(2) Use a spark-plug wrench to turn the spark plug (2) counterclockwise.
(3) Remove the spark plug (2) and spark-plug washer (1).
c. Cleaning. Clean the spark-plug body and poles with a stiff wire brush. Remove all carbon deposits from the spark-
plug gap and threads. Clean the threads and washer seat with a wire brush. Cover the spark-plug hole in the cylinder
head. Blow off dust and dirt from the spark-plug seat in the cylinder head with compressed air.
d. Adjusting.
(1) Always adjust the spark plug by bending the outer electrode mounted in the plug shell.
(2) The proper spark-plug gap is 0.025 inch. Use a wire gage to measure the gap and bend the outer electrode
until the gage just clears the electrode gap. Do not twist the electrode while bending it.
(3) If the spark-plug gap is too small, use a small screwdriver to enlarge the spark-plug gap by pushing the
outer electrode upward until the correct gap is obtained.
e. Testing. Test the spark plug on a spark-plug-testing machine. If the plug produces no spark, weak spark, or a
spark which jumps over the housing body, the spark plug must be replaced. If a spark-plug-testing machine is not
available, test the spark plugs as described below:
(1) Start the engine and place a screwdriver so that the bare shaft of the screwdriver is touching the terminal
head of the spark plug and the tip of the screwdriver is approximately one fourth of an inch from the cylinder
head. Be sure to hold the screwdriver on insulated handle.
(2) If the engine misses every time when the spark jumps from the tip of the screwdriver to the cylinder head,
the spark plug is operating.
(3) If there is no spark between the screwdriver tip and the cylinder head, the spark-plug cable is defective and
must be replaced.
(4) If the spark jumps between the screwdriver tip and the cylinder head, but there is no noticeable change in
the operating rhythm of the engine, the spark plug is defective and must be replaced.
f. Installation (fig. 36).
(1) See that the spark-plug seat in the cylinder head is free from dirt and corrosion.
(2) Install a new washer (1) on the spark-plug body (2) and screw the spark plug into the seat until it is
fingertight.
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