Why do I keep breaking chains?
 

I've never had a chain break on a bike until I got a Felt Q620 about a year and a half ago. The other day, a 3rd chain just broke. There is no way that I've put enough miles on this bike to justify going through chains like this. I've worn out plenty of chains in the past (stretching), on other bikes and always replaced them without them breaking.

Is it possible that there is something fundamentally wrong with the components in the drive train on this Felt Q620 that would unduly stress the chains?

I'm looking for some feedback before I go back to the lbs with my complaint.

What part of the chain breaks?

The three possibilities I can think of are: A damaged or twisted tooth on a chainring or cog that can damage a link; rough shifting under heavy pedalling load (also known as a 'loose nut behind the wheel'); and improper installation.

Improper installation is by far the most common cause of chain breakage.

How are you connecting the chain after sizing?
IF you are just pushing the existing pin back in, that's the reason.

Outer plates the last 2 times. I don't remember the first time.

I use a quick link to connect the chain. That has never been the failure point.

I will look into the possibility of a damaged/twisted tooth.

I don't typically shift under heavy load, and certainly don't ride this bike any differently than any other in that regard.

Improper installation is possible, I suppose.

Has any other part of the chain been "spliced"?

No. The chains were new. I've had no reason to break the chains anywhere.

Every once in a blue moon a chain manufacturer overly heat treats the link plates causing them to be brittle. Sachs (pre SRAM) had this issue in the 1980s (or was it 1990s) for a short period. More frequently, but still uncommon, is a chain on a new bike that was assembled poorly, the pin isn't fully inserted into the side plate. This is the typical user install problem if a connecting link wasn't used. As mentioned first by Wilfred. Then more common is the hammer shifter who doesn't let off the pressure when shifting. This is usually what will create a twisted or bent tooth on either the cogs or rings. Then this "new" problem continues the chain breakage possibilities, even with reformed shifting technique. Andy.

You've broken three different chains in a year and a half? Something is indeed fundamentally wrong with something in your drivetrain or you ride off-road under extremely harsh conditions. Even an MTB shouldn't brake chains that often.

do you haul your bike on a vehicle with some sort of bumper rack that could be rubbing the chain?

One key to the possible causes is exactly HOW they break.

There are two basic modes of failure.

1- a plate works it's way out to the end of the pin then falls off under load, causing the opposite plate to bend under load and slide the pin out. The most common causes of this type of failure is hard shifting under load, something that each "improvement" in shifting makes easier to do, and splicing via pushing pins back in which makes chains more vulnerable to plate movement.

2- plate fracture. This is rare because chain companies understand that this points right back at them, and make every effort to ensure that this is not a common mode of failure. Plate fracture can have a number of causes, from tolerance issues between the pin and hole diameters, to bad heat treating, failure to bake out ions after plating, and exposure to chemicals which can embrittle the steel. If you have plate fractures you should immediately make the chain manufacturer aware of the problem, because it's something they need to know and track. They may ask about how you clean the chain, but if diligent will log the issue and watch for more complaints of the same.

Twisted links usually don't lead to failure, but they do cause skipping which in turn can cause added stresses.

So, I don't believe there's anything inherent to the bike or it's drivetrain, but you need to try to analyze what's happening because you should not be breaking chains for any reason.

What chain are you using? Some are directional. Correct chain for the groupset? Chain length? Quick link used?

its an 8 speed Cassette on a Mountain Bike . you may just be a Thrasher . and hard shifting into gears Late.

Thanks for the replies.

I am going to consider improper installation as the most likely cause unless I can find an issue with teeth being damaged or bent.

I am eliminating riding style as I don't ride that bike any differently than my others. I have over 11,000 miles on my touring bike and have never broken a chain on it -- it's current chain has over 4,100 miles. And as I said, I have never had a chain break on any other bike than this Felt.

While I do in fact haul my bikes on a bumper rack, I load them with the drive train away, so there is nothing to rub against the chain. (good suggestion though) And again, it is only the Felt that has issues.

Since you've virtually eliminated installation as a factor (you use a connector which hasn't failed), you're left with few possibilities. Unless you bought all the chains together on within a narrow time interval, defective chains are likewise unlikely (what are the odds of buying 3 defective chains).

It's possible that you're cutting the chains too short (LT big/big+ 1"), but that's easy enough to rule in or out.

So, we're down to something about the sprockets, and you.

Question, this bike is Hyperglide, what were your prior bikes? If not Hyperglide, then I see that as the difference. Hyperglide makes overly aggressive possible, and can break chains in a way that non hyperglide bikes can't.

BTW- you never said whether the breaks were off the pin type or fractured plates.

FBinNY's post still has me curious if the outer plates are cracking and splitting, or if the pin is pulling out and separating from the outer plate.

Got any pictures? Are you using the same 9-speed chain on the LHT? Despite your humility, I'm finding it hard to believe that installation error could be the problem, since you've managed so many miles on other bikes without a problem. Perhaps Andy is on the right track that you've simply gotten a couple of chains from a bad batch.

EDIT: Simul-post with FB's latest! :lol:

Could the OP be unintentionally using a single speed chain and stressing it sideways? Just trying to think what would stress the chain enough to fail.

Your guess is as good as anyone's -- and it's all just guess work until the OP answers the questions.

Sorry that I haven't answered all the questions. Here's a couple more answers:

I did not buy the chains at the same time.

I don't think the chain has a directional requirement.


I actually did say that the outer plates failed the last 2 times but I couldn't remember what happened the first time. Now, however, I am not sure the plates failed this last time. It looks like the pins on the quick link broke loose. This all happened in the dark at -2F on my way to work and when I got the bike back home I assumed that part of the chain was left laying in the road. Now I am not so sure there is anything missing other than the other part of the quick link.
http://bikeforums.net/attachment.php...hmentid=437538

I never heard of Hyperglide before. The bike I referred to with over 11,000 miles is a Surly LHT. I can't say whether it has Hyperglide or not, but unless it comes stock, then it does not.

I hope I have not left any questions unanswered. I thank you for your patience and your insights.

In this photo, it isn't the chain that broke but the connector. Do you remember if that was the case on the other ones?

I do see a cracked hole at the solid end, but it's impossible to know if it caused or was the result of the failure. I've heard of (but never seen) Sram link issues where links somehow manage to unlatch, which may be why Sram moved to links that latch positively.

Without assigning blame, if the prior failures were also at the connector, I'd look at another brand of chain, either Shimano which doesn't use connectors, or maybe KHS which does.

The 2nd time a chain broke, the outer plates flat out split open.

This time the quick link may be the culprit. I wonder if I am taking a gamble by reusing a quick link. Maybe they are not designed to be removed and reinstalled too many times? It would sure be worth it to me to replace it every so often if that would keep me from breaking down in the middle of nowhere.

By the way, I think the bike came with a KHS chain.

I've cut a lot of chains and re-connected them with the same pin that I pushed out and none of them have failed at the cut link. These chains have been on all my personal commuter bikes and bikes that I've refurbed for friends. As long as you only cut the chain at that link once you should be okay. Just make sure that the link moves freely as normal. If my personal bikes have a quicklink and I have some sort of opportunity to replace the chain or shorten the chain I will remove the quicklink. I've had a few pop loose. I've also seen some bikes come with the wrong quicklink for the chain that's installed.

Are you taking the chain apart a lot to clean it? If so stop doing that! instead use a chain cleaning machine like the Park to clean the chain. Every time you take the chain apart you weaken that link more and more. In addition to that problem incorrectly installed pin will make a chain fail fast.

Here is how a chain is to be put together: www.cyclingnews.com news and analysis

The others mentioned shifting under load, but do you cross your gears? meaning do you ride in the largest front gear and the largest 3 rear gears, and or do you use the smallest front gear and the smaller 3 rear gears? that is crossing and it puts a lot of stress on chains. Some folks say chains are tough and cross chaining or shifting under load won't break a chain, I'm not sure, I've never broke a chain in 40 plus years of riding including racing and training in the mountains of California where I shifted a lot under hard load.

It's also possible you somehow are using a chain that is too short (too long won't cause a chain to break it will would instead have sloppy shifting and cause the chain to drop).