Gravely 424 - Page 26

b. Drain fuel
tank and
carburetor.
c.
Clean exterior of tractor.
d.
Spread a light
fflm of oil over
any exposed
surfaces subiect
to corrosion.
e. Pour
tablespoon of oil
into
spark
plug
hole, crank
engine slowly by hand
and replace spark
plug.
f,
Store in dry
place.
ENGINE
TESTS
Crankcase Vacuum
Test:
A
partial
vacuurn should
be
present
in the
crankcase
when
engine
is operatirg at nor-
mal temperatures. An
efigine in
good
condition
will
have crankcase vacuum
of 5 to 10"
water
column
as
read
on
"U"
tnbe water
manometer
or
*
to
l"
Hg. as calibrated
on mercury vacuum
gauge.
Crankcase vacuum
eheck
is
best
accomplished with
the
"U"
tube
manometer.
If
vacuum is
not in the
speeiffed
range, this could
be attributed
to one or
more of the following
factors
-
the condition easiest
to remedy should be
checked ff:st:
A. Clogged
Crankcase Breather
can
cause
positive pressures
to
build up
in the crankcase. Disassemble
breather
assembly,
thoroughly clean,
then recheck
pressure
after
re-installing.
B.
Worn
oil seals
can
cause lack
of vacuum.
Oil
Ieakage is usually
evident around
worn
oil seals,
(See
Oil Seal
Replacement
Instructions).
C. Blowby, Ieaky
valves
can also
cause
positive
pressures.
These conditions
can
be conffrmed by making
com-
pression
test
on engine.
Construction
-
"fI'Tube Manometer
Vacuum
gauges,
mercury and water manometers
are available
commercially.
A water
"U"
tube
mano-
meter is simple
to construct
if limited usage does
not
warrant purchase
of commercial
produet.
To construct
water
manometer, proceed
as follows:
(a)
Procure length
of clear
plastic
tubing.
Bend
tube
to form
"U"
and mount
on board
as
shown
in aceom-
panying
illustration.
Make gradual,
rather than sharp
bend in tube.
(b)
Measure
inside, straight section
of tube and
mark
inch increment
from 0 ta 12".
tc)
Procure
cork
having
outside diameter
which will
be a
snug fft in
the oil ffll hole.
Drill hole in
center
of
cork to receive
one
end of tube.
(d)
Pour
water
{colored
for easier reading) into tube
until
level
reaehes
the approximate
halfway
mark
on
scele.
When using
manometer,
place
cork end into oil
ffll hole
(other
erd open
to atmosphere) and measure
difference
between
eolumns. If water
column
is higher
Figure 19
-"U"
Tube Monometer
in tube
connected to
engine,
vaeuum
or negative
pressure
in indicated. If the
higher
column
is on the atmos-
pheric
side of
manometer,
positive pressure
is
present,
Compression Test:
the results
of
a compression check
can
be used to
determine
if
an
en$ne
is in
good
operating
condition or if reconditioning
is needed.
Low
readings
can
indicate
several
conditions
or a combination
of the
following
con&tions:
t
P
R
t
s
s
u
R
t
9,5
}.IEASURS
OITTERENCE
BElilttN CoLUl.f{S