As per title really, would this product be suitable to repair a cracked seat tube (aluminium frame)?

Anyone used it before? If so, was it successful?

cheers 8)

anyone?

the list of applications they give is pretty much all stuff that's not under stress.

I'd be very wary of trusting what is, in effect, a glue for the sort of repair you want.

Also, it's not clear how hot you have to get the metal but with Alu frames you can destroy the heat treatment if you get them too hot.

Swerve it mate. Your seat tube would have the structural integrity of an ale can after a dose of durafix.

it's a 'low' temperature weld isn't it? they say it "uses no flux… …A low working temperature of 732° F (392° C)" Would this be OK?

I'll also be inserting a rod into the seat tube, fixing it in place and machining it out for a 27.2mm seatpost (currently takes a 30.9mm post).

Hoping this combination will form a good strong repair?

This is the crack by the way…

If you're doing that, then why not just cut off the seat tube at the crack, bond a new insert all the way down with a 27.2mm reamed core? 😉

How the? 😯
Not enough seatpost?

I always run a 440mm to stop that happening.
I'm amzed people will run ultra short/cut down seatposts to save g when the consequences are so severe.

looks like someone didn'#t have enough seat tube in the frame?

400 deg C is low temp for an alu weld, but your still going to be heating it. What do plan to do about post-weld heat treatment? Is this even applciable – what material is your frame (suspect 6000 or 7000 series).

As others have said, you are filling the crack with something different to the parent material. The applications listed on the website are pretty vague/non-structural. I woudl imagine that, evne if you fill the crack, it'll be back again soon enough as either the frame material local to the crack has been weakened by the heat or the filler is softer than the material around it.

Prob not what you want to hear, but if 'brazing' (because this is effectively what it is) aluminium was such a good idea why isn't everyone doign it this way? Sounds like snake oil to me, for this application at least.

The previous owner did unfortunately run it with too tall a post, though from what he says it was still past the minimum insertion point (and wasn't run this way for a very long length of time either, just one section of a run), 'twas just too much leverage for the frame design (it's an Intense Socom… picked it up cheapish off the classifieds, now I just need to repair it! hopefully… 😯 )

Well cosidering its position I would take off all but enough to put a seat clamp on and use a long post with a good deal in the frame, or take a smaller amount off and put an insert in.

I might have been tempted to work out how to fix it before I bought it 😉

We used to do local heat-treat where i used to work. Not an alu tho. So a weld repair and re-heat treat might be possible?

I might have been tempted to work out how to fix it before I bought it

Well, I did have an idea (of sorts 😉 ): 'weld' the crack with this Durafix then do the insert… 🙂

What Stoner says +1

why not just cut off the seat tube at the crack, bond a new insert all the way down with a 27.2mm reamed core?

what will that look like? I'm hoping to get a nice neat repair, if possible 😆

hmmmmmmmmmmm……

I'd not have bought it in the first place, but if it had been mine that had cracked……………

have a length of pipe machined with an OD thats a very tight fit in the tube, probably either ask intense for this or experiment with fractions of a mm over the seatpost diameter, insert this into the frame, aiming for a fit you can push in my hand but not pull out, with an inner diameter as narrow as you dare go, forget 27.2, go 26.8 or smaller if you can! Try retro BMX shops for realy narrow, long seatposts.

Then get some woven glass cloth from a chandelry, the tighter/finer the weave the better, soak strips (arrouns 1cm wide) of it in epoxy and wrap the whole area in cloth, if you can jig up some kind of vac-bag arround it, so much the better.

I've seen a SC chameleon with a completely detatched headtube rebuilt like this 🙂

Chop it off, file the crack out, bond in a good v stiff 30.9 post at the right height for your needs. Buy several saddles so when the wear out you can replace with the exact same model.

I hope it was v v v cheap.

Don't know much about the stresses that would occur on that section but how about stress relieving the area (drilling the crack ends) and using a very long seat post which is always significantly in the tube. If the damage was caused by too little post then you can ensure that that particular load won't occur again. However, whether that weld is mostly under compressive or tensile loading I couldn't say. I'd agree with consensus that that weld stuff would just fail in no time at all if the weld is under significant tensile loading.

Ooops, took ages over that post, seems I'm echoing other, which surely proves what a good idea everyone's onto!

Thanks for the advice chaps, appreciated. I did get the frame for a reasonable price (15% of new or thereabouts, once I sourced a 2nd hand shock for it), so hopefully it'll turn out to be a 'good' purchase… It'll only get occasional use, I've never really tried DH before, this should give me an excuse to! 😆

I'm hoping to get a nice repair that will be covered by a new powdercoat of the frame, so I'm trying to avoid mutilating it if possible…

How does this sound: insert a aluminum rod (right the way into the seat tube), bond this in place (with what?) and then have it machined out for a 27.2mm post. In addition, get a shop to use this Durafix stuff to fill the crack and leave a relatively smooth surface, ready for powdercoating… Will the Durafix cause any ill effects, or is the worst case that it'll just do nothing at all?

cheers 🙂

Epoxy resin will bond your sleeve in nicely. Are you also going to cut a slot out, otherwise how will you clamp the seatpost? Is a 1.85mm thick ally insert + epoxy + exisiting seattube thickness sandwich going to flex enough to do that?

Make sure it is a LONG sleeve.

You'll not do owt but something cosmetic for that crack.

Drilling the ends of the crack can be difficult, as you can't always see/guess where the end of the crack is, given the crack can be less than microscopic.

not sure you'll be able to powsercoat onto the durafix?

if it's just for cosmetics, why not just a bit of isopon over it and a rub down? The issues with heating the frame if you use the durafix still apply.

You'll not do owt but something cosmetic for that crack.

That's kind of what I thought, so the sleeve insert is the main 'strengthening' aspect of the repair, right?

Are you also going to cut a slot out, otherwise how will you clamp the seatpost? Is a 1.85mm thick ally insert + epoxy + exisiting seattube thickness sandwich going to flex enough to do that?

Hadn't thought of that 😳 Maybe a machine shop could taper the sleeve towards the end so a clamp would work OK?

I'd be very surprised if anything other than getting it welded or perhaps the GF repair will repair it in any meaningful sense.

A 1.85mm tube isn't that strong…and you don't know that the st isn't internally butted meaning that a longer post or insert will be supported properly.

Even if you fit a sleeve inside the existing reamed slot for the post (I'll digress a bit here – stay with me – not sure even it's clear cut how you do this…. the new sleeve will have to be a slight clearance fit to a) fit inside the seat tube and b) optimise the bond line – assumign you epoxy it in….. but the act of sliding the new insert in will wipe any adhesive off the insert. I would go against using and interference fit as a) you will introduce tensile mean stresses in the seat tube which will accelerate your existing crack or any other stress concentrations in the area and b) the inside profile of the seat tube MAY not be constant all the way down, so you may have to get the seat tube reamed out anyway) there is a difference in stiffness between the material above and below the existign crack. Your sleeve is going to be pretty thin, so even if it is bonded in perfectly, it will still allow the crack to flex and the crack may propagate further (the seat tube has basically no bending stiff left based on your picture and assuming the crack is the same on the other side). The tapered sleeve to allow clamping also sounds like a dodgy plan as you want to concentrate the clamping force at one location so the rest of the tube isn't stressed…. and your brittle epoxy bond also isn't stressed.

Structurally, there are so many reasons why I don't think you'll ever end up with a 'neat' fix.

EDIT: al wins fastest-finger 😉

Would my calculation be correct, you paid about £400 for the frame?

15% off new! You are mad!

I would have just about concidered it at about 80% off new!

Even if you can use an insert on that, I wonder how much strength the whole lot will have – the remaining section of seatpost welded to the frame is now a *lot* shorter, and the section of tubing above the crack, even if it's bonded, is going to add nothing to the strength. (Unless you can get the cracked welded as well, and I dunno how successful that's likely to be.)

Mebbe you may have more joy with getting someone to cut out the whole of the existing post/weld and weld in a new section, if you can find anyone that'll weld thin-guage stuff. (There's more than a few custom motorcycle builders in the uk, but I suspect the tubing they use is somewhat thicker).

I *think* Orange used to handle repairs to ally frames some years ago, perhaps they might have some useful addresses ?

FWIW I've got a mate's old Enduro frame (for the spare stays/shock/link), that's got a similar crack..

Re wiping out the bonding agent – must be possible to do it (tho' you wouldn't want an interference fit). Argos have a service to fix stripped BB shells, which is to ream them out and fit a sleeve – I assume that's bonded-in. Likewise bonding's been used on CF frames for some years, and the Windcheetah recumbent uses a cruciform of ally tubes of about 2" diameter bonded into various ally castings

Ha ha I just worked it out as £2000 which is it?

does say of new so think £400 is right.

BTW re. welding – IIRC 7000 series ally doesn't generally need heat-treating, whereas 6000 does

Wiping of the adhesive – if you were designing the joint properly, you'd taper both parts specifically so they don't slide over each other during assembly, and for the BB shells you would use a much bigger clearance between the parts so that the adhesive acts as a filler as well as an adhesive so the shell can be aligned independantly of the reamed hole. Here, as Cynical-al alludes to, the wall thickness of the shim will be a couple of mm, which limits how thick the bond line will be (to f-all!)…. plus, the shim is goign to have to be at least 200mm long and proabaly as long as you can get away with.

gaffer tape it !

>taper
Ah, I see.

He mentioned a 27.2 post – he could use 25.0, that'd give a *bit* more insert material to play with (tho' whether that's enough..)

15% off new! You are mad!

That'd be 'of' new guv'ner, not 'off' 😉

Would my calculation be correct, you paid about £400 for the frame?

I paid £230 posted for the frame, then bought a PUSH'd Roco WC shock (off the classifieds) to suit for £105 posted = £335 all in (around 15% of new price on CRC, with a DHX 5.0). I need to get the mounting hardware for the shock and that's it…

Ideally I'd like a nice tidy repair; in a perfect world one that isn't obvious and leaves me with a nice 'as new' looking frame (after powder coating). Maybe I'm after the moon on a stick 😆

He mentioned a 27.2 post – he could use 25.0, that'd give a *bit* more insert material to play with

That's true, but for the 'neat' fix, you are clamping the seatpost into the insert and then relying on the adhesive bond between the insert and the seat tube to take the riders weight on the saddle, plus any fore/aft or lateral loads….. if the OP is prepared to do this as a back-street repair then the best of luck (a pro job is goign to cost as much as he's paid already), but I don't think I'd want to ragging down a mountain only to suddenly find the insert floating about inside seat tube and the existing crack has propagated all the way through!!!!!!

Phone up Extra and ask how much a new front end would cost you. I asked when I was wondering about insuring my front end to post back for a warranty issue, IIRC they said about £500. If it's only that much, you've still got a very cheap socom.

WTF was someone doing putting the seat up on a socom anyhow?

Go nuts get it welded. All this bonding shims covering it in glue sound time consuming messy and well err shit.

Did something similar. Find a post thats .1 mm oversize. Clean the frame out exceptionally well , ditto the post. Freeze it. Warm frame and if you have got them clean enough the post will slide in. Leave to expand to fit. Cut off to give new frame. Slot as needed. use thin post to fit saddle to. Hopefully you found one that matched the ID of the one you shrunk into the frame. The numbers do match in some cases. No heat stress or force involved. It does work. I spliced a very cracked seat tube like this. Expansion bolt resin filled the crack then it was spray. Invisible joint and perfect function. Years of fun.