Hercules JXD - Page 17

TM
9–1706
9
ORDNANCE MAINTENANCE
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( 5 ) Valve clearance .- ( a ) Remove the valve covers and adjust the
push rod screw to valve stem clearance to 0.006 inch on both intake
and exhaust valves . Be sure engine is thoroughly warmed before
adjustment
.
( 6 ) Make a visual inspection for evidence of cracked valve spring
coils or scored valve stems .
( 6 ) Carburetor .- ( a ) Remove bottom bowl of air cleaner by loos
ening winged nut on each side . Clean out all old oil and dirt . Refill
to oil level groove with new engine oil and install . Filtering element
should never be removed from cleaner .
( 6 ) Inspect carburetor flange and intake manifold gasket for leaks .
( c ) Check carburetor float level as described in section XI .
( d ) If necessary , adjust idling screw until engine runs evenly and
steadily with leanest possible mixture . Engine should be thoroughly
warmed before adjusting carburetor .
( e ) Clean carburetor fuel filter .
( 7 ) Fuel pump .- ( a ) The pressure from the fuel pump is measured
with a fuel pump pressure and vacuum gage . Connect adapter tee
into fuel pump outlet line and connect gage hose to adapter tee outlet
( fig. 193 ) . Normal pressure should be between 21/2 and 4 pounds .
This
gage
is also
used
to check
the
vacuum
condition
in
the
vacuum
pump
. Connect
hose
to
pump
inlet
. When
motor
is running
, this
vacuum
should
pull
from
8 to 10 inches
.
( 6 )
Remove
sediment
bowl
and
screen
for
cleaning
.
( c )
Inspect
for
worn
parts
and
replace
if
necessary
.
C. Vacuum tests . - A vacuum gage is a useful aid in an engine
tune - up . Before testing be sure that engine is thoroughly warmed .
The gage is attached at the rear of the intake manifold . Gage
readings indicate condition of vacuum existing in all the space of
the intake manifold between the throttle valve and the piston on the
suction stroke . Take
readings
with engine
running
at 500 rpm unless
otherwise specified
.
( 1 ) Normal engine . A normal engine pulls a vacuum of 18 to
21 inches . The vacuum reading will drop to about 2 inches when
the throttle is opened and will rebound to about 25 inches when throttle
is
closed
.
( 2 ) Steady needle , slightly low vacuum . - If the engine pulls a
vacuum of 13 to 16 inches with a steady needle , it would indicate the
possibility that the piston rings or oil is in poor condition . With
slight needle motion it would indicate late ignition timing .
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