Ovals are not circlular

[Ajax Bay]

I have a band-on front derailleur (Shimano FD-6603 triple) which I plan/hope to use on a new build. It is marked as 31.8mm and the new (to me) frame's seat tube is 31.8mm OD (on seatpost clamp and measured). But the band is not 'round': it's below 31mm on one diameter and above 32mm on the diameter at right angles.
I used the derailleur with a shim (but not a metal one - mistake) on a 28.6mm seat tube (for maybe a year/10,000km) and I assume that sufficient tightening to keep it in place bent the hinged part (hence the reduced diameter). It's alloy (assume Al mainly). Image below is a new one (not mine).
I seek advice on how best to return the band physically to its circular design. Doesn't need to 'move' far so I think that work-hardening is not a threat.

http://media.canyon.com/download/manuals/Manual_FD_6600_EN.pdf

 

[C R]

I have a band-on front derailleur (Shimano FD-6603 triple) which I plan/hope to use on a new build. It is marked as 31.8mm and the new (to me) frame's seat tube is 31.8mm OD (on seatpost clamp and measured). But the band is not 'round': it's below 31mm on one diameter and above 32mm on the diameter at right angles.
I used the derailleur with a shim (but not a metal one - mistake) on a 28.6mm seat tube (for maybe a year/10,000km) and I assume that sufficient tightening to keep it in place bent the hinged part (hence the reduced diameter). It's alloy (assume Al mainly). Image below is a new one (not mine).
I seek advice on how best to return the band to its circular design. Doesn't need to 'move' far so I think that work-hardening is not a threat.
View attachment 533410
http://media.canyon.com/download/manuals/Manual_FD_6600_EN.pdf

I have the impression that the bands on Shimano FDs are meant to be used with inserts regardless of the diameter of the seat post, and the band itself is not round by design.

 

[Ajax Bay]

The 2 shims shown in the diagram (link below image) are to reduce the 31.8mm band to 28.6mm size.

 

[C R]

The 2 shims shown in the diagram (link below image) are to reduce the 31.8mm band to 28.6mm size.

Fair enough. The only way I can think of returning it to its shape would be to tighten it slowly onto a bar of the desired diameter, but not sure how long it would need to stay to make sure it keeps its shape.

 

[Ian H]

If it's expanded front to back, stick it in a vice and very gently squeeze it, checking frequently. If it's the other way, wedge something of around 32/34mm (doesn't need to be circular, but preferably softer than the clamp, e.g. wood) and gently tighten the clamp, again checking frequently.

Of course you could just try it on the new frame and see whether it returns to shape. You should be able to judge if it is conforming before the frame is dinged.

 

[Ajax Bay]

Can't get it on the new frame's seat tube, Ian, as the 'short' diameter prevents me so doing. Same goes for tightening it onto a tube of (say 32mm, @C R : I can't get it round it.
The problem, as I see it, is that it's 'contracted' front left to back right so I can't squeeze it out in a vice. I'll have a go at your 'the other way'.

 

[C R]

Can't get it on the new frame's seat tube, Ian, as the 'short' diameter prevents me so doing. Same goes for tightening it onto a tube of (say 32mm, @C R : I can't get it round it.
The problem, as I see it, is that it's 'contracted' front left to back right so I can't squeeze it out in a vice. I'll have a go at your 'the other way'.

When you say you can't get it round, do you mean that the bolt won't reach?