How to stop chain falling off

[lulubel]

My bike has just come back from a service at my LBS, and I now have some new problems that I'd rather solve myself because if I take it back he'll want me to leave it again, and I've already been without it 3 days this week.

So, on my ride today, I've had 2 problems.

1 - the chain is rubbing on the cage in the middle/large and small/large chainring/sprocket combinations on my triple. I know I could solve this by adjusting the lower limit screw, but ....

2 - when changing from the middle to small chainrings under minimal load, the chain misses the small ring without so much as a clatter, and lands neatly on the bottom bracket. The only way to change from middle to small successfully is to stop pedalling completely, flick the lever, and then turn the pedals very gently until the small ring is engaged (by which time I've practically rolled to a stop!)

These things seem to contradict each other, so how can I fix both?

I'm quite annoyed, to be honest, because I'd managed to get it set up perfectly, after a lot of trial and error, and stopping every time I get to the bottom of a steep hill to put the chain back on is not my idea of fun!

 

[Angelfishsolo]

My bike has just come back from a service at my LBS, and I now have some new problems that I'd rather solve myself because if I take it back he'll want me to leave it again, and I've already been without it 3 days this week.

So, on my ride today, I've had 2 problems.

1 - the chain is rubbing on the cage in the middle/large and small/large chainring/sprocket combinations on my triple. I know I could solve this by adjusting the lower limit screw, but ....

2 - when changing from the middle to small chainrings under minimal load, the chain misses the small ring without so much as a clatter, and lands neatly on the bottom bracket. The only way to change from middle to small successfully is to stop pedalling completely, flick the lever, and then turn the pedals very gently until the small ring is engaged (by which time I've practically rolled to a stop!)

These things seem to contradict each other, so how can I fix both?

I'm quite annoyed, to be honest, because I'd managed to get it set up perfectly, after a lot of trial and error, and stopping every time I get to the bottom of a steep hill to put the chain back on is not my idea of fun!

It is "possible" there is not enough tension in the front mech cable so when dropping into the bottom gear the mech cage returns to its default "No cable" position.

 

[HLaB]

At a guess, if anything you are wanting to tighten the low limit screw to stop the chain getting thrown past the small chainrings; it sound to me that the angle of your front dérailleur is slightly out have a look on youtube, I think Park tool also have a good section on front dérailleur adjustment.

Edit: Park tool guide
Bike tutor text guide (you have to pay for the video guide :-( )
Various youtube guides

 

[lulubel]

It is "possible" there is not enough tension in the front mech cable so when dropping into the bottom gear the mech cage returns to its default "No cable" position.

And by turning the pedals very, very slowly, I'm giving it a chance to catch on the teeth of the small ring before it drops? That would make sense.

Well, it's worth a try. Which way do I need to turn the adjuster to increase tension? (As I said in my first post, it's usually trial and error!)

 

[lulubel]

At a guess, if anything you are wanting to tighten the low limit screw to stop the chain getting thrown past the small chainrings; it sound to me that the angle of your front dérailleur is slightly out have a look on youtube, I think Park tool also have a good section on front dérailleur adjustment.

But tightening the lower limit screw will make the rubbing on the cage worse, won't it?

Would they have taken the front derailleur off to do the service? I know it was aligned perfectly before I took it in because that was an early problem that my original LBS failed to fix (and I had to take it on a 60 mile round trip to someone who diagnosed and fixed it in about 2 minutes).

 

[Angelfishsolo]

And by turning the pedals very, very slowly, I'm giving it a chance to catch on the teeth of the small ring before it drops? That would make sense.

Well, it's worth a try. Which way do I need to turn the adjuster to increase tension? (As I said in my first post, it's usually trial and error!)

Turn barrel adjuster towards bike to tension the cable.

 

[mickle]

Call the shop and ask them - firmly - when it would be possible for you to bring the bike back and wait while they do the remedial work necessary. 'Today or tomorrow at your convenience' is the answer you should get.

It's the only way - if you fanny about with it they can use that with a stick to beat you with.

The ups and downs and ins and outs of front derauillieur adjustment are complex. With respect to your mechanical abilities its among the most difficult components to adjust, I know planty of folks who can do almost everything from replacing a bottom bracket to truing a wheel but can't get their head around the front mech.

Go for it if you must but your service is covered by warranty, why not let them fix it?

 

[HLaB]

But tightening the lower limit screw will make the rubbing on the cage worse, won't it?

Would they have taken the front derailleur off to do the service? I know it was aligned perfectly before I took it in because that was an early problem that my original LBS failed to fix (and I had to take it on a 60 mile round trip to someone who diagnosed and fixed it in about 2 minutes).

It may make the rubbing worse but it'll stop the deraillment. Adjusting the angle of the cage slightly will stop that. They may have loosened the derailleur for cleaning and not quite set it up right when they were finished. I can't say definitely however they did or did not, I wasn't there at the time

 

[lulubel]

Call the shop and ask them - firmly - when it would be possible for you to bring the bike back and wait while they do the remedial work necessary. 'Today or tomorrow at your convenience' is the answer you should get.

Go for it if you must but your service is covered by warranty, why not let them fix it?

Service covered by warranty? To coin a much used phrase, "This is Spain."

Unfortunately, life just doesn't work like that here. If you want something done, the answer is usually "manana", which literally translates as tomorrow, but is used to mean "when I get around to it". It's just the way things are. Even if I did make an arrangement with him, I'd just get there and he'd tell me he was too busy to do it right now, just leave it with him and pick it up "manana".

 

[lulubel]

It may make the rubbing worse but it'll stop the deraillment. Adjusting the angle of the cage slightly will stop that. They may have loosened the derailleur for cleaning and not quite set it up right when they were finished. I can't say definitely however they did or did not, I wasn't there at the time

OK, I'll have a look. It just isn't something I want to mess with if I'm likely to make it worse.

On a positive note, the problems it had before it went in have been sorted, but it's frustrating that the only thing that was working perfectly is now not working very well at all.

 

[NormanD]

I found This to be the best understanding video to watch .. I hope helps you sort the problem out lulubel

 

[lulubel]

Well, I went through every check I could find, and couldn't see anything obviously wrong.

The cage looks straight to me - or at least no less straight than the one in the middle picture on the Park Tools guide, which isn't perfectly straight. The cage isn't touching the chain "at rest" in any gear.

I was frustrated enough to put it on the turbo trainer (since I don't have a work stand) to go all the way up and down through the gears. I couldn't do it under "load" because I didn't want to use any resistance on the trainer when I've got a road tyre on the back wheel, but I did go through the gears spinning fast, and I couldn't get the chain to jump off. What I did notice, though, was that the chain was moving from side to side when the pedals were spinning fast, and catching the cage when it was at its closest points (middle/large and small/large). I'm not sure why that would be.

I have adjusted the cable tension. I started out trying to be careful and scientific about how far I had turned the adjuster, but ended up just turning it to "see what happened", since I didn't seem to be doing any harm. I'm not sure that I've done any good either, but the gears were working on the trainer.

I think I need to take it out on the road again and see what happens, and that will have to wait until tomorrow morning because it's far too hot now.

 

[Angelfishsolo]

What I did notice, though, was that the chain was moving from side to side when the pedals were spinning fast, and catching the cage when it was at its closest points (middle/large and small/large). I'm not sure why that would be.

That sounds as though there is some play in the bottom bracket.

 

[lulubel]

That sounds as though there is some play in the bottom bracket.

I thought the point of having it serviced (at least it is for me) is to eliminate any problems like that? (It also wasn't doing it before it went in, and I assume play in the bottom bracket would be due to wear?)

Could it be that the chain is too long? I used this calculator, and it says it should be 53 links. I've counted them several times now, and I keep coming up with 54.

 

[Angelfishsolo]

I thought the point of having it serviced (at least it is for me) is to eliminate any problems like that? (It also wasn't doing it before it went in, and I assume play in the bottom bracket would be due to wear?)

Could it be that the chain is too long? I used this calculator, and it says it should be 53 links. I've counted them several times now, and I keep coming up with 54.

As you say "It is Spain" One link should make very little difference. You can check the BB by holding the crank arms and trying to move them towards and away from the bike. Movement = BB play and either a BB replacement or maintenance depending on its' type.