Is it bent?

Patrick Lamb said:

Looking down at my big chain ring today, I noticed the chain wobbles
maybe 1/8" (as seen against the derailer) over one part of the ring as
I pedal. Is this part of the STI design, or is the ring bent and I
need to straighten it?

Shift to the other ring. Spin your crank and watch the tooth profile.
Is one tooth bent?

Now sight along the length of the chain as you backpedal. Do you see a
damaged or errant section? That can be dangerous so if the chain itself
varies attend to the before riding.
--
Andrew Muzi
<www.yellowjersey.org/>
Open every day since 1 April, 1971
** Posted from http://www.teranews.com **

"A Muzi" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

Patrick Lamb said:

Looking down at my big chain ring today, I noticed the chain wobbles
maybe 1/8" (as seen against the derailer) over one part of the ring as
I pedal. Is this part of the STI design, or is the ring bent and I
need to straighten it?

Shift to the other ring. Spin your crank and watch the tooth profile. Is
one tooth bent?

Now sight along the length of the chain as you backpedal. Do you see a
damaged or errant section? That can be dangerous so if the chain itself
varies attend to the before riding.

And not knowing what age your bicycle is can be a problem as well. Older
bicycles with adjustable bottom brackets could get loose enough for the
chainrings to wobble and all it required was proper adjustment.

Patrick Lamb said:

Looking down at my big chain ring today, I noticed the chain wobbles
maybe 1/8" (as seen against the derailer) over one part of the ring as
I pedal. Is this part of the STI design, or is the ring bent and I
need to straighten it?

1/8" isn't much, but also check for play in the bottom bracket because
that can cause the same symptom. Just get off the bike and see if you can
wobble the cranks.

On Mon, 23 Jun 2008 21:06:34 -0500, A Muzi <[email hidden]>

Quoted message said:

Patrick Lamb said:

Looking down at my big chain ring today, I noticed the chain wobbles
maybe 1/8" (as seen against the derailer) over one part of the ring as
I pedal. Is this part of the STI design, or is the ring bent and I
need to straighten it?

Shift to the other ring. Spin your crank and watch the tooth profile.
Is one tooth bent?

Now sight along the length of the chain as you backpedal. Do you see a
damaged or errant section? That can be dangerous so if the chain itself
varies attend to the before riding.

Thanks, I'll have to check it when my garage light comes up tomorrow
morning. (I could fix the other one, but that would take riding
time!) I didn't think about chain problems -- this one only has
500-1,000 miles on it, IIRC.

Pat

Email address works as is.

On Mon, 23 Jun 2008 19:20:59 -0700, "Tom Kunich" <cyclintom@yahoo.

com said:

"A Muzi" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

Patrick Lamb said:

Looking down at my big chain ring today, I noticed the chain wobbles
maybe 1/8" (as seen against the derailer) over one part of the ring as
I pedal. Is this part of the STI design, or is the ring bent and I
need to straighten it?

Shift to the other ring. Spin your crank and watch the tooth profile. Is
one tooth bent?

Now sight along the length of the chain as you backpedal. Do you see a
damaged or errant section? That can be dangerous so if the chain itself
varies attend to the before riding.

And not knowing what age your bicycle is can be a problem as well. Older
bicycles with adjustable bottom brackets could get loose enough for the
chainrings to wobble and all it required was proper adjustment.

It's only a couple years old, so I doubt that's the problem. I'll
check to make sure.

Pat

Email address works as is.

Ben C said:

Patrick Lamb said:

Looking down at my big chain ring today, I noticed the chain wobbles
maybe 1/8" (as seen against the derailer) over one part of the ring as
I pedal. Is this part of the STI design, or is the ring bent and I
need to straighten it?

1/8" isn't much, but also check for play in the bottom bracket because
that can cause the same symptom. Just get off the bike and see if you can
wobble the cranks.

I'll double check, but since it's quite localized, I doubt if it's the
bottom bracket.

Pat

Email address works as is.

"Patrick Lamb" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

On Mon, 23 Jun 2008 19:20:59 -0700, "Tom Kunich" <cyclintom@yahoo.

com said:

And not knowing what age your bicycle is can be a problem as well. Older
bicycles with adjustable bottom brackets could get loose enough for the
chainrings to wobble and all it required was proper adjustment.

It's only a couple years old, so I doubt that's the problem. I'll
check to make sure.

Well, sealed bottom brackets could have a bad bearing in them as well. So
the idea is to see if the movement follows the cranks arms because of a
loose bearing, because the crank or rings are loose or because of a bent
chainring.

Patrick Lamb said:

On Mon, 23 Jun 2008 21:06:34 -0500, A Muzi <[email hidden]>

Quoted message said:

Patrick Lamb said:

Looking down at my big chain ring today, I noticed the chain wobbles
maybe 1/8" (as seen against the derailer) over one part of the ring as
I pedal. Is this part of the STI design, or is the ring bent and I
need to straighten it?

Shift to the other ring. Spin your crank and watch the tooth profile.
Is one tooth bent?

Now sight along the length of the chain as you backpedal. Do you see a
damaged or errant section? That can be dangerous so if the chain itself
varies attend to the before riding.

Thanks, I'll have to check it when my garage light comes up tomorrow
morning. (I could fix the other one, but that would take riding
time!) I didn't think about chain problems -- this one only has
500-1,000 miles on it, IIRC.

Responding to myself, bad form, I know. However...

The chain looked pretty straight as I sighted up it. As I suspected,
there's about 3" of ring that's displaced inward, by just about the
width of the chainring. I'm guessing it got bent leaning up against a
pole or tree at some point, or maybe the bike fell over and hit the
ring on a curb.

Is it worth trying to fix it? I'm sort of leaning toward leaving it
as is, to make sure I don't make things worse by trying to bend it
back. It's a Shimano Deore crank, and I don't know if the big ring is
steel or some flavor of aluminum.

Pat

Email address works as is.

"Patrick Lamb" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

Is it worth trying to fix it?

You can bend it back and in some cases it's almost perfect.

Patrick Lamb said:

Is it worth trying to fix it? I'm sort of leaning toward leaving it
as is, to make sure I don't make things worse by trying to bend it
back. It's a Shimano Deore crank, and I don't know if the big ring is
steel or some flavor of aluminum.

Try to determine if the ring is bent or the arm of the spider at that
location is bent. If both chainwheels move in as you spin the cranks,
it's the spider arm - if one moves in, it's the chainwheel.

A good way to straighten the arms is to use an adjustable wrench, 8" -
10", on the spider arm itself and gently bend the spider back into
shape. Spin frequently to check as you go and get a feel for it. For
the chainwheels, you may need two adjustable wrenches, one on either
side of the bend to lever it back out to where it belongs. If the bend
is tricky, you might have to get more creative with placement and
levers.

They do bend easily, so work slowly.