Cox (engines)

The Cox engines are internal combustion engines used in the model . LM Cox Manufacturing Co., Inc. was founded in 1945 to be resold in 1996 in Estes, which will cease production in 2009. When they stopped producing their engines, the remaining parts stock was resold to a buyer private Canadian, and starts producing parts again, Cox International.

For more than half a century, they propelled boats and cars, but the area in which they were most used is that of model aircraft , especially in free flight and circular flight. Millions of these engines have been produced and sold worldwide, and have become and remain the world’s most popular Class 1 / 2A .049 (0.8cc) motors. Even if the production of engines has stopped recently, they continue to be sold in abundance, sometimes still in new condition [ref. necessary] .


Most of the engines built Cox in this business are engines of 0,049 cubic inches, or 0.8 cm 3 . These are 2-stroke engines, using a filament plug to ignite the air / fuel mixture in the cylinder (for more information, refer to the Two-Cycle Cycle page ). The fuel intake is controlled by a needle, and is sent into the cylinder via a non-return valve (also called hip) or a rotary valve.

The fuel used is a more explosive mixture than conventional gasoline, and generally consists of methanol (60 to 70%), castor oil (20%), and nitromethane (10 to 40%).

The first Cox engines

  • 045 O-Forty-Five (1949) :

Even though it was not completely produced by Leroy Cox, it was he who supplied most of the pieces and who designed it. It served as a “pack” that was added to cars to propel them. It was a big step forward for his time, as this engine included gearboxes, a tank, a flywheel and a silencer, all in one pack all-in-one.

  • 1952 Space Bug :

The Space Bug was the first engine built entirely by Cox. It was designed for circular flying and was sold for $ 6.95 , and included a metal tank at the back, operating on the principle of the check valve.

The “Bees”

  • Babe Bee 1956 049 ( 0.8 cm ³) :

The Babe Bee is the first Cox engine to have an extrusion- shaped casing (a less expensive process than the old crankcase manufacturing technique, which used a cast aluminum housing). It includes a 5 cm 3 tank and has been sold with thousands of RTF kits worldwide, and remains Cox’s best-known engine.

  • 1957 Pee Wee .020 ( 0.33 cm ³) :

With the huge success of the Babe Bee, Leroy Cox decides to start building an engine that is two times smaller than the Babe Bee: the Pee Wee .020. It keeps exactly the same construction as its big brother, and always uses the principle of the check valve.

  • 1958 Golden Bee :

The Golden Bee is actually a Bee Babe whose tank has been enlarged (8 cm 3 capacity ), and is colored in gold. The hoses in the tank have been rearranged for aerobatic aircraft to be fueled regardless of orientation. The following versions had modified transfer channels in order to have greater power.

  • 1996 Venom :

The Venom is an engine designed for high performance, using a balanced and lightened crankshaft. The piston was designed as the Tee Dee (slightly tapered cylinder). The problem was that the engine produced at the chain was different from the prototype, and the piston was too light, which could cause, at high speed, the detachment of the top of the piston. Only 1000 of these engines have been manufactured, making them quite rare (price going to more than 300 dollars in new condition).

The Tee Dees

  • 1961 Tee Dee 049 :
    A Cox Tee Dee .049 and .051 side by side

This engine is probably the best Cox engine. This engine was “THE” engine for competitions for many years. It was developed by Bill Atwood, specifically engaged to develop the range of Tee Dee. It has a modified cylinder (slightly conical shape, to ensure a better seal), two additional transfer channels on each side. The crankshaft is balanced precisely to ensure better performance.

  • 1961 Tee Dee 051 :

The Tee Dee .051 is just an adapted version of the .049 to be used in class “A”. It is physically the same as the .049, only the bore is different.

  • 1994 Tee Dee .051 RC :
    A Cox Tee Dee .051 RC

This version of the Tee Dee was specifically designed for RC flight, so it included an RC carburetor and a silencer. Because of the silencer, the Tee Dee .051 RC did not include sub-induction. Only 2000 engines were produced, making it the second most sought-after engine after Venom.

The Tee Dees will be available in several other displacement, from 0.010 to 0.15 cubic inches.

The mechanics of Cox engines

Cylinders and pistons

There were a lot of different types of cylinders, with 3 different wall thicknesses. They were all interchangeable, which was a problem when buying used engines. The first engines had a relatively thin wall, which turned out to be a disadvantage, as they folded quite easily during a crash or when dismounted. The following generations have been expanded only at the level of the exhaust, and finally the last generations have been widened over the entire length, allowing the installation of a ring of control of gases.

Sectional view of some Cox cylinders

This image above allows to see the different sections of the cylinders, and the transfer ports.

The # 1 is a Tee Dee cylinder with two additional ports on each side of the first transfer channel.

No. 2 is a cylinder with a grooved exhaust, thus reducing the risk of burns, and with a thicker wall.

No. 3 is a cylinder of Black Widow, with the walls of the cylinders enlarged than the exhaust ports.

The No. 4 is a pre-1955 cylinder with a thin wall, used in Space Bug, Space Bug Jr, Thermal Hopper and Strato Bug. Note the thread diameter of the candle which is smaller than the newer models.


Five types of candles were produced for Cox .049 engines. These candles also served as a bolt, they covered the entire top of the cylinder. Therefore, when the candle was worn, it was necessary to replace the whole breech.

The different models of Cox candles

N ° 1: Standard candle, before 1955. Low compression, with a hemispherical shape, smaller thread than the following engines. This candle has only been used on Space Bug, Thermal Hopper, Space Bug Jnr and Strato Bug.

No. 2: Standard candle, after 1955. Low compression, also with a hemispherical shape, with a larger thread. It was used on all the engines until its replacement in 1980 by the model n ° 325.

N ° 3: Standard candle. Low compression, hemispherical shape. Used on all engines except Tee Dee, Killer Bee, Venom, QZ and Texaco. This candle replaced the model n ° 302-1 in 1980.

No. 4: High compression candle, trumpet shaped, with 2 cooling fins. Used only on Tee Dee, Killer Bee, QZ and Venom.

No. 5: Texaco candle. Low compression, hemispherical shape. Only for Cox Texaco, it allowed a better cooling with its 5 fins, which allowed this engine to have a better power.

However, these candles were often considered too expensive, and some then obtained unofficial candles, manufactured by other manufacturers. Still others modified their candles squarely to fit a thread and screw a standard candle.


This section is empty, insufficiently detailed or incomplete. Your help is welcome! How to do ?

Check valves

This section is empty, insufficiently detailed or incomplete. Your help is welcome! How to do ?

Unofficial products

Davis Diesel conversion kits

These kits can convert these engines into diesel, so as not to be dependent on candles considered too expensive. It is a cylinder head that is screwed in place of the candle, and whose compression ratio can be adjusted via a screw [1]  [ archive ] . Since diesel has a higher compression than “glow”, it is often necessary to change the crankshaft for a reinforced version. Davis conversion heads can be used on Pee Wee .020, Tee Dee and Medallion .049 / .051, and all .049 check valve motors.

Tarno carburetors

These carburetors, developed in Quebec, were equipped with RC settings. Marketed in 1978, they were available in Tee Dee and other non-return valve versions. Unfortunately, they have hardly met with any success and have quickly disappeared, because of their dubious reliability.

The RTF planes of Cox

This table lists the main aircraft sold by LM Cox Manufacturing. It is still in English, but in translation

Year Model Cat. # Engine Notes
1953 TD1 400 Space Bug .049 Cox’s first RTF
1954 TD3 600 Space Bug Jnr .049
1956 TD4 Trainer 5100 Babe Bee .049
1957 Super Cub 105 5200 Babe Bee .049 Replaced by the Super Cub 150
1958 Lil Stinker 5300 Pee Wee .020 First aircraft powered by a 020 engine
1958 Super Saber 5400 Pee Wee 0.020
1959 P40 Warhawk 5500 350-1 Super Bee .049 Babe bee with double transfer channel
1960 Commanche 5600 0.15 Sportsman 2.5 cm motor 3
1960 PT-19 Trainer 5700 Babe Bee .049 Other versions have been released: 5710, 5761, 5900 and 6300
1960 Curtiss Pusher (Kit) 5800 350-2 Babe Bee .049 First RTF kit
1961 Airplane Shinn 2150-A 6200 190 Production Engine
1962 Ju87D Stuka 6400 190-1 Production Engine
1962 P51B Bendix Trophy Racer 6600 190-2 Production Engine
1962 Super Cub 150 5200 190-4 Production Engine Update Super Cub 105
1963 Curtiss SB2C Helldiver 7000 190-3 Production Engine
1963 L-4 Grasshopper 7200 190-4 Production Engine
1963 Spook 7420 290 Spook Engine Flying wing (in kit)
1963 P51B Mustang aircraft 7600 190-2 Production Engine
1964 P40 Kittyhawk 8400 Super Bee .049 RAF version of the Warhawk P40
1964 Spitfire 7800 350-6 Silver Bee .049 First version of the Spitfire replaced in 1966
1965 Curtiss A-25 Bomber 7100 190-3 Production Engine
1966 RAF Spitfire 7800 Silver Bee .049 E version with the colors of the RAF
1966 T-28 7900 290 Production Engine
1966 QZ PT-19 Trainer 5900 QZ .049 PT-19 with a QZ engine
1967 AD-6 Skyraider 9700 190-6 Production Engine
1968 F2G-1 Corsair 7500 290 Production Engine # 7562 with flying accessories
1968 Pitts Special 8200 Pee Wee 020 Variation of the lil Stinker
1969 Thompson Trophy Corsair 27 2900 290 Production Engine
1969 Red Baron 5300 Pee Wee 020 Also released as “Red Knight”
1969 Mini Stunt Biplane 7300 Pee Wee 020 Another version of the lil Stinker
1969 Ryan ST-3 Super Sport 6200 (& 6200-80) Pee Wee 020 also available in trottled version 6200-80
1969 Ryan PT Army Trainer 6300 (& 6300-80) Pee Wee 020 same as 6200 & 6200-80 but in Army colors
1970 Corsair II 3900 290 Production Engine Chrome plated – left hand prop.
1971 Acro Cub 4600 190-4 Production Engine variant of the Super Cub
1971 rivets 6800 350-9 Production Engine popular design sought by collectors
1971 P51D Miss America Mustang 6900 190-7 Production Engine Stars and stripes color scheme
1971 P51D Mustang 7600 190-6 Production Engine bubble canopy
1972 Sopwith Camel 8000 191-0 Production Engine
1972 Fokker DVII 8100 191-2 Production Engine
1972 Fokker DR1 Triplane 8300 191-0 Production Engine
1973 Super Sport Trainer 8600 191-3 Production Engine Pink aerobatics trainer
1973 Bushmaster 8700 190-4 Production Engine convertible with floats and skis
1974 Super Stunter 5400 191-7 Production Engine First design with foam wings
1975 Cessna 150 4000 191-8 Production Engine Sure Flyer with autopilot
1975 Piper Comanche 4100 191-8 Production Engine Sure Flyer with autopilot
1976 Skymaster 4200 191-8 Production Engine Sure Flyer with autopilot
1976 P-39 Airacobra 4300 191-8 Production Engine Sure Flyer with autopilot
1976 Sky-Copter 7100 Pee Wee 020 First helicopter (free flight)
1976 Crusader Stunt Trainer 9000 191-9 Production Engine Foam wing stunter

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