Tightening AN fittings

coastalflyer · #1 09-29-2007, 07:49 PM

I have begun to tighten down some couples. I can't snug down the nuts without putting some twist in the (aluminum) fuel line. The final 1/8 turn or so of the nut seems to always twist the tubing. I tried putting a little grease between the collar and nut, and between the outside of the flare and the collar, but no real change. I do have some EZ Turn on the threads if that makes any difference. Is this situation normal? It doesn't seem good. A related question is how tight do I go?
Thanks

AlexPeterson · #2 09-29-2007, 08:39 PM

It sounds like you are using too much torque. The advised methods and torque specifications are found in Advisory Circular 43.13-1B. The table for AN tubing fittings is in Chapter 9. All chapters can be downloaded here:

http://rgl.faa.gov/Regulatory_and_Gu...E?OpenDocument

If that doesn't work, do a google search for 43.13 and it is (at least today) the first link shown.

Also, torques for various bolts, nuts, etc. are in chapter 7.

This is must-have stuff for any builder/maintainer.

coastalflyer · #3 09-29-2007, 09:42 PM

Thanks Alex,
I have a hard copy of AC-43.13 but didn't think to look there..duh! It shows a torque range of 110-130 inch pounds for 3/8" tube. I don't have a torque wrench set up to fit on the fuel fitting, and honestly never thought of using one for that purpose. I thought the "good n' tight" method would apply. I was wrong. Do most people actually use a torque wrench for this, or do it by feel? I hope I didn't just wreck that fuel line with all the specially fitted bends that I spent hours on. The flare is now showing some wear on the outside from the over tightening and the sleeve rotating on it.

lostpilot28 · #4 09-29-2007, 09:56 PM

Sorry to hijack this thread, but it's along the lines of a problem I'm having. I just installed the AN fittings to the brake pedal master cylinders and one of them only tightens down with the 90-degree elbow pointing sideways in front of the pedal. Basically, the brake hose is blocking the right pedal (the left one tightens down in the straight up position). I hope this makes sense.

Does anyone know if there's a fix for this? Could it be that the position of the starting thread on the AN fitting is indexed wrong?

N941WR · #5 09-30-2007, 06:29 AM

Quote:

Originally Posted by coastalflyer

Thanks Alex,
Do most people actually use a torque wrench for this, or do it by feel?

Most people torque them by using Crowfoot.

After you torque them, mark them with "torque seal", as you would any bolt. That will help your inspector and you know which bolts you torqued and which you did not.

cytoxin · #6 09-30-2007, 06:41 AM

torque them. if you over torqued them enough to twist the lines i would without hesitation replace them. you can however take a miniature tubing cutter or other device(hacksaw) and cut off just the flare. then go reflare and go from there. you really dont want a single flare that according to the book should be a double, overtorqued so it can crack at the pinch.*and before everyone who says ive been doing it this way for years chimes in .i do to. i just dont overtorque them.

AlexPeterson · #7 09-30-2007, 07:59 AM

Most of us are amazed at how little torque the various aircraft bolts and fittings are specified to, compared to what we might instinctively apply. Get a good torque wrench (search other threads talk about this) and follow the specifications - really. I would guess that if you twisted the tubing, you probably were 4 or 5 times the torque limit.

I completely agree that one should apply inspector's goop to each nut torqued, right then and there. Don't torque a row of bolts or fittings, then come back with the orange stuff. In fact, I am amazed at how many builders don't put the orange stuff on at all.

scard · #8 09-30-2007, 08:46 AM

Quote:

Originally Posted by lostpilot28

Sorry to hijack this thread, but it's along the lines of a problem I'm having. I just installed the AN fittings to the brake pedal master cylinders and one of them only tightens down with the 90-degree elbow pointing sideways in front of the pedal. Basically, the brake hose is blocking the right pedal (the left one tightens down in the straight up position). I hope this makes sense.

Does anyone know if there's a fix for this? Could it be that the position of the starting thread on the AN fitting is indexed wrong?

If you're talking about the NTP thread fitting into the master cylinder, I would keep turning it. It will be shockingly tight, but many people seem to have leaks there because they are too timid with those fittings. It will take it. These NTP fittings on the master cylinders are about the only place I would say to just get after it. There is a lot of meat in the surrounding unit. I had to put mine in the vise and get on the fitting with a big-***-wrench. I have my asbestos suit on for those that will be appalled. When you're trying to figure out what to do in these instances, keep in mind that sometimes there is a big difference between what people will admit in public, vs. the operational reality. I'm guilty too.

lostpilot28 · #9 09-30-2007, 01:12 PM

Quote:

Originally Posted by scard

If you're talking about the NTP thread fitting into the master cylinder, I would keep turning it. It will be shockingly tight, but many people seem to have leaks there because they are too timid with those fittings. It will take it. These NTP fittings on the master cylinders are about the only place I would say to just get after it. There is a lot of meat in the surrounding unit. I had to put mine in the vise and get on the fitting with a big-***-wrench. I have my asbestos suit on for those that will be appalled. When you're trying to figure out what to do in these instances, keep in mind that sometimes there is a big difference between what people will admit in public, vs. the operational reality. I'm guilty too.

Hi Scott,
NTP? Is that the nylon insert? I'm not talking about that...I'm talking about the blue anodized AN fitting that attaches to the braided hoses on the master cylinders. The nylon fittings I have cranked down tight, and they fit well.

The one I'm having a problem with is the AN fitting...by the time you get it to the "tight" point it's pointing out at 90-degrees to the right. The hose coming off of the fitting is positioned right in front of the brake.

scard · #10 09-30-2007, 01:28 PM

Quote:

Originally Posted by lostpilot28

Hi Scott,
NTP? Is that the nylon insert? I'm not talking about that...I'm talking about the blue anodized AN fitting that attaches to the braided hoses on the master cylinders. The nylon fittings I have cranked down tight, and they fit well.

The one I'm having a problem with is the AN fitting...by the time you get it to the "tight" point it's pointing out at 90-degrees to the right. The hose coming off of the fitting is positioned right in front of the brake.

No, I think we're talking about the same thing. The AN fitting with a tapered pipe thread into the master cylinder body.