broken chain on a fixed gear



A

autopi

Guest
so the other day i'm biking home and the chain (1/8") on my fixed gear
just up and breaks. i didn't notice anything abnormal up until that
point. although i was going at a good clip, i was fortunately able to
stop in time and didn't crash, but i was (am) alarmed, because i don't
know why it broke, and i don't want it to happen again, obviously.

the chain is (was) a SRAM PC-1, about 14 mos. old, iirc. from what i
can determine by looking at the chain, one of the plates just tore
apart where it holds the pin. this was not the master link. also, when
i went to unravel the chain from the cog, another link came apart,
though this one was not busted in the way the first one was. this was
also not the master link, i believe. i've put up some
photos--http://tinyurl.com/cyrjx--which show the gory remains of the
chain.

the bike had been inside my apartment and unused for the last month to
6 weeks. the chain was not particularly rusty (at least to casual
visual inspection), and did not squeak or seem stiff. it may have been
a tad bit tight, but i don't think by very much--if i pulled up on the
cable halfway between the chainring and cog, i could get somewhere
around 1/2" of play.

so...any theories as to what caused this and suggestions on how to
avoid it?
~v.
 
On Mon, 30 Jan 2006 22:27:06 -0800, autopi wrote:

> so the other day i'm biking home and the chain (1/8") on my fixed gear
> just up and breaks. i didn't notice anything abnormal up until that
> point. although i was going at a good clip, i was fortunately able to
> stop in time and didn't crash, but i was (am) alarmed, because i don't
> know why it broke, and i don't want it to happen again, obviously.

I don't blame you for being alarmed.
>
> the chain is (was) a SRAM PC-1, about 14 mos. old, iirc. from what i
> can determine by looking at the chain, one of the plates just tore
> apart where it holds the pin. this was not the master link. also, when
> i went to unravel the chain from the cog, another link came apart,
> though this one was not busted in the way the first one was. this was
> also not the master link, i believe. i've put up some
> photos--http://tinyurl.com/cyrjx--which show the gory remains of the
> chain.

Unfortunately, this link, too, is broken....

I can't imagine. I presume the chain saw occasional maintenance,
cleaning and lubrication when needed.

--

David L. Johnson

__o | A mathematician is a machine for turning coffee into theorems.
_`\(,_ | -- Paul Erdos
(_)/ (_) |
 
Nate Knutson wrote:
> did it ever derail and get jammed unhappily?
>

Some weeks ago I had a broken chain on my fixed gear (I started a
similar thread), the chain failed exactly the same way as yours.

The cause was probably that: chain derailed and got jammed, which ruined
it and made it fail later. It may be your case too.

Francesco
 
autopi wrote:
> so the other day i'm biking home and the chain (1/8") on my fixed gear
> just up and breaks. i didn't notice anything abnormal up until that
> point. although i was going at a good clip, i was fortunately able to
> stop in time and didn't crash, but i was (am) alarmed, because i don't
> know why it broke, and i don't want it to happen again, obviously.
>
> the chain is (was) a SRAM PC-1, about 14 mos. old, iirc. from what i
> can determine by looking at the chain, one of the plates just tore
> apart where it holds the pin. this was not the master link. also, when
> i went to unravel the chain from the cog, another link came apart,
> though this one was not busted in the way the first one was. this was
> also not the master link, i believe. i've put up some
> photos--http://tinyurl.com/cyrjx--which show the gory remains of the
> chain.
>
> the bike had been inside my apartment and unused for the last month to
> 6 weeks. the chain was not particularly rusty (at least to casual
> visual inspection), and did not squeak or seem stiff. it may have been
> a tad bit tight, but i don't think by very much--if i pulled up on the
> cable halfway between the chainring and cog, i could get somewhere
> around 1/2" of play.
>
> so...any theories as to what caused this and suggestions on how to
> avoid it?
> ~v.

A fixie chain gets a lot of abuse, particulalry from perhaps finding
it's 'tight' section, as all fixie chains have. Replace this very
inexpensive part more frequently. Altho I don't put that many miles on
my fixie chain, and altho I check it for wear often, I still change it
after each season.
 
sorry, the URL should read:

http://tinyurl.com/cyrjx

btw, it sounds like it might have been the chain derailing--though i
don't know what would have caused *that*. i hadn't mucked with the
wheel, chain, anything in probably 9 mos. or so, and i've only had it
derail one other time in the year and a half i've had the bike. it
happened on a flat, straight section of road, nothing in particular
stands out as being unusual...
 
On 30 Jan 2006 22:27:06 -0800, "autopi" <[email protected]>
wrote:

>so the other day i'm biking home and the chain (1/8") on my fixed gear
>just up and breaks. i didn't notice anything abnormal up until that
>point. although i was going at a good clip, i was fortunately able to
>stop in time and didn't crash, but i was (am) alarmed, because i don't
>know why it broke, and i don't want it to happen again, obviously.
[snip]
>the bike had been inside my apartment and unused for the last month to
>6 weeks. the chain was not particularly rusty (at least to casual
>visual inspection), and did not squeak or seem stiff. it may have been
>a tad bit tight, but i don't think by very much--if i pulled up on the
>cable halfway between the chainring and cog, i could get somewhere
>around 1/2" of play.

Cable? What cable?

>so...any theories as to what caused this and suggestions on how to
>avoid it?

Ignoring the anomaly of the term "cable", if you had 1/2" of slack in
the chain, I'd say that the chain probably climbed a tooth on the rear
sprocket and broke.

Check the chainline. On a fixie, it needs to be *dead straight*.
--
Typoes are a feature, not a bug.
Some gardening required to reply via email.
Words processed in a facility that contains nuts.
 
autopi wrote:
> sorry, the URL should read:
>
> http://tinyurl.com/cyrjx
>
> btw, it sounds like it might have been the chain derailing--though i
> don't know what would have caused *that*. i hadn't mucked with the
> wheel, chain, anything in probably 9 mos. or so, and i've only had it
> derail one other time in the year and a half i've had the bike. it
> happened on a flat, straight section of road, nothing in particular
> stands out as being unusual...
>

I know it can be tricky with matching cranks to BB to hubs, but a fixie
chain should *never* derail. Good god that scares the **** out of me.
\\paul
--
Paul M. Hobson
Georgia Institute of Technology
..:change the f to ph to reply:.
 
Paul Hobson wrote:
> autopi wrote:
>
>> sorry, the URL should read:
>>
>> http://tinyurl.com/cyrjx
>>
>> btw, it sounds like it might have been the chain derailing--though i
>> don't know what would have caused *that*. i hadn't mucked with the
>> wheel, chain, anything in probably 9 mos. or so, and i've only had it
>> derail one other time in the year and a half i've had the bike. it
>> happened on a flat, straight section of road, nothing in particular
>> stands out as being unusual...
>>
>
> I know it can be tricky with matching cranks to BB to hubs, but a fixie
> chain should *never* derail. Good god that scares the **** out of me.
> \\paul


I'll agree with that. I've ridden my fixers many thousands of miles over
the past several years in all kinds of weather, terrain and speeds and
never had a derail. If I derailed even once I wouldn't ride it again
until I understood why and fixed the problem. Chain line should be
perfect, chain ring should be centered and chain should not develop slack.
 
Paul Hobson wrote:
> autopi wrote:
>> sorry, the URL should read:
>>
>> http://tinyurl.com/cyrjx
>>
>> btw, it sounds like it might have been the chain derailing--though i
>> don't know what would have caused *that*. i hadn't mucked with the
>> wheel, chain, anything in probably 9 mos. or so, and i've only had it
>> derail one other time in the year and a half i've had the bike. it
>> happened on a flat, straight section of road, nothing in particular
>> stands out as being unusual...
>>
>
> I know it can be tricky with matching cranks to BB to hubs, but a fixie
> chain should *never* derail. Good god that scares the **** out of me.
> \\paul

I also was scared of derailing on the fixie. However the first fixed
rides I had a bad chainline/tension and I derailed several times.
Nothing special, sometimes the rear wheel just blocked (with a slick
racing tire you just skid for some meters), sometimes I just freewheeled.
I suppose it can be worse if it happens at 200rpm or so.

Francesco
 
On 31 Jan 2006 06:30:35 -0800, "autopi" <[email protected]>
wrote:

>sorry, the URL should read:
>
>http://tinyurl.com/cyrjx

Still broken. Is this perhaps posted on a machine that's only visible
from within the network at Northwestern? The error comes back that
pubweb.nwu.edu cannot be found. Being behind a campus firewall might
cause that.

>btw, it sounds like it might have been the chain derailing--though i
>don't know what would have caused *that*. i hadn't mucked with the
>wheel, chain, anything in probably 9 mos. or so, and i've only had it
>derail one other time in the year and a half i've had the bike. it
>happened on a flat, straight section of road, nothing in particular
>stands out as being unusual...

Sounds like the chainline may be a bit off, and the chain may have had
a bit too much slack. Also, check for bent or clipped teeth on both
sprockets.

--
Typoes are a feature, not a bug.
Some gardening required to reply via email.
Words processed in a facility that contains nuts.
 
On 31 Jan 2006 11:03:30 -0800, "autopi" <[email protected]>
wrote:

>ok, this is getting silly...i don't know why the photos aren't coming
>up. let's try these:
>
>http://www.freeimagehosting.net/aa8fdb754f.jpg
>
>and
>
>http://www.freeimagehosting.net/adb7e8616d.jpg
>
>i'll double check the chainline and the cogs tonight--thanks for the
>advice! (and yeah, i meant "chain" not cable--it was getting late last
>night...)

Looking at the edges of the inner sideplates, I think I see chewed
spots that would indicate that there's a chainline and/or slack
problem at the root of the failure, as more or less expected. Looks
like the chain could have used a drop or two of lube, too.
Metal-to-metal without lube can make it much easier for a tooth to
grab a link's sideplate and walk it up.
--
Typoes are a feature, not a bug.
Some gardening required to reply via email.
Words processed in a facility that contains nuts.
 
>...less-than-perfectly-orthogonal angle...

I think I once knew the meaning of orthogonal. If I did, I've long
since forgotten. In any case, isn't the pin supposed to be driven in
perfectly perpendicular to the plates? Which I don't think is
orthogonal, is it?

Did anyone else notice the rat chewing marks @ the 4th from the bottom
pin's roller and general vicinity? I doubt that could come from one
derailing event. My guess is repeated pounding on teeth caused by chain
or cog warpage or poor chain line.

For a simple & clear explanation of chain line measurement see "Zinn &
the Art of ... Bike Maintenance"

Now that Ma Po addled brain has had a little time to think about it,
isn't orthogonal the way pipe spool drawings are done in power plants,
refineries, etc? And the orientation of the po abused chain in the
photograph?

Best Wishes, John
 
On Wed, 01 Feb 2006 22:22:21 -0800, john wrote:

>>...less-than-perfectly-orthogonal angle...
>
> I think I once knew the meaning of orthogonal. If I did, I've long
> since forgotten. In any case, isn't the pin supposed to be driven in
> perfectly perpendicular to the plates? Which I don't think is
> orthogonal, is it?

Yes it is; they are synonyms.
>
> Did anyone else notice the rat chewing marks @ the 4th from the bottom
> pin's roller and general vicinity? I doubt that could come from one
> derailing event. My guess is repeated pounding on teeth caused by chain
> or cog warpage or poor chain line.

I just looked at the pic. That chain has clearly seen a lot of abuse, and
not much if any lubrication. But those rat-chewing marks might just be
grime, in a funny light.

--

David L. Johnson

__o | It is probably 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
 
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