Unbending a frame?

[Trg]

A friend got run down by a scooter on her cromoly mtb. The rear triangle got bent so that the
rear wheel now touches the left triangle near the BB. The rest of the bike is untouched. Is it
possible to unbend a cromoly frame? Will it be safe to ride after that, or should I just junk the
frame all together?

 

[Paul Southworth]

In article <[email protected]>, trg <[email protected]> wrote:
>A friend got run down by a scooter on her cromoly mtb. The rear triangle got bent so that the rear
>wheel now touches the left triangle near the BB. The rest of the bike is untouched. Is it possible
>to unbend a cromoly frame? Will it be safe to ride after that, or should I just junk the frame all
>together?

Should be fixable, although having an experienced person look at the damage and inspect for cracks
is a good idea. A rear triangle can be straightened pretty easily and safely and I wouldn't worry
about riding a crmo bike that had been cold set. Some steel mountain bikes (especially small ones)
take a lot of leverage to straighten. Done properly the rear triangle will probably be straighter
than it came from the factory.

There is a page on frame respacing on Sheldon Brown's site, that is essentially what you need to do.

--Paul

 

[Donald Gillies]

"trg" <[email protected]> writes:

> Is it possible to unbend a cromoly frame? Will it be safe to ride after that, or should I just
> junk the frame all together?

Well, I have more experience in this area than i like to admit. First step is to take it to the very
best bicycle shop in town. Or perhaps, take it to the shop in the poorest part of town. i have had
success with both methods.

The very best shop in town will have a wire-pulling jig. This is a jig that allows the frame repair
person to place a wire (and perhaps metal half-tube) almost anywhere on the frame, to apply precise
pressure and straighten an individual frame tube. When I locked up the rear wheel on my 1975 23.5"
raleigh grand prix (2030 carbon steel) it was bent in the right rear seatstay (about 0.5" bent
towards the seat tube), they pulled it out just fine. There was minor paint damaged but almost no
rippling in the tube at all.

The shop in the poorest part of town might have substantial experience in repairing "beater"
bicycles. I recently brought a raleigh international frame to one of these shops (Pedal Pushing, El
Cajon) where 80% of the stock in the shop was used, and the very best bicycle in the shop cost
$300.00. Anyway, they installed a heavy duty metal fork in the frame and used a custom jig to very
slowly pull the manganese-moly 531 frameset back into alignment. The owner of such a shop might just
be a wizard at fixing bent bicycles.

I would repair a bent frame once. If it bends again at the same place, junk it and get a new one.

Good Luck,

- Don Gillies San Diego, CA

 

[Sheldon Brown]

A shy person wrote:

> A friend got run down by a scooter on her cromoly mtb. The rear triangle got bent so that the rear
> wheel now touches the left triangle near the BB. The rest of the bike is untouched. Is it possible
> to unbend a cromoly frame? Will it be safe to ride after that, or should I just junk the frame all
> together?

This sort of bend is often correctable. See:http://sheldonbrown.com/frame-spacing.html

Sheldon "Leverage" Brown +--------------------------------------------------+
| If you have ties to Greater Boston, you might | enjoy a classic reproduction street map: |
| http://communityheritagemaps.com |
+--------------------------------------------------+ Harris Cyclery, West Newton, Massachusetts
Phone 617-244-9772 FAX 617-244-1041 http://harriscyclery.com Hard-to-find parts shipped Worldwide
http://captainbike.com http://sheldonbrown.com

 

[Bruni]

Frame builders do this routinely. We also can tell you if it needs more than alignment, like a
gusset or tube replacement. Tom
--
Bruni Bicycles "Where art meets science" brunibicycles.com
410.426.3420 trg <[email protected]> wrote in message
news:[email protected]...
> A friend got run down by a scooter on her cromoly mtb. The rear triangle
got
> bent so that the rear wheel now touches the left triangle near the BB. The rest of the bike is
> untouched. Is it possible to unbend a cromoly frame? Will it be safe to ride after that, or should
> I just junk the frame all together?

 

[A Muzi]

With few exceptions, you could not only expect a prompt and straightforward alignment at any shop
which services bicycle frames but with care and a few tools you could even do it yourself.

Be wary of the kibitzers - stay away from anyone who says "cold set" instead of the plain English
"bend" and especially avoid anyone who mentions heating the material.

If you remove the crank and crank bearing assembly, you can mount the bottom bracket shell in
aluminum or nylon jaws in a vise. From there, it is just muscle power and not much of that to bring
the rear end into line behind the front, using a straightedge and/or string and a caliper. It's the
most convenient/least clumsy way to hold a frame for these purposes (if you can manage some other
way that works for you, you'll save the fifteen minutes of crank service).

--
Andrew Muzi www.yellowjersey.org Open every day since 1 April, 1971

trg wrote:

> A friend got run down by a scooter on her cromoly mtb. The rear triangle got bent so that the rear
> wheel now touches the left triangle near the BB. The rest of the bike is untouched. Is it possible
> to unbend a cromoly frame? Will it be safe to ride after that, or should I just junk the frame all
> together?

 

[Werehatrack]

On Wed, 15 Oct 2003 11:49:44 +0200, "trg" <[email protected]> may have said:

>A friend got run down by a scooter on her cromoly mtb. The rear triangle got bent so that the rear
>wheel now touches the left triangle near the BB. The rest of the bike is untouched. Is it possible
>to unbend a cromoly frame?

It's not so much a question of unbending it, more one of "can it be bent back close to where
it started?"

>Will it be safe to ride after that, or should I just junk the frame all together?

Presumably, you wouldn't be asking this question if the option of taking the frame to a
specialist was economically feasible, so I won't bother pointing out the reasons why that would
be a better choice.

It's really hard to say what's needed or possible without seeing the damage, so I'll assume for the
sake of discussion that the stays have no obvious kinks and that the tubing is not crushed or
crinkled anywhere. Given that, CrMo tubing can be a bit brittle, but in my experience it's probably
not going to break unless there are severe bends involved. It might be possible to straighten the
damage, although I'll caution that this is not the sort of task that is likely to be successful in
the hands of the unskilled. The problem lies in the high probability that the bends may not be
reversible; that is, you may not be able to restore the stays to their original shape, and as a
result the dropouts may not end up in their original positions. Whether you can get them to a
*useful* configuration is a different question. If the damage is not too severe or complex, then
with sufficient care, if your abilities are up to the task, a useful end result may be possible. If
you want to try, there are a few hints about how to spread the rear of a frame here:

http://www.sheldonbrown.com/frame-spacing.html

Pay particular attention to the alignment issues.

Bear in mind that if the stays on either side are unevenly bent now, you will probably have trouble
getting the dropouts to line up. It will be essential to check dropout alignment prior to and often
during the straightening process. The task may not be simple; merely getting the rear spacing and
centering back to the right dimensions may not be adequate, but it's the place to start.

Good luck.

--
My email address is antispammed; pull WEEDS if replying via e-mail. Yes, I have a killfile. If I
don't respond to something, it's also possible that I'm busy.

 

[A Muzi]

trg wrote:

> A friend got run down by a scooter on her cromoly mtb. The rear triangle got bent so that the rear
> wheel now touches the left triangle near the BB. The rest of the bike is untouched. Is it possible
> to unbend a cromoly frame? Will it be safe to ride after that, or should I just junk the frame all
> together?
>
>
A simple lateral bend can be rectified promptly (cheap) at any place which customarily does
alignments. I'd look askance at people who say "cold set" when they mean "bend" and run from anyone
who mentions heating the material.

If you want to try it yourself, remove the crank and crank bearing assembly and hold the frame in a
vise at the hanger in nylon or aluminum vise jaw liners. Of course, if you find a secure and
convenient way to hold a frame without doing that, go ahead. I find that the least clumsy method.

Sight the stays so you can see exactly where the bends are and measure with straightedge or a string
with a caliper. Run a taut string from one frame end, around the head tube and back to the other
end. Measure the distance from the string to the seat tube on either side. If you have a 110-115cm
straightedge available , lay it on the side of the head tube and the seat tube, measure from it to
the inside face of the frame end and repeat on the other side. Make your frame as wide as the hub is
across the locknuts plus one millimeter. Muscle is enough and you won't need a lot of that - no
special tools or levers are needed. (You won't be able to get the frame ends parallel without
Campagnolo "H" tools or the equivalent)

Unless there is sharp crease, it will be plenty strong and just fine for the rest of its long life.
--
Andrew Muzi www.yellowjersey.org Open every day since 1 April, 1971

 

[Trg]

Actually, what I'm considering doing is buying a new frame from Nashbar or similar place and using
that with all the old parts to rebuild a mtb for my friend. I'm hoping to use the bent frame to make
a fixie for around town. In that case, without rear brake or derailler, I'm less concerned about
getting it exactly right. Close may be good enough.

What I'm worried about is the integrity of the frame after it's been bent and then bent back. I'd
rather not have it crumple under me at an inopportune moment.

> On Wed, 15 Oct 2003 11:49:44 +0200, "trg" <[email protected]> may have said:
>
>> A friend got run down by a scooter on her cromoly mtb. The rear triangle got bent so that the
>> rear wheel now touches the left triangle near the BB. The rest of the bike is untouched. Is it
>> possible to unbend a cromoly frame?
>
> It's not so much a question of unbending it, more one of "can it be bent back close to where it
> started?"
>
>> Will it be safe to ride after that, or should I just junk the frame all together?
>
> Presumably, you wouldn't be asking this question if the option of taking the frame to a
> specialist was economically feasible, so I won't bother pointing out the reasons why that would
> be a better choice.
>
> It's really hard to say what's needed or possible without seeing the damage, so I'll assume for
> the sake of discussion that the stays have no obvious kinks and that the tubing is not crushed
> or crinkled anywhere. Given that, CrMo tubing can be a bit brittle, but in my experience it's
> probably not going to break unless there are severe bends involved. It might be possible to
> straighten the damage, although I'll caution that this is not the sort of task that is likely to
> be successful in the hands of the unskilled. The problem lies in the high probability that the
> bends may not be reversible; that is, you may not be able to restore the stays to their original
> shape, and as a result the dropouts may not end up in their original positions. Whether you can
> get them to a *useful* configuration is a different question. If the damage is not too severe or
> complex, then with sufficient care, if your abilities are up to the task, a useful end result
> may be possible. If you want to try, there are a few hints about how to spread the rear of a
> frame here:
>
> http://www.sheldonbrown.com/frame-spacing.html
>
> Pay particular attention to the alignment issues.
>
> Bear in mind that if the stays on either side are unevenly bent now, you will probably have
> trouble getting the dropouts to line up. It will be essential to check dropout alignment prior
> to and often during the straightening process. The task may not be simple; merely getting the
> rear spacing and centering back to the right dimensions may not be adequate, but it's the place
> to start.
>
> Good luck.

 

[Paul Southworth]

In article <[email protected]>, trg <[email protected]> wrote:
>
>What I'm worried about is the integrity of the frame after it's been bent and then bent back. I'd
>rather not have it crumple under me at an inopportune moment.

Most cheap steel mountain bikes are so overbuilt that this is not a big concern unless there is
significant visible damage (ie, badly crimped or cracked tube). If you have to move it too far, it
may also fail when you move it back. But you can safely correct pretty substantial errors of
alignment in a steel bike with heavy tubes.

 

[Trg]

trg wrote:
> A friend got run down by a scooter on her cromoly mtb. The rear triangle got bent so that the rear
> wheel now touches the left triangle near the BB. The rest of the bike is untouched. Is it possible
> to unbend a cromoly frame? Will it be safe to ride after that, or should I just junk the frame all
> together?

Thanks for all the great answers!

 

[Sergio Servadio]

On Wed, 15 Oct 2003, A Muzi wrote:
> A simple lateral bend can be rectified promptly (cheap) at any place which customarily does
> alignments. ...

Andrew, you saved me the time to type your words. This very morning, in Padova, I watched the guy do
the job to a Frejus frame, circa 1950, I had brought in.

Nice to see what can be done with patience, care, little equipment and some ingenuity.

Sergio Pisa

 

[Jim Adney]

On Wed, 15 Oct 2003 23:50:07 -0500 A Muzi <[email protected]> wrote:

>I'd look askance at people who say "cold set" when they mean "bend"

Don't they mean the same thing? Cold set is the term used in the Reynolds literature, but bending is
just a more generic term. To me, if someone says cold set, it just means that he is more in touch
with bicycle frame terminology.

-
-----------------------------------------------
Jim Adney [email protected] Madison, WI 53711 USA
-----------------------------------------------

 

[Ted Bennett]

Jim Adney <[email protected]> wrote:

> On Wed, 15 Oct 2003 23:50:07 -0500 A Muzi <[email protected]> wrote:
>
> >I'd look askance at people who say "cold set" when they mean "bend"
>
> Don't they mean the same thing? Cold set is the term used in the Reynolds literature, but bending
> is just a more generic term. To me, if someone says cold set, it just means that he is more in
> touch with bicycle frame terminology.
>
> -
> -----------------------------------------------
> Jim Adney [email protected] Madison, WI 53711 USA
> -----------------------------------------------

Sure, they mean the same thing. But "bend" is such a direct and clear word that some would prefer a
less direct method of communication, such as "cold set". Which carries implications of snootiness,
of special knowledge or skill, or perhaps a more refined approach to metal than merely bending it.

This summer I met Andy Muzi in his shop in Madison. I got the impression from him that he becomes
impatient with puffery, and I'll bet that tossing out terms such as "cold set" in his presence
provokes some tooth-grinding. Muzi is both a skilled mechanic and communicator, and when he talks
about bending a frame back into shape, he chooses that word for clarity. Some would call that
"cold setting".

I wonder if cold setting is used to protect the tender ears of the frame owner.

--
Ted Bennett Portland OR

 

[Paul Southworth]

In article <[email protected]>, Jim Adney <[email protected]> wrote:
>On Wed, 15 Oct 2003 23:50:07 -0500 A Muzi <[email protected]> wrote:
>
>>I'd look askance at people who say "cold set" when they mean "bend"
>
>Don't they mean the same thing? Cold set is the term used in the Reynolds literature, but bending
>is just a more generic term. To me, if someone says cold set, it just means that he is more in
>touch with bicycle frame terminology.

I always thought it was a gentile euphemism to comfort the customer, and another example of made
up bike shop talk, of which there are many others. I confess I use it anyway more to be quaint
than exact.

 

[Jim Adney]

On Sun, 19 Oct 2003 05:19:17 GMT Ted Bennett <[email protected]> wrote:

>I wonder if cold setting is used to protect the tender ears of the frame owner.

I'm sure you're right. As another poster said, it's a euphemism.

-
-----------------------------------------------
Jim Adney [email protected] Madison, WI 53711 USA
-----------------------------------------------

 

[A Muzi]

> On Sun, 19 Oct 2003 05:19:17 GMT Ted Bennett <[email protected]> wrote:
>>I wonder if cold setting is used to protect the tender ears of the frame owner.

Jim Adney wrote:
> I'm sure you're right. As another poster said, it's a euphemism.

And it's one thing here where I would presume someone thought about the choice of words with good
intent. At retail, it's used to obfuscate and cow the consumer more often than not. That's why I
mentioned it.

--
Andrew Muzi www.yellowjersey.org Open every day since 1 April, 1971

 

[Trg]

Paul Southworth wrote:
> In article <[email protected]>, Jim Adney <[email protected]> wrote:
>> On Wed, 15 Oct 2003 23:50:07 -0500 A Muzi <[email protected]> wrote:
>>
>>> I'd look askance at people who say "cold set" when they mean "bend"
>>
>> Don't they mean the same thing? Cold set is the term used in the Reynolds literature, but bending
>> is just a more generic term. To me, if someone says cold set, it just means that he is more in
>> touch with bicycle frame terminology.
>
> I always thought it was a gentile euphemism to comfort the customer, and another example of made
> up bike shop talk, of which there are many others. I confess I use it anyway more to be quaint
> than exact.

Gotcha. I will bend the frame, and if I ever sell it, I will tell the buyer that I "cold set" it.