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Bicycle Mechanics Broken bottom bracket? Tacoed wheel? If you're having problems with your bicycle, or just need help fixing a flat, drop in here for the latest on bicycle mechanics & bicycle maintenance.

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Old 02-08-12, 05:03 PM   #1
Beanboy
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paint ripples on both chain stays near bottom bracket lug...fatigue?

Looking over my early 1990s Raleigh Grand Prix. Had the bike since new, only about 15K miles on it. Noticed paint ripples roughly perpendicular to the tubes. The ripple runs halfway around the chain stay on the drivetrain side (facing inwards towards tire), and about a quarter of the way on the other chain stay.

Both ripples are about a half-inch or so back from where the chain stays meet the bottom bracket lug.

Beginning sign of fatigue?

Last edited by Beanboy; 02-08-12 at 05:13 PM.
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Old 02-08-12, 05:16 PM   #2
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If this is a steel frame, wear a sandal or clean sneaker and step on the crank near the BB and push sideways, especially from the drive side. Have someone else look with good lighting from the other side of the bike. Does the crack expand and show a gap on the inside of the chainstay? If not, and you don't feel extra mush, then you should be okay to ride, until it does crack. If this is aluminum, do so at your own risk.
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Old 02-08-12, 06:00 PM   #3
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Cool, thanks for the advice. Rear stays are steel while the main tubes are aluminum. Should be good for a bit.

-B
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Old 02-08-12, 06:09 PM   #4
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Pictures always help.
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Old 02-08-12, 10:03 PM   #5
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steel chainstays and aluminum triangle? are the chainstays brazed, or welded, to a steel BB and then the BB, in turn, bonded to the seat and down tubes? just curious.
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Old 02-08-12, 10:24 PM   #6
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You got it... Brazed to BB, and the aluminum is bonded.
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Old 02-08-12, 11:28 PM   #7
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Cracking at the bottom bracket/chainstay area is a common failure point for a steel frame. Keep riding it though, the bike won't collapse causing instant death... They can sometimes be repaired after this happens, so who knows. You may get another 15K out of this frame.

There is nothing you can do in the meantime so just enjoy the bike as long as possible.
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Old 02-22-12, 10:53 AM   #8
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Finally snapped a couple of photos. Doesn't seem to be actual cracks present. Take it this would be a prime area for cracks to form however?
Attached Images
File Type: jpg framegrandprix.jpg (76.2 KB, 79 views)
File Type: jpg framegrandprix2.jpg (74.7 KB, 72 views)
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Old 02-22-12, 04:35 PM   #9
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Is not a crack and to me looks like has been like that since forever and you did not notice until a few days ago. Knowing raleigh maybe came out from the factory like that.
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Old 02-22-12, 05:04 PM   #10
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Sometimes bubbles form in paint due to under-paint corrosion. Your pics show only minor bubbling, but could warrant a BB removal and clean-out and drying out just to check. But that's not likely to yield anything if the corrosion is just superficial. What I do on some bikes is to thoroughly clean the area to look for fine cracks in the paint, then thoroughly dry, then get a light, almost matching metallic fingernail polish and paint the inside curves of the lug and the edges of the lugs. I try to be careful so to the casual eye, it just seems like a shadow of the lug or maybe is hardly visible at all.

The bubbling paint in your BB area is not likely to have cracks. On steel bikes, most often, I've seen cracks around the inside of the right chainstay near the bridge (if you have one), and just above the BB shell on the seat tube. I've never seen a left chainstay buckle, except one which was backed into a garage while on the roof rack of a car. Needless to say - total loss - garage, car, rack, and bike! Okay, the front wheel was salvaged and so were the derailleurs and brakes and maybe crankset. Hopefully, that wasn't you! :-)
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Old 02-22-12, 07:05 PM   #11
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Cracks don't normally "form" like that. Hard to say what the cause is but my first guess would be it's where the line of filler material stopped when the stays were attached to the bottom bracket shell. No doubt the filler is brass and paint doesn't like brass as nicely as steel. Pull the bottom bracket. I'd bet you can see that far down the chainstay. I think you might find the answer.
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Old 02-22-12, 08:26 PM   #12
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Looks like both chainstays match, so probably something to do with manufacturing sloppiness.
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Old 02-22-12, 08:38 PM   #13
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For the record, metal fatigue isn't visible in any way. It happens at the crystal structure, and take a very long time in steel. So ripples aren't an indicator of fatigue. Eventually actual cracks will form, but even then it takes a while for them to spread.

I'd ignore it, but if it looks like bubbles, then it's probably an indicator of rust forming underneath (looked at the rocker panels of your car lately?). To deal with rust strip, or sand off the paint locally, sand to bare metal, repaint with a rust preventative paint.
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Old 02-22-12, 09:54 PM   #14
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Technium frame?
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Old 02-23-12, 08:42 AM   #15
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No, crapnium.
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Old 02-23-12, 10:33 AM   #16
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Quote:
Originally Posted by Beanboy View Post


Finally snapped a couple of photos. Doesn't seem to be actual cracks present. Take it this would be a prime area for cracks to form however?
"Finally snapped" is a really bad way to start a reply. Glad its still ok.
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Old 02-23-12, 10:38 AM   #17
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If there are no matching ones at the top of the seatstays,your fine.The chainstays can't flex by themselves.Looks fine to me.

Last edited by Booger1; 02-23-12 at 10:41 AM.
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Old 02-23-12, 10:46 AM   #18
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Quote:
Originally Posted by Booger1 View Post
If there are no matching ones at the top of the seatstays,your fine.The chainstays can't flex by themselves.Looks fine to me.
I agree that they look fine, but (very) eventually the underlying rust (if any) will penetrate to a depth where the structure will suffer and cracks will form. It's a slow process, but it's fairly common that if/when well used steel frames crack, it's often along the lines of paint scratches and penetrating rust.

Meanwhile to correct the flex question. Chainstays can and do flex by themselves or at least in pairs. The direction of flex is sideways not up and down, but chainstay flex is significant, especially in hard climbing or sprinting. There's no safety issue because even if one breaks completely, the other will keep things together long enough for a safe stop.
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