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Thread: need help with aluminum fuel tank bung

  1. #1
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    need help with aluminum fuel tank bung

    hey guys im sure some of you are experts in welding these little things. im a amateur at best and maybe not even amateur. anyways I was thinking there must be some kind of technique to welding these AL bungs into fuel tanks. my first attempt to weld it in was a disaster. it welded in fine but when I went to screw in the cap I realized the bung was extremely distorted out of round and the cap wouldn't even screw in 1 thread. I have a couple more bungs, so ill remove the one I screwed up and try again.

    part of my problem may have been the welder setting and the other problem was likely my welding technique or lack there of. machine was on 180 freq if I recall. from previous projects im still using a bottle of 25/75 he/ar and I have cfh set pretty well. amps were set good.

    I figured most of my problem was because I put one tack weld at the 12 clock position and one at the 6 clock position then just welded continuously around the circumference. seems to me like this is the reason the bung ended up like a oval HAHA. what if I put four tack welds spaced evenly then welded the circumference in smaller increments so it doesn't have as much chance to pull out of round ? ive included some photo to show what I meen. I was thinking to leave the cap in while welding so it holds the shape but with my luck it will get seized in and ill have to cut the whole bung out again. so whats the secret to welding these little buggers in ?? btw the first photo is with the bung in a piece of cardboard just to demonstrate how it sits in the top of the tank just incase you weren't sure how it was positioned
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  2. #2
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    Re: need help with aluminum fuel tank bung

    I'd post pics of the weld too.
    What amps did you run? What flow rate? Balance?
    Dave J.

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  3. #3
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    Re: need help with aluminum fuel tank bung

    I do these all day long. You basically overheated it.
    Tack it in 2 or 3 places and weld about 1/4-1/2 of it. If need be put a chunk of copper on top of it for a few minutes and walk away while it cools.
    And move faster. I can do about 3/4 around in one pass, rotate and do the last 1/4 and toss it on the bench or floor to suck out heat and it won't warp.
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    Re: need help with aluminum fuel tank bung

    I would guess you overheated it too. I've done a few of them, and I tack it in 2 places and then weld it up in 3 or 4 passes. I had the machine set at round 140A if I remember correctly welding a bung to 1/8 aluminum. Remember your AR/HE mix should give you about 25% more heat, so make sure you turn down the power a little bit from what you would run with straight argon.
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  5. #5
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    Re: need help with aluminum fuel tank bung

    thnx for the help. ya I knew I overheated it but didn't know if there was some secret to the sequence of how much to weld between intervals. since this is my first go at a bung ill probly tack it in four even spots and that will break it down into smaller chunks. im welding it to 1/8" new 6061 plate. any tips on what I should use on the freq ? figured near 200 would be good last time but maybe I was wrong. seems like I have balance on 70 or so.

  6. #6
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    Re: need help with aluminum fuel tank bung

    Freq isn't going to make or break it. It's all preference. I can do that thing at 200hz or at 50hz. Doesn't matter. However I prefer to be 80 - 100 range.
    Get rid of the helium. That is going to hurt you more than help you. Save it for when you need it.
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  7. #7
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    Re: need help with aluminum fuel tank bung

    I weld aluminum bungs (3"-4" dia) to 1/8" all the time and use close fitting steel plugs above and below the bung with a 3/8"-24 bolt clamping the two plugs together with the bung sandwiched between them. The lower plug has flats on the sides so it has just enough clearance to fit through the bung after welding. I also have them connected with a small ball chain lanyard, so all I have to do is remove the bolt and lift the plug up and out of the bung after the weld is complete. It works well, reduces the number of tacks needed and pretty much eliminates distortion. I can get a pic tonight if that isn't clear.

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    Re: need help with aluminum fuel tank bung

    Stick a tap in there after welding. Practice, practice and more practice is how you get better

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    Re: need help with aluminum fuel tank bung

    Same thing happened to me. I just ran a tap through it. The next time I did another one exctly the same way with the same settings but I moved even faster. That one I did not have to run a tap in it. I have found the sweet performance weld in alum bungs require no tapping afterwards. Maybe they tap these a little "loose". Who knows.
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    Re: need help with aluminum fuel tank bung

    If you have to tap it after you are doing it wrong
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    Re: need help with aluminum fuel tank bung

    It's a really good idea to run the tap through. If it's cuts you know it got a little distorted

  12. #12
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    Re: need help with aluminum fuel tank bung

    Quote Originally Posted by LimitedSlip7 View Post
    I weld aluminum bungs (3"-4" dia) to 1/8" all the time and use close fitting steel plugs above and below the bung with a 3/8"-24 bolt clamping the two plugs together with the bung sandwiched between them. The lower plug has flats on the sides so it has just enough clearance to fit through the bung after welding. I also have them connected with a small ball chain lanyard, so all I have to do is remove the bolt and lift the plug up and out of the bung after the weld is complete. It works well, reduces the number of tacks needed and pretty much eliminates distortion. I can get a pic tonight if that isn't clear.
    I think a pic of it would be excellent
    Dave J.

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  13. #13
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    Re: need help with aluminum fuel tank bung

    im always looking for a better way. a pic of your fixture would be cool. but im hoping i can get it done with a few extra tack welds and some patience.

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    Re: need help with aluminum fuel tank bung

    Quote Originally Posted by motolife313 View Post
    It's a really good idea to run the tap through. If it's cuts you know it got a little distorted

    Thats a good tip.
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    Re: need help with aluminum fuel tank bung

    Hmmmmm As mentioned you must have over cooked them....I dont see that type of bung so i dont know the contraction rate
    but typically they dont shrink to where they dont work?


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  16. #16
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    Re: need help with aluminum fuel tank bung

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  17. #17
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    Re: need help with aluminum fuel tank bung

    Dumb question. Where are you guys purchasing these aluminum bungs from???

  18. #18
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    Re: need help with aluminum fuel tank bung

    I get my bungs and caps from a company called Pro Werks. I've occasionally had an issue with bung thread to cap thread clearances, but for the most part their stuff is high quality and decently priced.

  19. #19
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    Re: need help with aluminum fuel tank bung

    Quote Originally Posted by LimitedSlip7 View Post
    Name:  20160224_174655.jpg
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    That is very slick - thanks for the pics - the written description didn't do it justice
    Dave J.

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  20. #20
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    Re: need help with aluminum fuel tank bung

    That looks like complete overkill
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    Re: need help with aluminum fuel tank bung

    that holding device looks like a good idea.

    i was getting my bungs from ebay but theres alot of other places they can be found

  22. #22
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    Re: need help with aluminum fuel tank bung

    What size do you guys want, I sell a few different kinds
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    Re: need help with aluminum fuel tank bung

    Does that tool you made lock the bung in place so it can't move and you can get a few tacks on it?

  24. #24
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    Re: need help with aluminum fuel tank bung

    Quote Originally Posted by Gamble View Post
    What size do you guys want, I sell a few different kinds
    what size how much? Do you make them?

  25. #25
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    Re: need help with aluminum fuel tank bung

    Right now I have 1.5" and 1 5/8" and 1" is on back order for a bit. Toying with the idea of stocking 2"
    I will grab some pics shortly
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