Maintenance; Spark Plugs - MTD P61 Series Professional Shop Manual

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MAINTENANCE

The information in this manual applies to the MTD
engine. Some basic principles may apply to engines
produced by other manufacturers.
As the saying goes "an ounce of prevention is worth a
pound of cure". The same can be said about preventive
maintenance on outdoor power equipment. By chang-
ing the spark plug, air filter, and oil at recommended
intervals many failures can be avoided. Sometimes just
clearing off yard debris that has collected through use
can make the difference between a properly running
piece of equipment and the expensive inconvenience
of unplanned repairs..

Spark plugs

1. The spark plug used in the MTD engine is a
Torch model F6RTC gapped to .024"-.032" (.60-
.80 mm). See Figure 1.1.
Figure 1.1
NOTE: Champion RN14YC or NGK BPR4ES
are physically similar but do not match the
F6RTC in heat range. This difference in heat
ranges will effect performance and emissions. It
is recommended that only the torch F6RTC plug
be used in MTD engines.
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Chapter 1: INTRODUCTION
2. Wear rate will vary somewhat with severity of
use. If the edges of the center electrode are
rounded-off, or any other apparent wear / dam-
age occurs, replace the spark plug before oper-
ating failure (no start) occurs.
3. Cleaning the spark plug:
NOTE: It is not recommended to clean 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 abra-
sive 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.
4. Inspection of the spark plug can provide indica-
tions of the operating condition of the engine.
• Light tan colored deposits on insulator and elec-
trodes is normal.
• Dry, black deposits on the insulator and elec-
trodes indicate an over-rich fuel / air mixture (too
much fuel or not enough air)
• Wet, black deposits on the insulator and elec-
trodes indicate the presence of oil in the com-
bustion chamber.
• 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.
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