FS-120S III
It is of vital importance, before attempting to
operate your engine, to read the general
'SAFETY INSTRUCTIONS AND WARNINGS'
section on pages 2-4 of this booklet and to
strictly adhere to the advice contained therein.
Also, please study the entire contents of this
instruction manual, so as to familiarize
yourself with the controls and other features
of the engine.
Keep these instructions in a safe place so that
you may readily refer to them whenever
necessary.
It is suggested that any instructions supplied
with the aircraft, radio control equipment, etc.,
are accessible for checking at the same time.
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SAFETY INSTRUCTIONS AND
WARNINGS ABOUT YOUR O.S. ENGINE
INTRODUCTION, INSTALLING THE GLOWPLUG
RELOCATION OF CARBURETTOR CONTROLS
FUEL TANK, INSTALLATION
EXHAUST HEADER PIPE AND SILENCER,
THROTTLE LINKAGE,
NEEDLE-VALVE EXTENSION
FUEL LINES
CARE OF FUEL PUMP AND REGULATOR,
PROPELLERS
GLOWPLUGS, FUEL
PROPELLER AND SPINNER ATTACHMENT,
TYPE 70N CARBURETTOR
RUNNING-IN
IDLING MIXTURE ADJUSTMENT
VALVE ADJUSTING
CARE AND MAINTENANCE
O.S. GENUINE PARTS & ACCESSORIES
ENGINE EXPLODED VIEWS &
ENGINE PARTS LISTS
CARBURETTOR EXPLODED VIEWS &
PARTS LIST
ENGINE THREE VIEW DRAWINGS
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CONTENTS
STARTING
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5
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Remember that your engine is not a " toy ", but a highly
efficient internal-combustion machine whose power is
capable of harming you, or others, if it is misused or
abused. As owner, you, alone, are responsible for the safe
operation of your engine, so act with discretion and care at
all times.
If at some future date, your O.S. engine is acquired by
another person, we would respectfully request that these
instructions are also passed on to its new owner.
WARNINGS
These cover events which might involve serious (in
extreme circumstances, even fatal ) injury.
NOTES
These cover the many other possibilities, generally less
obvious sources of danger, but which, under certain
circumstances, may also cause damage or injury.
SAFETY INSTRUCTIONS AND
WARNINGS ABOUT YOUR
O.S. ENGINE
■
The advice which follows is grouped under two headings
according to the degree of damage or danger which
might arise through misuse or neglect.
WARNINGS
Never touch, or allow any object to come into
contact with, the rotating propeller and do not
crouch over the engine when it is running.
A weakened or loose propeller may disintegrate or be thrown
off and, since propeller tip speeds with powerful engines may
exceed 600 feet(180 metres) per second, it will be understood
that such a failure could result in serious injury, (see 'NOTES'
section relating to propeller safety).
Model engine fuel is poisonous. Do not allow it to
come into contact with the eyes or mouth. Always
store it in a clearly marked container and out of
the reach of children.
Model engine fuel is also highly flammable. Keep it
away from an open flame, excessive heat, sources
of sparks, or anything else which might ignite it.
Do not smoke or allow anyone else to smoke, near
to it.
Never operate your engine in an enclosed space. Model
engines, like automobile engines, exhaust deadly carbon-
monoxide. Run your engine only in an open area.
Model engines generate considerable heat. Do
not touch any part of your engine until it has
cooled. Contact with the muffler(silencer),
cylinder head or exhaust header pipe, in
particular, may result in a serious burn.
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NOTES
This engine was designed for model aircraft. Do not attempt to use it for any other purpose.
Mount the engine in your model securely, following the manufacturers' recommendations, using appropriate
screws and locknuts.
Be sure to use the silencer (muffler) supplied with the engine. Frequent exposure to an open exhaust may
eventually impair your hearing.
Such noise is also likely to cause annoyance to others over a wide area.
Fit a top-quality propeller of the diameter and pitch specified for the engine and aircraft. Locate the propeller on the
shaft so that the curved face of the blades faces forward-i.e. in the direction of flight. Firmly tighten the propeller nut,
using the correct size wrench.
Always check the tightness of the propeller nut and retighten it, if necessary, before restarting the engine,
particularly in the case of four-stroke-cycle engines. A safety locknut assembly is provided. Always use it. This will
prevent the propeller from flying off in the event of a "backfire", even if it loosens.
If you fit a spinner, make sure that it is a precision made product and that the slots for the propeller blades do not
cut into the blade roots and weaken them.
Discard any propeller which has become split, cracked, nicked or otherwise rendered unsafe. Never attempt to
repair such a propeller: destroy it. Do not modify a propeller in any way, unless you are highly experienced in tuning
propellers for specialized competition work such as pylon-racing.
Use an electric starter for this engine. The wearing of safety glasses is also strongly recommended.
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Take care that the glow plug clip or battery leads do not come into contact with the propeller.
Also check the linkage to the throttle arm. A disconnected linkage could also foul the propeller.
After starting the engine, carry out any needle-valve readjustments from a safe position behind the rotating
propeller. Stop the engine before attempting to make other adjustments to the carburettor.
Adjust the throttle linkage so that the engine stops when the throttle stick and trim lever on the transmitter are fully
retarded. Alternatively, the engine may be stopped by cutting off the fuel supply. Never try to stop the engine
physically.
Take care that loose clothing (ties, shirt sleeves, scarves, etc.) do not come into contact with the propeller.
Do not carry loose objects (such as pencils, screwdrivers, etc.) in a shirt pocket from where they could fall through
the propeller arc.
Do not start your engine in an area containing loose gravel or sand. The propeller may throw such material in your
face and eyes and cause injury.
For their safety, keep all onlookers (especially small children) well back (at least 20 feet or 6 meters) when preparing
your model for flight. If you have to carry the model to the take-off point with the engine running, be especially
cautious. Keep the propeller pointed away from you and walk well clear of spectators.
Warning! Immediately after a glowplug-ignition engine has been run and is still warm, conditions sometimes exist
whereby it is just possible for the engine to abruptly restart if the propeller is casually flipped over compression
WITHOUT the glowplug battery being reconnected. Remember this if you wish to avoid the risk of a painfully rapped
knuckle!
NOTES
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INTRODUCTION
Rocker Cover
Cylinder Head
Push Rod Cover
Drive Hub
Propeller Washer
Propeller Nut
Lock Nut
Exhaust Header Pipe
Carburettor Type 70N
Cover Plate
Crankcase
INSTALLING THE GLOW PLUG
Glow plug
Carefully insert plug, with washer,
fingertight only, before final tightening
with the correct size plug wrench.
Washer
Beam Mount
The FS-120S3 is the latest mid-range model in the well-estab-
lished FS-120S series of 20cc four-stroke engines. This series
extends from the standard suction-feed FS-120S-E to the
unique ultra-high performance FS-120S-SP, the world's only
production model engine to be equipped with a genuine crank-
shaft-driven supercharger.
The FS-120S3 is fitted with the new O.S. PD-07 diaphragm
type fuel pump and matching Type 70N carburettor incorporat-
ing a built-in pressure regulator. These features ensure that
fuel/air mixture strength is maintained at a constant level
through manoeuvres, for consistent performance and reliable
throttle response.
In the interests of improved durability, certain ferrous parts that
are particularly susceptible to corrosion in four-stroke engines,
have a corrosion resistant plating and, for the same reason, a
special grease-packed twin-sealed rear ball-bearing is used.
To maintain the four-stroke engine's reduced noise levels, the
FS-1203 is supplied with an O.S. Type F-5020 baffled silencer
(muffler) of substantially enlarged volume, as standard equip-
ment.
Where installation calls for a separate exhaust pipe and silen-
cer, these parts are available as optional extras. (See page 19
of this booklet.)
F-5020 Silencer
5
As supplied, the FS-120S3 has its throttle lever on the right hand
side and needle-valve control on the left. However, where more
convenient for certain installations, these positions may be
reversed after rotating the carburettor through 180˚ horizontally.
Proceed as follows:
1.
2.
3.
4.
5.
RELOCATION OF CARBURETTOR CONTROLS
Remove the intake pipe mounting screws from the cylinder head
(taking care not to lose the flange gasket) and the carburettor
mounting screws from the crankcase cover plate bracket.
Detach short tube connecting the carburettor to the pump unit
and gently rotate the carburettor through 180° without
separating it from the intake pipe or removing the enclosed O-
ring seal.
Re-install the complete sub-assembly of intake pipe and
carburettor, making sure that adjoining surfaces are clean.
Tighten screws evenly and firmly but not excessively.
Remove pump mounting screws from the crankcase cover
plate lugs, carefully rotate the pump clockwise one-quarter turn
and attach it to the second pair of lugs provided, taking care that
the central tube connecting the crank chamber to the pump
diaphragm chamber is not twisted.
Finally, make sure that all external tube connections are secure
and do not leak.
Intake Pipe
Mounting Screw
Intake Pipe
Throttle Lever
Carburettor
Mounting Screw
Needle Valve
FueI Inlet
PD-07 Pump
Pump Fixing Screw
Pressure Regulator
FS-91S2-P
6
10
~
15mm
Because the FS-120S3 powerful, large-displacement, single-
cylinder four-stroke-cycle engines, it is essential to use very
substantial engine mounting. Conventional wooden mounting
beams should be of rigid hardwood and of at least 15mm or 5/8-in
square section.
INSTALLATION
FUEL TANK
A fuel tank of approximately 450cc capacity is suggested. This
allows up to 14-15 minutes flying time, dependent upon the type of
fuel used, the size of the propeller and on the proportion of full-
throttle to part-throttle operation through the flight. Make sure that
the tank is well rinsed out with methanol or glow fuel before
installation and that the pickup weight is well clear of the bottom of
the tank when held vertically (see sketch). To prevent the pickup
from adhering to the tank wall under suction and restricting fuel
flow, slots may be filed in the end of the weight as shown.
Alternatively, a Bubbless type weight (Code No. 71531000) may
be used.
Make sure that the mounting beams are parallel and that their top
surfaces are in the same plane.
How to fasten the mounting screws.
Hardwood mounting beams
O.S. radial motor mount
(cast aluminum)
For filling or emptying tank
To fuel inlet
Air vent
Use thick-walled sillcone tubing
Tighten second nut firmly
down onto first nut.
Tighten this nut first.
Steel washer
5mm steel nuts
5mm steel screw
Spring washer or
lock washer
15mm min.
15mm min.
Hardwood such as
cherry or maple.
Spring washer
5mm steel Allen screw
Make sure that these mounting beams are accurately aligned and
firmly integrated with the airframe, reinforcing the adjacent
structure to absorb vibration. Use 5mm or larger steel screws,
preferably Allen type hexagon socket head cap screws, with
washers and locknuts, for bolting the engine to the bearers.
As an alter native to wooden beam mounting, a special O.S. cast
aluminium radial motor mount, complete with 5mm mounting
screws, is available as an optional extra part (Code No.71904200)
, where front bulkhead (firewall) type mounting is called for. Engine
installation should, in any case, be made in such a way that basic
maintenance can be conveniently carried out.
Front view
CORRECT
Side view
Top surfaces are in the same plane.
Re-align the surfaces
as necessary
INCORRECT
Top surfaces are not
in the same plane.
Opposite beam
Top surfaces are not
in the same plane.
Engine does not
rest firmly.
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