O.S. engine MAX-25LA Setup guide

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.
●
●

CONTENTS
SAFETY INSTRUCTIONSAND WARNINGS
ABOUT YOUR O.S. ENGINE
INTRODUCTION
INSTALLATION OF THE ENGINE
INSTALLATION OF SILENCER
BEFORE STARTING
ADVICE ON SELECTION OF FUEL,
GLOW PLUG & PROPELLER
STARTING THE ENGINE
RUNNING-IN (Breaking-in)
TROUBLE SHOOTING WHEN THE
ENGINE FAILS TO START
CARE AND MAINTENANCE
OPTIONAL PARTS & ACCESSORIES
10LA ENGINE EXPLODED VIEW &
PARTS LIST
15/25LA ENGINE EXPLODED VIEW
& PARTS LIST
CARBURETTOR EXPLODED
VIEW & PARTS LIST
10LATHREE VIEW DRAWING
2 ~ 6
7
8
9
10
~ 12
12
~ 14
14
~ 22
23
23
~ 24
26
~ 27
25
28
29
30
~ 31
CARBURETTOR
15/25LA CARBURETTOR
AIR-BLEED ADJUSTMENT
32 ~ 33
34
35
15/25LATHREE VIEW DRAWING
36
1

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.
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
These cover events which
might involve serious (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.
2

WARNINGS
Model engine fuel is poisonous. Do not
allow it to come into contact with the eyes
or mouth.Always store it in a
clearlymarkedcontainerand
out of the reach of children.
Never operate your engine in an en-
closed space. Model engines, like auto-
mobile engines, exhaust deadly carbon-
monoxide. 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.
•
•
•
•
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 also highly
flammable. Keep it away from open flame,
excessive heat, sources of sparks, or
anythingelsewhichmightignite
it.Donotsmokeorallowanyone
else to smoke, near to it.
•
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' recommenda-
tions, using appropriate screws and lock-
nuts.
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.
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.
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.
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
inanyway,unlessyouarehighlyexperienced
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
THEMAX-10LA,15LA,25LAhave been developed to
meet the requirements of beginners and sport
flyers.
Of modern design and having a separate needle-
valve 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
techniciansare combined to ensurea 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
Silicone Tubing
Crankshaft
Propeller nut
Propeller washer
Drive Hub Crankcase
Needle valve
Cover Plate
Fuel outlet
Fuel inlet
Glowplug
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 How to fasten the mounting screws.
Hardwood mounting beams
O.S. radial motor mount
(cast aluminum)
Tighten second nut firmly
down onto first nut.
Tighten this nut first.
Steel washer
3mm steel screw
Spring washer or
lock washer
12mm min.
12mm min.
Hardwood such as
cherry or maple.
Spring washer
3mm steel Allen screw
Front view
CORRECT
Side view
Top surfaces are in the
same plane. Re-align the surfaces
as necessary
INCORRECT
Top surfaces are not
in the same plane. Opposite beam
Top surfaces
are not in the
same plane.
Engine does
not rest firmly.
Rigid hardwood
(e.g. maple)
Installation in the model
A typical method of beam
mounting is shown below,left. O.S. radial motor mount
(Available as an optional extra part.
See parts list)
Make sure that the mounting beams are parallel
and that their top surfaces are in the same plane.
At least
12mm(1/2")
At least
12mm(1/2")
3mm steel nuts
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.
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.
INSTALLATION OF SILENCER
Assembly screw Cone baffle
Turn to requlred position
Exhaust outlet
Locknut
Exhaust pressure nipple
Modelenginesgenerateconsiderableheat.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.
Reminder!
9

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).
1.5 volt heavy-duty
dry battery or 2 volt rechargeable lead-acid cell (at least 5Ah)
If a 2-volt cell is employed,
use a resistance wire, as
shown, to reduce applied
voltage, otherwise element
will overheat and burn out.
Resistance coil
(nichrome wire)
Adjust applied voltage by changing the position of clip on
resistance coil until glowplug element is glowing bright red.
Battery leads
Raise
voltage to
increase
brightness.
Lower voltage to
reduce brightness.
Warning (Very hot)
Never touch the nichrome wire while the battery is
connected.
5 Plug wrench
Used for tightening glowplug. The
O.S. long plug wrench is available
as an optional accessory. For tightening
glowplug
10

9 Fuel can filter
Fit a filter to the outlet tube of
your refuelling container to
prevent entry of foreign
matter into the fuel tank.
(Refer to of STARTING
THE ENGINE section.)
Battery leads
Fuel Can Filter
12V Battery Starter
4
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.
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
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
fuelpumpsmaybeusedtotransfer
fuel directly from your fuel
container to the fuel tank.
Fuel bulb
Manual
Electric
Fuel pumps
11

Fuel and pressure lines
Connect suitable lengths of silicone tubing, as
illustrated, after installing the engine.
Silicone tubing
Use knife or razor blade. Do not use wire
cutters or pliers
Note: When cutting silicone tubing......
*If you should need to clean out silicone tubes, use methanol
or glow-fuel, not gasoline.
6 ~ 8 mm
Plumbing and position of fuel tank
Fuel level
Pay attention to tank height
Locate the fuel tank so that the top of the tank is 5-
10mm (1/4-3/8") above the level of the needle-valve.
Silencer (muffler) pressurized fuel system
To reduce variation in fuel "head" and ensure steady
fuel delivery at the carburettor, it is advisable to employ
a silencer (muffler) pressurized fuel system, i.e. to use
the silencer outlet nipple to pressurize the fuel tank as
shown left.
Fuel
Use a good quality commercial fuel or one of the blends
shown in the table. Fuel "A" is suitable for running-in and
ordinaryuse.Fuel"B"isforusewhenmorepowerisrequired
and for improved flexibility. Note that even a small quantity
of nitromethane (3-5%) will improve flexibility, making the
needle-valve adjustment less critical and improving throttle
response.Useonlymaterialsofthehighestpurity.Synthetic
oilsare permissible but are less tolerant ofa "lean run" than
castor-oil. If, therefore, a synthetic lubricant is used in the
fuel, readjust the needle-valve to a slightly richer setting, as
a safety measure, in case the fuel/air mixture becomes too
leanthroughmaneuversinflight.Ifahighernitrofuelisused,
the engine should be checked out to make sure that it is
sufficiently run-in to operate on that particular fuel without
overheating. Do not use fuels containing less than 18%
lubricant.
ADVICE ON SELECTION OF FUEL, GLOWPLUG & PROPELLER
12

AB
75%
20%
5%
65%
20%
15%
Methanol
Castor Oil
Nitromethane
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 naked 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.
Reminder!
7 ✕ 4
8
✕ 4
9
✕ 5
10LA
15LA
25LA
7
✕ 3 ~ 5,8 ✕ 4
7
✕ 5 ~ 6,8 ✕ 4 ~ 5
9
✕ 5 ~ 6
PROPELLER
Suggested propeller sizes are given in the table. As
the ideal propeller diameter, pitch and blade area vary
according to the size, weight and type of model, final
propeller selection can be made after practical
experiment.
Trainer & Sport
LA Series
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.
Running-in
Reminder!
GLOWPLUG
An O.S. A3 glowplug is fitted to the engine.
Other recommended O.S. plugs are Nos.8 and A5.
Carefully fit plug finger-tight, before final tightening
with the correct size plug wrench.
The role of the glowplug
With a glowplug engine, ignition is initiated by the
applicationofa1.5-voltpowersource.Whenthebattery
isdisconnected,theheatretainedwithinthecombustion
chamber remains sufficient to keep the plug filament
glowing,therebycontinuingtokeeptheenginerunning.
Ignition timing is 'automatic' : under reduced load,
allowing higher rpm, the plug becomes hotter and,
appropriately, fires the fuel/air charge earlier;
conversely,atreducedrpm,theplugbecomecoolerand
ignition is retarded.
13

Inatall a plug suitable for the engine.
Use fuel containing a moderate percentage of
nitromethane unless more is essential for racing
events.
Do not run the engine too lean and do not leave the
battery connected while adjusting the needle.
However, plug life can be extended and engine
performance maintained by careful use, i.e.:
Apart from when actually burned out, a plug may
need to be replaced because it no longer delivers its
best performance, such as when:
When to replace the glowplug
Filament surface has roughened and turned white.
Filament coil has become distorted.
Foreign matter has adhered to filament or plug
body has corroded.
Engine tends to cut out when idling.
Starting qualities deteriorate.
•
•
•
•
•
•
•
•
STARTING THE ENGINE
Preparations
1Installing the glowplug
Install washer on the glowplug
andinsertcarefully into cylinder-
head, making sure that it is not
crossthreaded before tightening
firmly. Glow plug
Washer
2Installing the propeller
First, install the propeller on the engine by tightening
the prop nut or spinner-nut lightly, and make sure of
the position where compression is felt, turning the
propeller counter-clockwise slowly. Then tighten
firmly as explained below.
Glowplug life
Particularly in the case of very high performance
engines,
glowplugs must be regarded as expendable
For accurately centering the
starter's rubber drive insert,
install an O.S. solid alloy
spinner-nut to the engine.
(Availableasanoptionalextra
part).
Alternatively, a spinner
assembly, enclosing the
propeller boss, may be
used, but make sure
that it isof sturdy
construction and that the spinner shell does not
loosen when the starter is used.
Wrench
14

Warning: When using a spinner assembly, make
sure that the notches in the spinner shell are
large enough to clear the propeller blades and so
do not cut into and weaken the blade roots.
Tighten the spinner nut firmly so that compression is
first felt around this position (i.e. with blades
horizontal) when turning the propeller in the direction
of arrow.
3Checking for gas leakage
4Filling the fuel tank
Check gas leakage by
turning the propeller
up to this position after
compression is felt.
Compression is first
felt around this posi-
t
ion when turning
the propeller slowly.
Dribble a few drops
of fuel around the
glowplug and look
for air bubbles.
If leakage is detected, remove the
glowplug, carefully wipe threads,
re-insert and tighten firmly.
Do not allow fuel to overflow into
silencer when refuelling, otherwise
engine may become flooded and
difficult to start.
Re-connect
fuel line
to engine after
tank is filled.
Fuel pump
Use a fuel can filter
(e.g. O.S. Super Filter).
Do not let dirt or
dust enter fuel can.
Disconnect fuel line from
the fuel inlet, and connect
it to the tubing from the
fuel pump.
Fuel (model
glow-plug
engine fuel)
15

Close
Open
Needle-valve
Open the needle-valve 4 turns(for 10LA), 3 turns (for 15LA),
1 turns(for 25LA) in the direction of arrow from the closed
position.
2
1
Fully closed position
Fully opened position Throttle
Close
Open
Fuel inlet
Fuel Tube
Fuel will flow
from tank to
carburettor as
propeller is
turned.
Place your finger
over the carburettor
to choke intake.
Turn the propeller
two revolutions
while watching
fuel line.
5Opening and closing of the needle-valve
6Setting the needle-valve
Turn needle-valve clockwise to close (for leaner mixture).
Turn needle-valve counter-clockwise to open (for richer mixture).
The position where the needle-valve stops is the fully closed
position. It may be convenient to remember the position of the
mark or set-screw at this time.
7Open the throttle fully
8Priming
16

After fuel has been drawn to the carburettor, flip the
propeller two more revolutions, with intake choked, to
draw fuel into engine.
Above procedure is called priming.
NOTE (IMPORTANT)
The quantity of fuel drawn into the engine by
priming is an important factor in starting the
engine successfully.
When the engine is being started for the first time,
turn the propeller two revolutions after fuel reaches
the fuel inlet, as described above. However, when re-
starting the engine immediately after a run, one
revolution, or even no priming at all may be required.
The engine's requirements will be quickly learned
with experience.
Priming quantity 9
Turn the propeller 3 to 4
turns counter-clockwise
smartly by finger in the
direction of arrow. Turn
approx. 10 turns instead
when the engine is cold.
Do not energize the glowplug at this stage.
17

10 Hold model securely when starting
11 Setting the throttle
12 Heat glowplug
Starter
Assistant should hold
the model so that it
cannot move forward
when the engine starts.
Be careful not
to be hit by propeller!
Glowplug battery.
Place as far to the
rear as possible.
Fully opened
position
Fully closed
position
Set at this Position.
1323
Starting battery
Connect battery leads as shown
(polarity is immaterial.)
13 Apply electric starter
Assistant
18

Check that the throttle is one-third open from the fully
closed position. Bring the starter into contact with the
spinner nut or spinner and depress the starter switch
for one or two seconds. Repeat if necessary. When
the engine fires, withdraw the starter immediately.
Attention: Never place your finger over the
carburettor intake when applying the starter. Such an
action will cause an excess quantity of fuel to be
drawn into the cylinder and result in hydraulic lock
that may damage the engine.
BEWARE of
the rotating
propeller.
14 Engine starts
If the engine does not start, refer to the TROUBLE
SHOOTING CHART on page 26-27.
In the interests of safety, keep your face and other parts of the
body away from the vicinity of the propeller.
Listen to the sound
carefully.
15 Needle-valve adjustment(1)
Slowly advance throttle to its fully open position, then gradually
close the needle-valve until the exhaust sound changes pitch.
Close the needle-valve gradually until a high-pitched exhaust
note begins to be superimposed on the lower-pitched sound.
19