ive cracked 2 pairs of campy crankarms at the arm/spider junction (one of those "oh i should file that area. eh, ill get around to it..." things :) )
both pair i caught when the crack had just started, but was too far gone to file out. told myself id swap when the crack went 1/3 of the way through the arm, and started looking for new cranks. both cases, it took approximately 1 month of riding 250+ miles/week for the crack to lengthen to 1/3 of the way through the crank (perfect! exactly how long it took me to find new cranks! :) )
i dont recommend this completely absurd and dangerous method of gathering data, in fact, i recommend against it entirely. but when you cant find the cranks you want, and cant afford the cranks that are available, and need to ride your bike for work, well... im still here, arent i? :)
best thing to do is file (my current pair is filed... really!), and regardless, check that junction point (and the pedal hole, and the spindle hole...) on a regular basis - say, whenever you clean your bike. older campy cranks are quite popular with messengers, and ive seen probably upwards of 20 broken ones in the past 10 years - all at the spots illustrated on the link chuck gave, and the legendary spider/arm junction.
i always have considered the filing bit to be fairly common knowledge - ive certainly run into it in every population of cyclists where ive been involved in campy cranks discussion. whether or not everyone who knows about it actually gets around to doing it, well, thats a different matter :)
-joel
> > I was asked by a local mechanic about filing Shimano and Campy cranks.
>> He was told that by filing a nice radius where the crank meets the
>> spider, that they would not crack. Does anyone have any experience with
>> this?
>> Thanks,
>> chris ioakimedes
>> Fairfax Califormnia
>
>
>It was fairly common knowledge and a fairly commonly done thing in
>Southern California to file the web at the junction of the arm and the
>spider in the mid 1970s and maybe/probably before. I don't know if this
>was commonly done else where, but I heard that it was a common enough
>practice among race mechanics in Europe.
>
>Campagnolo Record cranks routinely develop a small crack at the web with
>heavy use because the metal comes to a very thin, knife-like edge. If a
>crack is found there it can be file out and polished to keep it from
>propagating or you can file the crank before it develops this crack to
>keep a crack from forming.
>
>I have seen Campagnolo cranks crack and break at the pedal eye and in
>the middle of the arm where "COLNAGO" was pantographed in the flute, but
>I have never seen one break at the crank and spider junction. I sure it
>has probably happened though, since all parts, steel or aluminum, will
>break with enough abuse.
>
>I'm not aware of anyone filing Shimano cranks.
>
>Broken Bicycle Cranks site:
><http://pardo.net/pardo/bike/pic/fail/FAIL-001.html>
>
>Chuck Schmidt
>South Pasadena, Southern California
>
>.
>_______________________________________________
--
joel metz : magpie@messengers.org : http://www.blackbirdsf.org/
bike messengers worldwide : ifbma : http://www.messengers.org/
po box 191443 san francisco california 94119-1443 usa
==
i know what innocence looks like - and it wasn't there,
after she got that bicycle...