Seat post too small: what now?

[[email protected]]

Hello,
I am refurbishing an Al trekking bike which has a too small seat post:
in order to lock it, the "ears" of the frame have been squeezed
excessively (judging by eye) and almost touch. The seat clamp is too
small as well.
However, everything "works", i.e. the saddle is safely locked.

What should I do now? Replace everything with the correct size, or
keep it as it is (maybe Al is not elastic enough)?

Thanks

 

[DougC]

[email protected] wrote:
> Hello,
> I am refurbishing an Al trekking bike which has a too small seat post:
> in order to lock it, the "ears" of the frame have been squeezed
> excessively (judging by eye) and almost touch. The seat clamp is too
> small as well.
> However, everything "works", i.e. the saddle is safely locked.
>
> What should I do now? Replace everything with the correct size, or
> keep it as it is (maybe Al is not elastic enough)?
>
> Thanks
>
Look in your local phone directory form a machine shop, and go around
there and ask if you can buy a bit of aluminum shim stock.
......
-Or stainless steel will work too, but it can be a chore to cut. I find
a Dremel-type roto tool with a cutoff wheel works best.
~

 

[ddog]

Seatpost shims are about $5 and can buy several since shipping will
likely be $8 EXCEPT you are going to have to force the stem in to
expand the seat tube now and it won't be round. Google and try to find
out what size seat post you are supposed to have, and Kalloy makes
nice AL machined round steel posts that are easy to cut to size with a
hack saw blade and sand edges smooth. That way you can force the one
piece seat post in with adjustment clamp fully expanded out, where as
a 2 part post with shim may not be so easy. Seat shims are cheap
because it is not the best solution, and Kalloy AL machined tubes are
$10 at LBS or less online with shipping (same cost either way). They
make every size available in Kalloy tubes, at some vendor (basically
just round AL machined tubes). You will need a standard seat clamp for
about $5 (with dual direction adjustements), but those work fine: just
no single allen screw adjustment.

On Feb 5, 5:17 am, "[email protected]" <[email protected]> wrote:
> Hello,
> I am refurbishing an Al trekking bike which has a too small seat post:
> in order to lock it, the "ears" of the frame have been squeezed
> excessively (judging by eye) and almost touch. The seat clamp is too
> small as well.
> However, everything "works", i.e. the saddle is safely locked.
>
> What should I do now? Replace everything with the correct size, or
> keep it as it is (maybe Al is not elastic enough)?
>
> Thanks

 

[Mark]

[email protected] wrote:
> Hello,
> I am refurbishing an Al trekking bike which has a too small seat post:
> in order to lock it, the "ears" of the frame have been squeezed
> excessively (judging by eye) and almost touch. The seat clamp is too
> small as well.
> However, everything "works", i.e. the saddle is safely locked.
>
> What should I do now? Replace everything with the correct size, or
> keep it as it is (maybe Al is not elastic enough)?

Before spending a lot of $, try a shim made from a soft-drink can. I'll
bet one thickness is enough to show significant improvement, and I'm
confident at most two thicknesses of softdrink can will be adequate.

You may have to reshape the opening on the frame, which is probably
deformed by now. Not sure how well Aluminum will take to that.

Mark J.

 

[* * Chas]

<[email protected]> wrote in message
news:[email protected]...
> Hello,
> I am refurbishing an Al trekking bike which has a too small seat post:
> in order to lock it, the "ears" of the frame have been squeezed
> excessively (judging by eye) and almost touch. The seat clamp is too
> small as well.
> However, everything "works", i.e. the saddle is safely locked.
>
> What should I do now? Replace everything with the correct size, or
> keep it as it is (maybe Al is not elastic enough)?
>
> Thanks
>

It sounds like the ears have been clamped closed to their maximum and you
are asking about opening them so you can fit a larger seat post.

Does this frame have a steel or aluminum clamp ring or the standard seat
post bolt arrangement like what is used on most steel frames?

Aluminum isn't as malleable as steel. I would use some caution spreading
the aluminum as it could crack if you move it to far.

You could spread the aluminum a little so that you can fit a shim or a
larger seat post but if it aint broke....

Chas.

 

[ddog]

On Feb 5, 1:18 pm, "* * Chas" <[email protected]> wrote:
> Does this frame have a steel or aluminum clamp ring or the standard seat
> post bolt arrangement like what is used on most steel frames?
>
> Aluminum isn't as malleable as steel. I would use some caution spreading
> the aluminum as it could crack if you move it to far.
>
> You could spread the aluminum a little so that you can fit a shim or a
> larger seat post but if it aint broke....
>
> Chas.

Chas,

Yeah I forgot about AL. Like Donald below, just went through it all
with steel Raleigh with odd sizes I had to look up on Sheldon's
Raleigh site. Kalloy was my only good solution and it worked out
great. Just put my seat on post like Sheldon said, and it finally
snugged in there with rounded edges from sanding. I though AL frame
would have external AL clamps or alloy tig welded. Not sure what would
work well.

That's also a problem with thick clear powder coat, it seems to me
anyway, since the flexibility may crack it. Those flexible seat post
clamps are a bad design, allowing water inside and rust excited from
different metals tig welded too. I like the idea of external clamps
although supposed to be cheap feature. I think the flexible seat post
clamp idea is a cheap design that was not well thought out, and is the
first place a frame will deteriorate from normal wear and tear, not
including wrecks.

 

[ddog]

On Feb 5, 1:18 pm, "* * Chas" <[email protected]> wrote:
> Does this frame have a steel or aluminum clamp ring or the standard seat
> post bolt arrangement like what is used on most steel frames?
>
> Aluminum isn't as malleable as steel. I would use some caution spreading
> the aluminum as it could crack if you move it to far.
>
> You could spread the aluminum a little so that you can fit a shim or a
> larger seat post but if it aint broke....
>
> Chas.

Chas,

Yeah I forgot about AL. Like Donald below, just went through it all
with steel Raleigh with odd sizes I had to look up on Sheldon's
Raleigh site. Kalloy was my only good solution and it worked out
great. Just put my seat on post like Sheldon said, and it finally
snugged in there with rounded edges from sanding. I though AL frame
would have external AL clamps or alloy tig welded. Not sure what would
work well.

That's also a problem with thick clear powder coat, it seems to me
anyway, since the flexibility may crack it. Those flexible seat post
clamps are a bad design, allowing water inside and rust excited from
different metals tig welded too. I like the idea of external clamps
although supposed to be cheap feature. I think the flexible seat post
clamp idea is a cheap design that was not well thought out, and is the
first place a frame will deteriorate from normal wear and tear, not
including wrecks.

 

[Bill Westphal]

"[email protected]" <[email protected]> writes:

> Hello,
> I am refurbishing an Al trekking bike which has a too small seat post:
> in order to lock it, the "ears" of the frame have been squeezed
> excessively (judging by eye) and almost touch. The seat clamp is too
> small as well.
> However, everything "works", i.e. the saddle is safely locked.
>
> What should I do now? Replace everything with the correct size, or
> keep it as it is (maybe Al is not elastic enough)?
>
> Thanks

By clamping down on too small a seatpost you may have deformed the top
of the tube and the clamp, if the clamp is part of the frame. If you
try the next size up it probably won't fit now, and the LBS will have
to ream it. I wouldn't mess with it: just bring it to the LBS before
things get any worse. There's another tool if the post slides the
puts ridges on an alum post so you don't have to tighten the clamp as
much: that one saved me on my old 26.8 post, on an old french frame
with narrow 28.0mm outside diameter seat tube that they wouldn't ream
to 27.2. There are just too many subtleties to deal with this
yourself. Or you may have to either get the next size up post or get
a ready-made shim if one is available. It's impossible to really
solve this without seeing it, and without a lot of experience with
similar problems. This is one of the few areas where I actually take
the bike to the LBS.

Bill Westphal

 

[Donald Gillies]

The very first step is to remove the too-small seatpost and see if the
aluminum lug ears spring back apart again (which is quite possible.)
At least with handlebars, over clamping an old-style stem will cause
the clamp to fail prematurely. One example is 25.8 3TTT stems which
often failed clamping 25.4 GB handlbars on Raleigh Pro bicycles.

If the seat lug ears spring far enough apart to fit a larger, original
post, maybe with some grease and gentle persuasion, go for it - put in
an original-sized post.

I wouldn't get the seat lug reamed. What for? You have a seat lug
that has been traumatized, why inflict a second trauma ? I would
however, make sure that the largest seatpost possible is installed
into the seat lug. If you have to take a larger post and sand it
slightly to get it to fit, do it.

- Don Gillies
San Diego, CA, USA