Hmmmm....lugged or fillet brazed, this is just the seat tube inside diameter, which should be the same at the seat cluster or below. It sounds like the upper end may be out of round, perhaps from being clamped to a too-narrow seat post sometime in the past, or just from being bumped around during its 60 years of life. That's not at all unusual.
If this were my frame, I'd do some measuring with a micrometer, try to determine the right inside diameter (from measurements below the seat cluster) and spread/ream the top to the right size. If it really is 24.8, there should be no problem in reaming the whole thing to 25. This should be done by someone who knows how to do it. It's easy to gouge something when reaming.
Of course, you can sand down a seat post 0.2mm in diameter pretty easily, by hand, then polish it out so it doesn't look like it was touched. Doesn't require machine work. But I think this is a patch, not a real fix. I like to end up with things that are the way they should be.
Steve Maas Long Beach, California, USA
Peter Jourdain wrote:
> New Year's Greetings to all CR Members----
>
> I have thusfar met with no success in obtaining a
> 24.8mm seatpost. I certainly could (and very well may)
> keep tyring, but I was recently presented with another
> option---
>
> A local wrench/framebuilder suggested reaming out the
> area INSIDE the seat cluster on the frame by .2mm to
> accept a 25-mm seatpost, which can be easily had.
> (This work would be easier to perform than honing down
> the walls of a 25.0mm seatpost to fit the 24.8 frame
> opening.)
>
> Evidently the seat tube itself below the cluster has
> more than enough room to receive a 25.0 mm seatpost. I
> just need to "get past" the seattube cluster. This is
> a lugless, fillet-bazed randonneur built by a
> constructeur in 1947.
>
> My hesistancies are:
> 1. This might weaken the seatcluster structure?
> 2. It means the frameset will technically no longer be
> "original."
>
> Advice/comments?
>
> Thanks to all!
>
> Peter Jourdain
> Eerily balmy Whitewater, Wisconsin US of A
>
>
>
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