my crank arms fell off

Unicycles and Equipment
1

Does anyone have anything to say on loose crank arms? I was riding
around in the parking lot today. The pedals didn’t feel loose at all. I
was working on some left-footed skills. Then I was riding backwards a
bit, and as I was riding, my right crank arm just hit the ground. How
did this happen without my noticing? (What impresses me more than that
the crank arm came loose so quickly is that the nut managed to unscrew
itself just as fast.)

Another time, I was at a juggling convention. I just took my unicycle
inside, and got on, when I noticed the left pedal seemed loose. Upon
examination, I noticed that the crank arm was loose, and I was able to
unscrew the nut with my thumb.

Upon visual inspection, I can find no obvious problems with either my
hub, or the cranks. So, I guess I’ll just pound them in a bit, and hope
they stay.

Jeff Lutkus

Free e-Mail and Webspace - http://Unicyclist.com

2

Greetings

In message “my crank arms fell off”, Jeff Lutkus wrote…
>Does anyone have anything to say on loose crank arms? I was riding
>around in the parking lot today. The
pedals didn’t feel loose at all. I was working on some left-footed skills.
Then I was riding backwards a bit, and as I was riding, my right crank arm
just hit the ground. How did this happen without my noticing? (What
impresses me more than that the crank arm came loose so quickly is that
the nut managed to unscrew itself just as fast.)

Are you using cottered or cotterless cranks? Depending on which the
techniques of tightening are different.

>Another time, I was at a juggling convention. I just took my unicycle
>inside, and got on, when I noticed the
left pedal seemed loose. Upon examination, I noticed that the crank arm
was loose, and I was able to unscrew the nut with my thumb.
>
>Upon visual inspection, I can find no obvious problems with either my
>hub, or the cranks. So, I guess I’ll just
pound them in a bit, and hope they stay.
>
>Jeff Lutkus
>
>_____________________________________________________________
>Free e-Mail and Webspace - http://Unicyclist.com
>

Stay on top, Jack Halpern, IUF Vice President Website:
http://www.kanji.org

3

In article <20010610020210.DEDAE2755@sitemail.everyone.net>, Jeff Lutkus
<lutkus@unicyclist.com> wrote: )Does anyone have anything to say on loose
crank arms? I was riding around in the parking lot today. The pedals
didn’t feel loose at all. I was working on some left-footed skills. Then I
was riding backwards a bit, and as I was riding, my right crank arm just
hit the ground. How did this happen without my noticing? (What impresses
me more than that the crank arm came loose so quickly is that the nut
managed to unscrew itself just as fast.) ) )Another time, I was at a
juggling convention. I just took my unicycle inside, and got on, when I
noticed the left pedal seemed loose. Upon examination, I noticed that the
crank arm was loose, and I was able to unscrew the nut with my thumb. )
)Upon visual inspection, I can find no obvious problems with either my
hub, or the cranks. So, I guess I’ll just pound them in a bit, and hope
they stay.

What can happen with cotterless cranks is that they get stuck in unstable,
but temporarily motionless situations. They don’t come loose quickly, but
you might not notice they’re loose. When the cranks on properly, the four
sides of the hole in the crank are flush against the four sides of the
taper, and the bolt is flush against the crank. When the bolt gets a
little loose, the crank can wobble. Sometimes it will just break loose,
and you’ll get a “thunk” on every pedal revolution; other times it will
break loose, get a little out of alignment and then stick in such a way
that it’s jammed against the bolt and the taper. Then the bolt will loosen
some more and it might stick another way. This is how the crank can get
deformed, particularly if it’s aluminum, and unless you’re paying
attention you might not notice it’s happening. I think that’s especially
true if you’re working on unsual skills; if you’re just riding forward
you’ll probably feel the difference.

When you put the crank back on, you should clean and grease the tapers
first. One of the primary causes of cranks getting loose is that they
aren’t tight enough to begin with. When you install a crank on an
unlubricated taper, the friction between the two metal surfaces can lock
them together before the crank is all the way on. This then allows the
crank to wiggle during use, and eventually fall off. Grease lets you get
the crank on as far as it will go, and hopefully make the whole system
work right.

I would recommend against hammering a crank to get it on; you’re more
likely to deform the metal than get the crank on properly. -Tom (If you
have cotterless cranks, ignore everything I just said)

4

Check out http://draco.acs.uci.edu/rbfaq/FAQ/125.html for more than you
really wanted to know about why cranks fall off. This is from the
rec.bicycles FAQ.

I use red (permanent strength) Loctite thread locker on the crank nut.
That seems to keep the nut on and keeps it tight. At a minimum it makes it
less likely that you will loose the nut if the crank does get loose.

Instead of a little grease on the taper I have sometimes used Loctite
sleeve retainer (product number 609 or 640) on the taper. I use the
Loctite when I am feeling paranoid. I don’t know if it actually does any
better than a little grease but some times I like the peace of mind. My
Loctited cranks have never come loose on me.

You can find Loctite at some auto parts stores. Or you can now order it
from UnicycleSource.

This would all be moot if everyone switched over to splined ISIS drive
cranks. :slight_smile:

john_childs

>From: Jeff Lutkus <lutkus@unicyclist.com>
>
>Does anyone have anything to say on loose crank arms? I was riding around
>in the parking lot today. The pedals didn’t feel loose at all. I was
>working on some left-footed skills. Then I was riding backwards a bit,
>and as I was riding, my right crank arm just hit the ground. How did this
>happen without my noticing? (What impresses me more than that the crank
>arm came loose so quickly is that the nut managed to unscrew itself just
>as fast.)
>
>Another time, I was at a juggling convention. I just took my unicycle
>inside, and got on, when I noticed the left pedal seemed loose. Upon
>examination, I noticed that the crank arm was loose, and I was able to
>unscrew the nut with my thumb.
>
>Upon visual inspection, I can find no obvious problems with either my
>hub, or the cranks. So, I guess I’ll just pound them in a bit, and hope
>they stay.
>
>Jeff Lutkus
>
>_____________________________________________________________
>Free e-Mail and Webspace - http://Unicyclist.com

Get your FREE download of MSN Explorer at http://explorer.msn.com

5

John Childs wrote:
>
> Check out http://draco.acs.uci.edu/rbfaq/FAQ/125.html for more than you
> really wanted to know about why cranks fall off. This is from the
> rec.bicycles FAQ.

Wow! Way cool article. I’ll have to try it out when I get some new
Coker cranks.

6

Jeff Lutkus wrote:

> Does anyone have anything to say on loose crank arms? I was riding
> around in the parking lot today. The pedals didn’t feel loose at all. I
> was working on some left-footed skills. Then I was riding backwards a
> bit, and as I was riding, my right crank arm just hit the ground. How
> did this happen without my noticing? (What impresses me more than that
> the crank arm came loose so quickly is that the nut managed to unscrew
> itself just as fast.)
>
> Another time, I was at a juggling convention. I just took my unicycle
> inside, and got on, when I noticed the left pedal seemed loose. Upon
> examination, I noticed that the crank arm was loose, and I was able to
> unscrew the nut with my thumb.
>
> Upon visual inspection, I can find no obvious problems with either my
> hub, or the cranks. So, I guess I’ll just pound them in a bit, and hope
> they stay.
>
> Jeff Lutkus
>

Jeff, once that crank arm is perceived to be loose, it’s too late…if you
have alloy cranks. To keep the cranks tight, use locktite or some high
strength industrial adhesive. Torque the crank bolt/nut to 25 ft-pds.
Before a ride grab both pedals and check for wobble at the axle boss.

If you have blown out the Morse taper in the pedal boss, you can shim it
with very thin brass shims but this is only a temporary fix. Or you can
space out the outer surface of the crank boss in order for the nut/bolt to
seat firmly against the crank boss surface. Again, a temporary fix.

Next time, don’t let the cranks get loose.

George

Content-Type: text/html; charset=us-ascii

<!doctype html public “-//w3c//dtd html 4.0 transitional//en”>
<html>
<p>Jeff Lutkus wrote: <blockquote TYPE=CITE>Does anyone have anything to
say on loose crank arms? I was riding around in the parking lot
today. The pedals didn’t feel loose at all. I was working
on some left-footed skills. Then I was riding backwards a bit,
and as I was riding, my right crank arm just hit the ground. How
did this happen without my noticing? (What impresses me more than
that the crank arm came loose so quickly is that the nut managed to
unscrew itself just as fast.)
<q>Another time, I was at a juggling convention. I just took my
unicycle inside, and got on, when I noticed the left pedal seemed
loose. Upon examination, I noticed that the crank arm was loose,
and I was able to unscrew the nut with my thumb.
<r>Upon visual inspection, I can find no obvious problems with either my
hub, or the cranks. So, I guess I’ll just pound them in a bit,
and hope they stay.
<s>Jeff Lutkus <br><a href=“http://Unicyclist.com”></a> </blockquote>

<t><br>Jeff, once that crank arm is perceived to be loose, it’s too
late…if you have alloy cranks. To keep the cranks tight, use locktite
or some high strength industrial adhesive. Torque the crank bolt/nut to
25 ft-pds. Before a ride grab both pedals and check for wobble at the
axle boss.
<u>If you have blown out the Morse taper in the pedal boss, you can shim
it with very thin brass shims but this is only a temporary fix. Or you
can space out the outer surface of the crank boss in order for the
nut/bolt to seat firmly against the crank boss surface. Again, a
temporary fix.
<v>Next time, don’t let the cranks get loose.
<w>George <br> </html