Can an ally seat tube be stretched? Cannondale BoTE

[TreaderSteve]

Web info points to it being 27.2. A Hope 31.8 clamp sits nicely on the seat tube of my project frame, so the top doesn't seem stretched.

Bought a new Uno 400mm long 27.2 post, it measures 27.2, but is too small. Drat.
It waggles a tiny bit, even pushing it right in it doesn't 'tighten-up' which could possibly have happened if someone had rammed too big a post in and stretched it. I'd have thought that fairly improbable though - it seems bigger than 27.2 all the way down.

The top of the tube seems to measure about 27.4 or 5 - but that's not the greatest way of measuring and my calipers are a bit naff measuring inside tubes.

So, I'm stuck! Anyone got a BoTE and knows 100% for sure?!?

Mines the dark purple one, with tiny metallic pink flecks - I believe it's 1993.

Thanks
Steven

 

[Elev12k]

Re: 1993 M800 Beast of The East seatpost size (for sure!)?!

My two are 27.2

 

[TreaderSteve]

Re:

Thanks Elev.
Bu66er, bums and balls! Anyone any idea what might be wrong?!
My callipers are OK measuring outer diameters - my new post and 2 others in the shed all measure 27.2 well enough.
Could a too small post being previously fitted for example stretch out an ally seatpost tube through 'wiggling'?
I've only ever had steel frames and this 'dale frame is starting to do my head in, what with the bottom bracket thread being a bit fudged due to previous BB being fitted without grease and so being virtually welded in.
The post does wiggle to and fro so it ain't right - I know what a post feels like as it's inserted (fnar fnar)...

 

[StevieBob]

You could try and make a "shim" with some aluminium foil? That should be enough to compensate for some small differences in diameter. Maybe another option is use paper rolled up in the tube and measure that outer diameter?

Stretching an aluminium seat tube...don't think so. If the outer diameter of the tube is 27,5 I do not know what could have possibly been rammed in there that it would stretch a tube and fit. Aluminium does not bend/stretch well either, it would probably have given in. But I am no expert

 

[ishaw]

Re:

Might just be the manufacturing tolerance on the 27.2 post being smaller. I can see too small a post widening the top part of the seat tube, but no further.

 

[half cog]

Re:

Bought an airborne spectre ti frame only to find the seat post is 27.4 A 27.2 has a very small amount of rock . I could get a 27.4 in layback but to get an inline post meant spending a lot more than I wanted to.So.Cleaned my 27.2 inline post and masked off the clamp and sprayed it with black satin paint from a rattle can. the post must now be around the 27.4 mark as it now fits with no rock whatsoever. Let the paint dry well and then grease it well and away you go.

 

[TreaderSteve]

Re:

Thanks for all your thoughts. As the post is only a Kalloy Uno at £18, I've gone and bought a 27.4 from Ebay earlier today. See what happens when it rocks up!

 

[pete_mcc]

Re:

The variety of sizes in seatposts are frightening. I’ve bought alloy seatposts that are ‘supposed’ to be 27.2 that are closer to 27 or 27.4. Particularly cheaper ones.

Don’t shim with anything, it’s not a sound solution especially if you ever want to lower the seatpost. If it is oversized then have it reamed to 27.4mm or 27.6mm, it’s alloy so will ream easily, alternatively try different posts in it as their variance will shock you.

 

[elite504]

^^