The perils of mixing aluminium alloy and carbon fibre cycle components (removing a stuck seatpost)

When I first started road cycling, a friend suggested I could increase my comfort for not too much money with a carbon seatpost upgrade. A short while later I was the proud owner of a Deda Superzero post and it looked good, even if the marginal gains with me riding the bike were so small that they could be offset by an extra cup of coffee…

Fast forward a few years and my teenage son was borrowing my bike as he’d outgrown his. I went to adjust the seatpost and found it was stuck fast. And I mean stuck. Solid.

Obviously, this was fine for me to ride the bike but I couldn’t just leave it. Over time aluminium alloy (e.g. my frame) will bond itself to carbon fibre (e.g. my seatpost) and even though a bike mechanic had applied some anti-seize paste and I’d given the post a “wiggle” from time to time, I’d obviously left it too long since the last check.

So I hit the Internet and Googled “how to remove stuck seat post carbon aluminium”…

There’s a load of ideas on the Sheldon Brown bicycle technical info site.

And this thread at BikeRadar is useful too.

Added to which, there’s more info at Cycling UK including a health warning about cutting carbon fibre. The dust is nasty stuff…

I’d used penetrating oils and hot water on the frame but the bond was too tight – not enough space to get the oil down. So, with assistance from a fellow club member who was very generous with his time and use of his tools, I tried heating and cooling the affected areas of frame and post with a heat gun and some “Shock and Unlock”. Ideally, this would cool the post and heat the frame – the idea being that one will expand and the other contract, breaking the bond. Nothing.

Heating and cooling the seatpost Frozen seatpost

Then we tried the other way – even if it pushed the materials together it might break the bond on cooling. This was quickly followed by disaster – I attempted to move the post when it had been heated, it seemed to move, too easily and I found I’d actually twisted it and deformed the post.

Snapped seatpost

“Right, now that post is a write-off, at least the frame is OK, we’ll have to cut it out.”

We tried using naked hacksaw blades (wet seems to help and I also seemed to do better with 36T blades than 24T), a padsaw, even an electric reciprocating saw.

Cutting out the seatpost

Eventually (and I mean after many hours) I had cut some channels in the remains of the post but it still wasn’t coming out. The idea is that it should collapse in on itself once there’s a vertical cut that stops it pushing against the frame seat tube. What did happen though was that the carbon fibre delaminated and we were able to chisel pieces out using a variety of punches chisels and screwdrivers and a lot of GT85 (being careful not to damage the frame).

Eventually, the post came out, in thousands of pieces over a few more hours. And the depressing part, when the bottom section of the seatpost was removed (the last few inches hadn’t seized), we could see just how little effect the hacksaw had made that far down the post – there just wasn’t enough force to make a difference.

With the last of the pieces out I cleaned up the inside of the frame with some wire wool (using a bent coat hanger to pull it back up) and put the original aluminium seatpost back. There are some minor scrapes inside the seat tube and some paint cracks on the top section too so I’m not sure whether I’ve compromised the frame.

Seatpost removed

Thankfully, I brought forward my plans for a new bike, bought my son a larger frame for his and this one is now in semi-retirement, relegated to Zwift duties.

It took me (and a friend) at least 8, maybe 12 hours to remove that post so, if you do mix aluminium alloy and carbon fibre components, make sure you (re)move them regularly. 

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