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Singlespeed & Fixed Gear "I still feel that variable gears are only for people over forty-five. Isn't it better to triumph by the strength of your muscles than by the artifice of a derailer? We are getting soft...As for me, give me a fixed gear!"-- Henri Desgrange (31 January 1865 - 16 August 1940)

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Old 08-20-04, 01:16 AM   #1
Paraleisure
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Broken Crank?

Has anyone here ever broken the arm off of a crank coming to a stop quickly? I have a really tiny crack in my Campy crank, but it's awesome and super light and I don't want to stop using it. The alternative is to buy a 44t chainring and use my much lamer stock crank that came with the bike.
The crack is right where the arm meets the crank (spider? not sure what the right term is). I've never met anyone who's actually broken a crank, which is why I decided to just use it, but if someone here has, then I should probably reconsider...
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Old 08-20-04, 01:29 AM   #2
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Quote:
Originally Posted by Paraleisure
Has anyone here ever broken the arm off of a crank coming to a stop quickly? I have a really tiny crack in my Campy crank, but it's awesome and super light and I don't want to stop using it. The alternative is to buy a 44t chainring and use my much lamer stock crank that came with the bike.
The crack is right where the arm meets the crank (spider? not sure what the right term is). I've never met anyone who's actually broken a crank, which is why I decided to just use it, but if someone here has, then I should probably reconsider...
That's a really common problem with older campy and suntour cranks. There's a sharp edge there. If the crack is small, you can take a fine, round file to the area to get rid of it. The rounded area shouldn't crack again. I've done this to both Campy and Suntour cranks with great success, and if you're careful the rounded area can look really nice.

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Old 08-20-04, 01:31 AM   #3
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Thanks! I think I'll do exactly that this weekend.
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Old 08-20-04, 01:35 AM   #4
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Or, alternately, take off the Campy crank, put it back in its box with weirdo instructions (1. Rectify the thread of the bottom bracket shell by means of the Campagnolo tool 721, in order to remove any presence of varnish, and to assure a perfect concentricity between the two threads... 3. Do always lubricate the balls housing, with the special Campagnolo grease... and block the lockring by means of the Campagnolo tools 712, 712/1, 713), and sell it on ebay to finance the purchase of a track wheel for my girlfriend = forced fixed gear ("honey, where are the brakes?")
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Old 08-20-04, 03:32 AM   #5
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I personaly wouldnt ride that crank ever again.
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Old 08-20-04, 06:13 AM   #6
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I second not riding it again...cracks like that grow and aluminum fails rather catastrophically when it lets go. If I'm not mistaken, Branfordbike.com sells single crank arms.
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Old 08-20-04, 06:21 AM   #7
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Quote:
Originally Posted by jimv
If the crack is small, you can take a fine, round file to the area to get rid of it. The rounded area shouldn't crack again.
Dude, do not do that. The crank is done, hang it up as a trophy. A "lame", unbroken crank is better than a Campy cracked crank. Period.

I've broken 3 cranks, but they've all been mountain biking.
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Old 08-20-04, 08:08 AM   #8
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The idea of breaking a crank while comming down to a steep intersection with a red light and garbage trucks, busses, and old ladies scares the piss out of me. I'd get rid of the crank.
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Old 08-20-04, 08:11 AM   #9
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I'll be number 5 - never ride it again.

I've known people that had had crank arms come off the spindle before, and they didn't like it.

I've had a pedal come off and didn't like it.

A crank shattering while riding can be nothing but bad.

Wow I'm bored...

BUT DON'T RIDE THAT CRANK.

I feel better now.
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Old 08-20-04, 09:19 AM   #10
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I snapped my crank completely off while starting up from an intersection. It is a horrible feeling to have your crotch suddenly slam onto the top tube while your feet drag lifelessly. You're completely bewildered and wondering in disbelief at what just happened. Save yourself the humilation and by a new crank. I'm a light guy too, and this crank had no obvious fractures and it just totally failed without warning.
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Old 08-20-04, 01:41 PM   #11
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http://pardo.net/pardo/bike/pic/fail/000.html
broken crank pics here^

you've got to ask yourself: do ya feel lucky punk? well... do ya?

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Old 08-20-04, 01:46 PM   #12
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Thanks for all the warnings, I guess I better just switch. I'm biking up to the bike store today so I'll see if I can get a 44t chainring for my other crank. Although I am feeling lucky.
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Old 08-20-04, 05:10 PM   #13
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http://technology.open.ac.uk/materia.../mem-ccf4.html

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Old 08-20-04, 05:20 PM   #14
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It's gota take a hell of a lot to brake a fuking crank arm. Is this problem mostly with people trying to ride track bikes on the street and all the extra force applied with constantly speeding up and slowing down? I mean because track bikes are meant to go around in a circle and slow down only at the end of a race. I fence and it takes allot to brake metal parts (except blades that hapens over time and they are forged in a special way)and it seems to me that most cranks are pretty solid.
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Old 08-20-04, 05:43 PM   #15
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most of the failures seen aren't straight breaks, but happen over a period of time after a lot of fatigue and stress.

an initial impact/crack probably produced a stress raiser , and the cyclical stresses made the crack grow until there wasn't enough material to carry the stresses, and then the crank failed catastrophically.

corrosion from salt and other shi+e on the roads probably also has a part to play in this.

this is probably the time to advise everyoneto start a regular regime of polishing and checking for any cracks/deformation on load-bearing parts like cranks and stems.

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Old 08-20-04, 09:52 PM   #16
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I've also had a crank failure, and since then it has become my worst fear.

I was "lucky"; I was only going about 11 mph up a hill but out of the saddle. Even thgough I was going slowly, I still managed to mess myself up and take off alot of skin. When the pedal and bit of crank came off, the pedal slid out when my foot and pedal hit the ground...HORRIBLE.

Just think about: if you're out of the saddle and sprinting at 35mph, then you break a crank or a pedal, you've got nowhere to go.....BANG.

At least if you break a chain you've still got something to support your weight.

I can't think of anything worse to break than a pedal or crank in that situation.
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Old 08-20-04, 11:03 PM   #17
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hmm...gonna inspect my old-school dura ace cranks, right the hell now...also the cranks on my trials bike....they creak.
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Old 08-20-04, 11:22 PM   #18
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okay. so. i looked at my cranks, and it looks like there's a tiny little hairline crank, (but it could be a little scratch) on the outside of where the spindle connects on the left crankarm. dammit. could be a little scratch, but i showed it to my GF who isn't very bike savvy and i was like "look at this..." and she said "what, you mean that little crack?" guess i get to spend MORE money on my bike this paycheck....crap crappity crap stink.

sugino75s, or campy pista...already have the suginos and am pretty pleased with them, but maybe i want something different....hmmmm decisions decisions...

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Old 08-20-04, 11:22 PM   #19
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I luckily found a crack on anther pair of cranks that were the older Dura-Ace ones that have the "squarish" appearance.

I was changing all my stuff from one frame to another, and decided at the very last second to give the cranks a full clean before I put them on the new frame, then I saw a small crack inside the spindle hole which slips onto the axle.

I obviously chucked them.

Last edited by Fat Hack; 08-21-04 at 12:09 PM.
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Old 08-20-04, 11:43 PM   #20
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bah! i looked at it through a lighted magnifying glass, and now i can't tell. it looks like it's just a scratch, but how can i be sure? grrr....i'll take it somewhere tomorrow and get a second opinion.
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Old 08-21-04, 12:29 AM   #21
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Quote:
Originally Posted by OneTinSloth
bah! i looked at it through a lighted magnifying glass, and now i can't tell. it looks like it's just a scratch, but how can i be sure? grrr....i'll take it somewhere tomorrow and get a second opinion.
This is what I do:

"Sand" it with some steel wool to see if the scratch buffs out.

A crack will usually be a bit deeper

I think after a bit of buffing with the steel wool you can tell the difference between a crack and scratch, but it's hard to be honest, becasue the cranks cost good money, so you sit there trying to convince yourself that it's only a scratch.

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Old 08-21-04, 03:24 AM   #22
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http://technology.open.ac.uk/materials/mem/mem-dye.html
http://technology.open.ac.uk/materia...mem-dye-2.html

gotta love open university's site...

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Old 08-21-04, 08:34 AM   #23
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One of my crank failures, 2 tabs completely broken off and one cracked and on it's way.
.
.
.
.
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Old 08-21-04, 08:41 AM   #24
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What I dont understand is that you guys praise steel and look down at modern
components but then go an put vintage aluminium parts on your bike
from an age when aluminium components wherent really mature. (not everyone
of course)
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Old 08-21-04, 10:38 AM   #25
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Damn, those are some scary pics!
Especially the carbon fiber...


...and all those Campy cranks!!

Sohi... are you suggesting to use something other than Alu. components? Or, just more modern ones?
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