wordyshaman

I've recently had the luck of picking up a free frame-- a vintage lotus.

but the downside is that there is a pretty big fracture on the downtube, going almost all the way around the tube. I've thought about doing something like a fillet braze across the gap, but I'm afraid it might prove to be the weak point in the frame. Tig welding seems like the safer choice, but I don;t have access to that kind of equipment.

here's a pic of the gash. The previous owner sawed off the brazon shifter bosses and went a little too deep.

Mind you, I've never done any type of brazing before, so any input is welcomed

wrk101

If you do a search, you will find Tig welding to be routinely recommended. A nice Lotus is worth the cost, if you can find someone to do it. You need a professional welder to take care of it. I hate to see a Lotus ruined like this. I love my 84 Classique.

ultraman6970

Can be fixed? yes it can. How? If you know how to use a oxyacetylene, flux and stuff i tell you how. With tig will look too rough, it is easier but nah... oxyacetylene it is the way to go.

Basically u have to braze a metal sleeve (use another downtube piece from a junk bike) inside. Once you are done, sand it really well and you are done.

I would recommend to post this into the frame builders thread. I mean if you don't know how to use a torch better find somebody to do it for you. The finishing doing it this way is way better than using TIG in my opinion.

Easier to say than do it anyways. I have seen my master builder do it several times and for him is pretty easy. 30 mins or so.

Good luck

biker128pedal

It's a lug frame. Couldn't the tube be replaced?

FlatFender

Probably wouldnt cost much more than having it welded.

ultraman6970

yes it can be replaced too. whats less expensive for you.,

wordyshaman

This sounds like something I'd be interested in trying out-- DIY and low-budget

how was the sleeve fitted inside the original tube? would there be a lot of cutting involved? My main concern is having the inner piece stay in place during brazing. And will a propane torch do instead of oxyacetelene? I know the temperature won;t go as high, but any chance it can be compensated for by a lower-temperature silver braze?

wrk101: that is a great looking bike there! with some luck I'll be able to restore this bike to as fraction of its former glory

Thanks for the replies everyone

ultraman6970

I saw my master builder do the sleve trick many times. From what he told me one day the flux keep the sleeve in place, like glued it. What happens is that if you cut a tube the same diameter (technically a little bit smaller diameter, just cut a down tube piece from another bike and cut it in the middle then u'll be able to put it inside) than the down tube and you put it inside, the sleeve will fit pretty tight and barely move. Always u can use a pin or something to be sure it is in the right position, then cut it or something.

I believe people have gotten some success using map gas. I think the flux it is the most critical part because w/o the flux the silver or whatever u want to use wont reach the desired areas.

I recommend you again to post the question at the frame builders group they can give you more details.

Thanks

DannoXYZ 

There are multiple variables here and you have to juggle them with costs as well.

1. inner-sleeve. This structurally will work. However, how will you get it inside?

2. tube-replacement. Similar to above. In order to fit an inner sleeve, you'll need to remove at least two joints. The lug at the head/downtube and the head-tube. For the same effort, you might as well remove the downtube and replace the entire thing. Both of these procedures will require a precision jig to hold the pieces in alignment while they are loose.

3. TIG the crack. This will actually be the simplest and least costly. Will also ensure correct alignment as none of the lugs or tubing has to be removed. A butted joint that's filed down and polished will be strong.

However, in all three cases, this repair will be at one of the most highly-stressed part of the frame. You'll want to be careful about stress-risers. A sleeve will need tapered ends that blend smooth into the original tubing and you'll need to ensure that the silver/brass used has flowed to the very end.

HillRider

Depending on what you do, if you repair this frame it will certainly no longer be "free".

bikemeister

I think it depends on what you intend to do with the frame. If you're going to be married to it, I'd replace the tube. If it's to use awhile and then sell, have a professional weld it up.
Since it in a high stress area, you don't want to take any chances. Being you're a self admitted "newbie" welder, I wouldn't risk doing it myself and then having the frame fail on a downhill sprint or hard pedalling on a busy street. The hospital trip will certainly cost you!!!

well biked

+1. I mean, the whole idea behind making something like this worth repairing is that it's a nice frame with nice tubing (what kind of tubing is it?). If you send it off and have it repaired by a professional, yeah, they can replace the tube with something appropriate. Anything less, and my thinking quickly becomes, "hey, there's a lot of nice frames out there without a big crack in the downtube." Not worth the trouble or expense-

wordyshaman

This does sound like more trouble than the bike is worth. I'd venture it's some kind of tange, not exactly rare stuff. What attracted me to it was the solid-looking dropouts. It was going to be my beater bike, but at this point it sounds repairs will be a little risky.

But I'll probably give the sleeve idea a try.... it's winter break and there's not much else to do; sooner or later I'll be tempted to try it out, haha. I'll post the results here if I decide to go through with it.

Again, thanks for all the suggestions!