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Chain keeps falling off

Old 01-08-20, 05:21 AM
  #1  
frugihoyi
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Chain keeps falling off

I have a bike with only a back derailleur and the chain keeps falling off.

At first I noticed this happening almost every time I shifted to the lowest or the highest gear even though I had taken my time making sure I had adjusted everything correctly. So I bit the bullet and adjusted the mechanism so that I cannot shift to either of those two gears. But it still happens sometimes that I'll be cycling, not even changing gears, and the chain will just fall off the front sprocket.

This isn't the kind of bike where I can move the wheel back to tighten the chain and I don't think I need to remove a link either because it actually looks pretty tight already.

What could be the cause? Should I take some pics?
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Old 01-08-20, 06:15 AM
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did you check the limit screws correctly?
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Old 01-08-20, 06:15 AM
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Do you have a 1x specific chainring? This is what usually happens when someone creates their own 1x drivetrain by using a chainring that was designed for shifting.
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Old 01-08-20, 06:17 AM
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Originally Posted by dsaul View Post
Do you have a 1x specific chainring? This is what usually happens when someone creates their own 1x drivetrain by using a chainring that was designed for shifting.
i didn't know that this 1x chainring exists...!
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Old 01-08-20, 06:53 AM
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More information about your drivetrain would be helpful, e.g. how many chainrings, what rear derailleur, etc. Also, do you ride on rough roads/paths? Assuming that your chain and cogs are in good shape (and you really need to check these), the usual cause of chain drop is insufficient tension provided by the rear derailleur. The simplest thing to try is to shorten the chain; however more effective solutions are to install a clutch derailleur and/or a narrow-wide chainring (if you have a 1x setup.)
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Old 01-08-20, 07:33 AM
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Yes, I think I adjusted the limit screws correctly; I watched a tutorial and spent a lot of time on it.

Is 1x chainring the same thing as a sprocket? I have something like this in the front:




So no, it wasn't designed for shifting; all shifting occurs at the derailleur by the back wheel.

When I get home I can check what the derailleur is and take some pics.

I ride mostly on good roads.

install a clutch derailleur and/or a narrow-wide chainring
Not sure what these are.
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Old 01-08-20, 07:36 AM
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Add a front sprocket chain guide; plenty offered on the interwebs.
They clamp onto seat tube like a dérailleur just fixed.
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Old 01-08-20, 07:41 AM
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Originally Posted by Tamiya View Post
Add a front sprocket chain guide; plenty offered on the interwebs.
They clamp onto seat tube like a dérailleur just fixed.
That seems like a good solution!
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Old 01-08-20, 08:18 AM
  #9  
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Is the chain worn out?
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Old 01-08-20, 08:41 AM
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Photos for sure.

I believe that chain guide is a bit of a band-aid solution and would aid if the chain were jumping of the front end..

A chainwheel which is straight and true should allow shifting in the complete range
There are single front chainwheels and chainrings available, though it really will not matter.

Is the derailleur hanger bent/ has the bike fallen over?
IMO this is a very likely cause, as it would be nearly impossible to get the derailleur adjusted to
function correctly if the dropout or derailleur hanger is bent.
This is most likely, especially if the problem just started to happen without any component changes.

Is the wheel in the dropouts squarely( you mentioned that the wheel cannot be adjusted to affect chain length- I am curious why)

Any new parts, wheels etc.?

The frame alignment can also affect this. Do the string test for alignment-
Take a long piece of string around headtube and touch each rear dropout. The spacing of the string at the seat tube should
be equal on both sides.

Have you checked dropouts and other frame members to see if they have released from their proper connections?
Does the bicycle handle funny, not ride or track like it once did?
Can you ride it (safely) no handed?

Photos from side, top and and rear.
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Old 01-08-20, 09:55 AM
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As our friends sayed above, mounting a chainguide will be the cheapest solution and should be taken in consideration after checking the condition of rear derailleur, limit screws, indexing. The clutch is a part that is putting tension on the chain making it sitting more firmly to the sprockets . Have you converted yourself the drivetrain from multiple chainrings to 1 by ? You might run into a problem caused by chainline where the chain might be ok with the middle gears but can go out on the ends.
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Old 01-08-20, 07:49 PM
  #12  
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Chain could be too long.
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Old 01-08-20, 11:14 PM
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Increasing the RD spring tension worked for me. Sachs-Huret Eco.
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Old 01-09-20, 02:57 AM
  #14  
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I got this bike used and I don't know if it has been modified in any way. Also it was filthy, I spent four hours cleaning it and still couldn't get all of the gunk off (you can see that in the close-up pics). I think a high-pressure wash could do the trick but unfortunately I don't have access to such a tool. Here are some pics:












Originally Posted by 100bikes View Post
I believe that chain guide is a bit of a band-aid solution and would aid if the chain were jumping of the front end..
Which it is.

Originally Posted by 100bikes View Post
Is the derailleur hanger bent/ has the bike fallen over?
IMO this is a very likely cause, as it would be nearly impossible to get the derailleur adjusted to
function correctly if the dropout or derailleur hanger is bent.
This is most likely, especially if the problem just started to happen without any component changes.
I don't know if it is bent, can you tell from the pics? Also, it has been happening from the beginning but I got this bike used so I don't know if there have been component changes.

Originally Posted by 100bikes View Post
Is the wheel in the dropouts squarely( you mentioned that the wheel cannot be adjusted to affect chain length- I am curious why)
The wheel fits into a very specific spot, it's not like my other bike where I can move it back and forth. Can you see that in the pics?

Originally Posted by 100bikes View Post
Any new parts, wheels etc.?
Not sure, the bike is used.

Originally Posted by 100bikes View Post
The frame alignment can also affect this. Do the string test for alignment-
Take a long piece of string around headtube and touch each rear dropout. The spacing of the string at the seat tube should
be equal on both sides.
I haven't had time to do this yet, but I'll try it and report my findings.

Originally Posted by 100bikes View Post
Have you checked dropouts and other frame members to see if they have released from their proper connections?
Does the bicycle handle funny, not ride or track like it once did?
Can you ride it (safely) no handed?
Everything looks fine, I can easily ride it no-handed.

Originally Posted by VladAlex View Post
As our friends sayed above, mounting a chainguide will be the cheapest solution and should be taken in consideration after checking the condition of rear derailleur, limit screws, indexing. The clutch is a part that is putting tension on the chain making it sitting more firmly to the sprockets . Have you converted yourself the drivetrain from multiple chainrings to 1 by ? You might run into a problem caused by chainline where the chain might be ok with the middle gears but can go out on the ends.
I haven't converted anything, but maybe the previous owner did.
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Old 01-09-20, 03:06 AM
  #15  
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Worn chain or bent link on chain
Worn or bent chain ring (on crank)
Misaligned chain line
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Old 01-09-20, 04:14 AM
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The scrape or damage on the outermost edge of the rear derailleur indicates the bicycle fell over and derailleur hanger is bent.
It would be the root cause.

While you can align it by "cold setting/ bending" the derailleur and drop out, it may be a better job for a LBS or someone with a dropout tool.

The derailleur is is an odd mounting to dropout, and not one I am familiar with. Curious if it is someones solution to an earlier problem.

Best of luck.
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Old 01-09-20, 04:46 AM
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Good pictures and lots of em, that's great.

I might be wrong .. are those tension pulley teeth as worn as they seem to me? I haven't seen one looking like that before.
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Old 01-09-20, 04:53 AM
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Originally Posted by JoeTBM View Post
Worn chain or bent link on chain
Worn or bent chain ring (on crank)
Misaligned chain line
Most probably the above. That chain looks horrible. And no, you don't seem to have a chainring that looks like the product image you posted above.
Check chain wear, chainring wear, cassette wear. You can't use extremely worn out drivetrain components and expect to not have problems.
And yes, that pulley jockey looks so extremely worn out. Although that won't be a factor in the chain falling off.

There are hundreds of videos on YouTube showing you how to check for drivetrain wear, and hundreds more websites. You should have a look at some of them.

Also, your drivetrain is extremely dirty, and the chain doesn't appear to have any lubrication at all.

Last edited by tomtomtom123; 01-09-20 at 04:57 AM.
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Old 01-09-20, 08:14 AM
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I'll check out the video. What's wrong with my chain? To me it just looks dirty.
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Old 01-09-20, 08:28 AM
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Originally Posted by frugihoyi View Post
I'll check out the video. What's wrong with my chain? To me it just looks dirty.
There is a lot of corrosion, it's very dirty, and it looks very dry without lubrication. If it's been running this way for a very long time, then there is a possibility that it has become stretched and elongated. Have you started to research any of the suggestions or tried any of the solutions that anyone has recommended? One thing you should do (plus the other previous recommendations) is to measure the chain stretch.
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Old 01-09-20, 09:27 AM
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Originally Posted by tomtomtom123 View Post
There is a lot of corrosion, it's very dirty, and it looks very dry without lubrication. If it's been running this way for a very long time, then there is a possibility that it has become stretched and elongated. Have you started to research any of the suggestions or tried any of the solutions that anyone has recommended? One thing you should do (plus the other previous recommendations) is to measure the chain stretch.
I haven't had time yet, I'll do it latest this weekend.
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Old 01-09-20, 11:38 AM
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The jockey wheels on the rear derailleur are toast, completely worn out.
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Old 01-09-20, 01:51 PM
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https://cimg6.ibsrv.net/gimg/bikefor...1f39087eae.jpg

In this pic the chain looks elongated. It's not sitting in the grooves of the teeth at the 12 and 6 o'clock position on the chainring. It's sitting on top of the teeth and suggests it's very stretched. And the teeth wear on jockey wheels also matches that. Look at Shimano jockey wheels when they are brand new. They have a flat tip. Yours are very pointed. To get them like would take many thousands of miles e.g 10k miles+. Most likely your cassette and chainring if original are also completely worn out at this point. I don't think the current chainring will take a new chain and would start to jump as soon as you put power through the crank. a very worn ring will accelerate wear on a new chain. My advice is dont bother with that. Replace the drivetrain bits - chain, cassette, chain ring and jockey wheels.

Your chainring is a normal un-ramped chainring. It's not a 1x narrow wide. But you could replace it with one to improve chain retention.

And it looks like you spent 4 minutes cleaning this bike, not 4 hours. a degreaser like dish soap and a scourer sponge will remove most of that gunk.

Last edited by trailflow1; 01-09-20 at 02:27 PM.
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Old 01-09-20, 02:13 PM
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The cassette teeth look really bad on the middle cogs. Bet the chain is super worn out and skipping on the biggest and smallest cogs, and that gives the chain a chance to bounce off the chainring.

Time to go shopping for some new parts.

Last edited by ThermionicScott; 01-09-20 at 02:20 PM.
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Old 01-09-20, 04:00 PM
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I wonder if the tires are completely worn down. It looks super slick in the photos. If it weren't "slick" tires, then all of the groves on the tread have been completely worn away.
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