palisader

Hi all,

I bought a 2006 Felt F1C (new old stock) carbon frame. After building it up, I knocked a metal shim within the seat tube loose. The seatpost clamp only connect to the shim, which is to say the seatpost has no way to be fixed to the frame. Does anybody have any experience with this. My plan is to go at it with JB Weld.

Andrew R Stewart 

Ever thought of showing us a photo? Seat post shims are generally a sung/sliding fit inside the frame. A thick and filler containing epoxy, like JB Weld, might not be the best choice. I would thing a slow setting "normal" epoxy (like DP 460) might be better. But not knowing what kind of fit the shim has all this is speculation. Andy

palisader

Good idea. Attached here. It is difficult to pull out further than this, and I do not want to break something by tugging too hard. I might try to cool the shim with ice and then try to pull it out (I am putting in a seatpost with a seat to pull it out). Thanks for any help.

veganbikes

The shim would not be for the collar. Possibly to stiffen seatpost or properly size for a 27.2 seatpost or prevent corrosion or something.




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palisader

Thanks for the reply. So the shim is for the collar, and it narrows it to 27.2. That is, in the first photo, the shim is at the correction position, and the collar wraps around the part of the shim protruding from the frame. It is supposed to be fixed tight to the frame (based on how tight it was before, it came loose when I was making sure the seat post was snug, maybe I pulled a little too hard).

SoSmellyAir

So the seat post collar only goes around the shim without touching any part of the CF seat tube?

palisader

That is correct.

Trakhak

You might try emailing the Felt website for advice. The tech guys there were very helpful when I needed advice about the parts I needed to build up a 2006 NOS time trial frame.

Crankycrank

I don't know the correct answer but I would double check that the shim is supposed to have the clamp on it since the CF Seat tube has a notch in it to provide for clamping forces. Just mentioning that it's a possibility.

palisader

This is a good point. However, the shim was a notch in it (if you look in the second photo) and actually cannot be inserted completely into the frame. Then, the collar cannot possible be placed anywhere but on the shim. But it does raise the question, why would the seat tube also have the notch. I am not sure.

SoSmellyAir

Absent more specific advice from Felt, it seems the only two choices are to either (1) completely remove the shim or (2) gently tap the shim back into place. Is either possible?

palisader

Tapping it back in place is not sufficiently secure. It is free to rotate (but not move vertically). So I think I need to remove it, but I am struggling to do so without excessive force. I messaged Felt, so I will see what they say. Thanks for the advice.

icemilkcoffee 

Measure the outer diameter of the carbon seat tube. If you are lucky, it could be close to one of the stock sizes for seat post clamps
https://www.wolftoothcomponents.com/...seatpost-clamp
And then you can just put a clamp over the carbon tube.

squirtdad

it would seem that is the collar clamps on the shim, then if glued it would tend to break the glue joint with clamping... so thin, flexible maybe ? https://www.amazon.com/WEST-SYSTEM-f...02IZFPQE&psc=1

palisader

I am hereby updating everyone, with images. I pulled the shim out, with great effort, and unfortunately, despite my best efforts, I introduced a hairline crack (which I was making so sure not to do, but I accidentally pushed against the groove in the CF seat tube). I also did not have gloves so lord knows what carcinogens I exposed myself to.

Camilo

I don't have the same frame as yours, but it's a Felt Z frameset of similar vintage. It has what appears to be the same seat tube construction as yours.

I can tell you that the clamp definitely clamps onto the insert, not the carbon fiber seat post. It doesn't touch the CF, except resting on the top lip of the tube.

There is a metal insert inside the CF seat tube like yours. Mine's black anodized, but same principle. I call it an insert, not a shim - it is structural, not just taking up space as a shim, as far as I can tell. Yes, it reduces the ID of the seat tube to 27.5, but it provides the metal structure to clamp the seat post instead of the CF.

The metal insert protrudes about 1 cm above the seat tube. I haven't put force onto the metal insert (only hand strength on the insert itself, just now), but it doesn't slip to rotate or up and down. I've ridden the bike for over 10 years and the saddle has never twisted on it's own, nor have I tried to twist it. It certainly doesn't slip up or down as long as the clamp is torqued properly and I use assembly paste.

Both the metal insert and the carbon fiber seat tube have slits. The seat tube slit is at the rear, and one of the insert's slit lines up with it.



There is a thin metal shim that is around the protruding part of the metal insert. It also has a slit. The seat post clamp strictly clamps on the protruding part of the insert (via the shim)



The seat post clamp has an inner lip which prevents it from slipping over the carbon fiber seat tube. It clamps on the metal insert only (via the shim). I don't know why the carbon fiber seat tube has that slit, maybe so it can flex a little under clamping because the metal insert is bonded so well that when it flexes under clamping, it flexes the CF seat tube with it.



As a comment that does nothing to assist the OP's current situation - if I discovered that my insert slipped with super-minor force, i.e. not heaving on the saddle to see if I could twist it, I'd have probably pulled it out as far as it came with easy hand strength, smeared some epoxy on it, and put it back into place, assuming it was limited to how far it goes in, leaving the ~cm protrusion. Or I would have called Felt or contacted a trusted local bike mechanic to look at it and advise. But, I really doubt there's a lot of twisting force the insert is subjected to so my inclination is to think it would have been easy to just bond it a little bit to solve the problem.

At this point, I'd re-insert it with ample epoxy. I don't know what I'd do about the crack except maybe stop it with a tiny drill hole and include hope that by epoxying the insert into the tube, it will "splint" the crack, eliminating additional cracking. OTOH, again, stopping the crack, I think it would be easy, if not pretty, to repair externally, looking up CF repair online.

Crankycrank

From the looks of your photo in post #15 with the crack circled in red, it looks like there is a weird gap below the crack in the carbon layup where no weave is visible. This could possibly be the root of all the problems. I recommend contacting Felt. Maybe they won't offer any help for a 2006 frame but worth a shot.

Kontact 

Having dealt with a lot of Cervelo steerer tube inserts that unglued themselves, I can tell you that this is a really poor design. The problem with the steerer insert is that if you glued it correctly but tightened the stem at all while it cured, the carbon would compress and the glue gap would decrease. Then you would loosen the stem and the steerer would expand away from the insert, breaking the epoxy bond.

Similar problem here - the insert is bonded to the carbon seat tube, but then the insert is compressed by the collar and its diameter shrinks, breaking the bond with the outer carbon seat tube. The rear slot in the carbon is supposed to make it flex with the insert, but it is too stiff to do that well.

So, after sanding, acetone cleaning and greasing/masking anything you don't want to get epoxy on:
Take a stub of alloy seat post in the correct size, put it in the insert and then put the collar on and tighten it down, THEN epoxy the assembly into the seat tube and let it cure 24 hours. This will pre-compress the insert so it won't pull away from the carbon when you put the seat post back into the bike. Instead the epoxy will fill whatever gap and keep the insert and seat tube in contact.


This is just a poor design, but I think pre-compressing the insert will prevent future delaminating. If I haven't stated this clearly, please ask.


Bonus method: If you want to get the best possible bond with the aluminum, I have heard of some people sanding the metal with wet epoxy on the sandpaper right before bonding. This prevents the instantaneous oxidation that aluminum gets on the surface that decreases the bond quality.

Camilo

I'm not an engineer so I won't debate whether this insert in a CF seat tube is a good or bad design. But, isn't it a fairly common design for CF seat tubes? Are there bikes where there is no insert and the collar clamps directly onto the CF seat tube? I sincerely do not know, having owned, and still own only one CF bike, the one I picture above.

That said, we have two examples of the same Felt seat tube design, the OP and mine. Mine is rock solid after at least 10 years of use (I think it's a 2012 or so frameset... I'm the original owner but without doing some research, I can't remember when I bought it.).

The OP's seems to not be working but I wonder if he stressed it unnecessarily to make it twist free?

Would it have twisted free if he'd just installed the seat post and saddle and ridden it?

Like I said above, I haven't twisted the installed/clamped seat post with the saddle so don't know exactly how solid mine is. All I know is that it's never moved in 10 years of regular use.

palisader

I stressed it unnecessarily, without doubt. I have never used a carbon seat post, and was using a low torque, so I was twisting it to make sure it would not budge. Clearly I spend too much time in the gym or something like that.

Today I applied JB Weld and inserted the shim, and made sure to wipe away excess. I however did not use the seat post, since I would rather risk the shim going loose again then cementing my seat post into the frame (I have zero experience using epoxy to do anything). I will update with the results tomorrow.

It is clear from the glue on the shim that I had to chip off what went wrong. There is simply not much contact between the shim and the inside of the seat tube. The glue is binding in only a few places, and in other places it is sticking to nothing (the curvature of the seat stays and top tube means there is no carbon to be in contact with). In fact, the whole area is just filled with glue, as if they poured it in and called it a day.

Kontact 

This part needs to be firmly glued in place to prevent the nose of the saddle moving around and the insert from beating the carbon up until it fails.

The fact the I think it is poor design doesn't mean that Felt didn't manage to make it work 99% of the time. It's just that when it pops loose like this, it is not easy to just glue back in. That's why I suggested an added procedure that might mimic what they do in the factory to keep the bond under constant compression.