O.S. Engines GT55 User Manual

GT55

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

'SAFETY INSTRUCTIONS AND WARNINGS'

section on pages 2-5 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.

Two stroke gasoline engine for airplanes

1



SAFETY INSTRUCTIONS AND
WARNINGS ABOUT YOUR O.S. ENGINE

ABOUT THE ENGINE

ENGINE PARTS NAME

SILENCER / INSTALLATION

FUEL TANK & LINES

CARBURETOR WLA-2 PARTS NAME

CARBURETOR LINKAGE

IGNITION MODULE

PROPELLER

MIXING OF OIL

CONTENTS

RUNNING-IN / STARTING

NEEDLE ADJUSTMENTS

FLIGHT & MAINTENANCE

ENGINE EXPLODED VIEW

ENGINE PARTS LIST

CARBURETOR EXPLODED VIEW

CARBURETOR PARTS LIST

O.S. GENUINE PARTS & ACCESSORIES

ENGINE THREE VIEW DRAWINGS

MEMO

2-5

6

7

8

9

10

11-12

13-14

15-16

17

18-23

24-25

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.

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.

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.

3

WARNINGS

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.

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.

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

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.

4

When checking a spark plug with the power source
on, do not hold the plug, plug cap, high tension cord
nor grounding wire, or you will get a shock.

Install a top-quality propeller of the diameter and
pitch specified for the engine and aircraft.

Do not use a nylon propeller. It has the possibility of
flying apart due to strong centrifugal force caused
by high rpm.

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.

NOTES

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.

5

NOTES

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.

6

ABOUT THE ENGINE

This engine is designed for experienced fliers.
Beginners and newcomers should not use this
engine.

The engine unit, carburetor and igniter are
specially designed.

It offers broad power characteristics suitable for
sport flight as well as acro flight.

The large and dense cooling fins ensure
sufficient cooling against overheating.

The specially designed ignition module “IG-01” is
equipped with a micro computer and designed
not to operate at low rpm and run intermittently
when the battery voltage drops. It provide high
voltage for sure firing through the operating
range while utilizing a low current draw.

STANDARD ACCESSORIES

Spark Plug CM-6

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Exhaust Gasket GT55

Ignition module Assembly (IG-01)

7

Propeller Retaining Screws

ENGINE PARTS NAME

Spark Plug

Cylinder Head

Crankcase

Cover Plate

Velocity Stack

Carburetor Complete WLA-2

Drive Spacer

Pilot Shaft

RPM Sensor

Propeller Washer

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Sensor Leads

Battery Leads

Sensor Leads

High Tension Cord

Ground Wire

8

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.

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.)

Engine mounting face has been high-precision machined
flat. Make sure mounting face of the model is also flat.

SILENCER / INSTALLATION

The GT55 does not come with a silencer. Select an
effective silencer from commercially available ones.
(Mounting bolt pattern is the same as most other makes of
the similar engine size.)

Use 5mm 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 velocity stack so that the air intake will not be
restricted. (Cut out the cowling big enough if necessary.)

9

Use a tank designed for gasoline.
(Tanks designed for glow fuel use a rubber cap which is
deteriorated by gasoline.)

A 600cc tank will provide 13~14 minutes flight.

Install a commercially available gasoline fuel filter between
fuel tank and carburetor. (Clean the filter from time to time.)

For plumbing use TYGON F-4040 (Yellow color) or strong
nitrile rubber of more than 3mm ID and 6mm OD.
Replace tubing periodically as it becomes hardened.
(Replace tubing inside the fuel tank every six months.)

FUEL TANK & LINES

Use fuel line keepers at the end of the tubing to prevent at
from coming off.

This engine does not require a muffler pressurized fuel
system but be sure to provide an air vent.

Be sure to install an in-line fuel filter between the tank and
carburetor to prevent foreign matter in the tank from
entering the carburetor. Clean the filter periodically.

Be sure to use a gasoline resistant fuel tank cap.

Be sure to equip air vent pipe.

Be sure to use binding band to prevent from coming off.

Be sure to replace piping inside periodically.

To carburetor fuel inlet

Piping for re-fuelling

R

10

Fuel Inlet

CARBURETOR WLA-2 PARTS NAME

Carburetor Body

High Speed Needle

Idle Speed Stop Screw
(No need to adjust. Factory adjusted.)

Slow Speed Needle

Air Vent Fitting
(No need to connect in normal use.)

Throttle Valve Lever

Choke Valve Lever

High Speed Stop Lever

High Speed
Stop Lever Retaining Screw

Idle Speed Stop Lever

Throttle Valve Lever
Retaining Screw

Spring Throttle Return

11

1.

2.

3.

4.

CARBURETOR LINKAGE

Remove the throttle lever retaining screw. (Pay attention
not to lose this screw because it is special size.) Also, be
careful not to remove the idle stop screw and return spring.
If they are removed accidentally, assemble them being
aware of the small notch.

Then, remove the opposite side high speed stop retaining
screw. (Pay attention not to lose this screw because it is
special size.) At this time, be careful not to remove the
high speed stop lever.

Then, install the throttle lever with the throttle lever
retaining screw.

Then, install the idle speed stop lever with the high speed
stop lever retaining screw.

Connect the throttle linkage so that the engine
can be stopped via radio operation.

Connect the throttle linkage so that the engine
can be stopped by radio operation in case of
unexpected starting, or there is a possibility of
injury.

Throttle lever can be installed either on right or
left. Here is a changing procedure.

When loosening and tightening each retaining screw, do
so with the throttle valve at mid position.
(If the throttle valve lever retaining screw is loosened or
tightened with the throttle valve fully opened or closed,
excessive force will be applied, which will results in
breaking the lever.)

NOTE