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I have a Raleigh Caprice bike, about 7 years old, with sturmey archer 3 speed hub gears. There have been some problems with the hub gears in the past 9 months, which have been fixed by a mechanic.

Recently I had a puncture, and since taking the back wheel off to fix it, the chain keeps coming off and refusing to stay on. There is an unexpectedly loud 'bang' noise when it comes off.

I thought maybe I had not put the wheel on correctly (despite having done it several times before), so today I checked it all over.

There's no problem with the alignment of the wheel, the chainline looks fine, the chain isn't excessively worn and doesn't appear to have any stiff links and the wheel seems to be true. I put all the components relating to the hub gear back just as I always would before, and all the bolts seem adequately tightened. The chain is a bit mucky, but I don't think excessively so.

When I have the bike on the stand, I can turn the pedals and change through all the gears without problem. But when I try to ride it, the chain comes off. The first time today it came off as I moved the pedal backwards slightly to get it in the right position, but after I put the chain back on it happened again without any backpedalling. I think the chain is sometimes coming off at the front and sometimes at the back.

What else should I check or try? Could the internal hub gear be at fault?

I also thought I should check the cog that holds the chain at the front (chainwheel?), but I didn't really know what to look for. It did look a bit dirty/greasy but the teeth looked the right shape.

I'd be really grateful for any advice!

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    Some pictures will be helpful. Check the pedals: do they shake? – Alexander Jan 2 '16 at 17:50
  • Did you measure or just visually check your chain line? A few mm is way more important on a igh/single speed setup. Does the cog have a wobble? If you grab the crank arms can you get them wobbling left and right? Last question- did you pull your wheel back too far or not far enough and the chain tension is wrong? – BEVR1337 Jan 2 '16 at 18:30
  • Gidday and welcome to SE Bicycles. That's a really well written question with lots of pertinent details. I've never had an IGH so my only thought is chain tension is too tight - do you have a tensioner or is it adjusted by the axle position? – Criggie Jan 2 '16 at 23:29
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    Without photos it's really hard to tell. It used to work, you didn't change anything significant in terms of the parts you have, but now it doesn't work. So it's probably not assembled correctly. But we can't see what you've done without photos. – Nuі Jan 3 '16 at 23:13
  • My first guess would be that the chain isn't tight enough. – Daniel R Hicks Jan 5 '16 at 21:33
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In short: If chain comes off with horizontal drops (typical internal gear or single speed) the wheel has to be too far ahead. Try pulling wheel backwards until the chain can be moved <5 mm and tension the wheel properly.

Other possible issues are:

  • bent chainring or sprocket
  • wheel not installed properly
  • failed bearings in hub or bottom bracket

Worn chain is very unlikely. Also broken internal gears don't drop the chain.

  • Well, a worn chain would be one big reason for it not being tight enough. – Daniel R Hicks Jan 5 '16 at 21:32
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    That answer is just from my experience. I've serviced several internal gear bicycles even from early 1980's that had been in almost daily use, yet their chain had been just fine. A worn chain would just eat the sprocket and chainring, not come off, if tensioned correctly. – mkpaa Jan 9 '16 at 1:37
  • If the chain is very worn and the wheel has not been removed/re-tensioned ever (the rider has been lucky and not had to change tires or tubes for thousands of miles), then yes, the stretched out chain would have more slack than it would have had while brand new with the wheel in the exact same position. However, I think it's super unlikely that that would be the issue, since it would require riding thousands of miles without ever having to remove the wheel from the dropouts. – hairboat Aug 27 at 15:50
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Dropping chains in a no-derailleur setup can be caused by a lot of things:

Issues with the chain itself: bent or stiff links. Links often get bent when a chain derails when it's too loose, so just tightening the chain (fixing the original problem) doesn't fix it. Bent links can be hard to see.

Chainring and sprockets can have bent teeth.

Bad chainline. You're asking the chain to travel in a (slight) Z-shape, which it doesn't like to do. This could be caused by a few things:

  1. Misalignment at the wheel:

The wheel is mounted sideways in the dropouts, causing the chainring and sprocket to not be parallel. (Super obvious-- is the tire centered in the chainstays?)

Sprocket is bent.

Bearings in the hub are bad.

Axle is bent.

To check that, spin the wheel and watch the sprocket. If it wobbles, your hub is the problem. Could be bent axle or bad bearings or (rare) cracked or damaged hub shell.

  1. Misalignment at the chainring:

Bad bearings in the bottom bracket. (does the crank wobble when you flex it front-to-back, or side-to-side?)

Loose chainring. (does the chainring wobble, or are the bolts loose?)

Bent frame.

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