Seatpost slot pinching

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  • Hey, I've got a problem with seatpost slot pinching at the top when I'm tighten the binder bolt. I think measurement of the seatpost is good (24mm Peugeot size), because I've checked inner size of the tube, it goes in nicely and I think bigger size won't fit because it's already a tight fit with little bit of play, but when I tighten it down, the seatpost slot pinching at the top, so when I want to change the height of the seatpost I need to open it up with the screwdriver what is frustrating, because without it the seatpost won't move at all or be scratched a lot from the frame. I've tried with carbon paste, shim made from can but it's too tight to go in with a shim. I don't have any more ideas what to do with it. Some guy told me that I need to cut down the seatpost slot few mm down, but I don't know if it is a safe idea.

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  • The seat tube should be the correct internal diameter for the intended seatpost when the slot is straight.
    If it is pinching in, you are using a too small seatpost.

    I believe some other Peugeots used a 25.4

  • I'm not an expert, but maybe find a shop that has reamer that is equivalent to your seatpost, to sort out any imperfections down the tube.

  • I've tried with other 25.4 seatpost but it doesn't fit at all even with the slot opened up with screwdriver when the slot lines is parallel, maybe it's like 24. something or 25mm size? I've ordered the 24mm seatpost for Peugeots when I didn't check if the frame is pinching down, because the original one that came with the bike was also 24mm. All information that I readed online about Peugeot size from 80's low tier bikes is 24mm. I need to find some 25mm post and try with it maybe.

  • With the bolt out, the slots straight and the seatpost in, there is a gap around the seatpost.
    It's the wrong size, no doubt about it.
    The seatpost should snug to the tube when it is open like that with the slot straight.
    A larger one may not fit in now as the tube has probably been ovalised or distorted by the over tightening on the small post.

  • If it's already deformed by using wrong seatpost, it can be fixed to slide the bigger seatpost or not?

  • Little update, I've tried to fit the 25mm seatpost from other bike, no luck with that even after opening up the slot with screwdriver. Still the both of 24mm seatpost just having a gap around the tube. I think there is no different seatpost size between 24 and 25mm?

  • Hot Melt Glue

    Here is a radical but simple solution to the seat post problem - forget the clamp, just use hot melt glue.

    Clive Bonavia (google him) was an eccentric but excellent frame builder who used this method on all his later frames. He said it had three benefits: it saved him the trouble of making any kind of clamp, it saved the weight of the clamp and, most importantly, it prevented any water getting into the frame past the clamp (a common problem, causing corrosion).

    Clive's main business was joinery, so he knew all about glue. Although I think this material was intended for wood, it seems to work perfectly for this purpose. It can be reheated any number of times to adjust the seat post, and the amount of heat required to free the glue does not damage the paint.

    You should be aware that I'm just quoting Clive here, I'm not writing from personal experience, but in my experience he was always right about these technical matters.

    So I suggest you google 'hot melt glue', and don't forget to clean and degrease everything before assembly!

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Seatpost slot pinching

Posted by Avatar for marrac @marrac