It is normally more economical to replace the
spark plugs than to clean and regap them. It
also provides greater assurance that there are
no hidden cracks in the ceramic insulators which
could cause engine misfiring at high engine
speeds. Cleaning and inspection instructions
are given here in case it is necessary to reuse
the removed plugs.
b. Cleaning and Inspection.
Clean all parts in a well-ventilated area.
Avoid inhalation of solvent fumes and
prolonged exposure of skin to cleaning
solvent. Wash exposed skin thoroughly. Dry
cleaning solvent (fed. spec. P-D-680) used
to clean parts is potentially dangerous to
personnel and property. Do not use near
open flame or excessive heat. Flash point of
solvent is 100 ° to 138 ° F (38 ° to 59 ° C).
(1) Wipe the exterior of the spark plugs with a
cloth dampened with dry cleaning solvent (fed. spec. P-
D-680); dry thoroughly.
(2) Check the ceramic insulator for cracks,
porosity, and other damage.
(3) If the electrodes of the spark plugs are not
too badly burned, remove the scale and other deposits
from them. This can be done by a sand- blast-type
cleaner or with a contact file.
(4) Inspect the electrodes for severe burning,
cracks, and other damage. If it is necessary to reuse
the plugs, correct the contact gap to 0.025 inch.
(5) Replace any spark plugs whose condition is
Figure 4-20. Magneto-to-spark plug connections.
(1) Make sure all spark plugs are gapped to
4-35. Magneto and Spark Plug Cables
0.025 inch before installation.
(2) Install the spark plugs, using a socket and
(1) Refer to paragraph 4-24 for removal of
torque wrench. Tighten the spark plugs to 35 foot-
carburetor. Refer to paragraph 4-19 for removal of the
(3) Install the shielded spark plug cables on the
(2) Remove the four screws (1, fig. 4-19) and
spark plugs. Make sure the leads are not interchanged.
lock washers (2) that secure the cover (3) on the
Refer to figure 4-20 to ensure proper magneto-to-spark
magneto; remove the cover and gasket (4).
plug wiring if spark plug connection is doubtful.
(3) Disconnect the shielded spark plug cables
from the magneto end cap by unscrewing