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-   -   Did this weld ruin the frame? (https://www.bikeforums.net/showthread.php?t=1232703)

Syscrush 06-14-21 02:23 PM

Did this weld ruin the frame?
 
Hey all. I'm interested in this vintage mixte frame for my wife, but this booger weld makes me nervous:
https://cimg1.ibsrv.net/gimg/bikefor...e5f7bff219.jpg
It's on an old Motobecane frame which is almost certainly made of heavy gas pipe. Seeing such ham-fisted work on it makes me think that it would be crazy to trust that seat tube, but I'm here to see if I'm just being paranoid...

stevel610 06-14-21 02:58 PM

Not sure if the weld ruined the frame. I would not buy it for my wife as is.

bulgie 06-14-21 03:12 PM

I don't see anything fatal in the pic. More pics might help, unless what you've shown is the worst of it. Mixtes and step-throughs tend to have a fairly heavy seat tube due to bending loads there. I'd say "ride it and see" unless you're very risk-averse. Even in the worst-case scenario where it breaks, it will still not likely cause a crash, she'll just notice the handling get funny. Probably after a long time of creaking or clicking with each bump or pedal stroke as the crack starts small and slowly propagates. Typically the crack grows to at least halfway around before the rest lets go all at once, so you get lots of notice. Plus the crack (if there ever is one) would be in a very easy place to see.

Mark B

dsaul 06-14-21 04:21 PM

It's not pretty, but it wouldn't bother me from a safety standpoint. I've seen much worse welds on BMX frames that survived some pretty brutal treatment.

guy153 06-15-21 02:28 AM

Yes I agree with everyone, it doesn't look too bad (apart from being ugly) and probably won't fail. Especially if it gas-pipe tube-- you can get away with more since it's all just mild steel. It looks like he had a lousy fit up and then made a mess trying to fill in the gap. The ST itself probably escaped the worst of it because it's the edges of the notched tube that burn back (requiring the addition of more boogers). Actually whenever I see welds on frames that look suspiciously smooth and neat I wonder if this has happened, only they filed it down afterwards to hide their shame!

unterhausen 06-15-21 05:42 AM

I am trying to imagine why you would need to weld it in the first place. Brazing would have been so much better, because it would be impossible to clean the original brazing out. That's probably a lot of the splatter. So it may not even be a solid weld. I guess when all you have is a welder ...

guy153 06-15-21 06:12 AM


Originally Posted by unterhausen (Post 22102705)
I am trying to imagine why you would need to weld it in the first place. Brazing would have been so much better, because it would be impossible to clean the original brazing out. That's probably a lot of the splatter. So it may not even be a solid weld. I guess when all you have is a welder ...

Ah I see what you mean-- it's probably a repair. Hence all the horrible black paint. The ends of the bridge tube are brazed. So the original joint (which probably was brazed) failed and someone repaired it with a weld.

unterhausen 06-15-21 06:38 AM

Yes, it's obviously a repair, some of those rust spots are from welding splatter, which would never happen at the factory. On French bikes of this era, they would often have joints without enough filler for whatever reason. I always figured it was because the worker had trop de vin au déjeuner. Mixed weld/braze was very uncommon, although I suppose it's possible that was a spot weld to begin with. I'm not sure how easy it would be to find a good example.

dsaul 06-15-21 09:33 AM

If you look closely at the mess of black paint on that bridge, you can see what appears to be a horizontal split running most of the way through the back of the bridge. I suspect that there is a vent hole on the underside and this bike was stored outside, upside down, and the bridge filled with water and split when the water froze. That probably also caused a crack between the post and the bridge, and someone knew a guy with a welder that could fix it.

It still wouldn't concern me from a structural standpoint, but I would replace the bridge if it were mine.

unterhausen 06-15-21 09:47 AM

That's an interesting observation about the bridge. I was thinking it was u-shaped and open on the front, but it appears to be closed on the front and there are three spot welds on the back.

I would have to be getting this bike for free to even mess with it, but replacing the bridge seems like a good idea. Well, for someone that can braze, anyway.

Syscrush 06-16-21 09:00 AM

Thanks for the insights, all.

I've decided against this frame for a number of reasons. The comments and info here have been really interesting and helpful.


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