• If the seat shows
to
be
in
the middle
of
the valve face but
too
narrow,
use
the
45° cutter until the width equals 1.3 mm
(0.051
in).
• If the seat is
too
narrow and right up
near the
valve margin, then first
use
the
30° cutter and then the 45° cutter
to
get
the correct seat width.
• If the seat
is
too
narrow and down near
the bottom edge
of
the valve face, then
first
use
the 60° cutter and then the 45°
cutter.
Lapping
The
valve/valve seat assembly should
be
lap-
ped
if
neither the seat nor the valve face
are
severely worn.
1.
Apply a small amount
of
coarse lapping
compound
to
the valve face. Insert the
valve into the head. Rotate the valve un-
til the valve and valve seat are evenly
polished. Clean
off
the coarse com-
pound, then
follow the same procedure
with fine compound.
Continue
lapping until the valve face
shows a
complete and smooth surface
all
the way around.
Clean
off
the com-
pound
material. Applying bluing dye to
the
valve face and seat, and rotate the
valve. Check for full seat contact which
is
indicated by a grey surface all around
the
valve face where the bluing has been
rubbed away.
3-16
2.
After
all
work
has been performed on
the
valve and valve seat and
all
head
parts have been assembled, check for
proper
valve/valve seat sealing by pour-
ing
solvent into each
of
the intake ports,
then the exhaust ports. There
should
be
no leakage past the seat. If fluid leaks,
disassemble and continue to
lap
with
fine
lapping compound.
Clean
all
parts
thoroughly; reassemble and check again
with
solvent. Repeat this procedure
as
often
as
necessary
to
obtain a satisfac-
tory
seal.
Valve
springs
This engine
uses
two
springs
of
different
sizes
to
prevent valve float or surging. The
valve spring specifications show the basic
value characteristics.
1.
Even
though the spring is constructed
of
durable spring steel, it gradually loses
some
of
its tension. This
is
evidenced by
a
gradual shortening
of
free length.
Use
a vernier caliper
to
measure spring free
length. If the free length
of
any spring
has decreased more than 2 mm
(0.080
in) from its specification, replace it.
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