O.S. Engines 21RG-MX 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
NOTES CONCERING

THE RECOIL STARTER
GLOWPLUG
TOOLS, ACCESSORIES, etc.
CARBURETTOR CONTROLS

STARTING & INITIAL
RUNNING-IN('Breaking-in)

ADJUSTMENT

10

13
16

9

2~5

7

~

8

~

10

~

11

~

12

15

~

17

~

CARE AND MAINTENANCE
CHECKING OF THE ENGINE

6

TROUBLE SHOOTING WHEN THE

8

ENGINE FAILS TO START
ENGINE EXPLODED VIEW

9

ENGINE PARTS LIST
CARBURETTOR EXPLODED VIEW
& PARTS LIST

O.S. GENUINE PARTS &
ACCESSORIES

THREE VIEW DRAWING
MEMO

1

19

18

~

19

20~21

22
23

24

25

26~27

28

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.

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

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.

Model engine fuel is poison-

•

ous. 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.

WARNINGS

Never operate your engine in an en-

•

closed 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 boats.

•

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 most powerful
high-speed engines) may eventually impair
your hearing and such noise is also likely to
cause annoyance to others over a wide area.

For their safety, keep all onlookers

•

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

Take care that the glowplug clip or battery

•

leads do not come into contact with the
propeller or any other rotating parts. Also
check that the linkage to the throttle arm is
secure.

If your engine does not have a built-in recoil

•

starter, use an electric starter. The wearing
of safety glasses is also strongly
recommended.

When handling the boat immediately prior to

•

launching, be especially cautious.
Keep the propeller and other rotating parts
away from you.

4

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.

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 it is rotated over compression
WITHOUT the glowplug battery being
reconnected.

If your engine is fitted with a recoil starter,

•

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

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.

Do not attempt to disassemble the recoil

•

starter (if fitted). If you do so, the very
strong spring inside will be suddenly
ejected. This can be very dangerous.

5

The O.S. "RG Series" is a high-performance
water-cooled marine engine for small radio­controlled boats, especially sport type hulls.
A companion model, the MAX-21RG-MX in­corporating a recoil starter system is also
available.

Standard accessories

Glow Plug No.8

Flywheel No2E

Exhaust Header Pipe

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.

We do not recommend running your boat

•

on the sea, or in any other saltwater
environment. Under such conditions, it is
difficult to prevent the engine from
becoming corroded and, eventually,
inoperative.

BASIC ENGINE PARTS

Water Cooled Head

Carburettor
Type 20J

Cranshaft

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.

6

Glow Plug No.8

Beam Mount

Crankcase

MAX-21RG-MX

Starter Handle

Recoil Starter
Assembly No.5

Glow plug

Washer

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.

Rotate the retainer nut
gently until it stops.

Tighten a further 90-120˚

7

INSTALLATION OF THE FLYWEEL

Insert the taper collet on the crankshaft, taking care
not to push the crankshaft to the cover plate end.

Crankshaft

Flywheel

Taper Collet

INSTALLATION OF THE
EXHAUST HEADER PIPE

Select the screw
holes according to
the model.

INSTALLATION

Make sure that the engine mounting beams in the

1.

hull are parallel, with their top surfaces in the same
plane. If they are not, the engine will not rest firmly
as the engine mounting faces (undersides of the
mounting lugs) are precision machined to be flat
and in the same plane. Poor installation may not
only cause vibration, erratic running and loss of
performance, but may also damage the engine
itself by deforming the crankcase, cylinder, etc.

The mounting beams and adjacent hull structure

2.

should be as rigid as possible so that the engine
may develop its full performance. Use 3mm steel
screws, such as Allen socket-head type, with
locknuts, for bolting the engine to the mounting
beams.

If the holes in the mounting beams do not align

3.

exactly with the engine's mounting lugs, enlarge
them slightly with a needle file so that the mounting
screws pass through the holes smoothly without
being forced.

Chamfer inside edges of bearers.

NOTES CONCERNING THE RECOIL STARTER

REMINDER!

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.

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.

8

Try to avoid spilling fuel over the starter unit

◆

and its cord. Some fuels have a detrimental
effect on these parts.

The starter prevents the engine from being

◆

rotated in the wrong direction. The unit will be
damaged if you attempt to force the flywheel
in the opposite direction (i.e. clockwise when
viewed from the crankshaft end).

NOTE: Because, in the interests of personal
safety, dismantling of the starter mechanism
isstrongly discouraged, the Recoil Starter is
available for replacement only as a pre­assembled unit. However, some related parts,
such as Starting Shaft and Rear Adaptor, are
obtainable separately. (See Parts List.)

GLOWPLUG

Since the compatibility of the glowplug and fuel can
have a marked effect on performance and reliability, it
is suggested that the user selects the R/C type plug
found most suitable after practical experiments.
Generally, for a fuel containing about 30%
nitromethane, a medium heat range glowplug will be
suitable.
For higher nitro fuel, a cold rated plug may be
required, whereas, for lower nitro fuel, a hot rated
plug may be best. However, the O.S. No.8 glowplug
may be employed irrespective of the nitro content of
the fuel.

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.

9

Glowplug life

Particularly in the case of very high performance
engines, glowplugs must be regarded as expendable
items. 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 unless more is essential for racing events.

¡

Do not run the engine too lean and do not leave the
battery connected while adjusting needle.

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.

¡

Engine tends to cut out when idling.

¡

Starting qualities deteriorate.

¡

Foreign matter has adhered to filament or plug
body has corroded.

TOOLS, ACCESSORIES, etc.

The following items are necessary for operating the
engine.

FUEL

When the brand of fuel is changed, or the nitro content
increased, it is advisable to repeat the running-in
procedure referred to in the RUNNING-IN paragraphs.
For consistent performance and long engine life, it is
essential to use a good quality fuel containing NOT
LESS THAN 18% lubricant. Please note that with high­nitro fuels, although power may be increased for
competition purposes, glowplug elements do not last as
long and engine life will be shortened.

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.

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.

10

PROPELLER

Use well balanced propellers only. As the ideal
diameter, pitch and shape vary according to the size,
weight and type of model, final selection can be made
after practical experiment. As a starting point,
suggested propeller diameter is 40-44mm with a
pitch/dia ratio of 1.0-1.6 for Vee type hulls.

REMINDER!

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.

BATTERY INTEGRATED GLOWPLUG HEATER

Commercialy available handy glowplug
heater in which the glowplug battery
and battery leads are integrated.

ELECTRIC STARTER AND STARTER BATTERY

Use a 12-volt electric starter
with suitable battery for starting
the engine.(21RG-M)

FUEL PUMP

For filling the fuel tank, a simple, poly­ethylene "squeeze" bottle, with a suit­able spout, is required.

LONG SOCKET WRENCH

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

SILICONE FUEL LINE

This is required for the
connection between the fuel
tank and engine, also for the
water-cooling system.

11

CARBURETTOR CONTROLS

Two adjustable controls are provided on this carburettor.

●

The 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 carburet­tor's automatic mixture control system to cover the
engine's requirements at reduced throttle settings.

●

The Mixture Control Valve (Mixture Control Screw):

For adjusting the mixture strength at part-throttle
and idling speeds, to obtain steady idling and
smooth acceleration to medium speeds. The Mix­ture Control Valve has been factory set for the ap­proximate best result. First, run the engine as re­ceived, and re-adjust the Mixture Control Valve only
when necessary.

Mixture Control Valve
(Mixture Control Screw)

Needle-Valve

Fuel Inlet

Rotor Guide Screw

Throttle Lever

REALIGNMENT OF MIXTURE CONTROL VALVE

■

In the course of making carburettor adjustments, it is
just possible that the Mixture Control Valve may be
inadvertently screwed in or out too far and thereby
moved beyond its effective adjustment range.
Its basic setting can be reestablished as follows :

The basic ( factory ) setting is
as shown in the main sketch, i.
e. with the shoulder portion 'A'
exactly at a tangent to the throt-

Mixture Control Valve
(Mixture Control Screw)

Nozzle

tle rotor hole. To return the Mix­ture Control Valve to its original
position, first screw in the Mix­ture Control Valve, while look­ing into the rotor hole.
Then gradually unscrew the
Mixture Control Valve until 'A' is

Throttle Rotor Hole

precisely tangential to the rotor
hole (i.e. so that 'A' and 'B' are
superimposed) as in the main
sketch.

12

STARTING & INITIAL RUNNING-IN('Breaking-in')

When starting the engine, put the hull on a stand, etc.
out of the water.

For long life and high perfomance, every engine
needs to be 'run-in' or 'broken-in'. With care, running­in of the engine can be carried out with it installed in
the boat. Be sure to use a muffler-pressurized fuel
system.

In case of the 21RG-M

■

Set the needle-valve. Turn the needle clockwise

◆

slowly, without forcing, until it stops.
Then, reopen the needle-valve 2-1/2turns counter­clockwise.

Mark

Open

Priming

◆

Open the throttle fully and place your finger over

•

the carburetor to choke intake.

Turn needle-valve clockwise to

Close

close (for leaner mixture)

Turn needle-valve counterclock­wise to open (for richer mixture)

Turn the flywheel by hand to draw the fuel to the

•

fuel inlet.
Turn the flywheel two more revolutions to draw the

•

fuel inside the engine.

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 flywheel 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.

Open the throttle very slightly:

◆

13

This is to avoid unnecessarily
high revolutions when the en­gine starts.

◆

Heat the glowplug by connecting the battery leads.
Make sure that the direction of rotation of the
electric starter is correct, namely, clockwise.

If necessary, reverse leads on battery to provide

◆

clockwise rotation.
Hang the starter belt over the flywheel and starter

◆

and depress the starter switch for one or two
seconds. Repeat if necessary. When the engine
fires, withdraw the starter immediately.

Warning:
Do not apply the starter to a flooded engine and
never place your finger over the carburettor in­take when using the starter. This may cause an
hydraulic lock and bend the connecting-rod.

In case of the 21RG-MX

■

Take the same procedure as

•

the 21RG-M to the point of
"Heat the glowplug by
connecting the battery
leads".

Pull the starter handle

•

briskly straight out several
times to start the engine.

Starter Handle

◆

To stop the engine, fully close the throttle to cut off
air supply.

PRECAUTIONS
When starting the engine,
the hull is off the water and
the engine is run with no
load, and with even below
half throttle engine r.p.m.
come high. Prolonged
running with this condition may result in the
seizure of the connecting rod and crank pin.
Never run the engine with high r.p.m. (never open
the throttle beyond the starting setting) with no
load (i.e. the hull is off the water).

14

Warm up the engine by running it at around idling
setting for a while after starting,

As with the engine of a full size boat. High r.p.m.

◆

operation without warming up will shorten engine
life or damage it.

Leaving the Needle-Vale set at the starting setting

◆

of 2-1/2 turns open, run the boat several times with
the throttle fully open until at least three full tanks of
fuel have been consumed. (It should be noted, at
this stage, it may not be possible for the engine to
idle reliably because f the over-rich setting of the
Needle-Valve.)

This completes the initial running-in stage. For the

◆

remaining period of running-in, refer to the
adjustment procedures detailed later. The boat will
need to be run or about 10 tanks of fuel to complete
the running-in period.

Note!
If as a result of your boat being capsized, the
engine takes in water, remove the glowplug,
invert the engine and eject water by carefully
turning the flywheel, first by hand and then with
the electric starter. Make every effort to ensure
that no water remains in the engine before
attempting to restart it, or it may be damaged by
an hydraulic lock.
To ensure that any traces of water (which may
also cause internal rusting if not dealt with) are
flushed out, use an appropriate water-displacing
spray lubricant.

15

ADJUSTMENT

WARNING
Running the engine with the boat out of the water,
without load and without cooling water, will seri­ously damage it, due to overheating. Therefore,
always lower the boat into the water immediately
after the engine has been started, so as to pre­vent over-speeding and to allow cooling water to
be forced up to the cylinder-head. Having carried
out the initial running-in (''breaking-in'') proce­dure as described before, complete the running­in as follows:

1.

2.

:

Open the throttle slightly
from the idling position
and start the engine,
following the procedure
described previously.

Fig.-1

Lower the boat into the water, gradually open the
throttle and run the boat straight ahead for 20 to 30
metres at full throttle. Now return the model and
close the needle-valve 20 to 30

°

. Repeat the run,

taking note of the improvement in speed.

Continue with further runs, gradually closing the

3.
needle-valve (20 to 30

°

at a time) until no further

increase in speed is obtained.

If the needle-valve is closed beyond the optimum

4.

setting, the model will slow down, accompanied by
visibly diminished exhaust smoke. In this case,
immediately throttle down and return the model to
shore. Re-open the needle-valve approximately
one-half turn and repeat the runs until the
optimum needle setting is found.

Aim to have the model achieving its highest

5.

performance after the engine has consumed about
one liter of fuel. Having found the optimum needle­valve setting, make a note of the number of turns
necessary to quart this from the closed position.

With the engine run-in and the optimum needle-

6.

valve setting determined, the mixture control valve
should be checked as follows:

16

7.

Launch the boat and gradually open the throttle to
its fullest extent. If at this point, the engine puffs
out a good deal of smoke and does not accelerate
smoothly and rapidly, it is a sign that the idling
mixture is too rich. Therefore, turn the mixture
control screw clockwise 45 to 60

°

. Repeat the run

and recheck the result.
If, on the other hand, the idling mixture is too lean,

8.
the engine is likely to speed up momentarily, then
cut out abruptly when the throttle is re-opened. In
this case, first turn the mixture control screw
counter-clockwise 90

°

to make sure that the
mixture has become richer, then make
incremental adjustments, each way, until an
acceptable balance between rich v.lean settings is
achieved. Carry out these adjustments patiently
under actual running conditions, until the engine
responds quickly and positively to throttle
movements. Use a small screwdriver to adjust the
mixture control valve via its slotted screwhead in
the center of the outer end of the throttle rotor.

With the optimum mixture control valve position,

9.
light smoke is visible during high-speed running
and engine r.p.m. increase smoothly during
acceleration.

10.

Remember that, if the engine is operated with the
fuel/air mixture slightly too lean, it will overheat and
run unevenly or cut out. As with all engines, it is
wise to set both valves a little on the rich side of the
best rpm setting, as a safety measure. When the
best balance of mixture adjustments has been
determined and, especially as the engine becomes
fully run-in, it will probably be found that the idling
speed has increased. Readjust the throttle opening
by means of the trim lever on the transmitter, so
that the lowest idling speed, without risk of stalling
the engine, may be obtained.

WARNING

:

For safety reasons, it is advisable to stop the
engine before carrying out adjustments to the
Mixture Control Screw.

:

Note
Once the correct carburettor settings have been

established, it should be unnecessary to alter
them. Such slight Needle-Valve readjustments as
may be required to compensate for variations in
atmospheric conditions will not normally affect the
other two controls. Slight readjustments may be
necessary for optimum performance if different
types of fuel, glowplugs or propellers are used.

17

CARBURETTOR CLEANLINESS

Proper functioning of the carburettor depends on its
small fuel orifices remaining clear. The minute
particles of foreign matter that are present in any fuel,
can 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
carburettor and, furthermore, that this filter is
frequently cleaned to remove dirt and lint that
accumulate on the filter screen. Finally, occasionally
remove the needle-valve holder from the carburettor
as shown below and extract any remaining foreign
matter that may have lodged in the location shown.

Remove this with an
8mm spanner

Dirt and fibrous matter
mostly accumulate here

CARE AND MAINTENANCE

To ensure that you obtain long life and peak
performance from your engine, observe the follow

1

As previously observed, foreign matter in the fuel
can cause problems. Therefore:

●

rinse out the fuel tank with methanol or fuel before
installing it.

●

Install a fuel filter to the fuel delivery tube between
tank and carburettor.

●

Install a fuel filter to the outlet of your squeeze
bottle, or to the pump inlet if you use a manual or
electric pump. *

●

do not leave your fuel container open needlessly.

O.S. 'Super-Filter' (L) is available, as optional ex-

✽

tra,to deal with this problem. To fit this filterto the
outlet tube inside your refuelling container, will pre­vent the entry of foreign material into the fuel tank.

2

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

18

ing.

3

At the end of each operating session, drain out any
fuel that may remain in the fuel tank. Afterwards,
energize the glowplug and try to restart the engine,
to burn off any fuel that may remain inside the en­gine. Repeat this procedure until the engine fails to
fire. Leaving fuel residues within the engine can
result in difficult starting after a period of storage. It
may also cause corrosion. To reduce such risks, it
is helpful to inject some corrosion inhibiting oil into
the engine's air intake. Rotate the engine many
times to distribute the oil to all the working parts.

4

Drain the water remaining in the water cooling
head, and wash out with methanol, then inject cor­rosion-inhibiting or moisture-displacing oil.

5

When cleaning the exterior of the engine, use me­thanol or kerosene. Do not use gasoline or any
solvent that might damage the silicone fuel tubing
or any plastic parts of the boat hull.

6

When the engine is not in use remove the glow­plug and rinse out the interior with kerosene (not
gasoline), by rotating the crankshaft. Shake out re­sidue, then inject light machine-oil through the plug
hole again rotating the shaft to distribute the pro­tective oil to all working parts.

7

In the event of water having entered the cylinder,
crankcase, etc., refer to the procedures recom­mended in the footnote to "running-in" section.

Avoid unnecessary disassembly of your engine.

8

CHECKING OF THE ENGINE

After a long use, the engine will not develop the
standard performance due to wear of parts. It is
suggested to replace the parts, such as ball bearings,
connecting rod, cylinder & piston assembly and
crankcase, as necessary after checking when the
following symptoms are found.

●

Idling gets unstable and/or the engine stops at
idling.

●

Engine sound changes and the engine tends to
overheat.

●

Power drops extremely.

19

TROUBLE SHOOTING WHEN THE ENGINE FAILS TO START

Four key points

For quick, reliable starting, the following four conditions are required.
1 Good compression. 2 Adequate "glow" at glowplug. 3 Correct mixture.
4 Sufficient electric starter rotating speed.

If the engine fails to start, or does not keep running after being started, check symptoms against the
following chart and take necessary corrective action.
Note: The most common causes of trouble are marked with three asterisks, the less common problems
with one or two asterisks.

Symptom

Engine fails
to fire.

Factor

4

2

3

Cause

Sluggish rotation

★

Glowplug battery

★★

discharged.

Glowplug element

★

is burned out
Something wrong

★

with battery leads.

★★

Engine "flooded"

★

Insufficient fuel.

. . . . . . . . . . . . .

. . . . . . . . . . .

. . . . . . . . . . .

. . . . . . . . . . .

. . . . . . . . . . . . .

. . . . . . . . . . . . . .

Corrective action

Recharge the electric starter battery.
Pull the recoil starter briskly.

Recharge lead-acid cell or replace dry battery. (Note: An unused,
or almost unused, dry battery may sometimes be of insufficient
capacity if it is "old stock".)

Replace glowplug. Check that applied voltage is not too high.
Check glowplug heating using other leads.
Close needle-valve fully and remove glowplug, Apply starter to

pump out excess fuel. Re-start engine.

Refer to p.9

20

Symptom

Engine fires
intermittently but
does not run.

Engine fires once or
twice, then fails to fire.

Engine starts but revol­utions decrease and en­gine eventually stops.

Engine starts, then
revolutions increase
and engine cuts out.

Engine stops when battery
leads are disconnected
after starting.

Factor

★★

2

★★

3

★

4

★★

2

★★

3

★★★

3

★

3

★★

3

★

2

Cause

Incorrect heating of
glowplug.

Excess fuel

Sluggish rotation.
Glowplug battery

discharged.

Insufficient fuel
Mixture too rich.

Fuel not reaching
the engine.

Mixture too rich.
Mismatch of glow plug

and fuel.

. . . . . . . . . . . . . . . .

. . . . . . . . . .

. . . . . . . . . .

. . . . . . . . . . . .

. . . . . . . . . . . . . . . .

. . . . . . . . . .

. . . . . . . . . . .

Corrective action

Voltage too high or too low. Re-check and readjust referring to

. . . . . . . .

"BEFORE STARTING"
Continue to apply starter. If necessary disconnect battery from

glowplug and leave for a few minutes, then re-energize plug. If
engine still does not start, remove glowplug and pump out excess
fuel.
Then re-start.

Recharge the electric starter battery.
Recharge lead-acid cell or replace dry battery.

(Note: An unused, or almost unused, dry battery may sometimes
be of insufficient capacity if it is "old stock".)

Refer to p.9

°

Close needle-valve half turn (180
then re-start.

Make sure that tank is filled with fuel. Check that there is not
something wrong with fuel tubing (kinked or split). Check that
carburettor is not clogged with dirt.

) and wait for several minutes,

Close the needle-valve a little.

. . . . .

Change fuel or glowplug.

21

MAX-21RG-M/MX EXPLODED VIEW

C.M2.6X18

1

2

22

6

7

4

C.M2.6X18

8

4

3

5

0

9

r

e

--A

✽

Type of screw C…Cap Screw M…Oval Fillister-Head Screw

F…Flat Head Screw N…Round Head Screw S…Set Screw

-

C.M2.6X7

t-2

y

=

t

C.M2.6X7

w

q

M.+2.6X7

t-1

MAX-21RG-M/MX ENGINE PARTS LIST

No.

Code No.

2 3704 100

1

2 3603 000

2

2 3906 000

3

2 3817 000

4

2 3605 000

5

2 5382 000

6

2 3981 700

7

4 1614 000

8

2 3601 000

9

0

2 3430 000

-

2 3602 000
2 3602 030

-

-A

23

=

q

w

e

r

t

t

-1

t

-2

y

2 3614 000
2 3607 000
2 3813 001
2 3602 050
2 3601 800
7 3003 000
7 3003 100
7 3003 200
2 3813 001
7 1608 001
7 1802 030
7 2103 520

The specifications are subject to alteration for improvement without notice.

Water Cooled Head Assembly
Cylinder & Piston Assembly
Piston Pin
Piston Pin Retainer(2pcs.)
Connecting Rod
Carburetor Complete (Type 20J)
Carburetor Retainer
Crankshaft Ball Bearing (Front)
Crankcase
Crankshaft Ball Bearing (Rear)
Crankshaft
Crankshaft
Gasket Set
Cover Plate
Screw Set
Starting Shaft
Rear Adaptor
Recoil Starter Assembly No.5

Recoil Starter Body No.5

Oneway Clutch No.5
Screw Set
Glowplug No.8
Flywheel No.2E
Exhaust Header Pipe

Description

For RG-M
For RG-MX

For RG-M

For RG-MX

For RG-MX

For RG-MX

For RG-MX

For RG-MX

For RG-MX

CARBURETTOR EXPLODED VIEW & PARTS LIST

5

-1

1

1

✽

Type of screw
C…Cap Screw M…Oval Fillister-Head Screw

F…Flat Head Screw N…Round Head Screw S…Set Screw

S.M3X3

2

6

7

9

8-5

-4

8

3

-1

3

4

8-2

S.M3X3

-1

8

8

8-3

No.

1

1-1

2

3

3-1

4

5

6

7

8

8-1
8-2
8-3
8-4
8-5

9

Code No.

2 4981 405
2 6381 501
2 5381 203
2 6781 309
2 4881 824
2 6781 506
2 5382 100
2 5381 220
2 2681 953
2 7881 900
2 4981 959
2 4981 837
2 6381 501
2 7381 940
2 6711 305
2 9015 019

Throttle Lever Assembly
Set-screw
Carburettor Rotor
Mixture Control Valve
'' O '' Ring (2pcs.)
Rotor Spring
Carburettor Body
Rotor Guide Screw
Fuel Inlet
Needle Valve Assembly
Needle
'' O '' Ring (2pcs.)
Set-screw
Needle Valve Holder Assembly
Ratchet Spring
Carburettor Rubber Gasket

Description

The specifications are subject to alteration for improve
ment without notice.

24

O.S. GENUINE PARTS & ACCESSORIES

GLOW PLUG

■

No.8

(71608001)

A5

(71605100)

■

MARINE UNIVERSAL
JOINT

(22442009)

4mm

■

SUPER JOINT
TUBE 21

(72106300)

■

T-2030 TUNED SILENCER

(72106030)

SUPER FILTER

■

(72403050)

(L)

CRANKSHAFT

■

CLAMP

1521

(71530200)

■

LOCK WASHER

(10sets)

M3

(55500002)

■

DUST CAP SET

φ

(73300305)

3

(For carburetor nipple)

(73300812)

φ

8

(For T-2030 tuned silencer)

25

LONG SOCKET WRENCH

■

WITH PLUG GRIP

(71521000)

MAX-21RG-M THREE VIEW DRAWING

SPECIFICATIONS

Displacement

■

Bore

■

Stroke

■

Practical R.P.M.

■

Power output

■

Weight

■

3.46cc/0.211cu.in.

16.6mm/0.654in.

16.0mm/0.630in
3,000

~

35,000r.p.m.

1.7ps/28,000r.p.m.
317g/11.18oz.

29.6

UNF 1/4-28

45

JAPAN

67 21.5

88.5

26

59.5

74.5

Dimensions(mm)

φ

21

3.3

4-

33.5

10.5

37

MAX-21RG-MX THREE VIEW DRAWING

SPECIFICATIONS

Displacement

■

Bore

■

Stroke

■

Practical R.P.M.

■

Power output

■

Weight

■

3.46cc/0.211cu.in.

16.6mm/0.654in.

16.0mm/0.630in
3,000

~

1.7ps/28,000r.p.m.
389g/13.72oz.

29.6
45

35,000r.p.m.

UNF 1/4-28

JAPAN

67

107

27

Dimensions(mm)

φ

4-

3.3

21

37

33.5

59.5

74.5

40

10.5

MEMO

28

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R

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P

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A

B

L

I

S

H

I

N

G

T

H

E

S

S

T

D

A

R

N

A

D

C

Copyright 2001 by O.S.Engines Mfg. Co., Ltd. All rights reserved. Printed in Japan.

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6-15 3-Chome Imagawa Higashisumiyoshi-ku
Osaka 546-0003, Japan

URL : http://www.os-engines.co.jp

TEL. [phone]

FAX. [phone]

090100