Just snapped 20-yr-old crank arm...

I've been riding an Exel crank on my commuter for 20 years now.
Actually, it was on my first racing bike. Today it snapped. My foot
hit the ground on a bumpy dirt road uphill, with the pedal still
clipped to it. No crash. Man, that was a first. I suppose it's
something you don't want to happen too often. I wonder if this kind of
thing is going to start happening with all this 20-year-old alloy
stuff I'm using right now... Oh well! I must have another crank in a
box around here somewhere...

--JP

Jeff Potter writes:

I've been riding an Exel crank on my commuter for 20 years now.

Was it standing in your garage that long or did it get any mileage?
How much? Where did it break and how does the break look? If it was
bad material, the fracture will be uniformly colored. If it broke
gradually from a crack initiation it will show waves from the clean
(last failure) to the initiation point.

Actually, it was on my first racing bike. Today it snapped. My
foot hit the ground on a bumpy dirt road uphill, with the pedal
still clipped to it. No crash. Man, that was a first. I suppose
it's something you don't want to happen too often. I wonder if this
kind of thing is going to start happening with all this 20-year-old
alloy stuff I'm using right now... Oh well! I must have another
crank in a box around here somewhere...

As I have related often, failures at the pedal eye occurred on my
bicycle about every 10,000 miles on the average for more than 25
years. That's a lot of cranks and they were mostly Campagnolo and
later Shimano. Since then I modified the pedal end of the cranks so
they no longer fret, cause crack initiation, and break off through the
pedal eye.

So where did your crank break?

Jobst Brandt

wrote in message ...
Jeff Potter writes:

I've been riding an Exel crank on my commuter for 20 years now.

Was it standing in your garage that long or did it get any mileage?
How much? Where did it break and how does the break look? If it was
bad material, the fracture will be uniformly colored. If it broke
gradually from a crack initiation it will show waves from the clean
(last failure) to the initiation point.

Thanks, Jobst, yer the man! : ) The break is 2" above the pedal eye.
It is half white, half black and all rough with 1/8" roughnesses. I
rode it about twice a week half the year. But that crank might have
been idle a few years over those 20 yrs. My riding is irregular and I
swapo among bikes so I can't estimate it well.

[ ]
As I have related often, failures at the pedal eye occurred on my
bicycle about every 10,000 miles on the average for more than 25
years. That's a lot of cranks and they were mostly Campagnolo and
later Shimano. Since then I modified the pedal end of the cranks so
they no longer fret, cause crack initiation, and break off through the
pedal eye.

Sounds cool.

Ya know, this is about my first bike part failure. I ride with what
many call "crap." Old parts, lots of nice old Campy, tho; duct tape
here and there; it all works but some folks laugh. It's not in as bad
of tune as some racers' stuff I've seen (bent, hardly functioning
levers, bars, etc.). But I haven't had failures. Not that often
anyway. Maybe once a decade. More often due to simple accident---and
even then only once a decade as well (like bungie falling into spokes:
once). I have had a few rear axles break over the years---but never on
my racing bike for some reason. Bikes sure seem robust and tolerant by
and large. Perfect machines for me! : ) Especially when you branch
out to HPVs---I've had cargo bays last and work hard for years made
out of coroplast and zipties. I've gotten good speed gains from
ducttape and pieces of lycra. This is the scale of materials I like to
work with. : )

So where did your crank break?

Jobst Brandt

wrote
... Since then I modified the pedal end of the cranks so
they no longer fret, cause crack initiation, and break off through the
pedal eye.

Can you kindly point to where you have described the modifications. I
recall you writing about similar design issues with lug nuts on auto wheels,
but I must have missed your description of the actual mods.

Cheers, Shawn

On Tue, 25 May 2004 22:17:17 GMT, "Shawn Amir"
wrote:

wrote
... Since then I modified the pedal end of the cranks so
they no longer fret, cause crack initiation, and break off through the
pedal eye.

Can you kindly point to where you have described the modifications. I
recall you writing about similar design issues with lug nuts on auto wheels,
but I must have missed your description of the actual mods.

Cheers, Shawn


Dear Shawn,

Here's one of Jobst's posts on his lug-nut pedal
modification:

http://groups.google.com/groups?selm...&output=gplain

David Damerell has done us all a favor by taking the time
and trouble to host a 700kb picture of Jobst's modified
pedal and crank:

http://www.chiark.greenend.org.uk/~d...ndt-cranks.jpg

At full size, the picture clearly shows the split in the
conical washer around the threaded pedal shaft and
corresponding conical depression in the pedal eye.

You can find more details by searching for "jobst lug" at:

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

While google groups is slow to include new posts (up to a
day's delay), it's easily accessible (no newsreader needed),
offers a simple search, and goes back to the crack of doom
for rec.bicycles.tech.

Carl Fogel

wrote:
As I have related often, failures at the pedal eye occurred on my
bicycle about every 10,000 miles on the average for more than 25
years. That's a lot of cranks and they were mostly Campagnolo and
later Shimano.

good lord, that scares the crap out of me. would you venture a guess at
the standard deviation of those failures? (not that i'm worried with
16,000 miles on my current crank and memories of a catastrophic failure
behind me).
--
david reuteler

David Reuteler writes:

As I have related often, failures at the pedal eye occurred on my
bicycle about every 10,000 miles on the average for more than 25
years. That's a lot of cranks and they were mostly Campagnolo and
later Shimano.

Good lord, that scares the crap out of me. Would you venture a
guess at the standard deviation of those failures? (Not that I'm
worried with 16,000 miles on my current crank and memories of a
catastrophic failure behind me).

I don't know but that was more than one per year and the last
Campagnolo Cranks were C-Record that failed in less than 3000 miles.
That's when I switched to Dura Ace and finally modified these to put
an end to crank inspections before every ride. Although others had
failures, I had more than average occurrences. These my be affected
by the gears I ride and the terrain. I weight 180 lbs.

http://tinyurl.com/adls

As you can see, there are a lot of tours in between 1960 and 1990
whose reports were lost but they were much like the ones described.

Anyone who is good at searching the web for old postings and can find
those reports (that appeared on REC.BICYCLE) would be greatly
appreciated. I have not been able to find them and the people I rode
with and are mentioned in them would love to have copies.

Jobst Brandt

wrote:
How much? Where did it break and how does the break look? If it was
bad material, the fracture will be uniformly colored. If it broke
gradually from a crack initiation it will show waves from the clean
(last failure) to the initiation point.

Please could you post a (link to a) picture showing these waves.

Also, you mention "crank inspection before every ride". What should
one look for?

Thank you,
Konstantin.

On 26 May 2004, Evan Evans wrote:
Old bikes are nice to look at but you are taking your chances riding
them. Even the best components ore subject to fatigue. If you ride
much a new bike every once & awile is cheep insurance. One trip to the
emergancy room will go along way on that new bike.

You are taking your chances every time you ride what you know
nothing about. Better be well acquainted with your equipment,
whether old or new.

Sergio
Pisa

Old bikes are nice to look at but you are taking your chances riding
them. Even the best components ore subject to fatigue. If you ride
much a new bike every once & awile is cheep insurance. One trip to the
emergancy room will go along way on that new bike.