Ball bearings you say? 3D printed BB crankcase.

I was wondering how long it was going to take for that new carb fuel inlet to be spotted. I accidentally left it on the carb when it took the picture. I had one crumble when it was installing a carburetor and thought there must be a better solution.

The brass fuel barb is 3-56 threaded one from Clippard. The barb is too small for regular size .049 fuel tubing and only works with the .010/.020 fuel tubing. They are also almost $1 a piece too.
I did approach Matt and he is also working on an alternative solution.



I also tried to do a direct print of the entire part. Being so small I can’t get fine enough detail on the barb fitting. I might be able to change the design of this so the barb comes out round vs oval. This prints as an overhang so I would have to teardrop shape the barb for it to come out round on the 3D print. This would also require a lot of cleanup work where just tapping a hole would be easier with a threaded nipple.

Jason if the problem is only the size of the fitting fuel tubing, then what I would do is attach an 010 or 020 size, short  fuel tube to the nipple so that the barb will hold it, then pull the larger, 049 size fuel tube over the other end of short 010 size tube, and  run it up to the 049 engine...I may also pull a small spring - the one used in Babe Bee tanks - into the 010 size tube to prevent it from collapsing under the external pressure by the 049 tube..or would just add a copper or aluminum tube connector in between the 010 and 049 tubes etc...

My garage-tuning solution, not ultimately professional, but would still be working with your small nipple, and be several orders of magnitude better and more reliable than the all-plastic COX fuel nipple...I would still be interested in buying such a hybrid solution...

These fittings would fit the .049 size fuel tubing but have a painfully slow shipping option.


https://m.aliexpress.com/item/32696220692.html?trace=wwwdetail2mobilesitedetail&spm=2114.12057483.0.0.2d50546d9TXC5Y

They are for pneumatic hose but should work fine. They will be larger than the Clippard 3-56 version.

I made the fuel inlet thicker for more strength. I tried to crush a glass filled Zytel Version with my fingers and could not even get it to deform it’s that strong. I need to test it with fuel to make sure there still isn’t an issue with leaks.

Good to see that you will soon find the solution !!! I believe the small nipple size is just cosmetics, if the larger size is difficult to source, I would still happily compromise on the small one...we are modelers anyway and need our part of innovations when completing our fuel systems on our planes..

Any word on the threaded insert?

They came in today. I need to update the drawing to make the screw boss bigger and enlarge the hole size. Backplate will be updated as well. 5/8-18 Bottom tap came in also but I need to take the first 2 tapered threads off of it on the grinder.

More tweaks but eliminating the potential of stripped screw holes is worth it.

I have set up the 65 deg carb mount with a Killer Bee .049
Will be bench testing the throttle function and peak power
with the APC 4.4x4 labeled as a .049 Free Flight Prop.

Well that makes more since , i was thinking it had something to do with the cly. placement But didn't want to sound stupid and say something about the size of the insert >> guess i missed a line . Looks good Brad why is it U use .020 spinners on .049 engines again ( i am having brain farts i guess )

Less mass out at the end of the driveline for less wobble, reduced heat and increase in rpm.
Helps to center the prop / insets a bit and allows the use of a E starter.

Thanks Brad , makes since to me