
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.
Inline four-cylinder overhead-valve
four-stroke-cycle engine
1
SAFETY INSTRUCTIONS AND
WARNINGS ABOUT YOUR O.S. ENGINE
NOTES WHEN APPLYING AN
ELECTRIC STARTER
ABOUT THE ENGINE
ENGINE PARTS NAME
INSTALLATION
FUEL TANK & LINES
GLOWPLUG
MIXTURE CONTROLS
PROPELLER
GLOWPLUG HEATING
FUEL AND LUBRICATION
CONTENTS
STARTING
RUNNING-IN ("Breaking-in")
THROTTLE VALVE ADJUSTMENT
FLIGHT & MAINTENANCE
VALVE CLEARANCE ADJUSTMENT
ENGINE EXPLODED VIEW
ENGINE PARTS LIST
CARBURETOR EXPLODED VIEW
& PARTS LIST
O.S. GENUINE PARTS & ACCESSORIES
ENGINE THREE VIEW DRAWINGS
2-4
5
6
7-8
9-10
11
12
13
14-15
16-17
18
19-22
23
24-26
27
28-29
30
31
32
33
34

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. Contact with the mu ffler(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.
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.
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. Also,
check the tightness of all the screws and nuts before restarting the engine.
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.

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 carburetor.
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
5
NOTES WHEN APPLYING
AN ELECTRIC STARTER
Do not over-prime. This could
cause a hydraulic lock and
damage the engine on application
of the electric starter.
If over-primed, remove glowplug,
close needle-valve and apply
starter to pump out surplus fuel.
Cover the head with a rag to
prevent pumped out fuel from
getting into your eyes.

6
The O.S. IL-300 (Dia-Star) is a four-cylinder inline
overhead-valve four-stroke-cycle engine of 50cc
displacement. The engine maintains the same
features of stress free starting, super smooth idling
and high torque power which is always the hallmark
of O.S. large size multi-cylinder engines. With it’s
finely detailed design and outstanding scale
appearance, the engine’s quality is second to none.
ABOUT THE ENGINE
STANDARD ACCESSORIES
Glow Plug Type F
(installed on the engine)
Valve adjusting tool kit
(4pcs.)
Exhaust Pipe Assembly
Exhaust Pipe
Exhaust Pipe Lock Nut
Exhaust Gasket
Feeler gauge 0.04mm
Feeler gauge 0.1mm
Hex. key 1.5mm
Wrench 5mm
Booster Cable Set
Leads for glow plug with clip
Lead for earth (ground)
(4pcs.)
(1pc.)
Radial Motor Mount Set
Mount attachment Screws
Engine mounting screws (M5X25)
Lock washers (ø5)
Blind nuts (M5)
(4pcs.)
(4pcs.)
(4pcs.)
(4pcs.)
7
ENGINE PARTS NAME
Crankcase
Rear Housing
Carburetor Type 80P
Intake Manifold
Gear Cover
Center Manifold
Carburetor Extention Pipe
Push Rod

8
Lock Nut
Propeller Washer
Propeller Nut
Cylinder Jacket
Front Housing
Exhaust Pipe
Cylinder Head 1
Drive Hub
Crankcase Under Cover
Cylinder Head 2
Cylinder Head 3
Cylinder Head 4
9
Needle-valve extension
The needle-valve 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. An L-shaped rod, of 1.6-1.8mm dia. and
appropriate length, should be inserted into the needle's
center hole and secured by tightening the set-screw in the
needle-valve knob with a small Allen key. If a longer
extension cable is required it is suggested that one be
fabricated as per the illustration.
NOTE:
O.S. does not offer the extension cable as an accessory
item.
Do not use an excessively long unsupported extension as
this may vibrate and cause the needle-valve setting to vary
or even damage the needle-valve thread. Always provide a
suitable support at the outer end.
It is essential that the firewall is strong and rigid (e.g. at
least 15mm thick) and firmly integrated with the structure of
the aircraft.
INSTALLATION
M5 Blind nut
Firewall
M5x25 screw
5 Lock washer
At least 15mm (0.6")
rigid hard wood
It is suggested to install the engine upright.
M5x15 screw
Lock washer
Set-screw
Set-screw
Hook
Knob
Cable
Needle
It is suggested to use Lock Washers (available as an
optional extra) with engine installing screws or apply
LOCTITE to the screws to prevent them from loosening.

10
Exhaust pipe adjustment
The direction of the exhaust pipes 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 cylinder head. Use a 12mm
wrench.
12mm wrench
Loosen
Tighten
Lock nut
Exhaust pipe
Carburetor cleanliness
It is recommended that the fuel is passed through a filter
when the tank is filled and that a good in-line filter is
installed between the fuel tank and carburetor.
Occasionally remove the needle-valve holder from the
carburetor and rinse out the locations shown below with
methanol or fuel. Be careful not to lose the gasket when
removing the needle-valve holder from the carburetor.
Squeeze bottle
Dirt and fibrous matter
mostly accumulate here.
Dirt and fibrous matter
mostly accumulate here.
Needle-valve holder
11
FUEL TANK & LINES
Make sure that the tank is well rinsed out with methanol or
glow fuel before installation and that the pickup weight is
well clear of the bottom of the tank when held vertically.
Locate the fuel tank as close as possible
to the carburetor, or the fuel level
difference will affect the engine running
when the model is upright or inverted.
Set the fuel tank position so that the
carburetor center line is 1/3 lower than
from the tank top when the model is
placed horizontal.
Approx. 15mm
1/3
Be sure to follow the instructions concerning the
relationship between fuel tank and carburetor position, or
the expected stable idle running will not be obtained even
with adequate carburetor adjustment.
For plumbing, use heavy duty silicone tube of 2.5mm inner
dia and 5mm outer dia.

12
GLOWPLUG
The role of the glowplug
Glowplug life
Particularly in the case of very high performance engines,
glowplugs must be regarded as expendable items. 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.
Do not run the engine too lean and do not leave the
battery connected while adjusting the needle.
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.
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
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.
Since the compatibility of the glowplug and
fuel may have a marked effect on
performance and reliability, it is suggested
to use the O.S. Type F plug when it is
necessary to replace. Carefully install plug
finger-tight, before final tightening with the
correct size plug wrench.
13
MIXTURE CONTROLS
The Needle Valve
When set to produce maximum power at full throttle, this
establishes the basic fuel/air mixture strength. The correct
mixture is then maintained by the carburetor's built-in
automatic mixture control system to cover the engine's
requirements at reduced throttle settings.
The Mixture Control Valve
This meters fuel flow at part-throttle and idling speeds to
ensure reliable operation as the throttle is opened and
closed. The Mixture Control Valve is factory set for the
approximate best result. First run the engine as received and
readjust the Mixture Control Screw only if necessary.
Two mixture controls are provided on this
Carburetor.
Needle Valve
Mixture Control Valve
Mixture Control Valve of the carburetor is set at basic position
( a little on the rich side) at the factory. However, minor
readjustment will be required for a fuel used, atmospheric
conditions and a model. When a good result is not obtained
with the factory setting, readjust it according to the MIXTURE
CONTROL VALVE ADJUSTMENT section. Please note
during a running-in period flights should be made with a
slightly rich needle setting. Therefore, during a running-in
period proper carburetor responses will not be obtained.
Adjust it for optimum position after the running-in is
completed.
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.
Throttle Lever
Fuel Inlet
Rotor Guide Screw

14
18x10-12, 20x8-10, 22x8
PROPELLER
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.
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:
Type
Size (DxP
)
Sport/Scale
1.
PROPELLER & SPINNER ATTACHMENT
There is a risk, particularly with powerful 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:
To be equal
To be equal
Ream to 13.5mm dia.
Use a propeller that has a
hub of more than 40mm dia.
Ream the propeller shaft hole to 13.5mm 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. (not supplied).
2.
15
3.
Add the special tapered and slotted locknut and secure
with a 14mm wrench while holding the prop nut with the
17mm wrench. (not supplied).
Propeller washer
Propeller washer
Propeller nut
Propeller nut
Locknut
Locknut
Drive hub
Drive hub
Back-plate of spinner
The Safety Propeller Locknut can
be used provided that the width is
between 21.5mm and 26mm.
Make a habit of always checking the tightness of the
propeller before starting the engine. Remember that,
especially with wooden propellers, there is a tendency for
the material to shrink, or for it to be reduced by the
serrated face of the drive hub. Retighten the propeller nut
if necessary after loosening the Safety Propeller Locknut.
The locknut should be tightened firmly after retightening
the propeller nut.
NOTE:

16
GLOWPLUG HEATING
Glowplug battery
It is necessary to use a glowplug battery of fairly large
capacity (10Ah or more) as this is required to heat four
glowplugs simultaneously.
A heavy-duty 1.5-volt dry battery or (preferably) 1.2-volt NiCd battery may be used.
Ni-Cd (nickel-cadmium) 1.2-volt rechargeable battery
Use a 10-Ah cell, or 4 to 5 2.0-Ah cells (as commonly used
for electric-powered R/C cars) wired in parallel and with
short heavy leads (to minimize voltage drop) to the
connection point on the fuselage.
Glowplug leads
The plug leads are fitted with special snap-on connectors
that ensure firm contact with O.S. plug. They are a "click" fit
and are not suitable for use with most other makes of
glowplug.
The earth (ground) lead is fitted with a plug terminal which
should be connected to the engine by means of one of the
mounting screws.
Make sure that no part of the wiring touches the cylinder
head or cooling fins.
Keep wiring away from the fuel tank where it might cause a
fire in the event of a short-circuit.
Switch should have
sufficient capacity.
Install Ni-Cd battery in the fuselage, and switch on or off by means
of transmitter. (On-board battery)
1.2 volt Ni-Cd battery with
more than 10 Ah capacity.
1.
A commercially available glowplug heating source will
enable you to turn the current on or off by using a
transmitter auxiliary channel establishing a more reliable
idle.
17
If glowplug leads are extended
together as a single cable, use
heavier wire, e.g. 2.0mm
multi-strand copper core as
supplied for earth lead.
2
2
2.0mm
Earth (ground)
lead
Fasten to the
motor mount.
Glowplug re-heat
Under normal conditions, the engine will idle sufficiently
slowly with the throttle closed to permit a safe landing
approach. However, if conditions (atmospheric, fuel,
tank location etc.) are unfavorable, there may be a
tendency for one cylinder to cease firing if the engine is
throttled down to a very low idling speed. This can be
prevented by installing a small on-board Ni-Cd battery
which will automatically re-heat the glowplugs when the
engine is throttled down to idling speed. A suitable
switch should be installed so that it is actuated by the
throttle servo only when the engine is throttled down.
2. Connect terminals to the
fuselage.
3. Install a jack on the
fuselage.
Ni-Cd
Ni-Cd

18
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.
Reminder!
Fuel
The IL-300 should be operated on a methanol based fuel
containing not less than 18% (volumetric) castor oil, or a top
quality synthetic lubricant (or a mixture of both), plus a small
percentage (5-20%) of nitromethane for improved flexibility
and power.
FUEL AND LUBRICATION
Lubrication
All parts of the IL-300 are automatically lubricated by the oil
content of the fuel mixture. It is suggested, however, to apply
small amount of machine oil or grease to moving parts of the
rocker arms before starting the engine.
The crankcase breather hole is located at the back of the
engine and is fitted with a brass nipple. Fit a length of silicone
tubing of approx. 2.5mm I.D. to this nipple to conduct away
the small amount of oil that escapes through the breather.
Make a habit of draining out the excess oil in the crankcase
at the end of each flying session. Leaving contaminated oil in
the crankcase for a long time will cause rust. Also, residual
castoroil will tend to solidify and lock the engine. Inject
corrosion-inhibiting oil into the crankcase to neutralize the
effects of any remaining contaminants.
Rear Housing
Breather Nipple
2.5mm Silicone tubing
Breather Nipple
19
STARTING
Precautions
For safety, please observe the following instructions
before starting the engine.
Start the engine by turning the propeller counterclockwise (i.e. normal running direction).
Do not start the engine with the throttle fully opened,
otherwise the model will tend to move forward
suddently due to the strong thrust of the propeller. Hold
both wings of the model when starting the engine.
Do not carry out carburetor adjustments (except needlevalve adjustment) while engine is running.
Use a high-torque electric starter.
Starting procedure is as follows:
Open the needle-valve 2 to 3 turns from the fully closed
position.
1.
open
Make sure that glowplugs are not connected to the battery.
Do not heat the glowplugs while priming.
2.
Close
3.
open the
throttle fully
Open the throttle fully and apply an electric starter for 5~6
seconds to prime the engine.

20
Set the throttle valve approximately 1/4 open from the fully
closed position.
4.
Fully open
Fully closed
Set at this position
Position the throttle stick at 2-3 scales advanced from the fully
pulled down position. Turn the prop “backwards” (clockwise)
by hand until it is against compression. This is to enable the
kinetic energy of the prop to subsequently assist the starter
through the compression stroke to start the engine.
Starting with an electric starter.
5.
Make sure that the direction of rotation of the starter is
correct.
Connect the glowplug battery.
Apply the electric starter.
Connect the battery to the glowplug.
Electric starter
Make sure that the
direction or rotation
is correct.
21
When the engine starts, open the throttle valve fully and
keep it running initially (approx. 10 seconds), with original
needle-valve setting.
6.
Open the
throttle fully.
Make sure that all four cylinders are firing
7.
The engine is running properly if white smoke is emitted
through all four exhaust pipes. A slight spray of fuel will be
discharged through the exhaust pipe of any cylinder that is
not firing.
If a cylinder ceases firing, reduce the throttle setting to
approximately 1/4 open from the fully closed position and
re-connect the glowplug battery. The rpm will increase when
all cylinders are firing steadily.
A slight spray of fuel may be emitted through the exhaust
pipe if a cylinder is not firing.

22
Now disconnect the glowplug battery.
8.
Adjust the needle-valve
9.
Abrupt adjustment of the needle-valve may cause the
engine to stop, especially when it is new and insufficiently
run-in.
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.
Practical best (optimum) needle-valve setting
Approx. 40
Maximum rpm setting
("Lean")
"Rich" needle-valbe
setting when starting
the engine.
Rpm starts to decrease.
Close the needle-valve
gradually and slowly.
Engine stops.
Re-starting the engine when warm
To re-start the engine when warm, simply re-energise the
plugs and reapply the starter with the throttle in the idling
position. If the engine does not start, disconnect the battery
from the glowplugs and re-prime. Initially, the high
temperature inside the combustion chambers may turn the
liquid fuel into gas and emit it through the exhaust pipes.
Therefore, repeat the priming procedure once or twice until the
cylinders become cool enough for restarting.
Note:
Make sure that the throttle linkage is made so that the
throttle is fully closed when the throttle lever as well as
trim lever on the transmitter are fully pulled down.
How to stop the engine
Pull down the throttle lever and trim lever on the transmitter
fully.
23
RUNNING-IN ("Breaking-in")
Obtain an 18x12 or 20x8 propeller for running-in.
↓
↓
1
2
1. Running-in on the ground
Start the engine
Set the needle-valve 500-1,000r.p.m. lower than
maximum r.p.m. setting and run approx, 10 seconds.
(It is suggested to use a tachometer.)
Open the needle-valve approx. 1,000r.p.m. lower
than above setting and run approx. 20 seconds.
Repeat above procedure, i.e., richening and leaning the
mixture until the engine has approx. 10 minutes of running
time.
Keep the throttle fully open, using only the needle-valve to
change r.p.m. Prolonged running-in on the ground is not
suggested because the purpose is just initial running-in
to increace engine temperature gradually close to that of
maximam r.p.m.
NOTE:
2. Running-in in the air
Start the engine
Fly the model.
NOTE: Avoid prolonged heavy load flight.
With each successive flight, close the needle-valve slightly,
until, at the end of 10 flights, the needle-valve is set for
optimum position.
Finish running-in.
The carburetor can now be adjusted for optimum throttle
performance following the instructions given in the next
section.
Set the needle-valve approx 40 open from
optimum position (approx. 40 open from
maximum r.p.m.).

24
THROTTLE VALVE ADJUSTMENT
Needle-valve adjustment
Adjust the needle-valve following the instructions given in
STARTING section.
Mixture control valve adjustment
The carburetor of your IL-300 has been factory set for the
approximate best result with the fuel tank located in the normal
position (i.e. close to the back of the engine and where the
level of the needle-valve is at 1/3 height of the tank), but the
setting may, in some cases, vary slightly in accordance with
fuel and climatic conditions.
After running-in is completed and the needle-valve is set at
optimum position (approx 40 open from maximum r.p.m.
position), check the idle speed and adjust only when
necessary.
25
Start the engine.
open the throttle fully .
Adjust the needle-valve.
Close the throttle gradually.
Set the idle speed.
Open the throttle fully.
Does the engine
regain full power?
Continue running at high speed
for 5 seconds.
Close the throttle.
Run at idle speed for 5 seconds.
Does the engine stop?
Apply full throttle.
Does the engine
regain full power
immediately?
OK
Re-set the idle speed
a little higher
Set the thr ot tl e op en in g by
means of the throttle trim on
the transmitter so that the lowest
practical speed, without risk of
the engine stopping,is obtained.
The position where the lowest
pos sible r.p. m. ,w ith steady
running, is obtained.
Approx 40˚ open from maximum
r.p.m. setting.
Yes.
No.
Yes.
One of the cylinders ceases firing.
Disconnect the glowplugs from the battery.
Make sure that all 4 cylinders are firing.
Make sure glowplug switch is on.
The engine hesitates before picking
up to full speed, or appears to run at
medium speed with reduced power.
Check mixture adjustment at idle
speed. Make sure that all cylinders
are firing.
Adjustment should be carried
out after stopping the engine.
Do not move needle-valve
while adjusting other controls.
Repeat the procedure while opening and closing the
throttle until the best result is obtained.
Attention: Do not leave the battery connected while adjusting the carburetor.
One of the cylinders
ceases firing.
One of the cylinders
ceases firing.

26
Adjusting the mixture control valve
If the engine hesitates, puffing
out a good deal of smoke, before
picking up to full speed, it is
probable that the idle mixture is
too rich.
1.
Mixture Control Valve
Screwdriver
Turn 30
In this case, it will be necessary
to turn the Mixture Control Valve
clockwise to lean the mixture.
About 1/12 turn (30 ) should be sufficient.
Alternatively, if the engine stops
or is slow to pick up speed,
without smoking or a strong
exhaust note, it is probable that
the idle mixture is too lean.
2.
Turn 30
In this case, it will be necessary
to turn the Mixture Control Valve
counter-clockwise approximately
1/12 turn (30 ) .
Thirdly, if the rpm increase but the engine appears to run
with reduced power, it is probable that one of the cylinders
has ceased firing. You may detect this by the difference in
exhaust note and rpm compared with previous full-throttle
running. The cutting out of the cylinder may be caused by
the idle speed being set too low or the idle mixture being
too rich.
3.
In the case of the idle speed being too low, re-set the idle
position a little higher by means of the throttle trim on the
transmitter. In the case of the idle mixture being too rich, turn
the Mixture Control Valve clockwise about 1/12 turn (30 ).
Normal safe idle speeds are in the region of 2,000 r.p.m..
NOTE:
As this is four-cylinder four-stroke-cycle engine, firing
strokes occur every half revolution (180 ), that is, two
firings take place every one complete revolution.
Therefore, at first you may have an impression that the
engine is idling at higher r.p.m. than actual running r.p.m.
It is recommended to check the engine r.p.m. with a
tachometer.
Changing the make of glowplug or fuel may sometimes
require re-adjustment of carburetor throttle.
Realignment of mixture control valve
In the course of making carburetor adjustments, it is just
possible that the Mixture Control Valve setting may be
upset.Its basic setting can be re-established as follows:
Turn the Mixture Control Valve counter-clockwise until it stops,
then screw it out 3 turns. This is the basic position.
NOTE:
If an on-board glowplug re-heat system is installed,
mixture adjustment at idle speed should be carried out
with this in operation.
27
FLIGHT & MAINTENANCE
It is necessary to warm up the engine as with a full-size
aircraft or automobile. Do not attempt to take-off immediately
after the engine has been started. Allow the engine to run at
full throttle for at least 10 seconds before releasing the model.
Checking before flight
Make sure that all four cylinders are firing.
Make sure that engine runs steadily at idle speed.
Make sure that engine is fully warmed up.
Please pay attention to the matters described below to
ensure that your engine serves you well in regard to
performance, reliability and long life.
As previously mentioned, it is vitally important to avoid
operating the engine in conditions where dust, disturbed by
the propeller, may be deposited on the engine and enter its
working parts.
Remember to keep your fuel container closed to prevent
foreign matter from contaminating the fuel.
Install a fuel filter to prevent dirt and dust in the fuel
container from entering the fuel tank. O.S. Super Filters (L)
is available as an optional extra.
Install an in-line fuel filter between the tank and carburetor
to prevent foreign matter in the tank from entering the
carburetor.
If these precautions are neglected, restriction of fuel flow
may cause the engine to cut out, or the fuel/air mixture to
become too lean causing the engine to overheat.
Clean these filters periodically.
The use of modern high-performance alcohol based model
engine fuels, while promoting cooler running, improved antidetonation combustion and increased power, have the
disadvantage of causing corrosion due to the acid by-products
of combustion. The use of nitromethane in the fuel can also
contribute to the problem.
Care and Maintenance
Do not close the needle-valve and mixture control valve too far
as this will cause a lean setting and over heating of the engine.
This can, in turn, create nitromethane oxide leading to internal
rusting of the engine. Always adjust the needlevalve slightly on
the rich side of peak rpm.
Do not leave unused fuel in the engine at the conclusion of a
day’s flying. Accepted practice is to cut off the fuel supply while
the engine is still running at full throttle, then expel as much
fuel residue as possible by turning the engine over 20-30
seconds with the electric starter. Finally, inject some after-run
oil through the glowplug hole and turn the engine over several
times with the electric starter.
When the engine is not to be used for some months (for example,
as between flying seasons), a worthwhile precaution is to remove it
from the airframe and, after washing off the exterior with alcohol
(not gasoline nor kerosene), remove carefully the carburetor with
intake pipe, glow plug and all silicone tubing and put them safely
aside. Then, immerse the engine in a container of alcohol. Rotate
the crankshaft while the engine is immersed. If foreign matter is
visible in the alcohol, rinse the engine again in clean alcohol.
Finally, shake off and dry the alcohol ,and inject some after-run oil
in the glowplug hole and rotate the crankshaft several times by
hand. Reinstall the carburetor with intake pipe and glowplug on the
engine and keep it in a dry place after putting in a vinyl bag.

28
0.04mm
VALVE CLEARANCE ADJUSTMENT
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, with the aid of the O.S. Valve Adjusting Tool Kit.
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.
Remove all the glowplugs except the one installed in the
cylinder that you want to check.
2.
Note:
Each glowplug should be re-installed in to the original
cylinder. You may start to check and adjust with any
cylinder.
Turn the propeller counter-clockwise until compression is
first felt, then turn it futher a 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.)
The standard valve clearance, on both inlet and exhaust
valves, is between 0.04mm and 0.1mm(0.0015-0.004 inch),
measured between valve stem and rocker arm. Use the
0.04mm and 0.1mm feeler gauges to check clearances.
(See Fig.1)
0.04mm
Feeler Gauge
Rocker Arm
Valve
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 0.1mm 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.
Fig.1
If a clearance is found to be outside either of these limits, it
should be reset as follows.
29
0.04m
m
0.04mm
Carefully loosen the locknut
on rocker-arm 1/4-1/2 turn
with 5mm wrench. (Fig.2)
1.
Loosen approx.1/4 to 1/2 turn.
Wrench
Locknut
2.
Turn adjusting-screw approx.
1/2 turn counter-clockwise to
open gap, using appropriate
tool-i.e. Allen hex key. (Fig.3)
Adjusting
Screw
Allen Key
Turn approx.1/2 turn.
3.
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.
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.
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.
Re-tighten locknut while holding adjusting screw stationary.
(Fig.5)
4.
Hold at the
screw head.
Tighten Locknut.
Fig.5
Fig.4
Fig.3
Fig.2

30
1
1-1
1-2
2-1
2
3
4
5
6
6-1
6-2
6-3
6-4
7
8
9
10-2
10-1
10
11
12
13
14
15
16
17-1
17
18
19
20
19-1
21
22
23
24
25
26-1
26
27
28
29
30
32-1
31
32
43
44
45
46
47
48-1
48
49
41
50
C.M2.6x7
C.M3x8
C.M3.5x10
C.M3x14
C.M3x8
C.M2.6x7
C.M2.6x7
C.M3.5x10
C.M2.6x7
C.M2.6x7
C.M3.5x10
C.M3.5x10
C.M3x10
S.M3x3
17-2
33
34
36
35
37
38
39
40
41
42
35
79871020
79871110
79871120
79871145
79871070
M2.6x7
M3x8
M3x10
M3x14
M3.5x10
ENGINE EXPLODED VIEW
Type of screw
C...Cap Screw M...Oval Fillister-Head Screw
F...Flat Head Screw N...Round Head Screw S...Set Screw
CAP SCREW SETS
(10pcs./sets)
Code No.
Size
Front Housing (4pcs.) Under Cover (8pcs.)
Intake Manifold A (2pcs.) Gear Cover (2pcs.)
Intake Manifold B (4pcs.)
Carburetor Retaining Screw (1pc.)
Idle Gear Retaining Screw (1pc.)
Rocker Support Retaining Screw (4pcs.)
Housing Alignment Retaining Screw (2pcs.)
Front Housing (6pcs.) Rear Housing (8pcs.)
Pcs. used in an engine
1
1-1
1-2
2
2-1
3
4
5
6
6-1
6-2
6-3
6-4
7
8
9
10
10-1
10-2
11
12
13
14
15
16
17
17-1
17-2
18
19
19-1
20
21
22
23
24
25
26
26-1
27
28
29
30
31
32
32-1
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
48-1
49
50
45566000
46564000
46210100
46208010
29208200
46231000
46501600
46562100
46031005
46501000
46501500
46514300
26530008
46502100
46514000
46502300
46502200
46030008
46512000
45587180
46513200
45067319
46562000
22631019
46513000
46515000
46501816
46501800
22681953
46513100
46501700
71910100
79870050
71615009
72200071
72200060
46504300
46504310
45061202
46504410
79871120
45461610
45461510
26381501
46160000
46160100
45460200
45060309
46160400
46504110
46504210
46504100
46504200
44014010
45269000
45269100
45069200
44003400
44003200
44006000
46505000
44003100
46503300
46503400
23325340
79872035
46581000
46568300
45515000
46568000
46568100
46568200
31
PARTS LIST
The specifications are subject to alteration for improvement without notice.
Description
Code No.
No.
Description
Code No.
No.
Rocker Arm Assembly (1pair)
Rocker Arm (1pc.)
Tappet Adjusting Screw
Rocker Support Assembly
Rocker Support Retaining Screw (10pcs.)
Rocker Arm Spacer
Rocker Arm Shaft
Rocker Arm Shaft Retaining Screw
Valve Assembly (1pair)
Valve (1pc.)
Valve Spring (1pc.)
Valve Spring Seat (1pc.)
Valve Spring Retainer (2pcs.)
Cylinder Head 1&3
Cylinder Head 2&4
Cylinder Head 1&3 (W/Valve Assembly)
Cylinder Head 2&4 (W/Valve Assembly)
Head Gasket
Exhaust Pipe Assembly (1pair)
Exhaust Pipe
Exhaust Pipe Lock Nut
Piston Ring
Piston
Piston Pin
Connecting Rod Assembly
Cylinder Liner
Cylinder Jacket
Cylinder Holding Volt Set
Nut (2pcs.)
Spring Washer (20pcs.)
Carburetor Complete (Type 80P)
Carburetor Extention Pipe
"O" Ring (1pc.)
Center Manifold Assembly
Intake Manifold A Assembly
Intake Manifold B Assembly
Push Rod (2pcs.)
Cam Follower (1pc.)
Lock Nut Set
Drive Hub
Woodruff Key
Crankshaft Bearing F
Front Housing
Camshaft Bearing Spacer
Camshaft Bearing F
Crankcase
Crankcase Under Cover (1pc.)
Under Cover Gasket (4pcs.)
Crankshaft Bearing FR
Crankshaft F
Coupling Bearing
Crankshaft Coupling
Crankshaft R
Crankshaft Bearing R
Drive Gear
Drive Gear Key
Idle Gear Washer (2pcs.)
Drive Gear Retaining Screw
Camshaft
Camshaft Bearing R
Idle Gear
Idle Gear Bearing
Rear Housing Assembly Pipe (W/Screw & Nut)
Rear Housing
Breether Nipple (No.1)
Idle Gear Thrust Washer
Gear Cover
Radial Motor Mount Set
Blind Nut M5 (10pcs.)
Glow Plug Type F
Booster Cable Set
Valve Adjusting Kit

32
1
1-1
1-2
1-3
1-4
1-5
2
3
4
5
5-1
6
7
8
9
10
27681900
27681970
24981837
26381501
27381940
26711305
22781420
22781411
46581200
26781309
24881824
45581820
22681953
46581100
45515000
79871110
S.M3X3
1-1
1-2
1-3
1-4
1-5
1
5-1
2
3
4
5
6
7
8
9
C.M3x8
10
Type of screw
C...Cap Screw M...Oval Fillister-Head Screw
F...Flat Head Screw N...Round Head Screw S...Set Screw
The specifications are subject to alteration for improvement without notice.
Description
Code No.
No.
EXPLODED VIEW & PARTS LIST
Needle-valve Assembly
Needle Assembly
"O" Ring (2pcs.)
Set Screw
Needle-valve Holder Assembly
Ratchet Spring
Throttle Lever Retaining Screw
Throttle Lever
Carburetor Rotor
Mixture Control Valve Assembly
"O" Ring (2pcs.)
Roter Guide Screw
Fuel Inlet (Nipple No.1)
Carburetor Body
Carburetor Rubber Gasket
Carburetor Retaining Screw (10pcs.)
33
(72200130)
(46210300)
(71531000)
(72403050)
(79870050)
(55500004)
(71521000)
(79871010)
(79871110)
(79871120)
(79871145)
(71531010)
(79871070)
M2.6x7
M3x8
M3x10
M3x14
M3.5x10
(46569000)
COLLECTOR EXHAUST PIPE
BOOSTER TERMINAL KIT
NON-BUBBLE WEIGHT
SUPER FILTER (L
)
LONG SOCKET WRENCH
WITH PLUG GRIP
O.S. GENUINE PARTS & ACCESSORIES
PROPELLER
LOCKNUT SET FOR 4C SPINNER
CAP SCREW SET (10pcs.)
The specifications are subject to alteration for improvement without notice.
M5
BLIND NUT (10pcs.)
LOCK WASHER (10sets)
M5
NON-BUBBLE WEIGHT
S
3/8"-M5 (L)

34
12.5 cc x 4 / 0.765 cu.in. x 4
25.8 mm / 1.02 in.
24.0 mm / 0.94 in.
1,800-8,000r.p.m.
2,350 g / 82 oz.
Dimensions (mm)
THREE VIEW DRAWING
Specifications
Displacement
Bore
Stroke
PracticalR.P.M.
Output
Weight
43
116
48.6
43
33
76
40
50
90
72
113
78.5
96
80
133
173
40
40 40
113
234.3
40
121.3
43
29
C
Copyright 2006 by O.S.Engines Mfg. Co., Ltd. All rights reserved. Printed in Japan.
600 91870 1 108 03
TEL. (06) 6702-0225
FAX. (06) 6704-2722
6-15 3-Chome Imagawa Higashisumiyoshi-ku
Osaka 546-0003, Japan
URL : http://www.os-engines.co.jp