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Welding/Repairing cracks on car frame

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  • Welding/Repairing cracks on car frame

    Im doing some repairs on the front end of a drag car, and were I am working the frame has some cracks in it. I was always told to drill a small hole at the end of the crack to prevent it from spreading, once thats done then it can be welded. Just wondering if this is true or if anyone has any other suggestions. Anything will help. Thanks.

  • #2
    ya u can drill your holes if you want the best bet is to remove all weld metal that is cracked. If its not the welds ,gough the cracks out with a small zip wheel or sumthin like that evan a file cause u are working on a tube chassis car or no?

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    • #3
      In the aviation world on tubing structures, the normal procedure is to drill the ends of the crack as you mentioned, and installing a sleeve over the cracked area and welding the sleeve in place. There is actually a very detailed manual on tubing repair titled AC43.13-1B do a google search and download the PDF from the FAA. Tubing repairs start at page 4-80 I believe.
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      • #4
        On light truck frames, the procedure is similar to what was mentioned for tubes.

        A crack on a flat surface is reinforced by a diamond shaped plate. Same thickness as parent metal. If the crack is 3" long, make a square that is 3.5" in the diagonal and have the diagonal cover the crack (you will have to grind down the weld - so a 100% penetrating weld is preferred.)

        The idea is to spread whatever stresses caused the first crack around a bit.

        If you weld a square plate over the crack, with square edges parralel to the crack, the same forces that made the first crack will now be concentrated at the edge of the square plate. If you rotate that square plate 45 degrees, the stress risers will be at 45 degrees to the original crack - effectively spreading them out.
        ''/\
        / | \
        \ | /
        _\/

        Where the vertical line is the original crack. Call it a diamond, call it a square rotated, (call it a rhombus). whatever.
        Last edited by con_fuse9; 04-14-2010, 09:10 AM.
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        • #5
          Whatever method of repair that you choose, you really should invest in a penetrant dye check system. These are cheap compared to other crack detection methods and do a pretty good job. The dye system will show you how far the crack really goes and where it starts and stops, so that you may repair the entire cracked area.
          Sometimes there's no second chances.

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          • #6
            Originally posted by davinci2010 View Post
            Whatever method of repair that you choose, you really should invest in a penetrant dye check system. These are cheap compared to other crack detection methods and do a pretty good job. The dye system will show you how far the crack really goes and where it starts and stops, so that you may repair the entire cracked area.
            Great until you go to get all of that ultra thin oil out of the crack for cleaning
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            • #7
              Point taken. I prefer magnaflux, but he's probably not going to go that far. Or you could just drill holes where you think the crack ends and weld it up with the unidentifiable rod you found in the back of your uncle's garage, then go 200 m.p.h. down track. You weld on aircraft, you know what I was getting at.
              Last edited by davinci2010; 04-15-2010, 02:51 AM.
              Sometimes there's no second chances.

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              • #8
                Originally posted by davinci2010 View Post
                Point taken. I prefer magnaflux, but he's probably not going to go that far. Or you could just drill holes where you think the crack ends and weld it up with the unidentifiable rod you found in the back of your uncle's garage, then go 200 m.p.h. down track. You weld on aircraft, you know what I was getting at.
                Yep, I know. So many things are a "double-edged sword" when it comes to repairs. On aircraft repairs, standard methods say you dont even weld the crack up. Just stop drill it ( just beyond the end of the visible crack ), and weld the reinforcement patch/sleeve over it. There is a lot more to it than that though as it depends on the crack location, and size.
                "Better Metalworking Through Research"

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                • #9
                  Agreed. I've had mixed results with stop drilling in non critical projects when using only my eyes to identify the start and stop of a crack. I think if it is a tube chassis, and tech o.k.s the location of the repair I would go with your idea and sleeve it. He did not specify what class he is running in, or where in the front end the crack is. Tech inspectors may get a little picky on this one, even if the frame is not ever cut or actually seperated. They may consider a sleeve a splice or a joint. I would check with a tech inspector first.
                  Sometimes there's no second chances.

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                  • #10
                    Is it M/S or C/M?

                    If the crack is not in the roll bar/Cage area I'll bet you will find the Tech guy won't say anything. I could be wrong, they may if it is an obvious hazard, but most times they are just interested in the tubes that protect the driver.
                    The way it was explained to me......, they don't care if you wreck, only that you survive if you do.
                    If you look at an SFI chassis book, they only diagram the cage itself, However it is obviously in you best interest to make the repair safe.

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