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Old 07-07-12, 07:24 PM   #1
joejeweler
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Componant Failures, Maybe We Should Be ADDING Weight To Key Components!

On a recent google search i came across this government study of componant failures in the real world that have sometimes resulted in serious injury or death. I was a bit surprised, really, considering the R&D that goes on.

Specifically, i was really taken back by the failure of the Campagnolo crank arm! I'm not singling them out, btw,......generally a mighty fine bunch of parts. But if it can happen there, it might behoove us all to take a close look at some of the key components we entrust with our well being......

.........and maybe not strive to aquire the "lightest" of everything that are geared for the racing crowd. They regularly replace key parts long before their day of failure might arrive through extended use, something WE rarely would do!

Me,....i'll carry the extra weight on such things as crank arms. My 1987 vintage Shimano Deore XT FC-M730 crankset made for MTB use (and on my Schwinn Cimarron) is going to be duplicated on my 1977 49cm Schwinn Paramount loose frame once it arrives next friday or so. I've got a old school quality Dura Ace BB-7400 bottom bracket coming already, and a set of those beefy FC-M730 crank arms also. Going to make a hybrid more upright comfort city cruiser out of that one! Some Serfas "Drifter" 700 X 32 tires on the way, as is a 5 speed alloy wheelset off an older 1980 Schwinn Super Sport and stored for a long while. They were reasonably priced until i can locate a beefier wheelset for longterm.

......that light stuff i'll pass on,......when my butt's on the line!


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Excerpt From: http://pardo.net/bike/pic/fail-009/000.html

Bicycle crank failure II
From http://technology.open.ac.uk/materia.../mem-ccf4.html as of 2004/01.

Yet another fatigue failure in a bicycle crank spider arm. This was a high quality component that had very high load cycles but was in excellent apparent condition until the final fracture that unseated the rider in heavy city traffic. Fortunately no long term injury occurred.

The fatigue crack initiated exactly at the location of the maximum tensile bending moment, close to the crank axle on the tensile side of the crank.



The crack progressed slowly through the crank arm (dark area) until the remaining fragment was incapable of supporting the bending moment generated by the force on the pedal and the crank arm fractured rapidly.



This long term fatigue crack in a high quality component took a considerable time to nucleate from a machining mark between the spider arms on this highly stressed surface. However once initiated propagation was rapid and accelerating as shown in the increased spacing of the 'beach marks' on the surface caused by the advancing fatigue crack.



This unfortunate incident may have been prevented only by very close visual inspection or dye penetrant testing (see below) on the component during the relatively short crack propagation phase.

Last edited by joejeweler; 07-07-12 at 07:40 PM.
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Old 07-07-12, 09:07 PM   #2
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Uh, not exactly the latest light weight crank there. That thing was old when the internets were new.
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Old 07-08-12, 12:06 AM   #3
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Yeah, and the OP riding old bikes doesn't make any sense from his point of argument, either. I'll also point out that the DuraAce he's stoked to put on is exactly the light, race ware he earlier railed against.

I dig the OP wants to be safe, but he needs to spend more time thinking about the matter, because he's confused right now.
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Old 07-08-12, 12:27 AM   #4
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Forging aluminum, alloying , for stiffness, has its trade offs..
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Old 07-08-12, 07:43 AM   #5
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If you ride quite a bit components will break or wear out.
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Old 07-08-12, 09:56 AM   #6
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Steel cotter cranks?...oh forgot...broke one of those too.

Most products are going to fail eventually. You make your choices and live with them. I chose things for durability rather than light weight, appearance or cost. In many cases today the engineering is allowing products to be designed with a set life cycle, they just don't bother to tell you that up front. Case in point: I have a small Canon bubble jet printer, BJC-85 purchased new in 1999. Had an issue with it around 2005, called tech support. The question was asked how many pages had been printed with it, turns out I was at about 3 times the design life, the tech made a couple of suggestions that cleared the problem up and it is still printing along at probably 6 times the design life. Eventually it will wear out, when it does I have a newer version of the same printer, new in the box ready to go.

From the description of the Campy crank above there was a flaw in the original that eventually caused it to fail, what is missing is the usage and the life cycle information.

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Old 07-09-12, 09:07 AM   #7
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Quote:
Originally Posted by chaadster View Post
Yeah, and the OP riding old bikes doesn't make any sense from his point of argument, either. I'll also point out that the DuraAce he's stoked to put on is exactly the light, race ware he earlier railed against.

I dig the OP wants to be safe, but he needs to spend more time thinking about the matter, because he's confused right now.
You sir, are a total opposite of the anatomy of a donkey's head!

My '1987 Schwinn Cimmarron had maybe 200 hours on it when it went into storage 23 years ago. So she may be "old" in years, but young at heart with a LOT of life still in her. Being old has NO corrolation with being worn out, and i'd venture a guess that the 18" 4130 chromoly bi-oval double butted main frame will long outlast me and a few more generations!

My "point of argument" was simply pointing out a study of componant failure i found interesting and wished to share. My posting this topic was not a "rail" either,......and i believe it is you, sir, who is confused!

BTW, the '87 vintage Shimano Deore XT bottom bracket and triple crankset i've thought so much of (from a strenth POV), that i have decided to use those EXACT componants on my Paramount city comfort bike build.

I picked up a Shimano XT FC-M730 BIOPACE Crankset, 175mm, 26/36/46 here last night:
http://www.ebay.com/itm/290737254718...84.m1439.l2649

....and an appropriate NOS Shimano XT Bottom Bracket BB-M730 Square Taper 68 122 2 days ago here:
http://www.ebay.com/itm/320930923348...84.m1439.l2649

The crankset is no lightweight for sure,......but at 178 lbs i doubt i will ever stress the arms, and about as safe as you can EVER find! I believe Shimano overbuilt this particular crankset at a time they were just getting into the MTB componant business and didn't want any surprises. Pretty sure no hollow cranks here.

.....even going to use an XT PD-M730 pedal set (same set that is on my Cimarron). Bought these also last night. http://www.ebay.com/itm/300734589634...84.m1439.l2649

I cleaned out my original pedal set and regreased the ball bearings a few weeks ago,....another solid unit. I find these pedals perfect to use with most any sneaker or decently thick supporting sandle for around town. Just don't like being locked into the pedals on the street/sidewalks.

Last edited by joejeweler; 07-09-12 at 09:37 AM.
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Old 07-09-12, 11:44 AM   #8
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Waitaminit -- this wasn't even on the OP's bike! So all we have is a singular account of something that can happen to any crankarm, short of a 1-piece crank. Sometimes pedal strike or incorrect torquing can precipitate breaks along flaws in the metal, but it may take a long time for problems to manifest.

Any bicycle part can break. Sheesh.
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Old 07-09-12, 01:01 PM   #9
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Especially a part that looks like it could well be upwards of 30 years old...
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Old 07-09-12, 03:10 PM   #10
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There was a known problem with some Campagnolo cranks. They tended to crack at the thin area there. It's a bad design, not a weight weenie problem.

People used to file the sharp edge with a round file to help prevent it.

It is a good reminder to inspect the bike and it's components. These failures were usually started with a tiny crack that took a lot of rides to break completely.

See this thread.

Last edited by rm -rf; 07-09-12 at 03:18 PM.
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