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Old 01-12-22, 10:08 PM
  #45  
scarlson 
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Location: Medford MA
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Bikes: Ron Cooper touring, 1959 Jack Taylor 650b ladyback touring tandem, Vitus 979, Joe Bell painted Claud Butler Dalesman, Colin Laing curved tube tandem, heavily-Dilberted 1982 Trek 6xx, René Herse tandem

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Originally Posted by dddd View Post
I'm not joking here, that crack's cause actually eminates from a safety requirement imposed on US-market bike suppliers!

I've seen these failures caused by too wide of a taper on that nut on both Cinelli and 3T forged stems.

The nut was made longer and with a flared taper that got bigger than the hole, so not easily pressed into the hole AT ALL.

The reason for the longer/wider taper was to accommodate an alloy REFLECTOR BRACKET of approximately 3mm thickness, so without said bracket, the tapered nut ends up being forced too far into the lower clamp ear, leading to the ear splitting.

I always check for any sign of such a nut appearing to not fully seat against the rear of the clamp ear, it might be the last red flag given before...

There are a lot of these out there.
Right, right! OK, I'm not crazy. I postulated that earlier, but you probably missed it in the above doomscroll.

Originally Posted by scarlson View Post
Interestingly, it is known that the Cinelli 1E stem, which was designed to have a front-facing reflector bolted on the back, had a tendency to develop a crack similar to the one you show here, if the reflector was removed, because the tapered hole in the backside was not reamed large enough to accommodate the increased depth/diameter of the knurled nut sans reflector. Yet another way CPSC ruined changed things in the '70s.
My 1A with a similar crack to yours does, indeed, have an aftermarket nut - one of those Arnold Industries ultralightweight jobs. I think that's why mine cracked. It sounds an awful lot like the "non-critical" cracks mentioned by S. Barber on Velobase. Still riding it though - I'll post a picture tomorrow as the capstone of my dissenting opinion, and then I will shut up about it...
Here's mine. Still riding it. And before you ask, yes it looks like that even after I remove the nut. And yes, that's a crummy decaleur poorly brazed on. Bit of a rush job so I'd have a bike to take on my work trip to Michigan. The crack is because of the Arnold Industries lightweight aftermarket nut, which appears to have been the wrong size.

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