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Failed KMC chain - less than 100km indoor use

Has anyone had any experience of KMC chains failing prematurely? I have a 9 speed Sora equipped bike permanently on my Wahoo Kickr. The groupset is in good condition with no parts especially worn. The drivetrain is kept spotless and dry lubed regularly.

My old KMC X9 chain basically exploded about a month ago with countless broken links. I put it down to wear and tear, purchasing another KMC X9 however that chain did a similar exploding trick tonight and upon inspection there are at least 13 cracked links. It's done less than 100km indoors.

 I've used KMC chains for years with no problems but this really puts me off. Thankfully I was on the turbo so no harm done, but outside in traffic the result could have been very different!

I'm sure the retailer will warranty replace it but before I accept a replacement KMC I thought I'd canvass opinion here on possible causes?

If you're new please join in and if you have questions pop them below and the forum regulars will answer as best we can.

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22 comments

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Themadchemist | 1 year ago
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I've had 2 KMC chains fail on my campag 10spd equipped bike,probably 5yrs ago.. Fortunately they both broke within a mile of home and I was able to walk home. I did have a quick link on me for the 2nd one,but it was as quick to walk! After that I bought the proper (expensive) 10spd campag Chorus chain,and that's still on. Wouldnt buy another KMC chain as its painful when they break.. Oh,just to add..both chains came from well known online cycling retailers,so should have been genuine.

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levestane | 1 year ago
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Ride On | 1 year ago
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I had an "ultegra" chain break in a similar way after a short period of time. Pretty sure it was a fake.

I note your comments below about buying from a reputable dealer but doesnt mean a fake can't get into the system.

Send it back and ask for a replacement or write it off and buy from a local store.

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stonojnr replied to Ride On | 1 year ago
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Correct, but its just to counter the if you bought off ebay/aliexpress what do you expect comebacks. I don't buy from shops I don't have trust in, just to save a couple of quid.

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Ride On replied to stonojnr | 1 year ago
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Hahaha I did! Won't do that again.

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Sriracha replied to Ride On | 1 year ago
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And why are we told the brand of chain but not the name of the "reputable" online seller? The implication is that the online seller is beyond reproach, leaving only KMC's reputation in question.

The fault could be with either of them, whilst legally it rest with the seller regardless.

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stonojnr replied to Sriracha | 1 year ago
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For mine, I simply can't remember, I always keep a spare chain on hand at home,so if I get a problem I can fix it straight away, then order the spare replacement. By the time that new spare gets fitted and then breaks itself, it could be best part of a year later.

Lots of places sell KMC x9 chains, Wiggle/ChainReaction, Merlin, Halfords, Bike Inn, I order from whoever has available stock, so its not always the same retailer.

But it costs around 20quid, Aliexpress sell the "same chains" for around 10quid, I don't buy those.

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HLaB | 1 year ago
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I've never had a 9sp KMC chain but I did have an 11sp one fail (warped link) on its 2nd or 3rd dry ride. I've had quite a few KMC chains before that which lasted a high mileage until they've slipped or not sat correctly on the chainrings (not actually snapped), so I gave them another go and I've had no problem since.

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Simon E | 1 year ago
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I have been using KMC 9 speed chains for a long time and never had any issues.

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huntswheelers | 1 year ago
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Blimey...that is shocking... we have used KMC for years with no problem but there are some KMC fakes about and 9 speed versions were in short supply during Covid so I managed to stock Sram 9 speed chains at that time. I still have stock of those as the majority of my customers are 10 speed plus end users. I hope you get resolved soon, you could always try Taya as they always work well

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wtjs | 1 year ago
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My Vitus Sora 9-speed 'gravel' will soon have done 3 years and 15-18,000 miles- on a total of 4 chains: the original and 3 cheap KMC chains. I have a system where I remove them when they reach the first wear point using a Rohloff chain wear tool, and then bring them back in rotation until the second wear point. They have all been faultless, and I have never in 55 years of cycling broken a chain. I will then be moving to 46/30 and 11-34 from the present 48/32 and 11-32- this bike has done a lot of heavy trailer towing, and many muddy tracks such as the entire Pennine Bridleway

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Rendel Harris replied to wtjs | 1 year ago
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Always looking for ways to extend chain life, and you certainly get more mileage out of a KMC than I do; what's the advantage of removing then bringing back as opposed to just leaving on until it reaches the second point?

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wtjs replied to Rendel Harris | 1 year ago
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The presumed advantage is that the problems arise when you put a new chain on a worn cassette - so you put worn chains on worn cassettes, and the chain change over is an opportunity to clean the grime encrusted chain at least once during its life. I have followed this system for many years. Four chains seems to be about right for 2 alloy chainrings and a cassette

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grumpus replied to Rendel Harris | 1 year ago
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The idea is the chain wears faster than the cassette and putting a new chain on a part worn cassette doesn't run smoothly and/or wears the new chain rapidly. Take your chain off when it's half worn and fit a new one until that's half worn, then refit the first chain. You could use three or four chains depending on your chain:cassette wear ratio. Worth it? I don't know, I'm not that organised.

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IanMSpencer replied to grumpus | 1 year ago
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The main issue is ensuring you don't run an overworn chain on a cassette - or chain rings. A worn chain puts load on a single tooth and tends to ride up the tooth.

Once the teeth are worn, an unworn chain doesn't mesh properly with the teeth and under load slides up the worn tooth and in extreme cases skips.

The classic wear for a mountain bike is the 11T ring, which with its few teeth to spread wear, and tight radius is both prone to wear and slipping. Many MTB cassettes are ruined by on-road riding where the low gearing for off road tops out and people tend to do a lot of riding in it. I notice quite a few e-bike riders tend to rely on motor torque rather than using the full range of gears, and they will tend to have premature cassette wear.

I get 3 - 4 chains per cassette but don't bother with complicated routines. Simply avoiding excessive wear before changing the chain by checking wear. I've not had to change chain rings yet with that regime.

I know a local cycle mechanic who claims not to worry about chain wear but allows them to wear and then changes the lot but that seems a great way to risk an accident and chain rings aren't cheap.

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stonojnr | 1 year ago
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Yes I've had a KMC chain, 9speed also, snap multiple links on me and hadn't done anywhere near the mileage I'd expect for KMC chain. Though again bought from reputable online source, though the last one I bought from them came in a plastic bag, not the normal plastic case. my feeling is theres either a bad batch of them out there, or there are a large number of fakes in circulation.

I only replaced another broken KMC chain last week, probably more likely wear on this one, but it let go as I pulled away with an HGV sat an inch off my back wheel, who was also blocking a box junction for good measure, so that was exciting.

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IanMSpencer | 1 year ago
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KMC X9 is a decent chain and I fitted a gazillion of them in my time. Off hand I can't think of a reason why a chain would fail like that without there being some reasonably obvious drive chain problem, such as a distorted rear mech twisting the chain, but I'm sure you'd hear and see such an extreme fault. I would not be surprised with a single failure on a new chain, it does happen across all brands, though fairly rare, but multiple links I've never seen.

My instinct is that it is a fake chain, there are certainly fake KMC quicklinks around on Amazon. With all the messing about over the last couple of years, the other alternative is that KMC have outsourced to someone not making parts to spec.

My only doubt is that both your chains failed unusually. To have multiple links fail simultaneously doesn't make sense to me (not saying it didn't happen, just can't understand how a chain would fall into multiple pieces when a link failed), which does make me wonder if there is some issue on the bike. What sort of mileage had the old chain done? An X9 should be good for about 3000km assuming it is being ridden in a normal style. A caveat on trainers is that it is possible to put unusual loads through bikes, e.g. resistance cranked right up and grinding on the pedals (I've seen a hub destroyed by a trainer). If you are carrying a bit of weight, fit rugby player for example, out of the pedals and resistance high, might it be that you've put too much load through the chain?

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Cdl888 replied to IanMSpencer | 1 year ago
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Chain was bought from a reputable online retailer, one of the biggies so would be disappointed if it was fake.

I don't think it's a load issue. I'm no heavyweight at 78kg with a max power at sprint of about 1000w. Also all the rides on it bar one have been fairly tame recovery rides due to the heat and getting in some decent outdoor rides. 

Mech alignment and such like checked with no obvious issue. 

Old chain was definitely due replacement but still surprised to see so many cracked links.

To clarify, exploded is a bit colourful... one link totally snapped and upon inspection there are at least 13 links cracked. 

My gut is that I've just been unlucky with the last chain, but want to rule out any other cause. I have since found some forums from a few years back where KMC chains were failing but they claim it was a single bad batch with a particular marking that this one does not have. 

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Sriracha replied to Cdl888 | 1 year ago
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Cdl888 wrote:

Chain was bought from a reputable online retailer, one of the biggies so would be disappointed if it was fake.

Reputable online retailer, reputable brand of chain. Yet you have already decided where the fault lies - else why name the chain, but protect the retailer's identity. I'd trust KMC above any online retailer. And what about the "dry lube", why is that not in question too?

Quote:

I have since found some forums from a few years back where KMC chains were failing ...

You name it, there are "some forums" about it failing.

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Drinfinity replied to Cdl888 | 1 year ago
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My daughter had one go on her MTB the same way, although in that case it was a SRAM chain. I counted 17 cracked links. If I was back in the aerospace biz I would have had it tested to see if the heat treatment on the plates had been missed. 

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jonb replied to Drinfinity | 1 year ago
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A friend had something very similar. SRAM chain on a new bike - within a few weeks it had multiple cracked plates... I noticed when I was fixing his chain for the second time on the same ride 
SRAM replaced it under warranty (via the bike manufacturer)

 

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stonojnr replied to IanMSpencer | 1 year ago
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I think multiple links in the chain crack, so get weakened, and when you put a load through the pedals, in my cases its been to pull away from a stop or hitting a steep hill, and Im not generating stupid power I might be rugby player weight Im not rugby player fit, in that split second as the load spreads across the chain the weakest links fail.

this picture gives you some idea, as you can see the link to the left/down of the broken one is showing a hairline crack as well.

and it had only done at most half the mileage Id expect from it given it was basically only dry weather use and was in good nick for wear.

Ive had 3 chains break in 20 years of riding and 2 have been KMC chains within the past 2 years.

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