Ultegra Road triple crank cracks due to fatigue.

On Sun, 23 Jul 2006 12:27:24 -0700, jim beam
wrote:

my shoes are size 13, and i /never/ "polish" the crank. ever. in fact,
i find it hard to understand how it's possible if cleats are positioned
correctly.

I have size 8 1/2 feet and "polish" the crank all the time. I could
adjust my cleats to not do so, and I guess that'd be "correct" in
terms of protecting the cranks, but my knees would ache.

JT

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wrote:
Yes.
I'm aware of crack propogation in aluminium.

It looks to me as if the fatigue occurred in the inner half (bike side)
and the outside bit was sudden.
The inner bit looked all powdered, like a salt of aluminium.

I've never seen a crank crack before.

next time you go to a swap meet, look for the campy super record cranks
of which there are invariably always a number. unless it's n.i.b.,
it'll almost certainly be cracked where the spider meets the crank arm.

I've had several frames crack on
me, a couple of seat-posts, axles etc.

John Forrest Tomlinson wrote:
On Sun, 23 Jul 2006 12:27:24 -0700, jim beam
wrote:

my shoes are size 13, and i /never/ "polish" the crank. ever. in fact,
i find it hard to understand how it's possible if cleats are positioned
correctly.

I have size 8 1/2 feet and "polish" the crank all the time. I could
adjust my cleats to not do so, and I guess that'd be "correct" in
terms of protecting the cranks, but my knees would ache.

that's a bummer. you'll have to budget for a regular crank replacement
program if you want to minimize the risk of failure and injury.

On Sun, 23 Jul 2006 13:46:17 -0700, jim beam
wrote:

John Forrest Tomlinson wrote:
On Sun, 23 Jul 2006 12:27:24 -0700, jim beam
wrote:

my shoes are size 13, and i /never/ "polish" the crank. ever. in fact,
i find it hard to understand how it's possible if cleats are positioned
correctly.

I have size 8 1/2 feet and "polish" the crank all the time. I could
adjust my cleats to not do so, and I guess that'd be "correct" in
terms of protecting the cranks, but my knees would ache.

that's a bummer. you'll have to budget for a regular crank replacement
program if you want to minimize the risk of failure and injury.

How about some pedal extensions?

On Sun, 23 Jul 2006 13:46:17 -0700, jim beam
wrote:

John Forrest Tomlinson wrote:
On Sun, 23 Jul 2006 12:27:24 -0700, jim beam
wrote:

my shoes are size 13, and i /never/ "polish" the crank. ever. in fact,
i find it hard to understand how it's possible if cleats are positioned
correctly.

I have size 8 1/2 feet and "polish" the crank all the time. I could
adjust my cleats to not do so, and I guess that'd be "correct" in
terms of protecting the cranks, but my knees would ache.

that's a bummer. you'll have to budget for a regular crank replacement
program if you want to minimize the risk of failure and injury.

Yes.

JT

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On Sun, 23 Jul 2006 21:43:59 GMT, R Brickston
rb20170REMOVE.yahoo.com@ wrote:

On Sun, 23 Jul 2006 13:46:17 -0700, jim beam
wrote:

John Forrest Tomlinson wrote:
On Sun, 23 Jul 2006 12:27:24 -0700, jim beam
wrote:

my shoes are size 13, and i /never/ "polish" the crank. ever. in fact,
i find it hard to understand how it's possible if cleats are positioned
correctly.

I have size 8 1/2 feet and "polish" the crank all the time. I could
adjust my cleats to not do so, and I guess that'd be "correct" in
terms of protecting the cranks, but my knees would ache.

that's a bummer. you'll have to budget for a regular crank replacement
program if you want to minimize the risk of failure and injury.

How about some pedal extensions?

That changes the mechanics of pedalling substantially. Might work for
some people but not not for me.

JT


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jim beam wrote in
news
Mike DeMicco wrote

I wonder if Hollowtech can be to blame; it's a delamination with
sharp corners.

have you ever seen the crack nucleate from inside?

Don't know. From the pictures shown, how can one tell?

--
Mike DeMicco

thank you, thank you,

having lots of exeperience with parts failure on race cars, I was
beginning to think bike stuff failed differently - just kidding. The
bright shiny stuff is the last to fail. The discolored old looking
stuff is the first area of failure.


wrote:
On 23 Jul 2006 12:01:32 -0700, "
wrote:


Yes.
I'm aware of crack propogation in aluminium.

It looks to me as if the fatigue occurred in the inner half (bike side)
and the outside bit was sudden.
The inner bit looked all powdered, like a salt of aluminium.

I've never seen a crank crack before. I've had several frames crack on
me, a couple of seat-posts, axles etc.


Dear G.,

I think that you have the sequence backward.

This picture . . .

http://www.pbase.com/gearoidmuar/image/63965536.jpg

. . . shows a crank that began cracking on the pedal side.

The small dark area with the (| shape is where the failure began.

You'll see a series of fine lines (((( from the pedal-side. That's
where the original crack kept cracking a little more. These lines are
often called beachmarks or clamshell marks.

| | undamaged arm, pedal side

| (| first tiny crack starts at surface damage

| ((| crack extends a little further

| (((| a third crack lays down another line

|/\/\(((| sudden disaster when cracks reach central hole corners

(The actual pattern looks like a set of ripples expanding from a point
on the pedal side, but ASCII diagrams are crude.)

This fine cracking takes time, so the inner surface of that part of
the failure will often show corrosion.

When a critical point was reached, the rest of the arm broke off
abruptly, with a strikingly ragged, irregular surface that's going to
be uncorroded. The slowly cracking initial area also tends to be
rubbed smooth, while the area of abrupt failure is left rough.

The half-moon series of fine lines is well-known.

You can see similar crank failures he

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

This one is nice because it shows how the crack began on the pedal
side:

http://pardo.net/pardo/bike/pic/fail/FAIL-010.html

See figures 4 & 5 here for a quick description and diagram of
beachmarks:

http://www.sv.vt.edu/classes/MSE2094...y/fatigue.html

Note that the abrupt failure clearly occurs when the cracking from the
pedal side finally reaches the corners of the hole in the center of
the arm.

Cheers,

Carl Fogel

On 24 Jul 2006 01:10:10 GMT, Mike DeMicco
wrote:

jim beam wrote in
news
Mike DeMicco wrote

I wonder if Hollowtech can be to blame; it's a delamination with
sharp corners.

have you ever seen the crack nucleate from inside?

Don't know. From the pictures shown, how can one tell?

Dear Mike,

In this picture . . .

http://www.pbase.com/gearoidmuar/image/63965536.jpg

.. . . the start of the failure seems obvious, given the classic
beachmark pattern expanding from the initial point of failure on the
pedal side.

Cheers,

Carl Fogel

jim beam wrote:

snip

my shoes are size 13, and i /never/ "polish" the crank. ever. in fact,
i find it hard to understand how it's possible if cleats are positioned
correctly.

It's easy -- size 13 mountain bike shoes and neoprene or rubberized
fabric (Sugoi) booties for four (or more) months of the year. They add
a lot of bulk. I also have mobile ankles. By the way, I put probably
40K on an '80s Dura Ace crank which was beaten and polished, and it
never broke. I thought the Japanese cranks were pretty tough until I
broke the Ultegra triple. I am a little suspicious of the hollow
technology. -- Jay Beattie.