SCORPION 1975 LIL' WHIP User manual

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1975
Scorpion
Lil Whip
Service Manual
Engine Section
1-l

SERVICE MANUAL · 1975 SCORPION LIL' WHIP
ENGINE SYSTEM
Functional Description:
2-CYCLE ENGINE FUNDAMENTALS
The Rockwell 2- cycle air - cooled 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-cycle engines.
However, in order to get the best possible 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
widely used design today. It uses a mixture of
gasoline, oil 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 some
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,
simultaneous ly, opens the exhaust port and
closes the intake port. See Figs. 1-1 B & C.
1-2
INTAKE
EXH/ UST
TRANSFER
FIG. 1-1
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After the exhaust port is fully open and the in-
take port is fully closed, further piston trave l
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.
See Fig . 1-1 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 wi ll
prevent possible engine overheating, piston or
cylinder scoring, or eventual engine seizure .
Too much oil and not enough gasoline can l ead
to incomplete combustion, fouled plugs, carbon
build - up and muffler clogging.
SERVICE MANUAL - 1975 SCORPION LIL ' WHIP
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SERVICE MANUAL • 1975 SCORPION LIL' WHIP
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. 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 betweeen
the cylinder and the muffler are particularly
critical.
TUNED MUFFLERS
Tuned mufflers allow the engine to exhaust its
spent charge into 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
)
Tuning
Courtesy of Donaldson Muffler Co
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FIG. 1-3

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HOW TUNING WORKS
The megaphone effect of the expanded intake
tube scavenges exhaust gas from the cy lind er
allowing rapid replacement of th e 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 e ven 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.
SERVICE MANUAL -1975 SCORPION LIL' WHIP
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SERVICE MANUAL - 1975 SCORPION LIL' WHIP
TABLE OF SPECIFICATIONS
ENGINEMODEL
DESCRIPTION 2F
295-2
BORE
2.190
(55 .6mm )
STROKE
2.362"
(60mm)
DISPLACEMENT IN cc
294
COMPRESSION RATIO (a
ctua l) 12:1
IG NITION SYSTEM
Bosch F lywh eel Magneto
LIGHTING COIL VOLT AGE AND
12V 150W
OUTPUT
*TIMING BEFORE TDC (CENTRIFUGAL
.102-.112
WEIGHT ADVANCED}
TIMING BEFORE TDC ( CE NTRIFUGAL
.0 18" to .020"
WEIGHT RETARDED)
BREAKER POINT GAP
.014"to.Ol6"
. )
SPARK PLUG THREAD
14mm . x 1.25 - 3/4" reach
SPARK PLUG GAP
.020 "
(0 .5mm.)
SPARK PLUG-BOSCH (ORIGINAL
W260T2
EQUIPMENT}
.. ~~(~
TYPE OF ENGINE COOLI NG
Axial Flow Fan
ROTATION OF CRANKSHAFT
Counterclockwise (PTO side)
CARBURETOR
Walbro
FUEL /OIL RATIO
As Specified on Scorpion Oil Container
GASOLINE
95 octane, minimum (lead free not acceptable)
TYPE OF OIL Special 2-Cycle
Snowmobile Oil
* Do not exceed indicated advance, as thi s will re s ult in severe eng i ne damage.
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SERVICE MANUAL - 1975 SCORPION LIL' WHIP
TORQUE SPECIFICATIONS
CYLINDER HEAD NUTS
CYLINDER BASE NUTS
FLYWHEEL NUT
INTAKE MANIFOLD NUTS
FAN HOUSING SCREWS
FAN WHEEL NUT
PTO SIDE
TABLE OF SPECIFICATIONS
2F 295 -2
28-
32 Ft.-Lb.
16-18Ft.-Lbs.
56-72F t.- Lbs.
16-18 Ft. -Lbs.
16-18 Ft. -Lbs.
22 - 24 Ft.- Lbs.
Tightening Sequence for Cylinder Base Nuts
All Models
Tightening Sequence for:
Cylinder Head Nuts, Fan Housing, Intake Manifold
and Recoil Starter Clamps
8 0
'75
290
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SERVICE MANUAL · 1975 SCORPION LIL' WHIP
ROCKWELL TWIN CYLINDER ENGINES
MODEL 2F-295-2
DISASSEMBLY
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
1-8
Remove the three (3) hex head bolts on
the carrier. Remove carrier, lower pulley
assembly and V-belt. See Figs. 1-5, 1-6.
J
FIG. 1-4
FIG. 1-5
FIG. 1-6

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C. Upper Fan Belt Pulley Assembly.
Insert a 3/16" drill or a suitable punch
through the indexing hole into the im-
peller 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
SERVICE MANUAL - 1975 SCORPION LIL' WHIP
FIG. 1-7
FIG. 1-9
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SERVICE MANUAL - 1975 SCORPION LIL' WHIP
D. Flywheel Magneto
Remove the crankshaft nut using a 27
mm socket wrench. Pull the flywheel by
attaching flywheel puller 444-31-843 -2 to
the flywheel flange using bolts provided.
Screw the three bolts through the pull er
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.
NOTE: It is important that care is taken
to remove the positioning key in crank -
s haft before attempting to remove the
flywh ee l assembly. Failure to do this
could result in damage to advance
m ec hani s m.
l-1 0
FIG. 1-10
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FIG. 1-11
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FIG. 1-13