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Another chain stay crack

Old 09-05-22, 11:23 AM
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tmnguuyen 
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Another chain stay crack

Earlier last month, I posted a photo a a cracked chain stay on a Teledyne Titan, Today, i found out i have another crack on the chain stay of this Motobecane Jubilee Sport which i was going to bring to L'Eroica in Tuscany in October. Time to scramble to build up another one for the event.

Merde Ca Alors....

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Old 09-05-22, 11:30 AM
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I haven’t seen that kind of crack before. Definitely don’t want to rely on that frame for such an event , or anything , really. What size fame you take? Maybe someone can help out, BF members have been known to be quite helpful in these situations.
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Old 09-05-22, 11:36 AM
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Thanks for the reply. I ride a 51-52 cm. I have another frame with plenty of patina which i'm currently building up. Need to get a few hundred miles on the new build to make sure it is road worthy. I rebuilt the Motobecane a month ago and put in 300 miles since. This morning while cleaning the bike i found out it was a crack. All along i thought it was a grease line.... Now i know what that creaking sound was when i was climbing those 5% grades. My old eyes are so bad.
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Old 09-05-22, 12:13 PM
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That look a like a split along a rolled-from-sheet-and-welded tube.

Usually they put that seam on the bottom - feel the other one, is it seamed?
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Old 09-05-22, 02:31 PM
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Yup, its at the weld of rolled and welded type tube. Has it always been there? Almost looks like perhaps poor finish at the tube level or at Motobecane, just a guess. Either way not great.
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Old 09-05-22, 02:45 PM
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Interesting failure. When I broke a chainstay on a 1973 UO-8, the crack went most of the way around the stay, right in the middle of the chainring and tire clearance dimples, which is a high stress spot.
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Old 09-06-22, 01:49 PM
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Originally Posted by tmnguuyen
Earlier last month, I posted a photo a a cracked chain stay on a Teledyne Titan, Today, i found out i have another crack on the chain stay of this Motobecane Jubilee Sport which i was going to bring to L'Eroica in Tuscany in October. Time to scramble to build up another one for the event.

Merde Ca Alors....
,

and

Sorry man, you're not the first or the last to miss something on a purchase.

I did again recently but was lucky it wasn't life threatening.
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Old 09-06-22, 04:45 PM
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Originally Posted by Steelman54
Yup, its at the weld of rolled and welded type tube. Has it always been there? Almost looks like perhaps poor finish at the tube level or at Motobecane, just a guess. Either way not great.
Clean, braze, paint, ride.

(Do the other side as well, just in case.)
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Old 09-07-22, 03:59 AM
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Seamed Chain Stay Tubing

Seamed tubing is usually produced in this manner. A strip of sheet steel from a roll is fed through a series of roller dies until it forms a cylinder which then goes under a rotating electrode die which creates a welded joint. The external flashing can be removed by a number of processes including scarfing, turning, drawing or grinding. External seams are usually invisible in tubing.


Unless a seamed tube has been drawn over a mandrel there is almost always a visible internal seam.

Seamed chain stay.



Seamed head tube.



I've seen splits like on the OP's Moto before in really cheap tubing used for junk applications but never in bicycle tubes.

Because that's a highly stressed area, a hammersmithing repair would just be a band-aid.

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Old 09-07-22, 04:16 AM
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Originally Posted by verktyg
Because that's a highly stressed area,
Which is why the seam should be on the bottom, where the usual load will tend to force the edges together; if at the top they get pushed apart, so if there is any weakness from the seam that makes it worse.

I think someone put that stay in upside down - looks as though it's not dimpled, so a less noticeable mistake.
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Old 09-07-22, 06:47 AM
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I know -- braze on a disc brake caliper hanger and convert to disc brakes.

Seriously, though, I have strong reservations about those who attempt disc brake retrofits.
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Old 09-07-22, 12:28 PM
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Chain Stays

Originally Posted by oneclick
Which is why the seam should be on the bottom, where the usual load will tend to force the edges together; if at the top they get pushed apart, so if there is any weakness from the seam that makes it worse.
I think someone put that stay in upside down - looks as though it's not dimpled, so a less noticeable mistake.
From the 1960's on most chain stays came preformed from the tubing manufacturer. Since seamed tubing was so cheap to mass produce probably little care was taken to properly align the seam during manufacturing, especially since the seam was not readily visible from the outside.



Raleigh was one of the few major makers that used round tapered chain stays and that was on only a few Reynolds frames during the 1970's. Why? Probably because they were cheaper to buy from moma TI....

Production frames were mass produced. By the time that frame was made, Moto was probably using round oval round chain stays so there wasn't a choice to be made by whoever assembled the frame... Chain ring clearance was the only indentation put in by those builders.

Also, most chain stays, seat stays and fork blades were available pre-slotted for dropouts, with either domed or square ends which saved builders time and precluded orientation options...




Tubing failure modes. Axial or circumferential cracks are the most common failures in chain stays :


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Old 09-07-22, 03:35 PM
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Did not the Teledyne have a longitudinal crack also?

time for a Tesch S-22
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Old 09-07-22, 04:08 PM
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If only that was on the DS, you could make a custom stainless steel chainstay protector and braze it into place and nobody would be the wiser.

I'm with @Steelman54 that it may well have been a manufacturing defect. It almost looks like the paint curls into the seam (unless it has been repainted at some point).

The bike may well ride fine. You might look to see how the seam behaves when you put weight on the bike.
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Old 09-07-22, 04:29 PM
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Originally Posted by CliffordK
If only that was on the DS, you could make a custom stainless steel chainstay protector and braze it into place and nobody would be the wiser.

I'm with @Steelman54 that it may well have been a manufacturing defect. It almost looks like the paint curls into the seam (unless it has been repainted at some point).

The bike may well ride fine. You might look to see how the seam behaves when you put weight on the bike.
I stripped the bike. Not worth saving nor riding on a fractured frame. Moving on... unitl the next crack.
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Old 09-07-22, 04:30 PM
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Originally Posted by repechage
Did not the Teledyne have a longitudinal crack also?

time for a Tesch S-22
Yes, but i lost the photo for some reason. What's a Tesch S-22? Thanks
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Old 09-07-22, 08:48 PM
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Originally Posted by tmnguuyen
Yes, but i lost the photo for some reason. What's a Tesch S-22? Thanks
Tesch, main
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Old 09-08-22, 04:56 AM
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Motobecane Cracked Chain Stay

Originally Posted by oneclick
Which is why the seam should be on the bottom, where the usual load will tend to force the edges together; if at the top they get pushed apart, so if there is any weakness from the seam that makes it worse. I think someone put that stay in upside down - looks as though it's not dimpled, so a less noticeable mistake.
Originally Posted by Steelman54
Yup, its at the weld of rolled and welded type tube. Has it always been there? Almost looks like perhaps poor finish at the tube level or at Motobecane, just a guess. Either way not great.
Originally Posted by CliffordK
If only that was on the DS, you could make a custom stainless steel chainstay protector and braze it into place and nobody would be the wiser.
I'm with @Steelman54 that it may well have been a manufacturing defect. It almost looks like the paint curls into the seam (unless it has been repainted at some point).
The bike may well ride fine. You might look to see how the seam behaves when you put weight on the bike.
For everyone's edification, the bike is a 1982 Motobecane Jubile Sport with original factory paint. I think that the OP mentioned that he could hear creaking when he rode the bike. The crack most likely runs the length of the chain stay so a hammersmith repair wont accomplish much.



The 3 main tubes were straight gauge Vitus 888, the fork blades were too. The chain stays were "oval" meaning round-oval-round and on this model most likely made of cheap seamed tubing,



Motobecane produced many bikes during the 70's and 80's with better quality forks and main tubes but low quality seat and chain stay tubes. I have 3+ Motos made that way???



The 1982 spec sheet gives the partial details...



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Old 09-08-22, 09:35 AM
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Originally Posted by tmnguuyen
Yes, but i lost the photo for some reason. What's a Tesch S-22? Thanks
The s-22 has "tree trunks" for chainstays. Dave used a traditional cast bottom bracket shell and fillet brazed the chainstays and tubes OVER the cast spigots.
Down and seat tube were tapered to a large diameter at the bottom bracket end.
Built for Speed.

Just as you are such an "animal" cracking these stays, thinking you need all the help possible.
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Old 09-08-22, 03:41 PM
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Originally Posted by repechage
The s-22 has "tree trunks" for chainstays. Dave used a traditional cast bottom bracket shell and fillet brazed the chainstays and tubes OVER the cast spigots.
Down and seat tube were tapered to a large diameter at the bottom bracket end.
Built for Speed.

Just as you are such an "animal" cracking these stays, thinking you need all the help possible.
I wish i was that beasty, but it is just a POS bike.
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Old 09-14-22, 11:01 AM
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Originally Posted by tmnguuyen
I wish i was that beasty, but it is just a POS bike.
Just bad luck.
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Old 09-14-22, 07:29 PM
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Sorry to see that you had some bad luck too. I've had two frames crack.

Early 1990's Fuji titanium(not a CP one): I went to go out for a ride and saw the chainstay was cracked, near the bridge. Bummer, as it was meant to replace another that was several sizes smaller and borderline too small. I debated getting it repaired, but held off and got another Ti frame. It is still sitting in my basement, in case I decide to get it fixed later.

Mid-90's 753 Rivendell Road Standard: I bought it relatively cheaply with a dent in the downtube. It did not look that bad and the seller swore it was dented for years and he never had issues. I think I noticed it had cracked after the second ride. I got this repaired and back on the road.

Sadly, cracks happen. Maybe that is why I keep so many backup bikes.
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