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28
3.
E N G I
N
E
----------------------------------
F.
Construction of Cam Shaft, Valve Lift ers and Valve
The
com shaft
is
mode of
malleable cost
iron and
the
com and
shaft
are heat treated
and
finished by grinding.
Both ends of
the
com
shaft
ore
supportej
by
bearings
in the
crankcase.
A
cam gear
is bolted to one end and
engages
the
timing
gear,
which is
shrink-
fitted to the crankshaft
and
driven at a
1
:
2 reduction
ratio.
A 2. 5
x 1
0 mm pin on
the
other end of the com
shaft
drives the oil
pump.
(Fig.
3-34)
The com is
on
important
port
which directly affects the
performance
of the
engine.
As
it is
likely
to
cause
noise,
core must
be token to adjust
the
tappet
clearance correctly to
obtain
maxi
mum
performance
from
the
engine
.
The com
has
on
anti-shock
lift
curve
structure of
considerable
range before the valve
is
lifted to prevent
shock
and
noise.
T
oppet
clearance
must
be
adjusted to the
correct clearance
when
the
dynamo rotor
"T"
mark matches
the
mark
on
the
dynamo
stator,
as in
this position the
valve
lifter rides
on
the
cam bose circle.
Do not try
to
adjust tappet
clearance
when
the
valve lifter
rests
on
the
anti-shock curve of
the
com,
since such an adjustment is for
from
correct.
The
valve lifters
ore mode
of high carbon chrome steel o!"ld the com
contacting
surfaces
ore heat
treated
and
finished
by
grinding.
The
lifters
ore supported by the crankcase and
work to
convert
the rotary motion of
the com
shaft into reciprocal linear
motion.
The
lifters
ore
mounted
excentricolly with
the
center line of the
com
so that they rotate
around their
own
axis,
preventing
localized wear of the
cam
contacting
surfaces.
The
exhaust and
inlet valves ore mounted
in
a V
shape
against
the combustion chamber
and operated
by the
com
gear through the
com
shaft,
valve
lifters,
push rods and rocker
arms.
The
mechanism
is
basic
to
a
4-cycle overhead valve engine and
is
designed to
operate smoothly
at
high
speeds with sufficient
lubrication.
(Fig.
3-36)
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