Crank arm keeps coming loose

[Nick]

I recently built a fixed gear bike and the left crank arm keeps coming
loose. I have some grease in the square taper. What would cause the
bolt to unscrew?

-Nick

 

[Diablo Scott]

Nick wrote:
> I recently built a fixed gear bike and the left crank arm keeps coming
> loose. I have some grease in the square taper. What would cause the
> bolt to unscrew?
>
> -Nick

Sounds like the square hole in the left crank arm (apologies to the
purists) is shot. Could be from damage on initial installation, from
insufficient engagement, or from normal wear if it's an old crank. My
experience is once it starts coming loose it'll only get worse. You can
try rotating the arms 90° on the spindle in hopes of getting more
surface area and crank down real tight. Good luck and be careful.

--
My bike blog:
http://diabloscott.blogspot.com/

 

[Graham Steer]

I have had this problem with old cranks. I solved it by shrink fitting the
crank. To do this put the non pedal end in a pan of boiling water and get it
well and truly hot. Make sure to use gloves aluminium conducts heat quite
well. Then install the crank on the taper and tighten as quickly as
possible. A more extreme fit can be achieved by using a hot air gun rather
than boiling water but be careful!!!

"Nick" <[email protected]> wrote in message
news:[email protected]...
> I recently built a fixed gear bike and the left crank arm keeps coming
> loose. I have some grease in the square taper. What would cause the
> bolt to unscrew?
>
> -Nick

 

[Alex Rodriguez]

In article <[email protected]>,
[email protected] says...
>I recently built a fixed gear bike and the left crank arm keeps coming
>loose. I have some grease in the square taper. What would cause the
>bolt to unscrew?

No, grease is not the cause of your problems. A crank arm bolt that is
not properly tightened is the usual cause. You need to tighten the bolt
to 30ft/lbs and then leave it alone. If you rode the bike with the crank
loose, it is probably damaged beyond repair.
---------------
Alex

 

[[email protected]]

Nick Kirsch writes:

> I recently built a fixed gear bike and the left crank arm keeps
> coming loose. I have some grease in the square taper. What would
> cause the bolt to unscrew?

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

Jobst Brandt
[email protected]

 

[A Muzi]

Nick wrote:

> I recently built a fixed gear bike and the left crank arm keeps coming
> loose. I have some grease in the square taper. What would cause the
> bolt to unscrew?

No, nut insufficient torque would.

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

 

[Qui si parla Campagnolo]

Nick-<< I recently built a fixed gear bike and the left crank arm keeps coming
loose. I have some grease in the square taper. What would cause the
bolt to unscrew? >><BR><BR>

I say-damage to the left or right arm. No grease is a better idea, IMO, but
lack of torque is a bigger issue. If it has come loose and ridden that way,
chances are it is history. Dry spindle and about 30 ft-lbs on properly matched
crank/BB taper and it will stay tight.

Peter Chisholm
Vecchio's Bicicletteria
1833 Pearl St.
Boulder, CO, 80302
(303)440-3535
http://www.vecchios.com
"Ruote convenzionali costruite eccezionalmente bene"

 

[Werehatrack]

On 2 Dec 2004 08:51:15 -0800, [email protected] (Nick) wrote:

>I recently built a fixed gear bike and the left crank arm keeps coming
>loose. I have some grease in the square taper. What would cause the
>bolt to unscrew?

Insufficient torque the first time, and a wallowed taper thereafter.
You'll probably need to replace the left crank at this point.
--
Typoes are a feature, not a bug.
Some gardening required to reply via email.
Words processed in a facility that contains nuts.

 

[Tom Paterson]

>From: Werehatrack

>Insufficient torque the first time, and a wallowed taper thereafter.
>You'll probably need to replace the left crank at this point.

A torque wrench (Sears or other decent cheapie) will show how much torque the
mfg's recommendation requires, and perhaps help prevent a repeat. If you obtain
the torque wrench before you buy your new crank (complete or left-arm-only),
you could give that poor left arm one more chance, nicely greased for "reliable
readings" as it says in the FAQ. --TP