Cox model engine
All you ever wanted to know about the Cox .049
by Warren Leadbeatter - Australian Aeromeller - VH14782
Introduction
This article focuses on the Cox .049 series model aircraft engines.
Cox History
Cox model engines started out as Leroy M Cox Manufacturing in 1945. The company enjoyed a long period of strong growth until 1969 when Mrs Cox died and the company was sold to Leisure Dynamics. In 1983 Leisure Dynamics were declared bankrupt and the company was sold to a former Cox Engineer named Bill Selzer. In 1995 the company celebrated it's 50th anniversary and some new engines including the rare and very much sought after Venom were introduced. In 1996 the company was sold again to Estes Rockets / Centuri Corp. Quality and standards changed dramatically from this point on. In 2005 Cox moved back to the hobby market and are still available today via their website coxmodels.com [1] however they are now moving away from the internal combustion engines in favour of electric.
The Engines
Cox engines were mainly sold in RTF aircraft through department stores worldwide. A wide range of Cox engines were produced over the 50 odd years that the company was in growth. These range from the .010 cubic inch Tee Dee through to the .15 ci Conquest. There is a very good web site on the internet that goes into a lot of detail about the different engines at Martin Hepperle's excellent Virtual Cox Museum[2]
Early Engines
Covers years 1945 to 1960 and includes the Thimble Drome Space Bug, Space Bug Junior, Space Hopper, Thermal Hopper and Strato Bug all of which were .049 cubic inch engines or 0.8 cc and utilized a rear reed valve induction system and most included and integrated fuel tank. Some other engines that were produced in the early 60s were the Olympic and the Sportsman which were all rear induction rotary valve engines. The RR1 was an early engine that looked very similar to a Bee, but it had a rear rotary valve intake system rather than a reed valve. The RR1 is very much sought after by collectors and as such are worth quite a bit of money. The Strato Bug is also a rare beauty that is worth arounf $300US in 2008.
Bees
The Bees were the backbone of Cox engine production and included the ever popular Pee Wee .020 Babe Bee .049, Golden Bee .049 and Black Widow .049 engines. The Black Widow is a high performance version and has two fuel transfer ports instead of the one that the Babe Bee and original Golden Bee had, plus it also has a larger venturi. (0.082”)
All of these Bee engines included an integrated fuel tank and reed valve intake system. Other variations were the QZ (Quiet Zone) and QRC Quiet RC engines which were both supplied with mufflers, and the Texaco and Texaco Jnr, RC Bee and Dragon Fly.
High Performance Bees
Competition competitors who used modified Bee engines for higher performance discovered that the Standard Bees could only go up to 22,000 prm before they would self destruct. In 1995 and 1996 Cox produced the Killer Bees (049 & 051) and the Venom 049 both of which were high performance engines with strengthened crankshaft, improved reed valve intake system and different fuel transfer and exhaust porting, all of which contributed to these engine doing speeds of over 22,000 rpm and still holding together. However, the production Venom engine has a manufacturing fault in the piston and as such only 1000 were ever produced. This makes them a very much sought after item for collectors. They sell for around $250US in 2008 and buyers need to be very aware as there are a lot of fakes out there. It is important that you check with the seller to ensure that you are getting the 'real deal' before buying a Venom.
With regard to the Killer Bee there were two versions produced. The first one was in 1996 which was advertised as a high performance competition engine and it lived up to it's name, and the second was a 2002 version with similar looks and name but it was no more than a standard Bee. Check the following link [3] As with the Tee Dee 049 and 051 the two models can be distinguished by a black back plate on the 049 and a red back plate on the 051. The back plates are interchangeable so the only way to be sure is a groove on the 051 piston. ie. If it has a thin line about 1 mm up from the bottom of the piston it is an 051.
Medallions
These came after the Tee Dee and are also known as poor mans Tee Dee, these engines employ a front rotary valve fuel intake like a conventional model air plane engine. These are available in sizes 049, 09 and 15 ci in both Control Line and R/C versions although the throttle is rather crude and is derived by limiting the flow of the exhaust gasses, almost as though this were an after thought. The look similar to the Tee Dee but the cylinder, piston, glow head, crankshaft, carburettor body, needle and spray bar are all different to (ie cheaper) the Tee Dee. There is no such thing as a Medallion 051. Well at least it was never available commercially. A special run of 258 was done for the NFFS in the USA. They are all individually serial numbered.
Tee Dees
These are the high performance contest range of engines that in their time (ie 1960s and 1970s)pretty much out performed everything that came before. A peripheral ported true venturi instead of a conventional needle valve and spray bar, plus it has deep triple fluted transfer ports and a heavy duty crankshaft. Available in sizes .010, .020, .049, .051, .09 and .15 ci. The physical size of the 049 and 051 are the same so to distinguish them apart the Tee Dee 049 has a black carb body and the Tee Dee 051 has a Red Carb body. The 051 also has a small groove on the bottom of the piston so you can be sure it is an 051 if the engine has one of these. There are also some special versions with RC throttle (such as the Tee Dee .05 RC) and different exhaust port configurations as in the Tee Dee 15 Special and Special MkII. The 15 Special MkII has a single exhaust port and schnerle style intake porting.
Product Engines
These are pretty much Standard Bees and range from the 020 to the modern day Surestart 049. These engines are supplied in the Cox RTF model planes, helicopters, boats and cars and had different backplate configurations to match the toy they were fitted to. The Surestart Engine is a great little engine and can still be purchased new online. These start so very easily if you follow the instructions provided. The main reason for this is the choke tube fitted to the engine that makes priming very easy. I have personally started them 1st flick straight out of the box. Some of these engines are rare and collectible such as the P40 WarHawk engine dubbed "Super Bee". The Spook combat model engine is also fairly rare and has an aluminium backplate. The RTF model planes themselves are a whole story to themselves. There were dozens produced and all are collectible and make a good investment.
049 Cylinder & Piston Types
There are more than 12 different .049 cylinder head types and all are interchangeable between models. So you can see why it can be confusing as to which head belongs to which engine, especially when people can easily change things around.
The main differences seem to be in the internal transfer porting. Cox tried many different configurations in the search to get it right. The Tee Dee 049 cylinder was determined to be the best with a tapered cylinder, 2 transfer ports with 2 boost ports either side of the main transfer ports. They extended slightly above the main port to get the gases swirling to promote better combustion.
Later Bee engines used twin bypasses with one boost port and two twin slit exhaust ports.
When Cox tried putting mufflers on they discovered that Sub Piston Induction was causing a reduction in power because hot gases were being inducted rather than cool air. Removing the SPI fixed this hence you see newer versions designed for mufflers without SPI.
Engine Ports Bypass Boost SPI Tapered Nummber Stamped on cyl. 191 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 <96 Open 2 0 No No 6 QRC >96 Slit 2 0 No No None Killer Bee ‘96 Slit 2 1 Yes Yes* None Killer Bee ‘02 Slit 2 1 No No None Venom Open 2 2 Yes Yes* 3 Medallion <96 Open 2 0 Yes No 1 Medallion >96 Slit 2 1 No No None Tee Dee 049 Open 2 2 Yes Yes** 4 Tee Dee 051 Open 2 2 Yes Yes 5
- the Killer Bee and Venom had a special competition lightweight piston and a heavy duty crank shaft for speeds above 22K rpm.
- The Tee Dee crank was different to the Medallion crank also.
Glow Head Types There are 3 types of 'Cox' Glow Head available for the .049s however the best one is the 4th one that Cox didn’t make.
- 1. Standard Low Compression Head - designed for all engines except Texaco, Killer Bee, Venom & Tee Dee.
- 2. High Compression Head - designed for Tee Dee, Killer Bee & Venom
- 3. Five Fin Low Comp. Head for Texaco - allows better cooling for larger props on Texaco models.
- 4. Doug Galbreath Head with Nelson Plug combo. This will give you 2,500 rpm increase for very low price. Don't waste your money on the old Cox heads.
There are also some other after market heads available for using standard and turbo glow plugs, but from the reports I have heard, these are not much better than a standard Cox head.
Reed Valves
The oringinal early Bees has a dual reed valve setup which was replaced by the star shaped reed valve used in the Standard Bees. In the 90s the design was changed to an oval shape with a different housing. Either type reed will work in either housing. The original star reeds were brass, and the oval ones were stainless steel. You can also get both types in Mylar and Teflon. Some say the Mylar are the best, while others claim the Teflon are better. The claims are they make the engine easier to start and more importantly increases power. From my experience they don’t last like the metal ones do.
Props
Most 049 engines seem to go best on a 5x3 to 6x3 prop. To get any decent speed going you need to be spinning a 4 inch pitch prop at high revs. E.g. 4.75 X 4 prop with plenty on Nitro. Texaco engines are designed to use bigger props like a 7x4 at low revs. Don’t run a prop this big on any other 049 or you’ll cook the plug.
Running Tips
- Don’t be afraid to use 30% or more Nitro. Use 20% oil in your fuel (50/50 castor/synthetic)
- When using high nitro fuel it is necessary to lower the compression by installing up to 5 or more head gaskets.
- Don’t let the castor oil varnish build up inside the liner. If you find it won’t hold a needle setting it probably needs a good clean out with a scotch brite pad. This tip applies to any small engine.
- Keep the rest clean and you should be fine.
Piston ball socket joint free play
On some engines, particularly the ones built in the 1990s and later, the piston ball socket joint is very loose and will adversely affect performance. This can also happen to engines that have had a lot of use. The fix is to use a “reset” tool to tighten the ball joint back up again. The correct free play is .001 to .003 inches. This tool is still available from a company in the US called Davis Diesel and on eBay. One Black Widow engine I purchased even came with a genuine Cox ball reset tool. The ball reset tool was available for the 020, 049/051 and 09 series.
Diesel Conversion
Davis Diesel also manufactures and sells, heavy duty Bee cranks and diesel conversion heads. You can purchase these direct from their web site or from eBay. The DD cranks are similar in strength to the Killer Bee crank so can be used for high performance Bees also.
[4]
Want More Information?
Try these Web sites:
- Virtual Cox Engines Museum [5]
- 049 Collectors Forum – lots of info and pics plus a great email forum [6]
References