Engines of the Golden Era – Ohlsson Miniature

Now you own an OHLSSON Miniature Radial Mounted Airplane Motor. Your motor is a precision built model power plant, the result of years of experience in building miniature motors. It has been the aim of Irwin G. Ohlsson and Frank Bertelli, builders of OHLSSON Motors, to produce an engine simple in construction, powerful, and dependable in performance. An engine that would give many hours of successful model flights. The design and construction of the OHLSSON Motor is extremely simple. It can be taken apart and re-assembled with a screwdriver. Special care must be taken in removing manifolds to clean them properly and replace with new gaskets. Gaskets should be soaked in water to soften them before re-assembling. Radial mounting, an exclusive OHLSSON feature, makes it possible for the motor to be an integral part of the ship. It gives greater strength and accessibility to all motor parts. Operation of the OHLSSON Motor is not complicated. If you read and understand the operating instructions, you should, with a little practice know lust how your motor works. The important thing to remember is this-the better care you take of your OHLSSON Motor-the better it will perform for you.


Your OHLSSON Motor is a NEW engine. It has been assembled and run by expert mechanics at the factory. Yet it is a NEW motor and requires from 2 to 5 hours of block running before it is completely broken in. The fuel mixture is important and on it, to a great extent, depends the successful breaking in and operation of your motor. 3 parts of white, untreated gasoline to 1 part of S.A.E. 70 Valvoline oil is the best mixture for use in your motor. If you cannot get S.A.E. 70 Valvoline, use the best grade S.A.E. 70 motorcycle oil you can get.

For the best performance make sure you use fresh new batteries. For bench work and starting your motor, select 2 new No. 6 dry cells-the kind used to ring doorbells and make sure the dealer tests them to show you they de-liver full amperage. For flying-2 new flashlight cells will supply sufficient current for operation. Best results may be obtained by using the Special OHLSSON Multiple-cell Battery. Weak batteries are the cause of most motor failures.

Your OHLSSON Motor is delivered to you on a wood test block. This test block is NOT the motor mount for your ship. It does, however, show you the ideal position for each of the parts of the motor assembly. When you are installing your motor in your ship make sure you come as close as possible to the assembly as it is made on the test block. Study the position of the coil, gas tank and condenser with relation to the motor block. This will save you a great deal of trouble later on.

You should become familiar with the operation of your motor by starting and running it in the test block. By doing this you can learn the best way to start your motor. You can learn the proper needle valve and timer adjustments. You can do the very things with your motor that the government requires all airplane pilots to do-you can become completely acquainted with its operation BEFORE you attempt to fly it. Common sense and reasonable caution makes gasoline perfectly safe to use as fuel. Keep flames and inflammable material away from your motor. Be careful about filling the gas tank and try alwayS to run your motor in the open, When the engine is running your place is back of the propellor.


Study your motor so that you know all wire connections.

Make sure YOU have fresh, full strength batteries.

Make sure your gas tank is full of the proper fuel.

Fasten test block securely. The best place is in a firmly anchored vise.

Attach propellor correctly. The motor runs counter-clockwise.

Open needle valve according to the number of turns written on the tag.

Retard spark by moving the timer arm to the right of the cylinder line. This is in the direction opposite to the exhaust manifold.

Spin propellor a few times with the finger over the intake manifold to prime the motor.

Switch on—by completing spark circuit to batteries.

Spin prop 3 or 4 times or until motor starts firing, using 2 fingers to give the prop a quick flip.

As soon as your motor starts close the needle valve and advance the spark by moving the timer arm toward the exhaust valve until maximum R.P.M. is reached. With a little practice you can learn just how far to close the needle valve and to advance the spark. When the motor starts it is firing only on every other stroke. This is called 4-cycling. As the spark is advanced and the needle valve is closed to the proper point. the speed increases and the motor automatically starts to fire on every stroke. It is now 2-cycling. You can tel: this change by the increase in the roar of the exhaust. Only when your motor starts 2-cycling has it attained flying speed.

To stop your motor – disconnect one of the battery wires. Practice starting your motor and running it in the block until you get the feel of its operation. The more you know about your motor, the better flights you will get.


Your motor has been tested and run by expert mechanics at the factory before it is delivered to you. Failure to start usually is the result of weak batteries, fouled spark plug or fouled points.

If your motor does not start at once :
I. CHECK WIRING – Make sure all connections are intact. Make sure timer points are clean. If they are dirty, clean with gasoline and reset to a dearth-, e of .010″ to .01 5″. Timer points are set at the factory and should not be changed unless damaged or fouled.

2. CHECK FUEL – Make sure that your tank is full and that no dirt has clogged the needle valve.

3. RESET NEEDLE VALVE – according to the instructions on the tag that was fastened to it when you received the motor.

4. ADJUST TIMER ARM – so that the spark reaches the plug just as the piston reaches the top of the cylinder. You can tell when the piston is at the lop of the cylinder by looking into the exhaust manifold.

5. TEST SPARK PLUG – Remove plug, clean and check gap to .010″. Ground body of the plug and turn prop. A spark across the gap shows that spat k is reaching the firing chamber.

6. REPEAT STARTING OPERATIONS – If your batteries are fresh, if your connections are good, points and plug clean and adjusted correctly, tank and needle valve clean and adjusted, gas in the tank, your motor will start.


Don’t install your motor in your ship until you are completely familiar with its operation in the testing block. Study the assembly of the cylinder block, radial mounting, tank, condenser, coil and winding. Best flights are obtained by maintaining this assembly in the ship.

The radial feature of the OHLSSON Motor makes possible a more rigid mounting to the fuselage of the ship and reduces the possibility of serious damage in case of crack-ups. The best mount in the opinion of the designers is the riveted dural mount furnished with all OHLSSON KITS. It is light, rigid and strong and allows the correct assembly of all parts in the ship.

Special care must be taken to assure proper insulation of all electrical equipment. Coil, condenser, batteries or wiring must not be allowed to ground or short. It is well to remember that metal, even though it is covered with dope is still a conductor of electricity. The coil should be inside the ship and the condenser as close to the timer points as possible. The batteries may be placed anywhere inside the ship. Experience has proved that the best battery hook-up is one that allows the use of large dry cells for test block operation and motor starting in field work. The hook-up is a booster arrangement that supplies greater amperage when the motor needs it and cuts in the flying batteries only when the motor has attained flying speed.

OHLSSON Motors have flown successfully in every type of model plane. Their performance in ships designed by OHLSSON engineers has been almost phenomenal. OHLSSON Motors develop ample power to fly 3 to 8 pound models with ease.


OHLSSON Miniature Radial Mounted Motors carry a POSITIVE GUARANTEE against defective parts and workmanship. Every part of your motor left the factory only after the most careful testing and inspection. Operating failures can be reduced to a minimum by proper care. Take care of your motor and you will find that it will give you many hours of successful flights