Patching up a broken K2 frame

Discussion in 'Mountain Bikes' started by LJS, Nov 21, 2006.

  1. LJS

    LJS New Member

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    I have a 2002 K2 Attack 2.0 that broke its frame on the drive side chainstay, where it is welded to the drop-out end piece. The frame, or rather the weld, broke in two while trail riding after about 2 1/2 years of frequent use. The weld was probably weak as the metal of the chainstay tubing and the drop-out casting didn't show much heat penetration from the weld, it was just being held by the filet built up around the joint. I decided to try and salvage the bike as a winter training bike to use on an indoor trainer. The main triangle on the K2 has a five year warranty but the rest of the frame, on the full suspension portion, just had a one year warranty. My K2 dealer checked to see if a chainstay was available and found that K2 couldn't supply the part, and didn't have a complete frame to purchase either. K2 has recently sold their bike brand to Worldwide Cycle Supply, which also owns Iron Horse bikes, so K2 has gotten out of the bike business even though the Brand name survives
    With an aluminum frame there are not many options for repair. After the frame broke, I rode the bike home 6 miles, and was able to see how the joint was being stressed, as it moved around while riding. Pedaling tended to pull the broken joint back together, while coasting let the joint and rear wheel wobble around more. To repair it, I drilled and tapped two holes in the drop-out casting and screwed in two 6 inch 10/24 bolts, so that the other end would slide inside the open end of the chainstay tube as the casting was put back into position. The bolts were threaded into the casting as far as the tap would go, about an inch and a quarter. Then I filled the chainstay tube with J-B Weld to glue the rest of the length of the bolts into the inside of the chainstay, and clamped the joint together. Since most of the stress from weight on the bike tends to slide the joint straight up, these bolts should handle the main stress on the joint pretty well. The bike is now relegated to the trainer, and the repair is holding. I don't think I would trust it back on the street or trail again, but it will be interesting to see how long the repair lasts. Either the epoxy will begin to wear around the bolts, or the drop out casting will start to crack around the treaded holes drilled in it. The trainer actually puts stress on this area of the frame as it is clamped in by the rear axle skewer. If it lasts the winter on the trainer, I'll be tempted to take it out on the trail again to see how long it will hold together. Maybe it will last 2 1/2 years.
    Has anyone had any luck patching up an aluminum frame?
     
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  2. AngoXC

    AngoXC New Member

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    Its down here in Australia but these guys have alot to say about alluminium repairs...they claim they can fix anything.
     
  3. sogood

    sogood New Member

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    May not be relevant to OP's requirements for the bike. But I can't imagine a repaired tube could have the same mechanical (tensile) property as the original. So in this case, one side of the frame would be more or less stiff than the other and I would think would alter the ride characteristics.
     
  4. lumpy

    lumpy New Member

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    I would take it to a good welder and have them fix it before taking out on the trail - think aviation welder quality.

    I personally would never trust it outside and be worried about a failure at a critical time. I'd toss it in the recycle bin and get another frame.
     
  5. AngoXC

    AngoXC New Member

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    In the site I posted above, they not only re-weld the frame but gusset it. That would probably be the stongest option...and im not sure about the tensile strentgh but with not only a new weld, but a gusset, one would assume the loss in strength would be minimum.
     
  6. sogood

    sogood New Member

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    I would not worry about the strength if they really reinforce the weld. However, with one side of the rear triangle more stiff than the other, I am not sure what kind of dynamic changes there would be for the frame. Given the asymmetry of the two sides, would it still be stable in a fast descent?
     
  7. ding

    ding New Member

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    hi mate im new to this so..if your in the uk try www.apibikes.com they specialize in spraying mostly but also do a great deal of frame repair work. i havent tried them myself but im going by whats on thier website.
     
  8. LJS

    LJS New Member

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    Thanks for the link, very interesting. I have'nt found anyone in the states that seems interested in aluminum frame repairs.

    LJS
     
  9. alfeng

    alfeng Well-Known Member

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    You should consider getting a new swing arm as an alternative to re-welding it.
     
  10. bigpedaler

    bigpedaler New Member

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    MBA published an article a couple years ago about fixing frames; there's a company out there that does it (the problem is heat-treating, which MUST be done w/ aluminum after welding). other than that -- can't remember which issue or the name of the company -- broken frames usually end up as wall art.
     
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