broken crank arm

I sheared off my right crank arm near the pedal tonight while riding
home. I was thankfully making a left turn, so my weight was on the
left. The arm sheared as I was applying torque and it made me fall to
the right. My backpack saved me from serious injury as I landed on my
right side back. That crank is a 20+ years old Stronglight 105 (anyone
remember this one?). The crank had seen heavy usage for about 5 years
in the early 80's when it was on my only bike. Since then it's use has
been relatively light. Maybe a total of 15k-20k miles. I've weighed the
same all these years: 150#.

I know this has been discussed before, but can this be attributed
strictly to fatigue, or age, or poor design. This is a grooved, forged
"alloy" crank arm. Should I take any precautions to my other cranks
such as replacement at a certain point? (for example a Ritchey
non-grooved arm from the late 80's/early 90's that is on my primary CX
bike, which I use to -race - CX)
Thanks for any input.

BTW, I was going to replace the broken crank with a NOS Stonglight
93...


--
cliff

cliff wrote:
I sheared off my right crank arm near the pedal tonight while riding
home. I was thankfully making a left turn, so my weight was on the
left. The arm sheared as I was applying torque and it made me fall to
the right. My backpack saved me from serious injury as I landed on my
right side back. That crank is a 20+ years old Stronglight 105 (anyone
remember this one?). The crank had seen heavy usage for about 5 years
in the early 80's when it was on my only bike. Since then it's use has
been relatively light. Maybe a total of 15k-20k miles. I've weighed the
same all these years: 150#.

I know this has been discussed before, but can this be attributed
strictly to fatigue, or age, or poor design.

it probably failed because of fatigue [although lack of photos make this
a guess!] fatigue in this situation is typically a function of
design/manufacture execution, any damage & material. age can come into
it with some alloy systems also.

This is a grooved, forged
"alloy" crank arm.

consider that neither campy nor shimano, the largest manufacturers with
the largest r&d budgets, use grooved cranks these days. a smooth oval
design helps mitigate fatigue.

Should I take any precautions to my other cranks
such as replacement at a certain point? (for example a Ritchey
non-grooved arm from the late 80's/early 90's that is on my primary CX
bike, which I use to -race - CX)

unless you have access to crack testing equipment, periodic replacement
is the the only safe way to go. consider the maufacturer's warranty as
an indicator! you can also undertake regular visual inspection, but
it's no guarantee, especially if you don't have much experience of what
you're looking for.

Thanks for any input.

BTW, I was going to replace the broken crank with a NOS Stonglight
93...


i'd use campy or shimano. search on this group for the link to a
gallery of broken cranks. there's no new campy represented, and only
one freak shimano. unfortunately, stronglight is there more than once.

cliff wrote:

I sheared off my right crank arm near the pedal tonight while riding
home.

Ah yes - they usually go at that end.

snip

I know this has been discussed before, but can this be attributed
strictly to fatigue, or age, or poor design.

The pedal gnawing away at the face of the crank, and some fatigue.

This is a grooved, forged
"alloy" crank arm. Should I take any precautions to my other cranks
such as replacement at a certain point? (for example a Ritchey
non-grooved arm from the late 80's/early 90's that is on my primary CX
bike, which I use to -race - CX)

I would consider changing those if they have been riddden every week.
There are no hard and fast rules - it depends on your weight, road
surfaces, mileage, riding style etc etc.

On Tue, 26 Oct 2004 06:43:18 -0700, jim beam wrote:

consider that neither campy nor shimano, the largest manufacturers with
the largest r&d budgets,

and the largest marketing departments. I don't think there is anything
magic about their cranks.

unless you have access to crack testing equipment, periodic replacement is
the the only safe way to go. consider the maufacturer's warranty as an
indicator!

Oh, boy. Do you get a commission on this? Sure, things break.
Eventually. But it it ludicrous to replace every part based on the
manufacturer's warranty. Most spokes have no warranty at all, but in
properly-built wheels they can last for decades. I don't have any cranks
that old, but I have hubs and seatposts that are nearly 40 and going
strong.

Most parts, including cranks, don't go from pristine to failure without
some signs. Look at the cracks on that gallery of broken cranks; most
have a large area that is corroded, indicating the crack was there for a
long time before it completely failed. A simple visual inspection,
replacing parts that show cracks, is a better idea than replacing every
part when its warranty runs out.

i'd use campy or shimano. search on this group for the link to a gallery
of broken cranks. there's no new campy represented, and only one freak
shimano. unfortunately, stronglight is there more than once.

And Campy has many, many representatives, mostly from the same time period
as the stronglight that broke in this story. Maybe a good idea to avoid
cranks of that era, and to avoid those with grooves cut into them, but not
a particular endorsement of shimano or Campagnolo.

--

David L. Johnson

__o | You will say Christ saith this and the apostles say this; but
_`\(,_ | what canst thou say? -- George Fox.
(_)/ (_) |

cliff writes:

I know this has been discussed before, but can this be attributed
strictly to fatigue, or age, or poor design.

It's not poor design, there are still many stronglight 93/105 cranks
on the road (105 is just a 93 with rings that are missing a spider,
105bis is drilled as well.)

All cranks are aluminum. Aluminum has no lower fatigue limit. After
XYZ fatigue cycles, aluminum will fail. There is no way around this
problem.

About the only thing you can do is inspect the cranks for hairline
cracks regularly, possibly with a non-permanent magic marker which
will infiltrate the cracks and make them visible. For failures at the
pedal eye, you can use pedal washers and/or adopt jobst brandt's 45
degree chamfering (beveling?) technique on the pedal spindle, if you
have access to machine tools. search the usenet archives
(www.google.com, "Groups" link) for details

- Don Gillies
San Diego, CA

On Tue, 26 Oct 2004 15:23:50 -0400, "David L. Johnson"
wrote:

Most parts, including cranks, don't go from pristine to failure without
some signs. Look at the cracks on that gallery of broken cranks; most
have a large area that is corroded, indicating the crack was there for a
long time before it completely failed. A simple visual inspection,
replacing parts that show cracks, is a better idea than replacing every
part when its warranty runs out.

[jim beam wrote:]

i'd use campy or shimano. search on this group for the link to a gallery
of broken cranks. there's no new campy represented, and only one freak
shimano. unfortunately, stronglight is there more than once.

And Campy has many, many representatives, mostly from the same time period
as the stronglight that broke in this story. Maybe a good idea to avoid
cranks of that era, and to avoid those with grooves cut into them, but not
a particular endorsement of shimano or Campagnolo.

Dear Cliff, Jim, and David,

This is probably the gallery of broken parts that Jim and
David have in mind:

http://pardo.net/pardo/bike/pic/fail/000.html

Carl Fogel

On 26 Oct 2004 12:48:48 -0700, (Donald
Gillies) wrote:

cliff writes:

I know this has been discussed before, but can this be attributed
strictly to fatigue, or age, or poor design.

It's not poor design, there are still many stronglight 93/105 cranks
on the road (105 is just a 93 with rings that are missing a spider,
105bis is drilled as well.)

All cranks are aluminum. Aluminum has no lower fatigue limit. After
XYZ fatigue cycles, aluminum will fail. There is no way around this
problem.

About the only thing you can do is inspect the cranks for hairline
cracks regularly, possibly with a non-permanent magic marker which
will infiltrate the cracks and make them visible. For failures at the
pedal eye, you can use pedal washers and/or adopt jobst brandt's 45
degree chamfering (beveling?) technique on the pedal spindle, if you
have access to machine tools. search the usenet archives
(www.google.com, "Groups" link) for details

- Don Gillies
San Diego, CA

Dear Cliff and Don,

To search, go he

http://groups.google.com/groups?hl=e....bicycles.tech

select "search only in rec.bicycles.tech," and search for
"jobst damerell pedal eye," which will lead you to:

http://groups.google.com/groups?q=jo...4ax.com&rnum=1

or http://tinyurl.com/6ymve

which in turn mentions where David Damerell has very nicely
hosted a detailed picture for us of Jobst's conical washers
and chamfered pedal eyes.

All of which leads up to my question: has anyone else on
rec.bicycles.tech actually modified their pedal eyes like
this?

Carl Fogel

David L. Johnson wrote:
On Tue, 26 Oct 2004 06:43:18 -0700, jim beam wrote:


consider that neither campy nor shimano, the largest manufacturers with
the largest r&d budgets,


and the largest marketing departments.

that's not mutually exclusive to research or q.c.

I don't think there is anything
magic about their cranks.

"magic", no. "quality", yes.



unless you have access to crack testing equipment, periodic replacement is
the the only safe way to go. consider the maufacturer's warranty as an
indicator!


Oh, boy. Do you get a commission on this? Sure, things break.
Eventually. But it it ludicrous to replace every part based on the
manufacturer's warranty. Most spokes have no warranty at all, but in
properly-built wheels they can last for decades. I don't have any cranks
that old, but I have hubs and seatposts that are nearly 40 and going
strong.

one broken spoke in a wheel of many is not a catastrophe. a broken
crank is. the op has concerns about failure, and also has concerns
about not being able to see something similar in the future. short of
recommending they spend money on a dye penetrant kit & leaning how to
use it properly, the /safe/ advice is replacement. new cranks are
cheap, particularly if you have uncertain mileage, weight, strength &
habits of leaning up against nice scratchy stone walls.


Most parts, including cranks, don't go from pristine to failure without
some signs. Look at the cracks on that gallery of broken cranks; most
have a large area that is corroded, indicating the crack was there for a
long time before it completely failed. A simple visual inspection,
replacing parts that show cracks, is a better idea than replacing every
part when its warranty runs out.


i'd use campy or shimano. search on this group for the link to a gallery
of broken cranks. there's no new campy represented, and only one freak
shimano. unfortunately, stronglight is there more than once.


And Campy has many, many representatives, mostly from the same time period
as the stronglight that broke in this story. Maybe a good idea to avoid
cranks of that era

agreed - maybe i should qualify - i'd use /new/ campy or shimano.

, and to avoid those with grooves cut into them, but not
a particular endorsement of shimano or Campagnolo.

On Tue, 26 Oct 2004 21:32:30 -0700, jim beam wrote:

one broken spoke in a wheel of many is not a catastrophe. a broken crank
is. the op has concerns about failure, and also has concerns about not
being able to see something similar in the future. short of recommending
they spend money on a dye penetrant kit & leaning how to use it properly,
the /safe/ advice is replacement. new cranks are cheap, particularly if
you have uncertain mileage, weight, strength & habits of leaning up
against nice scratchy stone walls.

Replacement how often? Based on what criteria? By that logic, it would
be "prudent" to regularly replace brakes, seatposts, forks, frames,
stems, as well as bars and --- well, every single part, as a preventative
measure. The failure of a brake could be disastrous; the potential
risk of impalement due to failure of a seatpost is too awful to
contemplate. Bars and stems _do_ fail.

This all seems too scary to be "safe", and yet millions of cyclists manage
not to impale themselves on broken seatpost shards year after year.

Occasionally, some part may fail. For most riders, that is a very rare
event, and usually one that is not unpredictable. You should periodically
inspect every part for cracks as well as wear. Cranks, stems, bars, and
brakes should get a close examination, since they are known to fail --
depending on design. Most failures do not result in a catastrophe.

But if you consider it prudent to replace parts that show no signs of
failure on a regular basis, what you should be doing is replacing your
entire bike every two years, and that is neither cheap nor reasonable.

The amount of risk-aversion you are displaying suggests that you consider
cycling too dangerous to engage in.

--

David L. Johnson

__o | The lottery is a tax on those who fail to understand
_`\(,_ | mathematics.
(_)/ (_) |

(Donald Gillies) wrote in message ...
[...]
About the only thing you can do is inspect the cranks for hairline
cracks regularly, possibly with a non-permanent magic marker which
will infiltrate the cracks and make them visible. For failures at the
pedal eye, you can use pedal washers and/or adopt jobst brandt's 45
degree chamfering (beveling?) technique on the pedal spindle, if you
have access to machine tools. search the usenet archives
(www.google.com, "Groups" link) for details

- Don Gillies
San Diego, CA



I get concerned everytime this subject comes up. I have a bike with
old nuovo record cranks. I know that these have been used a lot before
I got them, and I am now using them.

I try to inspect the cranks regularly (once a month or so), with
careful attention to the pedal holes. However, there are so many scuff
marks all over the cranks and especially near the pedal holes-- it
makes me wonder if I am missing any cracks which may be in progress.

So my question:
Is it adviseable to "polish out" scuffs and scratches? I think if I
had a nice surface finish, I would be able see any cracks better.

-H.