unbending chain rings

methods of unbending chain rings? the SR CR was bent 3 mm on a chord of 20 mm from running the chain
between the chainstay and small CR while running the yellow light with the worn power link skipping
as I pressed forward.
1)A usual recommended method is grabbing one point with a visegrip and bending. experience indicates
the method usually produces one more bend rather than a straight piece,2)Or will the entire chord
section bend at once using hardwood or ply spanners from chord start to chord end, held between
vicegrips?,3) will the bend pressout? or does the pressout pressure need to approach the
material's malleable strength pointand, 4) ultimately? does the CR go to a machine shop for a
straight piece of work?

 

"g.daniels" <[email protected]> wrote in message
news:[email protected]...
> methods of unbending chain rings? the SR CR was bent 3 mm on a chord of 20 mm from running the
> chain between the chainstay and small CR while running the yellow light with the worn power link
> skipping as I pressed forward.
> 1)A usual recommended method is grabbing one point with a visegrip and bending. experience
> indicates the method usually produces one more bend rather than a straight piece,2)Or will the
> entire chord section bend at once using hardwood or ply spanners from chord start to chord end,
> held between vicegrips?,3) will the bend pressout? or does the pressout pressure need to
> approach the material's malleable strength pointand, 4) ultimately? does the CR go to a machine
> shop for a straight piece of work?

I prefer to use a large adjustable (Crescent) wrench. The large flat jaws allow for bending without
deforming and there are no bite marks after.

Mike - large left handed metric Crescent hammer.

 

I've never had GREAT success trying to straighten chainrings. The best method that I've found is to
remove it from the bike and use a flat surface such as a plate steel workbench to assess trueness.
Mark where you need to bend and which way and then bend it using a vise and an adjustable wrench.
The difficulty is, and why you have trouble doing it on the bike, is that you have to bend past
your desired point by about double in order to deform the material and make the new bend permanent.
It takes some trial and error and the results are difficult to measure accurately. If the ring is
bent toward the bike and not very much, I've also had success just hitting it at the high spot with
a hammer. If the bend isn't too great, it should work. If you're worried about asthetics rather
than function (3mm may not hamper usage at all..some are bent more than this from the factory),
just go buy a new one..you'll save yourself a lot of trouble and aggravation and you'll be happier
in the end.

Cheers,

Scott..
--
Scott Anderson

"g.daniels" <[email protected]> wrote in message
news:[email protected]...
> methods of unbending chain rings? the SR CR was bent 3 mm on a chord of 20 mm from running the
> chain between the chainstay and small CR while running the yellow light with the worn power link
> skipping as I pressed forward.
> 1)A usual recommended method is grabbing one point with a visegrip and bending. experience
> indicates the method usually produces one more bend rather than a straight piece,2)Or will the
> entire chord section bend at once using hardwood or ply spanners from chord start to chord end,
> held between vicegrips?,3) will the bend pressout? or does the pressout pressure need to
> approach the material's malleable strength pointand, 4) ultimately? does the CR go to a machine
> shop for a straight piece of work?

 

"Sheldon Brown" <[email protected]> wrote in message
news:[email protected]...
> g.daniels wrote:
> > methods of unbending chain rings? the SR CR was bent 3 mm on a chord of 20 mm from running the
> > chain between the chainstay and small CR while running the yellow light with the worn power link
> > skipping as
I
> > pressed forward.
> > 1)A usual recommended method is grabbing one point with a visegrip
and
> > bending. experience indicates the method usually produces one more bend rather than a straight
> > piece,2)Or will the entire chord section bend at once using hardwood or ply spanners from chord
> > start to
chord
> > end, held between vicegrips?,3) will the bend pressout? or does the pressout pressure need to
> > approach the material's malleable strength pointand, 4) ultimately? does the CR go to a machine
> > shop for a straight piece of work?
>
> i have an article about this at http://sheldonbrown.com/straighten_chw.html that tells how to deal
with
> this problem which may or may not be the chainring itself could be the crank spider is bent
> and not the chainring better not to bend the straight part to compensate for the bent part,
> n'es-ce pas?
>
> s. brown
>
> in Just- spring when the world is mud- luscious the little lame balloonman
>
> whistles far and wee
>
> and eddieandbill come running from marbles and piracies and it's spring
>
> when the world is puddle-wonderful
>
> the queer old balloonman whistles far and wee and bettyandisbel come dancing
>
> from hop-scotch and jump-rope and
>
> it's spring and the
>
> goat-footed
>
> balloonMan whistles far and wee
>
> e.e. cummings

I was wondering when someone would make the connection between e.e. cummings and g. daniels. A
couple of his posts reminded me of anyone lived in a pretty how town punctuated with references to
bike parts. -- Jay Beattie.