Fuel tank gasket goo?

Discussion in 'Boatbuilding' started by groper, Oct 29, 2013.

  1. groper
    Joined: Jun 2011
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    groper Senior Member

    I have some stainless tank caps made up for my fibreglass tanks... i need to bolt them down onto a seal of some sort.

    I was thinking of running a bead of goo around the tank top and setting the waxed cap in place with only light tension on the bolts. Then once fully cured, remove the wax and bolt it down tight onto the preformed goo gasket... will this produce a good result?

    What type of goo shall i use for long life and exposure to gasoline vapours etc?

    Heres a pic showing the cap in the tank, and a second cap on top...

    [​IMG]
     
  2. Mr Efficiency
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    Mr Efficiency Senior Member

    How about a gasket cut from nitrile rubber sheet ?
     
  3. groper
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    groper Senior Member

    Yeah i did think of that... $50 from the local supplier, so i was investigating other options which might work out a bit cheaper - yeah i know, im a tight a s s :D
     
  4. CDK
    Joined: Aug 2007
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    CDK retired engineer

    Use any of the Sikaflex polyurethane compounds. Once cured they are impervious to any fuel.
     
  5. michael pierzga
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    michael pierzga Senior Member

    You could use sika.

    It would be wise to use rubber tear drop spacers between tank top and fuel apparatus flange to prevent the compressed joint and its new gasket from being Sika starved.

    Perhaps a 2mm sika type gasket

    Mold release on one surface would be wise or you may never be able to dissemble in future

    A dip stick stand pipe is a very nice detail

    Threading the fasteners into your tank substrate will require thought.

    Fuel fill, intake and return pipe fittings at 45 or 90 degrees may make plumbing routing less space consuming

    Air vent fitting for refueling should be large diameter to prevent troublesome blow back on deck


    http://[​IMG] subir fotos online
     
  6. groper
    Joined: Jun 2011
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    groper Senior Member

    I've been reading through the sika data sheets and even the chemical/solvent resistant goo called sika tank only says upto 24hour immersion in gasoline based on their 3 month tests... Most goo I'm looking at don't recommend contact with petrol?
     
  7. michael pierzga
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    michael pierzga Senior Member

  8. Petros
    Joined: Oct 2007
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    Petros Senior Member

    most sealant or goop will not hold up to petrol long term. even in the auto industry they usually use a rubber gasket on fuel fittings on the tank, they are installed dry. Even than, some rubber sheet is not fuel resistant, so you have to purchase it specifically for use in a fuel system. I would use a rubber gasket made of the correct material, Permatex makes a fuel resistant goop, but I do not think it is meant to be used instead of a gasket, but along with one.

    This is not an issue to take lightly, even a small fuel leak in a boat can have serious consequences.
     

  9. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    There are two parts to this solution, the first is polyester urethane goo and the industry standard is PermaShield by Permatex. This is a flange and/or gasket seal (dressing) and can be used as a gasket maker, though it's not as good as use as just a dressing, with a gasket. EPDM (propylene) gasket material is the common choice, though some formulations aren't as good as others. Polyurethane is a better choice for immersion, but again depends of formulation.

    RTV's and cork are common, but not for immersion, just incidental fuel contact. Neoprene or nitrile can be better choices in this regard.

    Ultimately, I think your best choice is hydrogenated nitrile sheet, cut into a gasket and sealed with Permatex on the gasket to tank top side, but naked on the cap to gasket side. This will permit removal for inspection, yet a good mechanical seal when you bolt it back down. Unfortunately, buying this material in small quantities is difficult, as it usually comes on 54" rolls, but I'll bet a sample from a prospective supplier might be big enough to do the job. I have a number of sources for raw gasket materials in the USA, but this does no good to you. Look around and see who can provide raw gasket supplies down there.
     
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