which Loctite for loose headset cup?

[gregoryoftours]

I'm looking for a loctite retaining compound suitable for use with headset cups. Would 638 be ok? There are so many different types and it's not clear to me which is most suitable.

[Brucey]

I would suggest that you might be better off with araldite if there is any appreciable gap; IME it works better than bearing retaining compounds, which are

a) not really designed to fill appreciable gaps (they sell a gooier version that doesn't run away for this purpose) and/or
b) often only cure properly on bare metal (steel) surfaces, and thus don't give full strength on painted or plated surfaces.

hth

cheers

[Gattonero]

I'm looking for a loctite retaining compound suitable for use with headset cups. Would 638 be ok? There are so many different types and it's not clear to me which is most suitable.

The 638 is a high strength and formerly able to cope with gaps up to 0.2mm.
In practice, even when properly degreasing the surfaces you don;t really get the full strength nor the filling ability. If the headtube is so severely stretched you may need the thinnest shim you can make, as reinforcement.
The adhesive strength is not 100% on alluminium, but even on stainelss steel it will reach full cure, it only takes longer time.

I've had mixed results with it, as the headset is subject to several forces. Epoxy resin may do in extreme situations but is harder to remove and takes longer to cure (needs air, as opposed to the Loctite 638).

[Brucey]

Epoxy resin may do in extreme situations but is harder to remove and takes longer to cure (needs air, as opposed to the Loctite 638).

epoxy resins do not need air to cure; there are many different formulations but air isn't needed with any that I have encountered to date!

cheers

[cromo]

A long time ago I had a loose headset cup. I measured the headtube and cups with vernier calipers and used steel shim to make up the difference and give the correct interference fit. I did use a headset press for the installation and was expecting the metal shim to crease or tear as the cup was inserted, but it went in perfectly. Maybe I was lucky! I considered that repair as permanent and did not have any further issues with that headset cup.

[Gattonero]

A long time ago I had a loose headset cup. I measured the headtube and cups with vernier calipers and used steel shim to make up the difference and give the correct interference fit. I did use a headset press for the installation and was expecting the metal shim to crease or tear as the cup was inserted, but it went in perfectly. Maybe I was lucky! I considered that repair as permanent and did not have any further issues with that headset cup.

Yes you were lucky.
On a very thin gap is not easy to make a consistent shim to begin with, and to press it, too.

[Gattonero]

Epoxy resin may do in extreme situations but is harder to remove and takes longer to cure (needs air, as opposed to the Loctite 638).

epoxy resins do not need air to cure; there are many different formulations but air isn't needed with any that I have encountered to date!

cheers

While every time I had to use epoxy in confined spaces it defintely took a lot longer than usual. I guess depends from the epoxy itself and how reacts with different materials.
Perhaps you were talking of very big gaps? (which makes me think that non-integrated headsets are prone to fail in some frames)

[NATURAL ANKLING]

Hi,
Epoxy does require mixing well, also when it ages in the tin / container it takes longer to set.
Probably dependant on the use and thickness and temperature too.

They do make a gap filler (Loctite) IIRC will fill up to 0.5 mm, but can not find the info now.
Plastic Padding do Chemi metal filler which is excellent for gaps in this sort of thing, epoxy of course.

[Brucey]

While every time I had to use epoxy in confined spaces it defintely took a lot longer than usual. I guess depends from the epoxy itself and how reacts with different materials.

the reaction times vary with

- the materials you use
- how well they are mixed
- the ambient temperature during curing
and, er, that's it.

Epoxy resins undergo an exothermic cure (i.e they generate heat as the glue cures). Unlike typical threadlocking compounds there is no reaction with air, lack of air, water or anything else required; you can even cure epoxy resins even in a vacuum (provided the liquid constituents don't boil at low pressures). Possible residual thermal stresses in the joint aside, you get the strongest material (most crosslinking) if the epoxy is cured at high-ish temperatures (eg above Tg, the glass transition temperature).

Epoxy resins stick to metals etc in part because there are polar OH functionalities within the structure. Again (in contrast to other adhesives and threadlockers) whether these react or not with the abutting surfaces doesn't affect the cure per se even if it does affect the strength of the joint.

FWIW if you try gluing large lumps of metal together using epoxy it may appear to take longer than normal, but that is almost certainly because the parts are acting as a heat sink, thus inhibiting the self-acceleration of the cure (due to exothermic heating) that would otherwise occur.

If you want to fill a decent sized gap with epoxy, it is a good idea to use a filler of some kind. It is also a good idea to coat both surfaces but then assemble the joint just before the glue starts to thicken (any unused residue can be used as a guide to this, provided it is kept at the same temperature). Once the glue starts to thicken properly, you can heat the joint (eg using a hairdryer) and this will generate the strongest bond. However if you use too much heat, too early, the glue will tend to run out of large gaps before it has reacted.

BTW if you have 'old epoxy' it may appear to have 'gone off' in the container. Actually this rarely happens (unless the wrong lids have been put back on the tubes, or some other mixing has occurred); in reality the unreacted materials used are prone to crystallising over time and this can make them go hard. This can be 100% reversed by heating (a bit like with honey) and the materials can be made liquid again. Provided the working time of the adhesive is not going to be unduly shortened by so doing (which might be the case with some rapid type epoxies, but not usually with other types) you always get better, easier, mixing and a better end result if you heat the mixture as you are mixing it.

If you are doing a small job, a convenient method of heating is to half- fill a jam jar (with a good lid) with hot water and then to mix the glue on the top of the lid, which will be nicely heated (via the condensing steam within the jam jar) for several minutes.

cheers

[NATURAL ANKLING]

Hi,
While we are on it.
Opinions on Large Gap Loctite 660, for the OP?

I have just bought some Loctite 290, which is med strength thread lock which seals and is wicking, I use it for most stuff?

[9494arnold]

On my Cycle Mechanics advice I utilised a Shimano 105 headset which has a sprung ring outside the outer face of the interference area (I hope this makes sense..) on the lower race. (It was a few years ago, don't know if current 105 is same?)

[Gattonero]

Another thing to keep in mind, is that a noticeable gap is a potential failure for the headset if this is not fitted keeping it on the same axis: it only takes 0.2mm of offset between the top and bottom cup, to create an unfavourable situation.
Though the offset angle is modest, when thinking how long the headtube is vs the discrepancy, it is enough to get the ball bearings working off the ideal plane on their bearing race. Even before calculations are made, it's the field that shows too many of those problems arising from imperfect headset fit.
My advice would be not to keep the cups with a press, but with the actual headset completely fitted and made to spun, so to self-center the top and bottom cups when the adhesive is still curing

[NATURAL ANKLING]

Hi,

My advice would be not to keep the cups with a press, but with the actual headset completely fitted and made to spun, so to self-center the top and bottom cups when the adhesive is still curing

Yes, its a given this is how you would do it for sure.

[gregoryoftours]

My advice would be not to keep the cups with a press, but with the actual headset completely fitted and made to spun, so to self-center the top and bottom cups when the adhesive is still curing

Yes that's how I'd do it. Thinking that I will probably use epoxy, but I do want to be able to get the headset (a nice old Chorus threaded) out without trashing it or having to heat the frame and destroy paintwork etc. Is this gonna be a problem or will some sharp whacks with the expeller shift it even with expoxy?

[gregoryoftours]

On my Cycle Mechanics advice I utilised a Shimano 105 headset which has a sprung ring outside the outer face of the interference area (I hope this makes sense..) on the lower race. (It was a few years ago, don't know if current 105 is same?)

Do you mean a split crown race? That's good if your fork crown race doesn't fit well but doesn't help with cups that are a loose fit in the head tube.