O.S. Engines FS-40S User Manual

It is of vital importance, before attempting to
operate your engine, to read the general

'SAFETY INSTRUCTIONS AND WARNINGS'

section on pages 2-6 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.

CONTENTS

SAFETY INSTRUCTIONS AND WARNINGS
ABOUT YOUR O.S. ENGINE

INTRODUCTION,BASIC ENGINE PARTS
INSTALLATION
INSTALLATION OF CHOKE ROD, NEEDLE VALVE

EXTENSION, EXHAUST PIPE ADJUSTMENT(FS-26S)
SILENCER,

LINKAGE OF THROTTLE LEVER
BEFORE STARTING
FUEL AND PRESSURE LINES

ADVICE ON SELECTION OF FUEL,
GLOEPLUG & PROPELLER

STARTING THE ENGINE

2~6

11~12

13~14

~

15

22

~

25~26
27~29

32~35

21
23
24

30
31

36
37
38

RUNNING -IN
CARBURETOR

7

CARBURETOR AIR-BLEED ADJUSTMENT

8

TROUBLE SHOOTING WHEN THE
ENGINE FAILS TO START

9

VAL VE ADJUSTING

10

12

21

CARE AND MAINTENANCE
THREE VIEW DRAWING
ENGINE EXPLODED VIEW
CARBURETOR EXPLODED VIEW

& PARTS LIST
GENUINE PARTS & ACCESSORIES
MEMO

1

SAFETY INSTRUCTIONS AND WARNINGS ABOUT YOUR O.S. ENGINE

Remember that your engine is not a "toy", but a highly efficient internal­combustion machine whose power is capable of harming you, or others, if it is
misused.
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.

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

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.

2

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 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 cooled. Contact with
the muffler (silencer),
cylinder head or exhaust
header pipe, in particular,
may result in a serious burn.

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.

If you remove the glowplug from the engine

•

and check its condition by connecting the
battery leads to it, do not hold the plug with
bare fingers.Use an appropriate tool or a
folded piece of cloth.

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.

4

NOTES

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. If a
safety locknut assembly is provided with
your engine, 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.

Preferably, use an electric starter. The

•

wearing of safety glasses is also strongly
recommended.

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.

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.

5

NOTES

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!

6

INTRODUCTION

The FS Series engines are up-to-date
overhead-valve four-stroke-cycle engines
for model aircraft use and are the outcome of
a long period of technical development. The
FS Series engines are produced by the
world's oldest and largest model engine
manufacturing company; a company which
also pioneered the quantity production of
model four-cycle engines.

Accessories

FS-26S

•Silencer Body

•Choke rod

•Silicone tubing

INSTALLING THE GLOWPLUG

Install washer on glowplug and
insert carefully into cylinder­head, making sure that it is not
cross-threaded before tightening
firmly.

FS-40S

•Silencer Assembly

•Choke rod

•Silicone tubing

Glow plug

Washer

BASIC ENGINE PARTS

Glow plug

Silencer

Carburetor

Fuel inlet

Choke valve

Breather nipple

7

Rocker Cover

Drive Hub

Crankcase

Cover plate

Exhaust pipe

Propeller nut

Propeller
Washer

INSTALLATION

Installation in the model

A typical method of beam
mounting is shown below,left.

At least 12mm
(1/2") for FS-26S

At least
15mm(19/32") for FS-40S

Make sure that the mounting beams are parallel
and that their top surfaces are in the same plane.

CORRECT

O.S. radial motor mount
(Available as an optional extra part.
See parts list)

Rigid hardwood
(e.g. maple)

INCORRECT

How to fasten the mounting screws.

3mm steel nuts
for FS-26S

3.5mm steel nuts
for FS-40S
Spring washer or
lock washer

3mm steel screw
for FS-26S

3.5mm steel screw
for FS-40S

Tighten second nut firmly
down onto first nut.

Tighten this nut first.

Steel washer

Hardwood mounting beams

3mm steel Allen screw
for FS-26S

3.5mm steel Allen screw
for FS-40S

Spring washer

Hardwood such as
cherry or maple.

Front view

Top surfaces are in
the same plane.

Side view

Top surfaces are not
in the same plane.

Re-align the surfaces
as necessary

Opposite beam

Top surfaces
are not in the
same plane.

Engine does
not rest firmly.

O.S. radial motor mount
(cast aluminum)

8

INSTALLATION OF CHOKE ROD

The FS Series engines are equipped with self­reopening choke valves.
Cut the choke rod (supplied) to the length indicated,
then secire the rod by tightening the set screw, using

1.5mm Allen wrench (supplied), after installing the
engine.

Releasing the
choke rod allows
the choke valve

approx.
7mm

to open.

Frame sides
of fuselage

approx.
2mm

Choke rod

Choke rod

1.5mm
Allen key

Set-screw

NEEDLE VALVE EXTENSION

The needle-valve supplied with this engine is
designed to incorporate an extension so that, when
the engine is enclosed within the fuselage, the
needle-valve may be adjusted from the outside. Cut
the L-shaped rod supplied to the required length,
insert it into needle's centre hole and secure it by
tightening the set-screw in the needle-valve knob with

1.5mm. Allen key supplied.

1.5mm Allen key

Set-screw

EXHAUST PIPE ADJUSTMENT(FS-26S)

The direction of the exhaust pipe may be altered in
accordance with individual installation requirements.
The angle is easily adjusted by loosening the nut that
secures the exhaust pipe to the culinder head. Use
the 10mm spanner supplied. Recheck the tightness of
the nut after the engine has been run, but take care
not to touch the exhaust-pipe as it becomes very hot.

9

SILENCER

The FS-26S and FS-40S are supplied with silencers
as standard equipment.

Installation for FS-26S

Slide the silencer over the exhaust pipe, and secure it
with two set-screwssupplied with the silencer. Re­check tightness of screws when engine is hot.

Installation for FS-40S

Screw the exhaust header pipe into the exhaust port
until it "bottoms", then unscrew it just sufficiently to
achieve the required exhaust outlet angle. Secure the
pipe in this position by tightening the locknut firmly
against the cylinder head with the wrench supplied.
Then, screw the silencer onto the end of the header
pipe and tighten locknut firmly. Re-check tightness of
locknuts when engine is hot.

LINKAGE OF THROTTLE LEVER

First, ensure that the throttle rotor is fully closed when
the throttle-lever is in the closed position. Adjust rotor
stop screw if necessary. Then couple the lever to the
throttle-servo so that the rotor is fully closed when the
transmitter throttle stick and trim lever are in the fully
retarded position.

BEFORE STARTING

Tools, accessories, etc.

The following items are necessary for operating the
engine.

1 Fuel

Model glowplug engine fuel of good quality, preferably
containing a small percentage of nitromethane. (See
"Advice on selection of fuel, glowplug and propeller")

2 Glowplug

O.S. Type F glowplug is installed in the engine.

3 Propeller

Suggested propellers are shown in the ADVICE ON
SELECTION OF FUEL & PROPELLER section.

10

4 Glowplug battery

The power source for heating the glowplug may be
either a large heavy-duty 1.5volt dry cell, or preferably,
a 2-volt rechargeable lead-acid cell (accumulator).

If a 2-volt cell is employed,
use a resistance wire, as
shown, to reduce applied
voltage, otherwise element

1.5 volt heavy-duty
dry battery

or 2 volt rechargeable
lead-acid cell (at least 5Ah)

will overheat and burn out.

Warning (Very hot)

Never touch the nichrome wire while the battery is
connected.

Resistance coil
(nichrome wire)

Battery leads

Adjust applied voltage by changing the position of clip on
resistance coil until glowplug element is glowing bright red.

Raise

voltage to

increase

brightness.

Lower voltage to

reduce brightness.

5 Plug wrench

Used for tightening glowplug.
The O.S. long plug wrench is available
as an optional accessory.

6 Battery leads

These are used to conduct current from the battery to
the glowplug. Basically, two leads, with clips, are
required, but, for greater conve­nience, twin leads with special
glowplug connectors, as shown on
the right, are commercially available.

Battery leads

7 Fuel tank

For installation in the model, a 120cc(4.2oz.)
for FS-26S, a 150cc(5oz.) for FS-40S tank is
suggested.

8 Fuel bottle or pump

For filling the fuel tank, a simple,

Fuel bulb

Fuel pumps

polyethylene "squeeze" bottle, with a
suitable spout,is all that is required.
Alternatively, one of the purpose-made
manual or electric fuel pumps may be
used to transfer fuel directly from your
fuel container to the fuel tank.

11

For tightening
glowplug

Manual

Electric

9 Electric starter and starter battery

An electric starter is recommended
for starting.

10 Fuel can filter

Install a filter in the outlet line of your
refuelling container to prevent entry of
foreign matter into the fuel tank. (Refer to
of STARTING THE ENGINE section.)

3

11 Silicone tubing

Fuel Can Filter

This is required for the connection
between the fuel tank and engine.

FUEL AND PRESSURE LINES

Connect suitable lengths of silicone tubing, as
illustrated, after installing the engine.

Attention to tank height

Muffler to tank pressure line

Fuel level

Note: When cutting silicone tubing···

Silicone tubing

Do not use wire cutters

Use knife or razor blade

*If you should need to clean the silicone tubing, use methanol
or glow-fuel, not gasoline or kerosene.

or pliers.

Silencer (muffler) pressurized fuel system

To reduce variation in fuel "head" and ensure steady
fuel delivery at the carburettor, it is advisable to employ
a silencer (muffler) pressurized fuel system, i.e. to use
the silencer outlet nipple to pressurize the fuel tank as
shown at left.

Locate the fuel tank so the top of the tank is
5-10mm(1/4-3/8") above the level of theneedle-valve.

5-10mm

12

ADVICE ON SELECTION OF FUEL, GLOWPLUG & PROPELLER

Fuel

Use a good quality commercial fuel or one of the
blends shown in the table. Fuel "A" is suitable for
running-in and ordinary use. Fuel "B" is for use
when more power is required and for improved
flexibility. Note that even a small quantity of
nitromethane (3-5%) will improve flexibility,
making the needle-valve adjustment less critical
and improving throttle response. Use only
materials of the highest purity. Synthetic oils are
permissible but are less tolerant of a "lean run"
than castor-oil. If, therefore, a synthetic lubricant
is used in the fuel, readjust the needle-valve to
a slightly richer setting, as a safety measure, in
case the fuel/air mixture becomes too lean
through maneuvers in flight. higher nitro fuel is
used, the engine should be checked out to make
sure that it is sufficiently run-in to operate on that
particular fuel without overheating. Do not use

Methanol
Castor Oil
Nitromethane

Reminder!

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 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.

PROPELLER

Suggested propeller sizes are given in the table. As
the ideal propeller diameter, pitch and blade area vary
according to the size, weight and type of model, final
propeller selection will require in flight
experimentation.

A

75%
20%

5%

fuels containing less than 18% lubricant.

13

B

65%
20%
15%

Reminder!

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.

Sport & Aerobatic

FS-26S

FS-40S

GLOWPLUG

The FS-26S and FS-40S are supplied with an O.S.
Type F glowplug, specially designed for O.S. four­stroke engines.

9x6~7

10x7

~

7.5,11x6

9x7(3blade

)

Trainer & Sport

9x6

~

7,10x6,10.5x6

8x6(3blade
10x7,10.5x6,11x7
12x5

)

~

6,10x7(3blade

)

The role of the glowplug

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 become cooler and
ignition is retarded.

Glowplug life

Particularly in the case of very high performance
engines,

glowplugs must be regarded as expendable
However, plug life can be extended and engine
performance maintained by careful use, i.e.:

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.

When to replace the glowplug

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

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.

•

14

STARTING THE ENGINE

Preparations

1 Installing the glowplug

Install the washer on the
glowplug and screw carefully
into cylinder-head, making sure
that it is not cross-threaded
before tightening firmly.

2 Installing the propeller

There is a risk, particularly with four-stroke engines, of
the propeller flying off if the propeller nut loosens due
to detonation or "knocking" when the engine is run too
lean or under too heavy a load. To prevent this from
happening even if the propeller itself should slip or
loosen, it is recommended to use the special Propeller
Locknut Set (optional extra) with the FS-40S.

Wrench

Glow plug

Washer

Tighten the propeller nut
firmly so that compression
is first felt around this
position(i.e. with blades
horizontall) when turning
the propeller in the
direction of arrow.

3 Filling the fuel tank

Re-connect fuel line to
engine after tank is
filled.

Disconnect
fuel line from
the fuel inlet,
and connect
it to the
tubing from
the fuel
pump.

15

Fuel pump

Use a fuel can filter
(e.g. O.S. Super Filter).

Do not let dirt or
dust enter fuel can.

Fuel (model
glow-plug
engine fuel)

Starting

4 Opening and closing of the needle-valve

Turn needle-valve clockwise to close (for
leaner mixture).
Turn needle-valve counter-clockwise to
open (for richer mixture).

5 Setting the needle-valve

Turn the needle-valve in the direction
of arrow slowly, without forcing, until it
stops.

The position where the needle-valve
stops is the fully closed position. It may
be convenient to remember the position
of the mark or set-screw at this time.

Turn the needle-valve in the direction
of arrow from the closed position.

6 Open the throttle fully

FS-26S (3 to 3-1/2 turns)
FS-40S (2-1/2 to 3 turns)

Fully closed position

Fully opened position

Open

Close

Throttle

Close

Set-screw

Open

7 Priming

Fuel will flow from tank to
carburettor as propeller is
turned.

Turn the propeller
four revolutions
while watching
fuel line.

Turn the propeller 3
to 4 turns counter­clockwise smartly
by finger in the
direction of arrow.
Turn approx.
10 turns when the
engine is cold.

16

Close the air intake
by operating the
choke control.

Hold model securely when starting

8

Glowplug battery.
Place as far to the
rear as possible.

Assistant should hold
the model so that it
cannot move forward
when the engine starts.

10

Heat glowplug

Starting battery

Starter

Be careful not
to be hit by propeller!

9 Setting the throttle

Fully closed
position

Set at this Position.

Fully opened
position

Assistant

Connect battery leads as shown
(polarity is immaterial.)

11

Apply electric starter

17

Check that the throttle is one-third open from the fully
closed position. Bring the starter into contact with the
spinner nut or spinner and depress the starter switch
for one or two seconds. Repeat if necessary. When
the engine fires, withdraw the starter immediately.

Attention: Never place your finger over the
carburettor intake when applying the starter. Such an
action will cause an excess quantity of fuel to be
drawn into the cylinder and result in hydraulic lock
that may damage the engine.

12

Engine starts

BEWARE of
the rotating
propeller.

In the interests of safety, keep your face and other parts of the
body away from the vicinity of the propeller.

13

Needle-valve adjustment(1)

Slowly advance throttle to its
fully open position, then
gradually close the needle­valve until the exhaust sound
changes pitch.

Listen to the sound
carefully.

Close the needle-valve gradually until a
high-pitched exhaust note begins to be
superimposed on the lower-pitched
sound.

14

Disconnect battery leads

Disconnect the battery leads
from the engine with care so
that the plug clip does not touch
the rotating pro-peller.

If the engine stops when battery
leads are disconnected, close
the needle-valve a little (approx.
45˚) further, and restart the
engine.

18

15

Needle-valve adjustment(2)

As the needle-valve is closed beyond the initial readjustment,
the rpm of the engine will be increased and a continuous high­pitched exhaust note, only, will be heard.

Key to the needle-valve
adjustment.
(Turn 15-30˚ at a time.)

Turn the needle-valve 15-30˚ in the direction of arrow, and wait
momentarily for the change of r.p.m.
After the rpm of the engine increases, turn the needle-valve
another 10-15˚ and wait for the next change of r.p.m.

As the speed of the engine does not instantly change with
needle-valve readjustment, small movements, with pauses
between, are necessary to arrive at the optimum setting.

16

Needle-valve adjustment(Summary)

Practical best(optimum) needle-valve setting

Maximum rpm setting("Lean").

20~30°

"Rich" needle-valve
setting when starting

t

t

e

the engine.

r

d

a

t

o

s

t

.

s

e

n

s

o

i

a

t

e

u

l

r

o

c

v

e

e

d

R

o

t

e

E

n

i

n

g

s

s

p

t

o

Disconnect battery leads from
glowplug at about this point.

The engine may stop if the battery leads
are disconnected from the glowplug while
the engine is running rich.

NOTE: The above sketch is for reference purposes only.

Actual needle positions may differ from those shown.

19

On starting from cold, with the needle-valve
set at the rich starting position:

a good deal of white smoke is emitted.

As the needle-valve is closed and the r.p.m. increases

Exhaust smoke will be less dense and
grey in color.

Further needle-valve closure:

revolutions will increase and exhaust
smoke will be reduced.

Finally:

maximum rpm is reached and will fall off
(or engine will stop) if needle -valve is closed
any further. Exhaust gas will be very light.

Now, re-open needle-valve 20-30

This will produce the practical best
(i.e. optimum)
(lower than maximum rpm).
A light grey exhaust emission may be observed.

Take note of this position of the needle-valve.

rpm setting

°

Subsequent starting procedure

Once the optimum needle-valve setting has been
established (see "Needle-valve adjustment­Summary") the procedure for starting is simplified as
follows:

1) Open the needle-valve one half-turn (180˚) from
the optimum setting.

2) Open the throttle fully, place your finger over the
carburettor intake and rotate the propeller through
two revolutions to prime the engine.

3) Set the throttle one-third open from the fully closed
position, energize the glowplug and apply the
starter. When the engine starts, re-open the
throttle and re-adjust the needle-valve to the
optimum setting.

Note: When re-starting the engine on the same
day, provided that atmospheric conditions have
not changed significantly, it may be practicable to
re-start the engine on its optimum (running)
setting. Also, if the engine is being re-started
immediately after a run (i.e.hot), priming should
not be necessary.

16

20

17

How to stop the engine

Close the throttle to reduce to the lowest possible r.p.m.

Close

With the transmitter throttle trim lever fully retarded, adjust the
throttle servo linkage so that the throttle rotor is fully closed
(i.e.engine stopped) when the stick is fully retarded.

RUNNING-IN ("Breaking-in")

All internal-combustion engines benefit, to some
degree, from extra care when they are run for the first
few times - known as running-in or breaking-in. This is
because the working parts of a new engine take a little
time to settle down after being subjected to high
temperatures and stresses. However, because O.S.
engines are made with the aid of the finest modern
precision machinery and from the best and most suitable
materials, only a very short and simple running-in
procedure is required and can be carried out with the
engine installed in the model.The process is as follows:

1) Start the engine and, with the throttle fully open,

open the needle-valve an extra half turn (180˚)
from the optimum setting. This will produce a rich
mixture that will result in cooler running. Allow the
engine to run out a full tank on the ground. (Avoid
dusty surroundings.)

2) Now fly the model with the needle-valve re-set 20-

30 degrees open from the optimum setting ( i.e.
40-60˚ from the highest rpm setting).

3) Close the needle-valve very slightly on successive

flights so that the engine is running on its optimum
needle setting at the fifth or sixth flight.

21

CARBURETTOR

These engines are equipped with a throttle type car­burettor which provides a wide range of engine speed
control. With the throttle lever linked to a suitable
servo in the model, movement of the throttle control
on the transmitter will enable engine to be varied,
proportionally, from idling speed to full power.
The carburettor of your engine has been factory set
for the approximate best results and no adjustment
(except to the needle-valve) should be required
provided that the fuel tank is correctly located, as
previously described. After the engine has been run­in, check the operation of the throttle according to the
following chart. Re-adjust the controls only when
necessary.

22

Re-set the idling position at
a little higher r.p.m.

Start the engine.

Make sure that the throttle is
fully open.

Adjust the neede-valve.

Close the throttle gradually.

Find the idling position.

Fix the idling position.

Open the throttle fully.

°

20-30

open from maximum

r.p.m. setting.

The position where the lowest
possible r.p.m. ,with steady
running, is obtained.

Set the throttle opening by
means of the throttle trim on
the transmitter so that the lowest
practical speed, without risk of
the engine stopping,is obtained.

23

Engine stops.

Engine stops.

Engine stops.

Refer to the CARBURETTOR
AIR-BLEED ADJUSTMENT
section on page 24.

Does the engine
regain full power?

Continue running at high speed
for 10 seconds.

Close the throttle.

Run at idling speed for 5 seconds.

Does the engine stop?

Apply full throttle.

Does the engine
regain full power
immediately?

OK

Yes.

No.

Yes.

CARBURETTOR AIR-BLEED ADJUSTMENT

Pre-Flight Check

Start engine and adjust needle­valve as previously described.

Close the throttle gradually.

Find the idling position.

approx.
15

Repeat the procedure while opening and closing

the throttle until the best result is obtained.

Hold the model.

Hold model level, then slowly raise its nose.

If rpm increases.

˚

If engine runs unevenly or stops.

24

Stop the engine.

Note: Stop engine by
pinching fuel line
Do not touch
needle-valve.

These adjustments can be
made without stopping
the engine.
However, it is advisable for
beginners to stop the engine
for safety reasons.

Open air-bleed
screw.

Half turn at a
time.

Immediately point
nose down, so that
engine runs steadily
again.

Attention: Do not leave the glowplug connected to the battery

while adjusting the carburettor throttle.

approx.
15

˚

Stop the engine.

Close air-bleed
screw.

Half turn at a
time.

TROUBLE SHOOTING WHEN THE ENGINE FAILS TO START

Four key points

For quick, reliable starting, the following four conditions are required.

1 Good compression. 2 Adequate "glow" at glowplug. 3 Correct mixture.
4 Sufficient electric starter rotating speed.

If the engine fails to start, or does not keep running after being started, check symptoms against the
following chart and take necessary corrective action.
Note: The most common causes of trouble are marked with three asterisks, the less common problems
with one or two asterisks.

Symptom

Engine fails
to fire.

Factor

1

2

3

Cause

★

Sluggish rotation

Glowplug battery

★★

discharged.

Glowplug element is

★

burned out
Something wrong with

★

battery leads.
Engine "flooded" due to

★★

excessive priming.

Insufficient priming.

★

......

......

.....

....

....

.....

Corrective action

Recharge the electric starter battery.

Recharge lead-acid cell or replace dry battery. (Note: An unused, or
almost unused, dry battery may sometimes be of insufficient capacity if it is
"old stock".)
Replace glowplug. Check that applied voltage is not too high.

Check glowplug heating using other leads.
Close needle-valve fully and remove glowplug, then flip propeller to pump

out excess fuel. (Invert engine, if possible, while pumping out excess).
Re-start engine. (Priming is not necessary at this time.)

Repeat priming procedure referring to 7 Priming.

25

Symptom

Engine fires
intermittently but
does not run.

Engine fires once
or twice, then
fails to fire.

Engine starts but
revolutions decrease
and engine eventually
stops.

Engine starts,
then revolutions
increase and
engine cuts out.

Engine stops when
battery leads are
disconnected after
starting.

Factor

2

3

1

2

3

3

3

3

2

Cause

Incorrect heating of

★★

glowplug.
Over priming.

★★

★

Sluggish rotation.

★★

Glowplug battery
discharged.

★★

Insufficient priming.

★★★

Mixture too rich.

★

Fuel not reaching the
engine.

★★

Mixture too rich.

Mismatch of glow plug and

★

fuel.

.....

........

......

......

.....

.......

.....

.......

....

Corrective action

Voltage too high or too low. Re-check and readjust referring to "BEFORE
STARTING" paragraph 4.

Continue flipping propeller. If engine does not start after more than 10 flips,
disconnect battery from glowplug and leave for a few minutes, then re­energize plug and flip prop again. If engine still does not start, remove
glowplug and pump out excess fuel by flipping prop quickly.

Then re-start. (Priming is not necessary.)
Recharge the electric starter battery.

Recharge lead-acid cell or replace dry battery.
(Note: An unused, or almost unused, dry battery may sometimes be of
insufficient capacity if it is "old stock".)

Repeat priming procedure referring to 7 Priming.

Close needle-valve half turn (180
start.(Priming is not necessary.)

Make sure that tank is filled with fuel. Check that there is not something
wrong with fuel tubing (kinked or split). Check that carburettor is not
clogged with dirt.

Close the needle-valve a little.

Change fuel or glowplug.

°

) and wait for several minutes then re-

26

VALVE ADJUSTING

ALL O.S. four-stroke engines have their valve(tappet)
clearances correctly set before they leave the factory.
However, if, after many hours of running time have
been logged, a loss of power is detected, or if the
engine has to be disassembled or repaired as a result
of an accident, valve clearances should be checked
and readjusted, as necessary an O.S. Valve Adjusting
Tool Kit is available as an optional accessory.

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

• Feeler gauge 0.04mm

• Feeler gauge 0.1mm

• Hex. key 1.5mm

• Wrench 5mm

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:

(1)

1.

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

Turn the propeller counter-clockwise until

2.

compression is first felt, then turn it futher quarter
turn. 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.)

3.

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.)

27

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
necessary to readjust the clearance if the engine
runs satisfactorily.

0.04mm
Feeler Gauge

Rocker Arm

Valve

Fig.1

If a clearance is found to be outside either of

(2)

these limits, it should be reset as follows.

Carefully loosen the locknut on rocker-arm 1/4-1/2

1.

turn with 5mm wrench. (Fig.2.)

Locknut

Wrench

Turn adjusting-screw approx. 1/2 turn counter-clockwise

2.

to open gap, using appropriate tool -i.e. Allen hex key.
(Fig.3.)

Adjusting
Screw

Allen Key

28

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

Fig.2

Turn approx.
1/2 turn.

Fig.3

Insert 0.04mm feeler gauge between valve stem

3.
and rocker-arm and gently turn adjusting screw
clockwise until it stops.(Fig.4.)

Turn with fingers
until it stops.

0.04mm Feeler
Gauge

Re-tighten locknut while holding adjusting screw

4.

stationary. (Fig.5.)

Hold at the screw head.

Fig.4

Remove 0.04mm feeler, rotate prop through two

5.
revolutions and recheck gap.

6.

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

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.

Fig.5

Tighten Locknut.

29

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.

1.
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

2.
carburettor jet to be partially clogged.

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.

30

3.

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 carburettor while the engine is
running. Remaining fuel in the tank should also be
drained off.

Clean the exterior of the engine with a clean cotton

4.
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 blackened.

If the engine is not in use for a while (more than

5.
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
carburettor 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.

6.

THREE VIEW DRAWING

FS-26S/FS-40S

FS-26S

■

Displacement

■

Bore

■

Stroke

■

Practical R.P.M.

■

Power output

■

Weight

FS-40S

■

Displacement

■

Bore

■

Stroke

■

Practical R.P.M.

■

Power output

■

Weight

( )

-FS-

Specification

4.41 cc (0.269 cu.in.

18.5mm (0.728 in.

16.4mm (0.648 in.
2,200

0.41 bhp / 11,000 r.p.m.
268g (9.45 oz.

Specification

6.49 cc (0.396 cu.in.

21.2mm (0.835 in.

18.4mm (0.724 in.
2,200

0.65 bhp / 12,000
355g (12.5 oz.

40S

~

12,000 r.p.m.

~

12,000 r.p.m.

)
)
)

)

)
)
)

r.p.m.

)

Dimension(mm)

31

FS-26S ENGINE EXPLODED VIEW

C.M2.6X12

C.M2.6X18

2

4-2

4

4-1

8-1

C.M2.6X7

8

32

e

C.M2.6X7

r

✽

Type of screw

C…Cap Screw B…Binding Head Screw M…Oval Fillister-Head Screw

…

F

t

Flat Head Screw N…Round Head Screw S…Set Screw

9

y-1

u

y

3-1

3-2

5-4

5-3

5-2

5-1

0

=

-

q

w

s

o

i

3

1

5

7

6

]

\

-2

\-1

\

\-2

a

g

f

d

C.M2.6X7

p

[

FS-26S PARTS LIST

No.

Code No.

33

4 4113 000

1

4 5704 200

2

4 5761 400

3

4 5761 410

3

-1
4 5761 600

3

-2
4 5761 000

4

4 5761 100

4

-1
4 5761 200

4

-2
4 5760 010

5

4 5760 110

5

-1
4 5760 200

5

-2
4 5060 309

5

-3
4 6160 400

5

-4
4 4104 100

6

4 4104 010

7

4 5281 010

8

4 5281 700

8

-1

2 2714 100

9

4 4103 400

0

4 4103 200

-

2 2706 000

=

4 5705 000

q

4 4103 100

w

4 5784 000

e

4 5707 000

r

4 5771 000

t

4 4102 000

y

4 5702 100

y

-1

u

2 2630 002

i

4 4101 000

o

4 5762 100
4 5762 000

p
[

4 5701 100

]

4 4166 000
4 4166 100

\

4 4166 110

\

-1

\

-2

2 4881 824
4 5264 000

a

4 5231 000

s
d

4 5708 000
2 3009 006

f

2 3210 007

g

4 4125 000
4 5769 000
4 5769 100
4 5769 200
7 1615 009

Screw Set
Rocker Cover
Rocker Support Assembly
Rocker Support
Rocker Arm Retainer(2pcs.)
Rocker Arm Assembly(1pair)
Rocker Arm(1pc.)
Tappet Adjusting Screw
Valve Assembly(1pair)
Intake Valve(1pc.)
Valve Spring(1pc.)
Valve Spring Seat(1pc.)
Valve Spring Retainer(2ps.)
Cylinder Head(W/Gasket)
Cylinder Head (W/Gasket and Valve Assembly)
Carburetor Complete
Carburetor Retaining Screw(2pcs.)
Gasket Set
Piston Ring
Piston
Piston Pin
Connecting Rod
Cylinder Liner
Choke Valve Assembly
Cover Plate
Breather Nipple
Crankshaft
Crankshaft Spacer
Crankshaft Ball Bearing(Rear)
Crankcase
Thrust Ball(2pc.)
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)
Drive Hub
Propeller Washer
Propellern Nut
Silencer Assembly
Exhaust Pipe Assembly
Exhaust Pipe
Exhaust Lock Nut
Glow Plug Type F

Specifications are subject to alteration for improvement without notice.

Description

FS-40S ENGINE EXPLODED VIEW

C.M2.6X12

C.M3X18

2

5-3

3-1

5-4

5-2

5-1

3

3-2

4-2

4

4-1

8-1

C.M2.6X7

8

34

9

e

w

u

t

C.M3X8

✽

Type of screw

C…Cap Screw B…Binding Head Screw M…Oval Fillister-Head Screw

…

F

Flat Head Screw N…Round Head Screw S…Set Screw

y

r

0

-

=

q

i

]

\

-2

-1

\
\-2

a

d

s

o

p

o

5

7

6

1

\

g

f

[

C.M2.6X7

FS-40S PARTS LIST

No.

Code No.

1

35

4 5213 010

2

4 5204 210

3

4 5261 400

3

-1

4 5261 410

3

-2

4 5761 600

4

4 5261 010

4

-1

4 5261 110

4

-2

4 5761 200

5

4 5260 010

5

-1

4 5260 110

5

-2

4 5060 205

5

-3

4 5060 309

5

-4

4 5060 402

6

4 5204 110

7

4 5204 010

8

4 5281 020

8

-1

4 5281 700

9

4 5214 100

0

2 4203 410

-

4 5203 210

=

2 3356 000

q

4 5205 000

w

4 5203 100

e

4 5284 000

r

4 5207 000

t

4 5771 000

y

4 5202 010

u

2 2630 002

i

4 5201 040

o

4 5231 100

p

4 5262 010

[

4 5201 110

]

4 5266 010

\

4 5266 102

\

-1

4 5266 112

\

-2

2 4881 824

a

4 5264 000

s

4 5231 000

d

4 5208 010

f

2 3209 003

g

2 3210 007
4 5225 000
4 5225 010
4 5226 000

7 1615 009

Screw Set
Rocker Cover
Rocker Support Assembly
Rocker Support
Rocker Arm Retainer(2pcs.)
Rocker Arm Assembly(1pair)
Rocker Arm(1pc.)
Tappet Adjusting Screw
Valve Assembly(1pair)
Intake Valve(1pc.)
Valve Spring(1pc.)
Valve Spring Seat(1pc.)
Valve Spring Retainer(2ps.)
Cylinder Head(W/Gasket)
Cylinder Head (W/Gasket and Valve Assembly)
Carburetor Complete
Carburetor Retaining Screw(2pcs.)
Head Gasket
Piston Ring
Piston
Piston Pin
Connecting Rod
Cylinder Liner
Choke Valve Assembly
Cover Plate
Breather Nipple
Crankshaft
Crankshaft Ball Bearing(Rear)
Crankcase
Camshaft Bearing
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)
Drive Hub
Propeller Washer
Propellern Nut
Silencer Assembly
Silencer
Exhaust Header Pipe
Glow Plug Type F

Specifications are subject to alteration for improvement without notice.

Description

CARBURETTOR EXPLODED VIEW
& PARTS LIST

4

5

N.+M3X6

1

-1

2

1

M2.6X5

✽ Type of screw

C…Cap Screw M…Oval Fillister-head Screw F…Flat Head Screw

…

Round Head Screw S…Set Screw

N

TYPE FS-26S/FS-40S

C.M2.6X7

3

6

7

6

6

-3

-5

6

-4

-1

6

6

-2

S.M3X3

TYPE FS-26S

No.

Code No.

1

22081408

-1

1

22081313

2

45281200

3

45281100

4

45281700
22081811

5

45281910

6

45781970

6

-1

26381501

6

-2

45283960

6

-3

23011308

6

-4

6

-5

45281920

7

22081820

Throttle Lever Assembly
Throttle Lever Retaining Screw
Carburetor Rotor
Carburetor Body
Carburetor Retaining Screw(3pcs.)
Throttle Stop Screw
Needle-valve Assembly
Needle
Set-screw
Nozzle Assembly
Ratchet Spring
Nozzle Retaining Screw(2pcs.)
Air-bleed Screw

Description

TYPE FS-40S

6
6

No.

1

6
6
6

1

2
3
4
5
6

7

-1

-1

-2

-3

-4

-5

Code No.

22081408
22081313
45281120
45281110
45281700
22081811
45281910
45781970
26381501
45283960
23011308
45281920
22081820

Throttle Lever Assembly
Throttle Lever Retaining Screw
Carburetor Rotor
Carburetor Body
Carburetor Retaining Screw(3pcs.)
Throttle Stop Screw
Needle-valve Assembly
Needle
Set-screw
Nozzle Assembly
Ratchet Spring
Nozzle Retaining Screw(2pcs.)
Air-bleed Screw

Description

Specifications are subject to alteration for improvement without notice.

36

PARTS & ACCESSORIES

■

O.S.Glow Plug
TYPE F

(

71615009

Flexible Exhaust Pipes

■

)

For 40S
1010A (72108300

1010B (72108310

Radial Mount Set

■

For 26S (71908300
For 40S (71906000

)
)

Propeller Locknut Set

■

)
)

Spinner Nut

■

For 40S 1/4''-28 (23024008

NON-BUBBLE Weight

■

(

71531000

For 40S(45810100

)

37

Valve Adjusting

)

)

■

Tool Kit

(

72200060

Super Filter (L)

■

(

72403050

Long Socket Wrench With

■

)

)

Plug Grip

(

71521000

)

MEMO

38

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T

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A

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N

U

&

P

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F

O

R

M

A

N

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S

T

A

B

L

I

S

H

I

N

G

T

H

E

R

S

A

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D

A

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C

Copyright 2000 by O.S.Engines Mfg. Co., Ltd. All rights reserved. Printed in Japan.

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D

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

TEL. [phone]

FAX. [phone]

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

110101