Best glue to fix a crank

[zigzag]

some time ago i felt a small wobble in my right crank and on further inspection a pressed-in axle has come loose. i've pounded it out against a block of wood but never got round to fixing it (i believe it's fixable). i am wondering what sort of glue/epoxy/compound to use to keep it solid. it needs to be runny enough to get into micro gaps and become hard once it cures.

[IanN]

Would loctite 638 or 641 do it?

I'm not a mech engineer, so some proper advice required

[Jurek]

Loctite 638 and 641 are bearing retainers, and probably too viscous to do the capillary action thing you are looking for.

A thin cyanoacrylate adhesive is probably best - dob some onto some scrap plastic, pick the adhesive up with a toothpick, and use the toothpick to deliver the adhesive - rather than trying to deliver it from the spout of the bottle, where it can end up everywhere.
And don't use accelerator on it, although it speeds things up, it can compromise the integrity of the bond.

Before applying the adhesive I'd give the part a dousing / agitation (and repeat) in isopropyl alcohol beforehand, to try and ensure that the fissure is as clean as possible . If you are able to submerge it in isopropyl alcohol in an ultrasonic tank, and then dry it using compressed air, that would be ideal.

[LittleWheelsandBig]

This is not a trivial bonding problem and I don’t have enough specialist knowledge to give a specific recommendation.

Adhesives have maximum and minimum clearances to achieve their rated bonding capacity. Given you seem to have an interference fit between axle and crank, achieving the minimum clearance over a sufficient percentage of the area to be bonded might be tough. Most of the adhesive might be removed while you insert the axle in the crank.

You need something with a retarded gel time to give you enough time to refit the axle. Most cyanoacrylates set too quickly.

If you are determined to fix it, I would be trying to cool the axle to shrink it and retard the adhesive’s gel time. As long as you don’t go too far below the adhesive’s minimum application temperature, it should all work as the axle heats up after being inserted. I would be contacting the technical support folk of an adhesive manufacturer for specific advice.

[grams]

Tin foil.

(Really I’d stick it on eBay and make it someone else’s “thing I’m sure I can fix”)

[hubner]

If the crank has become loose on the axle with a wobble, I would have thought you'd need something to fill the gaps, eg epoxy with metal particles.

[Ian H]

I have had success filling micro-gaps with epoxy resin (Araldite) heated to the point that it flows freely (apply then heat).  Disadvantage is that, if it doesn't work first time, you won't get a second chance.

[sojournermike]

638 is good for headset cups in old frames, but I suspect you want ‘something more’.

291 will run into threads by capillary action, but is more threadlock and may well not be strong enough.

I’m sure I can fix it, but I have enough of those already....

[zigzag]

thank you for the suggestions so far. firstly, this crank is of no great value to me, so i don't mind messing it up, but i'd rather make it work of course. the complicated bit is that it is fairly tight fit and the axle would need to be pushed in in a controlled manner (in a large vice ideally, which i don't have). banging it in would shake most of the glue off, if it is liquid as necessary. can epoxy be cleaned off while it's still soft?

[LittleWheelsandBig]

Yes, before epoxy has cured, it is fairly easy to wipe off. Wear gloves as epoxy sensitisation is something to avoid and you don’t know if you are sensitive to exposure.

http://www.coatingspromag.com/articles/safety/2015/10/the-reality-of-epoxy-sensitization

[Gattopardo]

Would it be an idea to speak to loctite, as they have specialists, to see what they advise.  But am wary that you would be speaking to a sales person not a technical person.

[philip]

You probably want to remove the oxide layer before gluing. Sanding by hand might work, but some sort of blast cleaning would be better.

[Brucey]

if you coat both surfaces with epoxy and then assemble the joint, you can't help but end up with epoxy throughout the joint, wherever there is space for it. You will end up with a lot of epoxy outside the  joint too but that is no problem.

This is easy to try and should the joint go wobbly again, it won't be that difficult to disassemble the joint and try something else.

The bond strength of even basic epoxy is about one tonne per square inch.

cheers

[mzjo]

The correct Loctite for this is as far as I can tell 638 which is described in french as Bloc Presse fort and which is intended for things that need to be solid enough to require a press for disasembly. I have a bottle in the garage for gluing bearings into housings (although it is not a "Bearing Fit", it's a bit stronger than that).
I wouldn't recommend it in this case though. I bought my bottle 15 years ago and it cost about £35 then so it is probably more than you would want to pay to salvage the crank. I don't think it comes in those tiny (8ml?) doses that you find in accessory stores.
Best stick to epoxy. Slow setting Araldite (the proper one that takes 48 hours at room temperature to set) has done this sort of thing for me in the past quite successfully.

[morbihan]

From Waterworld out here, maybe 5200 sealant. Stuck a lot of stuff together with that over the years.