broken crank arm

Jim Beam writes:

OK, found it:

http://pardo.net/bike/pic/fail-001/FAIL-016.html

Yes, I remember this pic now - in the context of the washer
modification and mileage endurance. It's certainly an interesting
idea. When you position the two washer halves, do you position
them so the gaps are at 12o/c & 6o/c or just any old way?

They are positioned randomly since the split in the conical ring is
required mainly to get it onto the spindle after which it is forced
into intimate contact with the spindle by the taper. Radial load
(the one of interest) is transferred through its ID whose area is
smaller than I like. Ideally it would be part of the spindle, a
conical face in place of the flat one, with no additional interface
to stress. I'm not sure what the ideal taper angle should be but I
could measure a wheel lug nut on a car.

I'd position them with the joins at 6 & 12 o/c because of their
potential of being stress risers i.e. away from the principal break
points at roughly 3 & 9 o/c.

I don't think the gap constitutes a stress concentration whereas a
protuberance could be.

Other than that, it's definitely an interesting idea with a lot of
merit. Otoh, I suspect the reason it's not been used in a fully
integrated pedal design is because of serviceability issues. Spark
plugs with tapered seats in alloy cylinder heads are the devil's own
job to remove if they've been in for an extended period. Likewise
wheel nuts if the wheel is bare alloy at the taper [no steel
insert]. Ordinary pedals can be tough to service anyway, but
dissimilar metals with a taper, particularly when you consider that
they're seldom if ever tightened with a torque wrench, is going to
be an issue. Many big rigs don't use conical seats on their lug
nuts for this same reason - the wheel has to be field serviceable.

I think you'll find that conical faced lug nuts used with aluminum
wheels on cars and trucks work well with a little care, such as
anti-seize paste. Ordinary pedals have problems because they are
often installed with no lubrication and they fret continuously, the
reason for using a conical seat.

Jobst Brandt

All metals will fatigue after time. Some of newer hollow crank arm
technology used by Shimano, Campagnolo and other crank manufacturers
has increased the failure rate. Another factor to consider is that the
crank takes more psi than any part on the bike. For example it has
been estimated that a rider can exert up to 600 ft lbs per revolution
while climbing. Hitting a cramkarm on the ground while cornering is a
significant cause of crank failure. Both Shimano and Campagnolo have
changed from a lifetime to limited term warranty. Personally I was
very disturbed when Campagnolo stopped honoring it's lifetime warranty
to existing original owners who purchased products with the lifetime
warranty. There was some talk at the time that people were getting
their products warrantied and reselling them. Now this was unfair to
Campy, but they should have required the customer or dealer to return
the product.

cliff wrote in message ...
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...

Randall Shimizu writes:

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)

All metals will fatigue after time. Some of newer hollow crank arm
technology used by Shimano, Campagnolo and other crank manufacturers
has increased the failure rate.

I think you'll have top sow some proof for that claim. I for one,
have had fewer failures with recent cranks than years ago, but not
much. My modified pedal attachment has made a significant differences
but the broken crank gallery has failures that we rarely see today.

http://pardo.net/pardo/bike/pic/fail/FAIL-001.html

Another factor to consider is that the crank takes more psi than any
part on the bike.

I think you'll find by simple calculation that the chain, freewheel
pawls, spokes and some other parts are more highly stressed.

For example it has been estimated that a rider can exert up to 600
ft lbs per revolution while climbing.

Foot pounds are not stress. Stress is measured in psi. Besides,
where are the 600 ft lbs measured?

Hitting a cramkarm on the ground while cornering is a significant
cause of crank failure.

How do you know that? When did you see the last time a crank broke
from striking the ground? The failures recorded in the failed crank
gallery were not a result of ground contact nor were any of the many
cranks that broke on my bicycle.

Both Shimano and Campagnolo have changed from a lifetime to limited
term warranty. Personally I was very disturbed when Campagnolo
stopped honoring it's lifetime warranty to existing original owners
who purchased products with the lifetime warranty. There was some
talk at the time that people were getting their products warrantied
and reselling them. Now this was unfair to Campy, but they should
have required the customer or dealer to return the product.

Can you explain that? How were they making money from this supposed
unfair procedure. You must realize that you had to turn in a failed
crank for a new one, so how does this work. This makes no sense at
all.

Jobst Brandt

-snip-
Randall Shimizu writes:
Both Shimano and Campagnolo have changed from a lifetime to limited
term warranty. Personally I was very disturbed when Campagnolo
stopped honoring it's lifetime warranty to existing original owners
who purchased products with the lifetime warranty. There was some
talk at the time that people were getting their products warrantied
and reselling them. Now this was unfair to Campy, but they should
have required the customer or dealer to return the product.

wrote:
Can you explain that? How were they making money from this supposed
unfair procedure. You must realize that you had to turn in a failed
crank for a new one, so how does this work. This makes no sense at
all.

Campagnolo has never, contrary to popular myth, supported
any product with a lifetime warranty.

--
Andrew Muzi
www.yellowjersey.org
Open every day since 1 April, 1971

"A Muzi" wrote in message
...
-snip crank failure-

Jack Daniels writes:
Do you have any pics you can post of this? The only
dura-ace
failure on the "pardo" gallery is clearly from a loading
mode
oriented outside normal service.

wrote:
I think Carl Fogel has a picture of my DuraAce on his web
site
-snip-

wrote:
The only Shimano crank failure that I remember is Amit
Ghosh's odd DuraAce disaster--it failed in the middle and
may be the one that Jim mentions:
http://pardo.net/pardo/bike/pic/fail/FAIL-010.html
-snip-

They're a dime a dozen:
http://www.yellowjersey.org/photosfr...t/yesdeydo.jpg

Andrew, that looks like a T.A. crank arm and not a Shimano. --
Jay Beattie.