection and Servicing of Basic Engine Parts
99
5.2.3 Intake/exhaust valves, valve guides
(1) Wearing and corrosion of valve stem
Replace the valve stem is excessively worn or
corroded.
(2) Inspection of valve seat wear and contact surface
Inspect for valve seat scratches and excessive wear. Check to make sure the contact surface is normal.
The seat angle must be checked and adjusted if the valve seat contact surface is much smaller than the
width of the valve seat.
NOTE:
Keep in mind the fact that the intake and discharge valve have different diameters.
(3) Valve sink
Over long periods of use and repeated lapping,
combustion efficiency may drop. Measure the sinking
distance and replace the valve and valve seat if the
valve sink exceeds the tolerance.
mm
Valve stem
outside dia.
Standard Limit
Intake Ø7.955-Ø7.975 Ø7.90
Exhaust Ø7.955-Ø7.970 Ø7.90
mm
Standard Limit
Valve sink 0.30-0.50 0.8
30 mm 60 mm
(Valve sink depth)
Valve sinking depth
(Valve sink)
Depth micrometer
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