Top of Seat tube damage

[Ronald]

I just discovered a small problem on my 2004 Giant OCR0.

I have always needed to clamp the seatpost rather tightly, as the post has has an unfortunate tendency to drop every so slowly.

A small chip broke off underneat the seatpost clamp and in line with this chip a small crack can be seen in the top of the seat tube.
I can also feel a slight deformation in the seat post, but this is not easily spotted by eye.

In the pictures below I have taken out the insert that sits between seat tube and seat post.

Keen to hear a decent solution to this, as the bike is otherwise (still) spot on the mark!

 

[zophiel]

can you not cut it a bit lower then the crack.

The looks to be a fair bit of tube there

 

[Ronald]

can you not cut it a bit lower then the crack.

The looks to be a fair bit of tube there

About an inch and a half to the weld, obviously less to the bottom of the 'cut'.
This option has crossed my mind, but looking for opinions on it if possible.

 

[arknor]

if you cut it shorter there might not be enough flex for it to properly grab the post so you would have to make the cut out line longer too which may or may not be totally safe.
What if you put some form of tape around the inside as best you can the added friction should prevent the seat tube from sliding down
or a better idea put the tape around the seat post you would probably only need to wrap it around once or twice.

 

[neil_g]

if youve always had to over tighten it, perhaps the seat post is not the correct size.

if youre overtightening it enough to stress the metal, stands to reason it would crack.

 

[Vonhelmet]

Googling suggests it should be a 27.2mm seatpost with a shim, or 30.8mm without. Look at the bottom of your seatpost - it should have the diameter stamped on it.

 

[Ronald]

The seatpost has 27.2 written on it. I don't have a pair of callipers to measure and confirm the tube diameter... Using a ruler it seems clearly more than 31mm though and 31.6 seems quite common.

On the original sleeve I have, every second 1/8th section is of smaller diameter with the cut in one of the larger diameter sections. Cannot actually found a sample of that on Google images so I guess it is pretty uncommon... Might save a few grammes, but I suspect it is a contributing factor in my current problem: due to the width of the cut lines there is only a very very small section of tube touching the shim, and that is what has broken off completely. Thanks Giant

I found http://www.bikeforums.net/bicycle-mechanics/664318-giant-ocr-seatpost-shim-not-shim.html and creaking I can definately confirm, so If I can get rid of that in the process that would be quite cool.

Assuming a 31.6mm tube, would simply changing the seat post work, without doing anything to the top of the seat tube?