Parts; 5.1.1 Spark Plug - Stihl 029, 039 Service Manual

STIHL 029, 039
5. IGNITION SYSTEM
Warning: Exercise extreme
caution when carrying out
maintenance and repair work on
the ignition system. The high
voltages which occur can cause
serious or even fatal accidents!
1 = Ignition module
2 = Flywheel
STIHL 029 and 039 chain saws are
equipped with an electronic
(breakerless) magneto ignition
system which requires no outside
power source (battery or dynamo).
The system basically consists of an
ignition module and flywheel and is
easily accessible.
5.1 Repairing Component

Parts

5.1.1 Spark Plug
Troubleshooting on the ignition
system should always begin at the
spark plug.
In the event of starting difficulties, low
engine power, misfiring, etc., unscrew
the spark plug and check that it is the
approved type. Only the spark plugs
listed in the specifications may be
used. Other makes of spark plug are
unsuitable because they have long-
reach electrodes.
Sooted or carbonized spark plug:
- Use brass wire brush to clean the
spark plug and then blow it clear
with compressed air.
Note: Never use a steel wire
brush for this job.
Spark plug smeared with oil:
- Wash the insulator nose with a
grease solvent and blow it clear
with compressed air.
Electrode gap:
Electrode gap becomes wider as a
result of normal erosion.
Top:
Checking electrode gap with
feeler gauge
Bottom:
Resetting electrode gap with
Bosch spark plug gauge
- Check the electrode gap at
regular intervals with a feeler
gauge. It should be 0.5 mm
(0.02").
- Bend the ground electrode as
necessary.
Important: Always fit a new spark
plug if the electrodes are badly
eroded.
37