Aero seat post fix . Good idea bad idea ?
 

Hello .
I’ve a teardrop carbon aero seat post , broke the head off through my own roughness.
problem is the bike company have gone and the seat post is incredibly hard to get, carbon repair shop has said no to a fix ,
It’s 42mm longest point and 20mm wide section
just thinking would it be safe to buy a slightly bigger aero seatpost 48mm x 25mm to slip over the old down as far as the post clap . Mark position and liquid resin bond the 2 together by pouring fibreglass resin inbetween the gap of both ? Good idea or silly

Both posts CF? If so I'll bet the larger post will need significant cleanup inside (ie sanding and filing) to slip over the broken post but I don't see why it is not doable in concept. Use epoxy, not a polyester based resin. Be aware the epoxies "flow" as part of the cure cycle. That flow is wonderful for filling gaps but that epoxy will find a way to split the scene it you give it an avenue. (Dependent on how thick the epoxy is, warmth both generated in the cure and added from the outside and setting time.) Taping the joint ends with masking tape will do a lot to keep the epoxy behaved and will lift off after cure.

Safety-wise - if you bring the joint down to say 5mm above the clamp I cannot see anything worse happening than the seat slipping down that 5mm if all goes to heck. (Assuming you are road riding and not all out extreme BMXing.)

Another thought - that I've had before but never saw a way around: I like my seatpost set so the nose of the seat is almost a cm to the left. Always saw the aero posts that slid into aero seat tubes as a big compromise for me. But! with your proposal, I could twist the outer post slightly askew and set the seat right where I want it!

yes both are CF posts and thanks I was going to use a polyester resin as we have it at work for flat roofing I’m sure it would be ok ? . I’ve roughed up the outside of the small seatpost ready for the over slip . Tape the end as you said . I’m not 2 concerned about the weight anyway , more the fact it was only my second ride on the bike after buying 😂 and not dumping a £1k bike
Desperate measures got me thinking

You don't want to use polyester resin. Can we see a pic? Practically any carbon fail is repairable. When people say no immediately I would question their repair ability.

Your idea sounds like a possible fix if done well. Make sure there's a lot of surface contact area. Whatever epoxy you use will have a suggested joint gap for best results. Typical for this stuff (ill fitting parts) is that a few spots will be just right and a lot more won't be, so having a lot of overlap will help the numbers. I like the use of tape as a dam for seeping epoxy, done the same decades ago in the ski shop world fixing skies.

Depending on the fit of the "new" post over the "old" I might consider a building up of the old's top to better fill the new's ID. Fiberglass, carbon fiber ribbon come to mind. By holding the old post in the frame one could file down the added layers fairly easily and reduce the gaps. Relying on the epoxy only to fill gaps much larger than parts of a MM is a poor idea. I have heard of people mixing into the epoxy fibers, short cuts of glass or carbon, to better fill the gaps. I would only suggest a slow curing epoxy to give you time to handle/assemble the two posts. Can you give us an aprox amount of overlap between length the two posts?

A seat post failure is one of the lesser concerns I would have when riding. Although I will say riding a seatless bike is a lot harder than most would initially think:) Seriously we're not talking about highly stressed and structural frame or wheel parts. Broken bars, pedal spindles or cranks are usually a far worse thing to have happen. Andy

Unfortunately I can’t post pics as not 10 posts in yet 😂 it’s broken right where the post and seat clamp section meet . So I pulled the half round saddle bit clean away from the post. It’s a v narrow post , 42mm long 20mm wide to 5mm wide safety first in the carbon guys eyes

The new post I’ve bought should have around 4mm of play in most areas with more towards the front of the tear drop .
its a Dassi aero bike . Think I’ll stick to mass production bikes in future

If I might suggest the issue is the non common and round post, not the bike brand. While the brand did offer the bike with it's aero post no one forces anyone to actually buy it. Andy

True but to stick to more long running company’s may be a better option

Which won't eliminate the unique post shape unless you also eliminate their models that do use an aero post. It seems to me that a big aspect of this thread is the unique post shape, not the brand. Any brand can and does change specs periodically and will at some point to no longer support their older designs. This would have the same result, as the company going out of business, when their aftermarket parts are no longer available. Andy

Make a few more posts and get that picture up. ;) There are plenty of gelled Epoxies that will fill gaps and not run out of a joint.

Can you post some photos?

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Done
 

So after some searching I ended up with a UDM carbon aero post . £40
slight difference in shape but still tear drop . Had to file the paint off the old post to make it snugly fit .
packed the new post bottom inners with tissue and wedged down the old post First dipped in resin .
should have taped up the top of the old post as when I was filling the resin inbetween the 2 posts it started to rise up inside the old post aswell . Maybe just start small and let the resin dry first then fill the gaps .
works fine have my bike back