O.S. Engines 91HZ User Manual

It is of vital importance, before attempting to operate
your eng ine, to read the gene ral 'SA FETY
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.

1

2-5

6-7

8-9

10-12

17-21

25-29

35

42-43

44-45

46

30-34

22

36-37

38-41

13-16

23-24

47

48

CONTENTS

SAFETY INSTRUCTIONS AND
WARNINGS ABOUT YOUR O.S. ENGINE

NOTES ON INSTALLING,
COOLING-FAN AND CLUTCH

NOTES WHEN APPLYING AN ELECTRIC STARTER,
INSTALLATION OF THROTTLE SERVO

NOTES ON HEATING THE GLOW PLUG
INTRODUCTION, ENGINE PARTS NAME 

BEFORE STARTING,
INSTALLATION OF THE ENGINE

INSTALLATION OF THE STANDARD ACCESSORIES

GLOWPLUGS

CARBURETOR CONTROLS

STARTING, RUNNING-IN("Breakingin")

ADJUSTMENT

ADJUSTMENT CHART

CARE AND MAINTENANCE

TROUBLE SHOOTING

ENGINE EXPLODED VIEW & PARTS LIST

CARBURETOR EXPLODED VIEW & PARTS LIST

O.S. GENUINE PARTS & ACCESSORIES

THREE VIEW DRAWING

MEMO

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2

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.

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

Th e se co v er ev e nts wh ich
mig h t inv o l ve se r ious (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.

3

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WARNINGS

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

Model engine fuel is poison­ous. Do not allow it to come
into contact with the eyes or
mouth. Always store it in a
clearly marked container and
out of the reach of children.

Model engine fuel is also
highly flammable . Keep it
away from open flam e,
excessive heat, sources of
sparks, or anything else which
might ignite it. Do not smoke
or allow anyone else to smoke,
near to it.

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.

Never operate your engine in an en­closed space. Model engines, like auto­mobile engines, exhaust deadly carbon­monoxide. Run your engine only in an
open area.

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NOTES

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This engine was d es ig ned for model
helicopters. Do not attempt to use it for any
other purpose.

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

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 likel y t o c ause
annoyance to others over a wide area.

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.

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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.

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

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.

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NOTES

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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
metres) 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.

6

Notes on installing cooling fan and clutch

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.

It is recommended to use Crankshaft
Clamp 91 (Code No.71530510) available
as an optional tool.

7

Notes on installing cooling fan and clutch

Do not grip the engine mounting
beams with a vise, or the crankcase
will be distorted which will result in
engine breaking.

Vise

Beam Mount

8

NOTES WHEN APPLYING AN ELECTRIC STARTER

Because of this 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 over-prime. This could cause a
hydraulic lock and damage the engine
on application of the electric starter.

If over-primed, remove glowplug, close
needle-valve and apply starter to pump
out surplus fuel. Cover the head with a
rag to prevent pumped out fuel from
getting into your eyes.

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F

J

J

F

28
34

27

33

A

B

90°

90

°

A=B

Linking the throttle servo to the carburetor
Link the throttle servo to the carburetor using the throttle lever supplied.
Throttle control rod A and B should be equal length. Set the linkage so that
the servo output lever and throttle lever are parallel when the throttle stick on
the transmitter is at middle position. Installing hole intervals on the F lever and
on the J lever are different. Decide the lever to use according to the servo used.
Be sure to cut off another lever to avoid any interference.

10

Note on heating the glow plug

The heatsink head on the engine is
treated with an anodized finish which
does not conduct current. Therefore,
when heating a glow plug, connect
one lead to the glow plug and the
other to the head or cover plate
retaining screw.

Example

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Standard accessories

Glow Plug No.8

Needle Adjusting Screw (M2.6x5 2pcs.)

Needle Control Arm

Carburetor Complete 61E

Note:

As delivered, the carburetor is not
installed on the engine.

Carburetor Rubber Gasket

Head Gasket

(0.2mm)

This is a high performance engine
expressly designed for 90 size RC model
helicopters.
It performs perfectly from stable hovering
to dynamic aerobatic maneuver, which is
required for F3C competition. 61E
carburetor has three adjustable controls
which enables independent adjustment at
idling, hovering and high speed.
Needle control arm is supplied with the
engine as standard.
The needle can be tuned by the transmitter
in flight or with a fully enclosed engine.
The cover plate has a cell to accept a
sensor designed to install in the cover plate
from the Futaba GY-701 Governor.

INTRODUCTION

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Heatsink Head

Carburetor
Typr 61E

Crankshaft

Propeller nut

Crankcase

Glowplug

Beam Mount

Cover Plate

High Speed
Needle Valve

Fuel Inlet

Mixture Control Valve

Throttle Lever

Idle Mixture Control Screw

Mixture Control
Valve Stopper

Thrust Washer

Carburetor Rubber Gasket

Medium Speed
Needle Valve

Crankcase
Heatsink

Thermo Insulater

ENGINE PARTS NAME

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Items necessary for starting

Tools, accessories, etc.The following items are
necessary for operating the engine.

Glow Plug

O.S. No.8 is supplied with the engine.

Battery leads

Glowplug battery

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

1.5 volt dry cell

These are used to conduct current
from the batter y 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.

Battery leads

glowplug Igniter

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

Battery leads

In case of 1.5volt dry cell

12V Battery

Starter

Electric starter and starter
battery

An electric starter is recom­mended for starting.

Hexagon starting shaft

This shaft mounte d on an
electric starting motor is driven
into the shaft cup to turn the
engine.

BEFORE STARTING

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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.

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.

Reminder!

Fuel

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.

Alternatively, 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.

Manual

Electric

Install a filter to the outlet tube of your
refueling container to prevent entry of
foreign matter into fuel tank. O.S. ‘Super
Filters’ (large and small) are available as
optional extras.

O.S. Super Filter (Fuel Can Filter)

It is recommended to install a good in­line filter between the fuel tank and
carburetor to prevent entry of foreign
matter from getting into the carburetor.

Fuel Filter

Heatproof silicone tubing of approx.
5mm o.d. and 2.5mm i.d. is required
for the connection between the fuel
tank and engine.

Fuel Pump

Silicone Fuel Line

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TOOLS

Screwdriver

Necessary for engine installation.

1.5mm, 2mm, 2.5mm, 3mm

Necessary for carburetor adjustments.
No.1, No.2, etc

Phillips Screwdriver

No.1, No.2, etc.

Socket Drivers

5mm, 5.5mm, 7mm

Hex Drivers

8mm

Recommended for easy removal and replacement of
the angled and recessed glowplug, the O.S.Long
Socket Wrench incorporates a special grip.

End Wrenches

8mm, 13mm, 14mm, etc.

Needle Nose Pliers

Long Socket Wrench With Plug Grip