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Cox Model Engines

Cox Fokker DVII Ready To Fly Control Line Model Plane

Introduction

Cox Model Engines are used to power Model Aeroplanes, Cars and Boats. Cox engines were in production for more than 50 years, between 1945 and 2006.

This article provides everything you ever wanted to know about the Cox .049 cubic inch model aeroplane engine in one easy reference.

Cox History

The Cox range of model engines were the brain child of entreprenure Leroy M. Cox.

• L.M. Cox Manufacturing Inc. started out in Leroy's garage in 1945 where he made wooden pop guns for kids and employed local housewives to assemble them. Metal was scarce due to the war which is why the guns were made of wood.

• In 1946 metal became readily available again and comptitors quickly moved into the market making their metal pop guns cheaper, so Roy moved to something else, making metal tether cars for kids.

• In August of 1946 a fire in Cox's garage forced him to move to newer and larger premises.

• In 1947 Cox developed a racing car which used an engine manufactured by Cameron Brothers. The cars sold for $19.95 and generated $200,000 in sales in their first year of production.

• In 1949 Cox developed their own engine for the racing tether car made from parts from other engines. This engine was called the "O Forty Five" as it was .045 cubic inch displacement.

• In 1950 sales of the car began to fall so Cox moved on to development of a model plane engine. A project which took a year and nearly sent Cox bankrupt, the end result was the Space Bug .049 engine, Cox's first Model Plane engine.

• The Space Bug engine sets the scene for all the Cox engines that followed and it went into full production in 1952. This engine was so popular that it sent all the other model engine manufacturers to the wall.

• In 1953 Cox produced their first Ready To Fly (RTF) aeroplane the TD1 which was powered by the Space Bug engine.

• In 1956 Cox developed the Babe Bee 049 which had an extruded crankcase, not cast like the others, this engine sold for just $3.95 and stamped the final nail in the coffin of their cometitors who's engines were selling for around $20.00 The Babe Bee was a high quality high precision engine which started easily and was very reliable, unlike the competition.

• In 1957 Cox took over the Flying Circle at Disneyland which was a major coup for the company. The model planes were being flown each day in front of tens of thousands of people and they had a hobby shop right there full of Cox RTF planes. The Cox Flying Circle remained in operation until 1965 when it was closed to make way for expansion of Tomorrowland.

• In 1960 Cox hired an engineer named Bill Atwood, (who had already build his own line of engines), to develop a new line of competition engines. Atwood was responsible for the Tee Dee and Medallion line of engines. These engines put Cox on the map as the number 1 engine in the world for many years to come. He literaly wiped the competition off the map.

• In 1963 due to continuing growth the company moved to larger (225,000 square feet) facilities which were three times larger than the old site. During this time Cox got into Slot Cars for a short time but this fad died as quickly as it started.

• In 1969 Mrs Cox died and Leroy was having health problems of his own so he sold the company to Liesure Dynamics. Liesure Dynamics continued to expand the range of Cox Model Aircraft as well as adding trains, boats, rockets, kites and radio control boosting sales to 25 million dollars per year.

• In 1980 Liesure Dynamics filed for bankruptcy, taking Cox Model with them.

• In 1983 former Cox engineer Bill Selzer (who Cox hired in 1952) purchased the company out of bankruptcy. The company once again flourished into the 1990s with new products being added and another move to even bigger facilities.

• In 1995 Cox celebrated 50 years

• In 1996 Cox sold to Estes / Centuri Corp.

• In 2005 production all but ceases of the internal combustion engines and RTF models.

The Engines

Cox 049 Reed Valve Engine

Manufacturer	L.M. Cox Manufacturing Inc.
Class	1/2A
Engine	2-stroke
Power	42 Watts @ 15,000 rpm
Fuel capacity	5 cc
Fuel consumption	1 cc / min

Main article: Cox_Model_Engines

The Cox line of reed valve engines up until 1960 used a rear reed valve induction system. In the late 50s they played around with rear rotary valve induction before moving forward with front rotary valve induction for their Tee Dee line.

The 049 engine displacement is 0.049 cubic inches or 0.818 cubic centimeters. The Bore is 0.409 inches for the 049 and 0.041 inches for the 051 The Stroke is 0.386 inches for both 049 and 051 engines.

Early Engines

• 1949 O Forty Five Power Pak (Special Racer Car Engine)

This engine was the first designed by Cox but included some major parts (ie piston and cylinder) of the Spitzy .045 engine designed by Mel Anderson. It employed a twin reed valve which was later used for the Space Bug. The engine was a major engineering achievement for it's time, by incorporating reduction gears, fuel tank, flywheel and muffler all into one "Power Pak". The air intake was via one of the axles.

• 1952 Space Bug

The Space Bug was the first engine built entirely by Cox. It was designed for Control Line flying use only and was marketed as a "Competition" engine and sold for $6.95. Back then there was no Radio Control and Free Flight hadn't been considered by Cox at this time. The Piston and Cylinder were made from mild steel bar stock and the crankcase and fuel tank were cast aluminium.

• 1953 Thermal Hopper

The Thermal Hopper is basically a Space Bug without the fuel tank. It has a needle vavle and venturi mounted on an aluminium plate instead. These were designed for free flight or control line flying and allowed the user to put a fuel tank of their chosing on.

• 1953 Space Bug Jnr.

The Space Bug Junior is a Space Bug with a smaller plastic tank. This cheaper version also only had one intake bypass port and sold for $3.95.

• 1955 Strato Bug

The same engine as a Space Bug but included a two piece fuel tank which was cheaper to make than the original space bug tank. The later Babe Bee tank was simply a further developed version of this tank. This engine was only produced during 1955 and sold as a mid range sport engine for $5.95. As such not many exist today which makes them very rare and collectible selling for over $300US in 2008.

Standard Bees

• 1956 Babe Bee 049

The classic Babe Bee was the first engine Cox produced with an extruded machined anodized bar stock aluminium crankcase. This crankcase was machine made and was much cheaper and faster to make than the cast aluminium crankcase of the earlier models. This engine was also supplied in thousands of RTF (ready to Fly) aeroplanes sold in department stores worldwide. It has an integrated 5cc fuel tank.

• 1957 Pee Wee .020

Boeyed with excitment of the Babe Bee 049 Leroy wanted to make a half size version of the Babe Bee. So he did. And they called it a Pee Wee .020 Just like a Babe Bee only half the size.

• 1958 Golden Bee

The Golden Bee is a Baby Bee that has a larger (8cc), stunt vented fuel tank and has been anodized gold. The larger tank allowed the planes to fly longer while the stunt vents allowed the airplanes to fly inverted without fuel running out or the engine cutting out. The first versions of the Golden Bee had a single bypass intake port but later versions had two bypass ports making them slightly more powerful.

• 1966 QZ

QZ stands for Quiet Zone . It's Babe Bee with a muffler, twin bypass port cylinder and high compression head in an attempt to regain the power loss caused by the muffler. The later QRC engine worked much better.

• 1976 QRC

The QRC was a modified Babe Bee engine that had a muffler and larger (8cc) fuel tank. In the 70'snpoise became and issue and the Cox engineers discovered that when adding a muffler the engine would lose significant power. This problem was alleviated by installing a cylinder with no sub piston induction. The engine was designed for power launching Radio Controlled Gliders and had a red tank with a blue spinner.

• 1982 Dragon Fly

This engine was designed for the Radio Controlled model planes. It's basically a Baby Bee with a clunck tank and a muffler throttle.

High Performance Bees

• 1956 RR1

The Rare Cox RR1

The RR1 uses a rear rotary valve intake rather than a reed valve in an attempt to achieve more power. The engine came after the Babe Bee and looks very similar with it's anodized, machined extruded aluminium crank case and fuel tank. The power improvement was negligible so Cox reverted to the cheaper easier to build Babe Bee. The engine was made for quite a few years and sold for $6.95. It has become a collectors item due to it's uniqueness and pretty colours and is worth around $300-500US in 2008.

• 1959 Space Hopper

The Space Hopper was Cox's first attempt at a beam mount engine plus the first steps towards their greatest engine, the Tee Dee. The engine was basically like the Thermal Hopper was to a Space Bug. That is a Babe Bee without a tank, but a venturi and needle vavle relying on and external fuel tank. It is claimed it has as much power as a Tee Dee but how can this be if the Tee Dee was the most powerful engine? Anyway, this engine was short lived and made way for the Tee Dee in 1960. They look very retro and due to their apparent rareness are worth around $200US in 2008

• 1973 Black Widow

Cox Black Widow 049

During the 70s a couple of Cox engineers were playing around with different coloured Babe Bee and Golden Bee parts and came up with an all black engine with a red spinner. They hopped it up a bit with a dual bypass cylinder from a Medallion, a black Golden Bee tank and a slightly larger (0.062") venturi intake. The Black Widow was born. These engines were marketed as a High Powered Combat Engine.

• 1995 Killer Bee 049

The Killer Bee was a real good attempt at making a fast reed valve 049 engine from information that had been learned over the years of racing and competition. It had a tapered cylinder and lighter piston similar to the Tee Dee, a stronger balanced crankshaft and a new reed valve shape. They had a Yellow plastic needle valve. Later in 2002 Estes produced a Killer Bee that had none of these features but looked like the original Killer Bee except for the needle valve.

• 1995 Killer Bee 051

The Killer Bee 051 exisited so that modellers could fly the same plane in two competition classes (ie A and 1/2A) simply by changing the engine.

• 1996 Venom

Cox Venom with Galbreath/Nelson Head

The Venom was Cox's last attempt at making a really fast 049 mouse racing engine. Again taken from ideas learned from years of competition, this engine put all those ideas into an off the shelf product. It used the Killer Bee crank shaft loosely fitted into the crankcase, and a cylinder with porting very similar Tee Dee cylinder and tapered like the Tee Dee and with a ligthened piston like the Tee Dee. The rest of it was like a Black Widow. The problem was that the production engine was not the same as the prototype. A mistake had been made in manufacturing and the piston was lightened too much. This made the engine fast but the piston weak and they would blow the top off the piston after a few runs at high speed. As such only 1000 were made and they never bother to make anymore. They are now worth a lot of money (around $300US in 2008) in the box.

Tee Dees

• 1961 Tee Dee 049

This is without a doubt, Cox's greatest and most famous engine. This engine was "THE" engine to use in competition for many years. It was designed by Bill Atwood who had been hired by Cox specifically to produce the Tee Dee line of Competition engines. The important features of the Tee Dee are as follows:

• Tapered cylinder and a lightened and tapered piston
  • Result: tighter piston fit at TDC and less piston mass = more performance.
• Two deep bypass ports with two bypass booster grooves on each bypass port, extending slightly above the main bypass groove
  • Result: significantly better air fuel mixture induction = more performance
• True peripheral venturi
  • Result: more eficient fuel intake, fuel draw and induction = more perfromance
• Precision ballanced and milled crankshaft
  • Result: better fuel intake, better balanced engine = more performance

The famous Cox Tee Dee .049

• 1961 Tee Dee 051

The 051 was simply a Class A version of the Engine. Physically the same on the outside only the bore was different and the piston had a small groove in the skirt to differentiate it from the 049. The 051 also had a RED carb body.

• 1995 Tee Dee .05 RC

This engine had a proper RC carby and a full sized standard muffler and was designed specifically for RC flying. It had no Sub Piston Induction. Also reasonably rare these days.

Cox also built Tee Dee's in .010, .020, .09 and .15 size. All these engines were very successful.

A little known fact was also this: One of the things Cox wanted Atwood to do was make him a .010 engine. Cox had already tried to halve the size of the Pee Wee .020 but couldn't get it to run for some reason. The suspiscion surrounded a problem with the tiny reed vavle. Atwood found that the front rotary valve worked well on the .010 size hence the .010 was born. Why? Because Leroy Cox wanted one.

Medallions

• 1962 Medallion 049

Cox Medallion .049

Also know as the "Poor man's Tee Dee" these were similar to the Tee Dee in appearance but had cheaper parts on them, making them cheaper to buy. The cylinder was a non tapered twin bypass with no boost ports (like the one used on the Black Widow), the crank shaft was drilled out rather than milled like the Tee Dee, and the carb body was a one piece unit with a conventional needle valve and spray bar. These engines were marketed as a Sport / Stunt engine as they were much tamer and much less cantankerous then the Tee Dee. These are a great reliable easy to use little engine even today. You can pick them up for under $100US in 2008.

• 1995 Medallion 051

The .051 came about when a special order for 300 Medallions was placed on Cox by the National Free Flight Society in the USA. It was a gentlemans agreement done on a handshake and it nearly didnt happen when Cox was sold to Estes. But the determination if the NFFS resulted in the deal happening however Cox only came good with 258 engines. The NFFS engraved each engine with a serial number and kept a record of who purchased each engine. These are probably the rarest of all Cox Engines due to the small size of the production run.

The Medallion engine was also produced in .09 and .15 cubic inch size.

Product Engines

These are all variations of the Baby Bee with different backplates designed for different RTF aircraft.

• 1962 Product Engine

Babe Bee with plastic backplate and brass needle valve. Various shapes were used depending on the model they were fitted to.

• 1959 Super Bee

Babe Bee with twin bypass cylinder to give more power for the P40 Warhawk RTF model. Early version had 'P40' stamped on the cylinder. It had a standard Babe Bee tank.

• 1963 Spook

Babe Bee with an aluminium back plate for the Cox "Spook" combat model.

• 2000 Surestart

Another variation of the modern Babe Bee. These were pretty good because they have a choke tube attached to the grey plastic backplate. The choke tube makes the engine even easier to start. They were fitted to the very last RTFs (e.g. PT19 and Hyper Viper) before they went out of production.

Other Cox Engines

Cox COnquest 15 Free Flight/Control Line Engine

This article is not going to address these engines but their names are:

• 1959 Sportsman .15

Rear reed valve .15 sized version of the Space Hopper

• 1959 Olympic .15

Sportsman with twin ball races - designed for FAI Power FF event.

• 1965 Olympic .15 Drum Valve - protoyped only
• 1968 Concept II .35 & .40 - prototyped only
• 1976 Cox Conquest .15

This engine took over from the Tee Dee .15 as "THE" engine for FAI racing, combat and free flight for many more years until the Russian AAC Engines came along.

• 1976 Cox Conquest .40 - prototyped only

Cylinders

There were a wide range of cylinders produced with three different wall thicknesses. Most are interchangeable between all engine types which can create problems when buying a used engine. All early cylinders had a thin wall which was later found to need improvement because they bent easily in a crash or when trying to undo with a Cox wrench. Some people refer to these as Mk1 cyclinders. The next type was thickened at the exhaust ports. Also known by some people as Mk2. And the third type was thick all the way down from the fins to the bottom. This one facilitated the exhaust thottle ring and you guessed it, some people call this a Mk3 although Cox themselves never referred to them like this.

Refering to the Cyclinder Cross-sections above:

1. depicts a thin wall Tee Dee .049 cylinder with dual booster ports on the bypass port.
2. is a late model thick wall cylinder with slit exhaust and a single bypass booter.
3. is a Black Widow cylinder with no bypass booster.
4. is a pre 1955 cylinder from a Space Bug. Note how the thread diameter for the glow head is much smaller.

The best/most powerful cylinder piston combination is the number 4 Tee Dee 049 cylinder. This cylinder has a tapered grind and tapered and lightend piston so the piston fit gets tighter as the piston reaches top dead centre (TDC). The intake or bypass porting is 2 deep ports with 2 bypass booster ports on each bypass. This setup causes a swirling of the intake fuel air mixture which promotes better combustion. One of Bill Atwoods ideas no doubt. The Tee Dee cylinder was the basis for the design of the the Venom and Killer Bee Cylinders.

Engine	Exhaust Ports	Bypass Ports	Bypass Boosters	SPI	Tapered Grind	Number on cyl.
Space Bug	Open	2	0	Yes	No	None
Thermal Hopper	Open	2	0	Yes	No	None
Space Bug Jnr	Open	1	0	Yes	No	None
Space Hopper	Open	2	0	Yes	No	None
Product Engine	Open	1	0	Yes	No	2
SureStart	Slit	2	1	No	No	None
Babe Bee	Open	1	0	Yes	No	2
Golden Bee	Open	1	0	Yes	No	2
Black Widow pre 96	Open	2	0	Yes	No	1
Black Widow post 96	Slit	2	1	No	No	None
Texaco	Slit	2	1	No	No	None
QRC pre 96	Open	2	0	No	No	6
QRC post 96	Slit	2	0	No	No	None
Killer Bee ‘96	Slit	2	1	Yes	Yes1	None
Killer Bee ‘02	Slit	2	1	No	No	None
Venom	Open	2	1	Yes	Yes1	None
Medallion pre 96	Open	2	0	Yes	No	1
Medallion post 96	Slit	2	1	No	No	None
Medallion 051	Slit	2	1	No	No	7
Tee Dee 049	Open	2	2	Yes	Yes2	4
Tee Dee 051	Open	2	2	Yes	Yes	5

Notes:
SPI = Sub Piston Induction
¹ The Killer Bee and Venom had a special competition lightweight piston and a heavy duty crank shaft for speeds above 22K rpm.
² The Tee Dee also had a lightweight tapered piston and the crank was stronger and ported different to the Medallion crank.

Crank shafts

Babe Bee (left) - Killer Bee (right)

On the Bee engines there were 2 types of crank shaft produced. (and they are interchangeable)

1. All Bees with the exception of the Killer Bee and Venom had the same crankshaft that was only good for about 20,000 rpm before the conrod pin would break off.
2. The Killer Bees and Venon had a heavy duty balanced and lightened crank shaft that improved performance and could withstand speeds in excess of 22,000 rpm.

A company named Davis Diesel Development in the USA also make a similar crank shaft called a Killer crank for their diesel conversions. They found under the heavier touque loads caused by running diesel fuel, that the pins would break also hence they produced their own killer crank.

On the Tee Dees and Medallions the cranks are also interchangeable but quite different. The Tee Dee has a large square hole at the intake end of the crank whereas the Medallaion has a smaller round hole. The timing is also different.

Glow Heads

Cox Glow Heads

There were 4 types of Cox Glow Heads produced:

1. Pre 1955 Standard Head - Hemispherical shape - Low Compression - Smaller dia. threads - used on Space Bug, Thermal Hopper, Space Bug Jnr, Stato Bug and some early RR1s.
2. Post 1955 Standard Head - Hemispherical shape - Low Compression - Larger dia. threads - used on all post 1955 engines except Tee Dees, QZ, Killer Bees, Venom and Texaco.
3. Hi Compression Head - Trumpet shaped - High Compression - knurled top - used on Tee Dees, Killer Bees, QZ and Venom
4. Texaco Head - Hemispherical shape - Low Compression - 5 fins - used on Texaco Engine only. Allows greater cooling for engine swinging larger propellers.

After Market Glow Heads

1. Standard Glow plug head - uses standard conventional glow plug - Low compression - Standard Performance
2. Turbo Glow Plug Head - Low Compression - Med Performance
3. Norvel Freedom Glow Plug - High Compression - High Performance - Rare & Hard to get.
4. Galbreath Head with Nelson Plug Combo - High Compression - High Performance - Most Popular

Reed Valves

There were 3 main types of Reed valve produced:

1. Early engines - Space Bug, Thermal Hopper, Strato Bug - circular twin brass reeds
2. Bee Engines - star shaped single brass reed.
3. Later Bees, Killer Bees, Venom - oval shaped stainless steel reed.

Later variants of the oval reed were made of mylar and teflon. Some say mylar is the best while others prefer the stainless steel and then other prefer the teflon. Claims are that mylar and teflon are lighter and make engine easier to start and go faster, but they dont last as long as the stainless ones.

Propellers

049 engines go well on a 5x3 to 6x3 prop. A 5.7x3 APC works well. To get any suitable speed for mouse racing you're going to need a 4 inch pitch prop at high revs but to do this you'll need plenty of nitro. E.g. 4.75 X 4 prop with 40% Nitro. Texaco engines are designed to use bigger props. e.g. 7x4

Running Tips

• To make them go fast use 30% or more nitro. Use at least 20% oil in your fuel (50/50 castor/synthetic)
• When using high nitro fuel it may be necessary to lower the compression by installing up to 6 or more head gaskets.
• Don’t let the castor oil varnish build up inside the cylinder. If you find the engine won’t hold a needle setting then it probably needs a good clean out with a scotch brite pad.
• Keep the engine clean and free from dust and dirt.
  
  

Piston / Conrod ball socket joint free play

Cox Reset Tool

Sometimes the piston / conrod ball socket joint is very loose and will adversely affect performance. This can also happen to engines that have had a lot of use. To fix this use a Cox “reset” tool to tighten the ball joint back up again. The correct free play is .001 to .003 inches. This tool is available from Davis Diesel and on eBay. The ball reset tool is available for the 020, 049/051 and the 09 series engines. The .15 engines use a wrist pin so a socket reset tool is not required for these.

Diesel Conversion

Davis Diesel Development manufactures and sells, heavy duty Bee cranks (Killer cranks) and diesel conversion heads. You can purchase these direct from their web site or from eBay. The DD cranks are similar to the original Cox Killer Bee crank. Check Davis Diesel

References

• Virtual Cox Engines Museum
• Model Engine Collectors Journal
• American Model Engines Encyclopedia
• Yahoo 049 Collectors Forum