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  1. #1
    Senior Member peugeot mongrel's Avatar
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    Some frame repair advice needed

    Hi
    I just got a pretty rough 1982/83 Colnago Superissamo that I feel I need to rescue. It is full chrome under the paint. Pretty sure it is original paint and decals so I get to see first hand how it came from the factory. All the exposed chrome is poor, gone on the top of the fork crown and the tops of the lugs. I have painted a few classic cars & bikes and have the equipment so quality paint is mostly labor and not much in materials cost for me. I'm tracking down local chrome sources with bicycle tubing experience. This bike will be fore me, not to resell.

    I'm asking for suggestions on how to handle this dent if I re-chrome the frame. The dent will be under the paint.
    The dent is 25mm x 15mm x 2.5mm at its deepest.

    1. I am assuming if it is filled with braze it would take chrome and never pop out. Would it weaken it?
    2. Is it possible or practical or safe to "work it" to be not as deep, either from inside from the bottom bracket opening or maybe to pull from the outside by brazing on a lug to pull.
    3. Would it be better to just keep chrome off that part and fill it with a high quality filler (which I can do)?

    I am looking to understand all options before I talk to the man that would do the brazing.

    Any ideas would be greatly appreciated... Marvin










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  2. #2
    Senior Member
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    I'd replace the chain stay and call it a day.
    If you have to force it... you probably shouldn't.

  3. #3
    Andrew R Stewart Andrew R Stewart's Avatar
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    cale mentions the high road, and the best if some one else is riding the bike.

    Middle road is to fill with brass.

    Low road is to use bondo.

    One thing I'd be concerned about is the gauging that usually comes with these chain stay dents. So the middle or the high road is my advice. Andy.

  4. #4
    Senior Member peugeot mongrel's Avatar
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    The chainstay is stamped with CONALGO. That stamped chainstay makes the high road a little higher for me. Filling with brass seems better to me than a body filler. I was mostly wondering if it was possible or practical to push or pull the dent out a little to make it not as deep first, or if that effort would be of no real help.
    thanks
    Marvin
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  5. #5
    Old fart JohnDThompson's Avatar
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    Quote Originally Posted by peugeot mongrel View Post
    Filling with brass seems better to me than a body filler. I was mostly wondering if it was possible or practical to push or pull the dent out a little to make it not as deep first, or if that effort would be of no real help.
    You could try pulling the dent out, if you have access to the proper tools. That tubing is likely more difficult to work than automobile body panels, though, so don't expect miracles. And use lead solder rather than brass to fill the dents; it doesn't need structural strength, and the melting point is far lower than brass so less heat damage to the tube.

  6. #6
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    This is a tough one.

    As mentioned the high road would be to replace the stay. It's certainly a good idea if the bike will be refinished and ridden as it's hard to tell how compromised that stay is. Normally one can roll out a dent some taking the high points out some and making the deepest part of the dent less deep but this will be a challenge given the location and working room around the dent.

    The dent can of course can be filled with either metal or plastic filler and it matters little from a structural standpoint which way you go. There is a tendency to think that filling a dent with metal will give some structural benefit over bondo but the reality is that the metal is just acting as filler and will not make the tube any stronger. The metal will of course be less likely to fail and flake off years down the road but it won't make the stay as new.

    Certainly any brazing work will require that the chrome be removed which can be a monumental PITA. It could flake right off (pretty likely with older Italian bikes) or it might take the forever to sand or blast the stuff off. Any way you look at it brass/silver will not properly bond to the chrome and the heat needed to put the stuff on will cause the chrome bond to fail anyway.

    I think in things like this one needs to decide what they want - a usable bike or an original bike. If you want ti to look good then I'd fill the dent and repaint it. If you want to ride it then I'd replace the stay and make it a good rider.

    dave

  7. #7
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    ^ A good summary and I would only add that the structural consideration, will it be a strong frame after the repair, applies not only to the present owner but to any future owner who might regard the repaired frame as being a good rider.

    Edited to add: I think a good test for the OP regarding the question of using a filler is, "Would you ride the frame as it currently exists?"
    Last edited by cale; 01-17-15 at 11:07 AM.
    If you have to force it... you probably shouldn't.

  8. #8
    coprolite fietsbob's Avatar
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    in Art Metalwork there is a self made black smithed tool called a Snarling iron . in effect its a steel bar in a vise that fits inside something on the other end.

    Hitting it near the vise clamped end causes it to spring back and bang on something from the inside out on the Free end .

    would it be applicable here or affordable? IDK , just throwing it out .. I used the technique on thin non ferrous metals ..



    Hiring a pro, replacing the chainstay, repainting and re decaling & clear coating over it, is the way to go...wont be cheap, but C&V is not about saving Money anyhow..
    Last edited by fietsbob; 01-17-15 at 11:06 AM.

  9. #9
    Senior Member peugeot mongrel's Avatar
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    Thanks all. I am going to build it and ride it as it is. There is no crack and I can see if one starts. This frame can never be perfect. The stay replaced is obviously safer for a fast bike but the stay is Conalgo and date specific with the stamp and the inner crease. So a SL stay isn't a total match. Covering it and letting it go is bad ju ju. I am building it as my fast rider and will eventually paint it. So I have a while to work it out.
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