FAA Advisory Circular 43.13-1B
Acceptable Methods, Techniques, and Practices
Aircraft Inspection and Repair
AC 43.13-1B | 8. Engines, Fuel, Exhaust, and Propellers | 1. Engines | 8-16. Operational Problems
9/8/98
AC 43.13-1B
plug. If desired, the use of anti-seize com-
pound may be eliminated on engines equipped
with stainless steel spark plug bushings or
inserts.
(5) Screw the plug into the cylinder
head as far as possible by hand. If the plug
will not turn easily to within two or three
threads of the gasket, it may be necessary to
clean the threads.
NOTE: Cleaning inserts with a tap is
not recommended as permanent dam-
age to the insert may result.
(6) Seat the proper socket securely on
the spark plug and tighten to the torque limit
specified by the engine manufacturer before
proceeding to the next plug.
CAUTION: A loose spark plug will
not transfer heat properly, and during
engine operation, may overheat to the
point the nose ceramic will become a
“hot spot” and cause pre-ignition.
However, avoid over-tightening as
damage to the plug and bushing may
result.
(7) Connect the ignition lead after wip-
ing clean with a dry, lint-free cloth. Insert the
terminal assembly into the spark plug in a
straight line. (Care should be taken as im-
proper techniques can damage the terminal
sleeves.) Screw the connector nut into place
until finger tight, then tighten an additional
one quarter turn while holding the elbow in the
proper position.
(8) Perform an engine run-up after in-
stalling a new set of spark plugs. When the
engine has reached normal operating tempera-
tures, check the magnetos and spark plugs in
accordance with the manufacturer’s instruc-
tions.
8-16. OPERATIONAL PROBLEMS.
Whenever problems develop during engine
operation, which appear to be caused by the
ignition system, it is recommended that the
spark plugs and ignition harnesses be checked
first before working on the magnetos. The
following are the more common spark plug
malfunctions and are relatively easy to iden-
tify.
a. Fouling.
(1) Carbon fouling (see figure 8-6) is
identified by the dull black, sooty deposits on
the electrode end of the plug. Although the
primary causes are excessive ground idling and
rich idle mixtures, a cold heat range may also
be a contributing factor.
(2) Lead fouling is characterized by
hard, dark, cinder-like globules which gradu-
ally fill up the electrode cavity and short out
the plug. (See figure 8-6a.) The primary cause
for this condition is poor fuel vaporization
combined with a high tetraethyl-lead content
fuel. A cold heat range may also contribute to
this condition.
(3) Oil fouling is identified by a wet,
black carbon deposit over the entire firing end
of the plug as shown in figure 8-6b. This con-
dition is fairly common on the lower plugs in
horizontally-opposed engines, and both plugs
in the lower cylinders of radial engines. Oil
fouling is normally caused by oil drainage past
the piston rings after shutdown. However,
when both spark plugs removed from the same
cylinder are badly fouled with oil and carbon,
some form of engine damage should be sus-
pected, and the cylinder more closely in-
spected. Mild forms of oil fouling can usually
be cleared up by slowly increasing power,
while running the engine until the deposits are
burned off and the misfiring stops.
Par 8-15
Page 8-11