Chain Jam

[Matthew Williams]

My chain jammed in my front derailleur. What happened?

I wasn’t going fast or slow, I hadn’t shifted gears, and I wasn’t putting any unusual stress or power on the drivetrain. I was just cruising along a flat street, gently pedaling, when suddenly my cranks locked and I couldn’t pedal forward or backward. 

I coasted to a stop and looked down. The chain was fouled and jammed in the front derailleur, and the rear derailleur was parallel with the chainstays. I walked my bike home and took photos of the damage. I have many questions for you experts:

1: What caused this? How and why did my chain get jammed in the front derailleur? 

2: Does this breakdown have a name?

3: Is this something I did or failed to do e.g. bad shifting, lack of maintenance, is something bent or misaligned, or is it just the inevitable entropy from mileage and time?

4: How do I prevent this from happening?

5: How do I fix it and what tools will I need if I’m out on a long ride?

Photos below.

[Piaw Na]

It's possible that your chain is too long and all that happened was that the chain bounced and got caught up. Usually something like this is called "chain suck." I've had a chain wrap itself around the rear derailleur and ripped the entire derailleur hanger off (that ended the ride!), and I've had the front derailleur ripped off in similar fashion (ripping off the front derailleur does not end the ride). This in particular tends to happen to bicycles with triple chainrings, as all my bikes had. It's one of the reasons I've switched to 1x --- with a narrow-wide chainring, no FD, and a clutch derailleur these don't tend to happen.

[Joe Bernard]

I shall speculate: 

I see a chain on the middle ring that stayed stuck to the teeth at the bottom and came back up the backside until it jammed in the derailleur. 

Causes:

1. Old gloopy lube could stick to the chainring teeth. 

2. A worn tooth might snag the chain (I'm less convinced of this one). 

3. I see chain pickup pins on your rings which tells me you may also have crooked teeth (can't see them) on the middle ring to aid shifting..one of those may have caught the chain. 

4. It's a 10- or 11-speed chain and a smidge narrow for those rings. Riv claims they're good up to 10 but those Silver cranks were introduced when all Rivs used 8 or 9, they usually work with 10 (not 11) anyway but you may have gotten unlucky today. 

Solutions: 

Clean goop off, check for wear, on your next ride check to see if your chain is trying to catch on the bottom run as it passes the ring back to the rear derailleur. 

On Thursday, September 15, 2022 at 7:43:43 PM UTC-7 Matthew Williams wrote:

[Joe Bernard]

Clarifying: I don't actually know what chain you're using, I'm just wondering if you have a 10- or 11-speed chain on those 7/8/9-ish rings. A 10 should work but you could get unlucky, an 11 probably won't. 

[Nick Payne]

I'd say that your middle chainring is probably quite worn, to the point where the teeth refused to let go of the bottom run of the chain and carried it up and around until it jammed under the derailleur and top run of chain. As to how to avoid it, replace chainrings before they get to that point of wear. I can't see that using an 11-speed chain on older chainrings can cause a problem, as the width of the rollers has not changed as the number of speeds has increased (at least up to 11-speed). Leonard Zinn explains it here: https://www.velonews.com/gear/tech-faq-chain-width-explained-compatibility-queries-answered/.

I have unused chainrings dating all the way back to 6- and 7-speed days, the width of the teeth on them is no different to that on modern chainrings, and I've run 11-speed chains on the older rings without any problem. 13-speed Campagnolo Ekar is the only groupset I have where the internal chain width and chainring tooth width have both been decreased from the widths of fewer speed setups.

Nick

[Garth]

That FD .

If I only know classic looking FD's with their nice long cages, I'd say that particular FD looks like it's been chopped off. Of course that not literal, but functionally it has been. I can totaly see how such a cage could jam as seen in the photo. I can't see exactly how many teeth on the big ring but by what I can count it's more than 42 teeth, and those FD's supposedly are for a 42t ring max. I can't that in itself means anything, all that matters is the chain appears to have jammed where on a full cage FD it would not. 

You know, there are better ways to accomodate smaller rings that still use a traditional looking/functioning cage. Just scale it down, but just chopping it off in the front not lonly looks awful it looks like it actually was chopped off by someone in their garage. Spare me the "to each is own" nonsense, it looks awful. A big fancy coporate name doesn't make those behind the mask infallible to wonkiness. 

[Joe Bernard]

With the disclaimer that I highly doubt chain width is the OP's problem - it was just one of the possibilities I introduced, I think old goopy lube and/or a worn drivetrain are most likely - I do not agree with Mr. Zinn. My Wipperman 8-speed chain does indeed have a slightly wider inner width than my 11-speed from the same company. Is it enough to to change the 3/32 designation? Doubtful. Is it enough to mess up running my 11-speed chain on a 1x chainring labeled 9/10 speed? No. But there's a difference there, which is why I brought it up while I was throwing darts at the board to see how many possibilities there was for Matthew's problem. 

[ascpgh]

"Chainsuck"' usually traps the chain between the sides of the chainrings and the stay of the frame, carving paint and scratching the metal. I'd say when you get it all freed up to clean your chain (there is a quick link there) and measure a foot of it from pin center to pin center with a good ruler. I'll bet you'll fin i it more than 1/8" long on the far end. 

A worn chain won't fit well on chainring teeth, it will stick momentarily before disengaging. "Sucking".

A stretched chain will wear down the aluminum chainring teeth over time, making it not mesh well with a new chain (or the worn old one either).

A way to see the health of your chain and its fit with your chainrings is to pull on it at the mid point of its wrap arouns any of the chainrings. If it is engaging the teeth well it shouldn't be able to be pulled too much off the teeth. Stretched chain and/or worn teeth will let the chain be pulled away from the ring's teeth a fair mount.

I see daylight between one of the chainring teeth and the chain (obviously pulled tight in your photo) that leads me to believe you have one or both forms of wear going on.

Andy Cheatham

Piittsburgh

[Garth]

Regardless if the chain width is a contributing factor or not(It's the FD that is the crux of the issue), 5-8 speed chains are not the same inner width as 9-speed and above. 

Would I use an 11-speed chain on a 7-8 speed cassette/FW ?  Absolutely not. I've used a 9 to try and it worked okay, but have gone back to 8's as I prefer SRAM 8xx series chains to any KMC of the same speed. 

Chain width inner standards, from here : 

https://bike.bikegremlin.com/3555/bicycle-drive-chain-dimension-standards/#2For inner chain width there are the following standard dimensions:

• Single speed chains have inner width of 1/8″ (3.175 mm).
• Multi speed chains, from 5 to 8 have inner width of 3/32″ (2.38 mm).
• Multi speed chains from 9 to 12 speeds have inner width of 11/128″ (2.18 mm)

[lconley]

Lack of maintenance would be a prime factor in my mind. Keeping the drivetrain and the rim braking surface clean will prevent problems and extend the life of components.

Laing

Delray Beach FL

On Thursday, September 15, 2022 at 10:43:43 PM UTC-4 Matthew Williams wrote:

[James Valiensi]

Hi,

It appears the front derailleur was positioned too high. Your chain rings look okay. 

When the derailleur is in the middle spot, the bottom of the outer cage should be about 1/16” (1.9mm) above the tips of the big chainring.

Also, you have a lot of chain to get it wrapped up like that. I think it may be too long. If you wrap the chain around the big chainring and big cog, without going thru the rear derailleur, the chain should have 2 links more than needed to connect the loop. 

Best luck

James

<IMG_2979.jpg><IMG_2980.jpg><IMG_2981.jpg><IMG_2982.jpg>

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[Wesley]

I'm confused by folks who are saying the front derailer caused this. The chain that jammed was pulled up from the bottom of the chainring before it jammed in the derailer. The root problem is why did the chain stick to the chainring (defying gravity and the pull of the rear derailer) rather than releasing from the chainring? I don't know the answer - stiff chain links, bent chain, too narrow chain/too wide chainrings, sticky chain all seem plausible.

-Wes

On Thursday, September 15, 2022 at 7:43:43 PM UTC-7 Matthew Williams wrote:

[Joe Bernard]

Agreed, it's not a front derailleur problem beyond the fact that it exists and is on the frame. 

[Garth]

It appears the whole thing was just a "perfect storm" of stuff hitting the fan. The chain appears to be wedged in between the FD and the ring, so yes..... it is surely relevant beyond existing on the frame. The saddle, that's merely existing on the frame and having no part in this.

My best guess is as good/worthless as any other guess ! I've had some weird chain stuff happen on my Bombadil also, but never jammed up against the FD like that (9-speed cassette and chain w/7-8 speed crank). They don't always get along. My chains are all clean and in perfect working order, adjusted perfectly, yet still.... "every once in a while" in shifting .... W T F  just happened ?  

I do agree though with the gap of the FD being too high, at least in this particular case. Having a full FD cage "may" have prevented it from getting wedged in like it did or to that extent. I said "may", so don't anyone have a cow. .  .  .   moo . ;-)

We're all just trying to help a guy out of a "jam'.

[Joe Bernard]

I shall have a cow over the relevancy of the derailleur, it did not cause the problem, it was the place where the problem ended. The implement does not exist on my Riv, hence the chain suck would have ended at the chain eventually dropping out of the suck or - worst case - falling off my single chainring. Short of saying Matthew shouldn't have triple rings and a front derailleur - which would be insane, I'm not saying that - I can't see how the fd was a problem. The chain, it sucked. 

[Matthew Williams]

Thanks for your help, everyone. I very much appreciate it. Earlier this morning, I took my bike to the shop; here’s what we found and fixed:

1: The chain was stretched and kinked. 

2: The front derailleur was loose and out of alignment.

3: The front rings and rear cassette were all in good shape.

The chain was the original when the bike rolled off the Rivendell floor, so it’s over six years old and has at least 500 miles on it. I was a little surprised at the short lifespan of the chain, but I’m assuming that’s normal. We installed a new chain, and realigned, adjusted, and tightened the front derailleur.

For the past year, I’ve been hearing a “crack,” when I’m pedaling under power, but I haven’t been able to correlate the sound with a specific ring or shifting position. I was worried the sound was a broken tooth on the rear cassette, but the mechanic believes the sound has been the chain skipping or misaligning on the rear cassette.

If I was out on a long ride and this happens again, how would I fix the issue, and what tools would I need?

[Piaw Na(藍俊彪)]

Chains falling of a chainring is OK. You just stop and put it back on. I've done that many times and it's no big deal. I wouldn't even bother talking about it. A chain getting jammed inside the FD? That is occasion for much cursing.  A chain getting caught in the FD and then jamming in between the chainstay and the wheel or crank? That could be a bike ending problem.

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[Piaw Na(藍俊彪)]

Even on a mountain bike 500 miles would be a short lifespan for a chain. Last time I heard a "crack" on my  bike it was because my frame cracked. Since you use quick links, the appropriate tool to carry is granite talon tyre lever chain pliers: https://amzn.to/3xuE7j2. I'd also carry the a set of allen wrenches to remove the FD. (You may also need a screw driver to remove the FD cage so you can use the chain pliers).

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[Joe Bernard]

Hey Piaw, joke's on me. Matthew says the chain was stretched AND the derailleur was in a bad position! 🤣

Joe "hey, don't ask me" Bernard 

[Piaw Na(藍俊彪)]

I don't get it. How could an FD slip "up" the frame? Usually it slips down, no?

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[Joe Bernard]

I don't see anything about "up", he said - sorry for speaking for you Matthew - it was loose on the seattube and out of alignment with the rings. I'm not entirely convinced this made the problem worse btw, the chain was going to suck back up the rear of the chainring and run into a properly aligned fd, too. A chain doubled up in that cage was going to stop regardless. 

[Garth]

At the very least Mathew the appropriate size allen wrenches to loosen the FD cable and raise FD itself so you can see if the chain will come loose on it's own or requires a little tugging. If it requires more force, seeing that the RD is stretched out to the max you should release the chains quick link, if you can, but hold on tight to prevent a rebound effect and slowly let it return to shape. If it's all too tight, you may need to remove the RD to relieve the stress. Then, try working the jam with a little rocking motion if really stuck, avoid making it worse with more force. Of course I wasn't there so I can't for certain how I'd get it free exactly, but this is at least how I'd approach it. It helps to carry some nitrile disposable gloves too, 5 mil of okay but 6 or 7 is even better. I also carry a singly wrapped hand wipe.All the greasy gloves and wipe can be placed in one glove turned inside out, greasy side in !

[Matthew Williams]

I should add:

1: I don’t know if the front derailleur was loose or misaligned prior to the chain snarl. I’m wondering if the chain kink and the buildup of lube caused it to bind up. I was pedaling—but not hard—so when the chain hit the front derailleur, it knocked the derailleur loose and out of alignment. Maybe?

2: I mistyped the chain mileage—it’s probably closer to 4500 miles. I’ve had the bike for two years and I ride nearly every day, usually between 2 and 10 miles. I’ve also ridden several 30 to 50 mile day trips and one day of 100 miles (go me, finally!).

365 x 2 = 730
730 x 6 mile (daily average) = 4380 miles
4380 + 500 miles (day trips) = 4880 miles

[Joe Bernard]

This makes more sense! I had a feeling 500 miles was a typo. 

As for how to solve it on the road, a friend had this problem a couple years ago. She texted me about what to do (this was when she was still learning bike mechanics, she knows more than me now) and before I could think of something she had bounced the bike up and down and it shook free. When all else fails, bounce it! 🙃

[Piaw Na(藍俊彪)]

4500 miles does sound like that's enough to wear out a chain. You must have gotten lucky if it didn't wear out the sprockets and chainrings if you were riding a worn out chain for any length of time. A chain that's been elongated from wear can definitely wrap around the derailleur and get bent all out of shape. The new Park CC-4 wear indicator is something definitely worth getting. 

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[brizbarn]

I always carry a multi tool that has a chain breaker built in, and have used it more than several times to remove or add a link when I've broken my chain on a ride. the quick link pliers are a great tool to carry as well, but I don't currently have a small pair, so don't carry them, I carry a Leatherman in my pocket tho. Also carry a spare quick link, make it sure it is the correct size for your chain (9 speed in your case), and ideally the same brand as your chain.  Also a few extra links of chain are good to carry too.  And a little rag doesn't hurt either to clean your hands, or wipe off excess lube from chain.

I've had a small burr develop on my cassette which caused the chain to skip.  One could form on a chainring I presume, and cause the chain to suck like it did.