Bad Lag

This is the drive side arm from a Campagnolo Nuovo Record crank.

I didn't know they were detachable but I just found out - they are!

I was heading uphill, crossing Pacific Coast Highway, pedaling hard, the light having just turned green. It separated from the bike without warning and dumped me (pretty hard) onto the roadway.

Bad Lag

I have an old Sugino Mighty Comp I can use for now but (obviously) I need a new crank.

It is marked as 170 STRADA (4) (the number 4 inside a circle).

velomateo

That is where they tend to break, with small cracks visible at the inside of the radius of the corner. I have one that I’m monitoring at the moment, after seeing this I should probably switch it out.

juvela

-----

sure hope you were not hurt when this event occurred!

forum member bulgie has a sobering page on his site showing a collection of failed components & frames -

​​​​​​Broken Bikes & Parts


-----

Bad Lag

I would advise that if you can see a hairline crack, the crank is toast. I did not see any cracks in mine last time I looked. Still, it failed under load (200+ pounder, large gears, accelerating away from being stopped).

repechage

1984.
one really needs to inspect these things, my suspicion is that the fracture face will not all be clean, but will show one or more darker regions. Those darker areas are where is was fractured before failure.
the cracks that appear at the root of the inclusive angle between the art and the two chainring arms really need to be filed back to clean metal. A chainsaw chain file, fine with a constant diameter is my preferred tool.

repechage

Cannot edit, but PCH is a dangerous highway.

mpetry912 

these parts have a history of cracking / fretting at the thin part where the drive side arm joins the spider arms.

they can crack at the pedal eye too. I have seen both.

Remember these parts are approaching 50 years old. you may not know how they were treated by previous owners.

if you're going to run Campy Record / NR cranks, it is important that you keep an eye on them in the known problem areas..

OP went down but it could have been much worse. Glad he is OK.

The very last revision of these parts (1985?) had a slightly revised forging that may have mitigated the propensity to crack somewhat.

Lets be careful out there.

/markp

steelbikeguy

An argument can be made for filing that thin web of metal as a preventative measure too. No need to wait for a crack to appear.

The thin web of metal at that junction of the arm and the spider is prone to developing cracks. Once the cracks start, they can propagate without being easily visible. With the thin part of the web removed, the stress is less concentrated and it is less likely for cracks to start.

Here's a shot of one of my Campy Record cranks with the web filed (with a chainsaw file... they really work well for this).




It's not just the Campy Record crank that is prone to this failure... any crank manufactured with the same process and the same thin webs is a potential victim. I've filed my Sugino AT cranks for this reason. Here's one of them:




Even with this preventative measure, it's prudent to take a close look at them periodically and check for crack formation.

My secondary method to avoid cracks is to be thin and not very powerful, but I recognize that this isn't for everyone.

Steve in Peoria

RCMoeur 

I used to race on the same team as Jim Elliott (several-time RAAM competitor). Jim was a very tall guy - we said (half in jest) we couldn't draft him because the wind shadow was well above us (plus, he was a bit squirrelly). As I recall, Jim broke several sets of Record cranks in the 1980s, when fatigue and age wouldn't have been as much of a factor.

repechage

Here is a crank that when purchased - part of a project bike, had the cracks starting.
phase 1 material removal shown- note that the filing is not just flat across but sweeps around.

the very first Campagnolo Cranks had a circumferential slot centered about the BB spindle bore between the arms.
was probably a devil to machine way back so was dropped.

kroozer 

I had a Stronglight 93 crank that cracked in the same place, so it's not limited to Campy.

Chombi1 

I read somewhere that Stronglight actually used a softer aluminum alloy for thrir cranksets in the 80's, to avoid cracking.
Mavic also had cracking problems at the spider with their pre-starfish cranksets. Maybe that's why they came out with the starfish design which has a lot more material at the spider.....

mpetry912 

Stronglights are very soft. They are easy to split because the crank bolt never tightens up.

I don't trust them anymore either

/markp

cyclic_eric

Thinking in terms of the engineering history, it would be interesting to know if the average dimensions (height, weight, etc.) of athletes was taken into account when designing such parts. Or it could simply be, “Luigi keeps breaking the cranks, make them thicker.” 😆

Average heights per country by decade are not too hard to find (see link below). Weight data is not easy to find, but BMI is. As you may expect, Americans are a little taller and heavier than French and Italian men, and the numbers generally go up during the previous decades.

Heights of Americans, French, and Italian men by decade

Important: My post here is only regarding factors of engineering design. Please continue to enjoy bicycling whatever your individual statistics may be.

oneclick 

I'd be having a *very* good look at this line your crank:

oneclick 

Any crank I get that has such a sharp corner at the high-stress junction between the arm and spider gets it rounded.

I use files first, but after that do this: charge a bit of line with polishing compound, hold one end in the vice and pull the other tight by hand; run the corners you filed back-and-forth the line until they have a nice smooth suface.
Files will leave small marks, and that's where cracks start.

repechage

it’s dirty. When I clean it up a business nearby will run a non destructive test for cracks. I have to note that the machining of this 1975 arm is meh, there are undercuts in the profile, dull tool marks in the arm flute also, not one of Tullio’s best efforts.

Bad Lag

Well, I managed to remove the broken crank and replace it with an old Sugino Mighty Comp I have (vintage 1973).

I went looking for a replacement Campagnolo crank. They are out there, at least they are on ebay. The thing is, I don't have (and don't want) an ebay account.

I'm looking for some sort of online/retail seller who takes credit cards.

Later today, I will post some images of the two halves of the broken interface.

Right now, I'm going for a ride. It's 70 degrees, sunny and a cool breeze is blowing in off the ocean. Yeah, I am outta here, dudes!

repechage

This is one version of the no flute cranks that Campagnolo made late to address the fatigue issue. This appears in the forging, others appear CNC milled.




from bikerecyclery, lone arm 172.5, $174 plus ship.

Kabuki12

I have filed a couple of sets with a tapered round file and check them periodically . The crack did not return. I have done some climbing on those bikes with no witness of any more cracking.

steelbikeguy

wow!
that is a huge improvement!
I wonder how much warranty they paid out over the years for breaks at the junction of the arm & spider? Or did they claim that breaks were due to abuse or excessive use?

Steve in Peoria

steelbikeguy

I don't know, but I would guess that the answer is #2... "Luigi keeps breaking the cranks..."

To be fair/reasonable, the bike industry wasn't much for good engineering in terms of stress and strain calculations. We wouldn't be breaking so many Campy seatpost binder bolts, etc., if they were. The amount of data on customers was pretty minimal back in the 60's and 70's too. Big industries, like autos and aviation, presumably had better data, at least in terms of making stuff fit the majority of customers.

There's also the competing goal of making parts as light as possible, combined with the assumption that racers will be fairly light, but powerful. Not sure how well that matches with the loads generated by heavy and low-power recreational riders.

Having watched the military aviation industry over some time, I know that they do a lot of analysis up front and tons of testing of the final item, but still get caught with the customer using the aircraft in ways that they didn't expect, and early failures showing up as a result. The early F-18 Hornets ended up with early cracking at the base of the rudders, requiring some external gussets being added, as well as a strake added to leading edge extension to break up the vortices that were hitting the rudders during high AOA flight.



we now return you to the bike-oriented content that you tuned in for...

Steve in Peoria

Bad Lag

This very busy weekend is now over but I did manage to order a replacement crank set via ebay.

My fingers are crossed regarding product quality but also that no one hacks my card or accounts.

I may request a new Mastercard account number.

Bad Lag

For the Mechanics here:

I forgot to mention, there was a sizeable difference between where the Campagnolo and Sugino cranks sat on the spindle. The difference was large enough to require a readjustment of the front derailleur.

Otherwise I would give up my two highest gears and the chain falls off when going to the small ring. - the Sugino sits THAT much farther outboard than the Campgnolo. Bottom bracket is a Phil from about 1978.

I love riding this bike.