CliffordK

Here's a question.

If you take the seatpost out, can you use the binder bolt to pinch down the crack further?

I'd have to see what the binder bolt looks like to determine what is stopping it from clamping down.

If the threaded part is too long, you can grind or file the bolt shorter.
If the shoulder on the nut is too long, you can also grind or file the nut narrower.

freeranger

Hoping it's just a reflection on the seat tube, or something, but what is that I'm seeing on the right side of the seat tube--in the pic, looks like it could be a crack? Hope I'm wrong. If it is a crack, I wonder if a clamp around the seat tube (above the binder bolt, would work to hold. OOPS- Was looking more at the rear--wonder if there is enough material in the front of the seat tube for additional clamping? Looks like the rear of the seat tube is lower than than the top of the top tube, so an add'l clamp may not have anything to clamp onto at the rear.

Shimagnolo

Go to eBay and put this in the search box: (twin,dual) seatpost clamp

Multiple mfgrs make these.
Here is KCNC's web page: https://www.kcnc.com.tw/allproducts_detail_121.html

Note when ordering, there are two diameters to consider:
- The diameter of the seatpost
- The diameter of the frame tube.

I have twin/dual clamps on 2 of my bikes.
The upper clamp grips the seatpost and positively stops vertical slipping.
The lower clamp just prevents the post from rotating.

Photo of my Calfee with Thomson seatpost:

gkamieneski

Before doing anything drastic, I would clean the inside of the seat tube fastidiously with alcohol, making sure it is free of anything slippery and dry. Then use a generous amount of carbon paste on the seatpost, insert and torque to specs.

Iride01 

Yeah, looking at the pic, it's gotta be the bolt. For the moment...

Also look at your slot. It seems to be narrower at the top than below, but hard to tell from that angle. So when you say that diameter seat post fits snug, it might be simply because the seat tube is closed up at the top. So if that's so, then maybe you do need a wider post no matter what the mfr specs say.

Also, a little ham handed tightening of the clamp from previous times might have slightly bent the clamp boss the bolt goes through or caused the entire top of the seat tube diameter to grow.

MudPie

Is the bolt bottoming out against itself as you tighten it?

tough_boots

There is definitely no crack and the gap is actually pretty even— the slight angle of the picture might be misleading. I’m feeling pretty confident the bolt is just too long. It’s the same length as the old one which I assumed was original to the bike as it was a Raleigh branded bolt. Maybe it wasn’t original. The slipping isn’t extreme— it might drop half a centimeter after an hour ride. The shorter bolt should arrive early next week so we shall see.

Crankycrank

Yes, the bolt is too long as it can't tighten up any more. You can file away some of the length of the female side and if the male threads end up bottoming out on the female threads just cut or file some of the male threads down. If you would rather start out with a new proper sized bolt at least you'll know what length works after modifying the original. Does the original bolt still have a washer for the male side? If not that could explain why it doesn't fit now.

sweeks

Grease prevents the seat tube and seat post corroding and seizing. One of my bikes has a titanium seat post and seat tube. They are lubricated with a copper-based grease. When the bolt is loosened, the post slides like a trombone, but when the bolt is tight, even my 215 pounds won't make it budge.
Your binder bolt may not be generating enough pressure on the seat tube. The threads of the bolt should be lubricated with a high-pressure grease. I like a molybdenum disulfide grease for these applications. The places where the bolt heads rotate against the frame should also be lubricated. The object is to actually stretch the binder bolt to provide the clamping force. Friction on the threads and the bearing surfaces requires more torque to achieve the same amount of clamping force. You could also look for a binder bolt with a finer thread. As others have noted, make sure the threads on the bolt aren't bottoming out. Do you have a photo of the set-up? (EDIT: Never mind!)

EDIT 2: It looks to me as if the two halves of your binder bolt are meeting in the middle. If so, there is no further tightening available. You could fit one or two washers under one or both ends of the bolt assembly, or grind a small amount off the female ("nut") end to allow the heads to be closer together when fully tightened.

Dan Burkhart 

Yeah, I think your diagnosis is correct. The 16mm bolt will probably resolve the issue.

tough_boots

Alright alright… looks like the 16mm did the trick.

thook

brilliant! i have set back silver thomson elite. very nice to adjust and super light