Serotta Legend Seat tube Question
 

I recently picked up a legend ti frame (painted under the seatpost collar)and have been picking through my stuff to build it up. I assumed it would take a 27.2 post and a 31.8 seatpost clamp... although once I received it I found it takes a smaller clamp, roughly 29.4mm +/- (tube wall thickness measures about 1.1-1.2 mm). Either way I had problems getting a post to go in without an abnormal amount of persuasion.

It started gouging the 27.2 post I tried to put in, even with the clamp pulled off the frame. After I looked more closely it appears one side of the tube, at the seat clamp slit, is flared out slightly instead of being completely round and I am assuming this is where the problem stems from. Any ideas on an easy way to fix this?

The clamp that came with the frame is stamped 33, but measures closer to 30.0 diameter, so not sure the stamping is the intended size. I have no idea how this happened or could have happened, it was shipped with the clamp on, and the prior owner said they had a Thompson post in there with no problem... but my Am Classic ti post, and a few other posts wont go without some persuasion.

I was thinking I could file/dremel the slit in the tube, or use a flex hone, and see if that helps with the scratching issue, though not sure how effective it would be with titanium.
Thanks for the thoughts and suggestions

The tube sounds like it has been pushed out-of round by tightening in a too small seat post. Thomsons run pretty undersized IME.

Use a seatpost gauge and work it in to the 27.2 position and tighten down the proper seat post clamp (31.8-32.0)…alternatively, use a sacrificial post…old steel, cheap Kalloy, whatever.

-Mark in St. Louis

Serotta was pretty exacting with their tolerances, so 27.2mm was 27.2mm. I know of several Serotta dealers that wouldn't carry certiain seatposts because they were not always exactly 27.2mm. I bought an Ottrott used that the previous owner had managed to crimp the seat tube out of round at the collar, and the shop had to get a special tool to ream it. I would take the frame to someone you trust, and have them inspect it. Titanium is not easy to work with.

Regarding the front derailleur clamp, the seat tube of a Legend is swaged, so it is wider at the bottom than at the top. All of the Legends/Ottrotts I have owned have taken a 34.9mm clamp. I would take a pair of calipers to the seat tube where the clamp should go to get a precise measurement.

I know it takes a 34.9 F der clamp, it came with one mounted. The seatpost collar was the measurement that threw me. The seat tube wall thickness measures 1.1-1.2mm, so double that and add it to the seatpost diameter of 27.2 and you get 29.4-29.6... which seems an odd collar size to me, but I haven't owned a serotta before so that's why I mentioned it. Thanks

Doh, of course you were talking about the seatpost clamp.

Is this a 1990s or early naughts frame? With a clamp anywhere around 30mm and not greater than 31 1/2mm, and a seat post having recently emerged from it, it'd almost have to be. A true but sad story is that the later style seat tubes were partially a result of continual tight fits for 'posts in this older style seat tube. To complicate it, you're moving, in this frame, from one of the posts most likely on the "small" side of 27.2mm to on most likely on the "large" side of 27.2mm. Filing part of the slot, or flex-honing the tube may help with the scratching, but probably not the fit. If you're working with a frame this old and don't have access to some high quality cutting tools, I'd suggest finding a friend who has them or a successful old-school shop with someone competent to use them. I'd bring them your intended 'post and ask for the frame to be reamed to fit the post rather than ask for it to be reamed to fit a 27.2 'post. An adjustable reamer, and an extension if it's a 60+cm c-t seat tube, may be required.

The motorized seat tube reaming arrangement using during the production of frames would vibrate a screaming noise throughout the factory whenever we reworked those old beasts, to the dismay of most everyone in the building. Almost without fail they would come in as tight fits, not up to the current standards of fit, and needing to be reamed not simply as a quick matter of process, but because they weren't nice fits for what we liked as a 27.2 post of the modern day.

Do you have the Serotta seat collar? They were made to specific diameters for the intended frame.

I can measure ST OD on a couple of (older) Legends if it helps, but your math sounds right to me. I think all Serottas in that era used a "27.2" post. That said, actual size of nominally 27.2 posts can vary quite a bit. I have a Cannondale carbon post that's labeled 27.2 but measures on the small side for a 27.0. Clamping that post tightly enough to prevent slippage might deform the ST enough to make normal 27.2 posts a difficult fit.

I would probably work a cheap 27.2 around in it with plenty of lube and hope to free up the fit of the post you actually want to use. You can of course go straight to ream/sand ID, but you're removing material that was intended to be there if you do that.

You might try to find a burr on the ST ID. Most likely place would be the edge of the slot, but if someone snagged a post in it, it could be anywhere. Careful cleaning and inspection of the ID of the ST might turn up a burr that could be filed out.

Fwiw, when I used Campy Chorus Ti posts in Serotta's, the fit was really tight and it took some force to get the post in and out, leaving the post scored (sic?). Easton posts fit nicely, which is what I usually used.

It did not come w/ a serotta clamp, and I would like to find a nicer fitting one. I prefer not having to use shim stock to take up the difference. Anyone know who might make something close besides the Thomson 29.8?

Glad I'm not the only one with this issue.

I could have sworn I was doing something wrong, but how hard can it be to put the right size seatpost in a bike?

I just changed the 27.2 seatpost in my Concours. From an FSA carbon which was very tight, to a Uno carbon which went in just right.

I use a Thompson in Legend ...

Same here, but I didn't want to buy another post if I had a quality one already. So I ended up wet lapping the post to clean up the gouges (it was rough looking) as well as doing the same inside the seat tube. I noticed that gouging seem to occur around the seat stay welds. Even with copious grease the post is still tight but now I could reasonably insert it and adjust height.

Bontrager, easton ec70, shimano dura ace sp7410 njs and FSA slk posts will be slightly less than 27.2. Campy modern post 2000-on will be slightly larger 27.289+ same goes for dura ace sp7410, no njs logo 27.2+. i have 2 custom bikes that won't fit the campy modern post so i know the pain. i took the ti bike and couldn't find a shop that would ream it for a 27.2. Not if i didn't buy it from them. so let the suffering begin. enjoy....

If it's ovalized, reaming is not the best solution. A proper mandrel might make it more round--Buldogge's recommendation for using a sacrificial steel SP is right on. Find the correct clamp and a slightly undersized post, and all should be good. Use carbon paste if there's slippage...