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bent steer tube

Old 04-06-17, 11:30 PM
  #1  
jdfnnl
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bent steer tube

I have been trying to figure what to do about this bike with a bent steer tube. Before extracting it from the headset, it would turn smoothly when generally aimed straight but then would tighten up and have the most resistance turned 180 degrees. With the headset off, a straight edge revealed a slight bow in the steer tube with concavity toward the front while the fork also appears visually bent toward the front, apparently indicating in instance of trauma opposite that of a front-end collision.
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Old 04-06-17, 11:48 PM
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inspect the frame itself for corresponding crash damage
then either buy a new fork, or get a new bike
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Old 04-07-17, 12:10 AM
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That bike wasn't crashed into anything. The kind of bend you have is indicative of a bike that was used for jumps, or going down steps or curbs on a fairly regular basis.

That quality of frame and fork is relatively ductile, and can be straightened. BITD it was routine to straighten forks in much worse condition, but these days most shops would pass because of concerns over potential liability. If there's an old school "greasy fingernails" shop with an old time Mr. Fixit style mechanic, he'll probably do a good job at a reasonable price, otherwise, it's either straighten it yourself of dispose of it.

If you inspect the frame, keep in mind that you're not looking for the classic buckles under the top and down tubes, but instead for stretch cracks in the paint in that location.

FWIW - if it were mine, and I had use for a city or beater bike, I'd have no qualms about straightening and riding it. (except for the color)
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Old 04-07-17, 03:00 AM
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Good photo to show the problem.

Obviously take out the brake assembly, then remove the bottom head set outer bearing cup, then try, & see if its possible where the flex has been, maybe even a hairline crack. This being an older fork it has the flat top ornate fork crown, you maybe able to see if this has flexed. I personally would attempt to straighten it, but you have to be very careful to ensure the area where the bottom head bearing cup is that does not flex otherwise again it will bind when turning.

Again as correctly mentioned above an OLD school bike mechanic would attempt to straighten it
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Old 04-07-17, 05:31 AM
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Straighten fork blades, yes. But a bent steerer tube can't be straightened, it has to be replaced. OP, time for a new fork (because the cost of replacing a steerer tube and paint isn't worth it for your fork).
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Old 04-07-17, 07:20 AM
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If it is straightened & you re-assemble the bike, you maybe a few degrees out on the fork reach, but the wheel base should be 1.meter, or very close, sprint bikes tend to be shorter touring bikes longer: other forum members may have more precise measurements.
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Old 04-07-17, 01:06 PM
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I can visualize straightening the steer tube being manageable with some carefully placed blocks and a clamp, but the other question I have is about whether the line of the fork blades should be roughly parallel with the steer tube, which in this case seems much more difficult to fix without breaking the weld. The frame shows no sign of any collision trauma.

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Old 04-07-17, 03:37 PM
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Originally Posted by jdfnnl View Post
I can visualize straightening the steer tube being manageable with some carefully placed blocks and a clamp, but the other question I have is about whether the line of the fork blades should be roughly parallel with the steer tube, which in this case seems much more difficult to fix without breaking the weld. The frame shows no sign of any collision trauma.
Yes, the fork blades should start out in line with the steerer, before curving forward about halfway down.

As for straightening the steerer, yours isn't bent badly and can be staightened. The key is to fixture it so you're in control and any bending you do is where and how you want it. Once the steerer is straight, you fixture the fork by the crown, so you can straighten the blades independent of the steerer.

One technique that offers far less control, but can be effective for rough work is to place the fork down resting on fork ends and steerer, then press down on the crown. Observe as you do this to make sure you're getting the desired effect. Once it's closer, then you're ready for measurements and controlled force to get it to new condition.

BITD - it wasn't rare for new bikes whose boxes were dropped on their ends to come out of the box this way. The quick down and dirt method was to assemble the bike stand it up on both wheels and roll it into the wall. This was done until it was close, then checked or test ridden. About half the time, a skilled mechanic could get it back into good condition this way. Of course, this was for lower end bikes, and called for a degree of touch.
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Old 04-07-17, 04:58 PM
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love how you say rolling a bike into a wall calls for a degree of touch, though what I think of by "fixture it so you're in control" is this -->
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Old 04-08-17, 07:14 PM
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Back in the day I would have probably tried my Little Brute fork straightener on the fork by leaving the fork installed in the bike, turning it 180 degrees from normal, and then pushing it back into alignment. Made a lot of $$$ with the Little Brute, but that was in the day of steel forks and frames and usually the damage was just the opposite of what is shown in this case...fork pushed back due to a front end collision. I have seen instances of where a bent steerer tube would straighten out when the fork was aligned back into position.
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Last edited by richart; 04-08-17 at 07:24 PM. Reason: Added final sentence for clarity.
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