Chain jumping off sprockets

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paieye
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Joined: 29 Jun 2012, 7:48pm

Chain jumping off sprockets

Postby paieye » 9 Jul 2013, 7:37pm

After years of riding a wonderful 2-speed Brompton, I have been persuaded to invest in a 21-speed hybrid bicycle --- as well as, not instead of, of course.

The hybrid is terrific, but I find that the chain easily jumps off the sprockets when I change down. Is it wrong to pedal while you are changing down ? Is it wrong to change down when you are going uphill ? Does it matter if you set the rear gear to perhaps 5, and from then on work your changes just on the front gear ?

In other words, am I doing something wrong, or is there some adjustment to the drive that I ought to consider ?

The hybrid is a Raleigh Voyager, and the drive is -- I think -- a Shimano.

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531colin
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Joined: 4 Dec 2009, 6:56pm
Location: North Yorkshire

Re: Chain jumping off sprockets

Postby 531colin » 9 Jul 2013, 8:39pm

You have to pedal to change gear, or the chain can't move from one sprocket to another. Its best to just pedal gently at the actual moment of changing, which takes a bit of co-ordination going uphill, to avoid stopping!
When using the middle chainring of 3, you should be able to use all (7) sprockets. On the big ring, the big (low gear) sprocket is probably out-of -bounds, and on the small ring, the smallest sprocket or two should not be used.
Where does the chain go when it falls off?

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cycleruk
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Location: Lancashire

Re: Chain jumping off sprockets

Postby cycleruk » 9 Jul 2013, 8:45pm

A triple of questions.
Is this a brand new bike from a shop?
Are you talking front (chainrings) or back (sprockets) gears?
Do you mean the chain jumps clear of or just moves between sprockets?

Regarding changing gear.
You have to keep pedalling to change gear but it does help to reduce the pressure on the pedals while doing so.
Not ideal to change gear while riding up hill but sometimes needs must.

If bought from a shop then take it back and ask them just to check it out.
There's no such thing as a tailwind.
It's either a headwind, or you're going well.

paieye
Posts: 81
Joined: 29 Jun 2012, 7:48pm

Re: Chain jumping off sprockets

Postby paieye » 9 Jul 2013, 9:14pm

No, the bicycle is 2nd-hand. The chain drops down between the front chain-rings. I shall take it back to the (very helpful) shop tomorrow, and go from there.

PT1029
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Joined: 16 Apr 2012, 9:20pm

Re: Chain jumping off sprockets

Postby PT1029 » 9 Jul 2013, 9:24pm

If the chain is jumping between the front sprockets (chain wheels),
If jumping means falling between the chain wheels, then at some point in the past the chain has jammed and spread the chain wheels apart (ie, creates a bigger gap into which the chain can fall). Visual comparison with a known good crankset usually confirms this.
If jumping means catching the neighbouring chain wheel and rubbing/changing onto said neighbour, the crank and or chainwheels and/or BB axle bight be bend, or the BB bearings are totally worn out and loose. Back pedal the cranks round, the chain wheels should run true, if they move from side to side then something is bent as per above.
If the BB bearing is worn/loose, you should be able to wobble the (stationary) cranks from side to side by hand. Check any free play is the BB bearing and not the pedal bearings (better to hold the crank to avoid this).

paieye
Posts: 81
Joined: 29 Jun 2012, 7:48pm

Re: Chain jumping off sprockets

Postby paieye » 9 Jul 2013, 9:28pm

Thank you, I shall look at all of that.

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531colin
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Location: North Yorkshire

Re: Chain jumping off sprockets

Postby 531colin » 9 Jul 2013, 10:56pm

There shouldn't be space between the chainwheels for the chain to fit into. I suspect the bike has a cheap chainset with steel rings permanently riveted together, and its been bent at some time in the past. Its also possible the chain is damaged.......
Your secondhand bike may not be such a bargain.... :(

Binkyboy
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Joined: 29 Oct 2010, 5:05pm

Re: Chain jumping off sprockets

Postby Binkyboy » 10 Jul 2013, 1:02pm

I assume the chain and chainrings and cogs are all new or nearly new?
If not, an old chain on a new cog and/or chainring will skip, and any other combination of new/old.

paieye
Posts: 81
Joined: 29 Jun 2012, 7:48pm

Re: Chain jumping off sprockets

Postby paieye » 14 Jul 2013, 9:04am

The near-side gear-change unit has a small adjuster-wheel for this very purpose, and a small adjustment has eliminated the fault. Thank you all for your help.