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Technical Can you seal a gas tank...from the outside?

Discussion in 'The Hokey Ass Message Board' started by DRAFTStudio, Mar 25, 2019.

  1. DRAFTStudio
    Joined: May 27, 2015
    Posts: 13


    I know internal gas tank sealers exist and there's always brazing / lead to fill pin holes. But I was curious... would stripping a motorcycle gas tank to metal, externally, then laying down a few coats of epoxy primer sealer fill pinhole leaks from the outside?

    Or, technique number B, could you use tank sealer (Caswell / Red Kote) on the outside of the tank then paint over it?

    ...just curious really. It seems it would be much easier to remedy sealer issues on the outside of the tank instead of having to get that crap off internally.
  2. oldolds
    Joined: Oct 18, 2010
    Posts: 2,939


    Think about it this way... Chew a piece of bubble gum, blow a bubble. Now take the gum out of your mouth and try to blow the same bubble. Tell me how that works for ya.
  3. fastcar1953
    Joined: Oct 23, 2009
    Posts: 2,050


    They rust from the inside out . will still get rust in fuel line.
  4. winduptoy
    Joined: Feb 19, 2013
    Posts: 1,901


    Can you patch a tire on the outside?
    Sure, just don't expect it to stay inflated
    Bandit Billy and VANDENPLAS like this.
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  5. sometime around 1990, I cut the gas tank apart on my 39 gmc, sandblasted the whole thing, mig welded as many of the holes up as I could and closed up the holes I cut to blast the inside. covered the welds in bondo, then fiberglassed resin and mat on the out side. almost 30 years, and over 100k miles............and it sits under me in the cab.
  6. ROADSTER1927
    Joined: Feb 14, 2009
    Posts: 2,713


    All metal body putty stands up to gas. Gary
    lothiandon1940 likes this.
  7. BJR
    Joined: Mar 11, 2005
    Posts: 6,253


    Cover the outside with fiberglass cloth and resin. Should last for years.
  8. Rusty O'Toole
    Joined: Sep 17, 2006
    Posts: 9,068

    Rusty O'Toole

    You could fibreglass the outside but would need to seal the inside to stop rust or rust flakes will clog up your fuel filter.
  9. blue 49
    Joined: Dec 24, 2006
    Posts: 1,226

    blue 49
    from Iowa

    I built a tank and had some porosity in the mig welds in places. I plugged the gas line outlet and taped up my vacuum cleaner hose to the filler inlet. With the vacuum on, I brushed sloshing sealer on the seam in the bad places. I could see the sealer being pulled into the leaks. When I couldn't see it being pulled in anymore, I moved on. It worked well, although I did slosh the inside, too.

    j-jock likes this.
  10. Ebbsspeed
    Joined: Nov 11, 2005
    Posts: 4,946


    While gas tank sealing in automobile applications is similar to that used for motorcycles, maybe the guys over on the Jockey Journal might have more specific information since your post is about a motorcycle tank.
  11. Mr.Racer
    Joined: Jul 8, 2018
    Posts: 17

    from Ohio

    Used JB weld on a tank that was leaking gas while I patched it. Gas was running down my arm while I stuffed it up in there. Not sure how long it lasted. Neighbor kid needed a quick fix.
  12. oldiron 440
    Joined: Dec 12, 2018
    Posts: 1,495

    oldiron 440

    I used Everglades to fix a large leak with fuel running out probably 40 years ago, I made the mistake of tapping it in like you would to fill a rust hole in a fender, can you say OH SHIT!
  13. s55mercury66
    Joined: Jul 6, 2009
    Posts: 3,980

    from SW Wyoming

    I have used fiberglass resin alone to seal pinholes in several H-D tanks. It held up quite well for me, and I wish I had known how well it worked 40 years ago. These were just small holes though, nothing as large as the head of a pin.
  14. brigrat
    Joined: Nov 9, 2007
    Posts: 5,080

    from Wa.St.

    ClarkH likes this.
  15. jnaki
    Joined: Jan 1, 2015
    Posts: 4,278


    Anything can be done if the outside area of the metal is clean. If there is a surface grabbing area for the fiberglass mat shreds, multiple cloth layers, & resin, a gas tank can be fixed and last for quite some time. For us, it was a temporary solution, since we only had 30 days to stay and surf in Kauai, one summer. But, after talking to the owner of the house later in So Cal, the gas tank lasted for years.

    As far as your gas tank, it will be front and center, so what ever is covering the fix, has to be super smooth for the paint. Our leak was under a 1962 Rambler and it looked like many of the surfboard repairs I had made over the years. But, after installing and finishing the surface, the black paint made it look like it came from the factory.

    The immediate solution was to weld up the hole, but I did not like the situation of gas fumes in and around the opening and the smell of the empty tank. We could not wait for days to have the gas dry up and then use a welder to fix the leak. So, alternatives were chosen. It all worked out in the end and only one day was lost to the repair.

    tb33anda3rd likes this.
  16. 5brown1
    Joined: Apr 13, 2008
    Posts: 196


    Seal All will stop gas leaks. I used it to stop a seeping gas tank leak and painted over it. Multiple coats can be
    applied. I first learned of it when my hardware guy told me he saw a fellow stop a leak on a
    motorcycle gas tank while it was leaking.
    Blue One likes this.
  17. khead47
    Joined: Mar 29, 2010
    Posts: 1,612


    Ivory soap. No shit !
  18. A better ? Can ya put a band aid on a heart attack ?
  19. blowby
    Joined: Dec 27, 2012
    Posts: 6,408

    from Nicasio Ca

    Caution on fiberglass. Countless factory fiberglass motorcycle tanks, made before the ban on glass tanks in '75, have been ruined by ethanol. Polyester resin just won't hold up to it. It's been a boon for the tank sealer business as well as metal tank builders. Epoxy resin is the preferred type for fuel applications. And if considering a specific 'tank sealer' coating, make sure it is advertised as ethanol safe.

    All that assuming you plan to use ethanol..

    Yes, soap and seal all work well in a pinch...
  20. Do it right or replace the tank, there is no magic fix for a leak. HRP
    Rich S. likes this.
  21. rs57
    Joined: Apr 9, 2008
    Posts: 134

    from oklahoma

    FD3CFF5B-4CE8-4B43-BCD7-A553319AE2B5.jpeg 629430C2-7CA0-4462-B302-3FB406A51202.jpeg
    I have had good luck with the permtex
    Leak repair material
    Also if you can pull it and Clean it
    Red - kote is great for sealing and coating inside of tank
    But nothing’s better than a new tank
    As some of the guys have said.
    If it has several pinholes though
    It’s more than likely so thin best just replace it
    Last edited: Mar 26, 2019
  22. Desmodromic
    Joined: Sep 25, 2010
    Posts: 571


    I've been wondering since alcoholized fuel has been mandated, if problems have been experienced and expensive remediation required in other applications where FRP gas tanks have been commonly used. For example, gasoline stations have frequently used FRP buried tanks. Also, it has been common practice to use FRP gas tanks, often integral with and using a portion of the hull as part of the tank's enclosure. Does marine gas contain methanol? I wasn't aware that FRP tanks were banned; is this just for motorcycles? Cars? I have an old Bultaco with an FRP tank, that was built long before anyone anticipated the contamination of gasoline with ethanol.
  23. Heavy Old Steel
    Joined: Feb 1, 2019
    Posts: 54

    Heavy Old Steel

    I sealed an after market H-D tank that was never used before I got it but leaked on a seam, used JB weld and it lasted years before I sold the bike.
  24. Why not weld up the hole or find someone that can. HRP
  25. blowby
    Joined: Dec 27, 2012
    Posts: 6,408

    from Nicasio Ca

    Marine gas must contain ethanol, there's a lot of discussion about it on the web. Don't know about gas station tanks, I know a lot of them have been dug up and replaced around here but don't know why, assume they were leaking for some reason. I have a couple of bikes with glass tanks but I don't ride them often and when I do I drain the gas immediately afterward or use ethanol free gas. What you'll typically see is some outward swelling/bubbling of the tank, most easily seen if the paint is shiny, along the sides. I have seen this swelling go back down if the tank is drained and allowed to harden over a period of time. A friend of mine had his Norton tank start melting during a trip. The goop made it to the carb and the slide started sticking. I had some Marvel Mystery Oil with me and that cured the problem until he got home. I've had varying degrees of success with tank sealers, even the ethanol related ones. Look on Ebay for vintage metal gas tanks made in India, they are doing a booming business. Quality sketchy, apparently getting better.

    Be careful with the Bultaco tank! And if that desmo you have is an early Ducati be careful with that one too.

    I'm only aware of the ban on motorcycle tanks and it wasn't for melting, it was for fires in crashes.
  26. I have used Seal All for difficult repairs, including gas tank punctures and leaks for over 50 years. It is an MEK based product, so use gloves. On one emergency repair, the puncture in the tank was over 3/16 inch in diameter. I put a glob of Seal All on a piece of cardboard and held it to the puncture until I thought the product had set. The fix held for the remainder of the time I had that old beater.
    lothiandon1940 likes this.
  27. Gerrys
    Joined: May 1, 2009
    Posts: 327


    It will work for pinhole leaks in good metal. If you have any thin spots you will only have the thin metal with however may layers of epoxy until it rust through. Then you have have a epoxy paint tank. Would you want to be riding a bike with n epoxy tank full of gas?
    scrap metal 48 likes this.
  28. I am not sure you can paint over tank sealer. The tank sealer that was in my Harley tanks came out in a sheet when I removed it.

    Soldering is always a good way to repair a bike tank. Use a soldering iron not a torch.

    Epoxy is not real fuel proof. it is fuel resistant but will soften and pull loose. I ran from New York to the Ozarks using 2 part epoxy once. End of the day each day it would be saturated and leaking and I would have to drain the tank and replace it.
    lothiandon1940 likes this.
  29. G-son
    Joined: Dec 19, 2012
    Posts: 623

    from Sweden

    They used to make fuel tanks in fiberglass boats as a part of the boat, out of fiberglass and a suitable resin. used to work well, but with all the cr*p they put in the fuel today problems with the resin dissolving is getting more common. I'd be careful, and very picky when choosing resin for a job like this.
  30. Roger O'Dell
    Joined: Jan 21, 2008
    Posts: 1,080

    Roger O'Dell

    Click-patch is a temp repair for heavy jets

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