Loctite on AN fitting B nut
 

Is it good or bad practise to add blue loctite to the B nuts of AN fitting. considering the amount of vibration it seems like extra security to prevent the nut from loosening up.
Or is the standard tightning procedure sufficient to prevent this happening.
Thank you

Bad idea. Don't do it.

I don't think there is any mention of loctite, or any other thread locking compound in AC 43.13. Flare fittings have been around for a long time now, and loosening of them is not a known issue.

Failure to tighten properly, however, is a human issue.

The old WWII MS-series, the current AN-series, and the 37-degree industrial fittings don't require loctite.

Most flare failures are due to improper flare formation during tube construction, or improper torque during assembly. The usual torque mistake is OVERtorque, which results in cracking of the flare on the tube.

IMHO, no need for loctite, but learn how to form the flare properly (Lots of important details here), and don't overtorque when installing.

My Two Cents, YMMV.

+1
 

What PC said. Simple joint but takes practice.

They are assembled dry,,,no teflon tape either. Loctite hardens over time. You would not want a chunk of it break off and make its way to your engine.

OK, thanks all,
Yes, I am familiar with the AC.43.13 guidelines.
I will stick to that.
(Sometimes I tend to overthink or overdo things)

No harm in questioning "best practices", especially if it leads to an understanding of why it's considered best, recommended or required practice.

Finn

What has more vibration---your IO360 or a CAT bulldozer---careful with the answer. Think about it--
Enough said---
Tom

Tell you what , your butt knows the difference.

Torque seal and forget
 

As your building, or re-building, a good practice is to apply torque seal which is a great visual inspection aid that will validate 2 things..one, that you have torqued it for final time, and second, it will visually let you know if it is loose, or has been loosened during inspection or maintenance. I torque seal mine at the B-nut and the ferrule /tube. I prefer bright orange, but lots of colors available. In fact, I do the same for every bolt on the plane.

Just me
 

In the 70's, during my A&P school, I saw some B-nuts with safety wire holes and they were safety wired.

For me, I am planning to torque to spec and then torque stripping.

What about EZ Turn lube on flair fittings. The product sold through Aircraft Spruce is supposed to be, I thought, specifically for this purpose.

NO. The torque spec is for clean, dry threads. Adding a lubricant will result in the loss of the expected friction, so the threads will be over-torqued.
EZ turn is for pipe threads, where the seal is within the threads, and ideally metal to metal. Most people add a sealant/lubricant to the threads to ?help?. There is considerable debate as to how well EZ works as a sealant in fuel lines.

I use no loctite but triple torque.

1. tighten to torque value, then loosen.
2. tighten to torque value, then loosen.
3. tighten to torque value, final.

EZ Turn is a lube to be used very sparingly in a fuel valve...and it's arguably not the best choice for even that limited use.

Remember, EZ Turn is thick, sticky, and insoluble in fuel. A little dab loose in the fuel system can plug a carb jet and either kind of fuel injection.

When I do a tech inspection, if it doesn't have torque seal on it, it isn't torqued.

Excellent. It means you would pick up a wrench and check them for real.

I’ve had mixed results with Torque Seal. When checking some B nuts in my fuel system I discovered a few were loose after a few years, even though the Torque Seal looked perfect. What I found was that the hardened Torque Seal was slipping around the threads. So I don’t trust it much anymore and always put a wrench on these fittings to make sure they are tight.

Torque Seal
 

There was a recent article in Sport Aviation or Kitplanes showing torque seal applied but was kind of messy. I never do it this way, neatness counts. To avoid the torque seal slipping and giving a false positive torque reading, I run a very nice bead all the way along a line from the hose barrel to the flange nut on the fitting. This way, if the b nut rotates, it will break the torque seal on the flange nut. Here I found neatness counts. It the torque seal is messy, it is hard to tell if it broke loose. And if the torque seal does not have good adherence to the flange, it wont break when rotated.