91sxh C Spec P Manual

User Manual: 91sxh-c-spec-p-manual

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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 model, radio control equipment, etc.,
are accessible for checking at the same time.

CONTENTS
SAFETY INSTRUCTIONS AND
WARNINGS ABOUT YOUR O.S. ENGINE
NOTES ON INSTALLING,
COOLING-FAN AND CLUTCH

2-5

CARBURETOR CONTROLS

20-21

STARTING, RUNNING-IN ("Breaking-in")

22-24

ADJUSTMENT

24-27

NOTES ON INSTALLING THE ENGINE,
NOTES ON HEATING THE GLOW PLUG

INTRODUCTION

BASIC ENGINE PARTS,
INSTALLATION OF THE CARBURETOR

FACTS ABOUT GLOWPLUG

SUBSEQUENT READJUSTMENTS
CARBURETOR CLEANLINESS

ADJUSTMENT CHART

INSTALLATION OF THROTTLE SERVO

30
31

INSTALLATION OF THE ENGINE

CARE AND MAINTENANCE

ABOUT THE PUMP SYSTEM

EXPLODED VIEW & PARTS LIST

CARE OF FUEL PUMP

O.S. GENUINE PARTS & ACCESSORIES

32-35

FUEL TANK AND PIPING

13-16

THREE VIEW DRAWING

BEFORE STARTING

16-18

MEMO

SAFETY INSTRUCTIONS AND WARNINGS ABOUT YOUR O.S. ENGINE
Remember that your engine is not a "toy", but a highly efficient internalcombustion machine whose power is capable of harming you, or others, if it is
misused.
As owner, you, alone, are responsible for the safe operation of your engine, so act
with discretion and care at all times.
If at some future date, your O.S. engine is acquired by another person, we would
respectfully request that these instructions are also passed on to its new owner.
The advice which follows is grouped under two headings according to the
degree of damage or danger which might arise through misuse or neglect.

NOTES

WARNINGS

These cover the many other
possibilities, generally less obvious
sources of danger, but which, under
certain circumstances, may also
cause damage or injury.

These cover events which
might involve serious (in
extreme circumstances, even
fatal) injury.
2

WARNINGS
Never touch, or allow any
object to come into contact
with, the rotating parts.

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 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 engines generate
considerable heat. Do not
touch any part of your
engine until it has cooled.
Contact with the muffler
(silencer), cylinder head or
exhaust header pipe, in
particular, may result in a
serious burn.

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.
3

NOTES
These engine were designed for model
helicopters. Do not attempt to use it for any
other purpose.

After starting the engine, carry out any needlevalve readjustments after stopping the rotor by
closing the throttle to the lowest r.p.m..
Stop the engine before attempting to make
other adjustments to the carburetor.

Mount the engine in your model securely, following the manufacturers' recommendations,
using appropriate screws and locknuts.

Use an electric starter. The wearing of safety
glasses is also strongly recommended.
Press the rotor head down securely.

Install an effective silencer (muffler). Frequent
close exposure to a noisy exhaust (especially
in the case of the more powerful high-speed
engines) may eventually impair your hearing
and such noise is also likely to cause
annoyance to others over a wide area.

Take care that the glow plug clip or battery
leads do not come into contact with rotating
parts.
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.

Check the linkage to the throttle arm before
each flight.
Avoid sudden high r.p.m. immediately after the
engine is started, as the clutch will engage and
you may be struck by the rotor.

NOTES
Take care that loose clothing (ties, shirt sleeves,
scarves etc.) do not come into contact with the
rotor. Do not carry loose objects (such as pencils, screwdrivers, etc.) in a shirt pocket from
where they could fall through the rotor disc.
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.
Hold the rotor securely and keep well clear of
spectators.
Warning! lmmediately after a glowplug-ignition
engine has been run and is still warm,
conditions sometimes exist whereby it is just
possible for the engine to restart when turned
over WITHOUT the glowplug battery being
reconnected. Remember this if you wish to
avoid the risk of accidents.

Notes on installing cooling fan and clutch
Application is as follows:
Remove the crankcase rear cover plate from the
engine and rotate the crankshaft to the bottom
dead center (BDC) position.

Do not use a tool which
locks piston when
installing a cooling-fan
and clutch, or top of
the piston may be
damaged. Also, do not
insert a screw driver or
the similar into the
exhaust port.

Insert the crankshaft clamp so that its grooved
portion surrounds the crankpin and lower end of
the connecting rod and securely tighten the fan
or clutch onto the crankshaft.

BDC position

Rotate the crankshaft so that the
connecting rod comes to this position.

It is recommended to use Crankshaft
Clamp 7091 (Code No.71530500) available
as an optional tool.
It is made of durable engineering plastic
and locks the crankshaft without risk of
damage to any part of the engine.

Insert this groove onto
the connecting rod.

Note on heating the glow plug

Note on installing the engine
Cooling fan cover from some
helicopter models interferes the
heatsink head.
In this case, cut out the cover as
illustrated.

Heatsink head, crankcase and cover
plate of the engine are treated with
Alumite which does not conduct
current. Therefore, when heating a
glow plug, connect one lead to the
glow plug and the other to the head
of cover plate fitting screw.

Example
Example

Cut out according to the heatsink head.

INTRODUCTION

Note:

This is a pumped version of the 91SX-H
RING C Spec. Pump and muffler
pressurized fuel system ensure stable fuel
supply irrespectire of model attitude and
fuel level in the tank. Return system in the
carburetor ejects the excess fuel and
avoids getting rich at around idling. Easy to
adjust single needly Type 60M carburetor
incorporates a check valve which controls
the fuel supply at any r.p.m. range.

As delivered, the carburetor is not fit to
the engine.

Note:
Because of initial tightness, a standard
electric starter may have difficulty in
rotating the engine when cold, before it
has been adequately run-in. In this
case, use a high-torque type starter.
DO NOT, however, confuse tightness
with the symptoms of hydraulic lock
caused by an excess of fuel within the
cylinder - often the result of overpriming.
Attempting to force the engine to turn
over in this condition may cause
internal damage. Instead, remove the
glowplug, invert the engine and eject
surplus fuel from the combustionchamber.

Standard accessories
Carburetor Complete 60M
Glow Plug No.8

T nipple

Woodruff Key

Needle Adjusting Screw (M2.6x5 1pc.)
Silicone tube ( 2.5x 5.5xL300mm)
Instruction manual

INSTALLATION OF THE CARBURETOR

BASIC ENGINE PARTS
Heatsink Head

Carburetor
Typr 60M

As delivered, the carburetor is not fit to the engine.
Secure it as follows.

Glowplug

1. Loosen the retainer nut, press the carburetor well
down into the intake boss, compressing the rubber
gasket as shown in the sketch, before re-tightening
Nut.
2. Rotate the retainer nut gently until it stops, then
tighten a further 90-120 degrees. Do not overtighten the screw as this will damage the carburetor
body.

Pump Holder
Pump

0.2mm gap

Propeller nut

Carburetor Rubber
Gasket
Press down until the gasket becomes almost invisible.

Retainer Nut

Cover Plate
Beam Mount
Crankcase
Return Screw
Thrust Washer

60M One-way Valve

Crankshaft

INSTALLING THE GLOWPLUG

CORRECT

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

Side view
Front view
Top surfaces are in the same plane.

INCORRECT
Glow plug
Washer

INSTALLATION OF THE ENGINE

Top surfaces are not
in the same plane.

The under-surfaces of all O.S. engine beam
mounting lugs are precision machined flat and
exactyly parallel to the engine's horizontal axis. It is
essential that the engine mounts in the model are
also accurately made and aligned. If they are not,
they will cause stress and distortion within the engine
itself, probably resulting in loss of performance and
internal damage.
The recommended screws for securing the engine to
the engine mounts in the model are 4mm or 4-40
steel Allen type. It is also advisable to use lock
washers or LOCTITE to prevent nuts from loosening.

Top surfaces are not in the
same plane.
Engine does not rest firmly.

Re-align the surfaces as necessary

Make sure that only the undersurfaces of the engine’s mounting
lugs are in contact with the engine
mount.

ABOUT THE PUMP SYSTEM
Please understand the pump construction before
piping.
Pump functions in accordance with the engine
r.p.m. Rotating the engine by an electric starter
without connecting battery to a plug sucks fuel.
Prolenged this action may result in over priming.

If the main needle is set correctly, fuel return will
stop at around 60% throttle opening. Therefore, in
the high air flight that requires wider throttle
opening the engine runs under the effects of
muffler pressure, pump pressure and main needle.

NOTE:
Attempt to start the engine with over-priming may
result in bending a connecting rod and damaging
the engine.

During hovering that requires around half throttle
the engine runs under the effects of muffler
pressure, main needle, mixture control and retur
fuel volume.

Fuel is pumped from the tank and delivered to the
carburetor. Set the main needle a little rich at early
stage.
With this system the pump delivers the fuel at
constant pressure even at idling. Then,
unconsumed fuel is returned to the tank ria oneway valve which avoids getting rich at around
idling.

CARE OF FUEL PUMP
NEVER disassemble the fuel pump or pressure
regulator. Their original performance may not be
restored after reassembly.
NEVER insert anything into the inlet or outlet
nipples in an attempt to clear a suspected
obstruction.
Do not more the pump adjusting screw at the
center a the adjustment gets out of order and the
parts inside is damaged.

Pressure adjusting screw

ALWAYS use fuel filters. Keep the fuel tank
scrupulously clean and filter all fuel as it enters the
tank (e.g.via an O.S.'Super-Filter' Code
No.72403050) and use a good quality in-line filter
between the tank and pump. Remember to inspect
filter screens at regular intervals and rinse clean as
necessary.

Do not remain fuel in the pump. After finishing the
day's flight session, be sure to use out the fuel in
the pump. Stop the fuel flow to the pump with the
stopper and run the engine at idling to use out the
fuel in the pump. After stopping the engine, rotate
the engine by electric starter to eject fuel inside the
engine.

Do not clean the pump with organic solvent such
as kerosene, light machine oil, gasoline, thinner or
crc or the silicone rubbur parts inside is
detoriorated. Be sure to use methanol or fuel.

Next, connect piping from one-way valve for fuel
retur. There are two ways.

FUEL TANK AND PIPING
Install the engine and a muffler according to the
instructions supplied with the model. Then, connect
piping between tha muffler and fuel tank for muffler
pressurized fuel feed. Then, cut the silicone tube
supplied to 96mm and connect the pump and
carburetor with it.
Pump has fuel flow direction as shown in the sketch.
Be sure to connect between out nipple and carburetor
inlet nipple.

1. To return the fuel to the tank.
Connect between one-way valve and fuel tank. Fit a
nipple on the tank. This system ensures stable fuel
supply even with the 3D flight which requires
successire big throttle works.

Commercialy
available nipple

Nut
Washer

OUT
Fuel tank
Clear the burr, if any, off the hole to fit the nipple
with a cutter knife. Also clean the tank with
methanol to remove the dust or tank cut-off
particle.

1. To return the fuel to the tank

muffler pressure

Silencer

Commercialy
available nipple
Fuel tank
Fuel flow

Pump

2. To return the fuel in front the pump
using the T nipple.

muffler pressure

In this case, fitting an additional nipple on the tank is
not required. However, pumped out fuel pressure is
increased, and the main needle needs to be closed
further, which results in a sensitive needle reaction
and mixture gets lean at halh throttle with some
types mufflers. In this case, it is suggested to use
yhe pattern 1.

Silencer

Fuel flow
Fuel tank

T nipple

Pump

The pump requires running-in as with the engine. Be
sure to check the silicone tubes and connections
carefully for any cracks on the tubes and loose
connections as the engine runs ejecting excess fuel.

BEFORE STARTING
Tools, accessories, etc.
The following items are necessary for operating the
engine.
1 Fuel
Select, by practical tests, the most suitable fuel from
among the best quality fuels available in your country
for helicopter use. For the best throttle response, a
fuel containing 10% to 30% nitromethane is
preferable. Lubricants may be either castor-oil or a
suitable synthetic oil (or . a blend of both) provided
that they are always of top quality. For consistent
performance and long engine life, it is essential to use
fuel containing AT LEAST 18% lubricant by volume.
Some fuels containing coloring additives tend to
deterriorate and may adversely affect running
qualities. If in doubt compare to a fuel known to be
good.
Reminder!
Model engine fuel is poisonous. Do not allow
it to come into contact with the eyes or
mouth. Always store it in a clearly marked
container and out of the reach of children.

In case of 1.5volt dry cell

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.

Battery leads

2 Glowplug
O.S. No.8 glowplug is installed in the engine.
3 Battery leads
These are used to conduct current
from the battery to the glowplug.
Basically, two leads, with clips, are
required, but, for greater convenience, twin leads with special
glowplug connectors, as shown on
the right, are commercially available.

Make sure glowplug element
glows bright red inside room
or shadow.

5 Hexagon starting shaft
This shaft mounted on an
electric starting motor is driven
into the shaft cup to turn the
engine.

Battery leads

4 Glowplug battery
The power source for heating the glowplug may be
either a large heavy-duty 1.5volt dry cell, Ni-cd battery
or battery integrated booster.

6 Electric starter and starter
battery
An electric starter is recommended for starting.

1.5 volt dry cell
Battery Integrated booster

12V Battery
Starter

7 Fuel pump
For filling the fuel tank one of the
purpose-made manual or electric fuel
pumps may be used to transfer fuel
directly from your fuel container to the
fuel tank.
8 Fuel container filter
Install a filter on the outlet tube of your
refuelling container to prevent entry of
foreign matter into the fuel tank
9 Silicone tubing
This is required for the connection
between the fuel tank and engine.
ID 2.5mm and OD 5-5.5mm one
would be suitable.

Fuel pumps

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

Manual

For tightening
glowplug

Electric
Fuel Can Filter

Silicone tubing

If the silicone tube on the cover plate is damaged,
use commercially available 2mm ID and 5mm OD
silicone tube by cutting to 12mm length.

Silicone Tube
2x 5xL12mm

Joint Nipple
(Joint nipple and silicone tube are fit
on the cover plate.)

FACTS ABOUT GLOWPLUGS
Since the compatibility of glowplug and fuel may have
a marked effect on performance and reliability, it may
be worthwhile to choose the R/C type plug found
most suitable after tests. Recommended O.S. plugs
are No.8 and A5. Carefully install plug finger-tight,
before final tightening with the correct size plug
wrench.

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.

The role of the glowplug
With a glowplug engine, ignition is initiated by the
application of a 1.5-volt power source. When the
battery is disconnected, the heat retained within the
combustion chamber remains sufficient to keep the
plug filament glowing, thereby continuing to keep the
engine running. Ignition timing is 'automatic' : under
reduced load, allowing higher rpm, the plug becomes
hotter and, appropriately, fires the fuel/air charge
earlier; conversely, at reduced rpm, the plug become
cooler and ignition is retarded.

When to replace the glowplug
Apart from when actually burned out, a plug may
need to be replaced because it no longer delivers its
best performance, such as when:
Filament surface has roughened and turned white.
Filament coil has become distorted.
Foreign matter has adhered to filament or plug
body has corroded.

Glowplug life

Engine tends to cut out when idling.

Particularly in the case of very high performance
engines, glowplugs must be regarded as expendable
items.

Starting qualities deteriorate.

CARBURETOR CONTROLS
With a fixed-wing model, power failure is rarely a
serious threat to the safety of the aircraft since it can
usually glide down to a safe landing. In a helicopter,
on the other hand, it is vitally imporant that the engine
keeps running and that there is a quick and reliable
response to the throttle in order to ensure safe ascent
and descent of the model.
Two adjustable mixture controls are incorporated in the
Type 60M. They are as follows.

Idle MIxture Control Screw
High Speed Needle Valve
(Main Needle)

one-way valve

A The High-Speed (Main) Needle Valve
When set to produce maximum power at full
throttle, this establishes the basic fuel/air mixture
strength. This is then maintained by the carburetor's
automatic mixture control system to cover the
engine's requirements at reduced throttle settings.

Needle
Adjusting screw

NOTE
As the idle mixture control screw is applied with LOCTITE, at first times it is felt stiff, and it is suggested to
use a littli oversized screwdriver. The screw can be
turned only 90 degrees either way. Do not force to turn
further, or it may break or cause trouble.

B The Idle Mixture Control Screw
This provides the means of manually adjusting the
60K's mixture control valve. By setting the Mixture
Control Screw for the best idling performance, the
mixture control valve automatically ensures that fuel is
accurately metered to maintain the correct mixture
strength as the throttle is opened.

90 degrees

HEX KEY NEEDLE ADJUSTMENT
The knurled head of the main needle valve (High-Speed)
is provided with diagonal slots for use with a screwdriver.
Alternatively, formore positive location via an Allen
hexagonal key, these heads also have M2.6 internal
threads, into which M2.6x5mm Allen cap-head screw
may be fitted. To avoid risk of damage to the fuel
passages when tightening these screws, remove the
needle valves from the carburetor and use 'Loctite'
thread-lock compound to secure the screw.

Therefore, the Mixture Control Screw position will
vary with each model and set- up, and it is normal if
the Mixture Control Screw position is off center.

Graduations on the carburetor body
As shown in the sketch,
the carburetor has
graduation marks.

Fully opened position
89 degrees
Fully closed
position

BASIC POSITION OF MIXTURE CONTROL VALVE
(Mixture Control Screw)

Carburetor Rotor
Carburetor Body

When the triangle mark on the carburetor rotor meets
the far right mark, the throttle is fully closed. When the
triangle mark meets the top mark, the throttle is fully
open. The range is 89 degrees. You may use the other
three marks as the reference marking of throttle
opening to your preference when hovering.

As delivered, the Mixture
MIxture Control Screw
Control Screw is positioned
at the center as shown in the
sketch. Mixture gets lean
when the Mixture Control
Lean
Screw is turned right, while Thick
mixture gets rich when the
Mixture Control Screw is
Mixture Control Valve
turned left.

WARNING!
Never try to check the triangle mark position while
the engine is running and rotor is
rotating, or you may be hit by rotating rotor which
results in serious injury. Stop the engine and rotor
before checking the triangle mark position.

With a model helicopter, adjustments may vary due to
various factors such as climatic conditions, fuel,
muffler, main rotor, weight of the model, gear ratio, etc.

3. Preparation of the starter
Install the starting shaft to the
starter securely.
Improper installation will allow the
shaft to swing creating a
dangerous situation.

STARTING
Be sure to use a muffler pressurized fuel feed. Use
the same fuel as you intend to employ for actual
operation of your model.
1. Opening and closing of the Needle-Valve
Turn the needle clockwise to
close the needle-valve, and turn
the needle counter-clockwise to
open the needle-valve as shown
in the sketch.

4. Checking the rotating direction of the starter
Make sure that the starter rotates
to the direction shown in the
sketch. If the direction is reverse,
reverse the leads on battery.

Open

2. High Speed needle-valve:
exactly two turns open from the fully closed
position.(Note: If a different muffler is used, this
setting may require readjustment)

5. Inserting the starter shaft
Insert the starting shaft into the
shaft cup securely.

Idle Mixture Control Screw:
at basic position when the engine leaves the
factory.

6. Priming
Without energizing the glowplug,
open the throttle a little from the
idling position. Turn the engine
over using the starter until the fuel
is seen to reach carburetor.

NOTE:
If the throttle response is poor or the engine
stops due to a temporarily over-rich mixture immediately after the engine is started, pinch the
fuel line for one or two seconds until the engine
r.p.m. increase and the engine runs steadily.

7. Preparation of starting
Make sure that the transmitter
throttle stick is at the fully closed
position and the throttle trim at center
position, and make sure that idle-up
switch on the transmitter is off. Hold
the rotor head by hand so that rotor
cannot rotate when the engine is Started. Also, steady
the model with a foot on the landing gear skid.

Reminder!
Never touch, or allow any object to
come into contact with, the rotating
rotor.

8. Starting
Connect the battery to the glowplug and start the
engine by applying the starter. When started, switch
off the starter and withdraw the starting shaft after
making sure the rotation of the starter shaft stops.
9. Stopping the engine
Fully pull down the throttle trim on the transmitter.
In case the engine does not stop.
Hold the rotor head, and pinch the fuel line to stop the
fuel supply. If it still does not stop, pull off the fuel line
from the carburetor.
It is necessary to readjust the throttle linkage so that
the carburetor rotor is fully closed when the throttle
stick and throttle trim on the transmitter are fully
pulled Down.

RUNNING-IN ("Breaking-in")

ADJUSTMENT

All internal-combustion engines benefit, to some
degree, from extra care when they are run for the first
few times ー known as running-in or breaking-in.
This is allows the working parts to mate together
under load at operating temperature.
However, because O.S. engines are made with the
aid of the finest modern precision machinely and from
the best and most suitable materrials, only a very
short and simple running-in procedure is required and
can be carried out with the engine installed in the
model. For the first few flights with a new engine i.e.
while the engine is being run-in
set the needlevalve for a slightly rich mixture not excessively rich
as this may result in poor throttle response and cause
the engine to stope. About one half turn open from
the nomal setting will usually suffice.

Please observe the following before beginning to
make any adjustment.
High-Speed Needle Valve. Turn this
30 degrees (3 to 4 click) at a time,
initial adjustments; then in steps of
15 degrees (1 to 2 clicks) when
adjustments.

approximately
when making
approximately
making final

Idle Mixture Control Screw. Turn approximately 10
degrees at a time. It turns approximately 90
degrees both side from the center. Turn left to
enrich the idle mixture and turn right to lean the idle
mixture.

ADJUSTMENT PROCEDURE

The general course of adjustment procedure is
shown in the ADJUSTING CHART and is correct
for a fuel containing 20% lubricant and 15-30%
nitromethane.

As a safety measure, first check the transmitter
controls, including the throttle stick and trim lever
positions, and hold the main rotor securely before
starting the engine.

Bear in mind that fuels containing relatively large
percentages of power-boosting nitromethane operate
at richer mixture settings than are needed for mild
fuels and will, therefore, require the High-Speed
Needle Valve to be readjusted accordingly. The type
and percentage of lubricant used is also a factor
here, as noted later in these instructions.

1. Warm the engine by allowing it to idle for about 30
seconds. If the engine stops, advance the throttle
trim lever slightly to increase the idle rpm. Then
open the throttle sufficiently to 'float' the model
above the ground. lf, at this time, the engine is
slow to pick up and produces an excess of
exhaust smoke, the mixture is too rich. Correct
this condition by turning the Mixture Control Screw
clockwise 10 degrees. lf the mixture is extremely
rich, engine rpm will become unstable: opening
the throttle will produce a great deal of smoke and
rpm may drop suddenly or the engine may stop.
This condition may also be initiated by an
excessively prolonged warming-up period. lf, on
the other hand, the mixture is too Iean, this wiIl be
indicated by a marked lack of exhaust smoke and
a tendency for the engine to cut out when the
throttle is opened. ln this case, turn the Mixture
Control Screw counter-clockwise 10 degrees to
enrich the mixture.

This carburetor is not equipped with a throttle
stop screw. Instead, idling speed is adjusted
by means of the throttle trim lever on the
transmitter.

After about 10 seconds of idling, open the throttle to
'float' the model. lf the transition is smooth, the idle
mixture is O.K. If the symptoms of either rich or Iean
running are observed, readjust the Idle Mixture
Control Screw accordingly.

2. Having provisionally set the idle mixture, the next
step is to adjust the mixture for hovering flight.
Hover the model and actuate the throttle to observe
response over the medium speed range. lf the
engine smokes excessiveIy and throttle response is
poor, the mixture is too rich ; in which case, land the
model and turn the High-Speed Needle Valve
clockwise. Do not close the High-Speed NeedIe
Valve more than the recommended initial
adjustment (3 to 4 clicks) at a time, keeping it a little
on the rich side at this stage.
lf, on the other hand, hovering is not stable and
response to the throttIe is over-sensitive, or if the
engine tends to overheat, this indicates that the
mixture is too lean and should be corrected by
turning the High-Speed Needle Valve counterclockwise.
When satisfactory hovering flight has been achieved,
land the modeI again and re-check the engine's idle
qualities.

3. Now adjust the High-Speed Needle Valve to
achieve the best performance when the model is
flying at full throttle. lf, at full throttle, acceleration
is poor, the exhaust unduly smoky and the model
fails to reach expected straight line speed, the
mixture is too rich and the High-Speed Needle
Valve setting will need to be reduced.
lf, however, after smoothly acceIerating to
satisfactory high-speed straight and level flight,
power is lost when the model is puIled up into a
climb, the mixture is too lean. ln this case, land the
model immediately and readjust thw High-Speed
Needle Valve to a richer setting.

If both controls are alreday at their optimum setting,
some modification to these settings may be
necessary to achieve satisfactory mid-range throttle
response, but such readjustments should only be
made within the rarge where idling reliability and high
speed performance are not undnly compromised.

4. Having now found the optimum setting for the
High-Speed Needle Valve, re-check the engine's
idle performance, fine tuning the Idle Mixture
Control Screw, if necessary, to perfect the idle.
For helicopters, good throttle response at medium
r.p.m. (e.g. hovering speeds) is most important,
since this is a power range widely used in
helicopter flight. The optimum fuel / air nixture
strength at medium speeds is dependent on
obtaining balanced adjustment of both the Needle
Valve and the Mixture Control Valve.

SUBSEQUENT READJUSTMENTS

CARBURETOR CLEANLINESS

Once the engine has been run-in and the carburetor
controls properly set up, it should be unnecessary to
alter the mixture settings, except to make minor
changes to the Main (High-Speed) Needle Valve
occasionally, to take account of differences in climatic
condisitions.
However, as previously mentioned, the use of a
different fuel, particularly one containing more, or
less, nitromethane and / or a different type or
proportion of lubricating oil, is likely to call for some
modification to the High-Speed Needle-Valve
adjustment.
As a safety measure, it is advisable to increase the
High-Speed Needle Valve setting by an extra half-turn
counter-clockwise, prior to establishing the new
setting. The same applies if the silencer type is
changed. A different silencer may alter the exhaust
pressure applied to the fuel feed and call for a revised
Needle-Valve setting.
The use of a different glowplug, or changes to the
main rotor and its pitch angles may also require
compensating carburetor readjustments.

The correct functioning of the carburetor depends on
its small fuel orifices remaining clear.
The minute particles of foreign matter that are present
in any fuel can easily partially obstruct these orifices
and upset mixture strength so that engine
performance becomes erratic and unreliable.
It is recommended that 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 and,
furthermore, that this filter is frequently cleaned to
remove dirt and lint that accumulates on the filter
screen.
Finally, occasionally remove the needle-valve holder
from the carburetor as shown in Photo and extract
any remaining foreign matter that may have lodged in
the location shown in the sketch.
Remove this with
an 8mm spanner

Dirt and fbrous matter
mostly accumulate here

ADJUSTING CHART
High Speed Needle Valve - 2 turns opened from fully closed position.
Idle Mixture Control Screw - 2 turns opened from fully closed position.

Start the engine
Warm up the engine
Observe the mixture condition while "floating" the model
Rich mixture

Lean mixture
Turn the Idle Mixture
Control Screw counterclockwise 10 degrees

Turn the Idle Mixture
Control Screw
clockwise 10 degrees

Idling OK

Observe the hovering mixture condition
Rich mixture

Lean mixture
Open the High Speed
Needle Valve
(Turn counter-clockwise)

Close the High Speed
Needle Valve
(Turn clockwise)

Hovering OK
Land the model

Idle for approx: 10 seconds, then reopen throttle to
observe transition ("Float" the model)
Rich mixture

Lean mixture
Turn the Idle Mixture
Control Screw counterclockwise 10 degrees

Turn the Idle Mixture
Control Screw
clockwise 10 degrees

Idling OK
High Speed Flight

Rich mixture

Lean mixture
Open the High Speed
Needle Valve
(Turn counter-clockwise)

Close the High Speed
Needle Valve
(Turn clockwise)

High Speed Flight OK
Fine tuning of idling mixture

Rich mixture

Lean mixture
Turn the Idle Mixture
Control Screw counterclockwise 10 degrees

Idling OK

Fine tuning of hovering mixture

Hovering OK
Adjustment completed

Turn the Idle Mixture
Control Screw
clockwise 10 degrees

INSTALLATION OF THROTTLE SERVO
After the engine is installed in the helicopter, please
observe the following recommendations when linking
the throttle servo to the carburetor.

Locate the servo so that its output arm and the
throttle pushrod are, as close as possible, directry in line with carburetor's throttle arm, as
shown.

Servo output arm
Throttle control rod A and B should be equal
length. Set the linkage so that the servo output
arm and throttle arm are parallel when the
throttle stick on the transmitter is at middle
position. If differential throttle movement is required, make necessary adjustment at the
transmitter.

27m

Throttle arm

CARE AND MAINTENANCE
1. The minute particles of foreign matter, that are

4. Finally, inject some after-run oil into the engine. Rotate

present in any fuel may, by accumulating and
partially obstructing fuel flow, cause engine
performance to become erratic and unreliable.
O.S. 'Super-Filters' (large and small)are available,
as optional extras, to deal with this problem.
One of these filters, installed in the outlet tube
inside your refueling container, will prevent the
entry of foreign material into the fuel tank. It is also
recommended that a good in-line filter be installed
between the tank and carburetor.

the engine a few times by hand, to make sure that it
is free, and then with an electric starter for 4 to 5
seconds to distribute the oil to all the working parts.
Note:
Do not inject after-run oil into the carburetor as this may
cause the O-rings inside the carburetor to deteriorate.
These procedures will reduce the risk of starting
difficulties and of internal corrosion after a period of
storage.

2. Do not forget to clean the filters regularly to remove
dirt and lint that accumulate on the filter screens.
Also, clean the carburetor itself occasionally.

3. At the end of each operating session, drain out any
fuel that may remain in the fuel tank. Next, energize
the glowplug and try ot restart the engine to burn off
any fuel that may remain inside the engine.
Repeat this procedure until the engine fails to fire.
Remove the glowplug and eject any remaining fuel/oil
residue by rotating the engine with an electric starter
for 4 to 5 seconds while the engine is still warm.

ENGINE EXPLODED VIEW

ENGINE PARTS LIST
No. Code No.

C.M3x15

22
2

3
16

6
7
C.M3.5x10

15
21
2x 5xL12mm

14
20
19

10
9

13
11

Type of screw
C...Cap Screw M...Oval Fillister-Head Screw
F...Flat Head Screw N...Round Head Screw S...Set Screw

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22

29054200
29053100
29503400
29053210
27006000
27917000
29505010
29084000
45010002
46120000
26731002
29081719
29051010
27930000
29052100
29514000
29057020
22681953
29057110
29057100
72509000
29513000
71608001
27708200
29084610

Description
Heatsink Head
Cylinder Liner
Piston Ring
Piston
Piston Pin
Piston Pin Retainer (2pcs.)
Connecting Rod
Carburetor Complete 60M
Propeller Nut
Thrust Washer
Crankshaft Ball Bearing (Front)
Carburetor Retainer Assembly
Crankcase
Crankshaft Ball Bearing (Rear)
Crankshaft
Gasket Set
Cover Plate
Joint Nipple (No.1)
Holder "O" Ring
Pump Holder
Pump
Screw Set
Glow Plug No.8
Woodruff Key
T Nipple
Needle Adjusting Screw (M2.6x5) (1pc.)

The specifications are subject to alteration for improvement without notice.

CARBURETOR EXPLODED VIEW
C.M3x8

1-1
8
1

8-3

8-1

8-6

8-4

3-3
6

8-5
8-2

7
9
11

3-2
3-1

Type of screw
C...Cap Screw M...Oval Fillister-Head Screw
F...Flat Head Screw N...Round Head Screw S...Set Screw

CARBURETOR PARTS LIST
No. Code No.

1
1-1
2
3
3-1
3-2
3-3
4
5
6
7
8
8-1
8-2
8-3
8-4
8-5
8-6

27381410
22826131
29084200
29084800
27881810
27881800
27881820
45581820
29084100
27881330
27681340
27081900
27981910
24981837
46181940
46181941
26711305
46181950

Description

No. Code No.

Description

9 29084440 Return Screw
10 29084500 One-way Valve
11 29015019 Carburetor Rubber Gasket
Needle Adjusting Screw (M2.6x5) (1pc.)

Throttle Lever Assembly
Throttle Lever Retaining Screw (2pcs.)
Carburetor Rotor
Mixture Control Valve Assembly
"O"Ring (L) (2pcs.)
"O"Ring (S) (2pcs.)
"O"Ring (L) (2pcs.)
Rotor Guide Screw
Carburetor Body
Mixture Control Screw
Mixture Control Valve Stopper
Needle Valve Assembly
Needle
"O"Ring (2pcs.)
Needle Valve Holder Assembly
Needle Valve Holder
Ratchet Spring
Fuel Inlet

The specifications are subject to alteration for improvement without notice.

O.S. GENUINE PARTS & ACCESSORIES
DRIVE HUB

O.S. GLOW PLUGS

IN-FLIGHT CONTROL
NEEDLE VALVE

(27708010)

No.8

SUPER FILTER
(72403050)

(71705000)

(71608001)

A5
(71605100)
(L)

LOCK WASHER
M4 (10set)
(55500003)

CRANKSHAFT
CLAMP
7091 (For 70SZ-H, 91SX-H)

LONG SOCKET WRENCH
WITH PLUG GRIP

Needle Adjusting
Screw (5pcs.)
M2.6x5 (41621100)

(71521000)

(71530500)

Cap Screw Set
(10pcs. set)

M2.6x5
(79871010)

M3.5x10
(79871070)

THREE VIEW DRAWING

Dimensions(mm)

4- 4.2

SPECIFICATIONS
52

14.95 cc (0.912 cu.in.)
27.7mm (1.091 in.)
24.8mm (0.976 in.)
2,000-16,000 r.p.m.
3.1 ps / 15,000 r.p.m.
581g(20.5oz.)
56
42.5

87.4

43.5

UNF 5/16-24
JAPAN

Displacement
Bore
Stroke
Practical R.P.M.
Power output
Weight

42.6

56.4

88.7

MEMO

L I TY PRECISION & P
ERF
QUA
ED
OR

ISH
ING

E
ANC

UNEQ
UA

L
CEL
THE STAN ARDS OF EX
D

6-15 3-Chome Imagawa Higashisumiyoshi-ku
Osaka 546-0003, Japan TEL. (06) 6702-0225
FAX. (06) 6704-2722
URL : http://www.os-engines.co.jp
C Copyright 2003 by O.S.Engines Mfg. Co., Ltd. All rights reserved. Printed in Japan.

60091420

090301

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