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QB Fuel tank stripped threads

Navy76

Active Member
Recently I?ve been trying to install fuel level sender on my RV-14A QB right wing. I called Vans for help and tips. It?s very difficult to see what?s going on inside the completed tank. Vans suggested that things would be much easier if I removed the tank from the wing first. This would also facilitate the pressure test to follow.

This seemed reasonable, so today I built some cradle supports for the tank then attempted to remove it. Everything went fine except that two to the bolts that connect the rear of the tank to the spar appear to be stripped. They spin freely but never back out. I thought that if I applied some rearward pressure while turning the bolt tha maybe I could get it to reengage the thread. I put a pair of small vice grips on the head and pulled as I tried to back out the thread but no joy.

Both bolts are very difficult to get to. One of them I can?t even see without a mirror. The second one I can see and I can even see the threaded end of the bolt where it comes out of the nut plate. It just spins and spins in both directions with no axial movement.

I am really at a loss as to what to do. Both bolts are so inaccessible I don?t think drilling them out is really an option. Any ideas?

I am also wondering if anyone has experience with getting Vans to do the work? I paid a lot for the quick build kit and don?t relish the thought of having to pull a wing skin to repair a problem that I didn?t create.

Lyn Robertson
Corvallis, Oregon
 
Call Vans. I think you have a good case for shoddy workmanship here. For the record, my QB -10 came with those same bolts being too long. This was ?fixed? by the QB guys by using a stack of washers under each bolt head. Since I needed to remove the tank anyway (as you found out) no real harm other than using the correct size bolts from my spares.
Be careful trying to remove these. You do not want to damage the spar in any way.
 
That sounds like a major problem. I was a machinist for 15 years before becoming an RN. I've taken out many many broken and stripped studs/bolts.
I don't know about Vans doing any work so someone else more in the know will have to speak to that.
As far as your problem. I can't visualize whats going on. It sounds like the bolts were overtightened when assembled which broke the threaded part of the nut plate off which is now acting like a nut holding the bolt in place. Only suggestion is if you can somehow get a pair of thinly ground down pliers to grip the barrel of the broken nut plate then back the bolt out. Easy to say but can you get something like that up in there along with two hands??? There's no really right way here.... it's what ever works without any damage to the tank, wing spar etc.
With that said, the only other way which is my guess what you're going to end up doing is what you've mentioned. Just like the other access holes in the wing skins... cut another one. I don't see where you have a choice. The + side of this would be easy access when reinstalling or removing the tank if ever needed.
 
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Can you get a nut splitter in there?

https://m.lowes.com/pd/Kobalt-Nut-C...MIvaKLlvKa3QIVSLbACh3GmA5SEAQYAiABEgKJ8_D_BwE

If you can get this tool over the nut, it will split the side of the nut and you should be able to remove it from the bolt...

If its the bolts I'm thinking of. A nut splitter won't do it. These are AN3 bolts that go through the spar web into the L brackets on the rear web of the tank. The ones in between the most inboard ribs, where the wing walk goes are very tough to get anything on other than a socket on an extension. They are retained by K1000 nutplates. My bet is the nutplates are spinning. Its a bit scary to consider why they became that way.

Definitely talk to Van's. If you can get a video camera down in there even better.


----------PS: The only reason I risk opening my pie hole on this is, I'm the guy that bought the "barn-find" wings and went through similar problems. -KW
 
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The good news is that you are close to the mothership - hopefully they'll step up and fix this problem. This could be a big challenge to disassemble enough to access the brackets on the fuel tank that hold the nutplates.
 
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Nut plate

I would get an inspection camera from harbor freight and see if you can get a look at what is going on. 25% off on monday. It has a 38" reach.
 
Thanks for the feedback! I?ll call Van?s Tuesday and see what they say. These particular bolts are in the most inaccessible spots, almost anywhere else and I?d have more options. Murphy?s Law holds true again!
 
If the entire nut plate is spinning..... That might be a better scenario than the nut plate barrel broken off. At least it gives you something to grab onto. If that is the case then maybe a long piece of safety wire through one of the holes. I know that would be a mother bear to do! Like others have suggested, maybe a scope. I've blindly stuck my phone in camera mode way inside places and snapped a bunch of random pics to get a close up look. It may take several to get the one or two that yields some good information.
 
It seems to me there are two possibilities here.

One is that the plate nut is spinning, presumably because it wasn't riveted properly to the Z-bracket, or it was overtorqued and that broke the rivets, or possibly the ears off the plate nut.

The other possibility is that the bolt is actually broken, most likely at the root of the threads, which could be caused by the bolt being a little too long and the assembler just kept turning it to try to get it to draw tight when the plate nut was bottomed on the threads, and that broke the bolt. This seems like the most likely scenario to me, especially after the other comment above about finding one assembled with too long a bolt with some washers under the head.

If you can snake a small camera in there and watch, it would help answer which case you have.

It seems unlikely to me that the threads of the plate nut are stripped. It is pretty hard steel.


If it is the second case (broken bolts), then your idea of getting some rearward pressure on it as you turn it is the right idea, and maybe you just didn't get enough. See if you can get a straight-blade screwdriver in under the head, being careful not to gouge the face of the shear web of the spar. But also, if it is the case that both bolts are actually broken off, then it should be possible to remove all the other connections of the tank to the wing, and just remove the tank, leaving the broken bolts in place. The Z bracket would just slide off the ends of the broken bolts. Then with the tank off, you can punch the broken bolts out from the front, remove the broken bolt ends from the plate nuts (might be easier to just install new plate nuts) and it should be straightforward to reassemble everything, with proper-length bolts.

If it is the first case, you have to find a way to keep the plate nut from turning. I think you can drill a hole in the tank skin in the area between the spar and the rear tank baffle so you could feed some kind of tool in there. (*)

The safety wire idea mentioned above might work. If that isn't strong enough, then make a tool from a narrow strip of steel with a pin near the end that would fit into one of the rivet holes in the plate nut. with the plate nut turned perpendicular to the long tool, you hopefully can get enough torque to loosen the bolt. Otherwise, make a tool with two pins at the right spacing to fit into the rivet holes in the ears, and a semi-circular cutout between them for relief around the barrel of the nut. This tool would engage both of the holes in both ears of the plate nut. It might not even be necessary to actually get the pins into the rivet holes, it might work to just have the sides of the ears bear on the pins.

If you need help visualizing what the tool would look like I can make you a sketch, just send me a PM. But I'll be away until Wednesday.

(*) As I think about it, the rear-facing flange on the rear tank baffle probably comes back pretty close to the forward face of the spar? If so, then drilling a hole there will remove some of the bond area that is sealing the tank. If the flange is something like an inch wide, it may be OK to put a 3/8" hole in the middle of it without causing a leak.

I can't think of any other way to get access in there to grab the plate nut.
 
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I can't think of any other way to get access in there to grab the plate nut.

I'm leaning towards drilling the heads off those bolts. But, very carefully!

It will probably take quite a bit of patience to get the drill bit started exactly in the center of the bolt head. And, a snake drill, several carbide drill bits of the correct size and some cutting fluid.
 
If the bolts are broken, the tank should come off if all the other bolts and screws are removed.
Have you tried taking a small flat pry bar and putting pressure under the bolt head while turning the bolt? Hard to do with one hand but it can be done.
 
I'd advocate inspecting the nutplates/bolt threads with a remote camera if they're reachable before trying to pull tank off - if the bolts are broken should work but pulling the tank off isn't a trivial exercise itself since you're tucking dimpled skins over/under dimpled and countersunk surfaces. I carefully re-primed all these areas when I replaced tanks after removing them. Plus I can envision getting somewhat "stuck" with tanks in a partially removed position if bolts get wedged in place.

I don't see how you can cut bolt heads off easily in those tight spaces without risking damage to spar web. Seems like the last or next to last option to me (with last being removing skins and/or some degree of tank disassembly).

Bottom line - you want to be pretty sure tank will come away freely and/or be easily put back into place before committing.
 
Like mentioned before, use an inspection camera to see what the issue is,,,not speculate. If it?s the nut plate itself that is spinning you can see through the camera. Then take a metal scribe with a 90* tip and try to align it with a rivet hole as you turn the bolt. If you have an open rivet hole it will find its way in and that alone should be enough to hold the nutplate enough to get the bolt removed if you can get enough pressure on the scribe to keep it in the rivet hole.
 
I have to second Mr. Steve Smith's ideas. Excellent approach. And like has been mentioned... if the bolt itself is broken then the tank should still be removable. Until you get an inspection camera on it to see what you're up against you're just guessing and might do something unnecessary.
 
I am able to see the back side of one of the bolts with an inspection camera. Luckily it is only one rib outboard from the wing root and there happened to be a 3/8? hole in the root rib the I could put a camera in. I can see the end of the bolt spin as I turn the head so the bolt is not broken, nor is the nutplate broken or detached. That only leaves the threads being stripped on the bolt or on the nut plate.

Even though the bolts won?t back out, they are still tight enough that I haven?t been able to wedge anything between the spar and the back of the bolt to coax it back into the good threads at the end of the bolt.

The bolt I have the best access to is in the wing walk area where the ribs are only 3-4? apart, so it?s really hard to get any tools in there and still turn the bolt.

The other bolt is farther outboard, midway between the first two access holes. There is no way to even get a camera on the back side to see the nutplate. It?s in a compartment created by the spar, the aft bulkhead of the tank and the top and bottom skins of the tank.

Since it is critical not to damage the spar I think the only way to remove the bolt heads would be to remove the inboard bottom skin first so I can at least see what I?m working on. Even then it wouldn?t be an easy task.

I?m really hoping Van?s will step up and help me out. Best case is I remove the bottom skins and can then get the bolt heads off. Worse case is the spar gets damaged and the whole wing is toast. I am not inclined to take that risk since I didn?t cause the problem and paid for a functioning wing. It seem as though they?d be interested in getting to the bottom of this issue since either someone overtorqued the bolts at the factory or the bolts were substandard, neither of which should go un-remedied.

I recall getting some paper work with the wings warning that the fuel tanks were attached at the factory for shipping only and that the builder should closely inspect the tank attachment hardware. In my case it was all there. I had intended to check the torque on all of the bolts but hadn?t gotten that far before I decided to pull the tank.

At this point there?s not much else to do but wait until I can discuss this with Van?s.

I truly appreciate all the feedback. It?s humbling to realize how many people are willing to help.
 
Just wondering which two bolts are these? The tank attaches with the Z-bracket which each has three bolts and they are all well visible. There are also some other bolts that goes thru the Ribs to the spar which has nut on the back side but not part of the tank. Can you identify which two bolts are stripped?
 
Bavafa, the stripped bolts are both in the groups of three that hold the z-brackets on the aft bulkhead of the tank to the spar. I can see the head of one of them through the access hole but the angles are such that I can?t see the other one without an inspection mirror.

I am only able to see the back side of one of the bolts. This is a QB wing so all of the skins are on except the outboard bottom skin. Access to the bolts is limited to the access holes.
 
Bavafa, the stripped bolts are both in the groups of three that hold the z-brackets on the aft bulkhead of the tank to the spar. I can see the head of one of them through the access hole but the angles are such that I can?t see the other one without an inspection mirror.

I am only able to see the back side of one of the bolts. This is a QB wing so all of the skins are on except the outboard bottom skin. Access to the bolts is limited to the access holes.
Thanks for clarifying the bolts sets. Nutplates are fairly strong and not easy to strip, they must of cranked that bolt pretty tight to strip it.

Would it be possible to have some one pull the tank gently out and by that putting some outward pressure on the bolt while another person is unscrewing the bolt. This way you avoid scaring the spar and it might catch enough if the blot is striped.
I know it is a long shot but ought to be safe to try.

good luck.
 
Would it be possible to have some one pull the tank gently out and by that putting some outward pressure on the bolt while another person is unscrewing the bolt. This way you avoid scaring the spar and it might catch enough if the blot is striped.
I know it is a long shot but ought to be safe to try.

good luck.

+1 good idea.
 
+1 good idea.

+2 on Bavafa's suggestion to try prying forward on the tank, gently. Yes, this is worth a try. My hunch would be that the stripped threads will not want to allow a clean thread to get started again, but it might. If it does, twice, you are home free.

If not, drilling the heads off the bolts is the best approach I can see. You can either remove a portion of the lower skin, or you could cut an additional inspection port in the skin directly where the bolt is. It is going to have to extend aft far enough for you to get an angle drill in there with a short drill.

When you are done, you will have to make a cover for the hole. You can copy the way the standard inspection ports are made so the cover is flush, or you could just lap a cover over the outside of the skin. No one is going to look under there, so it really only matters to you.

Wow, it is really hard to strip a plate nut! Or a AN bolt. I would be about as happy with that employee as I would be of the guy that drilled a hole in the skin of the Soyuz!
 
I?ve only got room to work on one wing at a time. I?ve been working on the left wing and haven?t gotten back to trying to remove the right tank. I did call Van?s however and they recommended trying to put wooden wedges in between the inboard-most z-bracket and the spar to put some pressure on the bolt that is in the next outboard z-bracket. If that doesn?t work they recommended drilling out the bolts. While that might work for one of them the other is impossible to see and very difficult to even reach.

If it comes to drilling, I think I?ll return it to Vans and let them deal with it. It seems as though there is a high risk of damaging the spar and I don?t w,ant to take that risk for a problem caused by the factory.

I?ll updated this thread when I have more news.
 
I finally got the tank off. I ended up buying a tight fit 90 degree drill extension from ACS and then used a drill guide that I turned on my lathe to help me drill a #30 hole in the exact center of the cap screw head.
IMG_0009.JPG


Once that was done, I held the head with an ignition wrench to keep it from spinning and drilled it out to 3/16?.
IMG_0003.JPG


When the hole was deep enough, I held a flat bladed screw driver in the joint between the washer and the hex head and gave it a quick rap with a 6oz ball peen hammer and it snapped right off.
IMG_0001.JPG


Once I had the heads off of the cap screws, the tank was easily removed. One of the bolts came right out of the z-bracket when I grabbed it with a pair of vice grips and pulled back hard as I turned it to get it to re-engage the nutplate threads.
IMG_0007.JPG


Unfortunately, the other one wouldn?t re-engage no matter how hard I pulled so I?ll have to replace the nut plate.
IMG_0005.JPG


It ended up not being nearly as hard as I thought it would be but I never would?ve been able to do it without the right angle drill and my homemade centering drill block.

Thanks to everyone who offer help and advice. I truly appreciate it. Sorry if the photos didn?t turn out, it?s the first time I?ve tried inserting photos here.
 
So to follow up...how'd they end up all boogered up in the first place? Were they too long or something like that (thus screwing in past the threads)? Something else?

Just curious to know how that happened to begin with, as I'm sure many are (to avoid a similar problem).

TIA!

BTW, that's really good craftsmanship to get that done so cleanly...well done!
 
As far as I can tell, they were simply over tightened and stripped. They appear to be the right length and size. I suppose they might have come from a bad bunch of stock but outwardly the look fine.

I intend to take a real close look at the nutplate to make sure they?re not damaged. I am also going to replace all of the tank fasteners just in case there was a quality issue with the fasteners.

Lyn
 
Might be related.
During my build, I came across a nutplate that just didn?t feel right as I was trying to insert a fastener. Upon closer inspection, I discovered that the nutplate had never been threaded. The sidewalls of where the threads would be were solid material as if that step in the manufacturing process had been skipped. Over the remaining course of the build, I would carefully inspect each nutplate for proper threads prior to installing it and sure enough, I came across a couple more of varying sizes. I imagine that forcing a fastener into a nutplate that had never been properly threaded could mugger it up pretty good.
 
As far as I can tell, they were simply over tightened and stripped. They appear to be the right length and size. I suppose they might have come from a bad bunch of stock but outwardly the look fine.

I intend to take a real close look at the nutplate to make sure they?re not damaged. I am also going to replace all of the tank fasteners just in case there was a quality issue with the fasteners.

Lyn

That's gotta be hard to do, at least if you're tightening by hand. Those are AN-3s, right? So the torque should be IIRC 20-25 INCH-pounds.

Unless they were tightened with a power tool that was set wrong...?
 
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