Stuck Carbon Fibre post in Aluminium Frame

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dvines
Posts: 155
Joined: 23 Jan 2010, 8:57pm

Stuck Carbon Fibre post in Aluminium Frame

Postby dvines » 9 Jun 2014, 9:55am

Dear All,

My brother-in-law brought round yesterday his "latest purchase" from ebay which filled with dread as he's a non-cyclist.

Bianchi aluminium frame with low end campag, and carbon fibre-post.

Seat-post is stuck,, was supposedly freed by the local bike shop - he claims they freed it off, and said they had to "cut off the end as it had compound on it" and that it was free when he got it back.

Its now jammed again, and I can't shift it at all. Despite being a cyclist 30yrs doing all my mine mechanics, I have no idea how to proceed with this one.... having no experience of carbon fibre/ali frames.

if I heave any more I will bust the post, and the frame has a removable "clamp" so no binder-ears I could pry apart a little. There is a small mark in the paint of the frame which has me wondering if a crackis forming where the seat-tube/rear stays join.

Judging by the other things the shop did to the bike as a "service" - ie completely buggered every adjustment up, I am not confident what they did to the seat-post.

- snapped it off and broken part is still inside, Jammed it back in, overtightennedi it, put on wrong grease, maybe incorrect size post put in ? (Maybe this is why bike was on ebay...).

I did think if I could cut off top of the post and insert a reamer (I have a set of adjustables) I could ream the whole thing out...

Anyone any suggestions ?? My local framebuilding friend Cliff Shrubb (RIP) is no-more, so I have no decent local professional help....

David

robc02
Posts: 1667
Joined: 23 Apr 2009, 7:12pm
Location: Stafford

Re: Stuck Carbon Fibre post in Aluminium Frame

Postby robc02 » 9 Jun 2014, 10:14am

This happened to me with a frame that was still under warranty (several years ago). I had tried various methods including pouring boiling water over the outside of the frame and turning the frame while the seatpost head was in a vice. There was some movement to begin with but gradually the whole thing seized. The force applied caused the seatpost to snap.

The shop I bought it from was very helpful and removed it by using a screwdriver-like blade and a mallet to delaminate the remains of the seatpost. - The blade was inserted into the carbon and tapped down inside the seat tube. Gradually the remains of the post peeled away. The job was finished by using an undersized seatpost wrapped in abrasive paper. The most critical part of the job was getting the final layer of carbon away from the wall of the seat tube without deeply scratching it.

Valbrona
Posts: 2244
Joined: 7 Feb 2011, 4:49pm

Re: Stuck Carbon Fibre post in Aluminium Frame

Postby Valbrona » 9 Jun 2014, 5:33pm

I would get a 365mm Fibregrit hacksaw blade and cut two slots in the seatpost after sawing it off. And then whack with a mallet and something else.
I should coco.

peterbayliss
Posts: 90
Joined: 8 Apr 2008, 12:47pm

Re: Stuck Carbon Fibre post in Aluminium Frame

Postby peterbayliss » 9 Jun 2014, 6:20pm

Recently I got a carbon fibre seat post stuck in a steel frame, first I tried spraying GT85 (any penetrating oil will do) in to the seat tube via the bottle cage bosses and around the top and then sat the frame upside down. This did not work so after a few days of trying, I boiled a kettle of water and poured this over the seat tube avoiding the seat post and after a few seconds (~20 seconds) the seatpost came out easily, I think the oil inside might have helped lubricate it.
It is worth a try as the water is not hot enough to cause damage to the frame and the aluminium is a much better conductor than the carbon fibre so heats and expands faster.

If it does not work you can still try other methods but I was able to get the seat post out without damage to it or the frame. An old saddle can be used to provide leverage but with mine I could see the seatpost flexing so the amount of force I was prepared to try was quite low.

Brian73
Posts: 457
Joined: 11 Aug 2010, 10:32pm

Re: Stuck Carbon Fibre post in Aluminium Frame

Postby Brian73 » 9 Jun 2014, 6:20pm

Sheldon Brown has a list of ideas

http://www.sheldonbrown.com/stuck-seatposts.html
Last edited by Brian73 on 9 Jun 2014, 6:28pm, edited 1 time in total.

nicmarsh
Posts: 258
Joined: 14 Sep 2011, 5:12pm
Location: SE UK

Re: Stuck Carbon Fibre post in Aluminium Frame

Postby nicmarsh » 9 Jun 2014, 6:25pm

Are CF seatposts particularly prone to getting stuck??

peterbayliss
Posts: 90
Joined: 8 Apr 2008, 12:47pm

Re: Stuck Carbon Fibre post in Aluminium Frame

Postby peterbayliss » 9 Jun 2014, 6:43pm

nicmarsh wrote:Are CF seatposts particularly prone to getting stuck??


I think seatpost getting stuck is just a problem in general, in theory CF should get stuck less as they don't corrode. Aluminium seat posts are good at getting stuck in steel frames if they are not occasionally removed and greased as both metals can corrode bonding them together.

In my case it had always been easy to get out before but I didn't need to adjust it for a year or more so a very small amount of corrosion in the steel frame caused it to jam.

robc02
Posts: 1667
Joined: 23 Apr 2009, 7:12pm
Location: Stafford

Re: Stuck Carbon Fibre post in Aluminium Frame

Postby robc02 » 9 Jun 2014, 7:26pm

nicmarsh wrote:Are CF seatposts particularly prone to getting stuck??


There was clearly some powdery substance between my seatpost and frame tube - presumably the result of corrosion (aluminium oxide??). The seat post that replaced it, under warranty, started to suffer in the same way, but I caught it in time.

Subsequently, and on the advice of the shop I bought the frame from, I greased the seatpost before fitting it. Advice on this was contradictory at the time, apparently some greases can adversely affect the resin of the seatpost. The shop owner said he had seen enough of these problems to think that grease was the lesser of two evils. I believe there are now anti seize materials specifically made for carbon fibre / aluminium interfaces.

After a few months this seatpost cracked where it was clamped to the frame. I deliberately only clamped it tight enough to stop it slipping, though this was tighter than it would have been without grease, and it didn't seem overtight at all. I decided this was all too delicate and a lot of faff so I replaced it with a good quality aluminium seatpost (Thomson) and have had no problems since (well over 5 years).

User avatar
RickH
Posts: 4579
Joined: 5 Mar 2012, 6:39pm
Location: Horwich, Lancs.

Re: Stuck Carbon Fibre post in Aluminium Frame

Postby RickH » 9 Jun 2014, 7:29pm

nicmarsh wrote:Are CF seatposts particularly prone to getting stuck??

I thought the more usual problem was CF not gripping - hence the slightly gritty assembly paste you get for CF components (example).

Rick.

Brucey
Posts: 36159
Joined: 4 Jan 2012, 6:25pm

Re: Stuck Carbon Fibre post in Aluminium Frame

Postby Brucey » 9 Jun 2014, 7:34pm

dvines wrote: .....Maybe this is why bike was on ebay...


n'er a truer word....

I would suggest careful use of the padsaw will resolve the situation in your favour, at the cost of one crummy seat pin.

If your BiL wants to learn how to become a better bike mechanic, buying other people's 'bargain' dodgy cast-offs from e-bay provides as good a route as any. Foisting the work onto your friends and relatives is just not on though; unless you have agreed to sort it already, I'd suggest that you offer to show him how to do it, but that you won't lay a finger on it yourself; he has to do everything.

He'll learn something this way, I guarantee it.... :lol:

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

tim-b
Posts: 1075
Joined: 10 Oct 2009, 8:20am

Re: Stuck Carbon Fibre post in Aluminium Frame

Postby tim-b » 10 Jun 2014, 5:56am

Hi
peterbayliss said
in theory CF should get stuck less as they don't corrode


Sadly carbon fibre (CF) and aluminium are two materials that exhibit galvanic corrosion. In sea water graphite (a CF material) and aluminium are at opposite ends of the Galvanic Series which is not a good thing (the series can vary with different environments).
robc02 had no further problem when he fitted aluminium to aluminium because they are at more or less the same place on the series (same basic material, slight change in the alloy used?)

If you can electrically isolate the two (CF assembly paste?) the problem will be lessened. Aluminium and steel have the same problem for the same reason, which is why grease works well. Remove, re-isolate and refit from time to time.

Be very careful if cutting CF as has been suggested; the dust can be nasty stuff

Regards
tim-b
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