Repairing a Steel Frame
11-27-07, 04:55 PM
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Repairing a Steel Frame
Background Info:
I got a GT mountain bike frame (4130 CrMo, i think) for parts. The rear triangle was run over at some point and both seatstays/chainstays were smushed together. After stripping the bike and letting it sit for a few months, i remembered about the amazing forgiveness of steel.
The Idea:
I took an extra 2x2 i had from a previous art project, and cold set the rear triangle, bending the stays back into place. Without the proper frame alignment tools, the rear triangle looks pretty straight. I "adjusted" the derailleur hanger too, as that had been bent. So far, things look decent. There are some scratches and paint damage, but over all, it looks cosmetic.
The Theory vs. Practice:
Would the frame, obviously bent and then rebent, be strong enough to ride? I cannot imagine it is as a strong as it formerly was, but would it standup to a year or two of riding? Or would the stresses have weakened the steel frame too much? If it can be ridden, what are the limitations? Streets only? A little rough stuff? Any rough stuff?
So far, i have not dumped any money into, and the build plan is to use stuff from my parts bin and get inexpensive parts when need be. Would the frame collapse after one use, or is there a good chance it could be ridden again?
If this is in the wrong subforum (mountain bikes? alt bikes? utility?) please let me know and i'll remedy the situation. Thanks in advance for any and all help/input/advice!
I got a GT mountain bike frame (4130 CrMo, i think) for parts. The rear triangle was run over at some point and both seatstays/chainstays were smushed together. After stripping the bike and letting it sit for a few months, i remembered about the amazing forgiveness of steel.
The Idea:
I took an extra 2x2 i had from a previous art project, and cold set the rear triangle, bending the stays back into place. Without the proper frame alignment tools, the rear triangle looks pretty straight. I "adjusted" the derailleur hanger too, as that had been bent. So far, things look decent. There are some scratches and paint damage, but over all, it looks cosmetic.
The Theory vs. Practice:
Would the frame, obviously bent and then rebent, be strong enough to ride? I cannot imagine it is as a strong as it formerly was, but would it standup to a year or two of riding? Or would the stresses have weakened the steel frame too much? If it can be ridden, what are the limitations? Streets only? A little rough stuff? Any rough stuff?
So far, i have not dumped any money into, and the build plan is to use stuff from my parts bin and get inexpensive parts when need be. Would the frame collapse after one use, or is there a good chance it could be ridden again?
If this is in the wrong subforum (mountain bikes? alt bikes? utility?) please let me know and i'll remedy the situation. Thanks in advance for any and all help/input/advice!
11-28-07, 10:53 AM
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Hard to say for sure without pics. If there are no wrinkles in the chainstays or cracking in the paint, you're probably good to go. AS you aren't sinking any money into it or using it as a race bike, go for it.
Check the bb shell carefully too, there's a better than average chance that all the bending has distorted it beyond useablility.
Check the bb shell carefully too, there's a better than average chance that all the bending has distorted it beyond useablility.
11-28-07, 10:36 PM
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well usually rear triangle failures are not catastrophic, especially with steel. If you break a stay when riding, the tire will usually just start rubbing on the opposite stay. I would probably stay seated the first time you ride so you dont hurt yourself [as much] if the bike did fail
11-29-07, 11:12 AM
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I'll look the frame over, see if there are any wrinkles in the tubing, paint, etc. I left the bottom bracket in the frame, so i don't know if that would have helped support the shell.
I'll build it up and do some gingerly test rides. If it doesn't collapse in the first few test rides, would it be safe to assume, it's strong enough to serve as another beater/winter bike? Hard to tell without pics, info, etc.
I'll build it up and do some gingerly test rides. If it doesn't collapse in the first few test rides, would it be safe to assume, it's strong enough to serve as another beater/winter bike? Hard to tell without pics, info, etc.
