Jerry Moos wrote:
We've had some extensive threads on this. Campy NR cranks had a transition from crankarm to spider that turned out to be a stress riser. They were also very hard alloy, which made for very long lasting rings, but also meant the alloy was more brittle and cracked more readily. Stronglight cranks, by comparison, were softer, so rings wore out more quickly, but they rarely cracked like Campy. Almost all used Campy cranks have small, sometime almost indiscernible, cracks at the transition from spider to crankarm. Occasionally these propagate and the crank fails. They can also crack and fail at the pedal hole, usually where scratches from curbs, etc. had created stress risers. I don't think this is a simple function of age, its more likely a function of the number and magnitude of stress cycles, which would relate roughly to mileage and maybe the weight and riding style of the rider. But scratches and scrapes probably accelearte failure also.
The bottom line is, inspect Campy cranks regularly, and if there is a serious crack, retire them. I did this on a 1968 Allegro Special, where I found a rather nasty crack in the NR left arm at the pedal hole before it failed on the road.
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One key statement, new (I think) to our discussions, is "[n]umber and magnitude of stress cycles." The new Wilson/Papadopoulos Bicycling Science reflects a fair amount of Jim P's effort in this area, which point to the importance of relatively infrequent but very large stresses. This could get into thinking about the frequency distribution of stress amplitudes, and makes for interesting reading, but it doesn't change Jerry's imprecation to inspect regularly.
harvey sachs
mcLean va