SCORPION Super Stinger 1975 User manual

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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

SERVICE MANUAL · 1975 SCORPION SUPER STINGER
E. Intake Manifold Assembly
Remove the four (4) intake manifold
nuts and washers. Remove manifold
assembly and insulators. See Figs. 1-14,
1-15.
.0,0 •-'• ,; <i *:
oo 00
FIG. 1-14
FIG. 1-15
1-l l

SERVICE MANUAL - 1975 SCORPION SUPER STINGER
F. Fan Housing and Armature Plate Assembly
Remove screw holding spark plug wire
bracket to fan housing. With a socket type 5
mm Allen wrench and impact driver, remove
the four (4) mounting bolts holding fan
housing to crankcase. (See Fig. 1-16).
Remove fan housing from crankcase (See
Fig. 1-
17).
Unplug connector housing coil wires. (Note
color coding of wires.) Remove armature
plate assembly and wires, as a unit, from
fan housing.
1-12
FIG. 1-16
FIG. 1-17 )

n
(
SERVICE MANUAL · 1975 SCORPION SUPER STINGER
Remove the fan by tapping the end of fan
shaft with a soft hammer. With a flat punch
and hammer, tap the inner race of the fur-
thest bearing in the housing. See Figs. 1-18,
1-19, 1-20.
FIG. 1-18
FIG. 1-19
'
\..._
FIG. 1-20
l-13

SERVICE MANUAL - 1975 SCORPION SUPER STINGER
G. Remove spark plugs with s park plug
wrench. (See Fig. 1-21.)
H.
Cylinder Heads
Remove cy lind er head nuts with a
13
mm socket wrench. Mark cylinder
heads before removal from cylinder.
Remove and discard gaskets. See Fig.
1-22.
I. Cylinders
Remove the e ight (8) cylinder base
nuts using a 13 mm socket wrench and
remove the eight (8) spring washers.
The cylinders may be removed. See
Fig. 1-23.
NOTE: IMP 0 R TAN T
If removal of cy linder s only is required, care
must be taken that the crankcase seal is not
disturbed. The removal of the PTO cylinder
will allow the placement of two bolts and
nuts with flat washers to apply constant pres-
sure to crankcase assembly. Bolts should be
placed in the cen t er two holes (adjacent to
the fan side cy lind er). See Fig. 1-31. The
second cylinder may now be removed.
1- 14
FIG. 1-21
FIG. 1-22
FIG. 1-23

r
n
c
SERVICE MANUAL · 1975 SCORPION SUPER STINGER
J. Piston and Wrist Pin
With needle nose pliers, remove circlips from
pistons. Heat the piston with a heat gun or
propane torch. Heat only to the point where
piston may still be held in hand. Push the pin
out.
K. To separate the crankcase halves, hold upper
portion of crankcase assembly in one hand,
lifting slightly and tap the end of the crank-
case with a soft hammer. The crankcase will
separate and the crankcase may be
removed. See Fig. 1-24.
\ .
.,
. ..
1
·
... ·'
("""'!) i
FIG. 1- 24
1-15

SERVICE MANUAL • 1975 SCORPION SUPER STINGER
L. Crankshaft Bearings
1-16
To remove crankshaft end bearings, use
bearing puller 444 -31 - 807-0. See Figs. 1-25,
1-
26, 1-27. Slip the puller half shells around
the outer bearing race and around puller
assembly. Slide the retaining ring over the
half shells. Using two (2) 27 mm wrenches,
turn the center bolt clockwise with one
wrench and use the second wrench to hold
the puller body. Before removing the PTO
side crankshaft bearing, insert a 1/2" 20 UNF
bolt, 1 /2" long, to protect the internal thread
of the crankshaft.
FIG. 1 -25
FI G. 1-26
FI G. 1 ·27

SERVICE MANUAL • 1975 SCORPION SUPER STINGER
ASSEMBLY
( A. Crankshaft Bearings.
(
Heat crankshaft bearings in oil (or oven) to
approximately 180 degrees.
Slide bearing on crankshaft.
B. Crankcase.
Inspect and clean both halves of crankcase.
The proper sealant material such as Per-
matex Hy - Tack Spray should be now sprayed
on crankcase sealing surfaces. See Fig. 1-29.
Before installing crankshaft into crankcase
lower half of it will be necessary that all
bearing outer surfaces be wiped clean of
foreign material so that proper sealing will
occur. After installing PTO thrust washer and
oil seal (inside groove of oil seal coated with
light grease) place the crankshaft carefully
into the lower crankcase half and properly
position all components. See Figs. 1- 30.
Placement of the upper crankcase half may
now be made. Be certain that the center seal
is lined up with the crankcase split line.
Tap upper crankcase half to seat with lower
half.
FIG. 1-28
FIG. 1-29
FIG. 1-30
l-17

SERVICE MANUAL · 1975 SCORPION SUPER STINGER
Install two crankcase holding bolts in the
center holes of the PTO side of crankcase.
(Fig. 1-31) Tighten finger tight.
C. Piston , Cylinder and Cylinder Heads
The pistons must be clean and free from car -
bon deposits and the piston rings must fit
freely in their grooves. Rings are marked for
proper side up. The arrow on the crown of
pistons must point toward exhaust side of
engine. Piston pins, needle bearings, check
plates and circlips may now be installed, ac -
cording to the procedure below. (Always use
new circlips.) See Figs. 1-32, 1- 33, 1-34, 1-
35.)
CIRCLIP OPENING HERE---'
FIG. 1-33
1·18
J
FIG. 1-31
()
FIG. 1-32
J

SERVICE MANUAL · 1975 SCORPION SUPER STINGER
1. Oil the piston pin end bearings.
2. Install one circlip in piston.
3. Heat the piston sufficiently to allow pin to
push into piston and install pin.
4. In stal l second circlip. (See Fig. 1-33 for
correct orientation of circlips.)
0
FIG. 1·34
FIG. 1-35
1-19

SERVICE MANUAL · 1975 SCORPION SUPER STINGER
In stall base gaskets on th e cy lind er studs and
position against the cy linder flanges (see Fig.
1- 36). With the use of a ring compressor,
lower cy lind ers one at a time over the
pistons . Ins tall base washers and nuts finger
tight. See Fig. 1- 37, 1-38.
Temporarily install the intake manifold
without gaskets and tighten manifold nuts to
sixteen (16) to eighteen (18) foot pounds.
See Fig. 1- 39. Cy lind er base nuts may now be
torqued to sixteen (16) to eighteen (18) foot
pounds as outlined on specification page.
The proper piston height can be measured at
the top of the cylinder . The edge of the crown
of the piston must not protrude above the top
of th e cylinder with the piston in the top dead
center position. If the piston does protrude
above the cylinder, a thicker base gasket
must be used. See specification page for
dimensions and color coding. It is important
that only one cylinder at a time be adjusted
or the crankcase will separate and lose it's
seal.
l - 20
FIG. 1·36
FIG. 1-37
(
FIG. 1-38