Arctic Cat Panther 1974 Manual page 116

SPARK PLUG INFORMATION
Heat Range
Proper spark plug heat range selection is very
important to the operation of the engine. When the
snowmobile is to be operated relatively slow, as for
trail riding, use a spark plug having a high heat
range to prevent spark plug fouling. And for high
speed operation, use a spark plug having a low heat
range.
HEAT RANGE - The ability of the spark plug to
dissipate heat away from its center electrode and
insulating material. This ability to dissipate heat is
controlled by the design of the spark plug insulator
and shell structure. The heat escape route followed
is:
1. Spark Plug Shell
2. Metal Washer (Gasket)
3. Rotor Housing Spark Plug Threads
4. Cool Air from Fan
A spark plug having a high heat range has a long
center electrode extension, which permits heat
transfer less rapidly. By comparison, a spark plug
having a low heat range has a shorter center
electrode extension, which permits rapid heat
transfer.
The remaining component affecting heat transfer is
the metal washer. To make sure the sea l between
the spark plug and rotor housing is adequate, the
spark plug is to be tightened to 16-18 ft. Ibs.
torque. If the spark plug is tightened excessively,
causing the metal washer to be flattened com -
pletely, the spark plug will burn colder than
expected because heat will be conducted too
rapid ly. Conversely, a spark plug tightened insuf-
ficiently will not crush the metal washer enough,
resulting in compression leakage, overheating and
possible rotor, rotor housing, and end cover
damage.
The correct spark plug to use in the Wankel
engine is a Bosch W240T1 or W240T2,
depending on engine serial number (see
Caution). Set the air gap at 0.020 inch.
IV-32
e
CAUTION
e
All KM-24 Wankel engines preceding engine
serial number 7565102 use a 1/2-inch reach
spark plug (Bosch W240T1). After engine serial
number 7565102, use a 3/4-inch reach spark
plug (Bosch W240T2). DO NOT USE A
3/4-INCH REACH SPARK PLUG IN ENGINES
PRECEDING ENGINE SERIAL NUMBER
7565102 BECAUSE THE ENGINE WILL BE
DAMAGED IF OPERATED.
Spark Plug Operating Conditions
Disconnect the high tension wire from the spark
plug; then remove the plug from the rotor housing,
using a 13/ 16-inch spark plug socket. Examine the
cond ition of the spark plug insulator to determine
the operating temperature of the engine.
1.
A tan or light brown insulator tip indicates
the correct spark plug and proper heat range.
2. A light gray or white insulator tip indicates
overheating caused by a lean carburetor
setting, loose carburetor, constant overloading
of the engine and an incorrect spark plug
(heat range too high).
3. A black or oily insulator tip indicates fouling
caused by incorrect fuel/air mixture ratio, a
rich carburetor setting or incorrect spark plug
(heat range too low).
e
CAUTION
e
A cracked, fouled or dirty spark plug is to be
replaced. DO NOT clean and reuse a fouled or
dirty spark plug; grit may be released into the
rotor chamber, causing engine damage.
Spark Plug Installation
Equipment Necessary: Graphite Grease, Torque
Wrench and 13/16-lnch Spark Plug Socket
. '
1. Apply a light fil m of graphite grease on the
spark plug threads.
2. I nstall the spark plug in the rotor housing and
tighten to 16-18 ft. Ibs., using a 13/ 16-inch
spark plug socket and torque wrench .
3. Connect the high tension wire to the spark
plug.