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Cox Engine of The Month
October-2018
Mudhen's

"Prototype T.D. .010 c.1960"



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Recent engine acquisitions

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Re: Recent engine acquisitions

Post  NEW222 on Mon Oct 22, 2018 10:43 pm

Ok Ken. You peaked my interest, so I got up to do some digging. The base of the cylinder as is in your first picture is thin. I removed the glowhead, and it does have life in it! I put it beside the OK Cub .074, and it was close in size, very much more than beside the. OK Cub .049. The only thing that differs is that there is an ever so slight raised dimple on the top center of the piston. I would say about the same as I see in so excited for the Cox engines. Thanks for your help in id'ing the engine. Once I go through and clean and fix these up, I will bench run them all. Thenjoy I will try and find suitable airframe for them.
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Re: Recent engine acquisitions

Post  KariFS on Tue Oct 23, 2018 2:41 am

Cool stuff guys! New's "box of treasures" are interesting... Before joining this forum I had no idea that there are (or were) so many other manufacturers of these little engines in addition to Cox.

And that Kobra! Our friend Ian presented one a while ago, been wanting one ever since. Fascinating little engine, I actually wish Cox had made one like it, or that there were an aftermarket crankcase available, that would accept parts of a "290" Smile
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Re: Recent engine acquisitions

Post  Oldenginerod on Tue Oct 23, 2018 3:04 am

NEW222 wrote:
Left to right, top row first
OK Cub 049A, OK Cub (model unknown), OK Cub .099, Ok Cub .074
The unknown Cub will be their first model .049.  It is known as the "Long Stroke" model. The case is the same, I believe, as the .074.  The fuel tank as pictured fits both size engines. The first .049 takes a long glow plug wheras all subsequent .049s use a short plug. No parts are interchangeable between the first .049 and the .049B which followed.
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Re: Recent engine acquisitions

Post  balogh on Thu Nov 08, 2018 11:59 am

I bought on ebay recently, and the postman just delivered this brand new, very early ( early 1960-s) production TD049 featuring:
1. Beautifully contoured No. 4 thin wall cylinder without flats on the top fin for wrench:

Later cylinders were first stepped wall then thick wall and flats on top fins are on these later ones only.

2. Tapered fit piston with tight pinch on TDC. The piston has the balljoint cup swaged into the piston crown, unlike later pistons that have the cup machined from the piston parent material itself:


3. Oiling hole in rod big end:


4. Thin web on crankshaft. Later production runs had the web thickened and a No2 stamped on the crankcase mounting bar:



5. No screen on venturi intake...screens appeared first around 1972-3:



Many of the above design features were changed over time as operating experience and cost cutting efforts dictated, including thick wall cylinder, thicker web, tapered piston- cylinder fit and oil hole abandoned etc.

All in all a nice historical relic I have been looking for long.


Last edited by balogh on Thu Nov 08, 2018 12:56 pm; edited 1 time in total
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Re: Recent engine acquisitions

Post  GallopingGhostler on Thu Nov 08, 2018 12:33 pm

Congrats on the find, balogh. No doubt the thinner profile was intended to produce a powerful lightweight engine. I imagine Cox engineers listened to top contestants for comments and resulting metal thickening came as a result for engine improvements.

I still like the older earlier engines, they are classics.
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Re: Recent engine acquisitions

Post  ticomareado on Thu Nov 08, 2018 1:19 pm

RE: Collection of Cubs-- especially .074. Does anybody have any extensive experience with these. I have a few of them (most in very good condition) and I have yet to run one that will put out any more wind than just an average .049B or A. I can't even find an advantage using a 7" prop. What was the point of this engine?
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Re: Recent engine acquisitions

Post  KariFS on Thu Nov 08, 2018 3:04 pm



That is a beautiful engine Andras! I agree the early engines have the purest form. Did you notice the early style Tee Dee head? My QZ came with one, and I replaced it with a new one because it was dirty Embarassed After looking at the cleaned up engine for a while thinking ”why does it look out of place?” I realized that the early High compression head looks different. It is externally just like a 302, but with the knurling. So I cleaned up and installed the original head, much better.

I have a couple of .051 versions with the step style cylinder (never understood the point of that shape), but haven’t come across one of those really early versions. Maybe I should start browsing eBay too Smile
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Re: Recent engine acquisitions

Post  balogh on Thu Nov 08, 2018 3:52 pm

Thanks GallopingGhostler and Kari...I like the classic contour of thin wall COX cylinders as they resemble the 4-stroke knuckle-head cylinders of old Harley Davidsons.

Kari I read somewhere that when COX realized the weakness of thin wall cylinders and wanted to increase wall thickness, the recess/groove seen under the exhaust ports on the step wall cylinders was machined because the honing tool required that groove. The later tools were different and the groove became obsolete and the thick wall cylinder was born.

Also thanks for calling my attention ho the high compression head on this engine! It really shows a different knurling than what we know on latest HC heads!

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Re: Recent engine acquisitions

Post  Mudhen on Thu Nov 08, 2018 4:48 pm

KariFS wrote:...I have a couple of .051 versions with the step style cylinder (never understood the point of that shape)...
Cox used the stepped, (grooved,) cylinder to provide a bearing surface the speed control sleeve.
It started with the throttle controlled P-40, (350-2,) that was released in mid-1968.
At the time it was referred to as a "Special Cylinder."
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Re: Recent engine acquisitions

Post  Mark Boesen on Thu Nov 08, 2018 11:23 pm

Duke prototyped the engine as a .049 for Comet, but switched to .07 once production started, after Comet they were sold as a 'hobby' engine and later sold as a .049

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Re: Recent engine acquisitions

Post  crankbndr on Fri Nov 09, 2018 7:39 am

Thats my favorite TD .049 and keep an eye for them. The cylinder has 4 boost flute also, no?
Need a similar Medallion to go with it.

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Re: Recent engine acquisitions

Post  balogh on Fri Nov 09, 2018 8:06 am

Yes it is No4 cylinder with 2 bypass and 2x2 booster flutes. Good luck for finding one they are rather rare find though..
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Re: Recent engine acquisitions

Post  crankbndr on Fri Nov 09, 2018 8:41 am

I find them but they always get a high bid so I'm not the only one looking. lol!
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Re: Recent engine acquisitions

Post  balogh on Fri Nov 09, 2018 9:30 am

Mine was a good deal at 42 bucks plus shipment
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Re: Recent engine acquisitions

Post  GallopingGhostler on Fri Nov 09, 2018 10:41 am

ticomareado wrote:RE: Collection of Cubs-- especially .074. Does anybody have any extensive experience with these. I have a few of them (most in very good condition) and I have yet to run one that will put out any more wind than just an average .049B or A.  I can't even find an advantage using a 7" prop. What was the point of this engine?

Don't have one of those, but have several A.C. Gilbert .074 Thunderheads. That was fairly typical for the day that the .074's produced the power of a Cox .049 Babe Bee, another reason why Cox dominated along with Cox's lower price. This is why Walt Musicano's Scientific CL designs designated engine range from .020 to .074. As in all, engines are usable if fitted to the right airframe.
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Re: Recent engine acquisitions

Post  KariFS on Fri Nov 09, 2018 11:11 am

Mudhen wrote:
KariFS wrote:...I have a couple of .051 versions with the step style cylinder (never understood the point of that shape)...
Cox used the stepped, (grooved,) cylinder to provide a bearing surface the speed control sleeve.
It started with the throttle controlled P-40, (350-2,) that was released in mid-1968.
At the time it was referred to as a "Special Cylinder."

Yes, I understood why the thick part appeared, but not why the thin area remained Very Happy

balogh wrote:
Kari I read somewhere that when COX realized the weakness of thin wall cylinders and wanted to increase wall thickness, the recess/groove seen under the exhaust ports on the step wall cylinders was machined because the honing tool required that groove. The later tools were different and the groove became obsolete and the thick wall cylinder was born.

That is probably the reason, makes sense definitely. Many times when there is an odd feature like that, one that does not improve the aesthetics, and does not make sense when engineering of the final product is considered, the reason lies somewhere in manufacturing and tooling.

I always figured, if you need the cylinder to be thicker at the exhaust port area than at the bottom flange, why still machine a groove and a flange Huh... Engineers are lazy, drawing extra lines is laborous, manufacturing hates extra phases in machining and bean counters hate unnecessary cost. But if they had an expensive honing tool or a fixture, they probably wanted to get all the ”mileage” out of it before scrapping.

Learn something new every day I Love This Forum!
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Re: Recent engine acquisitions

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