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Straightening a steel frame - OK to do?

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Straightening a steel frame - OK to do?

Old 06-08-05, 10:02 PM
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jur
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Straightening a steel frame - OK to do?

My son got T-boned some time ago (he was crossing illegally and got bumped by a car which headlight broke), he escaped unhurt save a rash or two but his bike was not so blessed.

The front wheel was bent badly, as were the chain rings, but he bashed away at them at the site until they looked OK and then continued on to university. I checked the wheel that night, it was astonishingly straight, the chain rings still had some wobble but are working mostly fine.

However, he said he can't ride loose hands anymore, so I checked the fork, and sure enough it looked bent. On closer inspection, the frame is twisted, the head tube no longer aligns with the frame when looking from the front and the top tube is also bent. We dismantled the bike and tried straightening the frame, but only succeeded in breaking various bits of wood and writing off a woodworking clamp. That frame is one tough customer, I dunno how the hell it got like that with my son unhurt.

We first tried holding down the seat tube while wrenching the head tube, but lacked enough leverage. Then we clamped the head tube down and levered the seat tube and broke the clamp. The we used a long steel bar in the head tube, protected by an aluminium sleeve, clamped that down with a mother of all clamps, and levered the seat tube. We could not develop enough leverage to pass into the plastic deformation of the frame.

So here's the question: Should I write the frame off, or can it be straightened? Any tips for doing so?
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Old 06-08-05, 11:13 PM
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New frame, next. That is unless it's some special frame.
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Old 06-08-05, 11:52 PM
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Straightening a frame like that would be very difficult. Would not suggest it as a DIY project.
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Old 06-09-05, 09:34 AM
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When the top tube is bent and the headtube is no longer aligned, this requires a framebuilder to repair. You can't just "bend it back".
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Old 06-09-05, 09:59 AM
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It got bent, it can get un-bent!

You'll have to figure what is bent, what has to be done to correct it and how to do it. Even thinking about where it was hit and what forces were the cause and then kind of reverse them.

One of the best devices for that are "hydraulics". If you can get something clamped down and then apply some hydraulic pressure to the correct point and in the correct direction, it'll bend! The hydraulic jack is much easier to control than manual methods.

Bending might be easier than twisting. A chain can be used, attached to two points, with a hydraulic jack in between, pressing on the center.

Be creative!
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Old 06-09-05, 10:31 AM
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Originally Posted by CATZ
It got bent, it can get un-bent!
True enough. But unless it is a special frame it is not worth the time and effort to do it, nor the expense of having it done for you. Steel road bike frames are a dime a dozen - hell, I've got a roller that just needs tubes, tires, and cables that you can have for $50.00, and you can find complete steel road bikes at most any thrift shop for cheap.

Your time would be better spent stripping the bent bike for parts, and using them to build up a bike on a donor frame.

IMO.

John D.
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Old 06-09-05, 06:29 PM
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I would buy a new bike or frame and cannabilize the bent one for parts.


After all, when an automobile's frame is bent, the car is usaually written off as "totaled." I unfortunately ruined a beautiful '66 Chrysler Newport by kinking the frame. (I also kinked my lower jaw. oops.)


Steel, and auminum is actually even worse about this than steel is, looses a great deal of structural integrety when it is violently bent. Factory processes do their bending in slow carefully cntolled increments, baskhing the frame out of these increments damages the tubes, bashing them back in damages them more.


If you really MUST bend the frame back into shape, I would suggest building some form of jig to do so with, to be sure you get it perfectly aligned. Bend it too far and you've just aggrvated the problem.
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Old 06-09-05, 09:43 PM
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I have done rear triangle repairs and I race on one of them, but front triangle is a whole nother ball game. The only way I would consider doing a diy on that is to get an EXACT fit heavy pipe for the head tube and seat tube. If it is loose fit, it will ovalize or damage either. I would be more inclined to replace or talk to a pro builder. One other item to consider is the frame junctions. If the paint is sizably cracked in any areas around the tubing, look Very closely as it may indicate a fatigued joint. That leads to premature failures.
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Old 06-10-05, 12:28 AM
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Hit it in the exact spot, only on the other side, with another car.
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