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What is: "AN Spacer 4D (1/8" washer)???

Saville

Well Known Member
On Drawing 16A of the RV 7,8 "Wing Fuel Tank (Left Shown) the fuel tank vent connections are shown.

To connect the vent line to the outside world one uses an

AN 833 -4D Bulkhead Ell

...which goes through the T-703_R root end.

on the inside of the tank, one is supposed to slip a washer and then tighten the nut over the washer.

The identification in the plans of the washer is:

AN Spacer 4D (1/8" washer)

What is that? Which washer? What is the outside diameter? There isn't a lot of space for it before you hit the raised edge of the lightening hole.

What is the washer made of? Steel? Aluminum?

Looking around on AS I don't see one with a roughly .5" ID and 1/8" thick.

Any pointers to what I should get for that would be helpful

Thanks!
 
You're looking for one of these. It is a large AL spacer washer. Only purchased from Van's.

dsc05182.jpg

Image from Joshua's RV-9A Project at rv9a.pacificrimsound.com
 
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As I recall, mine still had the blue plastic on it.

The part is something Vans punches out from flat stock.
 
You're looking for one of these. It is a large AL spacer washer. Only purchased from Van's.

dsc05182.jpg

Image from Joshua's RV-9A Project at rv9a.pacificrimsound.com


Yes that's the part I'm looking for. The plans say
AN Spacer 4D (1/8" washer)

And I just ordered:

AN SPACER, 4D Washer 1/4 fitting


I hope that's it.
 
Yes that's the part I'm looking for. The plans say
AN Spacer 4D (1/8" washer)

And I just ordered:

AN SPACER, 4D Washer 1/4 fitting


I hope that's it.

It is. The 4 is 4/16 (1/4) diameter for the 1/4 vent line fitting (833-4D) and 1/8 thickness. The D = aluminum for material it made from.
 
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Ordered? That's a two minute part from scrap.

Bob

Perhaps for you. But you are completely unaware of my setup.

Bought my airplane built. It's in a hanger. I have no machine shop at the hangar.

I do have some tools in my home cellar - about 45 minutes away. I do not have a bandsaw. I'd have to make this item using a drill press, jig saw and hand file.

I don't know what the OD dimension is. So it's hard to know what size to make it in the first place. Any mistake and it's back and forth from the hangar to the cellar.

So for me, in this case, time is far far FAR more valuable than money. If I order them they are exactly what they need to be - no muss no fuss.
 
I think you can order the part from Vans no problem. I do think you may be too worried about the specific dimensions of the part. It's a 1/8" piece of aluminum with a hole drilled in it. The purpose of the washer is to provide enough material thickness so that the bulkhead fitting nut can be tightened fully.

Not sure what you are trying to do here but as builders we see this as a trial task. The washer I assume is just part of a much bigger problem that you are trying to address. I would be more concerned about your skills for that issue than the washer itself. Perhaps you could share that info.
 
I think you can order the part from Vans no problem. I do think you may be too worried about the specific dimensions of the part. It's a 1/8" piece of aluminum with a hole drilled in it. The purpose of the washer is to provide enough material thickness so that the bulkhead fitting nut can be tightened fully.

Not sure what you are trying to do here but as builders we see this as a trial task. The washer I assume is just part of a much bigger problem that you are trying to address. I would be more concerned about your skills for that issue than the washer itself. Perhaps you could share that info.

I did order the part from Vans as I mentioned above. And I know what it's there for. I just want the right part.

Plus I didn't understand the nomenclature on the plans - I like to understand things.

To be honest I don't see the need for a big long explanation of what I'm doing just to find out what that part is. I try not to waste people's time with lots of verbiage about something no one cares about and that often never gets read.

But here you go:

The AN833 Ell has a little bit of gas leaking around it. You can turn the Ell a little. A previous owner globbed some Proseal on the outside of the AN833 but that has failed.

Therefore it's not tight - not installed properly. Also, the fact that you can turn it means that either the vent line is turning with it or the vent line B nut is loose.

So my intention is to open up the access plate, remove the AN 833, clean the area, and install a new AN833 properly with a new washer, new nuts and some Proseal. Then screw on the vent line B nut, check the fuel sender and re-attach the access plate.

2 years ago I had a problem with a dripping vent line (the very same one )- it was dripping gas out the vent air intake. I attached a fitting and a plastic hose to the intake and while blowing some air into the intake and with my ear on the wing I heard bubbles coming out of the end of the AN833 that is inside the tank. That mean the vent line b-nut was loose.

Sure enough after removing the access plate and looking in with a borescope the b-nut wasn't even started. I'm not sure it ever was. I tightened the B-nut and the problem was solved.

However I should have also checked the nut securing the AN833 to the rib - it, too, may have been loose. I wish I had thought to check it because now I have to remove the access plate all over again, which is a pain. But it should go faster this time having done it once before.

If I'm going to remove a part and then put it back, I like to use new parts when possible and reasonable. I have no idea if the builder even used a washer there. There have been a few things on this plane that gave me pause. So I want to have washer on hand.

What if the nut that's there is rounded some? A new one would be better.

So, in order to get this job done as quickly as possible, while doing it properly, I'm assembling all the parts I may need, beforehand. If I don't need them then it's a small expenditure. If I do - they are right there, brand new, ready to go. In order to have a couple of those washers on hand I have to understand what they are. I recognized that they are 1/8" thick but that's all. The washer did not have a standard name which you can look up on AS .

So I asked if anyone here would clue me in as to dimensions. Pazmanyflyer gave me good info, as did others, but not the OD. If you look at his picture you will see the washer is close to the wing skin - so it cannot be too big.
 
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So I asked if anyone here would clue me in as to dimensions. Pazmanyflyer gave me good info, as did others, but not the OD. If you look at his picture you will see the washer is close to the wing skin - so it cannot be too big.

You seem to understand that the part you are asking about is just a spacer, so the O.D. isn't all that critical.

The actual part is 1.25 in overall diam. with a a .438 diam hole in the center, and .125 thickness.
Since it is just a spacer, if there is interference on one edge, it can just be trimmed for clearance as needed.
 
You seem to understand that the part you are asking about is just a spacer, so the O.D. isn't all that critical.

The actual part is 1.25 in overall diam. with a a .438 diam hole in the center, and .125 thickness.
Since it is just a spacer, if there is interference on one edge, it can just be trimmed for clearance as needed.

Right I understand the OD isn't critical - now. When I first asked the question I didn't know all of that.

But I like to save as much time as I can so if I get one that's the right size to start with then I might save a little time. Though being aluminum it wouldn't take much.
 
Saville, great explanation. You?ll find on this wonderful site that, at times, you get the ?wrong? kind of advice. Most of it is well-intentioned though. Take it with a pinch of salt. I remember once asking for advice on the length of expensive cable I might require to run from the wing top to the panel. Well, some guy told me I should just go and measure it!😂😂 The fact that I was 4,000 miles away from my project and unable to do so probably hadn?t occurred to this helpful person. Some people just can?t help themselves. Thankfully, most contributors here try their best to be helpful.
 
As an aside, for someone who is admittedly ignorant and learning, can someone enlighten me as to why is it that fuel fitting nuts, such as the one that will be tightened down on this spacer, do not require lock washers to stay tight?

I received a couple of these 4D spacers and noted that they are slightly bowed and will not lie down flat underneath the nut. Consequently, as you start to tighten the nut it does not compress down nicely and evenly. Rather, the nut tightens in fits and starts as it rotates over the bowed spacer underneath. You don't get an even increase in torque as you are tightening. Makes me worried whether I will get the proper torque, and if I don't, that the nut might later vibrate loose. Made me wish a lock washer was there to insure it stays tight. --- But apparently all this isn't a concern?

After getting my first set of spacers from Vans bowed, I ordered a new set, and they also came bowed. Contacted Vans about it, and was told that that's just the way they come, on account of the manufacturing process. They are made by being punched out of a flat piece of stock, so they are all slightly bowed. I tried to flatten it by putting it between the jaws of a vice - no joy, it just springs back.
 
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As an aside, for someone who is admittedly ignorant and learning, can someone enlighten me as to why is it that fuel fitting nuts, such as the one that will be tightened down on this spacer, do not require lock washers to stay tight?
.....................
Made me wish a lock washer was there to insure it stays tight. --- But apparently all this isn't a concern?

A good question and one I've been mulling over myself. Did the nut come loose because there is no locking?

If you put the bowed side of the spacer against the rib, will tightening the nut put a little flex on the spacer thus acting like a lock washer?
 
A good question and one I've been mulling over myself. Did the nut come loose because there is no locking?

If you put the bowed side of the spacer against the rib, will tightening the nut put a little flex on the spacer thus acting like a lock washer?

Aluminum is soft stuff. So the nut and the washer will both deform slightly and so will the threads and it should hold just fine. There are 1000s of these out there. You just have to be careful to scrunk it down firmly without stripping the threads. Yes, scrunk is a word. I learned it from a master metal maker who sold me a torch and the brass fittings leaked. After scrunking they were fine. It means tighten it, then a bit further. Ok, skrunk probably isn't a word but strangely enough when he emailed me with that advice I instantly understood what he meant. It is something that I associate with non ferrous metals because they are much easier to deform.
 
I also intend to put Proseal between the spacer and the rib. That might help to hold things together.

Knowing how far to "scrunk" is an art. I tend to under-scrunk because I'm afraid to strip out the fitting. I usually have an A&P check my work. He has a well calibrated "elbow click" ;)
 
It's a word, alright...in Scots :)

SKRUNK, v. tr. and intr. To shrink, to crumple up, to become shrivelled or hard (Cld. 1880 Jam.). Deriv. skrunkle, id. (Ib.). Ppl.adj. skrunkit, -ilt, pinched, scanty (Kcd. 1925 Jam.), also in reduced form skrunk, shrunk, dried (Mry. 1928).

Sc. 1868 D. M. Ogilvy Willie Wabster 7:
Skrunkit and slidderie as the strone.

Abd. 1928 :
The dubs has begood te skrunkle wi' the freest a'ready.
 
A good question and one I've been mulling over myself. Did the nut come loose because there is no locking?

If you put the bowed side of the spacer against the rib, will tightening the nut put a little flex on the spacer thus acting like a lock washer?

I didn't complete the job yet. Hopefully we'll receive some answers to address the concerns (actually I see some are coming in as I'm writing). Obviously guys are building these tanks all the time using these spacers, so I guess it has not been an issue.

But if you've never tightened fuel fitting nuts before, it really makes you wonder as you are tightening down a critical fuel fitting nut, with no lock washer, and feeling the torque increase and decrease in a herky-jerky way as the nut rotates over the bowed spacer below. If you then unscrew the nut, you'll also notice that it doesn't loosen evenly, and then all of a sudden it just comes free off the spacer. So not evenly progressive torque tightening down, and not loosening up.

Actually, before you even get to the issue of the bowed spacer messing with your torque, there is the question of whether you are going to use a torque wrench to get the proper torque, or just go by "feel." The nut is on a line, so obviously you can't just use a normal socket on a torque wrench -- you will need a crow's foot attachment. Well, that particular nut is huge -- 13/16ths if I recall -- and neither my local harbor freight nor anyone else around carries a crow's foot that big in stock. So you'd have to special order it online.

For these reasons, I asked someone at the airport who's built a lot of fuel lines about it. Turns out he doesn't have a crow's foot that size either! His response was "you just tighten it by feel until it's good and tight and it will hold." Pretty much the same response others now appear to be providing, regarding the "skrunking."

So it sounds like it is probably really common that folks are just doing these things by feel -- because how many people are going out and special-ordering an over-sized 13/16ths crow's foot to mount on their torque wrench to complete the job?

Well, as for me, a person who hasn't tightened a lot of fuel fittings by feel, the idea of doing it by feel (and no lock washer) wasn't exactly giving me the warm fuzzies to start with. Then when I noticed how the nut doesn't tighten (or loosen) evenly on top of the bowed spacer, I got even fewer fuzzies about doing it by feel. So I guess I may end up special-ordering the damned huge crow's foot (that I'll probably use exactly once). But even then, everyone knows that to get proper torque with a torque wrench you're supposed to have a nut and threads that are free from any interference that prevents smooth, progressive tightening -- and you won't have that with the bowed spacer underneath. Anyway, by now I suppose everybody's ready to pelt me with rotten tomatoes for nitpicking concerns and details, so I'd probably better drop it. But for some reason the possibility of a fuel line coming loose in flight makes my mind think that way.
 
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TBH, I don't recall any of my spacers being bowed when I built my 7. I'd probably be as concerned as you are about it, and find a way to a) get flat ones in the first place, or b) flatten out the ones I have, or c) make my own that are flat.

But, as I said, none of the ones I got, in any size (IIRC, there are two that Van's sells) were malformed. Weird.
 
I didn't complete the job yet. Hopefully we'll receive some answers to address the concerns (actually I see some are coming in as I'm writing). Obviously guys are building these tanks all the time using these spacers, so I guess it has not been an issue.



For these reasons, I asked someone at the airport who's built a lot of fuel lines about it. Turns out he doesn't have a crow's foot that size either! His response was "you just tighten it by feel until it's good and tight and it will hold." Pretty much the same response others now appear to be providing, regarding the "skrunking."


So it sounds like it is probably really common that folks are just doing these things by feel -- because how many people are going out and special-ordering an over-sized 13/16ths crow's foot to mount on their torque wrench to complete the job?

With a built tank it's really tough. One could mount the AN833 to the rib before the rib is mounted on the tank. But you and I don't have that option available.

Anyway, by now I suppose everybody's ready to pelt me with rotten tomatoes for nitpicking concerns and details, so I'd probably better drop it. But for some reason the possibility of a fuel line coming loose in flight makes my mind think that way.

I don't think you are nitpicking. You (and I) are trying to think things through given that we don't have years of experience with these things. When people on the forum give us help with our out-loud thinking it's very much appreciated.
 
Craftsman sells the crowsfoot wrenches. Most builders ended up buying a set as I did. Look on ebay. They may even be sold individually, I'm not sure. Some people are more by feel than others. On my plane every fitting and nut has been torqued to spec. Does that make my assembly better than others? I can't say for sure, but I'm comfortable with it and I have no doubts in my mind.

On my build I covered the fittings with the sealant. I'm not worried about the nuts coming off.

Search here about the cork gaskets too. They eventually leak. I used sealant directly as others have done.

If you haven't figure out what to do about the washers being flat I'd say just flatten them. Put them in a vise and squeeze them flat. If you don't have a vise the just whack them a couple of times with a ball peen hammer. Again it isn't that critical. You need to put sealant around the area where the fitting goes through the rib. I then put a little more around the fitting after it had been pushed through the rib before I slid the washer on. Then I put the nut on. Attached the tubing nut. Every thing was torqued then I covered the whole thing with sealant.
 
Search here about the cork gaskets too. They eventually leak. I used sealant directly as others have done.

When I pulled the access plate off a couple years ago, it had the cork and I re-installed it with just the sealant. Never leaked a drop.
 
I am glad you are concerned when working on your plane and try to get a complete understanding of what is what, but you really are overthinking this. tighten it down so it does not move, proseal it and move on. its not that critical, it need to be tight enough so the fitting does not rotate. thats about it.


bob burns
rv-4 N82RB
 
Ok guys, thanks for the replies. As Saville said, they are appreciated.

By the way, I realized I happen to have a 13/16ths socket (from a 1/2" drive ratchet/socket set), and I just discovered that socket is so big it will fit down onto the nut over the top of the nipple of the AN833. Of course, my torque wrench that provides the low torque values required for torquing the nut is 3/8" drive. But I have a converter that allows the 3/8" drive torque wrench to drive a 1/2" drive socket. So turns out that's a way to get the proper torque on the nut without buying the large crow's foot. I plan on torquing it to the proper spec and then surrounding it with tank sealant.
 
BTW I got the AN spacers yesterday. They are "potato-chipped". Not extensively but quite noticeable if you lay one on a flat surface and press on the edges.
 
Anyone happen to know the thickness of the T-703_R rib material?

As an aside, for someone who is admittedly ignorant and learning, can someone enlighten me as to why is it that fuel fitting nuts, such as the one that will be tightened down on this spacer, do not require lock washers to stay tight?

I received a couple of these 4D spacers and noted that they are slightly bowed and will not lie down flat underneath the nut. Consequently, as you start to tighten the nut it does not compress down nicely and evenly. Rather, the nut tightens in fits and starts as it rotates over the bowed spacer underneath. You don't get an even increase in torque as you are tightening. Makes me worried whether I will get the proper torque, and if I don't, that the nut might later vibrate loose. Made me wish a lock washer was there to insure it stays tight. --- But apparently all this isn't a concern?

A.


This post of yours has been sticking in my mind ever since I read it.

Today I removed the access plate and then removed the AN833. Mine was loose - you could turn it slightly.

Your post suggests you could not get it tight enough....

What if the threads on the AN833 end such that the thickness of the rib plus the 1/8" washer isn't quite enough to allow the nut to tighten. What if yourun out of AN833 thread?

I say this because on my other tank - which has never leaked, there is a spacer on the OUTSIDE. Plans don't show that but I wonder about it. Maybe it's there to take up a little extra space while also providing some extra sealing since it's probably Prosealed.

I'm going to look at the AN833 tomorrow and see if there'e enough thread to handle two spacers.

Anyone happen to know the thickness of the T-703_R rib material?
 
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