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.

1

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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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3

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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4

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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5

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-Epowerful, 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

8



NEEDLE-VALVE EXTENSION

The needle-valve supplied with this engine is designed to
accept an extension so that, when the engine is enclosed in a
cowling, the needle-valve may be adjusted from the outside.
An L-shaped rod, of appropriate length, may be inserted in the
needle-valve knob center hole and secured by tightening the
set-screw with a 1.5mm Allen key.

THROTTLE LINKAGE

Before connecting the throttle to its servo, make sure that the
throttle arm and linkage safely clear any adjacent part of the
airframe structure, etc., as the throttle is opened and closed.
Connect the linkage so that the throttle is fully closed when
the transmitter throttle stick and its trim lever are at their
lowest settings and fully open when the throttle stick is in its
fully-open position..
Carefully align the appropriate holes in the throttle arm and
servo horn so that they move symmetrically and smoothly
through their full travel.

Install these in the following sequence.
Screw the header pipe into the cylinder head until it " bottoms
", then unscrew sufficiently to achieve the desired exhaust
angle and tighten the locknut securely with a 17mm wrench.
Screw the silencer onto the outer end of the header pipe and
tighten the other locknut.
The application of a heatproof silicone sealant to the threads of
the exhaust system is recommended to reduce the risk of joints
loosening and the leakage of exhaust gases and oil residue.

EXHAUST HEADER PIPE & SILENCER

Reminder:
Model engines generate considerable heat and contact
with the header pipe or silencer may result in a serious
burn.
If you need to tighten the silencer joints, which may
loosen when they are hot, use a thick folded cloth for
protection.

9

The choice of propeller depends on the design and weight of
the aircraft and on the type of flying in which you will be
engaged. Determine the best size and type after practical
experimentation.
As a starting point, refer to the props listed in the
accompanying table.
Slightly larger, or even slightly smaller, props than those shown
in the table may be used, but remember that propeller noise will
increase if blade tip velocity is raised, due to higher rpm or if a
larger-diameter / lower-pitch prop is used.

PROPELLERS

Type Size (DxP

)

Stunt planes

13x11-12, 14x10-11, 15x8, 16x6-7

15x8, 16x6-7, 18x5-6

Scale models

Make sure that the propeller is well balanced. An
unbalanced propeller and / or spinner can cause serious
vibration which may weaken parts of the airframe or
affect the safety of the radio-control system.
DO NOT forget the WARNINGS and NOTES on propeller
and spinner safety given on pages 2,3 and 4.

Warning:

PROPELLER & SPINNER ATTACHMENT

Ream the propeller shaft hole to 8.0mm bore with an
appropriate reamer, checking that the hole is exactly
centered.

Install the prop to the engine shaft, followed by the retaining
washer and prop nut and tighten firmly with a 17mm
wrench.

There is a risk, particularly
with powe rful four-stroke
engines, of the propeller flying
off if the prop nut loosens due
to detonation ("knocking") in
the combustion chamber when
the engine is operated too
lean, or under an excessively
heavy load.

Obviously, this can be very hazardous. To eliminate such
dangers, the O.S. Safety Locknut Assembly was devised.
Install this as follows:

Lock Nut

Propeller Washer

Propeller Nut

1.

2.

3.

Add the special tapered and slotted locknut and secure
with a 14mm wrench while holding the prop nut with the
17mm wrench.

10

FUEL

The FS-120S-E should be operated on a methanol based fuel
containing not less than 18% castor-oil, or a top quality
synthetic lubricant (or a mixture of both), plus a small
percentage (5-15%) of nitromethane for improved flexibility
and power. The carburettor is adjusted at the factory for a fuel
containing 20% lubricant and 10% nitromethane.
Some commercial fuels also contain coloring additives as an
aid to fuel level visibility. In some cases, these additives have
indicated slightly negative effects on performance. We would
suggest that you use such fuels only if you are satisfied that
they do not adversely affect running qualities when compared
with familiar standard fuels.
When changing to a fuel brand or formula that is different
from the one to which you are accustomed, it is a wise
precaution to temporarily revert to in-flight running-in
procedures, until you are sure that the engine is running
entirely satisfactorily.

Reminders:
AII 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.
Though not as volatile as gasoline, model engine fuel is
also highly inflammable.
Keep it away from an open flame, excessive heat, sources
of sparks, or anything else that might ignite it. Smoking is

firmly discouraged.

Since the FS-120S-E is intended to be started with an electric
starter, the addition of a spinner assembly for centering the
starter sleeve is desirable. Special propeller locknut sets are
available for use with spinners.
Use a good quality well balanced spinner, enclosing the
propeller boss. Make sure that it is of precision-made and
sturdy construction so that the spinner shell cannot loosen
when the starter is used.
Make sure the spinner notches do not interfere the propeller.
If they do, cut the notches to clear off.

11

GLOWPLUGS

The role of the glowplug

Glowplug life

Particularly in the case of very high performance engines,
glowplugs must be regarded as expendable items.

Install a plug suitable for the engine.

Use fuel containing a moderate percentage of nitromethane
unless more is essential for racing events.

Do not run the engine too lean and do not leave the battery
connected while adjusting the needle.

However, plug life can be extended and engine performance
maintained by careful use, i.e.:

With a glowplug engine, ignition is initiated by the application
of a 1.5-volt power source. When the battery is disconnected,
the heat retained within the combustion chamber remains
sufficient to keep the plug filament glowing, thereby continuing
to keep the engine running. Ignition timing is 'automatic' :
under reduced load, allowing higher rpm, the plug becomes
hotter and, appropriately, fires the fuel/air charge earlier;
conversely, at reduced rpm, the plug becomes cooler and
ignition is retarded.

Apart from when actually burned out, a plug may need to be
replaced because it no longer delivers its best performance,
such as when:

When to replace the glowplug

The FS-120S-E is supplied with an O.S. Type F glowplug,
specially designed for O.S. four-stroke engines.

Filament surface has roughened and turned white.

Filament coil has become distorted.

Foreign matter has adhered to filament or plug body has
corroded.

Engine tends to cut out when idling.

Starting qualities deteriorate.

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12

CARBURETTOR

The Needle Valve

This is used to establish the fuel/air mixture strength
required for full power when the throttle is fully open.

The Mixture Control Valve (Mixture Control Screw)

This is used to establish the mixture strength required for
steady idling and a smooth transition to medium speeds.
(The varying mixture strength required between part-throttle
and full-throttle running is automatically adjusted by coupled
movement of the throttle.)

The Throttle Stop Screw

For establishing the minimum idling speed.

The sequence in which these controls are adjusted is
explained in the succeeding sections, under Starting,
Running-in and Idling Adjustment.

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Three adjustable controls are provided on this carburetor.

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Needle Valve

Mixture Control Valve
(Mixture Control Screw)

Throttle Stop Screw

Rotor Guide Screw

Photo 2

Photo 3

STARTING

Be sure to use a high-torque electric starter.

Hand starting is very dangerous as this is a bug capacity
four stroke glow engine and sudden strong knocking may
occur with priming quantity, engine temperature, fuel used,
etc.

WARNING:

13

Use the choke valve only when the fuel does not comes to the
carburetor with above procedure.

Check that the current to the glowplug is switched off.

Check that the polarity of the starter battery leads rotates the
engine counter-clockwise when viewed from the front.

Open the needle-valve 2.5 turns when the muffler
pressurized is applied, or 3 turns when the muffler
pressurized is not applied from the fully closed position and
temporarily set the throttle in the fully open position.

Apply the starter and press the starter switch for 5-6
seconds, or until fuel is seen to emerge from the exhaust
outlet, indicating that the cylinder is now primed.

Energize the glowplug and apply the starter. If the starter
fails to rotate the engine completely, this may be due to the
cylinder being over-primed, or to the starter battery being
insufficiently charged.

1.

2.

3.

4.

5.

6.

Check these conditions and, instead of pressing the starter
button after applying the starter, have the starter spinning
before applying it to the engine, to give it a "running start".
When the engine starts, slowly open the throttle, leaving
the needle-valve at its rich starting setting to promote cool
running conditions.
However, if the engine slows down because the mixture is
excessively rich, the needle-valve may be closed a little to
speed it up until it runs evenly.

Now disconnect current to the glowplug and gradually close
the needle-valve so that revolutions are increased. Make
adjustments to the needle in small steps. Abrupt changes
at this stage are likely to cause the engine to stall. Restart
the engine by simply applying the starter with the glowplug
re-energized and the throttle at its starting setting.

7.

8.

Disconnect the glowplug battery.

Close the choke valve.

Turn the propeller counter-clockwise slowly by hand until
the fuel reaches the carburetor.

Release the choke valve.

CAUTION:

9.

Excess quantity of fuel in the engine makes the engine start
difficult and may result in an hydraulic lock that may
damage the engine.

Close the throttle-arm to within 15-20° of the fully closed
position and slowly turn the prop "backwards" (clockwise)
by hand approximately 1.5 turns until it is arrested by
compression.This is to enable the kinetic energy of the prop
to subsequently assist the starter through the compression
stroke to start the engine.

CAUTION:
Regard the choke valve as a supplementary device to draw
the fuel to the carburetor. Do not apply an electric starter
with the choke valve closed or turn the propeller too much,
which may result in an hydranlic lock that damage the
engine. Apply an electric starter only after making sure that
no extraordinary stiffness is telt when rotating a propeller.
Do not use the choke valve to stop the engine which also
causes an hydraulic lock and damage the engine. Be sure
to disconnect the glowplug battery when rotating a
propeller by hand which may cause a heavy insure with
sudden and strong knocking.

14

Start and adjust the engine as detailed in the starting
instructions.

Now open the throttle fully and run the engine for no more
than 5 seconds with the needle-valve tuned to produce near
maximum r.p.m., then, immediately, slow the engine down
again by opening the needle-valve approximately 0.5 turn.
The rich mixture, so induced, will cool the engine, at the
same time providing increased of lubrication.

Allow the engine to run like this for about 10 seconds, then
close the needle-valve again to speed it up to near
maximum rpm for another 5 seconds.

Repeat this process, alternately running the engine fast and
slow by means of the needle-valve, while keeping the
throttle fully open, then begin to extend the short periods of
high-speed operation until two full tanks of fuel have been
consumed.

Following the initial running-in session, check for any
looseness in the installation due to vibration, then allow the
engine a period of moderately rich operation in flight.

For the first flight, have the needle-valve set on the rich
side and adjust the throttle trim on the transmitter so that
the engine does not stop when the throttle is closed to the
idle setting.

WARNING:
When ground running the engine, avoid dusty or sandy
locations. If dust or grit is drawn into the engine, this can
have a ruinous effect, drastically shortening engine life in
a matter of minutes.

RUNNING-IN (continued)

1.

2.

3.

4.

5.

6.

With each successive flight, close the needle-valve very
slightly until, at the end of about 10 flights, the needle is set
for full power. Do not "over-lean" the mixture in an attempt
to extract more power.

If overheating should be suspected at any time during flight
(i.e.if the engine begins to "labor") reduce power by partially
closing the throttle and land the aircraft to enable the
needle-valve to be readjusted to a richer setting.

7.

8.

Note:
Remember that, when the engine is not yet fully run-in,
the carburettor cannot be expected to give its best
response in flight. Abrupt operation of the throttle, for
example, may cause the engine to stall. Therefore, at this
time ,the aircraft should, as far as is possible, be flown at
an altitude sufficient to enable an emergency landing to
be safely made if the engine stops.

RUNNING-IN ("Breaking-in")

For long life and peak performance, every engine needs
special treatment when new, known as "running-in" or
"breaking-in". This is a process during which the engine is
operated under strictly controlled conditions at the beginning
of its life, in order to avoid the risk of immediate damage to
certain components through becoming overheated or stressed
and to help working surfaces to become smoothed and
aligned for maximum mechanical efficiency thereafter.
With some engines, this can require a tediously protracted
period of bench running, but, as O.S. engines are
manufactured to fine tolerances and from the finest quality
materials, a relatively brief running-in period is sufficient and
can be completed with the engine installed in the aircraft.
The recommended procedure is as follows :

15

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Start the engine, open the throttle fully and set the needle­valve slightly rich (30-45°) from the highest r.p.m. setting.

Close the throttle to the idle position. Allow the engine to
idle for about 5 seconds, then reopen the throttle. The
engine should accelerate smoothly back to full speed.

If, instead, the engine responds sluggishly and emits an
excess of white smoke from the exhaust, the idle mixture is
too rich. Turn the mixture control screw approx. 45°
clockwise to lean the idling mixture.

On the other hand, if the engine hesitates before picking up
speed or even ceases firing completely, the idle mixture is
likely to be too lean. Turn the mixture control valve 90°
counter-clockwise to substantially enrich the mixture, then
back again 45° clockwise.

IDLE MIXTURE ADJUSTMENT

In paragraphs 3 and 4 above, the 45° total movements are,
of course, approximate. It will be necessary to fine-tune the
mixture control screw 10-15° at a time to reach the best
setting for optimum throttle response.

Continue re-checking the idle mixture setting until the
engine responds smoothly and positively to operation of
the throttle at all times.

In the course of making carburetor adjustments, it is just
possible that the mixture control valve may be inadvertently
screwed in or out too far and thereby moved beyond its
effective adjustment range.

Realignment of Mixture Control Valve

1.

2.

3.

4.

5.

6.

Once the engine has demonstrated that it can be safely
operated at full power, the carburettor can be adjusted for
optimum throttle response, following the instructions given
in the next section.

9.
The basic (factory) setting is as shown in the main sketch, i.e.
with the shoulder portion 'A' exactly at a tangent to the throttle
rotor hole. To return the mixture control valve to its original
position, first screw in the mixture control valve, while looking
into the rotor hole. Then graduakky unscrew the mixture
control valve until 'A' is precisely tangential to the rotor hole
(i.e. so that 'A' and 'B' are superimposed) as in the main
sketch.

Its basic setting can be reestablished as follows:

Mixture control valve

Nozzle

Throttle rotor hole

CARE & MAINTENANCE (laying up)

The fuel pump assembly, carburettor/pressure-regulator and
silicone tubing must be cleansed separately in methanol or
glow fuel. On no account must they come into contact with
kerosene. Before completely reassembling the engine, make
sure that no kerosene remains inside that could find its way
into the pump unit, carburettor, etc.Inject, sparingly,
preserving oils, rust inhibitors, etc.

Debris tends to
accumulate in
this area

unless approved for silicone­rubber products. An appropriate
alternative here may be one of the
high-quality synthetic lubricating
oils. Finally, seal the engine in a
heavy polyethylene bag until
required for reinstalling in the
airframe.

16

Note:
Valve clearances of all O.S. four-stroke-cycle engines
must be checked and reset ONLY WHEN THE ENGINE IS
COLD. Procedure is as follows.

Remove the cover from the rocker-box on top of the
cylinder-head, using the correct size Allen hex key.

1.

（Ⅰ）

Turn the propeller counter-clockwise until compression is
first felt, then turn it a futher quarter revolution. At this point,
both valves should be closed. (If the prop driver ('drive
hub') of your engine is engraved with a letter 'T', this mark
should now be at the top.)

2.

The standard valve clearance, on both inlet and exhaust
valves, is between 0.04mm and 0.10mm(0.0015-0.004
inch), measured between valve stem and rocker arm. Use
the 0.04mm and 0.10mm feeler gauges to check
clearances. (See Fig.1.)

3.

Note:
If the gap is found to be less than 0.04mm, it is not
necessary to readjust the clearance if the engine has
good compression and starts easily.

Equally, if the gap exceeds 0.10mm but is not more than

0.14mm (i.e. the thickness of both feeler gauges inserted
together), it is not essential to readjust the clearance if
the engine runs satisfactorily.

Fig.1

（Ⅱ）

If a clearance is found to be outside either of these limits,
it should be reset as follows.

Carefully loosen the locknut
on rocker-arm 1/4-1/2 turn
with 5mm wrench.
(Fig.2.)

1.

Locknut

Wrench

Loosen approx.
1/4 to 1/2 turn.

Fig.2

0.04mm
Feeler Gauge

Rocker Arm

Valve

• Feeler gauge 0.04mm

Valve clearances are correctly set before any O.S. engine
leaves the factory and, in normal use, will seldom require
abjustment. However, if,after a very considerable amount of
running time has been amassed, a loss of power is detected,
or if the engine has been disassembled for repair, these
clearances should be checked and reset as necessary. For this
purpose, a valve adjusting kit comprising two feeler gauges, a
5mm ring spanner (box wrench) and a 1.5mm Allen key, is
available as an optional extra.

VALVE ADJUSTING

The kit comes in a plastic case and includes:
(Code No.72200060)

• Feeler gauge 0.1mm

• Hex. key 1.5mm

• Wrench 5mm

17

Re-tighten locknut while
holding adjusting screw
stationary. (Fig.5.)

4.

Hold at the
screw head.

Fig.5

Tighten
Locknut.

Remove 0.04mm feeler,
rotate prop through two
revolutions and recheck
gap.

5.

If clearance is correct, loosen the locknut on the other
rocker-arm and repeat steps 1 to 5 above. Finally, replace
rocker box cover.

6.

Remember:
Excessive valve clearance will cause loss of power, due
to valve (s) not opening sufficiently. On the other hand, a
total loss of clearance may cause difficult starting due to
valves not closing properly, resulting in loss of
compression.

2.

3.

Turn adjusting-screw approx.
1/2 turn counter-clockwise to
open gap, using appropriate
tool -i.e. Allen hex key.
(Fig.3.)

Fig.3

Fig.4

Adjusting
Screw

Turn approx.
1/2 turn.

Allen Key

Insert 0.04mm feeler gauge
between valve stem and
rocker-arm and gently turn
adjusting screw clockwise
until it stops.(Fig.4.)

0.04mm Feeler
Gauge

Turn with fingers
until it stops.

18

CARE AND MAINTENANCE

To ensure that you obtain long life and peak performance from your
engine, observe the following.

Avoid running the engine under dusty conditions.
If necessary, lay a sheet of plywood or hard-board in front
and under the nose of the model when starting the engine.

Foreign matter in the fuel can cause the carburetor jet to be
partially clogged.

1.

2.

Therefore:

rinse out the fuel tank with methanol or fuel before installing
it.

Install a fuel filter in the fuel line between tank and
carburettor.

Install a fuel filter in the outlet of your squeeze bottle, or to
the pump inlet if you use a manual or electric pump.

do not leave your fuel container open needlessly.

check filters periodically and clean them when necessary.

Clean the exterior of the engine with a clean cotton cloth.If
this is not done, oil and dirt will burn onto the outside of the
engine each time it is run and the engine will soon become
discolored.

If the engine is not in use for a while (more than two
months) remove the glowplug and rinse out the interior with
kerosene (not gasoline), by rotating the crankshaft. Shake
out residue, then inject light machine-oil through the plug
hole and carburetor intake, again rotating the shaft to
distribute the protective oil to all working parts.
Gasoline, thinner, kerosene and light machine oil cause
swelling and deterioration of plastic parts, "O" rings and
fuel tubing. Use methanol for cleaning these engines.

Avoid unnecessary dismantling of your engine.

3.

4.

5.

6.

Do not leave raw fuel in the engine at the conclusion of a
flying session: it may cause corrosion. The best practice is
to disconnect the fuel line from the carburetor while the
engine is running. Remaining fuel in the tank should also be
drained off.

19

RADIAL MOTOR MOUNT

O.S.GLOW PLUG TYPE F

EX EXHAUST HEADER PIPES

FLEXIBLE EXHAUST PIPES

BOOSTER TERMINAL KIT

BOOSTER CABLE SET

LONG SOCKET WRENCH
WITH PLUG GRIP

Inside

Outside

O.S. GENUINE PARTS & ACCESSORIES

(71904200)

(71615009)

(72200130)

(72200110)

72108201
72108211

A
B

120
240

(72109200)

(72109300)

(71521000)

(72200060)

M2.6x7

(79871020)

M2.6x15

(79871050)

M3.5x12

(79871080)

M3.5x20

(79871100)

Code No.

Type

Length (mm)

VALVE ADJUSTING TOOL KIT

LOCK WASHER

(10sets)

BLIND NUTS

(10pcs.)

CAP SCREW SET

(10pcs.)

(71531000)

(72403050)

(71531010)

NON-BUBBLE WEIGHT

SUPER FILTER (L

)

The specifications are subject to alteration for improvement without notice.

NON-BUBBLE WEIGHT

S

(79870040)

(55500003)

M4

M4

(79870050)

M5

(55500004)

M5

(45910300)

(45910200)

PROPELLER
LOCKNUT SET FOR SPINNER

5/16"-M5

5/16"-M4

20

EXPLODED VIEW

Type of screw

C...Cap Screw M...Oval Fillister-Head Screw

F...Flat Head Screw N...Round Head Screw S...Set Screw

1

2

3

3-2

3-1

4

4-1

4-2

5

5-4

5-3

5-2

8

5-1

6-4

6-3

6-2

6

6-1

7

9

10

11

12

13

14

15

16

17

21

27

28

28-2

28-1

28-2

29

18

19

20

22

23

32-1

32

33

31

30

24

26

25

24

C.M3X8

C.M4.0X10

C.M2.6X15

C.M3.5X20

C.M2.6X7

(C.M3.5X12)

21

PARTS LIST

The specifications are subject to alteration for improvement without notice.

1
2

3
3-1
3-2

4
4-1
4-2

5
5-1
5-2
5-3
5-4

6
6-1
6-2
6-3
6-4

7

8

9

10
11
12
13
14
15
16
17
18

45507010

45503100

45505010

29017004

45506010

45503210

45503400

45484000

45581000

45569420

45504021

45504111

45560410

45560310

45560220

45560140

45560040

45560410

45560310

45560210

45560130

45560030

45061202

45561110

45561010

45761600

45561410

45561401

45504210

45513010

45566000

45501110

45562010

45231100

22681953

45501020

45514010

45530010

45502040

45510100

45508200

45508030

45520000

29031009

45564000

45566310

45566111

45566101

19
20
21
22
23
24
25
26
27

28
28-1
28-2

29

30

31

32
32-1

33

71615009

45526400

45526300

45526200

45526100

45526010

45525011

45525001

Description

Code No.

No.

Description

Code No.

No.

Screw Set
Rocker Cover
Rocker Support Assembly
Rocker Support
Rocker Arm Retainer(2pcs.)
Rocker Arm Assembly(1pair)
Rocker Arm(1pc.)
Tappet Adjusting Screw
Intake Valve Assembly(1pair)
Intake Valve(1pc.)
Valve Spring(1pc.)
Valve Spring Retainer(1pc.)
Split Cotter(2ps./1pair)
Exhaust Valve Assembly(1pair)
Exhaust Valve(1pc.)
Valve Spring(1pc.)
Valve Spring Retainer(1pc.)
Split Cotter(2ps./1pair)
Cylinder Head
Cylinder Head (W/Gasket and Valve Assembly)
Intake Pipe Assembly
Carburetor Complete
Choke Valve Assembly
Piston Ring
Piston
Piston Pin
Piston Pin Retainer
Connecting Rod
Cylinder Liner
Cover Plate

Crankshaft
Crankshaft Ball Bearing(Rear)
Gasket Set
Crankcase
Breather Nipple
Camshaft Ball Bearing (1pcs.)
Camshaft
Cam Cover
Push Rod(2pcs.)
Push Rod Cover Assembly(2pcs.)
Push Rod Cover(1pcs.)
Push Rod Cover "O" Ring(2pcs.)
Cam Follower(2pcs.)
Crankshaft Ball Bearing(Front)
Thrust Washer
Drive Hub
Woodruff Key
Lock Nut Set
Silencer Assembly
Silencer Body
Exhaust Header Pipe Assembly
Exhaust Header Pipe
Exhaust Joint
Exhaust Joint Nut
Header Pipe Nut
Glow Plug Type F

22

The specifications are subject to alteration for improvement without notice.

CARBURETOR EXPLODED VIEWS
& PARTS LIST

1

1-1

2

3

3-1

4

5

6

7

8

10

11

9

9-1

9-4

9-5

9-2

9-3

S.3X3

N.+M3X22

S.3X3

45581700

45581820

26711305

27381940

26381501

24981837

45581970

27481900

22681953

22381300

45515000

45581100

26781506

24881824

26781309

45581200

26381501

24981405

1

1-1

2
3

3-1

4
5
6
7
8

9
9-1
9-2
9-3
9-4
9-5

10
11

Type of screw

C...Cap Screw M...Oval Fillister-Head Screw
F...Flat Head Screw N...Round Head Screw S...Set Screw

Description

Code No.

No.

Needle Valve Assembly

Needle

"O" Ring (2pcs.)

Set Screw

Needle Valve Holder Assembly

Ratchet Spring

Carburetor Body

Rotor Guide Screw

Fuel Inlet

Mixture Control Valve Assembly

Carburetor Retaining Screw (2pcs.)

Throttle Lever Assembly

Set Screw

Carburetor Rotor

"O" Ring (2pcs.)

Rotor Spring

Carburetor Rubber Gasket
Throttle Stop Screw

23

Dimensions(mm)

Specifications

THREE VIEW DRAWING

Displacement
Bore
Stroke
Practical R.P.M.
Output
Weight

19.96cc / 1.218cu.in.

30.4mm / 1.197in.

27.5mm / 1.083in.

2.000-11.000r.p.m.

1.9ps / 1.93hp / 11.000r.p.m.
864g / 30.5oz.

24

MEMO

C

Copyright 2003 by O.S.Engines Mfg. Co., Ltd. All rights reserved. Printed in Japan.

TEL. [phone]

FAX. [phone]

6-15 3-Chome Imagawa Higashisumiyoshi-ku
Osaka 546-0003, Japan

URL : http://www.os-engines.co.jp

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