19
MAN-88 – UK
12- SPARK-PLUG THERMAL DEGREE
The engine is supplied with a standard
NGK BR9EG
spark plug which represents
a
good
compromise between the needs of a good break-in and the racing needs in normal
conditions.
Use of different spark plugs is possibile and, as a general information, we are attaching a
correspondence list among spark plugs of other brands, based on
thermal degree
, which
represents the capacity of the spark plug to dissipate the internal heat. The colour of the
various parts of the spark plug more exposed to the combustion flames gives a good
indication on the adequacy of the thermal degree and on the carburetion. It is necessary
though to understand which of the two parameters has to be changed and only the
experience tells how to identify the most proper thermal degree of a spark plug as lean or
rich mixtures can generate the same final look which can be also achieved with a hot or cold
spark plug.
See table:
an excessively warm spark plug shows the
symptoms listed aside.
ATTENTION:
Use a warmer spark plug with cold or rainy
climates
§
Extremely clear color, porous look and
calcification of the electrodes and of the internal
insulator.
§
Irregularities in the ignition, preignition and
detonation with tendency to perforate the top of the
piston .
§
Note: some of these symptoms can be
achieved also with lean mixtures.
A correct thermal degree shows:
§
Color of the insulator end from yellow grey to
dark brown for mixtures respectively lean or rich.
An excessively cold spark plug shows the
symptoms, listed aside.
ATTENTION:
Use a colder spark plug with hot climates.
§
Insultator end and electrodes covered with black
shady soot.
§
Ignition difficulties.
§
Note: a wet or oily electrode could also mean
an excessively rich mixture.
COMPARISON TABLE BASED ON
THE THERMAL DEGREE
HOT
BOSCH
NGK
CHAMPION
WO8CS
BR9EG
N54R
WO7CS
BR10EG
N52R
WO6CS
BR11EG
COLD
