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Medallion 09 and 15 needle threads? Cox_ba12




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Medallion 09 and 15 needle threads? Empty Medallion 09 and 15 needle threads?

Post  ffkiwi Fri Mar 31, 2023 5:11 pm

Anybody know what the actual needle thread is on a Medallion .09 and .15.....the supply of NVAs for these is almost non existent these days....and the Med 049/09 ones not a lot better.....yes you can find the needles...Matt has them....but the spraybars are several orders of magnitude scarcer than hen's teeth...!

It strikes me that if I knew the needle thread, I could machine up a few spraybars....its nothing particularly challenging...just tedious-assuming I can find a tap in the appropriate-no doubt fairly obscure-thread. For me the 15 size is a more pressing need than the 049/09 one.

And when I say tedious...do this little exercise...sit down with a piece of paper...draw a piece of hex brass stock and work out how many individual machining and threading operations it takes to convert that piece of hex brass into a spraybar ....it can be up to 16 or so, depending on the fine detail-not including any fixtures you may have to make...

Suggestions for a tap source-assuming someone knows the thread-are also welcome.

ChrisM
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Post  GallopingGhostler Fri Mar 31, 2023 10:00 pm

ChrisM @ffkiwi , I don't know about the Medallion .15, but for the Medallion .09, Bernie already has the answer. I know this from earlier research, because I was considering installing my Medallion .09 in an aircraft where I needed a longer needle to pass through the cheek cowl. These I believe are the same needles on the Cox .049 Sure Starts. See:

https://coxengines.ca/back-end/cox--049-needle-valve-brass-long-3.html

Cox International wrote:

Features:

Thread size : 2/80
Total length: 41.5 mm (1.6")
Includes matching spring
Brand new Original Cox items

Application:

Most Cox .049 reed valve engines with hoseshoe backplates
All Cox .049 Medallion engines
All Cox .09 Medallion engines
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Post  ffkiwi Fri Mar 31, 2023 10:54 pm

Well that's steer worth following up...on that basis the 15 thread might be something like a  3-80 or 4-80....and that led me to the HD Chasen Co-where they stock a lot of taps and dies in threads I'd never even heard of....a quick check of a Med .15 needle reveals the thread diameter to be 0.1095....so that makes it a slightly undersize #4 screw diameter...and they do offer 4-64 and 4-80 threads..not exactly cheap though-the taps $30+ and the corresponding die $60+ ......I'll explore other sources and see what's out there from other suppliers....

The hex size-on the spraybar is 3/16"-so that's an easy size to source....

ChrisM
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Post  944_Jim Fri Mar 31, 2023 11:04 pm

I have samples of both engines, and I have some pretty fine thread pitch gauges. I also have some antique micrometers so I can get a gentle check on external thread diameters. Sorry, I won't have any taps that fine so I can't verify beyond the above measures. Expect them in the next 36-48 hours.
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Post  ffkiwi Fri Mar 31, 2023 11:28 pm

No hurry Jim-this is a back burner project....

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Post  aspeed Sat Apr 01, 2023 11:09 am

Sorry that I don't have any bigger Medallions to check.  I made a bunch of needles and spray bars for regular motors, some remotes.  It was slow going, but I have a Hardinge turret lathe, so it combines a few operations to save time and keep the concentricity.  State of the art in 1952.  Anyway, I used M2 pushrods for the needle valve and just made the spray bars as needed.  It took a split threaded collet to grab on to the pushrod thread and two plunge cuts to get the taper. I have tried a couple out and they seem to work OK, but have not put them on a plane yet.  There is a long story to go with that....MAAC....  The only down side that I can see is that I noticed some rust after a while, likely because I rinsed a set with water, not fuel.  I don't think that you would need to match the thread size and pitch of the original. Just use something that works.  I think I somewhat copied a Rossi size or whatever I had lying around.Medallion 09 and 15 needle threads? Aeromo29
Medallion 09 and 15 needle threads? Aeromo28
Medallion 09 and 15 needle threads? Aeromo30
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Post  aspeed Sat Apr 01, 2023 11:43 am

More pics Maybe notice that the back of the remote needle is tapped for 4:40 for mounting on the plane. Medallion 09 and 15 needle threads? Aeromo31
Medallion 09 and 15 needle threads? Aeromo32Medallion 09 and 15 needle threads? Img_4810
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