Cracks weldable on Pre war frame ?

Discussion in 'Motorized Bicycle General Discussion' started by MotoMagz, Jan 24, 2012.

  1. MotoMagz

    MotoMagz Active Member

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    So I was stripping down my frame for paint when I noticed 2 cracks.One on each side of the bottom bracket.I'm sure I can get someone to weld them,but will it last.I am worried about vibration and the the welded areas.As you can see in the photos the cracks are not on any welds.They are right in the metal.Tell me what you think.I think I'm bummed!
     

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  2. The_Aleman

    The_Aleman New Member

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    Kinda looks like that is a seam, not necessarily a crack, although there does appear to be cracking.
    I can't tell you if you can weld it or not, but I don't think it's a problem.
     
  3. MotoMagz

    MotoMagz Active Member

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    YES it is a seam.The cracks are opposite of each other so I would go with your answer of a seam not a crack.Which already sounds better.
     
  4. 2door

    2door Moderator
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    A welder proficient at TIG welding could repair those cracks easily. Done right, the weld will be stronger than the surrounding metal.

    My concern would be the inside diameter. If I'm seeing it correctly that's exactly where the inner bearing race will need to fit. That I.D (inside diameter) will need to be precise for a good fit.
    Good luck and let us know where you go from here.
    Tom
     
  5. bairdco

    bairdco a guy who makes cool bikes

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    i think it should weld up ok. the original frame's were brazed back then, so you might have to grind off all the brazing if it's in the way for the new weld. i'd bring it to someone who knows what they're doing and ask.

    as Tom said, the cracks are in the bottom bracket shell, where the bearing cups press in. if they BB shell is stretched out and the cups fit loose, you could have the welder tack them in for you. shouldn't hurt it, and you're not gonna pedal much anyways, right?
     
  6. scotto-

    scotto- Custom 4-Stroke Bike Builder

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    Or just braze it.....it will be fine.

    dnut
     
  7. thegnu

    thegnu New Member

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    one thing to remember any metal that has begun to "stress crack" like that has lost its strength , i would clamp those shut using band clamps weld them from the inside finish those welds smooth an then cut small peices out of a scrap bottom bracket an lay them over the top side an weld them on for the added strength. I have seen cracks similar to that "move" to one side or the other of the weld in the past , if you repair it this way you will never have another concern about that area.
    Gary
     
  8. Ibedayank

    Ibedayank New Member

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    to properly fix a crack first you need to stop the crack from growing. Just welding/brazing over the top will not be enough. You have to drill out the end of the cracks and V out the crack so you can get a new weld all the way through the metal. If its a brazed frame it must be brazed or you will weaken all the other brazing at that joint.
     
  9. MotoMagz

    MotoMagz Active Member

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    Okay I am going to prep the area.I will grind it out.I guess I will continue a 1/4 inch beyond the the end of the crack.I'm just going to get the grinder out and place the blade in side the crack which should clean it up just fine.Then I can V out the top of the crack.Idebayank if I weld this area that is not brazed it is just a crack(s) in the frame it will weaken all of the of the brazing on the rest of the frame???? Is this correct
     
  10. scotto-

    scotto- Custom 4-Stroke Bike Builder

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    In this situation, brazing will fill the cracks and give it enough strength for the application. It looks as though the cracks were caused by someone pounding too large of bearing cup into the bottom bracket shell. This is only a high-stress area if you're standing on 181mm cranks and are a real hammerhead such as Lance Armstrong. Get the picture?

    dnut
     
  11. Ibedayank

    Ibedayank New Member

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    you MUST DRILL a hole at the end of the cracks.
    if you are VERY careful controlling the heat by using wet rags on the parts you are not welding you can do it but the area can NOT have any brazing rod/brass color showing it will weakin the weld
     
  12. scotto-

    scotto- Custom 4-Stroke Bike Builder

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    Weld away!

    .wee.
     
  13. maniac57

    maniac57 Old, Fat, and still faster than you

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    On material that thin grinding a v-groove is optional. A good welder can control the current flow well enough with a TIG to avoid any inside diameter issues while still getting full weld penetration. Not a problem.
     

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