6. ELECTRODE WEAR:
Electrodes wear out during operation, which cannot be prevented. The causes
of electrode wear are sparking erosion and chemical effects.
Due to electrode wear, the gap viii enlarge. This leads in time to poor
starting of the engine when cold, misfiring and spark plug fouling.
7. SERVICING:
The spark plug must be checked for possible fouling at regular intervals,
particularly before the main operating periods of the engine. The insulator must
externally clean; the insulator tip exposed in the combustion chamber must not
have any heavy oil or lead deposits. Externally dirty spark plug can be washed
out in gasoline not containing oil; likewise, spark plugs with oiled tip. The
spark plug must then be dried with compressed air. Soot oil, carbon, lead and
sulfur coatings on the tip can be removed with the sand blaster of a spark plug
testing and cleaning limit.
Never clean the insulator with steel or brass brushes or anything made of
soft metal. They leave behind metal particles on the insulator surface which can
cause it to become con -ducting.
The electrode gap must be reset to .018 - .020" from time be bent within
certain limits for this purpose. For 2-stroke engines, this should generally be
done every purpose a spark plug feeler gauge is best used. With this also be
measured in a simple manner.
to time. The ground electrode can
8. MAKESHIFT TEST OF THE SPARK PLUG:
Lay the spark plug with the ignition cable connected on the engine casing and
crank the engine.
Causes of trouble: If sparks jump the electrodes, the spark plug is good;
nevertheless, oil, carbon or lead deposits that may be on the tip may cause
misfiring during operation.
Too large an electrode gap can likewise cause misfiring during operation.
30 to 50 operating hours, for which feeler gauge, the electrode gap can
Correction: Clean the spark plug with the sand blaster of the cleaning unit.
Measure the electrode gap with feeler gauge and reset if necessary. Nominal
value: 0.02 in.
I~ the spark plug does not spark, wither the plug is defective or there is no
ignition voltage at the spark plug. To establish~ the actual cause, proceed as
follows:
PULL off the ignition cable from the plug and hold at a distance of
approximately 1/8 in. from the engine (ground). With the spark plug removed,
turn the engine at starting speed.
SINCE it is difficult to keep the distance of 1/8" due to heavy engine
vibration, a test plug can also be used. Take any new or old (but good) spark
plug and bend out the ground electrode.
LAY the test plug with the ignition cable connected on the engine casing and
crank the engine.
IF sparks now jump from the ignition cable to the engine (ground) or at the
test plug electrode, the trouble is in the spark plug.
IF no sparks jump from the ignition cable to the engine or at the test plug
electrode, then the trouble is in the ignition cable or the magneto.
