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
l '
FIG. 1-3

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l'
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.
1-6

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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
1-7

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

(
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
1-9

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
)
FIG. 1-11
)
FIG. 1-13

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l_..~
E. Intake Manifold Assembly
Remove the four (4) intake manifold
nuts and washers. Remove manifold
assembly and insulators. See Fig. 1-14.
SERVICE MANUAL -1975 SCORPION LIL' WHIP
~ ~Hfk(~;
oo 00
FIG. 1-14
1-11

SERVICE MANUAL • 1975 SCORPION LIL' WHIP
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. 1-15).
Remove fan housing from crankcase (See
Fig. 1-16).
Unplug connector housing coi l wires. (Note
color coding of wires.) Remove armature
plate assembly and wires, as a unit, from
fan housing.
1- 12
FIG. 1-15
l)
FIG. 1-16

)
(
Remove the fan QY 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. 1-17,
1-18, 1-19.
SERVICE MANUAL· 1975 SCORPION LIL' WHIP
FIG. 1-17
FIG. 1-18
FIG. 1-19
1-13

SERVICE MANUAL - 1975 SCORPION LIL' WHIP
G. Remove spark plugs with spark plug
wrench.
H. Cylinder Heads
Remove cylinder head nuts with a
17 mm socket wrench. Mark cylind er
heads before removal from cylinder .
Remove and discard gaskets. See Fig.
1-20.
I. Cylinders
Remove the eight {8) cylinder base
nuts using a 13 mm socket wrench and
remove the eight (8) spring washers.
The cylinders may be remov ed. See
Fig. 1- 21.
NOTE: I M P 0 RT A N T
If removal of cylinder s only is requir e d, care
must be taken that the crankcase seal is not
disturbed . The removal of the PTO cylinder
will allow the placement of two bolt s and
nuts with flat wa s her s to apply constant pr es-
sure to crankcase assembly. Bolts should be
placed in the center two holes (adjac e nt to
the fan side cylinder). See Fig. 1- 29. The
second cylinder may now be removed.
l - 14
FI G. 1-20 ( )
( )
FI G. 1-21

J
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 sti ll be held in hand. Push the pin
out.
K. To separate the crankcase halves, hold upper
portion of crankcase assembly in one hand,
lifting s lightly and tap the end of the crank-
case with a soft hamm er . The crankcase will
separate and the crankcase may be
removed. See Fig. 1-22.
SERVICE MANUAL -1975 SCORPION LIL' WHIP
FIG. 1-22
1- 15

SERVICE MANUAL - 1975 SCORPION LIL' WHIP
L. Crankshaft Bearings
1-16
To remove crankshaft end bearings, use
bearing puller 444-31-807-0. See Figs. 1-23,
1-24, 1-25.
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. 1-23
FIG. 1-24
FIG. 1-25

(
ASSEMBLY
) A. Crankshaft Bearings.
Heat crankshaft bearings in oil (or oven) to
approximately 180 degrees.
Slide bearing on crankshaft.
B. Crankcase.
In spect and clean both halves of crankcase.
The proper sealant material such as Per -
matex Hy - Tack Spray shou ld be now sprayed
on crankcase sea lin g surfaces. See Fig. 1- 27.
Before installing crankshaft into crankcase
low er half of it will be necessary that al l
bearing outer surfaces be wiped clean of
foreign material so that proper sealing will
occur. After installing PTO thrust washer and
oi l sea l (inside groove of oil sea l coated with
li ght grease) place the crankshaft carefully
into the low er crankcase half and properly
position all componenets. See Figs. 1 -28.
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 low er
half.
SERVICE MANUAL • 1975 SCORPION LIL' WHIP
t
BEARING_j
FIG. 1-26
FIG. 1-27
\
,: l
FIG. 1-28
1-17

SERVICE MANUAL · 1975 SCORPION LIL' WHIP
Install two crankcase holding bolts in the
center holes of the PTO side of crankcase.
(Fig. 1-29) 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. 1-30, 1-31, 1-32, 1-
33).
CIRCLIP OPENING HERE----r
FIG. 1-31
1-18
r
FIG. 1-29
FIG. 1·30
_;

(
\,,
1. O il the piston pin e nd bearings.
2. In sta ll one circl ip in piston.
3. Heat the piston suff i cien tly to allow pin to
push into pi ston and install pin.
4. In sta ll second circlip. (See Fig. 1-31 for
correct or i entation of circlips. )
SERVICE MANUAL · 1975 SCORPION LIL' WHIP
0
FIG. 1-32
FIG. 1-33
J ·19

SERVICE MANUAL · 1975 SCORPION LIL' WHIP
Install base gaskets on the cylinder studs and
position against the cylinder flanges (see Fig.
1- 34). With the use of a ring compressor,
lower cylinders one at a time over the
pistons. Install base washers and nuts finger
tight. See Fig. 1-35, 1-36.
Temporarily install the intake manifold
without gaskets and tighten manifold nuts to
sixteen (16) to eighteen {18) foot pounds.
See Fig. 1-37. Cylinder 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 the 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.
1·20
)
FIG. 1-34
)
FIG. 1-35
FIG. 1·36