Crankarm is a crankarm?

landotter said:

Neighbor can't find the left crank on a utility bike after they moved
to town. It's square taper, 170mm. Would this Sugino work as a
replacement:

http://tinyurl.com/2jsmw9

It looks obvious, but then there's this mention of unicycling, and
well, I start to wonder...is there unicycle threading? Unicycle
tapering? Wouldn't surprise me with all the different standards in
cycling.

Should work. I believe there is a slight difference in the taper between
Shimano and Campag bits, but fair chance the bike with missing crank has a
Shimano type bottom bracket.
You'll need a crank fixing nut or bolt (depending on type of bottom
bracket), and a LH pedal. I assume the neighbour lost those as well.

Quoted message said:

Alternately, if somebody has a 170mm left crank that's doing no good
in a bucket, feel free to mail it to me. :-P

Even if I did have one, I wouldn't be surprised to find it will cost more
than $12 to mail it from this side of the pond.

- Nigel

--
Nigel Cliffe,
Webmaster at http://www.2mm.org.uk/

landotter said:

Neighbor can't find the left crank on a utility bike after they moved
to town. It's square taper, 170mm. Would this Sugino work as a
replacement:

http://tinyurl.com/2jsmw9

It looks obvious, but then there's this mention of unicycling, and
well, I start to wonder...is there unicycle threading? Unicycle
tapering? Wouldn't surprise me with all the different standards in
cycling.

Alternately, if somebody has a 170mm left crank that's doing no good in
a bucket, feel free to mail it to me. :-P

"landotter" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

Neighbor can't find the left crank on a utility bike after they moved

....

Quoted message said:

It looks obvious, but then there's this mention of unicycling, and
well, I start to wonder...is there unicycle threading? Unicycle
tapering? Wouldn't surprise me with all the different standards in
cycling.

....

Just a guess here but, wouldn't one would use two "left" crank arms on a
unicycle?
One with reverse threading and one with standard threading.

Dave

Quoted message said:

"landotter" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

Neighbor can't find the left crank on a utility bike after they moved

...

Quoted message said:

It looks obvious, but then there's this mention of unicycling, and
well, I start to wonder...is there unicycle threading? Unicycle
tapering? Wouldn't surprise me with all the different standards in
cycling.

...

John Smith said:

Just a guess here but, wouldn't one would use two "left" crank arms on a
unicycle?
One with reverse threading and one with standard threading.

Yes, that's correct.

Back to the OP - Lefts fail in high proportion to rights so replacement
lefts are readily available and cheap everywhere.
--
Andrew Muzi
www.yellowjersey.org
Open every day since 1 April, 1971

A Muzi said:

Back to the OP - Lefts fail in high proportion to rights so replacement
lefts are readily available and cheap everywhere.
--
Andrew Muzi www.yellowjersey.org

Unicycle arm sets are available for cheap:
http://www.bikepartsusa.com/product_info.asp?p=01%2D98134
http://www.bikepartsusa.com/product_info.asp?p=01%2D98133

Bike Parts USA has some unicycle parts, but there's probably better
sources out there.

Jeff

A Muzi said:

Quoted message said:

"landotter" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

Neighbor can't find the left crank on a utility bike after they moved

...

Quoted message said:

It looks obvious, but then there's this mention of unicycling, and
well, I start to wonder...is there unicycle threading? Unicycle
tapering? Wouldn't surprise me with all the different standards in
cycling.

...

John Smith said:

Just a guess here but, wouldn't one would use two "left" crank arms on a
unicycle?
One with reverse threading and one with standard threading.Yes, that's correct.

Back to the OP - Lefts fail in high proportion to rights so replacement
lefts are readily available and cheap everywhere.

Ya, that surprised me.Never would I thought that crank failure would be
common enough to create a market for individual crank arms.

I'll check with the local Jesus People Punks first as they are pretty
hip to the scavenging thing.

A Muzi said:

Back to the OP - Lefts fail in high proportion to rights so replacement
lefts are readily available and cheap everywhere.

Fascinating. I guess it makes perfect sense, since the spider
probably reinforces the right crank arm / spindle interface, assuming
that's where the left arms fail.

I suspect that failures at the pedal eye should be the same for both
left and right cranks, is this borne out by experience, all ye
professional mechanics and shop owners ??

- Don Gillies
San Diego, CA

P.S. If the failure rates at the pedal eye are different for left
vs. right crank arms, then is it perhaps because the twisting flexion
is higher on the left sides ??

A ceankarmlever is CRANK... except in bicycling where a different
regime holds the reigns.

http://www.m-w.com/dictionary/crank

Jobst Brandt

On 26 Jan 2007 12:35:03 -0800, [email hidden] (Donald Gillies)

Quoted message said:

A Muzi said:

Back to the OP - Lefts fail in high proportion to rights so replacement
lefts are readily available and cheap everywhere.

Fascinating. I guess it makes perfect sense, since the spider
probably reinforces the right crank arm / spindle interface, assuming
that's where the left arms fail.

I suspect that failures at the pedal eye should be the same for both
left and right cranks, is this borne out by experience, all ye
professional mechanics and shop owners ??

- Don Gillies
San Diego, CA

P.S. If the failure rates at the pedal eye are different for left
vs. right crank arms, then is it perhaps because the twisting flexion
is higher on the left sides ??

Dear Don,

The left pedal's driving force goes all the way down to the bottom
bracket.

The right pedal's driving force gets sidetracked and goes through the
sprocket to the chain.

Cheers,

Carl Fogel

A Muzi said:

Quoted message said:

Just a guess here but, wouldn't one would use two "left" crank arms
on a unicycle? One with reverse threading and one with standard
threading.

Quoted message said:

Yes, that's correct.

Quoted message said:

Back to the OP - Lefts fail in high proportion to rights so replacement
lefts are readily available and cheap everywhere.

I wasn't aware of more left crank failures. With my many crank
failures it was about even, most breaking at the pedal eye. Of
course that stopped occurring after I modified my cranks.

http://www.chiark.greenend.org.uk/~damerell/bikes/brandt-cranks.jpg

To what do you attribute more left crank failures?

Jobst Brandt

Quoted message said:

On 26 Jan 2007 12:35:03 -0800, [email hidden] (Donald Gillies)

Quoted message said:

A Muzi said:

Back to the OP - Lefts fail in high proportion to rights so replacement
lefts are readily available and cheap everywhere.

Fascinating. I guess it makes perfect sense, since the spider
probably reinforces the right crank arm / spindle interface, assuming
that's where the left arms fail.

I suspect that failures at the pedal eye should be the same for both
left and right cranks, is this borne out by experience, all ye
professional mechanics and shop owners ??

- Don Gillies
San Diego, CA

P.S. If the failure rates at the pedal eye are different for left
vs. right crank arms, then is it perhaps because the twisting flexion
is higher on the left sides ??

Dear Don,

The left pedal's driving force goes all the way down to the bottom
bracket.

The right pedal's driving force gets sidetracked and goes through the
sprocket to the chain.

Cheers,

Carl Fogel

Humph! After doodling a few diagrams, I don't like my half-remembered
explanation.

The force where the crank meets the bottom bracket is the same for
each side, so pushing down on the left pedal transmits the same force
to the left and right side of the bottom bracket.

The explanation for left cranks failing more often may be that the
left crank force is applied all the way out at the end of the left
pedal on an unsupported arm, while the right crank force is applied
over only half as much distance before the chain supports the arm,
steadying it.

That is, the left crank is free to wave and wallow, while the right
crank is steadied by the chain engaging the sprocket. Imagine a foot
pushing on the two pedals below

BB-------------------pedal left crank
x supported only at x

sprocket
BB-------chain-------pedal right crank
x y supported at x and y

Cheers,

Carl Fogel

On 2007-01-26, [email hidden] <[email hidden]> wrote:
[snip]

Quoted message said:

Quoted message said:

The left pedal's driving force goes all the way down to the bottom
bracket.

The right pedal's driving force gets sidetracked and goes through the
sprocket to the chain.

Cheers,

Carl Fogel

Humph! After doodling a few diagrams, I don't like my half-remembered
explanation.

I felt like I also half-remembered something like this, and I've found
the link:

http://sheldonbrown.com/brandt/installing-cranks.html

"[...] Loss of crank bolt preload is greater on left than the right
cranks, because left cranks transmit torque and bending
simultaneously while right cranks transmit these forces separately.
The left crank transmits driving torque through the spindle to the
right crank and chainwheel while the right crank drives the
chainwheel directly. Besides that, the right crank transmits torque
to the spindle only when standing on both pedals. Doing this with
the right foot forward (goofy footed) is the only time the spindle
transmits reverse torque. [...]"

Quoted message said:

Quoted message said:

On 26 Jan 2007 12:35:03 -0800, [email hidden] (Donald Gillies)

Quoted message said:

A Muzi <[email hidden]> writes:

>Back to the OP - Lefts fail in high proportion to rights so replacement
>lefts are readily available and cheap everywhere.

Fascinating. I guess it makes perfect sense, since the spider
probably reinforces the right crank arm / spindle interface, assuming
that's where the left arms fail.

I suspect that failures at the pedal eye should be the same for both
left and right cranks, is this borne out by experience, all ye
professional mechanics and shop owners ??

- Don Gillies
San Diego, CA

P.S. If the failure rates at the pedal eye are different for left
vs. right crank arms, then is it perhaps because the twisting flexion
is higher on the left sides ??

Dear Don,

The left pedal's driving force goes all the way down to the bottom
bracket.

The right pedal's driving force gets sidetracked and goes through the
sprocket to the chain.

Cheers,

Carl Fogel

Humph! After doodling a few diagrams, I don't like my half-remembered
explanation.

The force where the crank meets the bottom bracket is the same for
each side, so pushing down on the left pedal transmits the same force
to the left and right side of the bottom bracket.

The explanation for left cranks failing more often may be that the
left crank force is applied all the way out at the end of the left
pedal on an unsupported arm, while the right crank force is applied
over only half as much distance before the chain supports the arm,
steadying it.

That is, the left crank is free to wave and wallow, while the right
crank is steadied by the chain engaging the sprocket. Imagine a foot
pushing on the two pedals below

BB-------------------pedal left crank
x supported only at x

sprocket
BB-------chain-------pedal right crank
x y supported at x and y

Cheers,

Carl Fogel

Double humph!

A further difference is that the left pedal force is applied
out-of-plane to the left side of the crank, but is tranmitted mostly
in-plane on the right side of the bottom bracket to the sprocket:

--- idle right pedal
|
|
S sprocket and chain in plane
|
|
F-------F much less twisting force on right side of BB
|
|
|
|
P-- push down on left pedal out at P

pushing down on left side
force is applied out of plane on pedal
twists left crank at bottom bracket

When the rider pushes down on the right pedal, the effect of the
out-of-plane force on that side is reduce because of the chain and
sprocket support about half-way along the crank.

CF

jobst.brandt said:

Quoted message said:

Back to the OP - Lefts fail in high proportion to rights so replacement
lefts are readily available and cheap everywhere.

I wasn't aware of more left crank failures. With my many crank
failures it was about even, most breaking at the pedal eye. Of
course that stopped occurring after I modified my cranks.

http://www.chiark.greenend.org.uk/~damerell/bikes/brandt-cranks.jpg

To what do you attribute more left crank failures?

I suspect he is actually referring to the instances of ruined cranks due
to a loose fit on the spindle, which is much more common on the left side.

--

David L. Johnson

You will say Christ saith this and the apostles say this; but what canst
thou say? -- George Fox.

David L. Johnson said:

Quoted message said:

Quoted message said:

Back to the OP - Lefts fail in high proportion to rights so
replacement lefts are readily available and cheap everywhere.

Quoted message said:

Quoted message said:

I wasn't aware of more left crank failures. With my many crank
failures it was about even, most breaking at the pedal eye. Of
course that stopped occurring after I modified my cranks.

Quoted message said:

Quoted message said:

http://www.chiark.greenend.org.uk/~damerell/bikes/brandt-cranks.jpg

Quoted message said:

Quoted message said:

To what do you attribute more left crank failures?

Quoted message said:

I suspect he is actually referring to the instances of ruined cranks
due to a loose fit on the spindle, which is much more common on the
left side.

I thought of that too, when I saw Carl Fogel's quote from the FAQ in
this thread. I was thinking more of crank failure from breaking off
rather than a damaged square taper.

Jobst Brandt

"Ego sum rex Romanus, et supra grammaticam." - Sigismund

Quoted message said:

A ceankarmlever is CRANK... except in bicycling where a different
regime holds the reigns.

Quoted message said:

I was thinking more of crank failure from breaking off
rather than a damaged square taper.

A "square taper" is oxymoronic, except apparently for the
self-selected lexicographer of rbt.
-------------------------------
John Dacey
Business Cycles, Miami, Florida
Since 1983
Our catalog of track equipment: online since 1996
Phone: 305-273-4440
http://www.businesscycles.com
-------------------------------

John Dacey said:

"Ego sum rex Romanus, et supra grammaticam." - Sigismund

Quoted message said:

A ceankarmlever is CRANK... except in bicycling where a different
regime holds the reigns.

Quoted message said:

I was thinking more of crank failure from breaking off
rather than a damaged square taper.

A "square taper" is oxymoronic, except apparently for the
self-selected lexicographer of rbt.
-------------------------------
John Dacey
Business Cycles, Miami, Florida
Since 1983
Our catalog of track equipment: online since 1996
Phone: 305-273-4440
http://www.businesscycles.com
-------------------------------

Dear Jobst & John

On the one hand, isn't my octalink tapered?

On the other hand, anyone who wants to quibble about language should:

First, proofread for "ceankarmlever" errors.

Second, learn the difference between "reigns" and "reins" (no bonus
for "rains"😉.

Third, offer a short, clear, convenenient way to describe the
individual parts of the crank-thingy as opposed to the whole
crank-thingy assembly.

If we limit "crank" to mean just one arm, what are two cranks
connected by a bottom bracket? A meta-crank? An armed bottom-bracket?

And let's face it, "bottom-bracket" has a silly etymology.

I'll taper off now . . .

Cheers,

Carl Fogel

John Dacey said:

A "square taper" is oxymoronic, except apparently for the
self-selected lexicographer of rbt.

Itching for a flamewar? Come on, the cross-section is square.
Technically I would call it the frustrum of a pyramid, but....

--

David L. Johnson

It is probable that television drama of high caliber and produced by
first-rate artists will materially raise the level of dramatic taste
in the nation. -- David Sarnoff, 1939

David L. Johnson said:

John Dacey said:

A "square taper" is oxymoronic, except apparently for the
self-selected lexicographer of rbt.

Itching for a flamewar? Come on, the cross-section is square.
Technically I would call it the frustrum of a pyramid, but....

Dear David,

Thanks for the best quibble I've seen in months!

Some consider the second "r" in your "frustrum" to be a spelling
error, but not me--I'm going to steal your point and complain heatedly
if any poster is so dead to shame as to refer to mythical "square
tapers" on this newsgroup.

Cheers,

Carl Fogel