So I am looking at this rather clean frame advertised as..... "No dents of any kind and frame is solid and straight."

Next line down is this beauty....."Takes a 27.2mm seat post. Seatpost goes in about halfway then requires some effort to go further. If you ride the saddle height where it should be on a 54cm frame, then you will have no problems."

I emailed him some questions about this. I asked to insert the post in the seat tube, mark the post at the top of the seat tube when it begins to hang up, take the post out and measure and tell me how far into the seat tube the seat post goes before it starts to hang up. No responses so far.

Other than a very slightly dented seat tube, what other explanation could there be for this? Thanks for any info!

Corruption like rust or gunk is one option. I would ask him to shine a light down the ST and explain what he thinks the reason for the hangup based on what he can see.

This was my first thought as well. Once had a seat tube so dirty internally that the seat post size went up by .2mm once it was clean.
Was a very neglected bike.

My guess is the seller has tried this with only one seat post; so the problem could be on the seat post rather than on the seat tube.

Other than that, it's possible the seat tube was reamed out only as far as seemed necessary at the time.

Bear in mind that seat posts come in a variety of lengths, so we're talking about half of an unkown number.

Whatever the problem is, I doubt it would prevent me from buying a frame I wanted.

Could just possibly be the post he's using too. But I'd vote for roughness, or corrosion, starting where the end of the post sat all these years.

*Rudi beat me to it.

I bought a brand new (NOS) Italian frame a few years ago that was sized for a 27.2 post. However, my mechanic had to ream out the seat tube quite a bit to fit a seatpost in it due to paint overspray and perhaps other issues.

Like others here, I suspect surface rust inside the seat tube below where the seller normally has the seatpost positioned. Reaming the seat tube - about a one minute job - should fix the problem.

Should it be corrosion, you can use a 12Ga brass brush to knock off the loose stuff followed by a brake honing tool.

may not have ever been reamed in the first place. Most frames need reaming as the heat from brazing distorts the tubes at the junctions. Usually this just means reaming the junction a bit.

Probably corrosion, plus the guy might not even be greasing the post.

That thought occurred to me as well. Can you do any damage to the seat tube by repeatedly forcing an ungreased post into the tube, scar it up inside, gouge it, etc.? Would this also be resolved by reaming?

Thanks for the tip!

reaming tools are of limited length, usually just to ream the distorted tube junction section, so if the problem is further down it won't help. I would use the brass brush and hone tool first to see if that helps. It's unlikely to damage the seat tube from forcing a post in, and more likely to damage the post. I have seen a bulged seat-tube from a forced in oversized post, but that was only once. That person must have been pretty strong to do that.

Seat post may be long enough to be contacting a rivnut.(?) Best to look at this yourself.

Brad

My Cyclus reamer holder/handle will ream the seat tube to 270mm from the top of the ST.

If there is a concern about the reamer cutting too deeply into the tubing wall, turn the handle counter-clockwise (against the cutter edges) instead of clockwise.