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Old 01-12-22, 06:44 PM
Ride, Wrench, Swap, Race
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Join Date: Jan 2010
Location: Northern California
Posts: 8,359

Bikes: Cheltenham-Pedersen racer, Boulder F/S Paris-Roubaix, Varsity racer, '52 Christophe, '62 Continental, '92 Merckx, '75 Limongi, '76 Presto, '72 Gitane SC, '71 Schwinn SS, etc.

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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.
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