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28
fig.
3.
42
©
Valve spring vibrati on
@
Valve lift
20
fig
.
3. 43
Preset
of
to
rsion
bar
fig.
3.
44
©
Torsion
bar holder
3.
ENG
INE
d
4
Twisting
ang
l
e(degree
:
(SURGING PHENOMENON)
Surging is
a condition which
occu rs w
hen
the
neutral frequency
of
the
spring co incides
with the
operating
frequency
of
the load
or it
multiples,
setting
up
a
resonance.
Under
such
a
condition,
the
spring is
subjected
to
an
unusal stress,
resuling in
breakage due
to fat
igue
of
the
metal spring.
(Fig.
42)
PRESET TREATMENT
The normal
stress
strained curve
of
torsion bar
spring
under tw isting load is
shown by
0-
a-b-c-
d-e
.
{Fig.
4.
43)
Point c
is
the
yield
po int,
beyo
nd
whi
ch the
material
does not return
to
the
ori
gina
l
.shape.
Usage
range
of the
torsion bar spring is
betwe
en
a-b
,
theref
ore
, the
spring
should alwa ys return to
its
or iginal
shape
point o, however,
since
the
upper
limit
point b is close to the
yeild
point
c, there
may be
a
possibility
of
the
yield point being
ex-
ceeded even once, to some
point
d
,
the torsion
bar
spring
will
beco me permanently distorted to
a
new
shape,
o' -a'
-b' -c'.
However, now the
yield
point c'
has
been raised to a more remote distance
from the
new
usage of a'
-b'
making it
more di-
fficult
to
exceed the yield po int.
Tors
ion bars are subjected to
a preset treatment
to produced
the
above condition.
The inlet
and
exhaust
torsion
bar
springs
are
twisted
in
the
opposite
direction,
therefore,
the
inlet and exhaust torsion bars
shoul
d
not be
inter-
changed.
Further, when the present treatment is
accomp
lished with
the yield point being
raised
to
point d,
any
cracks in
the
material can be
easily
detected
prior
to
installation.
K.
Valve and Torsion Bar Spring Disassembly
l
.
Disassemble
the com
follower
and camshaft
in
accordance
wi
th
Section 3.2 G.
2.
Unscrew
the
torsion
bar
,
hold the
torsion
bar
arm in
the
direction
of the
arrow marked on the
end
of
the valve
spring
so as
to relieve
the
load
from
the
holder bolt.
(Fig. 3. 44)
3.
Remove
the torsion bar assembly.
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