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8e.3 Frame repair


This article is from the Bicycles FAQ, by Mike Iglesias with numerous contributions by others.

8e.3 Frame repair

From: David Keppel <pardo@cs.washington.edu>

(Disclaimer: my opinions do creep in from time to time!)

When frames fail due to manufacturing defects they are usually
replaced under warranty. When they fail due to accident or abuse
(gee, I don't know *why* it broke when I rode off that last
motorcycle jump, it's never broken when I rode it off it before!)
you are left with a crippled or unridable bike.

There are various kinds of frame damage that can be repaired. The
major issues are (a) figuring out whether it's repairable (b) who
can do it and (c) whether it's worth doing (sometimes repairs just
aren't worth it).

Kinds of repairs: Bent or cracked frame tubes, failed joints, bent
or missing braze-on brackets, bent derailleur hangars, bent or
broken brake mounts, bent forks, etc. A frame can also be bent out
of alignment without any visible damage; try sighting from the back
wheel to the front, and if the front wheel hits the ground to one
side of the back wheel's plane (when the front wheel is pointing
straight ahead), then the frame is probably out of alignment.

* Can it be repaired?

Just about any damage to a steel frame can be repaired. Almost any
damage to an aluminum or carbon fiber frame is impossible to repair.
Titanium frames can be repaired but only by the gods. Some frames
are composites of steel and other materials (e.g., the Raleigh
Technium). Sometimes damage to steel parts cannot be repaired
because repairs would affect the non-steel parts.

Owners of non-steel frames can take heart: non-steel frames can
resist some kinds of damage more effectively than steel frames, and
may thus be less likely to be damaged. Some frames come with e.g.,
replacable derailleur hangers (whether you can *get* a replacement
is a different issue, though). Also, many non-steel frames have
steel forks and any part of a steel fork can be repaired.

Note: For metal frames, minor dents away from joints can generally
be ignored. Deep gouges, nicks, and cuts in any frame may lead to
eventual failure. With steel, the failure is generally gradual.
With aluminum the failure is sometimes sudden.

Summary: if it is steel, yes it can be repaired. If it isn't steel,
no, it can't be repaired.

* Who can do it?

Bent derailleur hangers can be straightened. Indexed shifting
systems are far more sensitive to alignment than non-indexed. Clamp
an adjustable wrench over the bent hanger and yield the hanger
gently. Leave the wheel bolted in place so that the derailleur hanger
is bent and not the back of the dropout. Go slowly and try not to
overshoot. The goal is to have the face of the hanger in-plane with
the bike's plane of symmetry.

Just about any other repair requires the help of a shop that builds
frames since few other shops invest in frame tools. If you can find
a shop that's been around for a while, though, they may also have
some frame tools.

* Is it worth it?

The price of the repair should be balanced with

* The value of the bicycle
* What happens if you don't do anything about the damage
* What would a new bike cost
* What would a new frame cost
* What would a used bike cost
* What would a used frame cost
* What is the personal attachment

If you are sentimentally attached to a frame, then almost any repair
is worth it. If you are not particularly attached to the frame,
then you should evaluate the condition of the components on the rest
of the bicycle. It may be cheaper to purchase a new or used frame
or even purchase a whole used bike and select the best components
from each. For example, my most recent reconstruction looked like:

* Bike's estimated value: $300
* Do nothing about damage: unridable
* Cost of new bike: $400
* Cost of new frame: $250+
* Cost of used bike: $200+
* Cost of used frame: N/A
* Cost of repair: $100+
* Personal attachment: zip

Getting the bike on the road again was not a big deal: I have lots
of other bikes, but I *wanted* to have a commuter bike. Since I
didn't *need* it, though, I could afford to wait a long time for
repairs. The cost of a new bike was more than I cared to spend.
It is hard to get a replacement frame for a low-cost bicycle. I
did a good bit of shopping around and the lowest-cost new frame
that I could find was $250, save a low-quality frame in the
bargain basement that I didn't want. Used frames were basically the
same story: people generally only sell frames when they are
high-quality frames. Because the bike was a road bike, I could have
purchased a used bike fairly cheaply; had the bike been a fat-tire
bike, it would have been difficult to find a replacement. The cost
of the frame repair included only a quick ``rattlecan'' spray, so
the result was aesthetically unappealing and also more fragile. For
a commuter bike, though, aesthetics are secondary, so I went with

There is also a risk that the `fixed' frame will be damaged. I had
a frame crack when it was straightened. I could have had the tube
replaced, but at much greater expense. The shop had made a point
that the frame was damaged enough that it might crack during repair
and charged me 1/2. I was able to have the crack repaired and I
still ride the bike, but could have been left both out the money
and without a ridable frame.

* Summary

Damaged steel frames can always be repaired, but if the damage is
severe, be sure to check your other options. If the bicycle isn't
steel, then it probably can't be repaired.


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