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|  MIL-S-7886B
with 3cc /gal. TEL (This may be ob-
With the engine operating at normal
rated sea level power and speed and with
tained from the Standard Oil Co. (In-
diana) as Formula No. L-7646.).
the mixture control in the full rich position,
readings shall be taken of engine rpm, mani-
Mixture strength -- that giving maxi-
fold pressure. carburetor air temperature,
mum thermal plug temperature.
etc. With no change in engine controls, a
Inlet air temperature
5` F.
water spray, using tap water at the rate of
Inlet air humidity 75
25 grains of
10 gallons per minute, shall be directed into
moisture per pound of dry air.
the cooling air stream ahead of the spark
Coolant flow 5
gallon per minute.
plugs for a period of 5 minutes. The spray
Jacket inlet temperature 265
5 F.
shall then be shut off and sufficient time al-
Oil temperature 190
10 F.
lowed for the engine to resume normal oper-
The power output for the final expected
ating temperature. This spraying cycle shall
10-inches Hg MAP shall be increased in in-
be repeated for a total of seven times. The
crements not to exceed 2 inches of mani-
engine shall not malfunction due to spark
fold pressure (at least 3 minutes shall be
plugs during this test. Upon completion of
allowed between each increase for condi-
the thermal shock test, the spark plugs shall
tions to stabilize) until continuous preigni-
be subjected to the following tests:
tion occurs as evidenced by an abrupt and
abnormal increase in the thermal plug tem-
Gas leakage (post-test spark
peratures. Manifold pressures shall be then
plug values applicable) . . . . . . . . . . (4.7.3)
decreased in 1-inch increments until t h e
Dielectric strength . . . . . . . . . . . . . . . . . . . . . . . (4.7,4)
spark plug operates continuously without
preignition for 3 minutes. The rating of the
4.7.7 Ground endurance test. A ground
spark plug shall be determined as the in-
endurance test of a least 1 50 hours shall be
dicated mean effective pressure, expressed
made with plugs installed in a minimum of
in pounds per square inch, corresponding
one-half the cylinders of a representative
to this manifold pressure and as corrected
service engine of the model for which the
for engine variability. The individual rat-
spark plugs is intended to be used. Spark
ings shall be within the limits of 90 percent
plugs of an approved type, where available,
and 110 percent of the average of all the
shall be installed in approximately one-half
ratings of the samples tested, For group B
the cylinders. The test shall be conducted in
tests, the ratings shall be within the limits
accordance with the 150-hour endurance run
established by the qualification tests. Upon
for the particular model of engine as speci-
completion of the heat rating test, the spark
fied in Specification MIL-E-25111 or as
plugs shall be subjected to the following
specified by the procuring activity, except
tests:
that the spark plugs shall not be removed
. . . . . . . . . . ..(4.7.2)
Resistor . . . . . . . . . . .
for servicing unless engine malfunctioning
Gas leakage (post-test spark
attributable to spark plugs is indicated. All
plug values applicable) . . . . . . . . . . (4.7.3)
spark plugs shall have the gaps set accurate-
Dielectric strength . . . . . . . . . . . . . . (4.7.4)
ly to 0 001 inch tolerance and a record shall
Spark plugs subjected to this testing shall
be made of all gaps at the time of initial
not be shipped as part of any contract or
installation, Spark plug gaps shall be check-
order,
ed to ascertain the rate of electrode erosion.
The fuel shall be that recommended for the
4.7.6 Thermal shock. A full set of spark
particular engine being used. The fuel shall
plugs shall be installed in a service engine
contain the maximum amount of tetraethyl
and subjected to a water spray under the
lead as permitted under Specification MIL-
following conditions:
G-5572. The specific fuel consumption shall
7
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