Machinists? Framebuilders? Seatpost insertion problem
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Machinists? Framebuilders? Seatpost insertion problem
Cross posting this, thinking maybe someone here has run into this problem on an older bike, or perhaps specifically on a UO-8.
OK I'll do my best to describe this. I am replacing the steel seatpost on my Peugeot UO-8 conversion with an alloy post. The seat tube is 25.4mm (so is the alloy post) but the original steel post is something like 22mm with a shim.
The problem is that there is a raised seam of metal on the inner diameter of the seat tube - like a "ridge" running down the back of the inside of the seat tube . (It's a cheap old bike and I'm assuming the tubing was rolled and then welded along this seam rather than the tube having been extruded or drawn.)
Anyways, with the original 22mm+shim setup, this seam of metal was a non-issue. But now that I'm trying to fit a 25.4mm post in a 25.4mm tube, this seam is creating interference, and I can't get the post in the seattube more than about an 1.25inches.
What, in your professional or non-professional opinion would be the best way to remove a raised seam of metal on the inner diameter of a 1inch tube? I would like at least 3 or 4 inches of seatpost insertion. My dremel can only reach about 1-1.5inches. Would a "pencil" extension/adapter for the dremel be the best plan? A round file?
Thanks for the help,
Mac
OK I'll do my best to describe this. I am replacing the steel seatpost on my Peugeot UO-8 conversion with an alloy post. The seat tube is 25.4mm (so is the alloy post) but the original steel post is something like 22mm with a shim.
The problem is that there is a raised seam of metal on the inner diameter of the seat tube - like a "ridge" running down the back of the inside of the seat tube . (It's a cheap old bike and I'm assuming the tubing was rolled and then welded along this seam rather than the tube having been extruded or drawn.)
Anyways, with the original 22mm+shim setup, this seam of metal was a non-issue. But now that I'm trying to fit a 25.4mm post in a 25.4mm tube, this seam is creating interference, and I can't get the post in the seattube more than about an 1.25inches.
What, in your professional or non-professional opinion would be the best way to remove a raised seam of metal on the inner diameter of a 1inch tube? I would like at least 3 or 4 inches of seatpost insertion. My dremel can only reach about 1-1.5inches. Would a "pencil" extension/adapter for the dremel be the best plan? A round file?
Thanks for the help,
Mac
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Originally Posted by sac02
Cross posting this, thinking maybe someone here has run into this problem on an older bike, or perhaps specifically on a UO-8.
OK I'll do my best to describe this. I am replacing the steel seatpost on my Peugeot UO-8 conversion with an alloy post. The seat tube is 25.4mm (so is the alloy post) but the original steel post is something like 22mm with a shim.
The problem is that there is a raised seam of metal on the inner diameter of the seat tube - like a "ridge" running down the back of the inside of the seat tube . (It's a cheap old bike and I'm assuming the tubing was rolled and then welded along this seam rather than the tube having been extruded or drawn.)
Anyways, with the original 22mm+shim setup, this seam of metal was a non-issue. But now that I'm trying to fit a 25.4mm post in a 25.4mm tube, this seam is creating interference, and I can't get the post in the seattube more than about an 1.25inches.
What, in your professional or non-professional opinion would be the best way to remove a raised seam of metal on the inner diameter of a 1inch tube? I would like at least 3 or 4 inches of seatpost insertion. My dremel can only reach about 1-1.5inches. Would a "pencil" extension/adapter for the dremel be the best plan? A round file?
Thanks for the help,
Mac
OK I'll do my best to describe this. I am replacing the steel seatpost on my Peugeot UO-8 conversion with an alloy post. The seat tube is 25.4mm (so is the alloy post) but the original steel post is something like 22mm with a shim.
The problem is that there is a raised seam of metal on the inner diameter of the seat tube - like a "ridge" running down the back of the inside of the seat tube . (It's a cheap old bike and I'm assuming the tubing was rolled and then welded along this seam rather than the tube having been extruded or drawn.)
Anyways, with the original 22mm+shim setup, this seam of metal was a non-issue. But now that I'm trying to fit a 25.4mm post in a 25.4mm tube, this seam is creating interference, and I can't get the post in the seattube more than about an 1.25inches.
What, in your professional or non-professional opinion would be the best way to remove a raised seam of metal on the inner diameter of a 1inch tube? I would like at least 3 or 4 inches of seatpost insertion. My dremel can only reach about 1-1.5inches. Would a "pencil" extension/adapter for the dremel be the best plan? A round file?
Thanks for the help,
Mac
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How about using a 25.0mm alloy post with a pop-can shim that allows for that raised seam? Bikepartsusa.com has a Laprade style alloy post in that size: https://www.bikepartsusa.com/product_...&p=01%2D127543
Neal
Neal
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Bikes: '62 Peugeot UO8, '63 Schwinn Superior, ;72 Peugeot PX-10, '74 Motobecane LeChampion, '74 Peugeot UO18
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UO-8 Rebuild
I had no problem putting a 25.4 Kalloy seatpost on my UO8. However I'd try to hone out the seattube if you can't get it to fit.
#7
Unique Vintage Steel
A good LBS or frame builder should be able to ream the seat tube enough to remove most of not all of that seam I'd think. My Gazelle's seat tube was a very very firm fit for its 27.2 post till I took it to a local frame builder. 15mins later with the park reamer and the exact same post slid smooth.
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Posts and reaming seat tubes
The problem, as I stated earlier, is that, if you have a weld seam your reamer will not cut straight without a expandable pilot of some sort. If you use a standard reamer, it will cut to one side of the tube....the weld being harder than the tube and the weld seam being raised, it will force the cutter to the opposite side and cut the tube all goofy. On a non seamed tube, you can easily ream out for a tight fitting post. I have found alot of posts that were oversized and what should be done is, the post should be turned round and to the proper O.D. on a lathe. Alot of posts are also out of round too!
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I've heard of using a file for this problem, just file down the ridge for the first few inches inside the seat tube. Seems to me that would be the easiest solution if you're going to use a non-shimmed post-