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Ovalized seat tube repair

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Ovalized seat tube repair

Old 04-14-22, 12:34 PM
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Ovalized seat tube repair

Hi, everyone. I'm hoping you can give me some advice on repairing a problem with an ovalized seat tube opening.

I just bought a 1960's PX-10. The previous owner says it had a 26.2 seatpost in it when he bought it. I got just the frame. I was able to get a 26.2 post in, but just barely. However, there are visible gaps on either side of the post.





There was something like plumber's putty filling the slot. You can still see a bit that I haven't cleaned off. I was almost afraid to scrape it off, but it doesn't look to me like it was hiding anything awful.

The gap on the sides is big enough that I can slide a strip of paper between the post and frame -- about half an inch deep on the drive side and at least two and a half inches on the non-drive side (by which point it's beyond the amount of post I have inserted). I think this frame should take a 26.4 post and I'd like to get it back to that if possible, but I'd really like to save the paint, which is original and in very good condition on most of the frame.

I've read various threads on this topic, but I'd like to ask for feedback on my current idea before I proceed. I have this tool:



I bought it at an estate sale without knowing what it was, and I'll never use it for its intended purpose (part of a motocycle wheel balancer). I was thinking I could attach a ~26mm spacer of some kind on one end to keep it centered, insert the spacer and one of the cones into the seat tube, and use something to make an improvised slide hammer to tap the hole back into round. I believe the cones are aluminum. Will that work? If so, how hard can I safely hit it?

Other suggestions? Thanks!
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Old 04-14-22, 07:56 PM
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My usual first way to open up a squeezed in seat tube, at the binder, is to use the seat post as a lever. The frame will have some spring back so plan of levering it open further than the final size.

I have to say that looking at the binder slot and how parallel the edges of it are I wonder about your speculation of "correct" post size. It's not uncommon for a seat lug to suffer from heat induced deformation and a decreasing of the fore/aft fit. A factory could ream the seat tube, and risk loosing some tube wall just below the lug. Or they (or the LBS that assembled the bike) could select a slightly smaller post and if the binder held it tight enough to stay put all would be well.

So My first question would be does the seat post stay put or does it slip down under use? Many here have found it good advice to not try to fix a working part... I also wonder if the plumber's putty was to try to seal the post from water getting down in the frame. Have you pulled the BB and checked the condition at the base of the seat tube and that of the shell? If you found rust my speculation might hole water (bad sort of pun) Andy
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Old 04-14-22, 09:09 PM
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I think the most common original size for those is 26.4, so you're not too far off.

I like a quill HB stem with a wedge (not a cone) for expanding the slot from inside.. Make a shim that fits inside the frame (a piece cut off the bottom of a 26.2 post maybe?) and fits the 22.2 stem quill inside the shim. It needs to have a slit, i.e. a "C" shape not an "O". Alternatively, you could try a 1" quill stem made for a threaded 1-1/8" steerer, but those those are slightly rare. The 25.4 quill would be an OK fit on the frame, tho not great. No shim in that case.

Tighten the quill bolt to expand the frame from a few different angles, but remember your frame is already too wide so don't expand it that way. Push more on the pinchbolt ears, pushing them back and out. I tend to push them just a lttle beyond the final place you want them, so the subsequent reaming and/or honing steps won't take more metal off the area around the ears.

Then ream (optional) and/or flex-hone, until the 26.4 post fits nice, then clamp the pinchbolt ears back in. Remember honing removes only a tiny amount of metal so don't expect much from it, it's just for polishing out any reaming marks.

Important: check your seat tube for a cork, and remove it if it's there. With the seatpost and bottom bracket out, put a flashlight in the BB shell and make sure you can see it down the seat tube from the seatlug end. PX-10s of that era often had a factory-installed cork, and some of those frames completely rusted out from the puddle of water that collects on top of the cork.



A sad end for a nice PX.

EDIT: forgot to mention the irony of the decal partly visible in the pic. It says "INOXYDABLE" which means roughly "rustproof" or "unrustable". I think. (I don't speak French)

In addition to the frame being completely perforated by rust down where the cork was, there's also rust visibly spreading from under the "rustproof" decal. Rust, being made mostly of iron, loves irony.

Mark B

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Old 04-14-22, 10:03 PM
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Originally Posted by Andrew R Stewart
My usual first way to open up a squeezed in seat tube, at the binder, is to use the seat post as a lever. The frame will have some spring back so plan of levering it open further than the final size.
Can you tell me more about that? Specifically, how far would you insert the seatpost and how hard would you pull?

Right now, I've only got enough of the seatpost in to hold the bike in the stand, not enough to ride it. It was difficult to get it in at all, so I'm not sure I would say it's "working" in the current state.

There's some kind of thin metal sleeve in the bottom bracket. I'll pull that and check the condition.
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Old 04-14-22, 10:11 PM
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Originally Posted by bulgie
I like a quill HB stem with a wedge (not a cone) for expanding the slot from inside.. Make a shim that fits inside the frame (a piece cut off the bottom of a 26.2 post maybe?) and fits the 22.2 stem quill inside the shim. It needs to have a slit, i.e. a "C" shape not an "O".
I like this idea idea. Unlike Andy's seatpost as lever suggestion, it'll take some searching for parts, but I like the idea of direct pushing

There is a cork or dowel of some kind in the bottom of the steerer, but I wouldn't have thought to look for one in the seat tube. I'll check that out.
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Old 04-15-22, 01:17 AM
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Originally Posted by bulgie
Important: check your seat tube for a cork, and remove it if it's there. With the seatpost and bottom bracket out, put a flashlight in the BB shell and make sure you can see it down the seat tube from the seatlug end. PX-10s of that era often had a factory-installed cork, and some of those frames completely rusted out from the puddle of water that collects on top of the cork.
You were right. There was a cork in the seat tube. It smells like a chardonnay with hints of grease. It's out now. Thanks!
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Old 04-15-22, 01:58 AM
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Why did they put corks in seat tubes? Was it supposed to prevent rust? Or just to protect/destroy the habitat of the Portuguese cork lynx?
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Old 04-15-22, 05:27 AM
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Originally Posted by guy153
Why did they put corks in seat tubes? Was it supposed to prevent rust?
Well I doubt we'll ever hear it from someone who was there, so we can only speculate. My guess is they knew water spraying off the rear tire gets directed at the slit at the seatpost pinchbolt, and that slit is usually not sealed against water getting in. So they though "merde, can't let road grit slurry get into the bottom bracket bearing, let's cork it." A great idea until those frames start dying from rust perforation at the top of the cork from constantly having a little puddle there.

The cork might still be considered a great idea if everyone knew to take their post out, turn the bike upside down and drain the water out now and then. You'd want to give it time to dry out inside, maybe with help from a heat gun or blow dryer. Using and periodically replenishing some kind of anti-rust goop (Framesaver™ or some such) would also help. This scenario might actually be the best plan, as long as we really remember to do it. Or if everyone lived in Arizona.

In this world, where people don't always remember to do their periodic maintenance (and some of us live in Seattle), a more fool-proof plan is to make a hole in the bottom of the frame, to let the water out continuously. Lowest point while the bike is horizontal, right under the bottom bracket.

Even that can fail though. My wife's superlight steel roadrace frame rusted through the left chainstay at the dropout. We live in Seattle and she often rode her light race bike in the rain without fenders, even though she had a perfectly good fender bike. But sometimes you just want to ride the fast bike, right? And you might get caught in the rain though it was nice when you left. This bike got ridden hard and put away wet so often that there was a chronic puddle at the dropout end of the chainstays, because she always hung the bike by the front wheel as soon as she got home. I guess the right chainstay might have been rusted too, didn't saw thru it to find out, but the left one perforated. So, if I'd known all that, I could have made weep holes in the chainstays near the dropout, and the bike might have lived a longer life. But it went about 20 years, which is longer than some people thought that bike would last. It was made with the lightest tubes I could find, .6/.3 mm Prestige main triangle, some Columbus and some Excell, and weighed a bit under 2.5 pounds. The fork was (is) a bit under 1 pound. Those numbers are pretty light for steel, but I still believe it could have lasted much longer (like essentially forever) if not for the rust.

So the frame on her fast bike now is Ti. Problem solved?

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Old 04-15-22, 08:38 AM
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"Problem solved?" Mark B

Of course the problems only are shifted to other areas. Galvanic corrosion has claimed many a Al or carbon post. I know you don't think this (hence the ? after your last comment) but I suspect some still think Ti is the wonder metal and will never "rust", crack or otherwise fail.

Years ago I had the thought of what it would be like if steel was "invented" tomorrow. Stronger and better holding an edge (remember that many materials are created due to the war industry, just like medicine ups its game due to wars) than bronze and no rot from bugs like wood gets. Think about what a "discovery" of steel would mean to our toys. Stronger and cheaper (but not lighter so Keith Bontrager's "make it light, strong and cheap; pick two" is safe) then Al. Able to be formed and joined with relatively simple and low skilled methods. Failures generally take time between the first evidence showing and complete structural collapse. And readily abundant across our world. We would see the latest and greatest racers being paid to ride bikes made from this wonder metal. All the Al and carbon bikes would be seen as old school and the mark of a luddite.


One possible reason to insert a wood bung down in a fork's steerer is to reinforce that area with a material that has a different failure mode then the steel steerers (of that era) have. Not sure I believe this but an interesting idea. Andy
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Old 04-15-22, 09:54 AM
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Originally Posted by bulgie

In this world, where people don't always remember to do their periodic maintenance (and some of us live in Seattle), a more fool-proof plan is to make a hole in the bottom of the frame, to let the water out continuously. Lowest point while the bike is horizontal, right under the bottom bracket.
The problem it seems to me with a hole in the BB shell at the bottom of the ST is that it will never be big enough-- water can surely still collect around the hole, just behind the welds. Make it any bigger and there's nothing to weld to (OK it probably could be done, but would risk the strength of the joint). A better strategy for ultimate frame life might be the minimum number of vents you need for welding and then seal them:

1. Don't drill BB shell at all
2. Drill ST where TT joins and where SS join. The seatpost can seal those holes.
3. DT can vent out of the bottle holes
4. There are usually small holes in hooded dropouts where they attach to the CS. All you need for welding. Could plug them afterwards, but the axle is already in front of them.
5. Use a seatpost that's capped at the top
6. I personally cap the bottom of the steerer too, with holes in it behind where the legs or segments are welded on. So the fork is all vented into the steerer, which then has the star nut cover thing on the top of course.

The main places water probably gets in are the ST, when the seatpost is open at the top, the BB when people ride through floods, and the bottom of the steerer. And I guess the bottom of the seat clamp is a possibility too. But if the seatpost fits well and is greased I don't think water will get in there. It may also get past the lower headset bearing and into the DT from there. This is why a hole venting DT to HT may be a bad idea (and you don't need it for welding because you have the bottle holes).

I realize this is a contentious subject so I'm probably going to find some opposition A lot of people think it's vitally important to vent everything with large holes.
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Old 04-15-22, 11:08 AM
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I'm pretty sure water gets in no matter what you do. It does seem a little counter-intuitive. But there should be a hole in the bb shell to let it out. And also, I had a friend that got water in his downtube and it rusted out. It was a fillet brazed frame. I would like to know if it had any holes into the bb shell, but I'm wondering if it would still trap water if they hole was centered in the tube.
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Old 04-16-22, 02:31 AM
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Originally Posted by unterhausen
I'm pretty sure water gets in no matter what you do. It does seem a little counter-intuitive. But there should be a hole in the bb shell to let it out. And also, I had a friend that got water in his downtube and it rusted out. It was a fillet brazed frame. I would like to know if it had any holes into the bb shell, but I'm wondering if it would still trap water if they hole was centered in the tube.
What if it's getting in through the hole everyone puts in the BB shell, and into the other tubes from there? Ofc on lugged frames there wasn't much option (unless you went around putting corks everywhere) but a TIG BB shell is just a tube. It might be best to leave it that way and not drill it anywhere. I did this on my last frame. But it will be ages before it rusts anyway (hopefully
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Old 04-16-22, 03:45 AM
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Originally Posted by guy153
The problem it seems to me with a hole in the BB shell at the bottom of the ST is that it will never be big enough-- water can surely still collect around the hole, just behind the welds.
No welds on a PX-10 (the frame being discussed) or any traditional lugged frame.
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Old 04-16-22, 08:06 AM
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I just replaced the crank on my gravel bike yesterday. It doesn't get ridden much in the rain and it hadn't been ridden in months because the gravel has been under snow. It was definitely swampy in there. So water gets in and doesn't leave. No drain hole in the bb shell. I have never seen a plugged drain hole, it doesn't have to be very big, 5-6mm. Fortunately, it's an all city and they have an anti-rust coating inside. I'm convinced it would have been dry if there was a drain hole. I also took the seat post out to make sure it wasn't corroding, and it was fine. Still had grease for quite some distance down the seat post. Who knows how the water gets in.

I should probably cut the seat post shorter.
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Old 05-24-22, 10:00 AM
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Closing the loop here for archival purposes, I applied the method suggested by @bulgie in post 3 of this thread, and it worked like a charm. Pictures and further elaboration can be found here: https://www.bikeforums.net/classic-v...d-px-10-a.html

Thanks, Mark!
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