O.S. Engines 21RG-X User Manual

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

'SAFETY INSTRUCTIONS AND WARNINGS'

section on pages 2-5 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 vehicle, radio control equipment, etc.,
are accessible for checking at the same time.

CONTENTS

SAFETY INSTRUCTIONS AND
WARNINGS ABOUT YOUR O.S. ENGINE

INTRODUCTION, BASIC ENGINE PARTS
INSTALLATION OF THE ENNGINE
INSTALLATION OF THE CARBURETOR

AIR CLEANER TYPE201 

NOTES CONCERNING THE RECOIL STARTER
GLOWPLUG
TOOLS, ACCESSORIES, etc.

CARBURETOR CONTROLS,
PRESSURIZED FUEL SYSTEM

STARTING THE ENGINE &
RUNNING-IN('Breaking-in)

2-5

7-8

9-12

12
13

13-14

15

15-18

IF THE ENGINE FAILS TO START

FINAL ADJUSTMENT

6

CARBURETOR CLEANLINESS

8

BEFORE STARTING THE ENGINE
CARE AND MAINTENANCE

GUARANTEE
O.S. GENUINE PARTS & ACCESSORIES
ENGINE EXPLODED VIEW

& ENGINE PARTS LIST
CARBURETOR EXPLODED VIEW

& PARTS LIST

THREE VIEW DRAWING

1

18

18-19

20

21

21-22

22
23

24-27

28-29

30

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 applies basically to ALL MODEL ENGINES and 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.

!


•

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.

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 operate your engine in an en­closed space. Model engines, like
automobile 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.

!


NOTES

3

!


This engine is intended for model cars.

•
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.

Fit an effective silencer (muffler).

•
Frequent close exposure to a noisy
exhaust (especially in the case of the
more powerful highspeed engines)
may eventually impair your hearing
and such noise is also likely to cause
annoyance to others over a wide area.

NOTES

•

The wearing of safety glasses is also
strongly recommended.

Take care that the glowplug clip or

•
battery leads do not come into contact
with rotating parts. Also check that the
linkage to the throttle arm is secure.

For their safety, keep all onlookers

•
(especially small children) well back
(at least 20 feet or 6 meters) when
preparing your model for running.

4

!


•

To stop the engine, fully retard the
throttle stick and trim lever on the
trans-mitter, or, in an emergency, cut
off the fuel supply by pinching the fuel
delivery tube from the tank.

Do not attempt to disassemble the

•

recoil starter.
If you do so, the very strong spring
inside will be suddenly ejected. This
can be very dangerous.

Do not extend the starter cord more

•

than 45cm (18"). Do not abruptly
release the operating handle. Allow
the cord to rewind smoothly while
still holding the handle.

NOTES

•

Pull the operating handle straight out
when starting the engine, so that the
cord does not rub against the vehicle
body or engine. This will help prevent
the cord from being damaged by
abrasion or engine heat.

•

Warning! Immediately after a glowplug­ignition engine has been run and is still
warm, conditions sometimes exist
whereby it is just possible for the engine
to abruptly restart if it is rotated over
compression WITHOUT the glowplug
battery being reconnected.

5

The MAX-21RG Series has been developed for
1/8 scale off-road 'buggy' and scale cars.It
provides a combination of performance and
value that brings it within the reach of a larger
group of R/C model vehicle enthusiasts, from
newcomers to experienced competitors. All
major parts of the MAX-21RG have been
redesigned. Its potential is very close to that of
the top-ranking MAX-21RZ motors, but it
remains easy to operate and is considerably
less expensive. The MAX-21RG has a
conventional crankshaft, while the MAX­21RG(P) employs a special crankshaft with
integral pilot shaft. The MAX-21RG-X and
MAX-21RG(P)-X have the addition of a built-in
O.S. recoil starting system. The starter unit
eliminates the need for a separate electric
starter and battery.

NOTE: With this engine, the piston will feel tight at
the top of its stroke when the engine is cold. This
is normal. The piston and cylinder are designed to
achieve a perfect running clearance when they
reach their normal running temperatures.

BASIC ENGINE PARTS

Carburetor

Beam Mount

Crankcase

Crankshaft

6

Heatsink Head

Starter Handle

Recoil Starter
Assembly No.5

MAX-

21RG-X

INSTALLING
THE GLOWPLUG

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

Glow plug

Washer

ENGINE INSTALLATION

Make sure that the vehicle's engine mounting surfaces
are level and in the same plane. Poor installation may
cause distortion of the crankcase, bearings, etc.,
resulting in erratic running and loss of performance.
The recommended screws for securing the engine are
3mm or 4-40 steel Allen hexagon socket type.
If existing holes in the engine mount do not align
perfectly with engine mounting lugs, enlarge them
slightly with a needle-file so that screws align with the
mounting holes.

Chassis

Chamfer inside edges of bearers.

Do not allow bottom
of crankcase to touch
chassis.

7

Avoid forcing the screws. Secure with locknuts. If the
bottom of the recoil starter housing touches the car
chassis, install the engine mount spacers (supplied)
between the engine's mounting lugs and the engine
mount. Use the M3x15 screws provided. With some
vehicles, it may be necessary to make minor trimming
modifications to chassis or body when fitting the engine.

NOTE:
Where spacers are supplied joined in pairs (see
sketch) separate them as shown.
Either face may be placed downwards.

INSTALLATION OF THE CARBURETOR

As delivered, the engine has its carburetor lightly
fitted into its intake boss. Secure it as follows.

Loosen the retainer screw, rotate the carburetor to

1.
its correct position and make sure that it is pressed
well down into the intake boss, compressing the
rubber gasket, before retightening screw.

Rotate the retainer screw gently until it stops, then

2.
tighten a further 90-120˚.
Do not overtighten the screw as this will damage
the carburetor body.

Separate

←→

Rotate the retainer nut
gently until it stops.

Tighten a further 90-120˚

Mount Spacer

Engine Mount

Engine Mount
Spacer

8

AIR CLEANER TYPE 201

This is a heavy-duty wet type air cleaner that has been developed specifically for 3.5cc 'off-road' model car
engines. It contains a specially impregnated filter element which more positively prevents highly damaging dust and
dirt from being drawn through the carburettor, yet allows engine performance to be maintained for longer periods
between element renewals. It is more compact than the standard O.S. HD Air Cleaner and this makes it easier to
install within a car body. This air cleaner is also supplied with a newly designed intake elbow that provides more
secure attachment to the caburetor.

Assembly Screw

End Plate

Filter Element

Center Screen

Element Base

9

Intake Elbow

Strap

Center T ube

Strap