Guerciotti GLX 84 Seat Post Diameter?
 

I used to have a Guerciotti GLX 84 and remember the seat post being 27.2 mm. I'm looking at one on the web and the seller seems certain it's a 27.0. It's SLX tubing so as far as I know it should be 27.2 but, then again, I've been wrong so many times I always look before telling someone what day it is ;)

Anybody know for sure?

I always thought SLX seat tubes were 27.2mm I.D....
That's what I have on my Pinarello Montello..... Your seat clamp ears/seat lug might have been deformed from over tightening, if a 27.2mm seatpost won't fit.....

I'm thinking someone put a 27.0 in there and cinched it down. There's some paint flaking near the binder bolt. It's a frame I'm looking at, would that be a deal breaker for you?

Not really. Steel frames can be quite forgiving of a small difference in seatpost, such as the 0.2mm difference you describe. You could either leave the 27.0 post or carefully enlarge the opening back to 27.2mm, both with little concern.

It's possible that the 27.0mm post is correct. What is the frame size? Large frames may use SPX tubing rather than SLX, even though the frame tube label will indicate SLX tubing. SPX tubing is slightly beefier to handle larger riders. I believe SPX tubing standard seat post size is 27.0mm standard, although some manufactures would ream the tube to 27.2mm.

Won't be a deal breaker for me if the damage to the paint is not so bad and can be retouched and any deformation of the seatpost clamp not to be so bad too that it cannot he "persuaded" with the right tools, back to shape. I had to do this on a couple of builds where the seatpost of the correct size just felt too tight. Just took my time with a large flat tipped screwdriver and an old beat up seatpost and got them both to spec pretty easy.....

I appreciate the prompt input, I'll need to decide by tomorrow if I'm going to make an offer. It's a 56cm so I'm guessing it'll be just like the 56 I had, it was SLX for the top, down and seat tubes. The paint I'm no so concerned with, I'll have him send me a rear shot of the seat cluster lug.

All this may be for naught; he's a little high on what he wants so if he won't come down any he may have to keep it.

I recall mine being 27.2mm.

27.2mm would be the nominal post size for a Guerciotti GLX. However, as noted, larger frame sizes often used SPX, which would utilize a 27.0mm post. 56cm is small enough that it would be SLX and use a 27.2mm post. Sometimes, manufacturers installed smaller posts due to tube distortion from heating, slag build-up, etc. However, that should not be the case with a GLX, as the importer, Ten Speed Drive, performed all the frame preparation in-house, including seat tube reaming. Starting in 1986, Ten Speed Drive even did the painting. So, unless somebody at Ten Speed Drive missed the reaming operation, its sounds like the original owner simply installed a seat post that was one size too small, probably from his previous bicycle. This is not a concern due to the ductile nature of the seat tube and lug. It would not prevent me from buying the frame/bicycle, nor would it even warrant my asking for a discount.

I'm very appreciative of this knowledge here. I made an offer (not based on the seatpost lug thing); now I'm just waiting.

We couldn't get together on price. Thanks for the info folks.