Help. My self-extracting crank bolts spontaneously self-extract

Benjamin Weiner wrote:

David Damerell wrote:

I don't see why not.
Practical observation; I've installed cranks with a 6mm allen key on which
I've then ridden thousand of miles without anything bad happening.

This happens, but it's also an example of the NASA theory of failure
analysis: we did it before and nothing broke, so we'll keep doing it.
There is some margin for error for people who are light on equipment.
Heavy people, mashers, people who stand on the pedals a lot will
have more failures.

Theoretical basis; Mark Hickey says 30 foot-pounds. My 6mm allen key is
about 4" long, and I reckon I can lean on it with about half my body
weight.

NFW. 4" is way too short. You aren't actually applying the force at
the very end of the allen key handle, and you aren't really putting
half your weight on it. I recommend borrowing a torque wrench (or buy
a cheap beam-type one) and trying it. The crank doesn't reach a hard
stop like a nut and bolt and it is really surprising how much you have
to reef on a nominal 16" long torque wrench handle to reach 30 foot
pounds - I sometimes give up at 25 ft-lb, the lower end of the spec
range.

Ben's probably right - if you figure 3.5" as the center of your
effort, you'd have to put over 100 pounds (45kg) of push on that
skinny little wrench. I know it IS possible to do that, but it will
be VERY uncomfortable at best (and virtually impossible for most
people). You can test the concept by lifting 100 pounds of anything
with a hard handle the width of that allen wrench - it will hurt. Or,
if you weigh about 200 pounds, put two allen wrenches on two
horizontal surfaces and lift yourself off the ground with only your
thumbs, on top of the allen wrenches. That's how hard you have to
push to get to the required spec.

It IS amazing how far you have to turn the bolt to get the proper
torque AFTER it gets up to about 20 ft/lbs - there are a lot of
amazing molecular-level things going on in the interface between the
spindle and crank, and doing it with a torque wrench once will help
you figure out how to do it right even without a torque wrench.

Mark Hickey
Habanero Cycles
http://www.habcycles.com
Home of the $695 ti frame

On Mon, 17 Nov 2003 12:45:48 +0000, Michael Tordoff wrote:
-snip-
cranks start "clunking" after less than 10 miles -snip-

"David L. Johnson" wrote in
message ...
-snip-
sounds like the cranks are shot. Square-taper cranks can easily be damaged by riding them
while they are loose. Once the tapers get rounded they will never be
right again. Repeated loosening is a sign of that.

JP wrote:
Or maybe not a problem at all. On my first good bike I did a novice's
job of tightening the crank bolts on my Record crank and had several
occurences of loose crank arms happening a long way from a wrench.
Eventually I did get them tightened down properly and got many years
of use out of them.

I frankly don't see how riding cranks with loose bolts is going to
round the tapers, unless they are so loose that you spin them on the
spindle. I also think it would take a lot of effort to compress the
alloy in such a way that you could not get them to tighten square on
the spindle. I think the issue is the surface area of the crank that
could be damaged by banging around a loose crank, versus the surface
area of the crank that contacts the spindle when it is properly
torqued. One thing I can't visualize at all is how this could lead to
making it impossible to keep the bolts tight.

I'm not saying it is impossible to ruin a crank by riding it with a
loose crank arm, I'm saying that I think it is a lot more difficult
than the impression you get from the experts here, and I'd guess that
a lot of people have been convinced that their cranks were ruined when
all they needed to do was torque them down properly. (Don't know about
splined cranks, though.)


Yes, you make a good point. It certainly is a question of
degree. The OP should indeed lubricate the fasteners well (
both the threads and the faces) , lubricate that tapers if
his religion allows that ( I do; others don't), torque
properly to the rating for that crank ( or 40Nm if no other
number is indicated), and then carry a wrench along on rides
for a while just in case.

Yes, you're right that there's no harm in doing the job
correctly, even at this late date, to see if the cranks are
still useful.

That being said, the more experienced writers here are
cynical because we are familiar with the usual crank sales
process, which is :
commiseration and sympathy, lubricate fasteners and tapers,
torque crank properly, sell new crank two days later after
it loosens once again.

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

Benjamin Weiner wrote:
David Damerell wrote:
Theoretical basis; Mark Hickey says 30 foot-pounds. My 6mm allen key is
about 4" long, and I reckon I can lean on it with about half my body
weight.
NFW. 4" is way too short. You aren't actually applying the force at
the very end of the allen key handle, and you aren't really putting
half your weight on it.

Aren't I? Hold the crank with one hand, the key with the other, and
*hoik* my feet off the floor?
--
David Damerell flcl?

Mark Hickey wrote in message . ..

NFW. 4" is way too short. You aren't actually applying the force at
the very end of the allen key handle, and you aren't really putting
half your weight on it. I recommend borrowing a torque wrench (or buy
a cheap beam-type one) and trying it. The crank doesn't reach a hard
stop like a nut and bolt and it is really surprising how much you have
to reef on a nominal 16" long torque wrench handle to reach 30 foot
pounds - I sometimes give up at 25 ft-lb, the lower end of the spec
range.

Ben's probably right - if you figure 3.5" as the center of your
effort, you'd have to put over 100 pounds (45kg) of push on that
skinny little wrench. I know it IS possible to do that, but it will
be VERY uncomfortable at best (and virtually impossible for most
people). You can test the concept by lifting 100 pounds of anything
with a hard handle the width of that allen wrench - it will hurt. Or,
if you weigh about 200 pounds, put two allen wrenches on two
horizontal surfaces and lift yourself off the ground with only your
thumbs, on top of the allen wrenches. That's how hard you have to
push to get to the required spec.

What changed? Are cranks softer now? Has the wide(r) availability of
torque wrenches lifted everyone's standards? Have we simply learned
more?

No intention to be disagreeable; I'm merely curious. When I was
taught this stuff in the Nuovo Record era, the mechanics at Turin in
Chicago said to take the bike down from the stand, stand it on its
wheels, and turn the Campy Peanut Butter Wrench (which is only about
4-5" long) as far/hard as you could, really putting your weight on top
of it. Has that ceased to be good enough? Was it never really good
enough?

Peter Storey

In article ,
says...

No intention to be disagreeable; I'm merely curious. When I was
taught this stuff in the Nuovo Record era, the mechanics at Turin in
Chicago said to take the bike down from the stand, stand it on its
wheels, and turn the Campy Peanut Butter Wrench (which is only about
4-5" long) as far/hard as you could, really putting your weight on top
of it. Has that ceased to be good enough? Was it never really good
enough?

Unless you are really light weight and weak, that method will work well.
The reason is that most problems occur from not tightening the bolt enough,
not too much.
----------------
Alex

David Damerell wrote in message ...
Benjamin Weiner wrote:
David Damerell wrote:
Theoretical basis; Mark Hickey says 30 foot-pounds. My 6mm allen key is
about 4" long, and I reckon I can lean on it with about half my body
weight.
NFW. 4" is way too short. You aren't actually applying the force at
the very end of the allen key handle, and you aren't really putting
half your weight on it.

Aren't I? Hold the crank with one hand, the key with the other, and
*hoik* my feet off the floor?

Dear David,

On the one hand, I'm inclined to agree with you that
surprising things can be done with small tools.

On the other hand, I've had a Honda shop foreman
patiently demonstrate how wrong I was in roughly
the same situation. I put what was at the time
about 180 pounds of force onto a short allen key
in the manner that you describe and triumphantly
said, "There! That's tight!"

The foreman, a burly 250-pound fellow with fingers
like small bananas, was sitting on a stool and working
on the front wheel. He reached over and effortlessly
turned the key a quarter turn further with one hand,
pulling it down and toward him. "Not tight enough,"
was his laconic comment.

After using a torque wrench, he explained that much
of my weight had actually been so far up the short
key that it was more likely to tip the end of the
key in the recess and ruin things, not rotate it,
given the short end of the L-shape sticking out.

Grateful for his advice, I proceeded to break a
clutch tool, but that's another story.

Carl Fogel

Mark Hickey wrote in message . ..
(JP) wrote:

I'm not saying it is impossible to ruin a crank by riding it with a
loose crank arm, I'm saying that I think it is a lot more difficult
than the impression you get from the experts here, and I'd guess that
a lot of people have been convinced that their cranks were ruined when
all they needed to do was torque them down properly. (Don't know about
splined cranks, though.)

The problem is that the BB spindle is very hard, and the aluminum
crank is very soft. If the crank rotates on the spindle, the taper
fit is no longer square, but very slightly "bowed" on each of the
flats.

If the crank rotates 90+ degrees on the spindle, no kidding it will
mess up the crank. Do people really do this? I thought that what
happened (as it did with me) was that the crank got a little loose and
you could feel it flopping a little. I tightened the bolt by hand
enough to keep it from getting to the point where the crank would
start to round the flats against the spindle. Hard to do with the
Allen head bolts, though.

However, like it or not, most cranks that have been ridden any real
distance loose are ruined. Heavier, stronger riders will damage them
quicker, and will have less luck getting a marginal crank to stay put
once it's tightened. Lighter riders or those who spend very little
time out of the saddle will do much less damage to a loose crank, and
will have a better chance of successfully using a damaged crank.

It might depend on the stupidity of the rider. Stupid as I was in not
properly tightening the bolts, I *did* have sense enough not to try to
jam up hills or get out of the saddle until I fixed the problem, and
made a special effort to pedal smoothly to minimize the rattling of
the crank arm. You would think that, if nothing else, a certain
concern for sensitive parts of the anatomy would keep a rider with a
loose crank arm from getting out of the saddle.

I still think that the number of people who have at one time or the
other experienced a loose crank arm, when compared to the number of
people who ruined their cranks as a result of it, is probably pretty
big.

JP

(Peter Storey) wrote:

Mark Hickey wrote:

Ben's probably right - if you figure 3.5" as the center of your
effort, you'd have to put over 100 pounds (45kg) of push on that
skinny little wrench. I know it IS possible to do that, but it will
be VERY uncomfortable at best (and virtually impossible for most
people). You can test the concept by lifting 100 pounds of anything
with a hard handle the width of that allen wrench - it will hurt. Or,
if you weigh about 200 pounds, put two allen wrenches on two
horizontal surfaces and lift yourself off the ground with only your
thumbs, on top of the allen wrenches. That's how hard you have to
push to get to the required spec.

What changed? Are cranks softer now? Has the wide(r) availability of
torque wrenches lifted everyone's standards? Have we simply learned
more?

No intention to be disagreeable; I'm merely curious. When I was
taught this stuff in the Nuovo Record era, the mechanics at Turin in
Chicago said to take the bike down from the stand, stand it on its
wheels, and turn the Campy Peanut Butter Wrench (which is only about
4-5" long) as far/hard as you could, really putting your weight on top
of it. Has that ceased to be good enough? Was it never really good
enough?

I think the PBW is a little longer than that, and every inch
significantly reduces the pressure needed on the handle (not to
mention a bare hex key is much less comfortable to turn). Thing is,
there's certainly a margin of safety in the published spec, and I'm
sure most cranks won't fail at a somewhat lower torque. You could
reduce the torque on all the fasteners on your bike by half and you
would probably get away with it (at least for a while).

That said, I always figured "why not do it right"?

Mark Hickey
Habanero Cycles
http://www.habcycles.com
Home of the $695 ti frame

On Wed, 19 Nov 2003 01:28:26 +0000, A Muzi wrote:

I frankly don't see how riding cranks with loose bolts is going to round
the tapers, unless they are so loose that you spin them on the spindle.

Think in the other direction. I'm not talking about rounding the corners,
like a ruined spoke nipple, but in the direction of the axle. The flat
taper develops a flair at both ends, which increases the squirm that all
cranks have, which allows the bolt to get too loose, so that it loosens
itself further from vibration.

I'm not saying it is impossible to ruin a crank by riding it with a
loose crank arm, I'm saying that I think it is a lot more difficult than
the impression you get from the experts here

Maybe you've never seen a crank ruined this way. It really does happen,
and is fairly easy to do.

--

David L. Johnson

__o | There is always an easy solution to every human problem - neat,
_`\(,_ | plausible, and wrong. --H.L. Mencken
(_)/ (_) |

On Wed, 19 Nov 2003 08:04:07 +0000, Peter Storey wrote:

No intention to be disagreeable; I'm merely curious. When I was taught
this stuff in the Nuovo Record era, the mechanics at Turin in Chicago said
to take the bike down from the stand, stand it on its wheels, and turn the
Campy Peanut Butter Wrench (which is only about 4-5" long) as far/hard as
you could, really putting your weight on top of it. Has that ceased to be
good enough? Was it never really good enough?

Well a peanut-butter wrench (easily longer than 6", but let's not quibble)
gives several times the torque as most L-shaped allen wrenches, or
T-wrenches. It will probably be enough. Problem is, that tightening
these bolts with just a dinky allen wrench (2-3" long at most, and too
thin to really grab well) is impossible. I use allen key sockets, which
are a lot better.

--

David L. Johnson

__o | Become MicroSoft-free forever. Ask me how.
_`\(,_ |
(_)/ (_) |