SCORPION Super Stinger 1975 User manual

~···-
io·
1975
Scorpion
Super
Stinger
Service Manual
Engine Section
1

SERVICE MANUAL- 1975 SCORPION SUPER STINGER
ENGINE SYSTEM
Functional Description:
2-CYCLE ENGINE FUNDAMENTALS
The Rockwell 2-cycle air - coo l ed gasoline engine,
particularly the axial fan-cooled twin cylinder
engine, has become very popular today for
snowmobiles. It is uniquely qualified for this ap-
plication because of its high power output, light
weight and ease of lubrication, with fewer
moving parts than other conventional 2-cycle
and 4 -c ycle engines.
However, in order to get the best possib le use
and ensure that it retains its high degree of
dependability and endurance, it must receive
proper care and maintenance. Therefore, it is
necessary for us to know something about the
basic fundamentals of . this engine and how it
functions.
OPERATION
The Rockwell 2-cycle Twin Cylinder engine is of
the loop-scavenged third port type, the most
wide ly used design today. It uses a mixture of
gasoline, oi l and air for combustion, lubrication
and cooling. It fires on every stroke of each
piston. There ore two power strokes for every
revolution of the crankshaft.
As the piston moves upward in the cylinder it
draws the fuel/air mixture into the crankcase
through the intake manifold while at the same
time compressing fuel that has been forced into
the combustion chamber. See Fig. 1-1 A.
As the piston nears top dead center the spark
plug is fired and the compressed fuel/air mix-
ture burns and expands thereby forcing the
piston downward on a power stroke.
As the downward stroke of the piston turns the
crankshaft, it also starts to compress the
fuel/air mixture in the crankcase and,
simultaneously, opens the exhaust port and
cl oses the intake port. See Figs. 1-1 B & C.
1-2
I NTAKE
0
EXH/UST
TRANSFER
FIG. 1-1

SERVICE MANUAL· 1975 SCORPION SUPER STINGER
After the exhaust port is fully open and the in-
take port is fully closed, further piston travel
starts to open the transfer ports. The com-
pressed fuel/air mixture from the crankcase
then travels up the transfer ports and into the
combustion area.
After most of the burned exhaust gases have
left the cylinder, an incoming charge of fuel/air
mixture scavenges the combustion area giving it
a fresh charge and the cycle is then repeated.
SeeFig.l-1 D.
Because lubrication is dependent on the m1xmg
of oil and fuel, it is extremely important that
good quality oil and gasoline are properly
mixed. The proper ratio of oil to gasoline will
prevent possible engine overheating, piston or
cylinder scoring, or eventual engine seizure.
Too much oil and not enough gasoline can lead
to incomplete combustion, fouled plugs, carbon
build-up and muffler clogging.
l-3

SERVICE MANUAL· 1975 SCORPION SUPER STINGER
EXHAUST SYSTEMS
SELECTION
Selection of an exhaust system (including
exhaust manifold, intermediate pipes, elbows
and muffler), is a result of thorough test
procedures involving measurement of fuel con-
sumption, horsepower and noise level. Contrary
to popular belief, the exhaust system is not only
for quieting the engine, but also serves to in-
crease horsepower output (by as much as 25%).
Changes made to the original equipment exhaust
system by changing any component in the system
can result in loss of power and/or severe engine
damage. For these reasons, intermediate lengths
of pipe between the cylinder and the muffler are
particularly critical.
TUNED MUFFLERS
Tuned mufflers allow the engine to exhaust its
spent charge int o an adequate volume and
properly matched muffling system. More im-
portant, the mufflers that are tuned, incorporate
designs that suck the exhaust gas from the cylin-
der allowing fuel and air to rapidly replace it and
also "cram" over-scavenged fuel and air mixture
from the exhaust pipe back into the cylinder
using sound waves and sound energy. This is ac-
complished at the speed of sound which allows
the engine to produce higher torque at higher
RPMs.
1-4
Donaldson
FIG. 1·2
n
Tuning
Courtesy of Dona l dson Muffler Co
)
FIG. 1·3

SERVICE MANUAL· 1975 .SCORPION SUPER STINGER
HOW TUNING WORKS
The megaphone effect of the expanded intake
tube scavenges exhaust gas from the cylinder
allowing rapid replacement of the fuel/air mix-
ture from the crankcase. Reflected sound waves
and sound energy stop over-scavenging and
return fuel/air mixture to the cylinder. It gives a
supercharging effect even though it operates
from the exhaust rather than the intake side.
Over-scavenging is also retarded by moderate
muffler back pressure. Silencing is accomplished
after power is maximized by acoustical packing in
the resonator outlet tube plus chambering and
baffling which gives an effective 2-pass muffler
design.
1·5

SERVICE MANUAL- 1975 SCORPION SUPER S TING ER
TABLE OF SPECI FICATIONS
ENGINE MODEL
DESCR IPTION 2F
440- 3 2F
400 -8 2F
440-8
2. 658"
2.559"
2. 658"
BORE
(67.5mm)
( 65.0mm)
(67.5mm)
J
STROKE
2.362"
(60mm)
DISPLACEMENT IN cc
428
398 428
COMPRESSION RATI ON (actual)
12.5:1 12:1 12:1
I GNITION SYSTEM Bosch
Flywhe el Magneto
LIGHTING COIL VOLTAGE AND
OUTPUT
12V 75W 1 2V 150W
12V 150W
*TIMING BEFORE TDC (CENTRIFUGAL .
102 - .112
.102-.112 .1 02- . 112
WEIGHT ADVANCED)
TIMING BEFORE TDC (CENTRIFUGAL .0
18" to . 020"
.018 " to .020"
.0 18" to .020"
WEIGHT RETARDED)
BREAKER POINT
GAP
.014"to .01 6"
SPARK PL UG THREAD
14mm. x 1 .25 - 3/ 4" reach
.020" . 020"
.020 "
SPARK PLUG
GAP
(0. 5mm .)
(0.5mm.) (0.5mm.)
SPARK PLUG-BOSCH (ORIGINAL
W260T2
W260T2
W260T2
EQUIPMENT)
TYPE OF ENGINE COOLING
Axia l Fl ow Fan
ROTA TION OFCRANKSHAFT
Counterclockwise (PTO side)
CARBURETOR
Wa l bro
FUEL/OIL RA TI O
As Specified on Scorpion Oil Conta i ner
GASO LI NE
95 octane, mini mum (lead free not accep t ab l e)
TYPE OF O IL
Special 2-Cycle Snowmobi le Oil
* Do no t exceed indicated advance, as this will result m severe engme damage.
1-6

0
TORQUE SPECIFICATIONS
CYLINDER HEAD NUTS
CYLINDER B
ASE NUTS
FlYWHEEL NUT
INTAKE MANIFOLD NUTS
FAN HOUSING SCREWS
FAN WHEEL NUT
RING GEAR SCREWS (6mm.)
RING GEAR SCREWS (8mm.)
SERVICE MANUAL- 1975 SCORPION SUPER STINGER
TABLE OF SPECIFICATIONS
-8 -9 2F- 440-3
2F-400-6 2F-440-5
19 28
to 32 ft./lbs.
16 to 18 ft./lbs.
44 to 50 ft./lbs.
56 to 72 ft./lbs.
56 to 72 ft./lbs .
16 to 18 ft./lbs.
16 to 18 ft./lbs.
22 to 24 ft./lbs.
6 to 7 ft./lbs. not applicable not applicable
10 to 12 ft./lbs.
not applicable 10 to 12 ft./lbs.
Tightening Sequence for Cylinder Base Nuts
0 0 8 0
PTO SIDE
0
G)
0 8
Tightening Sequence for:
Cylind er Head Nuts, Fan Housing, Ring Gear Flange, Intak e Manifold
and Recoil Starter Clamps
0
8 0 0
'74- '75
'74 - '75
®
290s
400s
340s
440s
AI I previous
G)
models
®
0 0
CD
1-7

SERVICE MANUAL - 1975 SCORPION SUPER STINGER
ROCKWELL TWIN CYLINDER ENGINES
MODELS 2F-400-.8
DISASSEMBLY
2F-440-8
A. Recoil Starter
Remove four (4) screws holding the
recoil assembly to the fan housing.
See Fig. 1-4.
See pages 1- 28 A, B, C for recoil starter
disassembly.
B. Lower Fan Pulley and Carrier Assembly
l-8
Remove the three (3) hex head bolts on
the carrier. Remove carrier, lower pulley
assembly and V-belt. See Figs. 1-5, 1-6.
FIG. 1-4
A
(.:
FIG. 1-5
FIG. 1-6

c
SERVICE MANUAL · 1 975 SC ORPION SU PER S TI NGER
C. Upper Fan Belt Pulley Assembly.
Insert a 3/ 16" dri ll or a suitable punch
through the indexing hole into the im-
pe ll er body. With a 17 mm socket
wrench, remove the fan nut , lock
washer , pulley halves and spacers. See
Figs. 1-7
,1 -8,1-9.
FIG. 1-8
FIG. 1-7
FIG. 1-9
1·9

SERVICE MANUAL - 1975 SCORPION SUPER STINGER
D. Flywheel Magneto
Remove the crankshaft nut using a 27
mm socket wrench . Pull th e flywheel by
attaching flywheel puller 444-31-8 43 -2 to
the flywheel flange using bolts provided.
Screw the three bolts through the puller
into the flange and tighten evenly. With
a socket wrench, tighten the puller bolt
until the flywheel loosens on the
crankshaft. See Figs. 1-10, 1-11, 1-12, 1-
13.
FIG. 1-12
NOTE: It is important that care is taken
to remove the positioning key in crank-
shaft before attempting to remove the
flywheel assembly. Failure to do this
could result in damage to advance
mechanism.
1- 10
()
FIG. 1-10
Q.
FIG. 1-11
FIG. 1-13