Causes of loose crankarm

http:[email hidden]

LBS expert suggested torque levels for the taper plus anti-seize on
all parts at 4-5" allen wrench plus a one foot length tube in this
case a surplus seatpost
than bear down on it till its not gonna monomoha, and bear down and
hold twice to form a set.
that cured the loosening suffered here.
i had (and still do, right) early aluminum phobia but no, the Al
"alloy" will not rupture in this instance but could slowly expand over
4-5 resettings giving a pepsi can shim fix.
the deore 105 with cartirdge BB wears well enough, keeping a close eye
on the chainline, and is outstanding spinning campared to the ball and
cone.

Anthony DeLorenzo said:

I've been having a problem with my left-side, square taper
crankarm loosening every 30 km or so. I'm riding a mountain
bike but it's all been flat, relatively smooth riding on snow.
I replaced the crankarm but that didn't seem to make any
difference. I'm using a Shimano BB- UN53 with Deore Cranks.

I used loc-tite and as much torque as I could muster when
installing them. The old crankarm showed some signs of
rounding, but nothing excessive, and obviously the new
crankarm was, well, new.

I recognize that the most likely cause of the problem is me:
I'm 6'6", 250+ lbs and a strong pedaler. However, as I've
ridden square taper cranks for years without ever having to
tighten them, including this particular set for a year on
another bike, I am wondering if either of these things may be
aggravating the problem on this bike:

1. Bent pedal spindle. I can feel that the left pedal axle is
slightly bent. I am wondering if this is skewing the force
applied to the crankarm and encouraging it to work loose.

2. Rubber washer. The rubber or plastic washer/dust cap
(similar to this one:
http://www.parktool.com/images_inc/repair_help/crank107.jpg)
cracked and broke away due to riding in cold temperatures. I
have no idea how this could make any difference, but it must
be there for some reason, so I thought I'd ask.

This is more to satisfy my curiousity than anything. As far as
solving the problem, I'm going to replace the crank, BB and
pedals; trying out an external bearing system (Truvativ GXP)
for the first time.

Does this article shed any light on your problem?

http://draco.acs.uci.edu/rbfaq/FAQ/8f.11.html

John

EXHUMED FROM TECH ARCHIVES

the shim fix has an extraordinary moment for those previously
wandering
into the shimit area
where the fix goes on for four hours or days when the first and only
choice was digging a deep...
butt hear! the beer can wall thickness is unbelievably the correct
dead
on finite shim
thickness for getting spindle and crankl back together dead center.
when i asked around about the beer can shim idea. i gotta resounding
negative from all lbs.
however, unlike many forays into this area-
the beer can shims worked right off the spindle
and have not failed
this is due to the purchase of three extra left aluminum cranks.
the question remains-is there a can with a thicker wall than standard
american brews?
maybe not as the thinner the wall the less can production cost.
for example the pull top is a ball point technical tour de stamping.
and remember copper anti-seize works - it just doesn't look like it
would
the answer comes from experience with concurrent crank/spindle and
pedal failure.

expletives deleted

Anthony DeLorenzo said:

I've been having a problem with my left-side, square taper crankarm
loosening every 30 km or so.

This is a standard symptom of a crank arm ruined by a too-loose initial
installation.

Quoted message said:

I'm riding a mountain bike but it's all
been flat, relatively smooth riding on snow. I replaced the crankarm
but that didn't seem to make any difference. I'm using a Shimano BB-
UN53 with Deore Cranks.

I used loc-tite and as much torque as I could muster when installing
them.

This is odd. New crank did this right away? Hate to ask, but did you
grease the flats of the bottom bracket? The answer should have be yes.

Quoted message said:

I recognize that the most likely cause of the problem is me: I'm 6'6",
250+ lbs and a strong pedaler. However, as I've ridden square taper
cranks for years without ever having to tighten them, including this
particular set for a year on another bike, I am wondering if either of
these things may be aggravating the problem on this bike:

1. Bent pedal spindle.

On which arm? The new one or the old? Replacing the arm obviously
should have made this problem go away.

Quoted message said:

2. Rubber washer. The rubber or plastic washer/dust cap (similar to
this one: http://www.parktool.com/images_inc/repair_help/crank107.jpg)
cracked and broke away due to riding in cold temperatures. I have no
idea how this could make any difference, but it must be there for some
reason, so I thought I'd ask.

??

Quoted message said:

This is more to satisfy my curiousity than anything. As far as solving
the problem, I'm going to replace the crank, BB and pedals; trying out
an external bearing system (Truvativ GXP) for the first time.

Maybe replacing the bottom bracket with a splined system will cure your
problem, but the whole thing does not make sense.

--

David L. Johnson

"Business!" cried the Ghost. "Mankind was my business. The common
welfare was my business; charity, mercy, forbearance, and
benevolence, were, all, my business. The dealings of my trade were but
a drop of water in the comprehensive ocean of my business!" --Dickens,

Quoted message said:

http:[email hidden]

LBS expert suggested torque levels for the taper plus anti-seize on
all parts at 4-5" allen wrench plus a one foot length tube in this
case a surplus seatpost
than bear down on it till its not gonna monomoha, and bear down and
hold twice to form a set.

Ignore this. You will be just as likely to break of the crank bolt as
anything else.

--

David L. Johnson

"Business!" cried the Ghost. "Mankind was my business. The common
welfare was my business; charity, mercy, forbearance, and
benevolence, were, all, my business. The dealings of my trade were but
a drop of water in the comprehensive ocean of my business!" --Dickens,

Anthony DeLorenzo said:

Hi All,

I've been having a problem with my left-side, square taper crankarm
loosening every 30 km or so. I'm riding a mountain bike but it's all
been flat, relatively smooth riding on snow. I replaced the crankarm
but that didn't seem to make any difference. I'm using a Shimano BB-
UN53 with Deore Cranks.

I used loc-tite and as much torque as I could muster when installing
them. The old crankarm showed some signs of rounding, but nothing
excessive, and obviously the new crankarm was, well, new.

I recognize that the most likely cause of the problem is me: I'm 6'6",
250+ lbs and a strong pedaler. However, as I've ridden square taper
cranks for years without ever having to tighten them, including this
particular set for a year on another bike, I am wondering if either of
these things may be aggravating the problem on this bike:

1. Bent pedal spindle. I can feel that the left pedal axle is slightly
bent. I am wondering if this is skewing the force applied to the
crankarm and encouraging it to work loose.

2. Rubber washer. The rubber or plastic washer/dust cap (similar to
this one: http://www.parktool.com/images_inc/repair_help/crank107.jpg)
cracked and broke away due to riding in cold temperatures. I have no
idea how this could make any difference, but it must be there for some
reason, so I thought I'd ask.

This is more to satisfy my curiousity than anything. As far as solving
the problem, I'm going to replace the crank, BB and pedals; trying out
an external bearing system (Truvativ GXP) for the first time.

Once ridden loose your left arm is likely toast. Bite it for another
$20, install a good left arm properly or get the shop to do it with a
written guarantee. Others will certainly disagree but I'd grease the
taper as well as the thread and exceed the mfr's torque rating by 10-20%
i.e., not 40lbs but rather 45~50lbs.

The broken plastic trim ring is merely aesthetic and irrelevant to the
problem. No glue or adhesive will make any difference here.

Remove the left pedal and spin the spindle. If it wavers get a set of
pedals; they're cheap.

Remove, lube, torque your right crank too. It may have been installed by
the same person who did your left.
--
Andrew Muzi
www.yellowjersey.org
Open every day since 1 April, 1971

David L. Johnson said:

Anthony DeLorenzo wrote:

[...]

Quoted message said:

Quoted message said:

1. Bent pedal spindle.

On which arm? The new one or the old? Replacing the arm obviously
should have made this problem go away.

Why? I was thinking same old bent pedal on the new arm, and that sounded
like a real possibility for the culprit.

Ben C said:

David L. Johnson said:

Anthony DeLorenzo wrote:

[...]

Quoted message said:

Quoted message said:

1. Bent pedal spindle.

On which arm? The new one or the old? Replacing the arm obviously
should have made this problem go away.

Why? I was thinking same old bent pedal on the new arm, and that sounded
like a real possibility for the culprit.

Oops, I misread that. Ignore it.

--

David L. Johnson

"Business!" cried the Ghost. "Mankind was my business. The common
welfare was my business; charity, mercy, forbearance, and
benevolence, were, all, my business. The dealings of my trade were but
a drop of water in the comprehensive ocean of my business!" --Dickens,

right. i worked the way thru the problem on successive 50 mile
commutes wher the crankarm came loose 2-3 times over two months. And
you get to the point where you're thinking the casue is unknown among
30 possibilities but there aren't 30 possibilities its just that the
damn thing isn't on there tight enough.
prep is omniportant: clean all surfaces, remove burrs, galls and rips
with a fresh small trianglar file. clean off filings. the use
antiseize. and red lock on the bolt threads, blue lock on screw
threads.
also be sure all the parts are in there in the corect order with the
correct sides in and out.
if compulsive, wipe down all parts like washers, screw and bolt mating
surfaces and film those surfaces with red or blue (using care with red
near a screw fastner) as the lock provides a more effective surface
press when torquing the stcked unit together.
yawl cantell this drove me nuts for awahile right? MF! and at 2AM!

then do the component toss
and buy an octalink

On Wed, 21 Mar 2007 23:03:46 -0600, A Muzi <[email hidden]>

Quoted message said:

Once ridden loose your left arm is likely toast. Bite it for another
$20, install a good left arm properly or get the shop to do it with a
written guarantee. Others will certainly disagree but I'd grease the
taper as well as the thread and exceed the mfr's torque rating by 10-20%
i.e., not 40lbs but rather 45~50lbs.

Remove, lube, torque your right crank too. It may have been installed by
the same person who did your left.

I'd like to reinforce the above. Crank bolts are the only place on a
bike I use a torque wrench. If you've never used one on a square taper
BB you'll be amazed by how many turns it takes from "tight" to
properly torqued.

BTW, I always torque my crank bolts to 30 ft. lbs. on square taper
cranks. I converted from the units in some Shimano Service
Instructions many years ago and that figure has done the job
admirably.

--
jeverett3<AT>sbcglobal<DOT>net (John V. Everett)

John Everett said:

I'd like to reinforce the above. Crank bolts are the only
place on a bike I use a torque wrench. If you've never used
one on a square taper BB you'll be amazed by how many turns it
takes from "tight" to properly torqued.

BTW, I always torque my crank bolts to 30 ft. lbs. on square
taper cranks. I converted from the units in some Shimano
Service Instructions many years ago and that figure has done
the job admirably.

Agreed. I use 30 ft lbs as well, having converted a figure from
a different but forgotten source.

Not entirely ignoring Jobst's advice to never retighten, I live
dangerously and retighten once only to that tension after 50 km
or so.

John

John Henderson said:

Quoted message said:

I'd like to reinforce the above. Crank bolts are the only place on
a bike I use a torque wrench. If you've never used one on a square
taper BB you'll be amazed by how many turns it takes from "tight"
to properly torqued.

Quoted message said:

Quoted message said:

BTW, I always torque my crank bolts to 30 ft. lbs. on square taper
cranks. I converted from the units in some Shimano Service
Instructions many years ago and that figure has done the job
admirably.

Quoted message said:

Agreed. I use 30 ft lbs as well, having converted a figure from a
different but forgotten source.

Quoted message said:

Not entirely ignoring Jobst's advice to never re-tighten, I live
dangerously and re-tighten once only to that tension after 50 km or
so.

Just taking up "slack" after riding is not reasonable, considering
that initially tightening the crank bolt on installation to the
appropriate torque defines the press fit on the taper. If you
understand the mechanism by which bolt tension is relaxed, I don't
think you would follow this procedure in the future.

It doesn't take many crank rotations under load to relieve the crank
bolt of its preload. A sprint up the ramp of a railway under/overpass
is more than enough, whereas casually rolling 50km on flatland would
probably not relieve preload.

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

crank-fail-011 was split by that process.

Jobst Brandt

Quoted message said:

Just taking up "slack" after riding is not reasonable,
considering that initially tightening the crank bolt on
installation to the appropriate torque defines the press fit
on the taper. If you understand the mechanism by which bolt
tension is relaxed, I don't think you would follow this
procedure in the future.

It doesn't take many crank rotations under load to relieve the
crank bolt of its preload. A sprint up the ramp of a railway
under/overpass is more than enough, whereas casually rolling
50km on flatland would probably not relieve preload.

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

crank-fail-011 was split by that process.

Thanks Jobst. I appreciate your addressing the wisdom of an
initial retightening.

John