MTD AC3 Automobile Parts User Manual


 
AC3 Series of engines
6
Spark plugs
The spark plug used in the 32cc trimmer is a Cham-
pion RDZ19H gapped to 0.025” (.655 mm).
See Figure 2.3.
Wear rate will vary with severity of use. If the edges of
the center electrode are rounded-off, or any other appar-
ent wear / damage occurs, replace the spark plug before
operating failure (no start) occurs.
Cleaning the spark plug:
NOTE: We do not recommend cleaning spark
plugs.
Use of a wire brush may leave metal deposits
on the insulator that causes the spark plug to
short out and fail to spark.
Use of abrasive blast for cleaning may cause
damage to ceramic insulator or leave blast
media in the recesses of the spark plug.
When the media comes loose during engine operation, severe and non-warrantable engine damage may
result.
Inspection of the spark plug can provide indications of the operating condition of the engine.
Light tan colored deposits on insulator and electrodes is normal.
Dry, black deposits on the insulator and electrodes indicate an over-rich fuel / air mixture (too much fuel or
not enough air)
Wet, black deposits on the insulator and electrodes indicate the presence of oil in the combustion cham-
ber.
Heat damaged (melted electrodes / cracked insulator / metal transfer deposits) may indicate detonation.
A spark plug that is wet with fuel indicates that fuel is present in the combustion chamber, but it is not
being ignited.
Spark plug removal and installation
To replace a spark plug:
1. Disconnect the spark plug wire. See Figure 2.4.
2. Remove the spark plug using a 5/8” spark plug
socket.
3. Gap a new plug at 0.025” (.6 mm).
4. Install the spark plug and tighten to a torque of 100 -
110 in. lbs.(11 -12 Nm).
5. Follow steps 1 and 2 in reverse order.
6. Test run the trimmer in a safe area before returning it to service.
Figure 2.3
Figure 2.4
Spark plug wire
! CAUTION! CAUTION
Do not grab the spark plug wire
with pliers. Damage to the spark-
plug boot will result. A damaged
spark plug boot will weaken the spark of the spark
plug.