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|  MIL-S-7886B
4.5.2 Sampling instructions.
minute (for group A inspection,
the gas leakage may be deter-
4.5.2.1 Group A inspection. Each spark
mined for a 15-second interval).
plug shall be subjected to the group A in-
(b) Post-test spark plugs (after en-
spection, Spark plugs which have been re-
gine operation) -- 4.0 CC p e r
jected may be reworked to correct the de-
minute.
fects and resubmitted for inspection or
replaced with new spark plugs.
4.7.3.1 For 5 of the 25 spark plugs to be
subjected to the heat rating tests during
4.5.2.2 Group B inspection A s a m p l i n g
qualification tests, the shell threads shall be
plan conforming to Standard M I L - S T D -
cleaned and then lubricated with grade 1010
414 shall be applied as specified in the procu-
oil conforming to Specification MIL-O-
rement document (see 6.2).
6081 The spark plug, with gasket conform-
ing to Standard AN4027, shall be installed
4.6 Test condition. Unless otherwise speci-
in a pressure bomb and torqued to 125 per-
fied. the installation torque for 14-mm spark
cent of maximum installation torque. The
plugs shall be 240
20 pound-inches, and
assembly shall then be immersed in water,
for 18-mm spark plugs shall be 330
30
and nitrogen gas at 800 psi applied to the
pound-inches.
firing end of the spark plug. The nitrogen
which leaks past component parts will dis-
place the winter, and the volume displaced
4.7 Test methods. At the conclusion of any
will be a measure of the gas leakage which
of the tests specified herein, spark plugs
shall not exceed 0.6 cc per minute. This
shall be inspected and shall show no evid-
method for measuring gas leakage shall be
ence of mechanical failure.
used as the referee test.
4.7.1 Examination. Spark plugs shall be
examined to determine conformance with
4.7.4 Dielectric strength, The gap shall be
pressurized or immersed in a suitable in-
the manufacturer's drawings aind all the
requirements of this specification for which
sulating liquid to prevent firing when a
potential of 9,000 volts rms minimum, 60
no test method is specified.
cycles, is applied between the center elec-
trode and shell for a period of 3 seconds for
4.7.2 Resistor. Each spark plug shall be
group A inspection and 1 minute for all
checked for stability of internal resistance
other tests. There shall be no breakdown
and contact by measurement of the center
of the spark plug insulation.
wire resistance by the use of a low voltage
ohmmeter (8 volts or less). Center wire
4.7.5 Heat rating. The spark plugs shall
resistance values of any resistor type spark
be installed in a 17.6 test engine manufac-
plug shall be as specified in the manufactur-
tured by the Laboratory Equipment Cor-
er's draw, ings or specifications.
poration, Mooresville, Indiana. The follow-
ing standard conditions shall apply during
4.7.3 Gas leakage. The gas leakage of each
the test:
spark plug shall be measured by any method
which has been approved by the procuring
Speed 2,700 rpm, nominal.
activity. The rate of gas leakage shall not
Compression ratio 5,6 to 1.
exceed the following values when the firing
Spark advance 40 degrees BTDC.
end of the spark plug is pressurized at 800
Fuel 98 percent 1 degree benzol, 2
psi.
percent Specification MIL-L-6082,
grade 1100 non-additive aviation oil,
(a) New spark plugs -- 0.6 cc per
6
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