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water
jacket
and the
provision
of
numerous fins on
the
cylinders~
crankcase
and cylinder
heads. Therefore, some
recurrent knocks of
the
valves
a
nd
tappets, at
normal
clearances
between
the
valve·
stem (cap)
a
nd
the
rocker
en
d,
as well as an even
high-pitched
(not
s
hrill) noise
produ
ced
during operation of
th
e
valve
timing
gear
drive
should not be regarded
as an indication
of malfunction.
In the
case of
partial disassembly
involving the removal of
the
cylinder
heads, the thread of
the
n
ut
s
fasten'ing the
exhaust pipes,
a
nd
of
the cylinder head filters
should
be lubricated during assem-
bly
with
graphite
grease
type
BBH-1 GOST
5656-60.
Aft-
e r
10000
km run do not fail
to check the
condit
ion
of
valves.
a
nd
la
p
them
into
their seats, if
r equired.
Lapping the Valves
To lap the
valve into
the
seat
of
the
cylinder
head, slip a spring:
over
t
he
stem
of
the
valve
to be
lapped
,
apply a
thin layer
-
of
abra-
sive paste to
the chamfe
r
of valve
head
and,
a
fter inserting the
val-
ve with the pressing-out spring
into
the guide bush,
fit
an appliance
for .rotating the
valve
(a bit brace
or
a
drill) on
t
he end of
the
va lve
stem.
Use
may be also made of
a
piece of
a
petrol hose by turning it
between the
pa
lms
of
your
hands. Using
the
above
appliance,
rotate
t
he
valve in either
direction
in
such
a
manner that
the turn
in
one
direction is
about twice as
lon
g
as
the
turn
in
the opposite
direction,
i.
e.
ensure
that
the
va lve
is gradually turned
in one
direction.
When
changing
the
direction
of
turn"ing,
the valve must
be lifted
off its.
seat.
Lap
the valve
into
the
head
seat carefully .so as
n
ot to
remove
t oo mu ch
meta
l from
the working
chamfers
as this
will
reduce
the
nu
mber o.f permissible repa irs. Towards the
end of
lapping, reduce
the
amount of
paste
and,
a
t the last
stage, perform
lapping
with the
use of clean
oil.
A
lustreless
unifo
rm
colour
appearing
on
the wo
rking
surfaces.
of the
valve head
an
d
seat
is
an
indi cati on
of
a
satisfactory lap-
ping.
After
la
pp
ing,
thoroughly wash the valves,
the
valve seats,
guide bushes,
filler
and
compression
chamber
of the
cylinder head
until
the
abrasive paste is
comp·letely
removed.
Followi
ng
that,
check
whether the valves are
fitt ed
ti
ghtl
y, fo
r
which purpose
insta
ll
the
valves
in
place,
and pour kerosen
e fi
rst
into
the inl et, then
into
the exhau.st port
of
the
cylinder
head. The
ke rosene mus
t
not leak
out
within
30
s
after
filling. If
the
kerosene
starts
to
leak
before
the speci.fi ed period elapses
this
means that
an
ad
ditional la pping
is
required.
Spark Timing
To
faciilitate the
setting
of
the
igni
tio
n
advance
angl
e,
the
engi-
ne
f
lywheel
i<>
provided
on the
out
side
with marks
a
nd
letters " B"
28
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