O.S. engine GT120THU User manual

2-stroke gasoline engine for UAV
GT120THU
Instruction manual
Ver1.02
2020.OCT.26
O.S. ENGINES MFG. CO., LTD.

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CONTENTS
1. ABOUT THIS MANUAL ………………………………………………………………………………………….…………..………… 2
2. SAFETY INSTRUCTIONS AND WARNINGS ……………………………………………………………………..………………… 2
3. OVERVIEW of GT120THU ……………………………………………………………….……………………………..……… 3
4. SPECIFICATIONS of GT120THU ………………………………………………………………………………….………………… 3
(1) GT120THU engine
(2) OGA-200 generator
(3) ORF-200 regulate rectifier
5. THE NAME OF EACH PART……………………………………………………………………………………..……………………… 4-6
6. BATTERIES ……………………………………………………………………………………………………………………………..…… 6
(1) Battery of throttle & choke servo and starter switch
(2) Ignitor battery
(3) Starter battery
7. REGULATE RECTIFIER ……………………………………………………………………………..…………………………………… 6
8. COOLING SYSTEM ………………………………………………………………………………………………………………..……… 7
9. INSTALLATION OF THE ENGINE AND OTHER EQUIPMENT………………………………………………………………… 7
(1) Engine installation
(2) Fitting the silencer
(3) Air cleaner installation
10. FUEL TANK ………………………………………………………………………………………….……………………….……………… 7
11. PIPING ………………………………………………………………………………………………….……………………………..……… 8
12. WIRINGS ……………………………………………………………………………………………………….………………………..……… 8
(1) Wirings of throttle servo, choke servo and starter switch
(2) Wirings of starter switch
(3) Regulate rectifier output wirings
13. MIXING OF OIL ………………………………………………………………………………………………………..…………………… 8
14. BREAKING IN ……………………………………………………………………………………………………………………………..…… 9
15. START-UP INSPECTION ……………………………………………………………………………………………………….………… 9
16. PROCESS OF STARTING ENGINE ……………………………………………….………………………………………………… 9-10
(1) Getting gas in carb
(2) Choke
(3) Start the engine
(4) Dealing with engine start problems
17. WARMING UP THE ENGINE …………………………………………………………………………………….……….…………… 11
18. ADJUSTMENT OF CARBURATOR …………………………………………………….……………….…………………………… 11
(1) Adjustable range of high and low end needle
(2) Adjustment before taking off
(3) Adjustment during hovering
(4) Adjustment during flight
19. INSPECTIONS BEFORE FLIGHT………………………………………………………………………………………….….…………… 12
20. FLIGHT ……………………………………………………………………………………………………………………..….….…………… 12
21. MAINTENANCE AFTER THE FIRST FLIGHT ………………………………………………………….………….….…………… 13
22. OPERATION LOG ………………………………………………………………………………………………………………..….……… 13
23. PERIODICAL INSPECTION AND MAINTENANCE …………………………………………………….……….….…………… 13
(1) Inspection after 25-hour flight
(2) Inspection after 50-hour flight
(3) Inspection after 100-hour flight
24. AFTER-SALES SERVICE …………………………………………………………..………….……………………….………….……… 13
25. EXPLODED VIEW ………………………………………………………………………………….……………….….....……….……… 14
26. PARTS LIST ……………………………………………………………………………………………………………….…….……..……… 15
27. 3-VIEW DRAWING ……………………………………………………………………………..………………………..…………..……… 16

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1. ABOUT THIS MANUAL
It is of vital importance, before attempting to operate the engine, to read this booklet and adhere to the
advice contained herein. The “SAFETY INSTRUCTIONS AND WARNINGS” (below) must be read first.
2. SAFETY INSTRUCTIONS AND WARNINGS
(1) The power of the engine is capable of harming you, or others, if it is misused or abused. As an owner
you are responsible for the safe operation of the engine, so act with discretion and care at all times.
(2) The advice which follows is grouped under two headings according to the degree of damage or danger
which might arise through misuse or neglect.
WARNING-These cover events which might involve serious (in extreme circumstances, even fatal) injury.
ATTENTION- These cover the many other possibilities, generally less obvious sources of danger, but which,
under certain circumstances, may also cause damage or injury.
(3) WARNINGS
①Never touch, or allow any object to come into contact with the rotating propeller and do not crouch over
the engine when it is running.
②Gasoline is poisonous. Do not allow it comes 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.
③Gasoline 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.
④Carry 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.
⑤Refill the fuel tank only after the engine is well cooled down, or there is a danger of fire.
⑥The engine generates considerable heat. Do not touch any part of the engine until it has cooled.
⑦Observe 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.
⑧Never operate your engine in an enclosed space. Model engines, like automobile engines, exhaust
deadly carbon-monoxide. Run your engine only in an open area.
⑨Do not operate the engine or UAV aircraft alone or there is a possibility of injury.
⑩When adjusting the output of regulate rectifier, make sure it match the voltage of power supplies, or it
could bring a danger of fire.
⑪Do not charger the battery while the regulator rectifier is working since it could bring the danger of fire.
(4) NOTES
①This engine is designed for UAV aircrafts. Do not attempt to use it for any other purpose.
② Start the engine only after installing it in the UAV aircraft. Do not start the engine before installing it in
the aircraft, or there is a possibility of injury.
③ 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.
④ Mount the engine in the aircraft securely, following the manufacturers’ recommendations.
⑤ For people safety, keep all onlookers (especially small children) well back (at least 30 meters) when
preparing the aircraft for flight.
⑥When checking a spark plug with the power source on, do not hold the plug or the plug cap, the high-
tension cord, or you will get a shock.
⑦Always check the throttle linkage. If it is disconnected, throttle action becomes uncontrollable, which
may result in a serious accident.
⑧Take 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.
⑨Use an electric starter for the engine. To wear safety glasses is strongly recommended. If you try
hand starting, be sure to use a safety stick or heavy glove. Never attempt to start the engine with a bare
hand.
⑩Do not start the engine in an area containing loose gravel or sand. The propeller may throw such
material in your face and eyes and cause injury.

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⑪If you have to carry the aircraft 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.
⑫Turn off the ignitor switch 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.
⑬Just after the engine stopped, the engine may start with a crank even the ignitor switch is off. Do not
crank the engine, or there is a possibility of injury.
⑭Be sure to equip an on/off switch between the ignitor and a battery, which you can reach from outside the
aircraft to stop the engine if it is started unintentionally with the transmitter turned off.
⑮The throttle linkage should be made as it can be remotely controlled to stop the engine in case of an
unintentional start.
3. OVERVIEW OF GT120THU
(1) The engine is two-stroke gasoline engine designed for UAV aircrafts.
(2) The engine is equipped with an electric starter.
(3) The engine is equipped with a generator and a regulate rectifier to secure power supply (AC → DC
rectification and voltage regulation) for a long flight
(4) The engine is equipped with a throttle servo, a choke servo, a starter switch, a regulate rectifier and an
ignitor etc. onboard.
(5) The onboard generator OGA-200 of is a 3-phase alternating- current AC generator with an excellent
cooling system.
(6) The regulate rectifier is equipped with an open regulate circuit for high efficiency. The output can be
adjusted within 6V-30V.
(7) The engine runs counter-clockwise when viewed from the front. Consult us if you want to run it reverse
rotation.
(8) This is an air-cooled engine. For keeping the engine always in an appropriate temperature condition, a fan,
a shroud or other cooling system of your own are needed.
(9) The engine is only designed for UAV. Do not attempt to use it for any other purpose.
4. SPECIFICATIONS
(1) GT120THU engine
Type ： 2-stroke air - cooled engine
Displacement ：119.82cc
Bore × stroke ：44mm×39.4mm
Output power ： about 10ps(7.4kW)/7,500rpm
Practical RPM range ：1,500～8,000rpm
Weight ：5,620g (silencer & accessories included)
Fuel ： regular gasoline mixed with oil (gasoline：oil＝50：1)
Carburetor ：Diaphragm type/ Tillotson HS type
Ignition method ： battery CDI
Ignition plug ： CM-6 type
Lubrication method ： follow the lubrication instruction by the oil in the fuel
Fuel consumption ：about 100cc/min/7,000rpm(full load)
Ideal condition ： temperature -20〜50℃、height 0〜3,000m
Durable time ： over 500hrs (overhaul：every 100hrs)
(2)OGA-200 generator
 Type: Three-phase AC generator
 Back electromotive force constant: 1.43 mV / rpm
 Number of poles: 4 poles
 Rated voltage: 12 V
 Maximum current: 25 A (20 min)
 Rated current: 14 A
 Phase to phase resistance: 35 mΩ
 Gear ratio (GT 120 THU): 3.94: 1

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(3)ORF-200 Regulated Rectifier
 Type: 3-phase AC open type Regulate Rectifier
 Maximum input voltage: 100 V (AC)
 Rated input voltage: 60 V (AC)
 Maximum output power: 200 W (10 min)
 Maximum output voltage: 28 V
 Minimum output voltage: 6 V
 Maximum output current: 16 A
 Rated output power: 140 W
 Rated output voltage: 12 V
 Rated output current: 12 A
5. NAME OF EACH PART
Fig 1

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Fig 2.
Fig 3.

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№
名称
Name
備考/Note
1
ファンシャフト
Fan Shaft
2
E-6030L サイレンサー
E-6030L Silencer
3
取付けマウント
Mount
4
シリンダーブロック
Cylinder block
5
E-6030R サイレンサー
E-6030R Silencer
6
プラグキャップ
Plug cap
7
ハイテンションコード
High tension cord
8
スロットルサーボ
Throttle servo
9
燃料インレット
Fuel inlet
10
エアクリーナー
Air cleaner
11
キャブレター
Carburetor
12
プラグ CM-6
Spark plug CM-6
13
チョークサーボ
Choke servo
14
ﾚｷﾞｭﾚｰﾄﾚｸﾃｨﾌｧｲｱ ORF-200
Regulator/Rectifier ORF-200
15
チョークサーボコネクター
Choke servo connector
16
スロットルサーボコネクター
Throttle servo connector
17
イグナイター電源コネクター
Igniter power connector
18
ﾚｷﾞｭﾚｰﾄﾚｸﾃｨﾌｧｲｱ出力リード
Reg/Rec power lead
19
スタータースイッチコネクター
Starter switch connector
20
スタータースイッチ
Starter switch
21
スターター電源コネクター
Starter power connector
22
イグナイター IG-11
Igniter IG-11
23
スターターモーター
Starter motor
24
発電機 OGA-200
Generator OGA-200
25
ハイニードル
High end needle
26
スローニードル
Slow end needle
27
チョークアーム
Choke lever
28
チョークシャフト
Choke shaft
29
チョークバルブ
Choke valve
30
スロットルシャフト
Throttle shaft
31
スロットルバルブ
Throttle valve
32
スロットルアーム
Throttle lever
6. BATTERIES
(1) Throttle servo, choke servo and starter switch batteries
Power supply: 4.8V-8.4V
Use the radio control system (receiver) battery.
(2) Ignition battery (Attention)
Power supply: 6.0V-8.4V
Use an insulated power supply independent of the radio control system, starter and on-board equipment.
(3) Starter switch battery
Output power: 11.1～16.8V
Use the power supply, whose capacity of battery is 2,200mAh or more, the discharge power is 35C or more.
7. ABOUT THE REGULATE RECTIFIER
The factory setting of output voltage is 12V.
Refer to the ORF-200 regulate rectifier instruction to change the output voltage.
Not only does the output voltage concern with the electromotive capacity of generator, but also with the
rotation per minute of the engine, which means there is a possibility that the output voltage may not reach

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the set voltage. For example, at the situation setting output voltage is 12V, the generator speedup ratio
of GT120THU is 3.94:1/ the counter electromotive force is 1.43 mV/ conversion efficiency is around
85%)≒2,500rpm.
So when it drops lower than 2,500rpm, the output voltage will decrease proportionately.
8. COOLING SYSTEM
The engine cylinder block has to be cooled down while running since it is air-cooled. Since the propeller,
cooling fan and shroud are not provided with this engine. Prepare your own.
In case of making your own cooling system, the system is supposed to cool down the cylinder head
temperature (CHT fig. 4) lower than 180℃ to make the engine work properly.
Fig. 4 shows the temperature measuring point.
Fig.4
9. INSTALLATION
(1) Engine
Bolts for mounting it on the aircraft are not provided as accessories. Purchase 6 pieces by yourself.
The strength level of the screws should be higher than 12.9, which can be used as cap screws. Also, the
screws for meshing part with the engine are suggested to around 7-8mm (tightening torque 5.4 N･m).
(2) Silencer
Mount the silencer which is included in the accessories with M5X25 cap screw and nord-lock washer
(tightening torque 7.2 N･m). Apply the liquid gasket which is gasoline resistant, on the joint surface to
prevent oil leakage from it (ThreeBond TB1212).
(3) Air cleaner
Mount the air cleaner on the carburetor with the attached hose band (tightening torque 1.0 N･m).
10. FUEL TANK
(1) Fuel consumption of the engine is
“100cc/min/7,000rpm (full load)” in this manual.
Decide a fuel tank capacity according to it.
(2) Choose a gasoline resistant fuel tank. Do not
use a fuel tank for glow engines because tank cap is
not gasoline resistant.
(3) Wash a fuel tank with gasoline before the first use
to wash off remaining plastic pieces and dusts.
Fig.5
(4) Do not use muffler pressure from a fuel tank.
Make sure to have an air vent pipe for ventilation.
(5) Use the following tube for piping: Tygon® F-4040A, Fluoro rubber or Nitrile rubber (I.D. φ3.0～3.2mm,

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O.D.φ6.0～6.4mm). The tubes should be replaced periodically because they harden with age. A tube
in a fuel tank should be replaced in 6 months to one year.
(6) The fuel tank should have three separate tubes including one exclusively for refueling. Use φ0.6～0.8
mm the stainless steel wire clips to fix each of the tube.
11. FUEL TUBE
(1) Clip the joint part of each tube with φ0.6～0.8 stainless steel wire or hose accessory clips.
(2) Piping between the fuel tank and fuel filter, and the fuel and filter carburetor
① Use the fuel filter # 78300000 as shown in the Fig. 6, be
sure of the direction since it is vital for the fuel filter.
② The length of the each tube should have a margin of
10mm in addition to the shortest connection distance.
③ Fix the tubes firmly not to be moved by flowing wind
pressure, be careful not kink the tubes also.
Fig 6.
12. WIRINGS
(1) Wirings of the throttle servo, the choke servo, and the starter switch
①Connect the throttle servo to the throttle channel of receiver and set the direction of servo arm
movement, the fully open / close position (end point adjust) using functions of the transmitter.
②Connect the choke servo to an auxiliary (aux.) channel of the receiver and assign the channel to a 2 or 3 –
position alternate toggle switch. Set the direction of servo arm movement, the fully open / close position
(end point adjust) using functions of the transmitter.
③Connect the starter switch to an auxiliary (aux.) channel of the receiver and assign the channel to a 2-
position momentary toggle switch. Set the direction of the switch, the fully open / close position (end
point adjust) using functions of the transmitter. The starter switch determines on or off at the threshold of
1,500µs PWM signal, which is neutral position. So when you set the fully open / close position, 1,500µs
PWM signal should be included in the range of turn on / off the 2-position momentary toggle switch.
(2) Wiring of starter switch battery
Charging the starter use the its equipped XT90 type concave connector, the voltage of starter battery is 11.1
～16.8V, the capacity of it is needed to be over 2,200 mAh, use the more than 35C discharge capacity
power supply to charge it.
Attention:
Do not run the starter for more than 3 seconds at a time. Give the starter at least 3-second interval for
continual use. Otherwise the starter, lead wires and battery may get damaged.
(3) Wiring of regulate rectifier output
The output of regulate rectifier has two black lead wires and 14AWG wire which are pre-tinned without any
connector. However, you can wire it yourself depends on the equipment or connector you are using.
13. FUEL AND OIL MIX
(1) Use regular gasoline. (No need to use high octane gasoline.)
(2) Alcohol based glow fuel cannot be used in this engine because it cannot make the engine work properly,
and also the internal carburetor plastic parts will get damaged.
(3) Use high quality 2-stroke engine oil available on the market because some oil might accumulate carbon
residues in the combustion chamber and the exhaust port after several-hour operation and cause a
trouble. Check the combustion chamber if there is unusual residue in short period.
(4) Follow the oil manufacturer’s recommendations concerning the mixture ratio of gasoline and oil. If
there is no recommendation, mix with a 25:1 ratio. We have checked and approved the following oil
mixture ratio. ZENOAH 2-strokes genuine oil FD (50:1), KLOTZ ModeLube® (50:1), Castrol Power 1 – TTS
Racing (50:1). (This does not mean we guarantee the quality of these oils.)

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(5) With a gasoline engine, passages in the carburetor are narrower than that of a glow engine, therefore it is
very sensitive against foreign materials such as dust. It is suggested to use optional accessory Super Filter L
(Code No.72403050) when filling a tank in a model from a container for transportation or storage.
14. BREAKING IN AT FIRST TIME
Breaking process on the bench is not necessary for this engine since the engine is broken in for 10 minutes at
the factory before the shipment. But you need to keep in mind the several instructions as follows.
(1) Run the engine in rich adjustment during breaking in.
(2) Use the fuel at 25:1 mixture ratio with the oil you are using for actual operation.
(3) Break in the engine mounted in a aircraft with actual flying.
(4) The flying during breaking in is mainly hovering. Do not fly with additional payloads.
15. START-UP INSPECTION
Pre-operation inspections should be done as shown below.
GT120THUinspection before operation
Items to be inspected
Inspection contents
Method
Engine installation
Check if the engine is mounted correctly and if there is no loose screws
and bolts.
Visual
Silencer mounting
Check if the silencer is mounted correctly or there is a loose.
Visual
Air cleaner
Check if the air cleaner is firmly fixed and if there is foreign material on
it.
Visual
Propeller, clutch,
cooling fan
Check if the propeller, clutch, cooling fan are mounted correctly and
there is no loose screws and bolts.
Visual
Exhaust pipe
Check the exhaust pipe if there is foreign material in it.
Visual
Cooling air passage
Check the air inlet/outlet if there is foreign material.
Visual
Plug cap
Check the plug cap if it is fixed firmly to the spark plug.
Visual
Ignitor high tension
cord
Check if there is wear and tear out, or dirt on it.
Visual
Fuel tubes
Check if tubes are frayed, kinked.
Visual
Check if tube clips are fit firmly.
Visual
Electric wirings
Check if there is no cut, wear, and dirt.
Visual
Check if all connectors are firmly connected.
Visual
Oil leakage
Check if there is oil leakage from an engine.
Visual
Linkage
Check if rod ends and link rods are firmly connected.
Visual
Check if servo horns and servos are firmly fixed with screws
Visual
Remaining fuel
Check if the fuel tank is full.
Visual
Mixture oil
Check if gasoline and oil are mixed at correct rate.
Visual
16. HOW TO START THE ENGINE
(1) Inducing the fuel
① Turn on the transmitter.
② Turn on the receiver switch.
③ Turn off the ignitor switch.
④Close the choke valves of engine.
⑤ Open the throttle valve by 10 degrees from the fully closed position (the first idling position).
⑥ Use a starter to run it until the fuel coming through the inlet of carburetor.
Attention:
Do not run the starter for more than 3 seconds at a time. Give the starter at least 3-second interval for
continual use. Otherwise the starter, lead wires and battery may get damaged.

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(2) Choke
① Turn on the transmitter.
② Turn on the receiver switch.
③ Turn on the ignitor switch.
④ Close all choke valves of engine.
⑤ Open the valve by 10 degrees from the fully closed position (the first idling position)
⑥ Use the starter until the engine fires or “pop” (see the NOTE below)
⑦ Open the choke valve fully.
NOTE: Listen to the firing or popping sound carefully when you are using the starter to start the engine.
The sound is supposed to hear after using the starter for a few seconds. In case you cannot listen to the
sound, check the above article 9 – 12 again for the initial installation, or check if the article 16. (1) – (2) is set
up correctly. Then go to next step if everything is all right.
(3) Start the engine
① Turn on the transmitter.
② Turn on the receiver switch.
③ Open the choke valves.
④ Open the throttle valve by 10 degrees from the fully closed position (the first idling position).
⑤ Turn on the ignitor switch.
⑥ Inform your assistant or people around you that you are starting the engine.
⑦ Use a starter. Check the above article (2)-(3) procedures above again if it can’t get started for more than
3 seconds using the starter.
Warning:
Start it over than the position of fast idling might cause abnormal extra-output which could make propellers
or rotor move extremely fast. There is a possibility to damage yourself or things.
Attention:
Do not run the starter for more than 3 seconds at a time. Give the starter at least 3-second interval for
continual use. Otherwise the starter, lead wires and battery may get damaged.
(4) Countermeasures when the engine doesn’t start.
Possible reason:
Over rich (over choke) / over lean (not enough choking) the fuel mixture/incorrect throttle opening setting /
the ignition setting up is not done completely (for example, ignition switch is off) .
Follow procedures below:
①Check the power supply to make sure the switch is on / battery is charged/ wires are not got damaged/
connectors are properly connected etc.
②Check and make sure if the throttle valve is at the first idling position- not only the position of transmitter
throttle stick/ but also the position of fully opened throttle servo/ fully closed limit position (end point
adjustment)/ the direction of throttle servo movement (NORMAL⇔REVERSE).
③Check and make sure if it is not over choke- Remove the spark plug and check if the center and ground
electrodes get wet with gasoline.
If it does, it is over choke, follow instruction below
1. Turn off the ignition switch.
2. Remove the spark plug and the plug cap.
3. Fully open the chock valve.
4. Full open the choke valve.
5. Use the starter around 10 seconds.
6. Dry the electrodes of the spark plug by a blower, or wipe the gasoline on them with a cloth.
7. Put the plug procedures on the engine and fit the plug cap on it.
8. Repeat the above procedures (2)-(3).
④If the electrodes of spark plug are not moist or the exhaust port does not smell gasoline, there is not
enough choking. In case choking is still not enough even if you have repeated the procedures 16. (2) – (4)
②, the trouble may come from malfunction of the system rather than the problem of operation. Check the
article 10 – 11 above, check if the fuel filter is not clogged as well.

11 / 18
17. WARMING UP THE ENGINE
As a carburetor type, the engine sometimes hesitates, stalls, and has unstable idling when Cylinder Head
Temperature (CHT) is low, below 100℃. So warming up is needed when CHT is low by increasing the rpm
of idling (700 – 800 more than usual) and refraining from moving the throttle stick quickly. In case you
need quick warming up, increase the rpm of idling up to 3,000 – 4,000rpm, so that CHT raises more than
100℃ within several tens of seconds.
18. THE ADJUSTMENT OF CARBURETOR
(1) The range of adjustment by the slow needle and the high needle
Fig 7
Fig.7 shows the adjustment ranges. The slow needle affects even full throttle range and the high needle
affects 1/4 throttle opening. The slow needle and the high needle affect each other in a wide range
generally for gasoline engine carburetors, so both needles need to be adjusted in the range of hovering.
(2) Adjustment during taking off
When the engine is started and has stable idling, move up the throttle stick gradually for taking off.
①In case the engine “stutters” or “coughs” and hesitates to increase rpm without much power, the slow
needle is too rich. Turn in /clockwise the needle by 15 degrees and try taking off. Repeat the
procedure until you can take off the aircraft.
②In case rpm does not increase with sluggish acceleration, and the engine dies quickly, the fuel mixture is
lean. Turn the slow needle out/counter-clockwise by to richen the fuel mixture.
(3) Adjustment during hovering
Count the rpm of main rotor during hovering.
①In case the rpm of main rotor is higher than you desire, set the throttle curve lower and turn the slow
needle out/counter-clockwise by 30 degrees to richen the fuel mixture.
②In case the rpm of main rotor is lower than you desire and you lose altitude of the hovering aircraft,
probably the slow needle is set rich. Turn the slow needle out/counter-clockwise by 15 degrees to lean the
fuel mixture.
(4) Adjustment in flight
Basic engine adjustment during actual flight after breaking in
① Turn out/counter-clockwise the high needle by 30 degrees from the factory setting to check if it affects
hovering.
② Change the hovering mode to flight mode to fly around and check the engine performance in flight.
Losing power at full throttle, engine stall, over rev at lower rotor pitch are symptoms of lean needle
adjustment. When the needle adjustment is lean, the engine loses power and stalls abruptly. Start from
rich adjustment and lean the adjustment gradually.
③The engine gets overloaded and overheats even the slow and high needles are adjusted a little rich when
the main rotor maximum pitch is too high. Also, the engine overheats when it over-revved at low rotor pitch.

12 / 18
Note 1: The engine outputs 70 – 80% power at a half throttle position. Adjust the throttle stick position of
transmitter at around neutral for hovering using throttle curve and pitch curve setting functions.
Note 2: The needle adjustment of the engine in aircraft is closely related to the adjustment of throttle
curve, pitch curve, and governor functions of transmitter. So the total combination of these adjustments is
important.
Note 3: Applying spark plug ignition system to the engine, you can see rich adjustment symptoms relatively
easily and the engine hardly stalls because of stable ignition timing, on the contrary, it is hard to notice lean
adjustment and the engine sometimes stalls and overheats, so always start the adjustment with the needles
on rich side.
19. INSPECTIONS BEFORE FLIGHT
Check the following items after starting and warming up the engine.
GT120THU inspection contents
items
contents
Inspection Method
idling
Check if the engine runs stable at idling.
hearing/ using
tachometer
response
Move the throttle stick up and down during hovering to see if the
aircraft responses and if the speed of engine goes up and down.
Visual /hearing
inspection
Engine stop
switch
Check if the engine stops switch works.
Visual inspection
ignitor switch
Check whether the engine stops when the ignitor switch is turned
off.
Visual inspection
noise
Check if you hear unusual noise.
Hearing the sounds
smell
Check if you smell abnormal odor.
Smell the whole engine
radio control
system
Check if all the equipment work correctly when the engine is
running. (do the distance test and also see if it is working
normally during pirouetting)
visual inspection
Check and follow the instruction of UAV for inspection before flight.
20. FLIGHT
(1) Be prepared for unexpected troubles such as engine stall during flight.
(2) Using the engine management system ‘EM-100’, which is sold as an option by us, is recommended for
monitoring the engine speed, temperature, fuel level, the power supply voltage of igniter by the telemetry
function during flight.
(3) Cooling is more vitally important to gasoline engines than to a glow engines. If overheating symptoms
(loss of power at full throttle or the stick position of throttle goes up when hovering) are observed during
flight, immediately stop flying and carry out the following measures.
① Adjust the slow needle and high needle to make the air/fuel mixture as rich as possible within the range
you can continue flying.
② Set the throttle curve or pitch curve to make the overall engine rpm going up.
③ Prevent the air leakage from a cooling shroud if the engine is equipped with it.
④ Enlarge the cooling fan size.
(4) When an interval between two flights is short and the engine is still hot, although the overheating
symptoms could not be observed right after the first flight, the high temperature created by the former
flight can be transmitted all over the engine before the next flight, so the engine might show overheating
symptoms during the next flight. In this case, leave the engine until it is fully cooled down (in hot weather,
it may take more than one hour.) or run the engine for 4 to 5 minutes at idling.
21. INSPECTIONS AND TIGHTENING SCREWS AFTER THE FIRST FLIGHT
Check the following after the first flight of mounting the engine in an aircraft
(1) Tighten the screws of silencer again

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The silencer nuts and screws loosen due to the heat and vibration created by the flight, tighten them
again after the first flight following the instruction of 9.(2) silencer installation.
(2) Tighten the engine mounting screws
Tighten the engine mounting screws following the instruction 9. (1) Engine installation
(3) Check each part of aircraft again
The parts of aircraft would loosen due to the heat or vibration created by the engine during flight,
check them again to make sure every part has been tighten following the aircraft instruction.
22. OPERATION LOG
Inspection and maintenance of the engine is to be performed periodically based on operating hours.
So, it is necessary for you to write down operating log: date, place, starting time and ending time, each
operating time, total operating time, remarks.
23. PERIODICAL INSPECTION AND MAINTENANCE（Refer to the maintenance manual）
(1) Inspection after 25-hour operation
・Propeller
・Fuel tubes
・Fuel filter
・Plug cap & high tension cord
・Spark plug
・Throttle linkage
・Throttle servo
・Various fixing screws
・Various harnesses
(2) Inspection after 50-hour operation（Refer to the maintenance manual）
Maintain the items below in addition to the inspection after 25-hour operation.
・Remove carbon in a combustion chamber
・Adjust the tension of the generator pulley belt
・Inspect Regulator Rectifier
・Inspect the generator
(3) Inspection after 100-hour operation（Refer to the maintenance manual）
Follow the GT120THU maintenance manual to inspect the items below in addition to the inspection after 50-
hour operation.
・Every spare part of the engine
・Replace the fuel filter
・Replace the throttle servo
・Replace the fuel tube in the tank
24. AFTER-SALES SERVICE
For after sale service of the engine unit, contact us directly.

14 / 18
25. EXPLODED VIEW
FIG.8

15 / 18
26. PARTS LIST
№
Code
名称
Name
Note
1
79850100
ﾅｯﾄ M10X1.0
M10X1.0
Tightening Torque 44N･m
2
79871109
ｷｬｯﾌﾟｽｸﾘｭｰ M3X6(10 ｲﾘ)
CAP SCREW
M3X6(10/SET)
Torque 1.1N･m
3
4AA08000
ﾌｧﾝｼｬﾌﾄ
FAN SHAF
4
4AA70010
ﾄﾞﾗｲﾌﾞﾌﾟｰﾘ 3G63
DRIVE PULLEY 3G63
5
29708100
ﾃｰﾊﾟｰｺﾚｯﾄ
TAPER COLLET
6
79871520
ｷｬｯﾌﾟｽｸﾘｭｰ M5X20(10 ｲ
ﾘ)
CAP SCREW
M5X20(10/SET)
Torque 7.2N･m
7
29332000
ﾎﾞｰﾙ ﾍﾞｱﾘﾝｸﾞ(F)
BALL BEARING (F)
8
4AA01000
ﾌﾛﾝﾄｹｰｽ
FRONT CASE
9
74002320
回転ｾﾝｻｰ
ROTATION SENSOR
9-1
74002321
ｾﾝｻｰ ﾄﾘﾂｹﾈｼﾞｾｯﾄ(2 ｲﾘ)
SENSOR SCREW
SET(2/SET)
Torque 0.4N･m
10
28631000
ﾎﾞｰﾙ ﾍﾞｱﾘﾝｸﾞ(M)
BALL BEARING (M)
11
29708200
ﾍｲｺｳ ｷｰ
PARAREL KEY
12
4AA02000
ｸﾗﾝｸｼｬﾌﾄ一式
CRANKSHAFT ASSY
13
4AA07020
ﾄﾞﾘﾌﾞﾝﾌﾟｰﾘ 3G16
DRIVEN PULLEY
3G16
13-1
79820406
ｾｯﾄｽｸﾘｭｰ M4X6(10 ｲﾘ)
SET SCREW
M4X6(10/SET)
Torque 1.5N･m
14
4AA07050
ﾍﾞﾙﾄ 3GT-255-10
BELT 3GT-255-10
15
4AA32000
ﾎﾞｰﾙ ﾍﾞｱﾘﾝｸﾞ(ｼﾞｪﾈﾚｰﾀ)
BALL
BEARING(GENERATO
R)
16
54059001
ｼﾞｪﾈﾚｰﾀｱﾀﾞﾌﾟﾀ-
GENERATOR
ADAPTER
17
79871515
ｷｬｯﾌﾟｽｸﾘｭｰ M5X15(10 ｲ
ﾘ)
CAP SCREW
M5X15(10/SET)
Torque 5.4N･m
18
4AA07040
ｼﾞｪﾈﾚｰﾀﾎﾙﾀﾞ-
GENERATOR HOLDER
19
54053000
ｼﾞｪﾈﾚｰﾀｰ OGA-200
GENERATOR OGA-
200
20
27130020
ﾎﾞｰﾙ ﾍﾞｱﾘﾝｸﾞ(R)
BALL BEARING(R)
21
4AA01800
ﾘｱｹｰｽ
REAR CASE
22
4AA07070
ﾜﾝｳｪｲﾎﾙﾀﾞ-ｱｳﾀ-
ONE WAY HOLDER
OUTER
23
4AA07080
ﾜﾝｳｪｲｸﾗｯﾁ
ONE WAY CLUTCH
24
4AA07090
ﾜﾝｳｪｲﾘﾃｰﾅｰ(RTW-55)
ONE WAY
RETAINER(RTW-55)
25
4AA07110
ﾎﾞｰﾙ ﾍﾞｱﾘﾝｸﾞ(ﾜﾝｳｪｲ)
BALL BEARING(ONE
WAY)
26
4AA07100
ﾜﾝｳｪｲﾎﾙﾀﾞ- ｲﾝﾅｰ
ONE WAY HOLDER
INNER
27
4AA07130
ｽﾀｰﾀｰｽﾊﾟｰｷﾞｱ
STARTER SPUR GEAR
28
4AA07120
ｼﾑﾘﾝｸﾞ 12X16X1
SIM RING 12X16X1
29
79850121
ﾅｯﾄ M12X1.75LH
NUT M12X1.75LH
Torque 44N･m
30
4AA07140
ｽﾀｰﾀ-ﾓｰﾀ-
STARTER MOTOR
31
4AA07410
O-ﾘﾝｸﾞ (P15-FKM)
O-RING (P15-FKM)
32
4AA07190
ｽﾀｰﾀｰﾋﾟﾆｵﾝｷﾞｱ
STARTER PINION
GEAR

16 / 18
33
79871415
ｷｬｯﾌﾟｽｸﾘｭｰ M4X15(10 ｲ
ﾘ)
CAP SCREW
M4X15(10/SET)
Torque 3.6N･m
34
79872060
平ﾜｯｼｬ 6.0(10 ｲﾘ)
WASHER 6.0(10/SET)
35
4AA07210
ｽﾀｰﾀｰﾐﾄﾞﾙｷﾞｱ
STARTER MIDDLE
GEAR
36
79871410
ｷｬｯﾌﾟｽｸﾘｭｰ M4X10(10 ｲ
ﾘ)
CAP SCREW
M4X10(10/SET)
Torque 2.7N･m
37
4AA07240
ﾎﾞｰﾙ ﾍﾞｱﾘﾝｸﾞ(ｶﾊﾞｰ)
BALL
BEARING(COVER)
38
4AA07250
ﾘｱｶﾊﾞｰ
REAR CAVER
39
4AA07270
ﾃﾞﾊﾞｲｽﾌﾟﾚｰﾄｽﾃｰ
DEVICE PLATE STAY
40
4AA07400
ｼﾝｺﾞｳﾌﾞﾝｷﾕﾆｯﾄ SDU-01
SIGNAL DISTRIBUTOR
SDU-01
41
4AA07260
ﾃﾞﾊﾞｲｽﾌﾟﾚｰﾄ
DEVICE PLATE
42
79871140
ｷｬｯﾌﾟｽｸﾘｭｰ M3X12(10 ｲ
ﾘ)
CAP SCREW
M3X12(10/SET)
Torque 1.1N･m
43
4AA07290
ｻｰﾎﾞﾏｳﾝﾄ L
SERVO MOUNT L
44
4AA07280
ｻｰﾎﾞﾏｳﾝﾄ S
SERVO MOUNT S
45
4AA07300
ｻｰﾎﾞ BLA1HF
SERVO BLA1HF
46
79871030
ｷｬｯﾌﾟｽｸﾘｭｰ M2.6X10(10 ｲ
ﾘ)
CAP SCREW
M2.6X12(10/SET)
Torque 0.18N･m、
LOCTITE 222 使用
47
79872026
平ﾜｯｼｬ 2.6(10 ｲﾘ)
WASHER 2.6(10/SET)
48
4AA07060
ﾘﾝｹｰｼﾞﾎﾞｰﾙ
LINKAGE BALL
49
79850020
ﾅｯﾄ M2X0.4(10 ｲﾘ)
NUT M2X0.4(10/SET)
50
4AA07310
ﾎﾞ-ﾙﾘﾝｸ
BOLL LINK
51
4AA07330
ﾘﾝｸﾛｯﾄﾞ L39.5
LINK ROD L39.5
52
4AA07320
ﾘﾝｸﾛｯﾄﾞ L48
LINK ROD L48
53
54055000
ﾚｷﾞｭﾚｰﾄﾚｸﾃｨﾌｧｲｱ ORF-
200
REGULATE RECTIFIER
ORF-200
54
74002D00
ｲｸﾞﾅｲﾀｰ IG-11
IGNITION MODULE
IG-11
55
4AA07340
ｽﾀｰﾀｰｽｲｯﾁ SSW-100
STARTER SWITCH
SSW-100
56
4AA07350
ﾃﾞﾊﾞｲｽﾊﾞﾝﾄﾞ
DEVICE BAND
57
79872030
平ﾜｯｼｬ 3.0(10 ｲﾘ)
WASHER 3.0(10/SET)
58
28614000
ｼﾘﾝﾀﾞｰ ｶﾞｽｹｯﾄ
CYLINDER GASKET
59
4AA03200
ﾋﾟｽﾄﾝ
PISTON
60
29706000
ﾋﾟｽﾄﾝ ﾋﾟﾝ
PISTON PIN
61
29317000
ﾋﾟｽﾄﾝﾋﾟﾝ ﾘﾃｲﾅｰ(2 ｲﾘ)
PISTON PIN
RETAINER(2/SET)
62
4AA03400
ﾋﾟｽﾄﾝ ﾘﾝｸﾞ
PISTON RING
63
4AA03100
ｼﾘﾝﾀﾞｰﾌﾞﾛｯｸ
CYLINDER BLOCK
64
71669000
ｽﾊﾟｰｸ ﾌﾟﾗｸﾞ CM-6
SPARK PLUG CM-6
65
4AA15000
ｷｬﾌﾞ及びﾘｰﾄﾞｶﾞｽｹｯﾄ ｾｯﾄ
CAB.& REED GASKET
SET
66
4AB18000
ﾘｰﾄﾞﾊﾞﾙﾌﾞ
REED VALVE
67
4AA82000
ｷｬﾌﾞﾚﾀｰｲﾝｼｭﾚｰﾀ-
CARBURETOR
INSULATOR
68
4AB82000
ﾘﾍﾟｱｷｯﾄ HS-324A
REPAIR KIT HS-324A
69
79871540
ｷｬｯﾌﾟｽｸﾘｭｰ M5X40(10 ｲ
ﾘ)
CAP SCREW
M5X40(10/SET)
Torque 4.0N･m
70
4AB81000
ｷｬﾌﾞﾚﾀｰ HS-324A
CARBURETOR HS-
324A

17 / 18
71
4AB81410
ｽﾛｯﾄﾙｱｰﾑ
THROTTLE LEVER
72
4AA83000
ｴｱｸﾘｰﾅｰｱﾀﾞﾌﾟﾀ-
AIR CLEANER
ADAPTER
73
79871555
ｷｬｯﾌﾟｽｸﾘｭｰ M5X55(10 ｲ
ﾘ)
CAP SCREW
M5X55(10/SET)
Torque 5.4N･m
74
4AA84000
ｴｱｸﾘｰﾅ- PK-7E
AIR CLEANER PK-7E
付属品/ACCESSORIES
―
78300000
ｶﾞｿﾘﾝ用燃料ﾌｨﾙﾀｰ S
GASOLINE FUEL
FILTER S
―
70000001
ﾎｰｽｸﾘｯﾌﾟ φ6 (5 ｲﾘ)
HOSE CLIP 6
(5PCS/SET)
オプション/OPTION
75
4AA07390
ｻｲﾚﾝｻｰ E-6030R
SILENCER E-6030R
76
4AA07380
ｻｲﾚﾝｻｰ E-6030L
SILENCER E-6030L
77
55500006
ﾉﾙﾄﾛｯｸﾜｯｼｬ M5SP(10 ｲﾘ)
NORDLOCK
WASHERS
M5SP(10/SET)
78
79871525
ｷｬｯﾌﾟｽｸﾘｭｰ M5X25(10 ｲﾘ)
CAP SCREW
M5X25(10/SET)
Torque 7.2N･m

18 / 18
27. 3-DEMENSIONAL DRAWING (unit：mm)