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-   -   Seat clamp problems! Please help! (2008 Bianchi Pista Concept) (https://www.bikeforums.net/bicycle-mechanics/797696-seat-clamp-problems-please-help-2008-bianchi-pista-concept.html)

mydenimisraw 02-09-12 04:51 PM

Seat clamp problems! Please help! (2008 Bianchi Pista Concept)
 
After riding my newly bought Concept for a couple hours, the seat fell to the lowest position...

When I try to raise the seat and tighten the clamp (no matter how tight), the seat does not stay at my desired height, but falls back down to the lowest position.

The seat clamp is integrated so I cannot replace it... Do you guys have any solutions?

Thanks.

Please note that there are no cracks and that the post is the correct size.

Here are some pics of said seat clamp:

http://i.minus.com/ibi0zJWJkafzPc.JPG
http://i.minus.com/ibzJxSLbyHJn8N.JPG
http://i.minus.com/i2kYWw8gHhjnL.JPG
http://i.minus.com/ib2jgj7Iv4Qkfc.JPG

AlphaDogg 02-09-12 04:58 PM

The threads on the frame where the bolt goes in are stripped (just a guess).

fietsbob 02-09-12 04:59 PM

+1, my guess its threaded and the threads are stripped,
now you have to get the threads restored.

A machine shop may be able to install a helicoil, essentially a coil
of diamond shaped tempered steel wire.

you could also get a longer bolt and put a nut on the other end.

mydenimisraw 02-09-12 05:04 PM


Originally Posted by AlphaDogg (Post 13831793)
The threads on the frame where the bolt goes in are stripped (just a guess).

Any idea how I could resolve the problem if that were the issue?

mydenimisraw 02-09-12 05:07 PM


Originally Posted by fietsbob (Post 13831795)
+1, my guess its threaded and the threads are stripped,
now you have to get the threads restored.

A machine shop may be able to install a helicoil, essentially a coil
of diamond shaped tempered steel wire.

you could also get a longer bolt and put a nut on the other end.

I'll give it a go... Thanks!

bhchdh 02-09-12 05:13 PM

Can't tell from your post if the threads are stripped, if they are then there are good answers above. If they are not stripped I have two thoughts. The seat post may be the wrong size for the seat tube, or you may not be tighting enough. As a suggestion try some " carbon fiber assembly paste" on the post, it will add some friction and may stop the slipping.

FastJake 02-09-12 08:15 PM

+1 Make sure (again) you are using the correct size post. They come in increments of 0.2mm for a reason. Even if off by that much, they will not work or if they do you risk damaging something.

Carbon post in aluminum frame? Agreed, wipe off all grease and try some carbon assembly paste instead.

mydenimisraw 02-09-12 08:29 PM

I just rechecked the seatpost and it's definitely the correct size: 27.2

unterhausen 02-09-12 10:10 PM

I think it's rare that a seatpost will slide all the way in if it's the right size

If you can get access to a telescoping hole gauge, the bore should be 27.4 or less for a 27.2 seat post.

FBinNY 02-09-12 10:35 PM


Originally Posted by mydenimisraw (Post 13831814)
Any idea how I could resolve the problem if that were the issue?

If the threads are in fact stripped an easy fix it to replace the bolt with a seat post QR unit. Most of these have shank diameters smaller than the typical bolt and can just slip through. Likewise you can just use a bolt and nut, with a thinner longer bolt.

While you're fooling with it, you should try to see the real problem. Start by fitting the post and clamping gently. look at the slot, if the top closes to less than 1/2 the width of the bottom, your post is undersized and that might be the problem. If the tube closes to where the tube touches at the top, the post severely undersized and will never tighten regardless of how muchc pressure you put on the ears.

Also see if the ears touch in the back, which isn't rare when they've been overtightened and bent. Ears touching mean that they're partly collapsed, or cracking away from the lug, so check thoroughly.

If the slot is still parallel when tightened, and the ears don't touch, it should tighten, but if not try replacing the grease with carbon assembly paste, or my favorite fix. Put coarse lapping compound (grit in grease) on the 2" or so of the post that will be at the height of the pinch bolt. When clamped the grit bites into both the frame and post making a mechanical interlock that will hole with very little clamping force. If you use the lapping compound, be sure to completely loosen the post before making even small adjustments.


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