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PostPosted: Tue Apr 21, 2009 8:48 pm 
Dirt Disciple

Joined: Tue Apr 29, 2008 11:43 pm
Posts: 83
I bought a new bike at the weekend (I know, Elev12k, I wasn't going to, but you know how it is. It stops here though.)
It has 531 tubing so the seatpost diameter should be 27.2 according to a learned chappy on Retrobike. But my new darling has a side to side internal seat post clamp area diameter of 27.2 and a front to back diameter of 27. I measured it as fairly as possible with some measuring caliper things.

If you have a good look at the below photo you will notice 2 things: There are a lot of washers on the bolt (the allen key hole is proper mashed up), and theres a tiny crimp or bulge at the bottom of the slot. Ergo, some monster has tightened the clamp more than the good lord intended.

It scrapes my new seatpost most horribly.

Whats the best way to open it out again? It feels like it is a reduced diameter all the way to the bottom of the slot, so just levering with a screwdriver will not do the trick(note paint chip at top of slot).
I have a feeling hammering in a stout peice of wood would help, but I'm concerned I'd never get it out again...
Any tips welcome.

Image


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PostPosted: Tue Apr 21, 2009 8:54 pm 
Old School Grand Master
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Joined: Thu Jul 19, 2007 7:18 pm
Posts: 3798
Location: Staffordshire
[quote="ermsamermsam"]Ergo, some monster has tightened the clamp more than the good lord intended./quote]

Can't help you with the seat clamp but may I offer my thanks on you using the word "Ergo". You just don't see it around very much these days.
Thanks.


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PostPosted: Tue Apr 21, 2009 8:55 pm 
Retro Guru

Joined: Fri Apr 28, 2006 8:42 pm
Posts: 783
Location: Brighton
How about a shim (as discrete as possible) and then a smaller diameter seatpost? It only needs to be subtle. I'd be a bit worried though about the shim putting an unusual load on a part of the frame that's already "done some living".


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PostPosted: Wed Apr 22, 2009 12:02 am 
Retro Guru

Joined: Sun Dec 14, 2008 2:11 pm
Posts: 303
Side to side is 27.2mm and front to back 27.0mm? If the clamp has been overtightened wouldn't you expect the side to side measurement to have been reduced by at least as much as the front to back? I'd certainly have expected it to be reduced at least a bit.

The washers as evidence? Not so sure about that, I had similar on an old Carlton I built simply because I ended up using a bolt that was too long.

Anyway as for corrective treatment, get the clamp area nice and hot you don't want to be inducing stress fractures do you? Then get a sacrificial 27.2mm post and work it in there and work it around a bit while things are still nice and hot. Should do the trick even though the heating will almost certainly trash the paint.


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PostPosted: Wed Apr 22, 2009 11:55 am 
Dirt Disciple

Joined: Tue Apr 29, 2008 11:43 pm
Posts: 83
bollocks. Sounds like a right pain in the arse.


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PostPosted: Wed Apr 22, 2009 3:06 pm 
Retro Guru

Joined: Sun Dec 14, 2008 2:11 pm
Posts: 303
ermsamermsam wrote:
bollocks. Sounds like a right pain in the arse.


Indeedy.

Before you start you could try measuring the ID of the tube below the clamp area, just to make sure it really does need a 27.2 post. Maybe it's not really 531, or maybe it's odd 531 that takes a smaller post. Either way you wouldn't want to force the clamp out to 27.2mm only to find the tube lower down is 27mm. Maybe it's all out of shape from somebody trying to fit a 27.2mm post?

Unfortunately this is not something you can do with a standard vernier caliper.


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PostPosted: Thu Apr 23, 2009 9:23 am 
Retro Guru
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Joined: Thu May 17, 2007 2:23 pm
Posts: 991
Location: Hampshire
I had a clamp that did the same a while back and my LBS sorted it using an adjustable reamer to shave off the excess that was causing the scratches. You can pick them up from ebay or a local specalist tooling supplier. Just take it slow at a few thou at a time.
cheers


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PostPosted: Sat Apr 25, 2009 2:14 pm 
Retro Guru

Joined: Sun Aug 03, 2008 12:31 am
Posts: 585
Location: London
I wouldn't be sure it's been overtightened.

The slot looks like it's about the same width all the way down.

The extra washers could be because the seat bolt's loo long, as already mentioned.

It's possible that it's the side to side width that should be smaller if it was overtightened, also already mentioned.

Your seatpin might be bigger than 27.2mm.

I think maybe the framebuilder/factory didn't prepare the frame properly and didn't ream the seat tube.


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PostPosted: Sat Apr 25, 2009 5:51 pm 
Dirt Disciple

Joined: Tue Apr 29, 2008 11:43 pm
Posts: 83
Well, I gave it a gentle bit of radging. Using the end of a Ulock with the rubber coating I leavered back and forth, with out using too much force adn it has opened out a little.
Previously I could definately feel inside the tube the tigher area at the top of the tube where the clamp slot is compared to the area lower down.
Anyway, the 0.2mm has now been recovered and all is well.


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