verbs4us

My trysty mechanic, who takes care of my 1974 Masi Gran Crit, made a passing comment about "those old Campy cranks--you know they break..." He's knowledgable: he's a racer and when not on the bike, is a mechanical engineer for Sikorsky aircraft. He says the old NR cranks had a habit of sudden failure from accumulated fatigue. The arms just break, usually with no warning. He appaprently broke two back in the day. While he's my weight (about 140) he's a powerful rider and i'm luclky if I have half his power. But still...now I feel tentative pounding up those hills. My bike has been in one crash and there is no visual evidence that the cranks took a pounding then. They never creak. Any experience or advise here? Thanks!

rootboy 

He has a point. And way more experience than I have. But I think actual failures under load are quite rare.
Still, check the web where the arm meets the crank spider, under magnification, for hairline cracks. They do tend to develop stress cracks there, sometimes. If found, it can sometimes be removed by the careful use of a small burr or mounted stone in a Dremel. Or a small, round jeweler's file. If not found it can be a plausible preventative measure to do it anyway.

JohnDThompson 

Yes, they do have a reputation for failure due to a design flaw that leaves a significant stress riser where the spider merges with the arm. The solution to this is thankfully easy, simply use a small round file to remove the stress riser (the sharp edge where the arm merges with the spider:





N.B. this fix is only appropriate if done before a crack appears.

ThermionicScott 

Lots more broken crank gore here: https://pardo.net/bike/pic/fail-001/000.html#Crank

noglider 

140 pounds is light. How tall are you? Your size probably makes you safe.

Jobst Brandt had a lot of criticism for the Campagnolo crank of the 70's and 80's era. He is tall -- about 6'4" -- and was a very strong rider.

I'm still using mine and am not afraid. If I were big and strong, I might be afraid.

CroMo Mike 

The pictures I've seen of a broken Super Record crank arm show the break occurring across the corners of the square spindle hole, dropping the entire arm on the road. I can't visualize that happening from a crack developing at the arm/spider junction. Anyone seen where the crack goes from the arm/spider junction? I would expect one spider leg to break free and give plenty of warning of what comes next. At any rate, I have three NR/SR cranks in use with no cracks. I suppose some guys could break anything.

verbs4us

Thanks Tom--I'm 5'8" on a good day, and built like a climber--no bulk upsatirs (to which my wife will attest) (see pic)

noglider 

Cute picture. I wouldn't worry if I were you. I'm 5'9-1/2" and 166 lbs, i.e. a little bigger than you, so you should have a little less to worry about than I do.

John E

Having snapped a Sugino (Campag. clone) crank across the pedal eye during an out-of-saddle climb, I do recommend caution when using older components.

rootboy 

Right. I suppose in my first post I should have said that the crank arm to spider transition web CAN be a place where these cranks fail. But that is not the source of the catastrophic failures, AFAIK.

And the failure at that point isn't necessarily because of riders over-stressing them by heavy mashing. But probably by a design flaw, as JT indicates.

CroMo Mike 

Some interesting pictures there. Odd how many broke across the arm itself. Many had evidence of existing cracks before they finally let go. Looks like Campy isn't the only brand that can break.

rootboy 

Holy S**t. There's some ugly and scary stuff in there.

due ruote 

Here's a Deore I (or, more likely, the PO) broke. I was quite delighted to have spotted this fairly close to home! No hammering on the return trip. It's not a bad idea to look these things over from time to time.

noglider 

Maybe we should go back to steel cottered cranks!

mikeybikes

https://pardo.net/bike/pic/fail-001/FAIL-162.html

OldsCOOL

Death cranks!

verbs4us

OK guys--thanks for stoking my fear and paranoia. The follow-up question: If you were going to replace old Campy NR cranks on a classic bike (which is a rider, not a show bike) what would you choose? Should have the same Q. Very few I've seen have the slim lines of the old NR (probably for just the failure reason!). They look chunky and inelegant to my eye. Replacability of chainrings is a consideration, so Bob's Cranks machined in garage somewhere in North Dakota may not meet the "readily available" criteria. I had really bad expeirence with an early Sugino, so that's out. Thanks!

SJX426 

Impressive list of failures! Certainly not limited to NR/SR cranks!

Ex Pres 

I didn't see any Stronglight failures in that list. Doesn't mean they're never broken, though. But a Model 93 would be period appropriate for a '74 bike. I'm using a model 104 with an otherwise all NR group on a later date bike.

Here's a pic of my 104 in Velobase:

verbs4us

Thanks ExPres...There was a Stronglight failure in one of the photo sets. Unfortunately, finding replacement chainrings would fall under the impossible headline. I should have been clearer: What currently made new crankset would be appropriate? PS on the Stronglight...I love their look. I had a friend who had one on an Allegro (a really stiff crit bike, made in Switzerland) and it was a bit whippy. Not as bad as the Sugino, which felt like it was made of rubber, but not as stiff as a Campy.