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Old 05-11-12, 10:07 PM   #1
avuton
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Bike chain cracked / broken in 5 places?

Hello,

[Long story: TLDR; Chain cracked / broken in 5 places since new, wtf?]

I just bought a 2006 Specialized Crossroads XC Expert. It's my first good bike, but I've come across something I'd consider an anomoly.

I bike around 6 miles a day, to and from work for the last 3 days (since the day I bought the bike). Today, I left work, I heard rear derailleur/gears changing back and forth by themselves. Shruged it off, knowing that a tune up was around the corner for me, anyhow.

2 miles into my 3 mile trip, my chain severed at a link, my derailer arm broke, broke 1 spoke and damaged a few others. Luckily, the local bike shop fixed me up in less than 30 minutes. The bad? They fixed the major problems, but didn't look for any other issues. When I got home, I found 3 more cracked chain links . I see the one they fixed, I also see a previously fixed one (slightly patinaed).

I'm guessing this chain is original equipment; I'm really shocked this can happen this much.

So, along with my question, any comments are welcome.

I'm concerned, because the damage was relatively light this time, (no frame or other scratches) and I was only a mile from home.

Is this normal? Is it time for a new chain? Should I be getting a better chain? Should I be concerned? Is this preventable?

Thanks for your time.
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Old 05-11-12, 10:14 PM   #2
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Shimano Ultegra 6700?
There were a bunch of failures.
The search function should pull up some threads.
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Old 05-11-12, 10:22 PM   #3
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Perfect. Shouldn't have been so quick to post a new thread. Thanks.

That's the same as Shimano CN-HG73? Again, assuming this is original equipment.

Last edited by avuton; 05-11-12 at 10:25 PM.
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Old 05-11-12, 10:26 PM   #4
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If I were to find any more than 1 cracked link, I would replace the chain without hesitation. Either it's defective (as Shimmy said) or it's been neglected to the point that it's rusting inside. If it's an bike that's sat without maintenance for a number of years, it's possible that moisture has worked its way inside and has rusted and weakened the links.
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Old 05-11-12, 11:15 PM   #5
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For the record, it was an SRAM PC-951. I didn't realize it was printed right on the side of the chain (lots to learn, apparently). Time to find something better. Thanks for all the great advice.
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Old 05-12-12, 04:44 PM   #6
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Stress cracking of chain plates is something that was almost unheard of a decade ago, now it's getting more frequent, though still rare. There are a number of possible causes, including tolerance issues at the rivet hole, heat treat issues, and/or embrittlement of plates caused by hydrogen or chlorine.

I suspect that the reason that the problem is less rare (still not common) is that with the thinning of the plates to make narrower chains, they've had to change alloys, and heat treat to a more critical spec to make up for the loss of material. That leaves less margin for error, and plates that are less ductile and more prone to cracking vs bending. Side flex may also be a factor, but it's almost impossible to identify a single cause, though the fact that it seems to occur in clusters points to a manufacturing issue like heat treat or tolerance.

No company has been immune to this, and I've seen cracked plates happen with Wippermann, Shimano, and Sram. Shimano seems to have the most incidents, but that may simply reflect the greater number of chains in use. Given the stakes, I'd automatically replace the entire chain if I see a single stress cracked plate.

I now do a quick visual check of my 10s chains about once a month looking for cracks, though have yet to find any.

BTW- this is very different from how most chains break, when side stress or bad splices causes a plate to come off the end of a pin.
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Old 05-12-12, 04:54 PM   #7
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For the record, it was an SRAM PC-951. I didn't realize it was printed right on the side of the chain (lots to learn, apparently). Time to find something better. Thanks for all the great advice.
SRAM PC-951 chains are not bad. I used to run one on my (7 speed) bike even though it's a 9 speed chain because that's what the LBS installed on my bike when my chain snapped (because I had neglected to maintain it, the cheap stock KMC chain broke after 1000 miles). Since it became time to replace that chain (about 2000 miles later), I put a 6/7/8 speed SRAM PC-850 on it. No problems with that. SRAM chains are good and relatively cheap. I wouldn't recommend anything else (unless you want to spend a lot of money).
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Old 05-12-12, 08:01 PM   #8
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You didn't happen to soak the chain in Simple Green or the new water-based green eco-friendly odorless mineral-spirits did you?

Check out this thread: Whoops! Left my chain in mineral spirits for (way) too long
Compare the photos in that thread with the cracks in your chain.

Last edited by DannoXYZ; 05-12-12 at 08:11 PM.
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Old 05-12-12, 08:59 PM   #9
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Replace the the chain asp. Never run a bad or iffi chain you can buy a basic KMC that will work good on most bikes for about $10 at just about any bike shop.
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Old 05-13-12, 08:24 AM   #10
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You didn't happen to soak the chain in Simple Green or the new water-based green eco-friendly odorless mineral-spirits did you?
I did not. At this point I'm not sure exactly what caused it, but the chain did have a patina of some kind of (what I thought to be) light surface corrosion from the previous owner's maintenance. I keep it in my house now, so that's not really going to be an issue anymore; though the damage did look something like the mineral spirit damage. The LBS had a KCM chain they recommended and installed on the bike when I brought it back in yesterday. Biked around 20 miles yesterday, and I'm happy (for now). Gears need adjustment now, but I'll get with them about that tomorrow.
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Old 05-13-12, 12:01 PM   #11
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I've had good luck with 8- and 9-speed KMC chains.
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Old 05-13-12, 03:48 PM   #12
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I had to make an unscheduled visit to my LBS yesterday. I lost my chain while in 3 lanes of traffic. LBS said I fractured the link, he put on an KMC x9 and sent me on my way after tweeking the front and rear derailer's. The chain that broke was a factory from unit from Raleigh that came with my bike, had under 200 miles on it. Hope this chain lasts a bit longer
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Old 05-13-12, 04:07 PM   #13
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I had to make an unscheduled visit to my LBS yesterday. I lost my chain while in 3 lanes of traffic. LBS said I fractured the link, he put on an KMC x9 and sent me on my way after tweeking the front and rear derailer's. The chain that broke was a factory from unit from Raleigh that came with my bike, had under 200 miles on it. Hope this chain lasts a bit longer
Chain breakage due stress cracks like the OP describes is still very rare. Most likely you suffered the more common form of breakage where a plate falls off the end of a pin. This is almost from either of three causes.

1- bad assembly, which is unfortunately very common on new bikes where workers on the assembly line closing hundreds of chains per shift get sloppy.

2- aggressive shifting under load, where high side stress is created as the chain moves between the two sprockets. This is common among new riders who wait to long before shifting as they begin a climb, and suddenly find themselves force shifting. You can hear this happening as a loud crunching sound vs. the clickety-click of a normal shift. The rivets of all chains since 8s hyperglide are peened over the outer plate to prevent this, but that only provides a certain amount of protection. The solution is to learn to anticipate your gear needs so you still have enough momentum to lighten the pedal pressure during a shift.

3- cutting and splicing the chain by pushing a rivet back and forth with a chain tool. This was fine decades ago, but not suitable for hyperglide (by any name) cassettes of 8s or more. Pushing the pin out breaks the peened edge off, so when pushed back there's nothing to prevent rivet spread.

It's impossible to know exactly why your new chain broke. Most likely the first or second reason, so you need to reflect on your riding habits so that you won't have a repeat.
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Old 05-13-12, 05:38 PM   #14
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FBinNY, thanks for the great information!, I will pay more attention to my shifting habits in the future.
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Old 05-13-12, 07:23 PM   #15
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Maybe a little late in the game to ask since you just had the chain replaced anyway but out of curiosity - did you or any shop ever run a chain-checker across that chain to acertain the amount of wear on it? Its kinda rare for a chain to show that many defects without a lot of accompanying miles and abuse. Be interesting to know if it was long overdue for replacement - in which case your cassette may be next in line.
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