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slightly oval seat lug

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slightly oval seat lug

Old 08-17-15, 07:08 PM
  #1  
Ol Danl
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slightly oval seat lug

My recent purchase/project had the straight chromed steel seat post in as far as it would go, and it took clamping a vise grip on the top rim, then clamping the vise grip handle in my bench vise, then the spraying of lube and tugging and twisting on the frame for about 40 mins. to get it out. I guess it qualified as stuck. There was very little rust in the seat tube. The post measures 26.4, and the lug opening has that much space side to side, but slightly less front to back. It doesn't want to go back in -- sort of rocks side to side perched on top. I've verified the post diameter with 2 calipers and a micrometer, but I don't know if I should try a 26.2 or maybe try to file the lug out longer. The bike is a Carlton Super Course (not Raleigh), and I think I read on some thread of someone's Carlton having a 26.4 post. So I'm assuming it's the right size, but I don't know for sure.
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Old 08-17-15, 08:21 PM
  #2  
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Those seat tubes do get ovalized ! I had to recently work on a Trek a customer brought in, results of a poor shipping job.

Could not get the post out so went the cut off and saw it out route. Took 20 minutes or so. It was not too far in.

a check of the inside diameter was like what you found out, true in one direction but lacking in another. I had to send it to another shop in town to have the tube honed true.

Happy customer. Good luck with your project within a project !
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Old 08-18-15, 09:24 AM
  #3  
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Thanks for the response. I don't know if any local bike shops would attempt to straighten up this seat lug if it comes to that. I stuck a brake cylinder hone in there briefly, but it looks like it would just follow the existing shape. At this point, I think I may try a 26.2 post, and ask around about what shop might be able to do that -- maybe a machine shop?
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Old 08-18-15, 09:55 AM
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One other chance might be to get a sacrificial Seatposts and keep working it in there but not too much as getting it stuck completely and wobble it around in the bonded area. Be sure and keep a bolt clamp on the seat lug, just tight enough to keep the ears from expanding but not provide any binding itself.
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Old 08-18-15, 01:44 PM
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A LOT of bikes came from the factory with bad seat tube lugs. Some were ovalized by lugs that were out of round before brazing. Others distorted from excess heat applied while brazing on the the seat stays. Many are slightly bulged inside from over heating.



Before doing any work on the seat tube and lug, I take a large screwdriver and GENTLY spread the "ears" on the seat lug so that the split is parallel not squeezed too tight like this one.




Frequently seat tubes were never reamed or resized after brazing. The only reaming done was to remove overspray paint inside the seat tube during assembly.



We made a set of steel mandrels at our shop to round out seat tubes. That was back in the 70's.

Now I use 1/2" drive sockets to round out the top of the lug and seat tube starting with one that just barely fits and moving up one or two sizes (I have lot's of sockets).

I attach them onto a piece of 1/2" all thread rod with washers and nuts. At the top I use a larger socket with nuts and washer so that it works like a slide hammer to remove the rig after it's been GENTLY driven in.


Afterwards I ream the seat tube to size and run a brake cylinder hone into to it to smooth it out.



Most folks don't have the tools to do all of these corrections. If you take your bike to a shop to have the work done, check to see how many hammers they have on the work bench!



Try to find a shop with someone who knows how to fix your problem.

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Attached Images
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SeatLugTop.jpg (44.0 KB, 101 views)
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SeatTubeBulge2.jpg (38.6 KB, 99 views)
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Img_1706.jpg (91.6 KB, 106 views)
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LisleBrakeCylinderHone.jpg (11.8 KB, 103 views)
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BrushHone.jpg (8.7 KB, 102 views)
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SeatTubeMachining1.jpg (97.3 KB, 110 views)
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SeatTubeMachiningArrows.jpg (78.5 KB, 114 views)
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IMG_1320.jpg (88.4 KB, 101 views)
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IMG_1325.jpg (87.1 KB, 112 views)
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IMG_1324.jpg (104.7 KB, 109 views)
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SeatLugSqueezed.jpg (80.5 KB, 103 views)
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Sledgehammers.jpg (99.9 KB, 100 views)
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Last edited by verktyg; 08-19-15 at 02:44 AM.
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Old 08-18-15, 05:39 PM
  #6  
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Finding a shop that would undertake that here is unlikely -- I think aluminum and carbon fiber is mostly what they sell. When you drive in the socket to stretch the lug (I think it's only the lug that is out of round --maybe), do you go a little oversize, to allow for the metal to spring back? Like maybe 1 1/16" (1.0625) to stretch for the 26.4 seat post (1.039)? Or is that too much?
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Old 08-19-15, 03:35 AM
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Originally Posted by Ol Danl View Post
When you drive in the socket to stretch the lug (I think it's only the lug that is out of round --maybe), do you go a little oversize, to allow for the metal to spring back? Like maybe 1 1/16" (1.0625) to stretch for the 26.4 seat post (1.039)? Or is that too much?
Ol Dan, for starters I recommend spreading the "ears" on the seat lug first. The way to tell is the slot between them is the same width from to to bottom. That will frequently round out the the seat tube and lug quite a bit.

Tubes are not always round, same with lugs. When heated they may conform to each other. As I showed in my picture above, the tubes frequently have bulged areas inside the lug from overheating when the seat stays are brazed on.

That's why trying to measure the inside diameter of the seat tube with a pair of calipers isn't accurate - the bulges can be 1/2" to 1" down from the top and generally in localized areas.

I start off with the largest socket that will fit into the top of the seat tube without any force. Sometimes I only need 1 socket to round out the seat tube and lug... Sometimes 2 or 3.

A few years ago I bought an early 70's all Campy Gitane Super Corsa. I adjusted the seat for the first ride and it slid down so I readjusted it. When I got home, something didn't look right. The seatpost was 25.8mm and should have been 26.4mm! It apparently came that way from the factory.

It took some work to get the tube round....

To answer your question about "spring back", I sneak up on the bore moving it out a slight bit at a time so the tube doesn't move that much with each size socket. That way the spring back isn't significant.

I use the word GENTLY because you could crack the lug and seat tube if you get carried away!



I use sockets because there easy to work with and the all thread can be used as a slide hammer to get them out. You could use a mandrel too.

Hope this helps...


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Old 08-19-15, 06:28 AM
  #8  
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verktyg, thanks for sharing your wisdom. I'm definitely going to take my time with this, and will probably try the socket method. I think I'll probably stare at it a few days first.
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Old 08-19-15, 12:33 PM
  #9  
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I had a similar problem, used this method...

https://www.bikeforums.net/classic-vi...l#post17543598

Worked great, just take it slow and easy and check fit often.
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