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Technical I have a question about the flange when building headers

Discussion in 'The Hokey Ass Message Board' started by 36cab, Oct 4, 2019.

  1. 36cab
    Joined: Dec 2, 2008
    Posts: 896

    36cab
    ALLIANCE MEMBER

    I am going build my own fender well headers for a small block Ford. I noticed on headers bought from a shop that the there is usually a flattened welded bead around the primary tube openings on the back side of the flange. Does this flattened bead help the flange seal against the gasket and the head? Or can the primaries on the backside of the flange by welded flush and still get a good seal with the gasket and the head? I am guessing that the flattened bead bites into the gasket and helps with a good seal but I thought I should check with the HAMB experts.
     

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  2. squirrel
    Joined: Sep 23, 2004
    Posts: 55,942

    squirrel
    Member

    Keep in mind that production headers are built in a way that costs the least...that may not be a priority on your headers that you are making.

    A flat flange will seal, too.
     
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  3. Jmountainjr
    Joined: Dec 29, 2006
    Posts: 1,672

    Jmountainjr
    ALLIANCE MEMBER

    If you start with a thick flange that is flat, and don't over heat it during welding, it will seal with everything flush just fine. As Squirrel said, the production stuff is massed produced. The flange may have never been that straight and just having four contact points gives it a better chance of sealing.
     
    The Shift Wizard likes this.
  4. Thinner flange material can benefit from the little bit of raised "ring" because it concentrates the clamping force on the high spots. A decently thick flange shouldn't need any band-aides.
     

  5. On production headers that always leak I have never understood why the raised weld bead didn't encompass the complete bolt hole so you actually got a good clamp force when tightening the bolts.
    I use or make 3/8" flange plates and just do an inside perimeter weld and a light dressing. No leaks.
    Ready to coat Headers 004.jpg
     
  6. jimmy six
    Joined: Mar 21, 2006
    Posts: 14,802

    jimmy six
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    The 3-4 layer Mr. Gasket aluminum gasket help, expensive but hold up well on our dirt car rear crossover headers.
     
  7. squirrel
    Joined: Sep 23, 2004
    Posts: 55,942

    squirrel
    Member

    IMG_1436.JPG

    This is how I did the first set I made...I ground the flange flat, after welding. And then brazed the outer side of the tube/flange joint, to make damn sure it would not leak/break. They're doing fine
     
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  8. 36cab
    Joined: Dec 2, 2008
    Posts: 896

    36cab
    ALLIANCE MEMBER

    Thanks for all of the help. The flanges are 1/4" thick. My buddy is a great fabricator and he will TIG weld everything for me.
     
  9. 41rodderz
    Joined: Sep 27, 2010
    Posts: 6,540

    41rodderz
    Member
    from Oregon

    I think you would be better with 3/8 or 1/2 thick flanges than 1/4.
     
  10. Blue One
    Joined: Feb 6, 2010
    Posts: 11,459

    Blue One
    ALLIANCE MEMBER
    from Alberta

    1/4" is too thin, they will probably warp.
    3/8" is advisable.
     
  11. Marty Strode
    Joined: Apr 28, 2011
    Posts: 8,801

    Marty Strode
    Member

    I use 3/8" flanges, recess weld on the inside, and seal the outside with silicone bronze. IMG_7994.JPG
     
  12. Same here,
    3/8 flanges, filed flat on the gasket surface
    welded inside
    Brazed a fillet on the outside for support
     
  13. wvenfield
    Joined: Nov 23, 2006
    Posts: 5,580

    wvenfield
    Member

    When we made mine we added the ridge on the inside. Sorry, I don't think I have a pic.
     
  14. Paul
    Joined: Aug 29, 2002
    Posts: 16,389

    Paul
    Editor

    Store bought headers are typically assembled and welded in jigs, they stuff the tube through the flange and run a fillet weld around the protruding tube then surface grind it leaving the flat bead.
    When I build headers I bolt the flange to the head in the car, stick the starter tubes in as far as they can, then tack the starter tube to the flange. Then take the tacked together headers off to weld the flanges and bolt them to some loose heads to finish weld. This leaves the tube end flush with the inside of flange, and finish up pretty much like squirrel and others show and describe leaving the gasket surface flush and smooth.
     
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  15. flamedabone
    Joined: Aug 3, 2001
    Posts: 5,441

    flamedabone
    ALLIANCE MEMBER

    I built these the same way Paul is talking about. I have had the same pair of header gaskets on them since 2002. If you let the flat flange do all the sealing, they will never leak.

    [​IMG]

    -Abone
     
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  16. flamedabone
    Joined: Aug 3, 2001
    Posts: 5,441

    flamedabone
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    I have changed a lot of things on the car in the last 18 years, but still have the same header gaskets.

    [​IMG]

    -Abone
     
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  17. 41rodderz
    Joined: Sep 27, 2010
    Posts: 6,540

    41rodderz
    Member
    from Oregon

    Check header manufactures as well as epay. They should have what you need. Do not accept 1/4 " .
     
  18. lake_harley
    Joined: Jun 4, 2017
    Posts: 2,160

    lake_harley
    Member

    Ooohh, Marty! That's a beautiful 215!...or maybe the Cu. In. have been coaxed up a bit? I made a set of the individual flanges for my 215 Olds to build lakes headers. Working with just a hole saw or two and a die grinder with a 1/2" carbide cutter, it took a LOT of time to match up what I recall was a really odd-shaped exhaust port.

    Lynn
     
  19. daliant
    Joined: Nov 25, 2009
    Posts: 692

    daliant
    Member

    Store bought headers shown in the OP's picture in the first post are notorious for leaking, thin flanges, loosening of bolts, blowing out gaskets...etc.
    Factory manifolds on the other hand are nice and thick, machined flat, installed without gaskets, don't leak, etc..
    So... you be the judge.
    My money is on a nice flat and thick flange to do the best job.
     
  20. Mr48chev
    Joined: Dec 28, 2007
    Posts: 33,861

    Mr48chev
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    Jet96 likes this.
  21. I built mine the same as Jim. It was a long time ago, and used an oxy/acetylene torch, but the procedure was the same. Weld the flange side first, weld the outside of the flange to the pipe, and then grind the mating surface smooth.
    The reason I like grinding the mating side smooth, is that because header gaskets are fatter, and made of softer material, having the ridge on the header tears up the gasket over time and causes a leak.
    My trick for tightening, is to tighten from the center to the outside in small increments just like you would torque a cylinder head.
    I have been running headers of all brands for over 59 years, and rarely have had a problem (other than fitting with the cheaper brands).
    Bob
     
  22. seb fontana
    Joined: Sep 1, 2005
    Posts: 8,444

    seb fontana
    Member
    from ct

    In a 6 cyl build I made a exhaust manifold and used the typical header gasket but made .030 thick copper to duplicate the raised bead on a typical header and used hi temp rtv to glue them in place..
     
  23. sunbeam
    Joined: Oct 22, 2010
    Posts: 6,214

    sunbeam
    Member

    If you are worried bolt the flange to a head when welding
     
  24. Blue One
    Joined: Feb 6, 2010
    Posts: 11,459

    Blue One
    ALLIANCE MEMBER
    from Alberta

    If you think that will prevent warpage you’re mistaken.
    As soon as you unbolt it, residual stress takes over a the warpage is there anyway.

    Maybe less than without doing that but not completely eliminated.
     
  25. gimpyshotrods
    Joined: May 20, 2009
    Posts: 23,264

    gimpyshotrods
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    I always mill my flanges flat after final welding. If you don't have access to a mill, buddy up to someone that has one, or find a hod rod friendly machine shop.

    Always use the thickest flanges possible.
     
  26. squirrel
    Joined: Sep 23, 2004
    Posts: 55,942

    squirrel
    Member

    ...unless you're building a race car, then a thin flange is OK, because leaks don't matter so much, and steel is heavy
     
  27. Paul
    Joined: Aug 29, 2002
    Posts: 16,389

    Paul
    Editor

    After the header is fully welded and cleaned up I bolt it to the engine and heat the primary tubes at strategic areas to relieve the stresses, usually near bends, then final clean and paint.
     
  28. Paul
    Joined: Aug 29, 2002
    Posts: 16,389

    Paul
    Editor

    I try hard not to have any leaks, I want all the exhaust to exit the tail pipe behind me, leaks at the flange can mask other noises like loose valve adjustment or pinging, enough clean air pulled into the exhaust through scavenging can make very annoying backfire racket and even destroy a muffler.. I guess I'm talking mostly of street driven cars..
     
  29. squirrel
    Joined: Sep 23, 2004
    Posts: 55,942

    squirrel
    Member

    Yes, I agree about street driven cars...but there's more than one way to build a car, and the requirements vary. Thicker flanges are generally better, but not always. They add weight and cost, and may or may not be necessary for the particular car you're making headers for.
     
    Paul likes this.
  30. Paul
    Joined: Aug 29, 2002
    Posts: 16,389

    Paul
    Editor

    absolutely agree
     

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