Singlespeed & Fixed Gear - 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...

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.

Jim

Thanks! I think I'll do exactly that this weekend.

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?")

I personaly wouldnt ride that crank ever again.

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.

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.

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.

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.

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.

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?

fsnl
sparky

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.

http://technology.open.ac.uk/materials/mem/mem-ccf4.html

fsnl
sparky

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.

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.

fsnl
sparky

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.

hmm...gonna inspect my old-school dura ace cranks, right the hell now...also the cranks on my trials bike....they creak.

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...

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.

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.

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. :)

http://technology.open.ac.uk/materials/mem/mem-dye.html
http://technology.open.ac.uk/materials/mem/mem-dye-2.html

gotta love open university's site...

fsnl
sparky

One of my crank failures, 2 tabs completely broken off and one cracked and on it's way.
.
.
.
.

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)

Damn, those are some scary pics!
Especially the carbon fiber...
http://pardo.net/pardo/bike/pic/fail/colnago-carbon-001.jpg

...and all those Campy cranks!!

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

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

I would lean toward modern components, yes. I like this design :

http://www.businesscycles.com/graphics/cr7710.JPG

it has really soft lines without harsh edges that could create high stress areas. the carbon
crank is a prime exaple of bad design. they merged two different materials in a high stress area.
each material has different properties and flexes differently under loads. Its like a
steel stem with a aluminium handlebar. the hard steal eats through the alu pretty quickly.
a couple of years ago it was agreed that carbon fibre is not the right material for cranks
and suddenly they are everywhere. I saw a steel frame with glued and bolted on carbon
seatstays. whats the point? what are those people thinking? why not make a frame
where each tube is made from sections of carbon, titanium and scandium. that would give them
the marketing edge.

why not make a frame where each tube is made from sections of carbon, titanium and scandium. that would give them
the marketing edge.

Bloody Hell!! That's a frightening reality :D

the reason i put the old D/A cranks on my bike was because i got 'em for like, $20, and i couldn't afford anything new at the time. i've got some sugino75s on my other bike right now, and i'll probably end up going with those again.

the new dura ace cranks are nice looking, and i'm sure they're great, but i have a big problem with octalink.

i didnt mean that these cranks are the only one to buy. just this type of design as opposed to
the hard edges skinny design of older cranks.

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.

Jim

Jimv is absolutely right..I remember seeing a number of these cracks on cranks in the 70's..when you use the round file to remove just enough material to eliminate the crack..you've eliminated what is called in engineering terms a "stress riser". Kinda like..give a crack an inch and it will take a mile. If it's no longer there, it won't progress up the spider any further.

Jimv is absolutely right..I remember seeing a number of these cracks on cranks in the 70's..when you use the round file to remove just enough material to eliminate the crack..you've eliminated what is called in engineering terms a "stress riser". Kinda like..give a crack an inch and it will take a mile. If it's no longer there, it won't progress up the spider any further.The problem with this is, there may be structural damage that can't be seen that will eventually fail too. And if something has already begun to crack, especially if it's old, chances are it past it's useful life.

I'm a cheap bastard, but sometimes you have to know when to retire a part to the junk bin. Dental work is generally more expensive than a new set of cranks.

The problem with this is, there may be structural damage that can't be seen that will eventually fail too. And if something has already begun to crack, especially if it's old, chances are it past it's useful life.

I'm a cheap bastard, but sometimes you have to know when to retire a part to the junk bin. Dental work is generally more expensive than a new set of cranks.

Sure..in some cases with a crack it's best to retire the part..in this instance though I'm thoroughly familiar with the crack and crank in question. The area where the crack started at the spider is thinner and sharper than the rest of the crankarm/spider. Therefore, the removal of a small amount of material enough to eliminate the crack, leaving a rounded profile will solve the problem. If this thinner material had been removed at the factory, the crack would have never started.

Sure..in some cases with a crack it's best to retire the part..in this instance though I'm thoroughly familiar with the crack and crank in question. The area where the crack started at the spider is thinner and sharper than the rest of the crankarm/spider. Therefore, the removal of a small amount of material enough to eliminate the crack, leaving a rounded profile will solve the problem. If this thinner material had been removed at the factory, the crack would have never started.

I absolutely agree. I have always felt that this was an error in tooling design rather than structural design. Having said that, I think that if anyone is uncertain about the safety of this approach then by all means simply replace the part. I have however, made this 'repair' with great success more than once ... and I'm no light-weight at 250 lbs. Naturally if you find one of these cranks without the crack, it's definitely a good idea to remove the sharp edge as a preventative measure.... I guess that goes without saying.

Jim

Ok, so funny you guys should mention aluminum catastrophically failing....

Check out what happened to my bianchi tourer's stem while my friend was riding it.

The only warning it gave was some creaking the night before between pubs.

Soooo, yeah - I wouldn't use a cracked crankarm.