Fine Thread Needle Conversion

[coxaddict]

Decided to try my hand at converting TD needle valve bodies to fine thread assemblies using postage stamp parts.  

Used a No. 25 (.149") drill bit to enlarge hole.

[coxaddict]

Turned down a piece of K&S 3/16" thick walled aluminum tubing to fit

Pressed into body using a small vice

Drilled hole through new piece using a No. 60 (.040") bit

[coxaddict]

[OVERLORD]

Well done, that looks like the method discribed in RCM in 1977?

https://www.coxengineforum.com/t11875-fine-thread-nv-assembly-for-a-td?highlight=fine+thread

[davidll1984]

I have plastiques neadle body no insert for the neadle ??never use this piece I wonder what model of neadle can be used with it look smaler than .049 nva do y nead insert ? Just the neadle? Y wil try To Find it and get picturs

[coxaddict]

Thanks for the comments. I actually machined an aluminum tube and press fit the spray bar into it, aligning the fuel hole in the valve body. The fine thread spray bar has a shoulder on the nipple end that would prevent the holes from aligning, so I took some material off the valve body. You could also file the shoulder off the spray bar. No epoxy was used as all parts are held by a press fit.

[getback]

Good job on the conversion , was hoping you would tell us a little more about how you did it with great pictures .

[davidll1984]

I like the way you use to change the part once the insert is removed It is possible to anodize it to color it by the following look like Good upgrade i was tinking how To color wit that métal insert in To place i  think I can do it, but where can I find the part? Other than on the postal back plate ? I have a plastic one i want To complète i nead the nva inserts wit the plastiques seal ?
The way i thought i should complete i didn't think i should change the neadle as wel Now that I know a little more I'm looking for the right pieces To complète the parts for the plastiques one Is it possible to use the same part on both?

[coxaddict]

The hardest part of the conversion is finding the fine thread (128 tpi)  needle and spray bar. The pictures show the different types that I  found off of engines from early RTF models.  Some postage back plates had 80 tpi needles.  I can usually tell the difference by the step machined on the needle tip  With the needle screwed into the spray bar press the parts out towards the fuel nipple side as it has a tiny shoulder on that end.
 

[coxaddict]

I made a puller of sorts from some tubing, washers and bent broken needle valves.  I cut off the needle portion and ground a groove and a slight taper on one to clean the threads of the insert. It makes pulling the insert out easier.

[dckrsn]

Well done, that looks like the method discribed in RCM in 1977?

https://www.coxengineforum.com/t11875-fine-thread-nv-assembly-for-a-td?highlight=fine+thread

I converted one using the RCM method., using
K&S 5/32" od tubing. Surprisingly easy.
Bob

[coxaddict]

Yes the RCM method works.

[NEW222]

A great job done and some fine workmanship. Thanks for sharing your adventures of a needle valve!

[davidll1984]

tink i wil save my old nva and i will take an aluminum bar to form a half circle over its entire length then cut the pieces to make my new parts for anodisation wit new color I think I'll save some time maybe mony To like the post This is very inspiring

[coxaddict]

I have been experimenting with improving the fuel metering 80 tpi needle. I will be testing my mods soon. If anyone has any experience with any mods that work or not please comment.

[dckrsn]

Well done, that looks like the method discribed in RCM in 1977?

https://www.coxengineforum.com/t11875-fine-thread-nv-assembly-for-a-td?highlight=fine+thread

I converted one using the RCM method., using
K&S 5/32" od tubing. Surprisingly easy.
Bob

PS, CoxAddict, I didn't mean to poo-poo your technique. I was
commenting as one with minimum tools. You way is much more
refined. The RCM way is just functional. i like your technique better.
Bob

[coxaddict]

I appreciate everyone's input.  We can learn by sharing.   What's wonderful about Cox engines is that you don't have to spend a lot of money on them to have fun.   Nowadays most of my fixed income goes to paying medical bills.      I try to find ways to get the most from my hobby dollars

[bakergw]

Hi All,

I have tried and tested a very rough method of setting up a needle valve on a TD 049 given the difficulty getting NVB for them. i basically drilled the venturi through the side right through. Press fitted a standard 049 spray bar. Blocked off the 3 holes in the venturi, screwed it into the venturi body and used a normal surestart needle. My TD still screems and its a really easy and cheap way to keep a TD(d) running with the shortage of NVBs for them. The same would work with any spray bar you have. the position of the spray bar in the venturi is something I still sorting out, but it definately works really well. Just need to do more testing of moving the spraybar within the venturi and probably grinding down the OD of the spray bar to get more air flow. Or of course I can use my dremel to open up the venturi. Works really nicely and is simple. Would work with any spraybar and needle.

Cheers,
Gary

[OVERLORD]

Hi All,

I have tried and tested a very rough method of setting up a needle valve on a TD 049 given the difficulty getting NVB for them. i basically drilled the venturi through the side right through. Press fitted a standard 049 spray bar. Blocked off the 3 holes in the venturi, screwed it into the venturi body and used a normal surestart needle. My TD still screems and its a really easy and cheap way to keep a TD(d) running with the shortage of NVBs for them. The same would work with any spray bar you have. the position of the spray bar in the venturi is something I still sorting out, but it definately works really well. Just need to do more testing of moving the spraybar within the venturi and probably grinding down the OD of the spray bar to get more air flow. Or of course I can use my dremel to open up the venturi. Works really nicely and is simple. Would work with any spraybar and needle.

Cheers,
Gary

That becomes a medallion lookalike then. If your TD still screams indicates that the venturi setup doesn't matter and that the crankshaft makes the difference between the TD and the Medallion, not?

[bakergw]

Hi Overlord,

yes it does have a medallion sort of look. Does that mean the only difference between the TD with my carby setup and the medallion is the crank. Possibly. I have about eight 049 TDs and I like trying out different things to see what happens. I dont have great equipment, just me and my dremel so I try things out within my constraints. I would expect the medallion crank and the TD cranks to make a difference with their different timing. The spray bar as I have done will change the Venturi intake capability, air velocity, even the misting of the fuel etc. It well may be a really bad idea, but for me, it works, and has solved my problem, nicely, easily, simply and cheaply and I still have the performance that I seek. i definitely would like to use a finer NV in it though as they helping tuning quite a bit in my view.

Cheers,
Gary

[batjac]

A few months ago I decided to do  my own fine thread needle conversion, seen (here)

The Backwards Mark

[aspeed]

I suppose those postage stamp 128 TPI needles are unobtanium now like the Kirnkraft ones. I don't see why the 80 TPI needles can't work. The old Supertiger/Rossi needles with the split lock would work well as there was no slop. One 20th of a turn was exactly that. Anyway, just thought I would add another old picture of an even older remote needle sleeve I used on a speed plane about 45 years ago. It worked well in a tight cowl with the KK remote needle. It might save butchering an old hard to get needle assembly although I suppose it is a good improvement. I have also soldered up the steel hole for the needle to use a remote needle. That was more of a butcher job.

[coxaddict]

I have all these at my disposal but wanted to try something else.  Using a remote needle is something I'd like to explore.

[batjac]

I don't see why the 80 TPI needles can't work.

They can work for hard tanks or balloon tanks.  But for bladders they are too coarse.  With a fine needle valve on bladder, you have adjustability.  I did bladder on an 80TPI needle once, and it was less than a 1/4 of a turn from too rich to run, to too lean to run.  You've gotta be quick and precise using a coarse needle on start, and tweaking it in to the sweet spot is almost impossible.  

The Rough Mark

[davidll1984]

Sorry stupid question someone knows where to find the valves For these blue cap?? Y want To build m'y own modified parts I can easily reproduce the pieces if can find the components

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