Yanmar 4JH2E Service Manual page 41

Chapter 2 Basic Engine
3. Cylinder Head 4JH Series
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~4JH2
Series
3·2 Valve seat correction procedure
The most common method for correcting unevenness of
the seat surface with a seat grinder is as follows:
(1) Use a seat grinder to make the surface even.
As the valve seat width will be enlarged, first use a 70°
grinder, then grind the seat to the standard dimension
with a 15° grinder.
Seat grinder
Seat grinder
Intake valve
30°
Exhaust valve 45°
NOTE: When seat adjustment is necessary, be sure to
check the valve and valve guide.
If
the clearance
exceeds the tolerance, replace the valve or the
valve guide, and then grind the seat.
Seat width
(2) Knead valve compound with oil and finish the valve
seat with a lapping tool.
(3) Final finishing should
be done with oil only.
Lapping tool
Use a rubber cap type lapping
tool for cylinders without
a lapping tool groove slit.
2·8
NOTE: Clean the valve and cylinder head with light oil or
the equivalent after valve seat finishing is com-
pleted, and make sure that there are no grindings
remaining.
Lapping tool
NOTE: 1. Insert adjusting shims between the valve spring
and cylinder head when seats have been re-
finished with a seat grinder.
2. Measure vafve distortion after valve seat re-
finishing has been completed, and replace the
valve and valve seat if it exceeds the tolerance.
3·3 Intake/exhaust valves, valve guides
3·3.1 Wearing and corrosion of valve stem
Replace the valve· if the valve stem is excessively worn or
corroded.
l\.~,===j======='=l4j+-"
I 11111
v
30mm
(1.1811
in.)
Valve stem
outside dia.
Intake
Exhaust
60mm
(2.3622 in.)
Standard
07.960 ~ 7.975
(00.3134
~
0.3140)
07.955 ~ 7.970
(00.3132
~
0.3138)
mm(in.)
Wear limit
-0.13 (-0.0051)
-0.13 (-0.0051)
Printed in Japan
AOAI 029-9002