BadEnglish

How interchangeable are the cox .049? The cylinder, crank case, piston, con rod etc... of the killer bee and baby bee look almost identical but are they (besides different porting)? What about the TD? I'm thinking about building some engines from parts but don't want to dive into it and find out nothing fits.

Also, how is the cylinder attached to the crank case with cox engines?

Thanks

flyinrog

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I can tell you with absolute certainty that the cylinder screws into the crankcase, after that things get blurry but all the parts look the same from the outside (but their not), ask Dickeybird, or AJ, or William, or prole, or anybody but me.......Rog

William Robison

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Bad:

All the 0.049 engines have the same 0.406" bore, all the 0.051s have the same 0.410" bore.

Some few engines have a tapered bore, but that was a late development.

The 0.406" piston has a plain, unmarked side wall. The 0.410" piston has a circumfrential oil groove about 0.060" from the bottom. It is easy to tell them apart because of this groove. The barrels are not marked, they have to be measured, or try a 0.410" piston, if it goes in it's the larger bore.

In theory, any 0.049 piston and rod assembly will work in any 0.049 engine, regardless of the crankcase and cylinder. There are extremely minor variations in the cylinder bores and piston diameters, so selective fitting sometimes can be done advantageously. These variations are usually less than one tenth of one thousandth inch though, so unloess you have a cylinder at minimum size and a piston at maximum, you should never have a problem.

Any 0.049/0.051 barrel will screw into any 0.049/0.051 crankcase.

The reed engine crankcases were delivered in white, yellow, and black. They all interchange. The backplate/tank assembly will interchange as a set - the intake port was larger or smaller depending on the application. Check the port in the tank and backplate, if they are the same the two parts will work together. Or you can drill the smaller to match the larger. The "Product" backplates, the plastic ones without an integral tank, will work on any 0.049 reed engine.

When we get to the cylinder barrels themselves things do get complicated. There have been several threads about them, heres one:

http://www.rcuniverse.com/forum/m_95.../tm.htm#958975

And that'[s enough for now, maybe someone will come in on the barrels, or I can come back later.

Bill.

BadEnglish

Thanks for the replies guys:

While reading the other post William Robison included I noticed the variety of factory machined bypass ports. Could a smaller original port be effectively enlarged?

-BadEnglish-

William Robison

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Bad:

Using your Dremel, or similar tool, and a silicon carbide stone it's easy to reshape the ports. But be careful, it's easier to screw one up. Takes a steady hand and a good support for the part you're working on.

Reshaping the bypass ports was "All in a day's work" flying 1/2A speed around 1960. As well as retiming.

Bill.

Attached pictures show the single, double, and triple milled ports.

BMatthews

There were basically 3 styles of bypass ports. The first is the Baby Bee or single simple flute. Then there is the twin simple flute. And the final TeeDee option is the twin flute machined in using three drillings to establish a larger cross section.

Yes you can enlarge the cross section area of a basic twin flute design but if it's on a reed engine I doubt you'll see a LOT of difference. You can easily get more response through careful fitting and parts selection and using the right head and fuel.

Use the simple twin flute cylinder by using a fuel with more nitro and switch to a hemisperical or simple conic head. There is also a high compression trumpet shaped head but I found on my Tee Dees that these actually hurt the perfomance when using 25 to 30% nitro fuel and a 6x3. Perhaps for racing with little 4x4's or similar these heads help out the rpms. I couldn't tell you that.

You can mix and match all you want but in the end for reed based engines your best shot is the twin or TeeDee cylinder with a conic head and 30% nitro. It's a good combo. The carb seems to work best if you use one of the plastic product backplates. For a few more rpms you can remove the screen and lightly flare the mouth of the opeining. The tank rears are slightly more restrictive but not by much.

For TeeDees the engine is already as hot as you're likely to get without knowing a LOT about the porting and actually tuning it for a specific prop and nitro fuel using very subtle modifications to the crank and cylinder porting.

When you're mixing and matching I found that getting a cylinder to piston fit correct is very important. Mine always ran best if they were as loose as they can be and yet still start OK. Using one of the spring starters helps here a lot. Loose, of course, being relative. If it's sloppy then it'll rob power. Properly loose was where you could put light pressure on the prop when the cylinder is wet with fuel and the prop would leak from exhaust closing, over TDC and back to exhaust open in about 5 or so seconds. Any faster and it's too sloppy and any longer and it is too tight.

PS: OK I guess I stand corrected. I've never seen a double milled port. So add one more to the list.

Tim Wiltse-RCU

Bad,

Pages of info could be writen about interchanging Cox parts! All parts from the front rotor engines(TeeDees and Medallions) can interchange(i.e. cranks and venturi housings) and work together. All parts from the reed valve family of engines Babe Bee, BlackWidow,QRC,Venom,Dragon Fly,Killer Bee(both .049 and .051),Texaco,Product Engines and Golden Bee's will also interchange. The cranks are for the most part all the same with the Venom and old(better) Killer Bee cranks being lightened and balanced better. Backplates( black, red, white and gray) from the product engines will fit on any of the engines that came with a tank back, just need different screws. Starter springs and prop drive washers varied by engine and year as well but will interchange too. As for the cylinders..gees there just isn't enough room to talk about all of them. Basicly there is 5 different types, single bypass, basic twin bypass, T.D.William's third picture, Killer Bee twin bypass with boost port and Venom twin bypass with boost port with the latter two being pretty rare. The second picture William has is a Venom type cylinder. With in these types there is Sub Port Induction and Non-SPI. Plus the way they look on the outside i.e. thin wall, thick wall, wrench or no wrench slot... it goes on and on. As long as it is used the correct size piston the piston/cylinder set will work on any Cox engine. For heads there is the trumpet shaped two fin T.D. head and the basic low compression 3 fin head. Type of head depends on what you are using for a cylinder and your nitro content prop combo. This is the GREAT thing about Cox engines. You can take a box full of parts and build away!!!

Later,
Tim

DICKEYBIRD

Tim I thought that too until a couple years ago when I finally found the combination of Tee Dee parts I liked for sport R/C use and began assembling as many complete, ready to run Tee Dees as possible from my stash of parts. I found that there are some earlier Tee Dee crankcases and crankshafts that are different from the more common ones.

The "odd" crankshafts are slightly shorter and the crankcases that match them won't work with the later 'shafts and vice/versa. I only have 2 of them that are made this way and don't have a clue when they were made. I think they were possibly early production.

Just another example of how there just ain't any absolutes when it comes to Cox engines!

William Robison

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Milton:

You're right. I had forgotten that, I have one or two short cases also.

Thanks for the reminder.

Bill.

ajcoholic

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Actually, I did a few simple tests a number of years back. On a stock black widow dual bypass cylinder, I raised the bypass port timing up to ALLMOST (but not quite) level with the exhaust port. I gained an average of 1200 to 1500 rpms!! Easy mod.

And as for the porting, if you include the old time (space bug/sbjr, etc) there are many different types of port cuts - more than mentioned here anyway... as some have vastly different tops of the bypass, as well as there being single, double and triple cut bypass'...

AJC