My tig welded 'conical 853' has developed a crack headtube to down tube 13.6mm one side, and 7.9 the other. I use mig welding a lot in my work, can I weld this (I can of course) but will it change the properties of the 853 through the heat process mainly, to warrant not repairing it? Any other issues I should be aware of before attempting....
I doubt that's the metal that's cracked. A crack will follow a weld, or a stress point on one tube. I'd say that's quite possibly a crack in the paint or the laquer.
very unlikely that that is a metal crack... 853 is an air hardening steel, so the heating process actually make the frame stronger. If I were you i'd strip the area back with some nitromores or similar and have a look under the paint.
I wish that was the case Peter - I'm 99.9% sure it's a crack.
Did soulrider's not go in a similar fashion?
In any event 'd be checking it is a crack then asking a frame builder...IIRC MIG welding isn't used on bike frames for a reason!
Well all I've got to go on is one pic. And to me, that looks like a paint problem. If you're that sure it's a crack then you'll be ruining the paint anyway, so why not do as Nols suggests and strip a bit of paint off and have a look? If it's cracked, get it off to a framebuilder, if it's not, £30 at the powdercoaters and you're good to go! 
I'm awaiting reply from frame builders. That's the sort of info I'm looking for cynic-al. I've worked with steel for over 25 years, so the actual welding would be a piece of pi$$.
I think it may be due to the tubing thickness that MIG is not used (which is why you see it on only the cheapest of frames.
Yeah, of course I would need to strip the area of paint to weld it anyway. I have all the facilities for that http://www.peterflynnclassiccars.com but, don't want to wreck it by MIG, if that's going to be do irreversable damage.
Not the Thorn is it Pete?
Odd lines for a crack i'd say, normally they go with the weld not prependicular to it? Can you see anything inside the headtube at all?
Yep it is Paul! It's worse than I thought, just riding it round the garden and Waxoyl is seeping through the cracks both sides of the headtube, wipe it clean a minute or two later and bobbles of the stuff appear again - oh the irony!
Another bike that would rather kill itself rather than ride away from the IW!
Im surprised to say the least. Spoken to Thorn about it? No idea about their warranty tho.
Hope you get it sorted out.
You've held the frame upto the light and slowly turned it to see if there is an indent around the 'crack' itself?
Just seems wierd to go like that- if it really is a crack surely it'd have some small rippling or folded slighly?
853 is supposed to actually strengthen when welded so I wouldn;t worry about weakenign the frame - the question is really if there's enough metal there to actually successfully weld that'll hold together afterwards.
Even lookign at the pic I think the crack is nearly at the top of the TT - past that blob of sealant there.
Paul, yep spoken to Thorn, all their frames have a lifetime warranty, one of the reasons I bought it. But, they no longer make that model, the Sterling replacement they offered me is horrible, more of a touring bike with v bosses as well as disc, gone is the Reynolds tubing and it has ride limitations placed on it. No dropp offs etc. Their frame shop is gone too, so we're at stalemate on the situation at the moment. I'm sure it'll resolve itself in the end.
BTW, the pic is of the downtube joining the headtube wwaswas..
Hope you sort something out with them.
You might find you need a touring bike 'as well'
If you have access to bottles then I'd personally braze it. With a small area like that you might actually manage to braze it with a regular propane torch if no oxy-acetylene. Drill a tiny hole at each end of the cracks first.
You could then also braze on a small 1mm steel triangle gusset over the top on either side - done right it would look fairly tidy.
I would have thought SJS should be coughing up something - new paint wouldn't be an unreasonable thing to ask for (it is pretty obvious this isn't crash damage).
I thought it hardened, not strengthended? Which ctill doesnt explain the crack.
Dave Yates has got back to me, and advised not to repair it, especially as there is another similar crack appearing on the other side.
I do remember tightening up my headset/stem before the ride as I recalled some creaking, the last time - now I know the answer to that one!
SJS are still out on this one.
I had an old marin steel frame that started creaking, then we found the crack behind the headtube on the downtube.....
Pete, the only kind of repair I can think of is a bit of a bodge and would involve fabricating and welding on a strengthening plate under the downtube to try and even the load out. Otherwise it may require some pretty extensive (and probably pointless) surgery with a new headtube and possibly a new downtube too...
Pity as I always liked that Thorn.
You could always ask Dave Yates to build a lovely new 853 frame for you 
There is a possibilty that it can be repaired, by 'bronze welding' (not brazing) new head and down tubes in. Anyone any experience of this technique?
Hey Pete, can't offer any help I'm afraid, sorry to see your beloved Thorn poorly though!
Dez
I've got a little bit of metallurgical training, but specialise in er...'special steels' of other types (amongst other things). I'll be honest, welding of 853 isn't my specialism, so I wouldn't like to give a definitive answer. As you no doubt know yourself, there's a bit more involved in the application of air/self-hardening steels in this application.
If it's of interest, I know a very experienced chap that might be able to advise (he's also a cyclist & fan of steel frames), so if you want, I can drop him an email (if you could PM me a couple of photos of the crack it might be a help). The chap is thoroughly enjoying his retirement though, so it might be a week or two before I hear back off him - as he's normally off bike-touring, munro-bagging or grand-kid sitting!
I'd certainly be interested in his input - I've emailed you. Thanks
Dez - cheers
"but will it change the properties of the 853 through the heat process mainly"
a curious question
http://reynoldstechnology.biz/faqs/materials/4
"The chemistry of air-hardening steels like our 853 and 631 means that not only are they stronger than typical chrome-alloy 4130 type steels, but after TIG o r MIG welding, the heat-affected zone (HAZ) will be significantly stronger due to the grain structure formed on cooling in air. The positive result from this is a higher fatigue life for the joint - usually 30-60% better than an equivalent Cr-Mo joint. So less material can be used to achieve a particular target fatigue performance."
http://reynoldstechnology.biz/our_customers_sports_cars.php
"by 'bronze welding' (not brazing) new head and down tubes in"
bronze welding is probably slang for brazing.
Silver soldering is slang for brazing using silver based alloy.
Before cutting out the old head tube and downtube either measure the angles of H/T to Top tube and H/T to D/T plus D/T to seat tube. This will give you a guide for replacing them, or markout the layout by drawing around the frame with it placed on a large sheet of paper or plywood for example. This will make checking the new tubes easier before welding / brazing. Or there is the opportunity to change the head angle if you want, but requires some care and thought.
You can get a selection of tube thicknesses in 853 or 631 or any steel you like. Thicker wall thickness might be the better option (lower stress, stress = load/area).
http://reynoldstechnology.biz/assets/pdf/rtl_2010_parts_list.pdf
If you have air tools and rotary-burrs / small belt-sander then cutting out the old tubes will be easy, but with care though to leave a smooth and even surface on the old H/T and BB shell to be brazed to.
"Waxoyl"
to braze anything it needs to be clean, very clean, so any waxoyl needs to be thoroughly removed.
Thanks Macavity,
yes I have since discovered that bronze welding and fillet brazing is the same technique. My concerns over the heat, was re-heating a previously TIG 853 joint - the top tube. I should have made that clear.
I probably won't actually do the work, if I have it repaired - other than perhaps paint. Although, it wouldn't be inconcievable as I do have some oxy/acetelene kit, no bottles anymore - yearly rental was too much for the use I got from it.
Cheers
I've plumbed for the repair - I'll put up a pic when I get it back.
Custom or self buid custom another day..
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