I've got a bit of an issue with this Estermann frame and was hoping to get some opinions on how I should deal with it. I think that before it came to me that someone had installed a seat post that was too small and so they tightened the seat post clamp down too far to compensate. Consequently, the top of the seat tube was bent in a little bit causing it to be out of shape. I think that I've got the gap in the seat tube straightened out fairly well. Before it was visibly bent together too close. So now I'm not sure what size seat post will fit and I need to figure that out. I know that I'm stating the obvious here but if I use seat post that is too small, I'll just be repeating the same mistake. If I force a post that is too large, I'll probably compromise the frame as well as get the post stuck. I suspect that I'm not the first person to experience this problem. I've tried a 27.0 post as well as a 27.2 post but neither size seems to fit well. I know there are other common sizes as well but those are the 2 sizes that I have in my parts bin. Anybody here dealt with this before? Any suggestions?

You want to use the proper sized seat post. It's not so much the clamp you want structurally sound, it's the moving around & flexing you want to keep in-check. Too small & the result is like flexing a paperclip with every turn of the pedals.

If you can, & you have a snap-gage or a ball-gage & measure the internal diameter & go from there. One good measurement is better than a thousand guesses.

Honing, reaming, or very careful spot treatment with an abrasive & a drill or spoon/round file may be required.

If you can try multiple posts in the size that seems to fit best. Manufacturing of sized parts isn't as consistent as we would like it to be.

Was the 27.2 too big? It's unlikely that it's too small.

slightly oval seat lug

I agree with the snap gauge. If you don't have one, a local machine shop should be able to measure rather quickly, hopefully for free.
Just be sure to clean the I.D. thoroughly before attempting a measurement.

Or you could probably measure the seat tube OD circumference and deduct the wall thickness x2.

27.0 seemed slightly too big. I'm wondering if the correct size is 26.8.

If you have a dial or digital caliper, measure the opening diameter at several places around the perimeter. To me, the second photo looks like the sides of the opening at, say, 10 and 2 o'clock in that photo are "too straight" still. A better way to look at the opening is on the tube center line. You should be able to sort of average the measurements you get to determine a reasonable seatpost size. Better yet, take a piece of thin metal (or something else thin without stretch -- heavy tin foil might work) and make it fit snugly in the opening, then mark where the sheet overlaps itself, remove it, and measure the sheet to the mark -- that's a decent measure of the opening's circumference. Divide by pi and you have the diameter.

When people clamp in a too-small seatpost, they often deform the tube at the edges of the slit inward, as well, and create burrs there that will scratch a nice seat post, and also complicate getting the opening round again. I've removed these with judicious and careful use of a Dremel grinder followed by a fairly large-diameter file and then emery cloth wrapped on a dowel. Fingers are very sensitive instruments, I think, and can be relied on to gauge progress.

A good bike shop should have a set of reamers, to "circularize" the hole once it's as round as you can get it by mechanical means.

Common seatpost sizes are 27.4 (very rare), 27.2 (very common, for an "English" sized seat tube that's unbutted at the top, and Italian too), 27.0, 26.8 (lots of Japanese frames), 26.6 (common for metric-sized seat tubes unbutted at the top, such as French or Swiss), 26.4 (common for frames of lesser quality, or some with butts at the top of the seat tube), 26.2 (ditto) and going on down to, say, 25.4 and 25.0. Basically on 0.2 mm increments.

I read the post linked-to above by thinktubes and I'd add that if using verktyg 's large sockets method to re-round tubing (I've never done this), it may help to put a clamp bolt in the ears, and when you find a socket that seems to be working, keep tightening the ears together very slightly as the process is used, incrementally. I'll also add that it's a mistake, in my opinion, to "settle" for a smaller diameter seatpost than the frame really requires: a good close fit in the tube section beneath the clamp area is important too, to adequately support the rider and saddle, and prevent metal fatigue.

Addressing a "desperation" scenario: I once had a frame repaired (it had a rusted-through hole in the upper part of the seat tube, where previous idiot owner had stuffed paper towels into the tube under the seatpost, presumably to ****** water) by inserting a short section of steel frame tubing, slit in one place, and epoxying that in place; then it was reamed. The bike, a French one, took a 26.6 mm seatpost originally, and now has one that's 25.4 mm. No paint was burnt. There's a little mark where the rust-trough happened (now filled by epoxy), otherwise it's virtually impossible to tell it was done. Added 36 g to the frame's weight.

I've experienced this a few times, but found it fairly easy to resolve. I am "blessed" with a rather large selection of seat posts in various sizes, and my method, when building up an unfamiliar frame, is to find a seat post that will slide in, and feel if its bottom is snug in the seat tube. It will wobble if it isn't, and you'll feel it. If it wobbles I pry open the seat lug a bit and try the next size up, until I get the desired result.

Like Feldman says, manufacturing wasn't always that precise, so it really helps if you have a few different seat posts in every "size" to determine what the frame builder's intention must have been, size-wise.

After a visit to my LBS and trying out a few different seat posts, I believe that 26.6 is the correct size. Also, this frame was made in Switzerland and so that would be consistent with your suggestion. However, since the seat tube is no longer perfectly round, even a 26.6 doesn't fit in very well and I couldn't actually get a 26.6 to quite fit without some extra force. So my strategy for solving this is to use a 26.4 with a shim made from a soda pop can. I know that this isn't the best solution but given the condition of the frame, I think it will be adequate and safe enough. Except for the fouled up top of the seat tube, everything else appears to be straight and there aren't any dents or dings but the paint has certainly seen better days.

Thank you everyone for all the suggestions!

I think that is a Reynolds 531 decal on the down tube near the shifters. Doesn´t that mean your tubes are 27.2 mm? I may be wrong, though...

If the seat tube is deformed you may be able to "massage" it back into shape with a correctly-sized seat post, a mallet and a lot of lube and patience.

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frame manufactured with a METRIC dimension tube set

seat tube O.D. is 28.0mm rather than the 28.6mm O.D. found on a BSC/ISO dimension tube set

26.6mm is usually the largest diameter saddle pillar to be employed with such tubes


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suggestion:

rather than shim and employ a 26.4mm pillar it would be preferable to ream the seat tube into roundness - not for the purpose of enlargement - just enough to eliminate the out-of-roundness


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The one thing to do before any serious decision is to make sure there are no high spots where the SP rests in the ST, this can shoot you in the foot because it will have you using a post that is too small and shim or no may not hold tight.

I always clean and inspect/evaluate/address this by making sure the ST is clean, this alone can help if the SP doesn't hang up on crud and you can usually figure out where the bad high spots are to use a half round file on.

I always slightly and very carefully chamfer the top of the ST as a sharp edge here can jam things up from the jump.

A steel SP can be useful as it is rounded and harder so you can get a much better feel for the fit and it can be used by tapping on it to help reshape the ST to round.

This can be a bigger project if the BB is not sealed or doesn't have a sleeve, it needs to be removed if the ST needs much cleaning/work.

The upside is the BB gets overhauled which is never a bad thing if not for the practice alone.

Chiming back in to ad that IME, the seat tube is almost always suspect for crud, hamfisted butchery, lack of skill, patience and plenty else.

If you get the ST clean and at least the worst of the high spots smoothed out, you will get much closer to the correct size SP, especially if you employ a harder, chrome, rounded steel one for the bulk of the early futzing.

Once you get close, a good clean and greasing can really speed up a much more final determination with an alloy post, light grease applied for a good fit.

In the final analysis the grease is what mitigates the "interference" fit that jams everything up and sends us down the road to h**l.

And no disrespect but I see the reamer as a last resort if all else fails as it can do as much damage as good, especially in the wrong hands for lack of skill, understanding and patience.

The bottom line is if the ST/SP had been greased along the way, most of this discussion would be moot.

531 tubing, depending on the era, took anything form 26.4-27.2. The Reynolds decal appears to indicate that this is an late 70s / early 80s frame and a plain gauge main triangle. Depending on frame height, the seat tube might even have been "reinforced" by using thicker tubing. Can't quite tell from the picture if it's a 56cm or a 65cm frame. Either way, knowing Swiss frames and having owned an Estermann myself at one point, my guess would be 26.6-26.8, but as suggested above, you won't ultimately know if you don't "clean up" the seat tube properly. A local bike mechanic of mine (genius guy really) had a problem making a seat post fit, even though he knew the exact measure of the seat post that had to fit, and had to drill out the seat tube literally by a fraction of a mm to make it fit properly all around. Just look at the measures of the seat stems. We are literally talking a few mm at most so if there's a build up of anything on the walls, be it corrosion or the seat tube being a bit out of alignment (as might be the case here), the seat post just won't fit snug. Perhaps you have a local frame builder who can assist you in the undertaking, provided you don't want to employ that shim for the rest of your life. This frame surely is worth it as Estermann frames were among the best to come out of Switzerland. I assume you've done your research and read up on him fabricating frames for the the Olympics (1980 in particular). Best of luck.

Gitane1 I have read up on Estermann frames. This particular frame is size 58cm. I've taken an emery cloth a cleaned out the seat tube pretty well and I was finally able to finesse a 26.6mm seat post inside and I think that is the correct size. While this is a nice frame, the paint is somewhat beat to shreds and one thing that I just found out the hard way is that the bottom bracket threads are fouled up I suspect that someone tried to force an English threaded bottom bracket in the BB shell or something like that. So anyway I just installed a threadless bottom bracket yesterday and now all I really have left is the cables, chain and handlebar wrap. Almost all the parts I've used have come from the parts bin. This thing is going to be UGLY when I'm done.

You're right in that the Swiss employed a very peculiar bottom bracket thread (like the French did) and if someone tried to force an English threaded bb in there, it not only had the wrong thread but was also threaded the wrong direction. I wonder how they go it in in the first place . In either case, I totally understand you installing a threadless bottom braket and just wanting to get this thing on the road without too much additional cost. Enjoy it for what it is. I'm sure it's still a great ride.

Hi here, just to add to the discussion...since this is frame #1545 the frame is in deed from 1982. Very nice frame by the way. Congratulations

i would get a good read beyond the seat lug.
interestingly, in the heat effected zone below the lug the seat tube can bulge, so would be best to get multiple direction measures 4-5 cm below the top of the lug.

No. a Swiss BB is threaded same DIRECTIONS as Brit/ISO (that is the DS is a LH thread, NDS is RH) which is unlike the French or Ital BB with both sides RH threading.
But correct that Swiss uses the same metric dimensions and thread pitch as FR.
People actually HAVE gotten away with jamming a Brit/ISO BB unit into a Swiss BB shell but only if the cups were alloy and shell was steel. Even so it's a "jam-fit" and so not my reco, but apparently it's been done.

26.6 mm seatpost on a metric-gauge 531 tubeset makes sense for Swiss-built bike. My c.1974 Allegro is like that, with Swiss-threaded sand-cast BB shell to boot. I have seen Allegros with what appear to be factory-installed shims around the seatposts, too.

At one point I had a mid-70s Motobecane Grand Touring that was apparently originally Swiss-threaded that someone had crammed in a set of ISO/British Tange cups. It worked okay.