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Ovalized seat tube

Old 05-06-22, 03:01 PM
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Ovalized seat tube

OK, I know this has been covered a lot. I've searched and read many threads. I've read about various techniques. But for some reason I'm just having a hard time applying the information to my situation. Please have pity on a feeble-minded guy and offer me some guidance.

My situation is that I have 1960's PX-10 with great original paint and patina. I believe it should take a 26.4 seatpost, but the previous owner says it had a 26.2 when he had it. The 26.2 I have is a very tight fit. I can get it in, but only with a lot of struggle. I've only had it in enough to try it out, because it's requiring a lot of back-and-forth for every bit that goes in. (When I pulled it back out today, I did the zig zag thing and when it finally came loose I managed to hit myself squarely in the mouth with it.)

The part that I'm uncomfortable with is that it's too wide side-to-side. With the 26.2 seatpost in there, I can slide a piece of paper between the frame and the post. I took measurements with a digital caliper, and at the widest point it's about 26.94mm wide. Along the diagonals near the tab, it measures about 26.19mm.



There's a lot of material at the lug, so assuming it's only ovalized around the top it should be no problem to ream it out to 26.4. I'm concerned about the width though. Is it going to cause problems to have it too wide there? Is that common?

In another thread @bulgie suggested a method of making a C-shaped shim of the right size (perhaps cutting a section from an old seatpost) and then using something like a quill stem with a wedge to push it out from the inside. Depending on how the opening got it's current shape, it seems like that might draw in the sides. I like this idea. I'm just not sure I have the ability to pull it off. I'll be enlisting the help of The Bike Butcher of Portland on this, but I'd like to have a clear idea of what approach I want to take before I take it to him.

Suggestions?
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Old 05-06-22, 03:07 PM
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Originally Posted by Andy_K View Post
Suggestions?
There's nothing wrong with it.
It's French.
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Old 05-06-22, 03:15 PM
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Originally Posted by gugie View Post
There's nothing wrong with it.
It's French.
Oh, I forgot the French used oval seatposts.
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Old 05-06-22, 03:16 PM
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Originally Posted by gugie View Post
There's nothing wrong with it.
It's French.
Ha ha ha! Just spread those ears and clean the crud out of there!
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Old 05-06-22, 03:32 PM
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The measurements that you've taken at the top of the tube may not tell the whole story. I'd recommend finding a shop that has a proper reaming tool to correct it back to spec. What does the slot look like from the rear? The sides should be parallel.
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Old 05-06-22, 03:38 PM
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Originally Posted by Moe Zhoost View Post
The measurements that you've taken at the top of the tube may not tell the whole story. I'd recommend finding a shop that has a proper reaming tool to correct it back to spec. What does the slot look like from the rear? The sides should be parallel.
From the rear



The grey gunk on there seems to have been plumber's putty, BTW. The whole slot was filled with it.

Reaming does seem to be in order here, and I believe @gugie has the correct tool for that. I'm just trying to decide if I should try to do something about the extra width first.
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Old 05-06-22, 03:44 PM
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Originally Posted by Andy_K View Post
From the rear



The grey gunk on there seems to have been plumber's putty, BTW. The whole slot was filled with it.

Reaming does seem to be in order here, and I believe @gugie has the correct tool for that. I'm just trying to decide if I should try to do something about the extra width first.
Reamers are standing by.

There's a proper looking 26.6 seatpost on the big auction site right now. I'd like some feedback from others who might have done this before on equivalent seat tube. Don't want to get that area too thin.
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Old 05-06-22, 03:49 PM
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Originally Posted by gugie View Post
There's "proper" and then there's "Super Deluxe" -- which I have in hand and is a big (too big, probably) part of why I want to get it to 26.4.

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Old 05-06-22, 03:52 PM
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On motobecanes I've gone 26.4 and 26.6 to match seatposts I've had without issue. The o.d. was 28mm on both. My reamer is ancient but effective!
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Old 05-06-22, 04:12 PM
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That slot sure looks squeezed in to me. I predict re-shaping the slot, clean and de-burr will make it.
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Old 05-06-22, 04:26 PM
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I would pry those open just a little, feel for sharp edges use a crescent file, grab a steel 26.4 post with a saddle. Insert, with the steel you won't need to worry about scratching then you can work that thing back and forth, up and down, the steel post will help reshape. Check for sharpe edges again, usually the top front or back, and the pinch slot could need filing.

I had to open up the seattube on the Raleigh Professional, it had a 26.8 that was mangled from not being able to hold. I gently pried and massaged in a black steel 27.2, it took some time effort grease. I use a junk 27.2 alloy for checking for scratching.

It was extreme on the Professional, it was worth it.


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Old 05-06-22, 04:29 PM
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I've dealt with this exact situation a few times before.

I used the same technique on all of them, based not on metal removal but on forming the opening round again.

Get thee a steel or thick-walled 26.2mm post (with saddle attached).

Force(?) in the post to about 1" depth, give-or-take (starting with the full 1" and working down as needed).

Simply lean rearward on the saddle using hands backed up by chest weight if needed.
The ears will magically open to their original state, and the opening will become round.

Finally, install the bike's original 26.4mm seatpost, which is chromed steel and won't get scratched. If using an alloy post, often a bit of smoothing of the seat tube's ID using a half-round file will get you a perfect and burr-free opening that is friendly to the softer alloy.
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Old 05-07-22, 03:51 AM
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As others have said, don't ream, just bend it round again. The lug and tube at that point are not very hard and it should not take much work.

Reaming is a bad idea generally, the tube walls are not very thick. Recently there was posted here a picture of a seat tube that had been reamed, and the reamer went a tiny bit off-axis (a bent seat lug can do that). A few inches down the tube the bottom of the reamer had got so close to one side of the tube that it broke through the paint.
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Old 05-07-22, 09:48 AM
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Originally Posted by oneclick View Post
As others have said, don't ream, just bend it round again. The lug and tube at that point are not very hard and it should not take much work.

Reaming is a bad idea generally, the tube walls are not very thick. Recently there was posted here a picture of a seat tube that had been reamed, and the reamer went a tiny bit off-axis (a bent seat lug can do that). A few inches down the tube the bottom of the reamer had got so close to one side of the tube that it broke through the paint.
I should have noted that I always get the seat lug reasonable before I would ream. Also with a reamer I start small enough that I can work it in by hand as deep as I will want to go. Pretty hard to be off center then. If one is careless a reamer can do real harm.
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