JustMe

I would be interested in hearing from anyone that has experienced a broken chain with the newer Shimano CN-6700/6701 or CN-7900 that have the perforated plates on the inner and outer sides. There may be a significant problem with these chains that should be addressed.

skilsaw

How and where did your chain break?

A rivet fail and adjacent links disengaged?
Or did a perforated plate break?

JustMe

Like my post says, I would be interested in hearing from anyone that has experienced the problem. There seem to be a disproportionate number of people reporting this experience with these chains. There may be a potential for causing significant damage far beyond merely dropping a chain in mid stride. If you have some particular expertise in the design or manufacture of bicycle chains, please PM me with an indication of your background and basis of expertise.

HillRider

Are you a lawyer trolling for support for a class action law suit?

JustMe

If knowing that a particular component could cause sufficient damage to a 3,4 or 5K dollar frame set to render it useless, would you be interested in knowing about it ahead of time to avoid the consequences?? I seriously doubt broken bicycle chains result in causing the types of injuries and damages that justify the cost and expense of class action law suites. I am interested, however, in hearing from anyone that has experienced the problem, which seems to be excessively high in regard to the 6700/6701 chains. Do you have something to contribute that would shed light on the subject, or are you just trolling for a debate??

bradtx

JustMe, Did you have a chain fail? If so, are you looking for Shimano to replace whatever may've been damaged? Your question is too precisely vague for many of us.

Brad

HillRider

Not trolling for a debate at all, just trying to determine the basis for your question. Apparently you haven't personally suffered this failure nor has anyone you know so what's your motive?

FBinNY 

Motives aside, most chain breakage is the result of plates being pushed beyond the end of the pin. Usually this is rider error from aggressive shifting under load, or mechanic error from an improper closure.

Sometimes, though rarely, chains break because of plate fracture. This could be because of bad heat treating, other production factors, the result of exposure to chemicals which can embrittle the steel, or physical damage because of shifting under excessive load.

All chains experience a certain number of failures, knowing the nature of the failure the OP is interested in is critical to giving him an intelligent answer.

To the OP, you say there may be a... problem...and an excessively high failure rate. if you're looking for someone to confirm that suspicion, don't bother, just use other chains. If you want re-assurance that isn't possible because even a small percentage of failures is too high if it's your chain.

In any case, you'll get more help, and less suspicion of your motives, if you describe the specific problem rather than trolling (as in fishing) for general responses.

BikeWise1

I am a bike shop and have had zero problems with these chains. Is that what you're looking for? :-)

JustMe

The precise mechanism of failure has purposely not been described in an effort to avoid biasing whether a failure has been experienced. As described below, the mechanism is important, but capable of evaluation once the data is acquired.

Not only have I personally experienced the problem twice in the past 2 weeks on separate bikes, my research indicates a number of reported breaks associated with the 6700 chain. So the reason for my question is to determine if a significant number of people are experiencing the same problem. Create all the suspicions, or whatever you like, I wouldn't be bothering with this if it appeared to be within the normal rate of expected failures. IT DOESN'T.

Agreed. I would expect a certain number of failures for various reasons, many of which can be attributed to user conditions. As stated, the reason for the question is to determine whether the failure rate with this particular chain is beyond what would be considered within the norms. I agree that the mechanism of failure is certainly at the root of the issue, but the mechanism can be evaluated as a causative factor after any positive data of the overall failure rate is acquired. I am not looking for someone to affirm or disaffirm the root cause. I am looking for the objective data that may, or may not, provide a dispositive conclusion.

Thanks, but NO! It is statistically impossible to prove the absence of an event by the absence of data. I am interested in determining the presence of failure, not the absence of failure.

FastJake

I'm willing to bet it's also statistically impossible to prove anything by posting this here. What will your "results" be if three people come on here and say they've broken these chains, and 4 say they haven't had a problem? In addition, as FBinNY mentioned, there are various reasons a chain may fail, only one of them being a defective chain.

I doubt there are nearly enough people on here that:

- Run the CN-6700/6701 or CN-7900 chain
- Are actually AWARE that they run the CN-6700/6701 or CN-7900 chain

I have a Shimano chain on one of my bikes but I have no idea what the model number is, or any way of finding that out. Finally, your posts just sounded sketchy.

BikeWise1

Stamped right on the side plates.....

Totally agree. This looks like a fish hunt. How is the OP going to ascertain failure mode accurately in such a way that the data will be meaningful? Bike parts break. Some more than others. Does the OP plan to have samples of broken chains tested for metallurgy problems?

bradtx

JustMe, If you perform a Google search "cn6700 chain" you'll find that there is some history of inner link failures that Shimano has ID'd to 2009 production, if I read it correctly.

Brad

operator

I do.

We've sold 7900 and 6700 equipped bikes with their matching chains for over a year now. Not a single one has come back for chain breakage. We've neither received reports otherwise from other shops or from our shimano rep, or shimano canada.

If the OP is breaking 6700 chains, then it's time to upgrade your mechanic 101 skills. Or learn how to read techdocs.

Shimagnolo

Statistics fail.
People using the chain w/o failure, and shops selling/servicing the chain w/o failure *is* data.

operator

Yep.

Here's the OP's situation -

1) Broken 7900/6700/6701 chains leads to frame damage
2) OP is angry
3) Wants to blame the chain for manufacturing defect

Here's two possible cases

1) Whoever installing the chain is an idiot
2) There is pervasive unkonwn defect for which only the OP is subject to and only he has experienced among several others you can count on one hand

Gee, I wonder which.

All those pros riding 7900 chains for the last 2 years must be weak as hell. They haven't broken a single chain in the fashion the OP describes.

macdaddy16

JustMe .... I have had two similar instances with the CN-6701 Ultegra Chain.
1. In early November 2010, I had an Ultegra 6701 chain fail in the middle of the plates on both the inside and outside (looked like someone sawed the chain in half right in the middle of the plates). Luckily I was just getting ready to start my ride, I had just clicked in and started spinning up to speed, I stood up on the pedals to get a few good turns before settling into my sitting position when "WHAM" the chain snapped, not sure how i managed to stay on the bike other than dragging my left foot and ankle across the ground. The chain had less then 500 miles on it, and was factory installed on a new Specialized Tarmac Expert.

2. Yesterday January 16, 2011, my 15 year old son was out on a group with local club, at about the 30 mile mark the route brings them past our community, he dropped off and started heading home, because the remainder of the route crosses some major roads that I don't like him riding on unless I'm with him. I digress .... about 2 miles after he dropped off he slowed to cross an intersection, he got up out of the saddle and started to accelerate, as he transitioned back down to the saddle ... WHAM chain broke, he was not as lucky as I was, the handle bars snapped to the left and because he was in the process of sitting back down he did not go over the bars, both elbows and his left side took a pretty good beating as he slid across the road at about 25 mph. This was a brand new chain with less then 100 miles on it, hard to tell if the plates failed again, looks like it may have been at or near a connecting pin, it definitely was not at the re-enforced connecting pin. We just built up his bike with a new SRAM build kit for the upcoming race season, and since SRAM does not make Jr. Gearing cassettes we run Shimano Ultegra 14-25 with the matching chain.

Needless to say I'm done with the Ultegra stuff ... only DuraAce from now on. The local bike shop is going to warranty the chain, but since I put it on, they are holding the "party line" and insinuating that I did something wrong. Not looking to sue anyone, but Shimano has a problem with these chains, my son is going to be OK and that is the important thing.

OBTW, I consider myself an avg to above avg, recreational/sport rider, 5'-10"/170lbs, so I'm not mashing gears, or putting a lot of torque on the drivetrain like Cavendish would, my son is 5'8"/120lbs, and while he is a stronger rider then I am, he's still a "15 year old kid".

CCrew

I have the 6700's on three bikes with no issues. Add that to the stats pile.

mrrabbit 

Chains are a wear and tear item - they will break. Same for traditional spokes. Same for traditional solid and hollow axles. Likewise for bottom bracket spindles and axles. Same for traditional rims...

So if someone is looking for a class action suit - good luck.

On the other hand, frames, forks, bars, stems and crankarms are supposed to be designed such that catastrophic failures are not expected - even after long term use. Hence the reason why you see serious recalls in those areas when they occur. Hence furthermore the reason why business insurance IS MUCH MORE EXPENSIVE - easily 3-4 times more at at minimum for those who produce in those areas.

A wheelbuilder might pay 350.00-500.00 for insurance - a framebuilder 2000.00-3000.00. Wanna be a major manufacturer of cranksets...you are in for a shock!

I agree with a previous poster - even though chains break - it is pretty rare for the miles that are put on 'em. Either learn to install a chain RIGHT or pay someone else who knows how to do it for you. Quit whining! And if it is a drilled/slotted lightweight chain - then change it for a solid plate and solid pin version. Play with the superlight "racing" stuff...don't whine when it fails on you. Same goes for using OpenPros as everyday commuter rims, carbon stems and seatposts on heavily loaded commute bikes, etc.

It never fails - people who keep trying to have it boths way - a form of greed, and then whine about the result.

=8-)

SlowDave

I had a 6700 chain break after about 2500mi. Had a ticking in the drive train for a few rides I couldn't track down. Checked the chain and have a plate that broke at one of the rivets on the backside and no where near the assembly link. Poke around online and you find many similar stories.

operator

Yeah because a worn chain can never break right?

Enough with this idiotic thread already.

Burton

OK for what its worth - here`s my 2 cents.

I do tech support (mechanics) for four different shops and design support for one independent bicycle manufacturer. Personally I`m unaware of any `significant problem` with those chains.

But that doesn`t mean there might not be. Its becoming increasingly common for riders to buy over the Internet and install themselves.

And these particular chains all have something in common: They`re dirrectional. On top of that Shimano recommends that the reinforced connecting pin should be installed on the leading edge of the link.

So if chains are breaking because home mechanics aren`t reading instructions and are installing the chains backwards - shops would be unaware and Shimano wouldn`t be at fault anyway.

So I think you`ll have to dig a lot deeper to come up with any meaningful data that might indicate there`s a serious design problem. Rumors of a `significant number` just won`t cut it.

mrrabbit 

We need an emoticon with a briefcase carrying smiley chasing an ambulance.

=8-)

Al Criner

According to the reviews on MTBR.com, all chains are terrible.

SlowDave

"I would be interested in hearing from anyone that has experienced a broken chain with the newer Shimano CN-6700/6701 or CN-7900 that have the perforated plates on the inner and outer side" - How this thread was started.

What a shocking number of useless replies, what's with all the blind hostility? Where did he ask for opinions? This has to be the most hostile, useless forum I've ever seen.

So a "shop" hasn't had any of these break so that means it must be the installers fault and not the chains? Well I drove drunk all through my 20's and never got in an accident therefore driving drunk is safe right?

Wow!