mgopack42 

Seat post slipping. 1980s Ciocc. Everyone that tried to help me ID the bike assumed it was Aelle because of the 26.8 seat post. I broke the first binder bolt, and replaced it with one that didn't bottom out. Now it is still slipping, and I noticed this. The clamp ears aren't parralell, and the ear seems to show a crack in (hopefully) the paint. I got lots of advice about spreading the seat tube, and or reaming it, or shimming it. Am I in danger of the ears cracking off? Or is a bend more likely? I don't want to mess withrhwi paint if I can get away with it. Least than 2 weeks to Eroica.
thanks in advance

CliffordK

Have you tried to open that up a little, and perhaps try a 27.0 or even a 27.2 seatpost?

CliffordK

Oh, you had started another thread this morning.

https://www.bikeforums.net/classic-v...gured-out.html

Looks like the same advice.

It should be easy enough to cut the slot wider too, but that much pinching down, and I think you have an undersized post. A larger post should fit better, and be less likely to slip.

unterhausen

I am pretty sure that seat post is too small. As I said in the C&V thread, it would be helpful if you measured the seat tube down where it's not smooshed. But as Clifford says, getting a bigger seatpost would be a good test. My LBS has a collection of old seatposts, but maybe try a coop?

wsteve464

Pull the seat post and bolt assy and file/grind the gap to increase clearance between the 2 sides of the seat tube. It looks like the ears and tube have stretched possibly from over-tightening in the past.

Another solution is to buy a rack clamp for the seat post, looks like a seat post collar but tightens on the seat post only, and tighten it right above the seat tube collar ( I think Salsa makes one) Then once you can have the bike down for a while fix properly.

CliffordK

27.2 posts are pretty common. Co-ops, thrift stores, laying on the side of the street?

Open the slot and see if it fits.

Then, if it is binding more than you're comfortable, you can sand it down by 0.1mm or so all around (0.2mm total).

Either that, or if it is very close, hone the seat tube.

Lots of 27.0 posts on E-Bay. Some vintage ones too, if you don't need it too long.

https://www.ebay.com/itm/SR-Laprade-...n/254172332587

mgopack42 

Sorry i should have noted that I cross posted here, mostly to get an expert opinion on the ear being about to break off or not. All f the advice i got on the C&V, was excellent, and i plan to attempt one or more of the fixes offered there. I can get it fixed short term, I just would like to feel happy that it isn't going to fail right there. I will definitely have Gugie take a look on 4/5 when he and the bike are living together!

Andrew R Stewart 

I would be less concerned about the lug ear's crack (in the paint) and the ear breaking off then the ear beginning to distort from the bolt's compressive force. It's hard to see directly but I suspect that the lug's ears are hollow, or only lug wall thick and not filled with a sleeve or brass. Typical of a pressed lug (as opposed to a cast one that tends to have far more robust binder ears).

I would try to test fit a 27.0 and then a 27.2 post to see which fits the seat tube (and not the top portion where the lug is) best. Then manipulate the upper/lug portion to allow this post to work. After this then tidy up the binder slot's width AND LENGTH. With short slots the lug distorts more and the clamping ability is lessened. I would consider lengthening the slot to end 5 to 10 mm below the lug's lower edge and file a key hole to reduce the stress riser that a square bottomed slot has. I would also consider a slight reaming and honing of the seat tube to reduce any heat induced distortion and use assembly paste instead of grease on reassembly. Andy

unterhausen

I don't think the ear is going to fall off, just don't crank it down any more. Paint isn't intended to flex as much as it already has.

I really doubt it will take a 27.2 post, it's not that squished. Convince gugie to buy a Starrett 229b telescoping gauge for this task.

Doug Fattic 

One problem to check is whether the seat post hole is round. Sometimes all the brazing can ovalize the opening and give a false reading for the right size post. In other words a smaller seat post size will only fit through the narrowest part of the oval. When it is clamped and becomes round the smaller post is too small and extra clamping force is required.

The other problem is that your slot length is not as long as what is optimum. Even with the right size seat post in a round and not oval hole, a slot needs to be long enough to provide proper grip or not enough area inside the seat tube is applying enough force. What happens if the slot is too short is that the seat post will still slip or turn. Andy already mentioned this. The slot needs to be 1 1/8" long. Of course then the problem is that the slot is going into unreinforced seat tube. When I have repainted frames with short slots like yours, I braze on additional material so the end of a longer slot is still being reinforced. In addition the slot should be rounded and not square so it doesn't have a stress riser at its end.

100bikes

For what it is worth - you have the wrong size seatpost.

Is it possible that you have the seatpost inserted into the seat lug only about halfway?
There is a shadow in the photo which makes it appear that way.

Steel is forgiving.

Without the seatbolt in place, the seatpost should almost entirely slide in the seat tube, with some resistance
if it hasn't been honed.

Andrew R Stewart 

Doug's comment about the seat tube not being round is a good one. This frame is most likely brazed with a brass filler, most Euro frames are. It's not uncommon to see a heat distorted seat tube and lug on production frames. Sometimes the manufacturer does a better job at reducing this and/or reaming the ST to be more round (watching how thin the ST wall gets...), sometimes they don't. The quickest way to get that frame out the door is to use a "smaller then tube specs suggest" seat post and run the binder bolt tight.

While doing the exploratory work or the corrective work isn't hard to start, having an experienced hand and eye goes a long way to prevent future problems. This type of work is done less and less in most bike shops so younger wrenches might not have as much experience (as they have enthusiasm...). And the only opinion that counts is the one followed. Andy

pwyg

If I was to do a repair on that. I would 1st open up clamp by prying it open a bit. Ream the distortion out of the tube. They most likely did a poor job in the first place. You do a minimal ream to find actual size post you need. Once that is done drill a relief hole to prevent a crack. Surprised it had not happened already. Recut the slot a bit bigger. A good ream and proper fitting post will put less stress on the lug. The crack in the paint is probably from stretching of the steel. Those seat lugs are super soft and only got softer the way it was brazed. It was probably were not reinforced with a little stamped piece that used to be made to stiffen those stamped lugs.

unterhausen

taking a couple of measurements below the lug should tell you what size seatpost it should have. I didn't mention measuring front to back and side to side because I thought that the tube being ovalized was obvious. You can't make (or fix) what you can't measure