Salonistas,

I had a bit of distressing feedback on a recent build - within a couple of weeks of riding, the rider had a failure on his carbon post:

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The damage is to the rear of the post, where the seattube is split. By the sound of it, the failure was just above the top of the seattube. It was a parts bin seatpost of no especial pedigree and I didn’t put the bike together so I can’t rule out pre-existing conditions (and can’t comment re. torque and assembly paste) but it has worried me.

I’ve not got any good pictures of the seattube top style but you can just make it out here:
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It’s very similar to this Kirk, but rounded to the front rather than pointed. At the rear there is an curved cut away that leads into the slot.
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The seattube is a 31.8mm ID externally butted job with an aluminium shim pressed and Araldited into it and reamed to 27.2mm. The slot is probably an inch and a half, and the shim extends another quarter inch below the bottom of the shim. I lightly chamfered the inside top edge and the inside edges of the slot specifically to avoid doing any damage to carbon posts, and used a longer slot than usual in hopes of getting a nice gentle squeeze over a longer distance. The binder bolt is a steel cylindrical one, brass brazed on and with the seatstays shot directly into it, just like the Kirk.

Any advice? Is there anything else I need to do in future?

Ben