Andy_K 

I've talked about my recently acquired PX-10 in several threads already. Most recently, I showed @gugie's repair of the derailleur hanger in this thread and later in the same thread fretted over possible solutions to a problem with the steerer threads. The same frame also had an issue with an ovalized seat tube opening. It's probably unfair to call this frame "bungled" -- it's from the sixties and these are relatively typical problems. Much worse things have happened to bikes of similar age. In any event, I'm here today to celebrate yet another success in overcoming these problems. Following the basic method suggested by @bulgie in repsonse to my query on the Framebuilders forum (https://www.bikeforums.net/framebuil...be-repair.html), I have successfully opened the seat tube up enough to use the 26.4 seatpost I bought for it.

I bought the seatpost before I even had the frame in hand on the brash assumption that 26.4 would be the right size. When the frame arrived, the 26.4 post wouldn't fit. In fact, a 26.2 post I had didn't want to go in without a fight. Using the typical zig zag and brute force approach, I got the 26.2 post in a couple of inches. Then I observed that there was a visible gap on the sides of the post -- big enough to slide a piece of paper in without resistance. After removing the post, I confirmed with my calipers that the opening was indeed significantly wider side-to-side than it was front to back. A classic ovalized seat tube!

The method suggested by @bulgie was to find a shim that sits inside the seatpost and use a wedge-type quill stem to push out from the inside. Full details can be seen at the link above. Mark suggested perhaps using a piece cut from a 26.2 seatpost, with a section cut out to make a C shape. I'm a bit OCD, so I couldn't do anything that simple. I mulled it over for a couple of weeks and finally came up with an approach I liked. It had the merits of using pre-fabricated pieces and giving me the false security of claimed precise measurements for those pieces. I started with a seatpost shim with a 26.4 mm outside diameter and a 25.4 mm inside diameter. To that, I added a handlebar shim that adapted a 22.2 mm inside diameter to a 25.4 mm outside diameter. At this point you may be thinking, "You dolt! That's going to fill all the space a 26.4 seatpost would. It'll never work." Ah, but I thought of that! One of the things I already had was a 21.1 mm wedge type quill stem adapter for a Schwinn frame. That gave me the extra millimeter I needed to get it in the deformed opening. Here are my pieces.



The seatpost shim has a lip on it, which keeps it from sliding in. I taped the handlebar shim to the quill adapter to keep it in place until I could get it tight. The assembled "tool" slid in with no troubles.



Angling the tool so that it would push out against the ears, I tightened it down. I repeated this a few times with minor turns in between. In just a few minutes, my 26.2 seatpost was sliding in with no problems. Measurement with the caliper showed the opened was still too wide, but the 26.4 post felt like I could have maybe forced it in. At this point, I swapped out the 21.1 quill adapter for a proper 22.2 quill stem. There was enough room to get that in without a problem. A couple more rounds of tightening and checking, and now the 26.4 post slides in. It's still got a touch of resistance, but it goes in and out without requiring any zig zag motion. A bit of work with a hone will likely have it right as rain.



The icing on the cake here is that the eBay seller I bought the seatpost shim from has shims from 25.4 to every common seatpost size, so I'll be able to repeat this technique on other frames as the problem arises.

The Golden Boy 

Hey Bungled PX-10
Where have you been
Bungled PX-10

Narhay

Very enterprising. The closest to an ovalized seat tube I've come was some pinched lug ears that I massaged outwards with a seatpost.


What are your build plans with this one?

gugie 

Excellent work Andy! And now you have a tool that I don’t!

Andy_K 

To use a phrase I saw on Facebook SiR recently, I'm going for a build that is not original but sympathetic -- Simplex Criterion shifters, SLJ derailleurs, MAFAC Racer brakes and matching levers, Brooks B17 saddle, Normandy/Mavic wheels. The big divergences will be my usual Tecnomic stem with Soma handlebars, and a 50.4 Velo Orange crankset. I'm thinking blue bar tape and cables to match the lug lining. You can find pics of the parts, which I gathered before I had the frame, here: https://www.bikeforums.net/classic-v...ore-horse.html

Andy_K 

Well, I'd probably let you borrow it when the need arises.

Mr. 66

Sweet success! I've learned much since joining the forum

jdawginsc 

Impressive fudge of a tool. Probably tough to find shims for other seat tube sizes..., though 22.2 + handle bar shims would get you to 25.4, but then you'd have to find shims at specific diameters minus a bit for expansion (maybe 0.6mm short of the diameter of the seattube.

Andy_K 

Honestly, I'm not even sure the seatpost shim is strictly necessary. The handlebar shim properly affixed (with flexible electrical tape) to a 22.2 stem (or maybe just taped to the frame) would probably do the trick for anything up to 27.2. The wedge pushes pretty far out. I mentioned the false sense of security of the numbers. I liked the idea that my outer shim was the correct size for the tube, as if it would hold the seat tube round and keep me from overdoing it in the opposite direction, but honestly it's a 0.5mm piece of aluminum and probably wasn't capable of doing any such thing. I like it though. It feels useful, even if it isn't. Maybe once I switched to the 22.2 stem and had solid backing behind both sets of shims it was serving the purpose. I don't know.

Shims in "all sizes" are available here (except 27.2 is out of stock at the moment): https://www.ebay.com/itm/274564570922 For whatever reason, this seller has a full range of outer diameters for shims with 25.4 as the inner diameter.

jdawginsc 

Would too much space for the wedge actually push out in a bulge rather than a circle though.

That link is the key though... 3.2 outer lipped shim, and then plop in the shim that gets you within the 1.0 mm range you referenced.

Andy_K 

Quite possibly. In that sense my double shim + 21.1 stem adapter was very good for distributing the force along the proper curve of the tube. So maybe I wasn't just overthinking it. Next time I'll paint the shim to match the frame or some other such unnecessary complication.

bulgie 

I like the pusher being a bit smaller than the hole precisely because it lets me localize the force where I want it. We're not trying to enlarge the hole, just push it out where it needs it.
I have done this successfully with a 1" quill stem, the ones made for 1-1/8" threaded steerers. (somewhat rare but there was a brief interlude between the advent of "OS" steerers and the invention of threadless headsets.) No shims, just the 25.4 stem pushing against the 26.4 (or whatever) seat tube. I generally orient it so it pushes first against one seatlug ear, and then the other. Push a little, try the post, push a little more, maybe changing the orientation of the pusher as you see fit.

At one place of employment we had steel doodads made that were essentially the same thing but machined to a bit under 27.2 so they fit easily into the frames we made. They were for holding a painted frame in a bike stand but were also great for re-rounding seatubes on a repair. Bob Freeman of North Bend Washington still has one of those, scavenged from the wreckage when that shop closed down.

If I were to use shims I'd want them to be steel and as thick as possible for strength/rigidity.

Mark B

Andy_K 

Stein sells a "clamp" like that: https://steintool.com/portfolio-item...ll-clamp-tool/

@gugie has one, which he uses to hold bike in the stand, and we discussed trying that, but alas it only fits down to 26.6!


The seatpost shim I bought was listed as being steel in the sale ad, but that turned out not to be true. That shim by itself feels a bit flimsy, so I expect the handlebar shim I put behind it, which is also aluminum but much thicker, was necessary in my case.

bulgie 

Ooh that's really nice, maybe too nice? I might make myself one, for a bit less $$ and also I think the scarf angle should be shallower. That'll mean more turns needed on the screw, but more sideways pushing force. They probably made the right decision to keep the pushing force low for the intended use, pushing on the unbutted thin part of the seat tube below the lug, but I want MORE POWER! And I trust myself not to overdo it when using as intended, just to hold a frame in the stand. Actually I should make a couple sizes, to cover French bikes as well as 27.2.

"To a man with a new hobby lathe, everything looks like a turning project."

Mark B

gugie 

Shims are in compression. As long as the material is strong enough to withstand the sheer stresses, I wouldn't worry much about them being aluminum.

I'm reminded of the shim stock story in Zen and the Art of Motorcycle Maintenance. If aluminum shim stock (beer cans) can be trusted to keep your handlebars tight...

markk900

Love that anecdote and came in handy - had a spun bearing in a car carrying trailer that we repaired with a beer can shim - got us home.

jdawginsc 

I almost bought the Sten tools doo-dad a while back, but at $65 it really only would be useful for 26.6 to 27.2 frames (which are most, but not the ones 25.4-26.6)

As a frame holder, by the way, not as a de-ovalizer.

bulgie 

Yeah I meant when the "shim" is more of a force-spreader, for when you want the point-like load of a too-small "pusher" to be applied over a larger area of the inside of the tube.

But even then alu is probably fine, most times. Plus, some of the time I don't even want a force-spreader, I want more of a point force right where it's needed, then repeating as necessary, sometimes moving the prientation between iterations. Better control over what's happening.

From my time in production shops making a thousand+ frames, I tend to think of tools as something that need be used many times over years, and aluminum would not be good for that. But OP just wanted to fix one frame — alu is almost certainly adequate for a one-and-done. I retract my earlier recommendation for steel!

Mark B

Andy_K 

This is what I was thinking and why I like the idea of the shim matching the intended size of the opening, but as I think through it I can see why the material doesn't matter so much.

The way I was imagining it, the shim will be pushing against an ovalized surface that has a larger effective diameter when contact is made and the force will all be applied at the point of contact, but as the opening is spread to become round again, the shim will make contact with more of the surface area and the force will be distributed, so it kind of naturally deters ham-fisting it. I had initially thought that if the shim deformed, that effect would be lost, but now as I think through where the forces are being applied, there will be nothing applying a force that would deform the shim (because there's only the central point of contact when the frame tube is still ovalized). If you were pushing the shim against the narrower sides of the ovalized tube, which have a smaller effective radius than the shim, the shim would deform, but you shouldn't be pushing in that direction, right?

ThermionicScott 

I've played around with this idea, but can't find if I've posted my results. One drawback I can see to having it match the size and shape of your seat tube too closely is that you might over-expand the whole thing when trying to push out that last little bit.

gugie 

The forces to enlarge a steel tube diameter are far beyond what Andy's "expansion tool" could provide. If this weren't the case, DIY double-butted steel might be a thing.

Road Fan

I had the same thing on a motorcycle wheel. Having read Pirsig gave me the idea such a fix was ok. I unlaced the hub and degreased it, warmed it in the oven, Somehow I snuggled the precut (handcrafted, lol) shim in then the bearing. Let it all cool down to room temp and went forward to reassemble the hub, relace and true the wheel, remount the tube and tire, check trueness, then reinstall and get back on the road. Quieter! had to true the wheel a little more ...

ThermionicScott 

Even when it's slotted at the top?

gugie 

My assumption is that Andy would put a binder bolt in while doing this.

ThermionicScott 

Oh! I didn't even think about doing that, but there it is in the pictures. When I did it to my old 3-speed, I left the bolt out and just kept pushing a bit at a time and re-checking.