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14
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3.
E
N G I
N E
D.
Construction of Rocker Arms
The
rocker
arm is
on
important
port
as it transmits
motion
from
the
push rod to the
valve
by pressing the adjusting
screw
downward.
It
is
made
of
chromemolybdenum
steel
and
the
port
that contacts the
push
rod is
cementation
treated
and
finished by grinding.
E.
Disassembling
1.
Remove
cylinder
head cover as described in
3-2 B
1.
2
.
Remove
rocker
arm
shaft bolt and pull
out shaft.
Rocker
arm
can
be
removed from
cylinder
head
cover.
f
.
Assembling
Place rocker
arm
in
position,
insert
shaft,
tighten bolt and flt cylinder
head
cover as
descr
ibed in 3-2
C 3
.
G.
Construction of Valves
Each valve is
made
of heat-treated
steel
with high
resistance to heat.
Special considera-
tion was
given to the valve strength
and ability to
withstand wear
at
high
temperatures.
The
tightness of the valve
has
a
direct bearing
on the output
and low
speed stability
of
the
engine.
An
exhaust
valve
is
subjected
to
high
temperatures
from exhaust gases and
tends to warp
and
fail to
contact
the
valve
seat
perfectly
.
The
guide is also
subjected
to
high
temperatures,
preventing
the formation
of
an oil
fllm,
resulting in wear of tr.e guide
and
valve
stem
.
The
inlet valve is
cooled by
the
gas/
air mixture entering
the
engine, but
it
is
subject
to
a partial
vacuum when
the mi xture
is sucked
into
the engine,
so
that lubrication
oil tends to
enter
the
combustion
chamber through
the
guide.
The
inlet
valve seats tightly
and
wear of the guide and valve stem is
slow.
To reduce these inherent troubles
in
valves to
a
minimum,
special core was taken in
design.
For
the exhaust valve, the
head
was mode small to give good
heat
radiation
and
the clearance between the
valve
stem
and guide is comparatively large
to prevent
wear.
For
the inlet valve, the head is
Iorge
for
higher
effeciency
and
the
clearance
between the
val
ve stem and guide
is
os small
as
possible
to
prevent oil from getting into the combustion
chamber.
H.
Disassembling
1.
Remove
cylinder head as
described
in
3-2
B
3.
2.
Remove valves
with valve lifter
as
shown in
Fig. 3-14
.
I.
Assembling
1.
Apply
oil
to
the
valve stems
before
inserting
valves
in
cylinder
head.
(Fig.
3-15)
As
there
ore
no valve s_uides.
take
core
not to scratch
the
wall
of
the guides in
the
cylin-
der
head.
2.
Mour,t cyli r.der
head cover
as
descril
'
ed
in
3
-2
C.
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