O.S. Engines 25LA User Manual

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

'SAFETY INSTRUCTIONS AND WARNINGS'

section on pages 2-6 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.

SAFETY INSTRUCTIONS AND WARNINGS
ABOUT YOUR O.S. ENGINE

CONTENTS

TROUBLE SHOOTING WHEN THE

2~6

ENGINE FAILS TO START

26

~

27

INTRODUCTION

INSTALLATION OF THE ENGINE

INSTALLATION OF SILENCER

BEFORE STARTING
ADVICE ON SELECTION OF FUEL,

GLOW PLUG & PROPELLER

STAR TING THE ENGINE

RUNNING-IN (Breaking-in)

CARBURETTOR

15/25LA CARBURETTOR
AIR-BLEED ADJUSTMENT

10

12

14

23

7

8

9

~

12

~

14

~

22

23

~

24

25

CARE AND MAINTENANCE

OPTIONAL PARTS & ACCESSORIES

10LA ENGINE EXPLODED VIEW &
PARTS LIST

15/25LA ENGINE EXPLODED VIEW
& PARTS LIST

CARBURETTOR EXPLODED
VIEW & PARTS LIST

10LA THREE VIEW DRAWING

15/25LA THREE VIEW DRAWING

1

28

29

30

~

31

32~33

34

35

36

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.

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.

2

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.

A weakened or loose propeller may

•

disintegrate or be thrown off and, since
propeller tip speeds with powerful
engines may exceed 600 feet(180 metres)
per second, it will be understood that
such a failure could result in serious
injury, (see 'NOTES' section relating to
propeller safety).

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 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.

•

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 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.

3

NOTES

This engine was designed for model

•

aircraft. 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.

Be sure to use the silencer (muffler)

•

supplied with the engine. 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.

If you remove the glowplug from the engine

•

and check its condition by connecting the
battery leads to it, do not hold the plug with
bare fingers.Use an appropriate tool or a
folded piece of cloth.

Fit a top-quality propeller of the diameter

•

and pitch specified for the engine and
aircraft. Locate 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 nut, using the correct
size wrench.

4

NOTES

Always check the tightness of the propeller

•

nut and retighten it, if necessary, before
restarting the engine, particularly in the
case of four-stroke-cycle engines. If a
safety locknut assembly is provided with
your engine, always use it. This will prevent
the propeller from flying off in the event of a
"backfire", even if it loosens.

If you install a spinner, make sure that it is

•

a precision made product and that the
slots for the propeller blades do not cut into
the blade roots and weaken them.

Preferably, use an electric starter. The

•

wearing of safety glasses is also strongly
recommended.

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, unless you are highly experienced
in tuning propellers for specialized
competition work such as pylon-racing.

Take care that the glow plug clip or battery

•

leads do not come into contact with the
propeller. Also check the linkage to the
throttle arm. A disconnected linkage could
also foul the propeller.

After starting the engine, carry out any

•

needle-valve readjustments from a safe
position behind the rotating propeller. Stop
the engine before attempting to make other
adjustments to the carburettor.

5

NOTES

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.

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.

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.

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.
Keep the propeller pointed away from you
and walk well clear of spectators.

Warning! Immediately after a glowplug-

•

ignition engine has been run and is still
warm, conditions sometimes exist whereby
it is just possible for the engine to abruptly
restart if the propeller is casually flipped
over compression WITHOUT the glowplug
battery being reconnected. Remember this
if you wish to avoid the risk of a painfully
rapped knuckle!

6

INTRODUCTION

THE MAX-10LA,15LA,25LA have been developed to
meet the requirements of beginners and sport
flyers.
Of modern design and having a separate needle­valve unit mounted at the rear, where manual
adjustment is safely remote from the rotating
propeller, they offer the advantages of reliability
and easy handling, at lower cost. Like all O.S.
engines they are built to standards of engineering
excellence that have evolved through more than 60
years' experience in the design and production of
model internal-combustion engines. Advanced
modern precision machinery, top quality materials
and the efforts of highly skilled craftsmen and
technicians are combined to ensure a continuation
of the levels of performance, durability and
reliability for which O.S. is world famous.

The 'midnight blue' external finish may be
decolorized by very high surface temperature or
by certain solvents. Such decolorization does not
affect engine perfor-mance, however.

Cylinder head

Carburettor

Propeller nut

Crankshaft

Fuel inlet

Drive Hub

Propeller washer

Glowplug

Silicone Tubing

Crankcase

Fuel outlet

Needle valve

Cover Plate

Connect the short length of fuel tubing supplied
securely between the fuel outlet and the fuel inlet. In
the event of the tubing becoming damaged, it should
be replaced with a suitable length of best quality 5mm
ODX2mm ID silicone tubing. Use similar material to
connect the fuel inlet nipple to the fuel tank.

7

INSTALLATION

Installation in the model

A typical method of beam
mounting is shown below,left.

At least
12mm(1/2")

At least
12mm(1/2")

Make sure that the mounting beams are parallel
and that their top surfaces are in the same plane.

CORRECT

O.S. radial motor mount
(Available as an optional extra part.
See parts list)

Rigid hardwood
(e.g. maple)

INCORRECT

How to fasten the mounting screws.

Tighten second nut firmly

3mm steel nuts

Spring washer or
lock washer

down onto first nut.

Tighten this nut first.

12mm min.

Steel washer

12mm min.

3mm steel screw

Hardwood mounting beams

3mm steel Allen screw

Spring washer

Hardwood such as
cherry or maple.

Front view

Top surfaces are in the
same plane.

Side view

Top surfaces are not
in the same plane.

Re-align the surfaces
as necessary

Opposite beam

Top surfaces
are not in the
same plane.

Engine does
not rest firmly.

O.S. radial motor mount
(cast aluminum)

8

NEEDLE-VALVE EXTENSION

The needle-valve supplied with these engines is
designed to incorporate an extension so that, when
the engine is enclosed within the fuselage, the
needle-valve may be adjusted from the outside.
Cut a commercially available rod to the required
length, bend one end to an L shape, insert it into
needle's center hole and secure it by tightening the
set-screw in the needle-valve knob with 1.5mm. Allen
key.

INSTALLATION OF SILENCER

The angled exhaust of the silencer can be rotated to
any desired position in the following manner:

1) Loosen the locknut and assembly screw.

2) Set the exhaust outlet at the required position by
rotating the rear part of the silencer.

3) Re-tighten the assembly screw, followed by the
locknut. The standard silencer is quite effective but
reduces power to some degree.

Exhaust pressure nipple

Reminder!

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.

9

Assembly screw

Cone baffle

Turn to requlred position

Exhaust outlet

Locknut

BEFORE STARTING

Tools, accessories, etc.

The following items are necessary for operating the
engine.

1 Fuel

Model glowplug engine fuel of good quality, preferably
containing a small percentage of nitromethane. (See
"Advice on selection of fuel, glowplug and propeller")

2 Glowplug

O.S. A3 glowplug is installed in the engine.

3 Propeller

Suggested size is 7x4(10LA), 8X4 (15LA), or 9X5
(25LA).

4 Glowplug battery

The power source for heating the glowplug may be
either a large heavy-duty 1.5volt dry cell, or preferably,
a 2-volt rechargeable lead-acid cell (accumulator).

If a 2-volt cell is employed,
use a resistance wire, as
shown, to reduce applied
voltage, otherwise element

1.5 volt heavy-duty
dry battery

or 2 volt rechargeable
lead-acid cell (at least 5Ah)

will overheat and burn out.

Warning (Very hot)

Never touch the nichrome wire while the battery is
connected.

Resistance coil
(nichrome wire)

Battery leads

Adjust applied voltage by changing the position of clip on
resistance coil until glowplug element is glowing bright red.

Raise

voltage to

increase

brightness.

Lower voltage to

reduce brightness.

5 Plug wrench

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

For tightening
glowplug

10

6 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

Battery leads

commercially available.

7 Fuel tank

For installation in the model, a 70cc(2.5oz.) for 10LA,
a 100cc(3.5oz.) for 15LA, a 150cc(5oz.) for 25LA tank,
is suggested.

8 Fuel bottle or pump

For filling the fuel tank, a simple,
polyethylene "squeeze" bottle, with
a suitable spout,is all that is
required. Alternatively, one of the
purpose-made manual or electric
fuel pumps may be used to transfer
fuel directly from your fuel

Fuel bulb

Fuel pumps

container to the fuel tank.

9 Fuel can filter

Fit a filter to the outlet tube of
your refuelling container to

Fuel Can Filter

prevent entry of foreign
matter into the fuel tank.
(Refer to of STARTING

4

THE ENGINE section.)

10 Silicone tubing

This is required for the
connection between the fuel
tank and engine.

11 Electric starter and
starter battery

An electric starter is
recommended for starting.

12V Battery

Starter

Electric

Manual

11