I went to see this Bianchi some time ago. I knew from the seller's pictures it had quite lot of surface rust, but it was affordable for being a lugged Bianchi and roughly my size, which doesn't come around that often.

To my disappointment I noticed there was more damage than I had expected. The non-driveside chainstay was bulging some 5 mm underneath, paint was peeling around it and there was a roughly 1" long visible crack along the bottom of the bulge. My guess is it has somehow gathered water at somepoint, and left outside the water has frozen and expanded, causing the tube to bulge and eventually, crack.

The seller said he hadn't noticed it being there before, and offered to take it to his friend's car repair shop to be welded. I'm concerned whether it's likely for it to have have rusted through on wide areas, under the paint etc. and that the car guy couldn't fix it properly because the tubes would have too thin walls or too little unaffected metal to work with.

Now, what would it take to make this frame safe to ride? I've figured changing the chainstay by a professional framebuilder (which we don't have many around here) would be more than double the original asking price for the whole bike.
I don't need the fix to look like new or to shave grams, it's fine as long as it will not kill (or seriously maim) me, if you get the point.

I just want a frame to build up with some old thrifted components I've gathered, and affordable, small enough for me, lugged steel frames are few and far between.

Do you think the car repairman could weld this so it wwould be safe to ride? As far as I know, the main triangle (3tubi) is made of Oria Cro-mo and the rest is propably hi-ten, if that makes any difference.


underneath the chainstay



rust on down tube too

If the bike had good middle to upper tier components (which in your specific bike look to be low tiered ones), I'd buy it to scavenge them; too many risks (has it had frozen water in other tubes; how much and how deep is the inside rust; how sound is the frame in general, how long before it is unsafe; how much to invest to make it rideable versus looking for another model;...?) for my way of thinking. If you really like it, and it is somewhat a kind of Holy Grail for you, by all means go ahead but, if you can, wait for something better to come along. Good luck with whatever you set your mind, as it only has to satisfy you!

If I were to find this on one of my bikes I might just ride it till it gave up and finally did something... break completely or bend everything to uselessness.

I'd never buy a bike already in this condition unless I was very very desperate.

I'm not so much in favor of just a little weld to fix just the hole/crack not knowing what other areas might be thin already too. If the entire tube can't be replaced, I'd be more in favor of brazing a cuff made from a piece of another tube around it. But that might present it's own issues, though I doubt if would be worse than doing nothing.

Hard Pass.

You would actually ride this bike? Me, I would trash the frame.

+1. If the damage you can see is that bad, how much damage is there that you can't see. Find another frame.

You seem to stress the fact this bike is lugged which I assume you place some value in. There is no advantage in a lugged bike over say a tig welded frame and in many cases the tig welded frame would be preferred. A cheap rusty lugged frame is just that. No matter what your financial situation there is no reason to consider purchasing this frame.

Toast

Be glad you noticed this before you made the purchase and just walk away.

Last week in the garage two of the mechanics has removed a body from the frame on a pickup. I asked them why, and they said it was rusted to the point where it was not safe. I looked at it and remarked that it looked fairly solid. They replied that the trouble spot is on the inside of the frame and it has become two thin to be safe.
It is the damage that can't be seen that is the problem. Find something else.

Toyota? Had a boss who bought a Tacoma from a friend and noticed a noise after a few weeks. Took it to the local dealer and 3 weeks later had a new truck, the old frame was rusted through from the inside and about to snap in half with stress cracks already forming. Was considered unsalvageable.

OP, what you can see is the tip of the iceberg, there are much nicer bikes out there.

I'd say t hat if that frame was ridden, especially at speed, an hit a bump or pothole that it might break. I think that frame if ridden would be an accident just waiting to happen. Old Mr. Murphy says t hat when something breaks it does so at the worst possible moment.

Cheers

Our local framebuilder charges US$150 to replace a chainstay without paint, which would be most of the bottom bracket area and all of the dropout burnt and I would bet he would tell you he will have to charge you something for time to even see if he is willing to replace that stay.

Yes. Until it gave an issue by bending or breaking or new bike fever grabbed me.

Then I too would just trash the bike and send it to the scrapyard. Hopefully to be melted and made into something new.

I can't imagine ever wanting to buy a bike that isn't already in virtually perfect condition.