BMC Stupid f***ing slippy seatpost design

Hoping someone can help me and avoid me throwing my frame into a lake or killing it with fire.

I bought a BMC SLX01 second-hand on here a while back which features a new and useless take on an old system of securing a seatpost which worked perfectly well. It essentially the same idea as a quill stem, but as it needs to deal with much more load, doesn't stay where it's supposed to. I've tried so much to stop it slipping - torque to settings, torque above settings, carbon paste, hairspray(!). None of which has worked. At best, it'll hold for one ride. It's incredibly frustrating as it's a pretty cool frame and stiff AF, but due to the slippage issue, I now hate it with my whole heart.

My last resort is going to be a bit of innertube and a jubilee clip on the seat post just above where it meets the seat tube. Definitely questionable on a carbon seatpost, but I really don't know what else to do at this point short of getting it at the right height for me and liberally applying epoxy for a 'for-life' fix.

Any suggestions would be greatly appreciated.

Pic below for reference.

Thanks,
Tom

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When I had one of these I resorted to helicopter tape.

It was a long time ago, but I seem to remember that you have to get the line marks on the quill wedge and the post lined up perfectly. Before you install the post. You do this with the Allen bolt on the bottom. I’m sure you’ve already tried this. But that’s all I’ve got.

i had another version of that on a BMC slr01 but the rod was pulling a silicone? bung that would expand. the top part of the sytem with the hald turn of allen key was the same as yours so it was definilty another take on it from BMC.

If one would find a piece of the same material, cut it to shape between the carbon and alu wedge, maybe it would help with slippage once compressed.

With the idea being it's sticky enough not to slide up the post?

@Chaley - Yep, familiar with this approach and it's not working

So like a sort of silicone gasket that expands in the gap between the wedge and the post when compressed?

yes that's how this frame's seatposts worked .

the wedge was less at an angle, but it wasn't flat either. So there was silicone expansion and displacement as well.

edit :

How about an application of liquid chalk, as used by weight lifters, rock climbers etc to increase grip?

Thanks everyone, I really appreciate it. I'm going to throw the kitchen sink at it with a DIY silicone gasket, heli tape and either hairspray again or I might try liquid chalk instead, I've got some of that somewhere. Although, I don't know if there's a potential implication of something in the liquid chalk permanently binding alu somehow. Might just stick with hairspray.

I'll see how we go tonight.

Thanks again for everyone's input, this is why I love this forum.

Good luck! I’ve just been looking at the way they work and I’m wondering if some of your efforts should spent looking at where the top cam and the carbon tube, banjo meet. You could try a couple of wraps of PTF/plumbers tape around where the 2 join to give the cam a bit more throw?

You pre-set the position of the wedge from the bottom and then the bolt at the top/side of the post cams the long rod up to pull the wedge up and apply the expansion force?

What an overly complicated way to do it!

Could you get a clamp 3d printed that would fit over the post and create a shoulder that sits against the frame? Not sure if 3d printed plastic would be strong enough and metal might be impractical due to cost.

Actually, what about rather than epoxying the post in place 'for-life', build up a shoulder on the post out of epoxy? Then it's just a new post away from being back to stock if you need to sell.

I had a BMC SL01, bought it second hand and pretty sure it came with an ipad screen protector as a shim between the post and frame.

Minimising the friction in all that complicated bullshit which ends up pulling on the wedge is definitely necessary.

If all else fails, I'd consider sanding some lateral scratches on the wedge and the very lowest part of the post the help the carbon paste.