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CityCyclingEdinburgh Forum » Questions/Support/Help

1. AKen
   Member

   I have a single front chainring. Recently, the chain has occasionally started to slip off when pedalling - coming off onto the side away from the frame and towards the pedals. If I am not careful, it can then get jammed in the gap between the chainring and the guard that is attached to the chain ring.

   Does anyone have any advice on why this might be happening - and more importantly how to prevent it? I think it seems to happen when I am changing up to 1st gear

   Both the chain and the chainring are less than 9 months old so not badly worn.

   If I discover it is starting to slip off, I can sometimes persuade the chain to slip back onto the chain ring by dropping down several gears, as the chain is pulled left across the rear cassette to the larger rings, this seems to also pull the chain back left onto the front chainring. Any thoughts? Something to do with the adjustment on the rear derailleur?

   Posted 11 years ago #

2. wingpig
   Member

   Chainline.

   Perhaps exacerbated by nine months' wear, when the chain is towards the right-hand-side on the back it's too far to the right of the chainring - perhaps it's only started happening now as with fresher teeth and a snugly-meshing chain the chainring was able to keep a tighter grip on the chain. If your chainring is removable from the spider/crank you might be able to find some chainring bolt spacer washer things in a Bike Station to nudge the chainring a few mm outwards, otherwise you might need a different axle width of bottom bracket.

   Posted 11 years ago #

3. DaveC
   Member

   How long have you had the bike, or more to the [point how many miles have you ridden? Are the teeth nice and cleanly shaped like when new or are the more like shark's fins? When the chain wears the space between the pins gets further apart and the chain tends to ride up onto the teeth instead of sitting nicely with the pins between the teeth. This sort of slipping started happening on my Dawes at the start of spring and I changed the chainrings for Stronglight which are not the lightest but hard wearing.

   Posted 11 years ago #

4. AKen
   Member

   Thanks for the replies. I've had the bike for many years but replaced the chainring and chain around September last year so the teeth are still fairly well-shaped. But, as it's not the original ring, it's possible that the older one was a bit wider and putting a newer, more narrow one might create the situation described by wingpig above. I'll have a close look at what line the chain takes when in top gear.

   Posted 11 years ago #

5. remberbuck
   Member

   I'd agree with Wingpig that chainline might be the answer. I wonder if you are going where others do not. I'm guessing that you have no front derailleur

   Those of us who do know the grinding sound when the chain hits against the derailleur when the chain is out of line e.g. on the small front gear and changing to the smallest rear gear. It strikes me that if I had a single front gear then the chain could come off like yours particularly if I've been aggressive about changing up and as part of a sequence.

   One other less likely thought. Is your chain tension OK? I ask because I foolishly under tightened the chain on my single speed once and found that the chain was slipping off the front if I combined too powerful a down stroke with a bump on the road.

   Either way the power loss isn't funny.

   Posted 11 years ago #

6. AKen
   Member

   I had a look at this bike over the weekend. A quick 10-second check weekend revealed that one of the nuts/bolts holding the chain ring to the spider is missing (presumably worked loose and then jolted off by a bump)and another is not at all tight. I tried to tighten the loose nut but couldn't get sufficient grip on the back of the corresponding bolt with a screwdriver to stop it rotating when tightening. (Probably need the special tool, the name of which I do not even know.)

   Any ideas how easy it would be to get a replacement nut, spacer and bolt?

   Posted 11 years ago #

7. DaveC
   Member

   Are they both allen bolts? I may have a spare. Mine are the tarditional allen bolt and allen nut, more like a hollow bolt with smooth outer. Most shops will have them.

   Posted 11 years ago #

8. kaputnik
   Moderator

   Longshot, but is the replacement front ring of the "Hyperglide" type or similar? They have little ramps and bumps milled into the inside of the ring surface to assist the chain in shifting smoothly as a force begins to apply on it from the side.

   As the others note above, the extremities of chainline in top or bottom gear may be enough to encourage the chain to fall off.

   If it is one of those sorts of chainrings, next time I would look one out that doesn't have them.

   Another cheap solution (sometimes used in CX where there's a single front ring) is to fit an old or broken front derailleur permanently set into the right position using the limit screws, to stop the chain from dropping off.

   (Probably need the special tool, the name of which I do not even know.)

   Chainring bolt tool. There's one in the EBC starter tool kit.

   A friendly shop such as The Bicycle Works can probably sell you a single replacement bolt. Alternatively the Bike Station will have some kicking around and will probably just ask for a donation for it.

   Posted 11 years ago #

9. AKen
   Member

   Are they both allen bolts? I may have a spare. Mine are the tarditional allen bolt and allen nut, more like a hollow bolt with smooth outer. Most shops will have them.

   The bolts are tightened with an allen key and fit into a cylindrical nut with a slot at the end for the chainring bolt tool. I imagine the ones I have are pretty commonplace.

   Longshot, but is the replacement front ring of the "Hyperglide" type or similar?

   I'm not sure, would need to check this but it was a basic replacement so perhaps not.

   Another cheap solution (sometimes used in CX where there's a single front ring) is to fit an old or broken front derailleur permanently set into the right position using the limit screws, to stop the chain from dropping off.

   I think I have an old derailleur tucked away some where. I could give this a go but shall try the bike station first, they were very helpful last time I needed something.

   Posted 11 years ago #

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