Buy a Cox! ... but, what exactly do you buy?: KILLER BEE .051 1996

KariFS wrote:Mauricio, your engine does seem to have the Killer Bee cylinder. It has the narrow exhaust ports AND sub-piston induction (SPI), and the lower ports are wider.

Can you see the by-pass ports inside the cylinder? I am not sure how they are supposed to look as I don't have a Killer Bee in my collection yet.

The backplate seems correct, there is no steel mesh on the intake.

I think it's a very nice looking engine, and the "correct" Killer Bee crankshaft is available as a reproduction, so you can make it "complete" if you want.

Ken Cook wrote:         I have the Estes version of the Killer Bee which is not anodized gold. In addition, the red backplate to my knowledge was one indicator that the engine was to be .051 vs .049. However, the needle valve on your engine is not correct for the early Cox version as it has a knob and not the yellowish extension on it. The .051 piston for the Killer Bee had two grooves on it vs the Tee Dee which had one. The backplate also offered a larger intake opening vs stock backplates. The crank is what appears to be stock. Looking at your example though, I can only say you have a wonderful looking example and while some of the components may not be the early version, I certainly wouldn't be bashful in showing that one off. It looks great and I'm certain it will perform equally as well.

Ken Cook wrote:          The idea behind the pear shaped crank is that it's lighter. Lighter mass is easier to turn thus more rpm's. I personally feel that stock Cox crankshafts are superior equally that is until they break. I have broken a few of them but not consistently. I have to say that engine just is good looking. I think your going to find it to be quite a reliable and powerful engine. Ken

roddie wrote: Nice to see the engine running my friend! The Cox 5 x 3 as you know; is a good "all-around" propeller for the .049 reed (flapper)-valve engine. The company "APC" makes a 4.75" x 4" propeller.. that you may want to try. It is solid (rigid) true to pitch. The center (hub) hole requires a bushing for the Cox 5-40 propeller-screw. A short-length piece of soft (silicone) fuel-line can be used for this. Maybe you already have experience with this propeller?





I have a theory regarding crankshaft "weight" (rotational-mass) with regard to throttling a model engine. More "mass" (weight) enables the engine to stay running at slow-speed.. because of "inertia" working against compression. The transition from "slow to fast" will be adversely affected.. but this is of little concern with an airplane engine.

I have seen more favorable/consistent low-idle (slow-speed) results when installing a "fly-weight" (flywheel) in the form of a small precision steel flat-washer with the propeller. The washer requires a 1/8" (.125"/3.18mm) center hole for the Cox .049's 5-40 propeller-screw to balance and spin "true".

It's FUN to experiment with throttling these engines. I have achieved sustained sub-3K rpm operation with a Cox 6" x 3" propeller on a stock Cox Babe Bee engine.. "without" any weighting of the crankshaft. A muffler helps to keep the head-temperature (glow-plug) HOT.. to sustain combustion at low-speeds while in the air.

Your engine is similar in configuration; to the one I entered in the CEF "tach-race" this year.



Ron Cribbs was able to extract 19,560 rpm from it.. with the APC 4.75" x 4" propeller. The engine cylinder was a quasi Tee Dee-ported one from Cox International.. equipped with a Tee Dee (high-compression) glow-head, using one head-gasket. Fuel was high-nitro 30+%.

Your Killer Bee engine would like to "taste" fuel with more nitro. I would make an inquiry to "Sig Manufacturing" in the U.S.A. (Montezuma, IA) for a small (pint) bottle of their "Champion 35" 1/2A fuel.. which has plenty of castor (ricino) to protect your engine. A small bottle may be exempt from air-freight restrictions.

http://www.sigmfg.com/cgi-bin/dpsmart.exe/IndexFieldEquipmentF.html?E+Sig

RknRusty wrote:I always thought the original Cox Killer Bee had a diesel crankshaft, but I could be mistaken, so I'll defer to Ken on that. The cylinder is certainly a KB.

While tuning for tach races I always get the fastest runs from a stock babe Bee crank over the diesel crank. I'd say yours can most certainly be called a Killer Bee with no doubts. Very nice engine.
Rusty

balogh wrote:

roddie wrote: Nice to see the engine running my friend! The Cox 5 x 3 as you know; is a good "all-around" propeller for the .049 reed (flapper)-valve engine. The company "APC" makes a 4.75" x 4" propeller.. that you may want to try. It is solid (rigid) true to pitch. The center (hub) hole requires a bushing for the Cox 5-40 propeller-screw. A short-length piece of soft (silicone) fuel-line can be used for this. Maybe you already have experience with this propeller?

........quote]

Roddie,

I once bought a propeller which was very much similar in appearence and package to this APC, but it was exclusively for electric motor application, the paper tag stapled to the plastic bag had a warning on that. (You may want to see the backside of that white flip stapled to yours)

One reason why the bushing was also needed for that was the apparently larger electric motor shaft diameter for a 4.5....5.5 inch prop than the propeller screw of a COX engine. I read once - but do not necessarily believe - that the composite propellers are prone to fatigue-breaking under the cyclic load of an internal combustion engine.

I use the black nylon propellers even though their pitch might slightly change at high rpm-s, and never has seen one break in operation.

MauricioB wrote:
I forgot! ... I have read many times the term 3K or 4K ..mmm meaning: K ??

KariFS wrote:

MauricioB wrote:
I forgot! ... I have read many times the term 3K or 4K ..mmm meaning: K ??

The "K" means "kilo" (or thousand), so in this case 3K = 3000 rpm.

Nice to see your Killer Bee running. I am also very interested in all the throttling tests you, Andras, Roddie and many others conduct! Once I (or if I ever) learn to fly an R/C plane properly, a small sports model or an old-timer with a Cox engine will definitely be on the project list

1/2A Nut wrote:I own a real Killer Bee .049 the inside of the piston is copper coated and the piston / rod weight is 2.9g
Less than a standard piston 3.4g. The piston skirt is thinner too, note the polished walls on the inside of
the cylinder. The crank flywheel is lighter and has a drilled out crank pin. It comes with the fine thread
NV with nyrod extension. Black back plate .049 / Red for the .051 which had the ring around
the bottom of the piston skirt for designation. The real Killer Bee is made for screaming rpm and has
no reason to do anything else. Note I changed out the spinner and bolt to suit the APC prop the real
one is to the right first pic.



Mauricio your engine was the year they stopped making the high performance crank and light weight piston
the loss in rpm was notable, I am not sure what month the change was made. You many not have the fine
thread NV rather a 72tpi needle instead of the 128tpi . The cylinder was no longer matched and polished
they just started selling off what was left on hand as is. Still you have the larger intake that is helpful and
aggressive porting. You may have a red back plate but the cylinder / piston could be a .049

balogh wrote:Hi Mauricio,

In my opinion, especially the later owners of COX, Estes included, wanted to capitalize on the fame and reputation of older COX engines made in the heyday of COX, and sold engines under the same names,  assembled in similar configuration, but from less sophisticated parts, to retain profits earned on the older versions....Sure Start cylinders, normal pistons and cranks.

Nevertheless, because the porting of the cylinder on your engine as well as the backplate are like in the older Killer Bees, I expect this engine is an excellent runner. Did you tach it?

I home-assembled similar configurations (my Lil Roughneck has one on it, called TeeDeeReedie because of its cylinder) and it turns the black 5x4 (=4,8x4) prop of Bernie at near 20k i.e.while the  TeeDee 051 turns it around 21+k, i.e. less than 10% faster, if you remember my thread a few days ago.

1/2A Nut wrote:Yes Mauricio,
There is only 1 true build spec for the .049 and .051 Killer Bee
The low weight piston and crank make a big difference.
128 TPI NV lets you milk the top end rpm.
The polished inside of the cylinder minimizes break in wear for
best top end rpm.