Sunday, December 1, 2013

Uh-oh, Motobecane Jury frame failure! (Do all TIG welded frames fail?)

Close up of the crack in the weld and tubes.
 I had an unpleasant suprise recently when I was working on My Jury commute bike. I had replaced the fenders because the rear stainless steel one had broken off at the brake bridge. After installing new fenders and reconnecting the tail light wiring I discovered a small line across the weld of the bottom bracket(above). Pushing down on the crankarm expanded the line! I got a cracked frame at the bottom bracket (hereafter refered to as the BB)!

An uncropped view to show the extent of downtube crack.
 In the picture above, you can see how the hairline crack traveled from the back of the BB and along the downtube, then it curves downward.

Another close up.
This final shot shows the crack at the BB again. The weird thing about this is that it is almost identical to the failure I had with my Surly Steamroller about 3 years ago! The failure was again at the BB and it also took an almost identical track across and then down the downtube!

I wonder if this is a common problem with fixed gear, TIG welded bikes? Or is it that the Surly and Motobecane are just too cheaply made to be good fixed gear platforms? I'm not really hard on my bikes, I'm 57 years old, weigh 175 lbs, and both of these bikes were used soley for a relatively flat commute of 26 miles a day, (round trip), but I don't ride every single work day. So, I really don't think I'm putting an unusual amount of stress on these frames. Now, I realize that the Jury is a bargain basement frame, so it is no huge shock that it failed after 3 years of use, but I thought the Surly was a better quality frame, maybe not...

I'd be interested to hear from anyone regarding this type of failure on a TIG frame, please feel free to comment!

On the plus side, this has given me the chance to shop for a new frame! I had to be thrifty though, so no exotic lugged steel custom job right now. I went bargain hunting, since my commute to work will only continue for about 7 more months, (then retirement!)!  I'm going with another welded frame, but this time something completely different. I found a Performance Bikes "Ascent" aluminum single speed road frame on sale for $89, then another 20% of for a Black Friday sales event! I also found a nice Chrome-moly fork from Nashbar to go with it.

I have never owned an aluminum road bike before, so this will be a fun experiment, and if it does crap out, it will be interesting to see if it does so faster than the TIG welded steel!

10 comments:

  1. I was considering getting one of these as a beater, but now I see I should look elsewhere. Thanks for the update!

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  2. I just wonder if this is a problem common to TIG welded frames in general? Could be the stresses of fixed gears could be too much for a TIG welded bottom bracket? I've had this happen to two TIG frames, the Surly Steamroller and the Motobecane. Didn't happen to the old Raleigh lugged frame. I'm afraid my sample is too small to draw a conclusion from. But in any case, I don't think I would spend a lot of money on a TIG frame for fixed gear riding any more.

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  3. My understanding of TIG failures in materials (steel, titanium and aluminum) is that frequently it is an 'unclean' bond / impurities in the weld that overtime create that sort of crack. Also, with that being said, I had an aluminum 'Jake the Snake' that failed in the same manner. I am not a professional welder or metallurgist, but I've heard the term 'impurities in the weld surface' bandied about and in the metalwork classes I have taken cleanliness of the steel for both brazing and welding is often stressed.

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  4. It would make sense that this would be a problem with bargain priced frames like the Motobecane. It's disappointing to find it in a Surly, but then that's not a really expensive frame either. I can't speak to the quality of the Kona, I've never seen one up close...but it seems to be priced well above either the Surly of the Motobecane. I'm thinking I'll just stick to lugged frames from now on, (although I still have a fairly new Surly LHT (26 inch) to break first!) Oh, and the Performance aluminum SS frame hasn't broken yet!

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  5. Same kind of crack at the TIG weld of my Bianchi SL Lite. This one seems to start at the TIG BB weld and go around the back of the seat tube. Aluminum tubes in this case.

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    1. Geez, Bianchis too? I guess buying a welded frame is something of a roll of the dice!

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  6. Had two MB frames. First one fractured after 5 years and second after 2 on what is essentially a commuter bike. Dangerous frames in my view. Now looking at custom bikes from US fabricators.

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    1. Fortunately, when steel fails you get some warning...my Jury frame probably was cracked for a couple of weeks before it got my attention! But, yes, my experiences have led me to not trust TIG frames as well. Too bad, because there are lots of interesting bikes coming to market that are TIG'ed. But the fact is, I've sold off all of my Surlies. My last welded frame is my Performance Ascent SS, and I'm looking for a lugged replacement for that!

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  7. The crack started at the weld. Conclusion: porosity and too much heat applied to the material.

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    1. Yes, probably a common occurrence in economy bicycle frame building!

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