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Cox Engine of The Month
May-2024
1/2A Nut's

"Cox Tee Dee .051 RC Marine"



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Post  rdw777 Sat Apr 20, 2024 11:06 am

A few weeks ago the homemade throttle on my Ken Willard- Pageboy failed so I tried to come up with a better design…. The original worked well but was fragile….. It was made from thin copper and used a piece of roll your own cigarette paper for a gasket…. It was all soldered together and was not removable from the cylinder once installed…

The new design is a three piece unit and is removable to be able to maintain the gasket…. Made from .005 brass…. A piece of .002 soft copper covers the seam and is soldered on one side only to allow the brass band to be installed and removed as needed…. All held together with a spring made from .015 music wire….Took a few tries to get the spring right….Works great on the test test stand so far….

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Post  balogh Sat Apr 20, 2024 3:57 pm

Very neat design, Robert...how often do you heed to replace the paper seal? Does it get soaked in castor soon?
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Post  roddie Sat Apr 20, 2024 4:10 pm

balogh wrote:Very neat design, Robert...how often do you heed to replace the paper seal? Does it get soaked in castor soon?


I'm guessing that the paper isn't used in the new design. It appears to be a template for laying-out the .005" brass sheet with the hole-locations. The spring, .005" brass band and .002 copper sheet are the 3 pcs. that Robert mentions.
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Post  balogh Sat Apr 20, 2024 4:17 pm

Yes Roddie it may be...I thought the paper is still there because Robert wrote:

"The new design is a three piece unit and is removable to be able to maintain the gasket…"

My experience with my similiarly thin aluminum sheet and a circlip is that if the exhaust port edges are deburred properly - some marks of the wrench may have been left there- then the contact is tight enough to seal without a soft gasket like paper..
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Post  rsv1cox Sat Apr 20, 2024 4:46 pm

Neat, a drill index gives diameter options, a pulley adjustable pedestal drill press offers rotational control, a bit of wire clampled in the chuck and your in business. I never would have thought of it. A springy thingy maker!
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Post  roddie Sun Apr 21, 2024 12:01 am

I really like that design Robert! I tried something a little bit similar a while back.. but you've got a better thing going on there. Did you use a hole-punch (plier-type) to form the holes in the .005" brass sheet? That's the way I did it.. but I used a pop-rivet to bind my .005" brass collar.. and never took it any further to test.

I've also done the "wire-wind" method using the drill-press chuck with the same .015" music-wire; only with a much smaller winding-post...(sub.055" dia.) for making the spring-style whl. retainers that were popular hdwe. items included in the better 1/2A kits that had landing gear. Goldberg and Sig once supplied them.. but they're scarce items now.

Watch your in-box for a PM Smile



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Post  rdw777 Sun Apr 21, 2024 8:52 am

Thank you for your feedback on the throttle Gentlemen….. I didn’t take too many photos along the way on this project but will explain a few of the details further…. Yes, I kept the paper gasket as in the previous one, I got the idea initially for the gasket from this drawing I found in the forum ….

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I think helps to “fill in the gap” for inaccuracies that might find their way into tolerances for the mating surfaces….  It would probably work without it, I just chose to keep it in the design….When I took the old throttle apart the gasket showed signs of burnt edges so I thought it would be good to be able to replace it as needed…

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The dimensions for ring were found using a paper template…. The holes were first drilled undersized then reamed with a tapered needle file to final size…. This has to be supported on a block of wood with a hole for the file to pass thru to not distort the thin brass…The flat brass with exhaust ports was then massaged against a drill shank in the vise to form it into a circle….The cylinder was polished with 2000# paper to be as smooth as possible…. The inside of the ring is finished with 320# to help the gasket grip and travel with the ring…. To install, I wet the cylinder with castor so the gasket would cling to it… then slip the ring on, Last, the spring…

Winding the spring on a drill shank was trial and error because after it is wound there is spring back that increases its diameter….The the best drill/form ended up being .238” for .380” cylinder diameter… As noted, was done with a drill press with one end of the wire under  one of the jaws of the chuck and the other end in locking pliers…. Pulled very tight and rotate the chuck by hand… (Drill press unplugged and safety glasses on!!)…

One idea with the spring that did NOT work was to bend the control arm directly into the spring (to try and minimize soldered on parts)…. Although it would grip the ring tight enough it would it would act like a ratchet and the ring would advance when the control arm cycled…. So ended up soldering a copper control arm directly to the ring… 95% tin solder holds up to the heat OK…

Here’s the old throttle working, The new one is similar..

https://m.youtube.com/watch?v=rQbwuOJtVF0&pp=ygUTU3RlYW1wdW5rIFRocm90dGxlIA%3D%3D
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Post  balogh Sun Apr 21, 2024 9:14 am

Excellent control and idle, Robert..what keeps the paper gasket in posiyion i.e. stuck to the throttle ring, having their openings always overlapping?
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Post  rdw777 Sun Apr 21, 2024 9:32 am

balough wrote:Excellent control and idle, Robert..what keeps the paper gasket in posiyion i.e. stuck to the throttle ring, having their openings always overlapping?

Thanks Andras, I think at first a lot of hope and fingers crossed LOL!!!…..I think a good polish on the cylinder and a little rougher finish inside the ring is a good start….. After it gets hot a few times I think the paper “sets” …. The gasket never lost its orientation with the ring on the original….I let it run wide open for several minutes to heat things up on first try before moving  the throttle…
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Post  MauricioB Sun Apr 21, 2024 5:16 pm

Congratulations Roberto, your work is impeccable.
I really like the quality in general that makes all kinds of crafts.
Sincerely! Hand Shake

A few months ago I made an air valve for Cox .020, it is incorporated into the air inlet of the rear plastic plate of the engine.
I don't know if I've tried this, I don't remember, but this valve is intended as another possibility for rpm control.
These regulation works using an air valve are an inspiration to the instructions my friend Brad once gave me.

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Post  rdw777 Mon Apr 22, 2024 7:50 am

Gracias Mauricio !!!… The air intake for the .020 looks to be finely made…..Great skill on your lathe…. I would like to see it in operation when you test it… Very Happy
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