Two-Stroke Engine For Airplanes
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 INSTRUCTIONS AND WARNINGS |
2-6 |
ABOUT YOUR O.S. ENGINE |
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ENGINE CONSTRUCTION, |
|
NOTES WHEN APPLYING AN ELECTTRIC STARTER |
7-8 |
ABOUT THE ENGINE |
9 |
BASIC ENGINE PARTS |
10 |
BEFORE STARTING |
11-14 |
INSTALLATION |
15-17 |
INSTALLATION OF THE STANDARD ACCESSORIES |
18-19 |
FUEL TANK LOCATION |
20-21 |
MIXTURE CONTROLS |
22 |
GLOWPLUG |
23 |
STARTING |
24-26 |
RUNNING -IN, IDLING ADJUSTMENT CHART |
27-30 |
MIXTURE CONTROL VALVE ADJUSTMENT |
31 |
REALIGNMENT OF MIXTURE CONTROL VALVE, |
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SUBSEQUENT STARTINGPROCEDURE |
32 |
SUBSEQUENT READJUSTMENT, |
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CARBURETOR CLEANLINESS |
33 |
TROUBLE SHOOTING WHEN THE |
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ENGINE FAILS TO START |
34-35 |
CARE AND MAINTENANCE |
36-37 |
ENGINE/ CARBURETOR EXPLODED |
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VIEWS & PARTS LIST |
38-45 |
O.S. GENUINE PARTS & ACCESSORIES |
46-47 |
THREE VIEW DRAWING |
48-49 |
MEMO |
50 |
1
SAFETY INSTRUCTIONS AND WARNINGS ABOUTYOUR 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.
Install 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. Also, check the tightness of all the screws and nuts before restarting the engine.
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 carburetor.
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 glowplugignition 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
ENGINE CONSTRUCTION
With this engine, the piston will feel tight at the top of its stroke (TDC) when the engine is cold. This is normal.
The cylinder bore has a slight taper. The piston and cylinder are designed to achieve a perfect running clearance when they reach operating temperature.
Near TDC
Piston
Cylinder Liner
Crankshaft 
Slight taper
When the engine is cold. When the engine is hot.
7
NOTES WHEN APPLYING
AN ELECTRIC 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.
8
ABOUT THE ENGINE
This manual handles MAX-25AX & MAX- 35AX.
These are high performance two stroke engines designed for sport and aerobatic models.
Ample power enables to turn a one size larger propeller with lower rpm, which results in mild and pleasant exhaust sound.
The new carburetors needlevalve assembly has now been angled backward for safety.
New E-3080 silencer (POWER BOX) develops very effective muffling.
Also, the compact body enables it to be fit within most cowls.
25AX/35AX STANDARD ACCESSORIES
Glow Plug No.8
(suppplied with the engine)
Needle Valve Extension Cable Set
E-3080 Silencer Assembly
Silencer Retaining Screw (M3x28 2pcs.)
9
BASIC ENGINE PARTS
Cylinder head |
Glowplug |
|
Carburetor Type 21K
(Type 21L For 25AX)
Propeller washer
Propeller nut
Crankshaft
Cover Plate
Beam Mount
Crankcase
Drive Hub
MAX-35AX is shown.
10
BEFORE STARTING
Tools, accessories, etc. The following items are necessary for operating the engine.
Propellers
The choice of propeller depends on the design and weight of the aircraft and the type of flying in which you will be engaged.
Determine the best size and type after practical experimentation. As a starting point, refer to the props listed in the accompanying table. Slightly larger, or even slightly smaller, props than those shown in the table may be used, but remember that the propeller noise will increase, due to higher rpm or if a larger- diameter/lower-pitched prop is used.
SIZE(DxP) |
25AX |
9x5-6, 9.5x5, 10x5 |
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35AX |
10x6-7, 11x6, 12x6 |
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11
Warning:
Make sure that the propeller is well balanced. An unbalanced propeller and/or spinner can cause serious vibration which may weaken parts of the airframe or affect the safety of the radio-controlled system.
DO NOT forget the WARNINGS and NOTES on propeller and spinner safety given on front pages.
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.
Spinner
Since the 25AX and 35AX is intended to be started with an electric starter, the addition of a
spinner assembly for centering the starter sleeve is desirable. Use a heavy-duty, well balanced spinner either of metal or plastic.
FUEL
The 25AX and 35AX should be operated on a methanol based fuel containing not less than 18% (volumetric) castor oil, or a top quality synthetic lubricant (or a mixture of both), plus a small percentage (5-20%) of nitromethane for improved flexibility and power. (The carburetor is adjusted a little on the rich side at the factory for a fuel containing 18% lubricant and 15% nitromethane.) Some commercial fuels also contain coloring additives as an aid to fuel level visibility. In some cases, these additives have indicated slightly negative effects on the performance. We would suggest that you use such fuels only if you are satisfied that they do not adversely affect running qualities when compared with familiar standard fuels. When changing to a fuel brand or formula that is different
from the one to which you are accustomed, it is a wise precaution to temporarily revert to in-flight running-in
procedures, until you are sure that the engine is running entirely satisfactorily.
12
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.
Fuel Tank
A fuel tank of approximately 
180cc capacity for 35AX and 160cc capacity for 25AX is suggested.
This allows around 10 minutes flying time, dependent upon the type of fuel used, the size of propeller and on the amount of full-throttle to part-throttle operation throughout the flight.
GLOWPLUG IGNITER
Commercialy available handy glowplug heater in which the
glowplug battery and battery leads are integrated.
FUEL PUMP
Alternatively, one of the |
Manual |
Electric |
purpose-made manual or |
electric fuel pumps may be used to transfer fuel directly from your fuel container to the fuel tank.
Electric Starter and |
Electric |
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Starter Battery |
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Starter |
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Required when starting |
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the engine. |
12-Volt lead-acid battery |
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O.S. Non-Bubble Weight |
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To prevent the pickup from adhering to |
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the tank wall under suction and |
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restricting fuel flow, slots may be filed I |
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the end of the weight. Alternatively, O.S. |
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Non-Bubble Weight is available as an |
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optional extra. |
S |
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Fuel Filter
It is recommended to install a good in-line filter between the fuel tank and carburetor to prevent entry of foreign matter into the carburetor.
O.S. Super Filter (Fuel Can Filter) |
SILICONE FUEL LINE |
Install a filter on 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.
Heatproof silicone tubing of approx. 5mm o.d. and 2.5mm i.d. is required for the connection between the fuel tank and engine.
13
TOOLS
HEX Screwdriver
Necessary for engine installation. 1.5mm, 2.5mm
Phillips Screwdriver
LONG SOCKET WRENCH WITH PLUG GRIP
Recommended for easy removal and replacement of the angled and recessed glowplug, the O.S.Long Socket Wrench incorporates a special grip.
8mm
No.2, etc.
End Wrenches
10mm, etc.
SCREWDRIVER
Necessary for mixture control valve adjustments.
14
INSTALLATION
It is suggested to use as heavy and rigid as possible engine mounting for highest performance and safe running. Conventional wooden mounting beams should be of rigid hardwood and of at least 12mm or 5/8-in square section. Use at least 3mm steel screws, such as Allen type, with locknuts, for bolting the engine to the bearers..
Make sure that the mounting beams are parallel and that their top surfaces are in the same plane.
CORRECT
Front view |
Side view |
Top surfaces are in the same plane.
INCORRECT
Top surfaces are not |
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in the same plane. |
Opposite beam |
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Top surfaces are not in the |
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Re-align the surfaces |
same plane. |
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Engine does not rest firmly. |
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as necessary |
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15
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