O.S. Engines FS-120S-E User Manual
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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14-15
SAFETY INSTRUCTIONS AND
WARNINGS ABOUT YOUR O.S. ENGINE
INTRODUCTION, INSTALLING THE GLOWPLUG
BASIC ENGINE PARTS
RELOCATION OF CARBURETTOR CONTROLS
CHOKE VALVE
FUEL TANK, INSTALLATION
EXHAUST HEADER PIPE AND SILENCER,
THROTTLE LINKAGE,
NEEDLE-VALVE EXTENSION
PROPELLERS,
PROPELLER AND SPINNER ATTACHMENT
FUEL
GLOWPLUGS
CARBURETOR
CONTENTS
RUNNING-IN
IDLE 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
NOTE
STARTING
12-13
2-4
5
6
7
8
9-10
10
11
12
24
15
16-17
18
19
20-21
22
23
2
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 carbonmonoxide. Run your engine only in an open area.
Model engines generate considerable heat. Do
not touch any part of your engine until it has
coole d. Conta ct with the m uffler(sile ncer),
cylinder he ad 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.
Install 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 install 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
INSTALLING THE GLOW PLUG
Glow plug
Carefully insert plug, with washer,
fingertight only, before final tightening
with the correct size plug wrench.
Washer
The O.S. FS-120S-E is an aircooled, overhead-valve fourstroke-cycle engine for model aircraft use. It is produced
by the world' s pldest and largest model engine manufacturing company: a company which also pioneered the
quantity production at model four-stroke-cycle engines.
BASIC ENGINE PARTS
Rocker Cover
Cylinder Head
Push Rod Cover
Drive Hub
Propeller Washer
Propeller Nut
Lock Nut
Carburettor
Cover Plate
Crankcase
Beam Mount
Standard Accessories
Exhaust Header Pipe Assembly
Silencer Assembly
Glow Plug Type F
Please note that this engine is not supplied with any
tools (e.g. Allen keys, wrenches, etc.)
6
The needle-valve and throttle lever locations are
interchangeable by reversing the carburetor. This can be
done as follows:
Remove the carburetor carefully by unscrewing the two
screws which secure both carburetor and choke valve. (See
Photo 1.)
If the carburetor remains difficult to remove, slightly loosen the
two screws which secure the intake pipe to the cylinder head.
After reversing the carburetor, re-fit it to the intake pipe gently,
taking care not to damage the O-ring in the carburetor by
using foce.
RELOCATION OF CARBURETOR CONTROLS
Intake Pipe Retaining Screw
"O" Ring
Carburetor Retaining Screw
Choke lever
Set screw
Hexagon nut
Cap screw
Choke rubber pad
Photo 1
CHOKE VALVE
The FS-120S-E is equipped with a spring-loaded choke valve.
The choke valve operating lever can be located right or left by
transposing the hexagon nut and cap screw.
After mounting the engine in the model, secure the L-shaped
choke rod by tightening the set-screw.
If the rod supplied is too long, reduce it to the required lebgth.
If the rod length is more than 40mm (1 1/2 in.) its outer end
should be supported to avoid vibration.
7
Because the FS-120S-Epowerful, large-displacement, singlecylinder 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
The suggested fuel tank size is 400cc or 14 oz. This will give
approximately 10 minutes running time when some partthrottle operation is included. Locate the fuel tank so that the
centre line of the tank is 10 to 15mm below the centre line of
the needle-valve.
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)
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 alternative 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.
NOTE
If the model is left unattended with the fuel tank filled,
fuel may flow into the carburetor, causing it to "flood"
and making the engine difficult to start. Take appropriate
action to prevent this.
Centre line
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