Re: [CR]Masi seat post question


Example: Framebuilders:Alberto Masi
To: jimallen@nctimes.net
Cc: davidg@iag.net, classicrendezvous@bikelist.org
Date: Tue, 12 Feb 2002 20:09:36 -0800
Subject: Re: [CR]Masi seat post question
From: "Mark A. Perkins" <bicyclemark@juno.com>


Hello all:

As a person who has been a machinist, and who has worked in a manufacturing/production facility, I am surprised that there are people who are surprised that their 27.2 mm seatpost doesn't measure exactly 27.2 mm. Every manufacturing facility has a tolerance which the parts they manufacture are required to be kept within. The tolerance will be listed on the working drawings as something like 27.20 mm +0.05 mm & -0.10 mm. Meaning that if a part measures over 27.25 mm or under 27.10, the part is scrapped. What the 27.2 stamped on the post means is that the post will fit a frame with an approximate seat-tube I.D. of 27.2 mm (which is usually slightly over the 27.2 mm dia.).

The tube's I.D. being out of round is probably due to heat distortion during brazing. I like to use an adjustable reamer to clean up the inside of seat-tubes. This not only takes out some of that out of roundness, but it removes some of those burrs that gouge seatposts. Distortion can be caused in several other ways too, like overtightening the binder bolt while trying to install too small of a seatpost for the frame.

As for that 26.95 mm seat-tube I.D., without seeing it, I wouldn't venture a guess. Except that it (the tube) may not be what you think it is supposed to be. However, it sounds like it's supposed to take a 26.8 mm post.

Does anyone know what size post Columbus track tubing sets are supposed to take? I don't have a book handy at the moment. Maybe, since it's a track bike, the tubes are thicker than road tubes. I don't remember, but I know there's someone on the list who does.

My '77 Klein Team Super (Calif. built) takes a 27.4 post, and the seat-tubes were reamed or machined after welding. It's probably the smoothest seat-tube I.D. of all of my bikes. The post is a Weyless, and it came on the bike

Just my $.02 worth.

"Bicycle Mark" Perkins Fresno Cycling Club - Historian Fresno, California, U.S.A.

P.S.: Please guys, if you're unhappy with my use of the word tolerance rather than allowance, or the fact that I didn't explain more thoroughly, don't get technical on me with a rebuttal. My intention here is to explain why those seatposts don't measure exactly 27.2 mm. I had a guy email me a week or two ago, telling me what my point was, and that it wasn't what I said it was. Needless to say he was way off base, and way out of line.

On Mon, 11 Feb 2002 22:04:35 -0800 Jim Allen <jimallen@nctimes.net> writes:
> My Masi track frame (04 34) measured 27.2, my seatpost measured
> 27.13.
>
> Possibilities:
>
> Assuming correct measurements:
>
> Seat lug squeezed down from use of undersized seat post.
> Upside down seat tube. Seat tubes are single butted, 1.0x.07, thick on
> the bottom and thin at the top.
>
> Was there ever (to your knowledge) a correctly sized seat post in
> the frame?
>
> Good luck,
>
> Jim
>
> David Goerndt wrote:
>
> > I measured the post and the seat tube. The seat post measured 27.25mm and
> > the tube varied from 26.5 to 26.95. This was in the lug area as I couldn't
> > measure past the lug area.
> >
> > David Goerndt
> > Orlando, FL