Larry, Tim, Other Cox experts,What do you think about this C

LAST EDITED ON Mar-17-04 AT 10:45 PM (CDT)
 
Ran across this at Tower Hobbies and it looks to be a drop in replacement for the Sure Start HV engine. Worth the $39.99?

Rob Johnson
Orange,Ca.
From Tower Hobbies Web Site:

NOTES FROM OUR TECH DEPARTMENT
Sting the Competition with this New High-Performance .049 Engine by Cox!
This is a Competition Control Line Engine (NO THROTTLE).

FEATURES: Designed to run ultra fast with high nitro fuel, on small props.
Comes with a removable timing shim so it can run on lower nitro fuel
and bigger props, for sport flying.
"Zero-drag" snap starter spring
High-compression glow head
Maximum size venturi for free breathing
Cylinder and piston are taper-lapped to minimize drag at high rpm.

INCLUDES: One Assembled Engine w/Snap Starter, Backplate Mount, Glow Head,
Spinner, Wrenches, and Instructions.

REQUIRES: Fuel with at least 20% nitro content (can use CATP3173 or COOP1225)
Fuel tank and small fuel line.

SPECS: Displacement: .049 cu in
Weight: 1.75 oz.

COMMENTS: Conversion mufflers CANNOT be used with this engine!

That is the current production of "Killer Bee". The problem with the current version is that all the original "Killer" features as designed by Larry Renger were dropped so it will not be much better than the standard product engine used in the HV. The only good feature left would be the larger venturi openning and the high compression glow head. The gold anodize crankcase does look good.

Larry would know more...

LAST EDITED ON Mar-18-04 AT 00:45 AM (CDT)
 
Oddly enough, the original Killer Bee had the low compression head, as I recall. The reason was, that with the high compression head, it would outrun the average Holland Hornet, and the NFFS sanctioning body had set that as the maximum engine for nostalgia FF flying.

A clue as to the age of a KB is the needle valve. The originals had a very short needle with a piece of plastic knurled tube as an extension. This was because, at 21K rpm, we could NOT keep the vibration from backing the needle out any other way.

Current KBs don't even have the anodized crankcase, and I bet whatever you buy now doesn't either, photos not withstanding.

Get a killer crank from Davis Diesel, an old Tee Dee piston and cylinder, the Galbreath/Nelson head, and drill the backplate to 11/64th. Play with nitro (lots!) and head gaskets (also lots).

If you are brave/stupid/know what you are doing (generally we progress from one to the next) polish the crankshaft to fit the case as described elsewhere. Do a search on Designman, and it is around somewhere.

BTW, I just chucked a current needle valve into my lathe and drilled a 3/32" hole down almost to the base of the threads. Boy did that make it lighter! Should help a lot with the vibration problem.

Actually, you can make a good case for picking up every C*x rtf engine you can find and experimenting on them, mix and match, test fits, try stuff. They tend to be cheap and plentiful, and how else are you going to learn? What you learn on these will serve you well on any other engine.

Interesting that they specify taper lap on the piston and cylinder, as it would seem that the originals did NOT have it even though I always thought they did. I still have one NIB original, I guess I'll need to pull it apart and see.

Now what do you suppose, if you buy one of those engines, it comes with a non-anodized crankcase and non tapered P&C, could you do about it. False advertising complaints? Or has C*x heeded our rantings and actually restored the engine? ....... Naaaaaa

Larry,

I've been trying to upgrade the engine in my Mouse I racer. I've read quite a bit of info on engine configurations and setup. I received a couple of Davis killer cranks in the mail yesterday. I was surprised that the cranks have no counterbalancing features. (Solid disk.) When I fitchecked them into a BW case and a product engine case, the forward beveled edge rubs. There isn't much wear (polishing) on the case thrust bearing surface, so it's probably a tolerance stackup problem. Do you think a steel shim (washer) would work here? If I have to trim the cranks to clear the case, I'm wondering if I might as well try balancing them too.

Comparing your suggestions on venturi size, I was quite surprised to see 11/64" in one post. This seems too large, unless I'm missing something. I was going to remove the inlet screen and try .093".

I bought some Davis teflon reeds, too. Any experience with these? I've been running an x-shaped brass reed, but it is really beat up.

The plan was to end up with an engine with an old TD P/C (#4), Galbreath head with Nelson HD plug, BW case and tank, and an old style starter spring.

Thanks for the prior info!

Regarding the venturi size, don't forget that the 11/64" was for the RTF engine, which has a spraybar.

.093" is about right for a Mouse engine with integral tank.

Regarding the cranks, I would do some balancing on them. Specifically drill out the center of the crankpin down not quite to the corner where it hits the face of the crankshaft. Then grind flats
from just beyond the base of the pin to the centerline of the shaft. These could even be ground slightly concave.

Larry,

Thanks for the reply. Now I understand the venturi size difference. I'll try reworking the Davis crankshaft tonight.

Sorry I didn't answer all your questions.

I don't know about the crankshaft interference, I haven't run into it before. You could e-mail Davis.

I like the current stainless steel "nearly rectangular" reeds the best (I designed them, so I better!)

The rest of your ideas sound right on the money.

Larry,

I ground the beveled edge on the Davis crank disk last night. I then dressed the case interior. Seems like the cylinder boring operation deforms the crank clearance surface in the case. Went back and forth a bunch of times until it all cleared. Then I cut down the crank disk until it had about the same balance characteristics as the stock crank. I didn't drill the crank pin (yet).

On assembly, I found that the propeller thrust washer doesn't seem to seat on the crank shoulder. I may have to take it back off and dress the face of the case to provide clearance.... After all that, I should probably strip the anodizing, lap the bore to clean it up and get it re-anodized. Do you know anyone doing this?

Compression seems good, with a nice pop to it! I put in two .005" gaskets to start. Now for some new tank gaskets and into the plane she goes! Hope it's a runner, 'cause my backup engine last time was EMBARRASSINGLY slow!

Thanks for the help.

>A clue as to the age of a KB is the needle valve. The
>originals had a very short needle with a piece of plastic
>knurled tube as an extension. This was because, at 21K rpm,
>we could NOT keep the vibration from backing the needle out
>any other way.

Just something I've been curious about for ever. Was that piece of yellow plastic actually the inner part of a Gold-N-Rod?

Yup

Rob,

I hate Tower...that is the same picture they have had for years. The current Killer Bee that you will find is nothing like what you see in the picture. The current KB is just a plain old product engine( Babe Bee without the tank). Not anodized no special cylinder( twin slit with SPI), no special crank etc.

Take care,
Tim Wiltse

Here is a good comparison.

http://www.mh-aerotools.de/airfoils/cox_killer_bee.htm