Stuck seat post: steel to aluminium

[steveparry]

I have just bought a used nice Paul Hewitt tourer with Reynolds 631 steel tubing. I believe the frame was made about 2014. The previous owner told me he set the seat post to current height about 10 years ago. The post is aluminium. I am a couple of inches shorter than him and need to adjust it down. After unscrewing the seat bolt I found the seat post will not move. I have tried squirting WD40 around the top but it's still stuck. The seat pin itself unscrewed easily. Fortunately the seat tube top is designed with a slot for adjustment. I was thinking I could somehow wedge the seat pin holder apart a bit. See photos. I don't want to ruin the frame. Before I go any further what is the best way to free it? Thank you.

[rjb]

There's a thread in the too good to lose section offering advice on this frequent issue. Have a read through for ideas and suggestions.
viewtopic.php?t=16716

And
viewtopic.php?t=163090#p1877440

[Brucey]

....... The seat pin itself unscrewed easily.......

in British English 'seat pin' means the exact same thing as 'seat post' in American English.

Nearly all 'seized seat pins' (and stems) will come out provided they are pulled hard enough. This works because as a seat pin is elastically stretched, it also gets infinitesimally narrower. You can see this happening quite clearly in some materials eg. rubber, toffee etc. But the exact same thing happens in metals too, and although the effect is too small to see it is quite sufficient to get a tight seat pin out.

I think it was Archimedes who said 'give me a lever that is long enough, a place to stand, and I will move the World'. Well, when it comes to pulling seat pins, the BB looks like it might be a good 'place to stand' but it probably isn't; if the force here is high enough, there is a real danger of breaking the frame, so an alternative should be sought, ideally.

[pigman]

Get the bottom bracket out and pour some dismantling fluid (eg. Plus gas) down the seat tube while the bike is upside down. The effects won't be immediate, leave it a couple days to take effect.
I've never failed getting a seized seatpost out, but the worst I had destroyed the seat pillar by clamping it in a vice and turning the frame left and right while gently pulling the frame away from the vice

[rareposter]

I don't want to ruin the frame.

Understandable although I would resign yourself to probably ruining the seatpost.

If all else fails (having read and tried the stuff in the links), there are professional services available, eg:
https://theseatpostman.com/

[martin biggs]

This company might be worth a chat too , never used myself and have no connection

https://theseatpostman.com/

[PT1029]

Don't wedge the "seat pin holder" apart a bit. Not only will it damage the frame, it won't make any difference. The stuck/corroded bit is almost certainly further down the seat tube/seat pin.
If the bike has seat tube bottle bosses, you could remove a bolt and put your unsiezing/penetrating oil through the hole with the bike upside down, and leave for some days, and keep repeating.
Using a bottle boss bolt is easier than removing the BB, that said, it might be worth removing the BB in any case to prevent it too from corroding in place (hopefully it hasn't corroded in yet).

[Pneumant]

Also the seatpost could be quite long which makes extraction more difficult, penetrating oil / diesel might work but it has to attack / penetrate the layer of corrosion and this might extend some way down the inserted post. That method probably won't work. I have used caustic soda successfully in the past which was as a last resort when 'diy mechanical' methods failed! The risk is to the paintwork and also potentially dangerous if not careful. Whatever you do don't open up the seat collar! I'd be following the suggestion of using the seatpost man as he is quite close to you in Chorley. Normally bikes with seized seatposts are much cheaper because of the hassles involved, hope you got it for a good price to make up for the work involved in correcting the issue.

[steveparry]

It's currently upside down having sprayed WD40 down the seat post tube bottle cage mount hole. I'll give it a day or two to penetrate. I noted that when buying "Collection only" from eb*y I seem to have 14 days to assess and reject if I want. I think this is due to the 14 day 'right to return' for items purchased without posting/courier ie 'distance purchasing'. I may have to take up that option.

[rareposter]

It's currently upside down having sprayed WD40 down the seat post tube bottle cage mount hole.

WD40 is unlikely to touch it.
You need something like PB Blaster, it's a penetrating oil with a rust breaker. Even that might struggle if the seatpost has been in there with no movement for 10 years.

What happens is the aluminium turns to aluminium oxide which "welds" itself to the steel frame. It also takes up more volume so as well as being chemically welded in place, the seatpost has effectively swelled up.

Strip the frame down completely - everything except the seized seatpost off and out. That might give you some leeway in using the frame as a lever although as noted above, it's possible to bend or even break the frame doing that. If it doesn't work with household chemicals and the normal force you can put through it at home, it's time to consider returning it under eBay's selling rules or using a professional service like SeatpostMan that I linked to above.

[Brucey]

..... It also takes up more volume so as well as being chemically welded in place, the seatpost has effectively swelled up.......

if corrosion is active, the 'swelling' can be very enthusiastic indeed, exerting a huge pressure. Many years ago my weinmann side-pull brakes failed suddenly (ie. when I was trying to stop) because of this. In their wisdom weinmann had chosen to fit a threaded Al barrel adjuster into brass piece. Road salt had already caused sufficient corrosion to render the barrel adjuster immobile, meaning that I'd used a different way to adjust the brake, because I had no other choice. So I guess I knew there was a problem, but even so, I was not at all prepared for what happened next; I went for the brake (almost panic stations, because a little old lady had just staggered out in front of me without looking, as if drawn by invisible string from Woolworth's to Boots' across the road), whereupon instead of retardation as I'd expected, I was unceremoniously greeted by a loud 'click!' as the brass piece split wide open.

IIRC this forced me to take evasive action, else I would have skittled someone for sure. I bunny-hopped on and then off the pavement before I managed to stop using my remaining functional brake (IMHO two brakes are a very good idea, even with a fixed gear). The little old lady continued to beetle across the road, quite oblivious to what had nearly befallen her.

An inspection revealed that the aluminium piece had swollen, presumably creating enough stress to cause the brass piece to undergo a form of 'season cracking'. It is no exaggeration to point out that it is only the oxide layer on an Al surface which prevents it's spontaneous combustion; it is therefore no great surprise when corroding Al things get stuck in close-fitting holes.

Along with pulling very hard (which I believe to be essence of the seatpost man's technique), one of the very few methods which can be expected to work reliably is to use liquid nitrogen. In round numbers, with an Al seat pin in a steel frame, this is a lot like pulling hard enough to create 0.2% strain, something which otherwise requires a mighty force.

[steveparry]

I'm sure this 'straight pull' method is one of seatpostman's techniques: https://www.youtube.com/watch?v=mJ8R_Dqk1u0 watch from 23 mins in to see how it works. A later vid shows a force of 2.8 tonnes to extract an aluminium post from a steel frame... https://www.youtube.com/watch?v=tVXgnqm2qEs I've since spoken to the vendor from eBay where I bought it. He has agreed to refund me. It's such a shame as it's a really nice Paul Hewitt framed tourer. A 56cm frame was also pushing it for me as he is about 5'11 and I'm about 5'9". And the bike only cost £102 !

[Pneumant]

Price wise I don't think you have overpaid given the seatpost issue and even spending the same again to have the post extracted still places the bike below £250 and in good value territory. That is what I would do.
Size wise these compact frames can be made to fit many height / leg length combinations, for a start the Hewitt has a huge stack of headset spacers so the correct bar can be found and a shorter seatpost would look better anyway!

[rareposter]

Price wise I don't think you have overpaid given the seatpost issue and even spending the same again to have the post extracted still places the bike below £250 and in good value territory. That is what I would do.

Same. I might see if the seller would do a partial refund to cover some of the inconvenience but I'd be doing a complete strip and rebuild on a S/H bike anyway.

Other than the seatpost, it looks decent enough, be a shame to reject it completely just off the one issue. I don't think it's especially high risk either; a professional could almost certainly get that out without any compromise to the frame.

It's not like you've discovered a big crack that requires welding work!

[531colin]

If you are reasonably competent grinding metal, getting an Ali post out of a steel frame is easy.
Grind up a tapered reamer out of an old flat wood bit, one or two millimetres smaller than the seat tube internal diameter, and ream it out using a big mains drill.
It’s written up in one of the seatpost threads.
First check how long the post is, ie. how far down you are going to have to go. A spoke is useful here, hook the end round the bottom of the post.