How I dunnit...
I found that a 5/32” brass tube is a tight press fit in the Medallion NVA holes. The standard fine thread NVA from a postage stamp backplate is a loose fit in the tube. The first thing I did was take my calipers and measure across the sides of the venturi where the stock NVA goes. It’s 0.375” across. I cut a piece of tubing that width and then measured the venturi. The width of the throat is about 0.175”, so I marked 0.1” from each side of the tube. I then used my Dremel to cut out the center of the tube, leaving a thin strip between the ends. This made a nice carrier for the NVA barrel. Hmmm… the cuts were not too even. Next attempt I will take more time cutting the tube to ensure everything is square.
![](https://i.postimg.cc/7LqXmFFq/DSCN7940a.jpg)
![](https://i.postimg.cc/NMMDw1GV/DSCN7944a.jpg)
I then soldered the NVA barrel into the carrier, ensuring the brass strip was opposite the hole in the barrel. Afterwards, I took my jeweler’s files and smoothed and shaped the brass backing strip so that it was narrower than the NVA diameter to allow full air flow through the venturi.
![](https://i.postimg.cc/JhKxgT8Z/DSCN7969a.jpg)
![](https://i.postimg.cc/26KwjVV5/DSCN7979a.jpg)
![](https://i.postimg.cc/T3MtWLQL/DSCN7989a.jpg)
Before installing, I took some coarse sandpaper and ran it lengthwise along the carrier to knurl the tubing so it wouldn’t rotate in the plastic. Then I just pressed it in with the hole pointing down. The hole’s a little off-center, but since it’s bladder pressure that doesn’t matter.
![](https://i.postimg.cc/4x6BvfF8/DSCN7977a.jpg)
![](https://i.postimg.cc/9z3YTKP5/DSCN7992a.jpg)
![](https://i.postimg.cc/Wzq7dTkw/DSCN7997a.jpg)
![](https://i.postimg.cc/L4qdtPkN/DSCN8001a.jpg)
So, the first few times I tried to run the engine, it wasn’t starting. Seems the two Cox glow heads I tried were pretty weak. I put on a Merlin adapter and insert, and Bazinga! (©Chuck Lorre Productions, all rights reserved.) It seems a hair over-compressed, maybe. I may try another glow head gasket. But 18,650 or thereabouts seems pretty good. It’s a Medallion, not a TeeDee. Who knows what another gasket might gain or lose? I’ll fly it and see if I want to mess with it or just leave well enough alone.
Now that I’ve experimented and I know how I want to do this, I should be able to do the next one in about an hour. I have six or seven of the fine NVA assemblies on hand for further experiments. I find being able to do this with Medallions as well as TeeDees is quite nice. Also, next I am going to try this on a Medallion .09 I have on a White Lightning. Maybe this Thursday or Friday.
Mark