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228
FIAT - 850 PASSENGER CARS
Fig. 356 • Slowing a spark plug after sanding and washing.
Fig. 355 • Testing a spark plug for gas tightness.
electrode
I
since this would break the porcelain
insulator.
If the porcelain appears black and coated with
carbon deposits, pour some alcohol or gasoline in
the capsized spark plug and after a while scrub
with
a wire brush.
Tightness Test.
The tightness test of the parts which compose
a spark plug
I
that is insulator body and center
electrode. is made on test bench as shown in
fig.
355.
Screw the spark plug on to the Service Center
seat, then operate the manual pump lever until a
284 to 358 p.sj. (20 to 25 kg/em') pressure is ob-
tained.
Using an oil can, pour some drops of oil or
kerosene on spark plug (fig. 3SS).
If
the plug is
leaky, oil or kerosene will bubble out, most likely
between the insulator and metal body.
NOTE· Spark plugs should be tightened with a
torque of t8.1 to 2t.7 It.lbs (2.5 to 3 kgm) using a
torque wrench.
Electric Test.
Screw the spark plug on to the Service Center
seat; tightness is assured by the connector seal
on seat.
Adjust the tester spark meter point gap at .315"
(8 nun), then operate the manual pump lever. Take
care to push the lever all the way down each
time, so that the pressure gauge reads as
tabu~
lated hereafter:
Tester spark
Tester cell pressure reading
meter point Spark plug
gap
gap
Vuy good
Good plug
Faulty plug
plug
in
mm
in
mm
p.s.i. kg/em
I
p.s.i.
kg/em"
p.s.i. kg/em
- -
~ -
-- --
.315
8
.024
0.6
85
6
71
s
57
4
.028
0.7
71
5
57
4
SO
3.5
NOTE - Some sparks at meter points can be tol-
erated.
Should no spark be seen either at the plug or
at the meter, this is an indication that the plug
insulator is cracked and the spark takes place
internally between ground and electrode.
As a
result, the spark plug is unserviceable.
Place the
high tension
cable socket on the spark
plug and depress the switch button.
The following conditions may be experienced:
1) Looking through the eye piece, a vivid
spark is seen to issue through the plug electrodes;
if so, the plug is serviceable.
2) Spark occurs at the meter points. Decrease
the tester pressure and see at what pressure spark
issues through plug electrodes.
To judge on the
efficiency of the spark plug under test, compare
data with those shown
in
the table.
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