Serotta Seatpost Question

[mobmpls]

Picked up a 1991 Serotta Colorado II that came with a 27.2 CF seatpost. Doing a bit of a restoration so I want to switch back to something more like what was originally on it. Got a 27.2 Shimano 600 post that just won't go in. Even the CF post it came with (marked 27.2) is nearly impossible to fit in. Clamp/tube seems round, so I'm wondering if a 27.0 was OEM on this model? Catalog doesn't seem to mention seat post size. Any info helps - thanks!

[Black Dog]

27.2 and please post the serial number and year of your nice sweet ride here (http://forums.thepaceline.net/showthread.php?t=99078). We are compiling a data base of serial numbers and years of production for Serottas. Oh yea, get some pics of the bike up. There are a few of us that have 1991 CII's and we love them.

[David Kirk]

What is the frame size?

dave

[cmg]

measure the metal post with a caliper it's probably larger than 27.2 . campy posts tend to be like 27.289 or closer to 27.3 dura ace posts sp7410 that have a njs stamped on them are 27 while being marked 27.2 .

[cachagua]

Ream the seat tube to an accurate 27.2 and then try the posts, is what I'd do.

Grease and framesaver down in there, then you ride in rain and mud, a little scale builds up, and things become tight -- this is one of the ways seatposts get stuck. As long as you've got the post out, get back to the correct dimension in the frame (which you want to do no matter what post), and then see where you are.

[mobmpls]

Tried again with the grease to get the Shimano 600 27.2 post in - not going to go. Wondering if I can sand it down a bit? I've done that to a new Nitto stem on my old Peugeot and it worked well. Or am I better off trying other posts?

To answer the question, it's a 63cm frame and I'll definitely post some pics when it's done...

Thanks

[Black Dog]

Btw. David Kirk probably built the CII you are asking about. Any advice or info he has about your bike can not be surpassed easily.

[cmbicycles]

The tube may just be slightly deformed at the too from clamping a post too small, or who knows what. The clamp bolt is loose, right? ;) just checking. I wouldn't sand the post down, it is possible the seat tube is just slightly crushed at the opening.

Does the bike have a brazed on seat binder? If so, and you wedge a screwdriver in just enough to spread it a little can you get the post to go in more easily? If it's an external clamp it can still be done, it's just a little more delicate.

Does the old post have gouges in it from pulling it out? Do you have calipers to accurately measure the seatpost (s) & seat tube? Do you have a thick wooden dowel or some other pipe that you can gently roll around the opening of the seat tube? If no and you don't feel comfortable doing any of this it may be best to take it to your lbs.
Post pics anyway even if it's not done, look at it as a progress report.

[David Kirk]

This was a very long time, and countless bikes ago, but I'm guessing you need a 27.0 post.

If I recall correctly in the very early days of the Colorado the larger frames used a thicker seat tube (requiring a smaller seat post) which was very much the tradition then with steel bikes of all brands at the time. This was so common that most tube makers made the long seat tubes that would be used in big bikes thicker and one needed to use a 27.0 post.

At some point it was realized that this was silly and the tube makers made long seat tubes that would work with a 27.2 post and at that point all frames, regardless of size, used a 27.2.

Unfortunately there are only two ways to be 100% sure what size post you need -

- find a 27.0 post and try it. If the fit is good you should have to wiggle and twist it in using just a bit of force. It should not fall in nor should you need to break a sweat to get it in. It's a judgement call when it comes to 'how hard' it is to get in but when it's right you can feel it.

- accurately measure the ID of the seat tube. This is much easier said that done. One can't get a good number by using a caliper at the opening of the seat tube. In a perfect world this would work but in practice it never does. Distortion from heat and being clamped will make the opening near impossible to get good numbers on. There are two ways to get a good number -

- use a real bore gauge and measure the ID a few inches down into the seat tube
- use a graduated plug feeler gauge (looks like a seat post with steps getting larger as it goes up) and slip it in place and see what it says. This type of gauge varies tremendously.....some have very short steps that are only 1/2" long so they only read the ID right at the top of the seat tube (useless as described above) but the good ones have a few inches of each size so they one can get a real reading of the ID a few inches down.


If it were me and I was the average guy in my garage I'd buy a cheap 27.0 post and see how it fits. It takes the guess work of measuring out of the deal. If the 27.0 post fits as it should you can of course use a 27.0 post and call it a day however there aren't that many posts in that size available unlike back in the day......or you could have the seat tube reamed from 27.0 to 27.2. This is a bit tricky unless the operator really knows what the hell they are doing.....and frankly many don't. It sounds like .2 would come out of there with ease and it won't. That is a lot of material to remove. So a good sharp reamer in the hands of someone who knows how to use it and it would be fine. A dull reamer in the hands of a guy who saw a video once and it won't be great.

Lots of info - I hope that helps.

dave

[mobmpls]

Thanks for the good info - interesting that is may have been built with a narrower seat tube. I think I'll try to find a 27.0 post and see how that works. The carbon 27.2 that came with the bike is pretty gouged up and is very difficult to get in, though it does go in a bit as compared to the 600 post.

I'll try to get some pics this weekend...

[Black Dog]

It is possible that the posts you have are both a bit on the large end of the 27.2 nominal range (less than 27.2). If you have callipers you can measure them and see. A 3rd 27.2 post might fit if it is closer to 27.2 nominal (less than 27.2). David's advice is still spot on however. Also, you can test to see if the opening has been made too small by past over clamping by gently spreading the opening while trying to insert one of your existing 27.2 posts. Remove the bolt and use a flat screwdriver or reverse the bolt and place a dime in the gap and use the bolt to press against the dime and spread the opening.

[David Kirk]

FWIW - remember that the seat post size designation is not the actual size of the post - it's the size of the hole a post we call "27.2" should just slip into. By that I mean if you measure a 27.2 post it should not measure 27.2.......instead is should measure 27.15ish.

The seat tube ID should measure 27.2 but as noted above they are very difficult to get solid numbers on.

dave

[mobmpls]

Update on this one - got it cleaned up and put together. I think it came out nice. Only one test ride so far but the 27.0 post seems to be working. Still making minor adjustments...

[oliver1850]

Wish my CII was that nice.

[Ken Robb]

Thanks for the good info - interesting that is may have been built with a narrower seat tube. I think I'll try to find a 27.0 post and see how that works. The carbon 27.2 that came with the bike is pretty gouged up and is very difficult to get in, though it does go in a bit as compared to the 600 post.

I'll try to get some pics this weekend...

I wouldn't want to trust a carbon post that has gouges.

[alyosha_s]

love that paint scheme

[josephr]

Update on this one - got it cleaned up and put together. I think it came out nice. Only one test ride so far but the 27.0 post seems to be working. Still making minor adjustments...

--- two older Serottas here and both take a 27.0 seatpost. I'm no expert, but its not uncommon from what I understand. Looks super clean and very nice...ride the crap out of it!