downtube replacement problem

[duanedr]

Hi all,
I was given a frame that had a buckled downtube and was told that if I could fix it I could have it. I thought this might be a good learning opportunity since the DT is oval at the BB lug - so I took it. I got the old downtube out but destroyed the HT/DT lug. I bought a new lug and DT, squished the tube at the BB junction to fit the BB shell but, then found some other issues with the frame. I don't want to give up as I still think there is some learning to be extracted from the experience. I took a stamped lug I had that was intended for practice and cut the DT stub off and was preparing to do a sort of bi-laminate kind of thing but then thought I should ask around a bit whether i'm going at this the right way or not or if I'm just going to make a mess.

If I clean up the HT lug and miter the DT per the markings on the picture and then fillet braze the DT onto the lug with brass and then silver braze that to the HT, I should be ok, right? the DT is slightly larger than the DT stub was.
DTHTjunction.jpg

There are other issues with the rear of the frame so, it won't be ridden but, I do want to still see what I can do here.

Here's another one I was given. I replaced the top tube which was cracked but then found the ST appears cracked at the BB shell. It looks harmless for now so, I may build up for my son as a fixed gear to ride to school until it cracks or he grows out of it. He wants to paint it day-glo green with day-glo orange wheels. ??? It was my first use of silver (System 48) with lugs.
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thoughts, advice, ridicule?
Thanks as always!

[Eric Estlund]

the ST appears cracked at the BB shell. It looks harmless for now so, I may build up for my son as a fixed gear to ride to school until it cracks or he grows out of it...
thoughts, advice, ridicule?

If every one of the main tubes was broken, I'd walk away.

Take the DT you have and the seat tube you would need and just start in on something sound.

With every tube in bad shape odds are good the BB shell and rear stays are also compromised/ stressed. A good lesson in frame repair can also be when to walk away.

*Edit- I see these are two frames. The above still holds. On the first one, you may consider reshaping the lug more then adjusting the tube. It may also be worth doing both the sweat and fillet ends in brass at the same time.

[EricKeller]

If I clean up the HT lug and miter the DT per the markings on the picture and then fillet braze the DT onto the lug with brass and then silver braze that to the HT, I should be ok, right?

There are other issues with the rear of the frame so, it won't be ridden but, I do want to still see what I can do here.

since you aren't going to ride it, I don't think there is any question you should do what you want and see if there are any problems.

On the Bianchi, any reason why you wouldn't replace the seat tube? The secret to extracting tubes from lugs is to heat the tube, not the lug. And be patient

[duanedr]

Thanks for the input. You're really confirming my approach which always feels good!

The celeste frame had a cracked top tube which I replaced only to find that the seat tube appears cracked as well. it's fairly clear from the rest of the bike that it's lived a hard life so, I would imagine other cracks are not far away. My 12 year old son rides to school a few blocks away and right now, day glo bikes are all the rage among the cool kids so, we'll do that and watch for spreading cracks and toss it when it happens - to your point of knowing when to walk away. That should give me time to build him something myself.

The red bike had a buckled downtube and as I was working on it, I noticed left chainstay has either been kinked (how I have no idea??) or there was ongoing tire rub which has worn a groove in the tube so, i'm guessing it's not far from the junk bin either.

They were both acquired for free with intention of practicing skills so, i'm fine cutting them up as soon as i'm finished.

thanks again

[duanedr]

<< The secret to extracting tubes from lugs is to heat the tube, not the lug. And be patient >>

AAhhh, makes total sense now that you typed it out loud.

[cicli polito]

The secret to extracting tubes from lugs is to heat the tube, not the lug. And be patient

Just for another perspective, I have never, ever had good luck with heating the tube and not the lug in all of the replacements/repairs I have done. That doesn't mean it doesn't work though (more than one way to ____ a ____) and it's all based on what works well for you.

I do the gravity + hanging weight + big ass flame + heat on lug method. The key to this is the technical jargon: "big ass flame."

With regard to your original question, I agree your bi-lam repair at the HT end is a fine way of going about it, and I agree with Eric above that you should do both, with brass, during the same heat cycle.

[EricKeller]

I'll have to try the big-ass flame method next time

[MrkiMedo]

I do the gravity + hanging weight + big ass flame + heat on lug method. The key to this is the technical jargon: "big ass flame."

when applying "big ass flame", is there a risk that lugs or neighboring tubes can be overcooked ?

[cicli polito]

when applying "big ass flame", is there a risk that lugs or neighboring tubes can be overcooked ?

Definitely

[MagicCycles]

Sweet! The last Repair I did was a Tig welded bike. No Joy on heating anything. I just employed my trusty rotary tool and cut the bugger out. See the before and after photos.

Oh and I like the "Bigg Ass Flame" approach.

Cheers G
IMG_1969.jpgIMG_2072.jpgIMG_2089.jpgIMG_1972.jpg

[steve garro]

Sweet! The last Repair I did was a Tig welded bike. No Joy on heating anything. I just employed my trusty rotary tool and cut the bugger out. See the before and after photos.

Oh and I like the "Bigg Ass Flame" approach.

Cheers G
IMG_1969.jpgIMG_2072.jpgIMG_2089.jpgIMG_1972.jpg

I have to ask - seized seat post gone bad?
Only way I have seen that damage there.
- Garro.

[MagicCycles]

Steve,

YUP! Somehow he got the Seatpost seized. So he had some bozo cut it out at a "Machine Shop" /Bike shop. The ST was filled with metal fillings and looked like a piece of swiss cheese!!! He has a new seat post installed which was super long (approx. 400mm just to guess). It was the only thing that was providing structure for the frame and the ST. He also had the tube wrapped with "Gaffer's Tape" which is a cloth very sticky tape. He actually rode it for about a year before a local bike shop referred him to me to fix it.

cheers,
G