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Best way to fix bent alloy seatstay?

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Best way to fix bent alloy seatstay?

Old 05-23-20, 08:51 AM
  #1  
Dilberto
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Best way to fix bent alloy seatstay?

Many tell me to just toss it. A few has suggested using two wood blocks with channels carved out and slowly vise it back, with several long bolts and washers strategically placed. What say ye?

The amount of dropout deflection is small. Would low heat help to prevent paint chips?

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Old 05-23-20, 08:55 AM
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Originally Posted by Dilberto View Post
Many tell me to just toss it. A few has suggested using two wood blocks with channels carved out and slowly vise it back, with several long bolts and washers strategically placed. What say ye?

The amount of dropout deflection is small. Would low heat help to prevent paint chips?
Get out the jam and butter. It would go nice with ham and eggs.

Even a steel frame would be difficult to straighten.
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Old 05-23-20, 09:21 AM
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Brace the dropouts with a hub or steel rod so they can't move. Jack the two stays apart.
You might be able to spread the load on the good side and concentrate it on the bend on the other side. Use rags to save the paint.
Go slowly.
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Old 05-23-20, 09:29 AM
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Some patience, two vices, a block of wood, and a blowtorch on very low (will need to repaint).
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Old 05-23-20, 09:38 AM
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Nope, if that's aluminum you can't fix it. It doesn't respond to bending like steel does.
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Old 05-23-20, 09:48 AM
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Is there a problem with the functionality of this frame? Does it track straight? Does the rear wheel fit well? If the answers are no, yes and yes then I suggest don't do anything but ride the bike. If these are the answers then there's no functional issues and only cosmetic ones.

Al does not do well with multiple manipulations. Focusing the straightening to the same spot and with the exact support needed to end up with no remaining ripple or slight dog legging will be near impossible without very involved forms and control. Having done many steel (and a very few Al) stay straightening I can speak form experience that even with the bike industry provided tools this type of realignment is not straightforward (pun much intended). So consider any repair to be a make better but not great at best and mushrooming into really bad results at worst.

If the wheel sits slightly crooked (and I make no assumption that it did when new...) then a few file strokes on the LH drop out, well focused, will cure that. If this is "Greek" to a reader I suggest that reader not be the one to do so. The brake might be slightly off center but that's what spacers on the pad mounts, eye bolts and centering spring tensions are made to correct.

Given the nick name of this brand, crack'n'fail, I would suggest to deal with the wheel alignment in other ways then bending the stay. Andy
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Old 05-23-20, 09:50 AM
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^^^This. It's dead, Jim. It has crossed the rainbow bridge. It is pining for the fjord. If it were a person it would be at room temperature. It has gone into the light.
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Old 05-23-20, 10:09 AM
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Now I disagree with the doom and gloom posters who claim this frame is dead, toast, crossed the rainbow bridge. It's just a frame and it will continue to provide enjoyment for more miles. The real question might be "for how much longer" and this is anyone's GUESS. But we are dealing with a relatively safe failure mode and a location that's very easy to monitor. Al does tend to crack as the failure mode and the crack can travel fairly quickly, as in hours or days. But again this location is out in the open so if one keeps an eye on it there will be no surprises. Also the stay is well supported by other elements. The stay is attached at two ends (unlike a fork's steerer, which is also well hidden to view). The brake bridge helps locate the upper end of the stay. The rear axle/QR does the same to the lower end. additionally as the stay is under compression for it's largest stress the crack is not seeing significant tension or bending forces. So even if the rider should be clueless and ignorant of their duties to monitor (after deciding to continue riding this frame) AND if the stay should crack completely through the likelihood of a loss of control is extremely low. I've seen many Al frames with cracks in various locations, some far more concerning WRT safe control, that by the crack's surface showed much time (oxidation/grime collection) then a single moment complete failure. Most of the time the rider never even knew they frame had suffered a crack (and there's the real concern, ignorance can be harmful if carried on long enough and WRT the more stressed/unsupported locations (like a steerer or a fork blade)).

I would have no problem continuing to ride this frame while arranging for it's replacement, maybe longer too. But I don't ride Al frames or forks so it isn't my decision. Andy
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Old 05-23-20, 10:35 AM
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To your point, then, Andrew R Stewart, it is not a case of if, but when. I think that the "when" is dependent on if the frame is straightened or not. Your point is well taken that, if the frame is ridden as is, it has some life left in it. My response was to the OP's original question regarding straightening.

This is not a rare or even noteworthy frame. It is easily replaced. Given the nature of aluminum and its response to being bent back and forth and the skill required to effect a good repair, I'd still call it dead, though I agree that the failure mode will not be catastrophic.
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Old 05-23-20, 04:49 PM
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Aluminum doesn’t respond to this kind of stress as well as steel. You might be able to straighten it, but I wouldn’t trust the frame afterward.
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Old 05-23-20, 05:58 PM
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Nuke it from orbit... it's the only way to be sure!
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Old 05-23-20, 07:09 PM
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Garage wall art.
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Old 05-23-20, 07:28 PM
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The problem if you were able to straighten that frame out, is that the areas of the bends would most likely be what's known as work-hardened. Work-hardened areas are stress risers and cracks or breakage can form there. If that happens on a long ride you might have to walk home. Is a breakage at some unknown time something you're willing to accept the risk of?

If I had to keep that frame for riding I'd do as Andrew Stewart suggested in his first reply in Post #6 of this thread.

I don't know what a broken seatstay on aluminium alloy frame would do I did have the two seatstays on one of my steel MTBs fail at the seatube whilst I was riding a paved road one night on my way to a store. I rode very carefully the rest of the way to the store and then the few kilometres back home. Then I scrapped the frame as it wasn't worth repairing. Here's an image of the breaks.





Cheers
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Old 05-23-20, 07:35 PM
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Park tool actually makes a tool to pull those types of damage out of a tube. It has two feet that are spaced about 18" apart and a center pulling rod that pulls from the center of the bend point. It can be repaired but just needs some one with the tool and know how. Just my 2 cents on this. Smiles, MH
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Old 05-23-20, 08:32 PM
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Originally Posted by Mad Honk View Post
Park tool actually makes a tool to pull those types of damage out of a tube. It has two feet that are spaced about 18" apart and a center pulling rod that pulls from the center of the bend point. It can be repaired but just needs some one with the tool and know how. Just my 2 cents on this. Smiles, MH
That's good to know! If Park is onboard it sounds legit. I had no idea aluminum could be manipulated like that.
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Old 05-23-20, 08:50 PM
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Originally Posted by Barry2 View Post
Nuke it from orbit... it's the only way to be sure!
That's it! Game over, man! Game over!
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Old 05-23-20, 08:54 PM
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I have this tool and used it quite a few times. It will pull a tube this way or that way. What it won't do is to localize the bending in a manor that doesn't result in a shallow "S" wave to the stay. As both I and MM said the local area of the bend won't tend to unbend as easily as the area right next to it. This is why I made the additional commit about a vastly more involved method with forms supporting the stay in a way that will focus the rebending right at the point of the problem. Not a real likely chance that someone will make a set of split forms that fit the stay just so.

But I will also commit on MM's stay failure and how it is different then what this post is about. His was a dual stay brazing failure, both stay points of attachment broke at pretty much the same time. So no vertical support, other then that of the chainstays' bending reluctance, was left top hold up the bike. The Op's situation is different in that only one stay is at risk (or at least first, if the RH stay did brake and if their fracture faces were to no longer butt against each other in time the LH stay would not be enough to support the weight).

I've met my 3 post rule so I'll just read what happens form here on unless a new element is brought forward. Andy
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Old 05-23-20, 09:45 PM
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I actually like the suggestion to fabricate two 6" long Pine blocks, channeled-out to accommodate the tubing contours. Then, apply six strategically positioned long bolts on washers, to gently vise the bent section straight, while torque in sequence. Should the wood blocks be touching each other at full clamp, or should there be a slight gap?
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