creaking noise when right crank is pushed hard

[[email protected]]

Hi - i recently got a Trek 7.1 hybrid from a friend. it is second hand
and has had a fair life.

When i peddle hard, i get a creaking sort of noise just on the right
crank. It is most apparent on the highest (i mean largest) front cog
and smallest rear cog. It occurs in the pushing phase of peddling, not
as the right crank comes back around as i push on the left crank. I
can also hear/feel it when i am on the largest front cog but smallest
but-one rear cog. But much less so. Speed of crank rotation does not
seem to affect it.

It does not sound or feel like the peddle or crank are knocking
against anything.


I'm not sure if this has anything to do with it but, i had the bike
upturned the other day to check the gear cabling adjustments. When i
rotated (by hand) the cranks and the rear wheel got some real speed
up, it did not rotate 'true'. I mean, the rear of the bike vibrated
quite a bit (maybe just the energy in the rotation) but also it looked
like the rear gear cassette was rotating around a v slightly different
axis to the wheel itself). Not sure how worried i should be about
this!


Apologies if this is hard to decipher as i am not bike expert. I'm
just trying to work out if this is something i can fix myself,
requires a professional, and how much it might cost to rectify.

thanks.

 

[landotter]

On Jan 29, 1:44 pm, [email protected] wrote:
> Hi - i recently got a Trek 7.1 hybrid from a friend. it is second hand
> and has had a fair life.
>
> When i peddle hard, i get a creaking sort of noise just on the right
> crank. It is most apparent on the highest (i mean largest) front cog
> and smallest rear cog.

http://sheldonbrown.com/creaks.html

My guess: saddle or seat clamp needs grease and tightening, could be a
dozen other things.

 

[[email protected]]

On Jan 29, 2:44 pm, [email protected] wrote:
> Hi - i recently got a Trek 7.1 hybrid from a friend. it is second hand
> and has had a fair life.
>
> When i peddle hard, i get a creaking sort of noise just on the right
> crank. It is most apparent on the highest (i mean largest) front cog
> and smallest rear cog. It occurs in the pushing phase of peddling, not
> as the right crank comes back around as i push on the left crank. I
> can also hear/feel it when i am on the largest front cog but smallest
> but-one rear cog. But much less so. Speed of crank rotation does not
> seem to affect it.
>
> It does not sound or feel like the peddle or crank are knocking
> against anything.
>
> I'm not sure if this has anything to do with it but, i had the bike
> upturned the other day to check the gear cabling adjustments. When i
> rotated (by hand) the cranks and the rear wheel got some real speed
> up, it did not rotate 'true'. I mean, the rear of the bike vibrated
> quite a bit (maybe just the energy in the rotation) but also it looked
> like the rear gear cassette was rotating around a v slightly different
> axis to the wheel itself). Not sure how worried i should be about
> this!
>
> Apologies if this is hard to decipher as i am not bike expert. I'm
> just trying to work out if this is something i can fix myself,
> requires a professional, and how much it might cost to rectify.
>
> thanks.

I hope landotter is right and I'm wrong, for your sake, but I'm
thinking bottom bracket. Sheldons site is still a very useful tool
for dealing with that, but if you strike out with landotters
suggestions you may check the bottom bracket.

It's my understanding that the wheel being out of true would refer to
the rim wobbling in relation to the hub, not the cassette wobbling on
the hub. The hub and cassette being very slightly off could just be
the loose tolerances of inexpensive equipment. I wouldn't stress over
it. If the rim itself is out of true enough that it bothers you,
becomes noticeable or rubs the brake pads I'd true the wheel up, but
otherwise you're probably good.

Sounds like you're going to be able to do it yourself if you want to
take the time and learn a little as you go. I treat Sheldons site as
my cycle repair bible, and have learned to overtake MANY projects that
way. Good luck to you, and come back when you're done and let us know
what you did and how it works out.

Dan

Dan

 

[daveornee]

http://www.parktool.com/repair/readhowto.asp?id=98

Hi - i recently got a Trek 7.1 hybrid from a friend. it is second hand
and has had a fair life.

When i peddle hard, i get a creaking sort of noise just on the right
crank. It is most apparent on the highest (i mean largest) front cog
and smallest rear cog. It occurs in the pushing phase of peddling, not
as the right crank comes back around as i push on the left crank. I
can also hear/feel it when i am on the largest front cog but smallest
but-one rear cog. But much less so. Speed of crank rotation does not
seem to affect it.

It does not sound or feel like the peddle or crank are knocking
against anything.


I'm not sure if this has anything to do with it but, i had the bike
upturned the other day to check the gear cabling adjustments. When i
rotated (by hand) the cranks and the rear wheel got some real speed
up, it did not rotate 'true'. I mean, the rear of the bike vibrated
quite a bit (maybe just the energy in the rotation) but also it looked
like the rear gear cassette was rotating around a v slightly different
axis to the wheel itself). Not sure how worried i should be about
this!


Apologies if this is hard to decipher as i am not bike expert. I'm
just trying to work out if this is something i can fix myself,
requires a professional, and how much it might cost to rectify.

thanks.

Check out the Park Tools site section about creaking drive chain:



http://www.parktool.com/repair/readhowto.asp?id=98



What you are experiencing with the high speed vibration and wobble is "normal" and I doubt that it is any part of the problem. Of course, having perfectly balanced wheel assemblies and precise rotation, is desirable.

 

[Mike Jacoubowsky]

> When i peddle hard, i get a creaking sort of noise just on the right
> crank. It is most apparent on the highest (i mean largest) front cog
> and smallest rear cog. It occurs in the pushing phase of peddling, not
> as the right crank comes back around as i push on the left crank. I
> can also hear/feel it when i am on the largest front cog but smallest
> but-one rear cog. But much less so. Speed of crank rotation does not
> seem to affect it.

I suspect it wouldn't take long for a shop to run down a few noises on your
bike. Unfortunately, noises come in layers... you get rid of one noise, and
find out it was masking another.

If you want to try and run down things yourself, check out this page on our
website-
www.ChainReaction.com/noises.htm

--Mike Jacoubowsky
Chain Reaction Bicycles
www.ChainReaction.com
Redwood City & Los Altos, CA USA


<[email protected]> wrote in message
news:9397a0f0-24e2-44b8-bdce-d9e16db05b8f@i72g2000hsd.googlegroups.com...
> Hi - i recently got a Trek 7.1 hybrid from a friend. it is second hand
> and has had a fair life.
>
> When i peddle hard, i get a creaking sort of noise just on the right
> crank. It is most apparent on the highest (i mean largest) front cog
> and smallest rear cog. It occurs in the pushing phase of peddling, not
> as the right crank comes back around as i push on the left crank. I
> can also hear/feel it when i am on the largest front cog but smallest
> but-one rear cog. But much less so. Speed of crank rotation does not
> seem to affect it.
>
> It does not sound or feel like the peddle or crank are knocking
> against anything.
>
>
> I'm not sure if this has anything to do with it but, i had the bike
> upturned the other day to check the gear cabling adjustments. When i
> rotated (by hand) the cranks and the rear wheel got some real speed
> up, it did not rotate 'true'. I mean, the rear of the bike vibrated
> quite a bit (maybe just the energy in the rotation) but also it looked
> like the rear gear cassette was rotating around a v slightly different
> axis to the wheel itself). Not sure how worried i should be about
> this!
>
>
> Apologies if this is hard to decipher as i am not bike expert. I'm
> just trying to work out if this is something i can fix myself,
> requires a professional, and how much it might cost to rectify.
>
> thanks.

 

[A Muzi]

[email protected] wrote:
> Hi - i recently got a Trek 7.1 hybrid from a friend. it is second hand
> and has had a fair life.
> When i peddle hard, i get a creaking sort of noise just on the right
> crank. It is most apparent on the highest (i mean largest) front cog
> and smallest rear cog. It occurs in the pushing phase of peddling, not
> as the right crank comes back around as i push on the left crank. I
> can also hear/feel it when i am on the largest front cog but smallest
> but-one rear cog. But much less so. Speed of crank rotation does not
> seem to affect it.
> It does not sound or feel like the peddle or crank are knocking
> against anything.
> I'm not sure if this has anything to do with it but, i had the bike
> upturned the other day to check the gear cabling adjustments. When i
> rotated (by hand) the cranks and the rear wheel got some real speed
> up, it did not rotate 'true'. I mean, the rear of the bike vibrated
> quite a bit (maybe just the energy in the rotation) but also it looked
> like the rear gear cassette was rotating around a v slightly different
> axis to the wheel itself). Not sure how worried i should be about
> this!
> Apologies if this is hard to decipher as i am not bike expert. I'm
> just trying to work out if this is something i can fix myself,
> requires a professional, and how much it might cost to rectify.


Noises can be hard to track down as they resonate but start by removing
pedals, lube threads and torque properly (Campagnolo says 40nm. That or
a bit higher). Then grab the right pedal in your hand and press/pull. Is
the pedal cage loose on the body? Does any part of the pedal rock or
move? Are there bolts holding the pedal cage to the body? Are they
tight? Check left as well.
Test ride for noise.
Remove chainring bolts one at a time, oil or grease the male side and
torque them.
Test ride for noise.
See if the crank is properly torqued to the spindle( there are various
formats)Lubricate crank bolt threads.
Test ride for noise.
See if the crank assembly rocks in the bike (i.e., crank bearing
problems). Look to see if a visible gap shows between right side cup
flange and the frame. Crank bearing assemblies ('BB') require specialty
tools. If you identify a problem there, you can decide whether to invest
in tooling or to consult with your LBS.
Is your chain lubricated? Dry chains can be loud. Oil then test ride for
noise.
A worn chain will exhibit symptoms in the most frequently used gear
combination first, see 'chains' here:
http://draco.acs.uci.edu/rbfaq/FAQ/index.html
but they usually are not noisy from wear.

If you rear wheel has a reflector attached to a spoke, remove that and
try spinning the wheel again.

If it's still vibrating, see if the tire is evenly mounted by touching a
finger lightly as it spins. If it's lumpy, look at the edge of the tire
just above the braking surface. You'll see a molded raised line. That
line should be even and visible all around. If not, remove tire and
re-mount evenly before filling to pressure written on the tire sidewall.

With the wheel secured in the bike, does the wheel rock from side to
side in your hand? Bearing problems can be loud.

(While we're there, thinking of that noise, lubricate the cam in your
rear wheel quick release and lock it properly. The lever should leave a
print on your palm for a few seconds. If it was not secured, the wheel
can shift under pedal pressure and the noise will resonate through your
frame.)

If the reflector, tire or bearing are not the source of your vibration,
observe the spinning rim. Is it round? Does it waver side to side? Are
there dents? If any of those, is the spoke tension tight and even?
Again, this is perfectly approachable by the practical man but a
consultation with a competent mechanic may be of use as well.

p.s. The link above has much more related and useful information.
--
Andrew Muzi
www.yellowjersey.org
Open every day since 1 April, 1971

 

[A Muzi]

> [email protected] wrote:
>> Hi - i recently got a Trek 7.1 hybrid from a friend. it is second hand
>> and has had a fair life.
>> When i peddle hard, i get a creaking sort of noise just on the right
>> crank. It is most apparent on the highest (i mean largest) front cog
>> and smallest rear cog. It occurs in the pushing phase of peddling, not
>> as the right crank comes back around as i push on the left crank. I
>> can also hear/feel it when i am on the largest front cog but smallest
>> but-one rear cog. But much less so. Speed of crank rotation does not
>> seem to affect it.
>> It does not sound or feel like the peddle or crank are knocking
>> against anything.
>> I'm not sure if this has anything to do with it but, i had the bike
>> upturned the other day to check the gear cabling adjustments. When i
>> rotated (by hand) the cranks and the rear wheel got some real speed
>> up, it did not rotate 'true'. I mean, the rear of the bike vibrated
>> quite a bit (maybe just the energy in the rotation) but also it looked
>> like the rear gear cassette was rotating around a v slightly different
>> axis to the wheel itself). Not sure how worried i should be about
>> this!
>> Apologies if this is hard to decipher as i am not bike expert. I'm
>> just trying to work out if this is something i can fix myself,
>> requires a professional, and how much it might cost to rectify.

[email protected] wrote:
> I hope landotter is right and I'm wrong, for your sake, but I'm
> thinking bottom bracket. Sheldons site is still a very useful tool
> for dealing with that, but if you strike out with landotters
> suggestions you may check the bottom bracket.
>
> It's my understanding that the wheel being out of true would refer to
> the rim wobbling in relation to the hub, not the cassette wobbling on
> the hub. The hub and cassette being very slightly off could just be
> the loose tolerances of inexpensive equipment. I wouldn't stress over
> it. If the rim itself is out of true enough that it bothers you,
> becomes noticeable or rubs the brake pads I'd true the wheel up, but
> otherwise you're probably good.
>
> Sounds like you're going to be able to do it yourself if you want to
> take the time and learn a little as you go. I treat Sheldons site as
> my cycle repair bible, and have learned to overtake MANY projects that
> way. Good luck to you, and come back when you're done and let us know
> what you did and how it works out.

Thanks. Dan. You reminded me that a loose cassette lockring can also be
noisy.
The OP might see if the individual sprockets move on the cassette body.
If so, lube and torque the lockring.
--
Andrew Muzi
www.yellowjersey.org
Open every day since 1 April, 1971

 

[John Tserkezis]

[email protected] wrote:

> When i peddle hard, i get a creaking sort of noise just on the right
> crank. It is most apparent on the highest (i mean largest) front cog
> and smallest rear cog. It occurs in the pushing phase of peddling, not
> as the right crank comes back around as i push on the left crank. I
> can also hear/feel it when i am on the largest front cog but smallest
> but-one rear cog. But much less so. Speed of crank rotation does not
> seem to affect it.
>
> It does not sound or feel like the peddle or crank are knocking
> against anything.
>
> I'm not sure if this has anything to do with it but, i had the bike
> upturned the other day to check the gear cabling adjustments. When i
> rotated (by hand) the cranks and the rear wheel got some real speed
> up, it did not rotate 'true'. I mean, the rear of the bike vibrated
> quite a bit (maybe just the energy in the rotation) but also it looked
> like the rear gear cassette was rotating around a v slightly different
> axis to the wheel itself). Not sure how worried i should be about
> this!

Had a similar thing happen on my roadie a while back. Found the right crank
a bit loose. So I tightened it a bit.

It started creaking again some time later, but found it a bit loose once
again, so that probably explained it.

By this stage I was fed up with the thing and tightened the cr@p out of it,
and it hasn't given me any grief since.
--
Linux Registered User # 302622
<http://counter.li.org>

 

[Andre Jute]

On Jan 29, 7:44 pm, [email protected] wrote:
> Hi - i recently got a Trek 7.1 hybrid from a friend. it is second hand
> and has had a fair life.
>
> When i peddle hard, i get a creaking sort of noise just on the right
> crank. It is most apparent on the highest (i mean largest) front cog
> and smallest rear cog. It occurs in the pushing phase of peddling, not
> as the right crank comes back around as i push on the left crank. I
> can also hear/feel it when i am on the largest front cog but smallest
> but-one rear cog. But much less so. Speed of crank rotation does not
> seem to affect it.
>
> It does not sound or feel like the peddle or crank are knocking
> against anything.
>
> I'm not sure if this has anything to do with it but, i had the bike
> upturned the other day to check the gear cabling adjustments. When i
> rotated (by hand) the cranks and the rear wheel got some real speed
> up, it did not rotate 'true'. I mean, the rear of the bike vibrated
> quite a bit (maybe just the energy in the rotation) but also it looked
> like the rear gear cassette was rotating around a v slightly different
> axis to the wheel itself). Not sure how worried i should be about
> this!
>
> Apologies if this is hard to decipher as i am not bike expert. I'm
> just trying to work out if this is something i can fix myself,
> requires a professional, and how much it might cost to rectify.
>
> thanks.

A similarly annoying creak on my bike was eventually, after everything
else had been torqued up correctly, traced to the crank, the arm which
connects the pedal to the bottom bracket. The LBS twice tightened the
crank bolts but the creaks returned the same say, so I lost patience
and just did the job myself. I used a torque wrench and that did the
job for good. It might be a good idea if you have the tools to take
the bolt out and the arm off and just clean and grease everything so
it fits together smoothly.
If you know or can find the specific torque settings for your bike or
component, use them. If not, here are some general guidelines:

Cranks with square ends:
- steel 30 - 40 Nm
- aluminium 20 - 25 Nm
- Shimano 35 - 45 Nm

You can get crank bolts with Allen key heads or octagonal bolt heads.
The latter are much more convenient in requiring standard sockets that
fit the common kind of torque wrench. However, BBB sells a torgue
wrench kit with Allen bits.

Crank arm creak is pretty distinctive: it sounds like metal under
stress and it there only when pedalling. Here's a zero-tool, zero-cost
check: Stand the bike next to a pole in the ground, one pedal braced
behind the pole so that the cranks are horizontal. Hold the handlebars
and stand up with all your weight on the free pedal. If you hear
nothing, turn the bike around and repeat for the other pedal. You'll
hear the creak if it is the crank bolts that require tightening.

HTH.

Andre Jute
Real men eat quiche with their fingers

 

[Clive George]

"Andre Jute" <[email protected]> wrote in message
news:31e5ea45-4616-41ae-a6c7-79debcea2698@s27g2000prg.googlegroups.com...

> You can get crank bolts with Allen key heads or octagonal bolt heads.
> The latter are much more convenient in requiring standard sockets that
> fit the common kind of torque wrench. However, BBB sells a torgue
> wrench kit with Allen bits.

Hexagonal bolt heads, surely? Still tricky, since standard sockets have
walls which are too thick to fit.

I've actually got an 8mm allen 1/2" socket for my torque wrench/socket set.
Don't tend to use it though.

clive

 

[Andre Jute]

On Jan 30, 4:55 am, "Clive George" <[email protected]> wrote:
> "Andre Jute" <[email protected]> wrote in message
>
> news:31e5ea45-4616-41ae-a6c7-79debcea2698@s27g2000prg.googlegroups.com...
>
> > You can get crank bolts with Allen key heads or octagonal bolt heads.
> > The latter are much more convenient in requiring standard sockets that
> > fit the common kind of torque wrench. However, BBB sells a torgue
> > wrench kit with Allen bits.
>
> Hexagonal bolt heads, surely?

Thanks.

>Still tricky, since standard sockets have
> walls which are too thick to fit.

My local hardware stores let me carry stuff out to my bike or even
home to see if it is what I need, and then to put it back on the shelf
or pay if I want it. But right after I bought that thinwall socket, I
found in a drawer a complete set that I bought in Chichester about
1980 while I was living on Hayling Island in a house with big enough
garages to rebuild an old Bentley. God knows why I bought the thinwall
socket set, except that I'm a sucker for tool salesmen, because
Bentleys either had every bolt hexagonal and instantly accessible to
big handsful of tools as per railway practice, or twee but perfectly
scaled square bolt heads and nuts as per RR practice.
>
> I've actually got an 8mm allen 1/2" socket for my torque wrench/socket set..
> Don't tend to use it though.

It's an odd thing, that. Generally speaking, bolts and nuts and the
tools that fit them are sized to the torque intended to be applied to
them.

> clive

Andre Jute
Phi: The Golden Mean

 

[Tom Sherman]

Clive George wrote:
> ...
> I've actually got an 8mm allen 1/2" socket for my torque wrench/socket
> set. Don't tend to use it though.
>
I use my hex key [1] sockets quite a bit, especially where there is not
enough room to rotate a plain hex key 360° degrees.

[1] The proper generic name for these tools - "Allen" is a brand, not
the generic term.

--
Tom Sherman - Holstein-Friesland Bovinia
"And never forget, life ultimately makes failures of all people."
- A. Derleth

 

[Tom Sherman]

Andrew Muzi wrote a long list of things that creak on a bicycle:
> ...
>
Sometimes the creak is not from the bicycle, but one of the rider's
shoes instead.

--
Tom Sherman - Holstein-Friesland Bovinia
"And never forget, life ultimately makes failures of all people."
- A. Derleth

 

[RS]

In article <9397a0f0-24e2-44b8-bdce-
[email protected]>,
[email protected] says...
>
>
>Hi - i recently got a Trek 7.1 hybrid from a friend. it is second hand
>and has had a fair life.
>
>When i peddle hard, i get a creaking sort of noise just on the right
>crank. It is most apparent on the highest (i mean largest) front cog
>and smallest rear cog. It occurs in the pushing phase of peddling, not
>as the right crank comes back around as i push on the left crank. I
>can also hear/feel it when i am on the largest front cog but smallest
>but-one rear cog. But much less so. Speed of crank rotation does not
>seem to affect it.
>
>It does not sound or feel like the peddle or crank are knocking
>against anything.
>
>
>I'm not sure if this has anything to do with it but, i had the bike
>upturned the other day to check the gear cabling adjustments. When i
>rotated (by hand) the cranks and the rear wheel got some real speed
>up, it did not rotate 'true'. I mean, the rear of the bike vibrated
>quite a bit (maybe just the energy in the rotation) but also it looked
>like the rear gear cassette was rotating around a v slightly different
>axis to the wheel itself). Not sure how worried i should be about
>this!
>
>
>Apologies if this is hard to decipher as i am not bike expert. I'm
>just trying to work out if this is something i can fix myself,
>requires a professional, and how much it might cost to rectify.
>
>thanks.

Bottom Bracket

 

[Werehatrack]

On Tue, 29 Jan 2008 11:44:08 -0800 (PST), [email protected]
may have said:

>I'm not sure if this has anything to do with it but, i had the bike
>upturned the other day to check the gear cabling adjustments. When i
>rotated (by hand) the cranks and the rear wheel got some real speed
>up, it did not rotate 'true'. I mean, the rear of the bike vibrated
>quite a bit (maybe just the energy in the rotation) but also it looked
>like the rear gear cassette was rotating around a v slightly different
>axis to the wheel itself). Not sure how worried i should be about
>this!

No worries on this issue; the rocking you saw when the wheel was
turning with the cassette stopped is completely normal. It should be
ignored.

--
My email address is antispammed; pull WEEDS if replying via e-mail.
Typoes are not a bug, they're a feature.
Words processed in a facility that contains nuts.

 

[Scott Gordo]

On Jan 29, 2:44 pm, [email protected] wrote:
> Hi - i recently got a Trek 7.1 hybrid from a friend. it is second hand
> and has had a fair life.
>
> When i peddle hard, i get a creaking sort of noise just on the right
> crank. It is most apparent on the highest (i mean largest) front cog
> and smallest rear cog. It occurs in the pushing phase of peddling, not
> as the right crank comes back around as i push on the left crank. I
> can also hear/feel it when i am on the largest front cog but smallest
> but-one rear cog. But much less so. Speed of crank rotation does not
> seem to affect it.
>
> It does not sound or feel like the peddle or crank are knocking
> against anything.
>
> I'm not sure if this has anything to do with it but, i had the bike
> upturned the other day to check the gear cabling adjustments. When i
> rotated (by hand) the cranks and the rear wheel got some real speed
> up, it did not rotate 'true'. I mean, the rear of the bike vibrated
> quite a bit (maybe just the energy in the rotation) but also it looked
> like the rear gear cassette was rotating around a v slightly different
> axis to the wheel itself). Not sure how worried i should be about
> this!
>
> Apologies if this is hard to decipher as i am not bike expert. I'm
> just trying to work out if this is something i can fix myself,
> requires a professional, and how much it might cost to rectify.
>
> thanks.

Check the chainring bolts.

/s

 

[* * Chas]

"John Tserkezis" <[email protected]> wrote in message
news:[email protected]...
> [email protected] wrote:
>
> > When i peddle hard, i get a creaking sort of noise just on the right
> > crank. It is most apparent on the highest (i mean largest) front cog
> > and smallest rear cog. It occurs in the pushing phase of peddling, not
> > as the right crank comes back around as i push on the left crank. I
> > can also hear/feel it when i am on the largest front cog but smallest
> > but-one rear cog. But much less so. Speed of crank rotation does not
> > seem to affect it.
> >
> > It does not sound or feel like the peddle or crank are knocking
> > against anything.
> >
> > I'm not sure if this has anything to do with it but, i had the bike
> > upturned the other day to check the gear cabling adjustments. When i
> > rotated (by hand) the cranks and the rear wheel got some real speed
> > up, it did not rotate 'true'. I mean, the rear of the bike vibrated
> > quite a bit (maybe just the energy in the rotation) but also it looked
> > like the rear gear cassette was rotating around a v slightly different
> > axis to the wheel itself). Not sure how worried i should be about
> > this!
>
> Had a similar thing happen on my roadie a while back. Found the right
crank
> a bit loose. So I tightened it a bit.
>
> It started creaking again some time later, but found it a bit loose
once
> again, so that probably explained it.
>
> By this stage I was fed up with the thing and tightened the cr@p out
of it,
> and it hasn't given me any grief since.
> --
> Linux Registered User # 302622
> <http://counter.li.org>

When you hear hoof beats, think horses not zebras....

You hit on the probable cause. The crank arm might be slightly loose on
the BB spindle. It could have been that way for a long time and the BB
spindle has worn into the aluminum.

The bolt also could have been tightened so many times that it's bottomed
out against the BB spindle and crank arm is no longer tightly wedged onto
the spindle. Putting a second washer under the crank arm bolt with a hole
big enough to fit over the end of the BB spindle will usually fix the
bottomed out problem if that is the case.

Chas.