Suitable glue-Carbon fibre BB sleeve

[Brucey]

The sleeve is probably a very close fit (it didn't fall out did it?) Therefore the bonding will probably be minimal, almost unnecessary and would require an adhesive suitable for bonding two different materials and probably need to flex very slightly due to differing expansion properties of carbon and steel.

I'm off to bang my head against the nearest wall.

sorry, no, absolutely not. If there is the slightest movement or disbond between these parts the whole thing will fall apart again in a fairly short period of time, probably taking the frame out with it. CF is not even slightly resistant to abrasion, locally high loadings etc and nor is the matrix or what is left of the original bonding agent. Look at the picture. The idea that the surface in there is some kind of 'engineering fit' is just not on. The sleeve needs to be bonded in, like it was to start with.

Stuff gets adhesively bonded all the time and copes with small thermal strains caused by CTE mismatches quite well.

Normal BB cups are usually tightened so that they exert a load of several tonnes on the threaded fixings. Any experienced bike mechanic will tell you that if they are not tight enough then they can work loose and damage the mountings without any difficulty. This is exactly what will happen if a sleeve is just pushed in there with an uncontrolled fit and is expected to hold against such loads.

Prettty much a non starter I'm afraid.

Also ........ I wouldn't think it would be a good idea to clean the bottom bracket area with any solvent whatsoever. Solvent will most likely attack the resin, delaminate the weave and make the area swell, maybe not immediately.

Without seeing the bike I would imagine the bottom bracket needs to be held from one end whilst the other side is tightened so that you are not relying on the glue to hold the sleeve from spinning.

Oh and if you don't degrease using a suitable solvent you will not get a good adhesive bond. Believe it or not the resins etc they use are not going to fall apart with a sniff of degreasing solvent.... alcohol or petroleum ether will be fine. If you wanted something volatile that would attack the CF before it evaporated you would struggle to find anything that would do it.

Do some sums; if the sleeve is bonded in correctly you should be able to apply at least double the required tightening torque with no risk to the joint whatsoever. You can't hold a BSC BB as you describe anyway; the left and right threads don't work in your favour.

cheers

[Dave W]

I suggest the op contacts someone who knows what they are talking about.

It might even be that the carbon weave and resin is laid up wet around the sleeve during manufacture which would explain the tight fit and lack of any visible adhesive.

[Mick F]

I suggest the op contacts someone who knows what they are talking about.

+1

[bikes4two]

West system Epoxy should do the trick http://www.westsystem.com/ss/

For gap filling various fillers are available. There is good information about bonding metal deck fittings from The Gougeon Brothers book on boat building http://www.westsystem.com/ss/assets/HowTo-Publications/GougeonBook%20061205.pdf

Hope this helps

Hi Norman,

Thanks for those links - the pdf book was particularly informative in respect of the thinking behind their epoxy resins and its uses and applications. I've yet to read about or find anything else that quite matches the criteria in a glue/epoxy resin that I'm looking for in the way the West Systems products do.

The Fiberglass Boat Repair Kit (105-K) comes in at about £30 and contains small amounts of the 105 Resin, 205 hardener and adhesive filler that's needed here. Living on the south coast gives me access to many ship's chandlers who I'm sure will have stock.

Thank you to those who have contributed to this thread (and indeed the other linked thread on the BB issue - I will keep the BB thread updated as work progresses).

[Brucey]

...It might even be that the carbon weave and resin is laid up wet around the sleeve during manufacture which would explain the tight fit and lack of any visible adhesive.

That is an interesting notion and I suppose that is possible, but

a) the fit clearly wasn't that tight (an aluminium sleeve would have been virtually destroyed during removal if it were; certainly burred) and

b) there looks to be adhesive in the BB shell (from manufacture or otherwise) to me.

More importantly, the internal radii are strongly suggestive of a (possibly foam, more probably inflatable) core that is removed from the frame through the BB shell after manufacture. Except for joints (which might not be where you expect them to be) and assembly of subassemblies I don't think they use wet layup for mass-produced bike frames; too variable, too labour intensive. Most mass-produced frames/subassemblies are made using moulds and cores these days I think. A few are made using RTM techniques but most use pre-preg.

You can read up a bit about CF for bike frames generally here;

http://fitwerx.com/carbon-fiber-frame-manufacturing-techniques-part-one-of-a-three-part-series-on-carbon-fiber

I don't think it is too far off the mark.

You can read about current Trek OCLV CF production (which won't be a step change in every respect vs a 2007 frame) here;

http://www.bikerumor.com/2013/03/13/trek-factory-tour-part-3-us-based-oclv-carbon-bike-production/

see what I mean about the joins not being where you expect them to be?

cheers

[steady eddy]

Plus one for WEST System - I have used this for boat building and repair and for coating external joinery for many years and have even resin bonded bolts in to brick work with it. Do wear gloves as your skin can get sensitised to it. Make sure the surfaces are clean and grease free - acetone is ideal- before you try to bond with it. Only mix small quantities as it can generate lots of heat as it goes off.

[bikes4two]

I suggest the op contacts someone who knows what they are talking about.

+1

Yeh, I have tried that - the local Trek dealership said yes they have re-bonded BB sleeves before but on viewing my Trek said it couldn't be done. On the other hand, contributions to this & the linked thread suggest it is possible.

The dilemma is if you do find someone who allegedly 'knows what they are talking about' but your own knowledge is not sufficient to test that, then it's a leap of faith still.

So armed with the collective wisdom gleaned from this forum, plus my own engineering knowledge, I'd rather give it a go myself.
Wish me luck.

[bikes4two]

The Praxis conversion - an interesting concept but the BB hole in my frame is not large enough. Thanks anyway.

[cycleruk]

Cleanliness is obviously needed as I'm sure you are aware.
I would roughen the sleeve surface as is practicable.
Would it be any advantage to undercut the surface, or even ribbing, fractionally, leaving an original bit at each end.
Block off any holes in the frame, as Brucy advised, perhaps with styrofoam but leave a slight indentation to allow some grip in the shell.
There are quite a few company websites selling "glues" and some have various snippets of advice. It might be worth perusing the WEB as there are sites that are not actually connected with "glues" but have used it for other reasons. (hobby, car & boat sites etc.).
An article I picked up on stated that "5 minute" epoxy dried fast but could be brittle when fully dried. (would that matter?)
With 24hr epoxy - another said don't add more "hardener" to make it set quicker as that will leave voids in the adhesive.
And don't forget to protect the threads in the BB to stop the "glue" contaminating them.
The problem I can see is filling between the BB and shell completely to give good adhesion.
Good luck with the job.

[Dave W]

Sorry chaps I could be thick but what is the need to fill the frame with foam, add bits to the sleeve or poke fibreglass into voids?

If the manufacturers of the bike didn't need to do it - why would the op?

Bikes4two, keep us posted - plenty of pictures, you never know we might need to do the same one day.

[Brucey]

the original sleeve did fail.....

But any adhesive bonding operation relies on having a good joint area, and adhesive filling the joint which must be assembled with a controlled bond line thickness.

Being able to modify the assembly slightly allows you to control these things better even when doing a DIY bonding operation as a repair.

cheers

[Dave W]

Brucey, my God you're hard work!

The failure was most likely the wrong bottom bracket fitting or the way it was tightened. It was probably overcompressed - enough to crack the bond and buckle under pressure.

[Brucey]

the original BB sleeve would have seen a large tension load when the ST BB unit was fitted, as originally discussed, and this would have contributed to the failure.

I think they only made the Madone frame with that design of BB sleeve for a couple of years; the sleeve was basically the same as in other Trek frames but I wonder if they removed a bit too much CF from the BB area in that particular frame design? I think that these sleeves were not perfectly reliable even if a H-II BB is used.

As others have suggested it is very difficult to assemble a sleeve like that in a BB shell like that whilst ensuring complete adhesive coverage. Anyone who has assembled parts like these would know that. The suggestion of using foam plugs is a good one because it makes it much easier to ensure complete adhesive coverage in the joint without introducing stress raisers down the plugged tubes.

BTW on the subject of basic adhesive techniques;

-roughening is a good idea
- degreasing is essential
- controlling bond line thickness is important
-complete adhesive coverage is essential

On the latter point if you are bonding one tube inside another, the only simple DIY way to ensure full joint coverage is to block any holes in the wall of both tubes, apply adhesive to both surfaces, then assemble the joint carefully. To a first approximation you need to use about double the minimum quantity of adhesive to be certain that there are no regions without enough adhesive in them. If it sounds like you wind up with half the adhesive splurging out of the joint, that would be about right. If you want to stop the surplus adhesive from getting stuck the threads, you can use vaseline. However it is a worry that this might get into the joint; it wouldn't take much to corrupt the joint. A (faintly devious) alternative improvised 'stop-off' material is to use correction fluid. Adhesive won't stick to the threads with a coating of this in the way, and any contamination of other surfaces is blindingly obvious.

If you are mixing epoxy resins the two parts can be incredibly viscous which can make them difficult to mix without getting bubbles in the adhesive that won't float out. It is normally the case that they are much easier to mix, apply etc if they are a little less viscous. A simple way of acheiving this is to heat the materials slightly before you start to mix them. Some materials become about as viscous as single cream when heated this way, vs more 'treacly' when cold. This will also reduce the working time and shorten the curing time too if the temperature is held above ambient, but the joint strength is improved with many epoxies if they are cured hot. Check the application notes for the adhesive. You may find that applying hot adhesive to a colder workpiece will immediately increase the viscosity of the adhesive once it it on the workpiece and sometimes this is a good thing; it is easy to apply and then stays put for a bit longer.

As someone else pointed out there are dozens of little tricks that are useful to know when tackling jobs like this. At least this joint is more or less self-fixturing; some jobs are almost impossible to do because the parts are not self-fixturing and the working time of the adhesive is so long that the parts will move.

cheers

[nullemont]

contact Trek for advice on what to use. Contact details are on their web site.

[cycloret]

(I'm not sure which of the two threads to post in, as this is the most current, here goes.)

I'm following this thread with some interest. I bought a Madone 5.5SL frame on eBay a few years ago. By fitting a Hollowtech-2 BB it looks likes I've avoided the OP's problem. I've another carbon frame to which I was thinking of fitting a square taper BB.

Would it be most ill advised to fit a square taper BB on a carbon frame designed to use a Hollowtech-2 type BB (outboard cup bearings)? To do so would invite BB failure as experienced by the OP? Is this the most likely cause for the failure?

Are all square taper bottom brackets just as bad as each other in this situation? There are different sorts of ST BBs, traditional with free ball bearings, Shimano or Campag cartridge BBs, TA cup and ball-race type and others perhaps.

Assuming the OP gets the sleeve fitted, is a Hollowtech BB his only option?