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Two stroke twin-cylinder

gasoline engine for airplanes

It is of vital importance, before attempting to operate your 

engine, to read the general 'SAFETY INSTRUCTIONS 

AND WARNINGS' in the following section 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.

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

NOTES

These cover events which might involve serious 

(in extreme circumstances, even fatal) injury.

These cover the many other possibilities, generally 

less obvious sources of danger, but which, under 

certain circumstances, may also cause damage or 

injury.

WARNINGS

ABOUT THE ENGINE

STANDARD ACCESSORIES

ENGINE PARTS NAME

INSTALLATION

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.

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.

Switch off the ignition module to stop the engine or 

fully close the throttle valve via the transmitter to 

shut off the fuel supply. Otherwise there is a 

possibility of injury.

Immediately after the engine is stopped, the engine 

may start with a crank even when the igniter switch 

is off. Do not crank the engine, or there is a 

possibility of injury.

Be sure to install an externally operable switch for 

the ignition system battery to stop the engine if it is 

started unintentionally with the radio transmitter 

turned off or there is the possibility of injury.

Connect the throttle linkage so that the engine can 

be stopped via radio operation.

Always check the throttle linkage.If it is disconnected, 

throttle action becomes uncontrollable, which may 

result in a serious accident.

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.

Use an electric starter for this engine. The wearing of 

safety glasses is also strongly recommended. 

If you try hand starting, be sure to use a chicken stick 

or heavy glove. Never attempt to start the engine 

with a bare hand.

Be sure to carry out adjustments of the high speed 

needle and slow speed needle after stopping the 

engine.

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.

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.

Install 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 washer and 

propeller installing screws using the correct size 

wrench. Always check the tightness of propeller 

installing screws and retighten them, if necessary, 

before starting the engine. Also, check the tightness 

of all the screws and nuts before restarting the 

engine.

When checking a spark plug with the power source 

on, do not hold the plug, plug cap, high tension cord , 

or you will get a shock.

Install a top-quality propeller of the diameter and 

pitch specified for the engine and aircraft.

Any propeller requires utmost attention to handle. 

Be sure to follow the instruction manual supplied with 

a propeller.

This engine was designed for model aircraft. 

Do not attempt to use it for any other purpose.

Start the engine only after installing it in the model. 

Do not start the engine before installing it in the 

model, or there is a possibility of injury.

Be sure to use an effective silencer (muffler). 

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.

Mount the engine in your model securely, following 

the manufacturers’ recommendations.

For their safety, keep all onlookers (especially small 

children) well back (at least 10 meters) when 

preparing your model for flight.

NOTES

Model engines generates 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 results in a serious 

burn.

Observe the laws and regulations in each 

country and district concerning the usage, 

transportation and storage of gasoline. Ask 

details at fire station in each district.
Never operate your engine in an enclosed space. 

Model engines, like automobile engines, exhaust 

deadly carbon-monoxide. Run your engine only 

in an open area.
Do not operate the engine nor model alone, or 

there is a possibility of injury.

Carry out the mixing of the gasoline and 

oil outdoors or in a well ventilated place 

away from any source of fire to prevent the 

possibility of a fire.
Refill the fuel tank only after the engine is 

well cooled down, or there is a danger of 

fire.

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.
Gasoline is poisonous. Do not allow it 

come into contact with the eyes or mouth. 

Always store it in a clearly marked 

container in a cool and dark place and out 

of the reach of children. There is a 

possibility that it may damage your health.
Gasoline is highly flammable. Keep it away 

from an open flame, excessive heat, 

sources of sparks, or anything else which 

might cause it to ignite. Do not smoke or 

allow anyone else to smoke near to it.

This engine is designed for experienced fliers.  

Beginners and newcomers should not use this engine.
The ignitor and the carburetor are specially designed 

for the engine.
The normal rotation direction of the engine is 

counterclockwise facing to the propeller.
It offers broad power characteristics suitable for 

sport flight as well as acro flight.
The specially designed ignition module “IG-10” is 

equipped with a micro computer and designed not to 

operate below 120 rpm.
The positions of the throttle lever and the choke 

lever can be changed at desired angle by yourself.
A silencer is not included in the box since we do not 

sell it.  Purchase a suitable one in the market. 

Spark Plug CM-6 (2pcs.)

Ignition module

Assembly (IG-10)

Battery Leads Sensor Leads

High Tension Cord

Spark Plug

Cylinder Block

Rear Housing

Carburetor Complete

HS-324A

Sensor

Leads

Use a tank designed for gasoline. (Tanks designed 

for glow fuel use a rubber cap which is deteriorated 

by gasoline.)
A 1,000cc tank will provide 12~13 minutes flight.

(With full throttle, it will provide 7~8 minutes flight.)
Install a commercially available gasoline fuel filter 

between fuel tank and carburetor. (Clean the filter 

from time to time.)

FUEL TANK & LINES

Use a strong enough material for the mounting face 

of the model, such as birch ply firewall of more than 

8mm thick.
Make sure the mounting face of the model is flat. If it is 

uneven, work on it to be flat. (When shims are added 

to change the thrust angle, work on it to be flat.)
The surface of the radial mount is precisely 

machined flat. Make sure the mounting face of the 

model is also flat.

Use 6mm steel hex socket head bolts to install the 

engine. (Do not use brass, soft steel nor aluminum 

screws, because they are not strong enough.) Also, 

use the Nord Lock Washers (optional extra) and 

other anti-loosening washers or apply locking agent.
Be sure that there is sufficient air intake and outlet 

area on the model for engine cooling to avoid 

overheating. (Pay careful attention to the cooling 

since a gasoline engine generates more heat than a 

glow engine.)
Secure at least a 30mm dia. area around the air 

intake of the carburetor so that the air intake will not 

be restricted. (Cut out the firewall big enough if 

necessary.)

RPM Sensor

Drive

Spacer

Radial Motor Mount

Propeller Washer

Cap Screw M5x50 (6pcs.)

Propeller Washer

Front Housing

GT120T

Ignition module IG-10

Plug Cap

Battery

Connector

Sensor Connector

Propeller

Retaining Screw

Sensor

Connector

Throttle Lever  (2pcs.)

Summary of Contents for GT120T

Page 1: ... installing it in the model or there is a possibility of injury Be sure to use an effective silencer muffler 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 Mount the engine in your model securely following the manufacturers recommendations For their safety keep all onlookers especially small children w...

Page 2: ...stem Do not use any propeller which has become split cracked or nicked even very slightly or received strong impact even if no apparent damage is visible PROPELLER SPINNER ATTACHMENT Since the GT120T 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 U...

Page 3: ...nce reliability and long life Check the tightening of each screw especially engine installation screws and silencer installation screws each time Also for the first 4 to 5 flights tighten the screws after each flight Cooling is more vitally important to a gasoline engine than to a glow engine If overheating symptoms loss of power at full throttle or exhaust note at mid speed changes from cloudy on...

Page 4: ...ngine SPECIFICATIONS C Copyright 2017 by O S Engine Mfg Co Ltd All rights reserved Printed in Japan 60093430 011800 1 2 3 4 5 6 7 8 8 1 8 2 9 10 11 11 1 12 13 14 15 16 17 18 19 20 28603100 28614000 28603401 28603200 29706000 29717000 28602100 4AB08000 29708100 29708200 29332000 4AB01000 74002A20 74002321 28631000 4AB02000 26730005 4AB01800 4AB28000 4AB18000 4AB15000 4AB21000 4AB81000 4AB81410 7400...

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