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Thread: Broken frame

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    Broken frame

    The chainstays broke on my full suspension mountain bike broke this weekend. I can get a replacement chainstay but it will cost alot more than paying someone to weld it for me. It broke the tube next to the weld but not at the weld. If I get it repaired will it foreber be weaker were it broke?
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    Noob mikezs's Avatar
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    Quote Originally Posted by dabee1106 View Post
    If I get it repaired will it foreber be weaker were it broke?
    If it's a good quality weld, it should be stronger than before as there's extra reinforcing material added.

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    Senior Member demoncyclist's Avatar
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    If that is an aluminum frame, it is probably impossible for the average welder to repair. You should take it to the shop where it was purchased. There may be a warranty on the frame.
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    Junior Mint jimn's Avatar
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    I don't know about suspension swing-arms, but aluminum frames are heat-treated after welding. If you have a welder fix the break, the properties of the aluminum may be so changed that it breaks again fairly easily. So, unless you can get someone to weld it for really cheap, and don't mind being the crash test pilot, you will need to replace the part.

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    I agree with jimn
    I was taught that the weekest part of the weld is the heat effected zone next to the weld, thats why most fractures are right next to the weld line. "stress is reduced by heat treatment, weld prep design and weld proceedure"
    If you look at the original weld it is designed so as not to create a:- direct virtical shear stress line.
    p.s. There are also different grades of filler rod /wire with different tensile strenghts so make sure the right one is used
    sorry I can't be more helpfull but it's been years since I last welded aluminum.
    Paul

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    Old fart JohnDThompson's Avatar
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    Don't bother welding it; it will break again in short order.

    If you're the original owner of the frame, I'd look into getting warranty replacement or at least a discount on repair.

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    The pic isn't clear- but it almost looks as if this is a solid insert rather than a tube. Either way... if properly welded and heat treated a break here shouldn't occur unless it's a design flaw, or some outside factor- like a little help from gouging caused by chain derailment, etc. Then of course we don't know if the alloy is the best choice to resist breakage.

    I'd be inclined to go for a new swingarm so I had some recourse in the event it happens again. Then wrap it with some sort of protecter to resist damage from thrown chains.

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    Senior Member himespau's Avatar
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    Yeah, definitely if you're the first owner go to the lbs to see about a warranty.
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    Senior Member gyozadude's Avatar
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    Aluminum frames in general can't be re-welded or reformed without a significant process of heat treatment. So, yes, a really good welder might be able to get in there and weld, but unless he has the ovens to bake the frame (and this takes hours/a day) the joint will never be that strong, and unless he has superbe atmospheric conditions in his fab, re-welding aluminum is very difficult on jagged breaks. You need to start with very clean aluminum which is rapidly welded right after cleaning to prevent oxide from forming on the exterior which I here creates micro-fracture sites in the weld that will fail again.

    Hope you're okay and didn't suffer physically. Let us hear about the warranty.
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    Map maker cbchess's Avatar
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    replacement swing arm is the best way to go IMHO

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    Member 76Crescent's Avatar
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    Quote Originally Posted by arceye View Post
    I agree with jimn
    I was taught that the weekest part of the weld is the heat effected zone next to the weld, thats why most fractures are right next to the weld line. "stress is reduced by heat treatment, weld prep design and weld proceedure"
    If you look at the original weld it is designed so as not to create a:- direct virtical shear stress line.
    p.s. There are also different grades of filler rod /wire with different tensile strenghts so make sure the right one is used
    sorry I can't be more helpfull but it's been years since I last welded aluminum.
    Paul
    Ding Ding Ding. We have a winner!

    I'm a certified welder. I've done a good bit of TIG welding which is how your frame was made. Like others have said aluminum frames are heat treated, and this is not possible/practical for most people even with really nice welding setups. Also like others have said aluminum is weakest around the weld not at it, so it would likely break next to the weld very soon. It's not worth your money to pay anybody to weld it. Sorry. Try and get a warranty or buy a new swing arm.

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    It was not covered under warrant because I bought the bike used. My buddy welded it for me for free but it broke again first ride after being repaired so now a new swingarm is on the way. I was not hurt in any way but chainstay was rubbing on tire when sitting on the bike so the tire took most of the abuse. Thanks for the help everyone.

  13. #13
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    How to fix it if you really need to fix it.
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