Keep losing chain

[PhilD]

Dear all,

I regularly ride four different cycles (not all at once, before anyone
suggests it!): two with deraileur gears and two with hub gears. Three
cycles are fine, the fourth keeps losing the chain. The problem bike
is a Giant Expression N7, which for those not familiar has hub gears,
so no chain flapping about, so no reason for the chain to fall off.

What's going on?

I only lose the chain by the wheel, not by the pedals. It is possible
that hitting a bump in the road triggers an unwanted jump, though that
may be coincidental. Nothing looks broken or worn (the bike is just
over 1). The jumping is intermittent (there was no problem last
Saturdey, but I lost the chain yesterday, for example), and only
started about 4 months ago.

Do any of you have any suggestions as to what to consider to right
this wrong, please?

Thanks,

PhilD

--
<><

[Paul Boyd]

PhilD said the following on 21/11/2007 10:13:

> Do any of you have any suggestions as to what to consider to right
> this wrong, please?

It sounds to me like it isn't tensioned properly.

--
Paul Boyd
http://www.paul-boyd.co.uk/

[Peter Clinch]

PhilD wrote:

> cycles are fine, the fourth keeps losing the chain. The problem bike
> is a Giant Expression N7, which for those not familiar has hub gears,
> so no chain flapping about, so no reason for the chain to fall off.

Just because you're not derailing to change gear doesn't mean "no
excuse". Indeed, with no /automatic/ chain tensioning as you get with a
spring loaded deraiieur/tensioner, possibly more of an excuse.

> What's going on?

I guess you may need to tension the chain. Not having an N7 myself I'm
not sure how one would go about that, but the typical mechanisms are
either horizontal rear dropouts, in which case loosen the back wheel and
pull it back a little (or lose a link from the chain and take up the
difference moving it forwards, if it's already as far back as it'll go),
or an eccentric bottom bracket, in which case move it around so as to
tighten the chain.

Pete.
--
Peter Clinch Medical Physics IT Officer
Tel 44 1382 660111 ext. 33637 Univ. of Dundee, Ninewells Hospital
Fax 44 1382 640177 Dundee DD1 9SY Scotland UK
net http://www.dundee.ac.uk/~pjclinch/

[James Thomson]

"PhilD" > a écrit:

> The problem bike is a Giant Expression N7, which for those not
> familiar has hub gears, so no chain flapping about, so no reason
> for the chain to fall off.

> What's going on?

You probably just have a little too much slack in the chain. You can slide
the hub back in the rear dropouts to take up slack. When you're done, check
that you can turn the cranks backward freely (no tight spots).

Another possibility is a poor chainline, which can lead to the chain
climbing off the sprocket under load. If you feel the chain tightening
before it jumps off, this is the likely cause.

http://www.sheldonbrown.com/chainline.html

James Thomson

[Pete Biggs]

PhilD wrote:
> Dear all,
>
> I regularly ride four different cycles (not all at once, before anyone
> suggests it!): two with deraileur gears and two with hub gears. Three
> cycles are fine, the fourth keeps losing the chain. The problem bike
> is a Giant Expression N7, which for those not familiar has hub gears,
> so no chain flapping about, so no reason for the chain to fall off.
>
> What's going on?
>
> I only lose the chain by the wheel, not by the pedals. It is possible
> that hitting a bump in the road triggers an unwanted jump, though that
> may be coincidental. Nothing looks broken or worn (the bike is just
> over 1). The jumping is intermittent (there was no problem last
> Saturdey, but I lost the chain yesterday, for example), and only
> started about 4 months ago.
>
> Do any of you have any suggestions as to what to consider to right
> this wrong, please?

Have a go at increasing chain tension if you can -- but don't have it quite
as tight as possible. There should be some "give", otherwise you'll get
excessive friction and wear within the chain. You'll be able to feel it
when turning the cranks by hand if there is too much drag.

~PB

[Jonathan Schneider]

Maybe the derailler's chain tensioner is gunged up and needs cleaning
and lubing. It certainly afflicts my commuter from time to time.

Jon

[PhilD]

On Nov 21, 10:32 am, Peter Clinch > wrote:
> PhilD wrote:
> > cycles are fine, the fourth keeps losing the chain. The problem bike
> > is a Giant Expression N7, which for those not familiar has hub gears,
> > so no chain flapping about, so no reason for the chain to fall off.
>
> Just because you're not derailing to change gear doesn't mean "no
> excuse". Indeed, with no /automatic/ chain tensioning as you get with a
> spring loaded deraiieur/tensioner, possibly more of an excuse.
>
> > What's going on?
>
> I guess you may need to tension the chain. Not having an N7 myself I'm
> not sure how one would go about that, but the typical mechanisms are
> either horizontal rear dropouts, in which case loosen the back wheel and
> pull it back a little (or lose a link from the chain and take up the
> difference moving it forwards, if it's already as far back as it'll go),
> or an eccentric bottom bracket, in which case move it around so as to
> tighten the chain.


Thanks (and to others who gave the same suggestion). I will have a
look at my spanners and see if there's one that will fit the wheel
nuts!

PhilD

--
<><

[Rob Morley]

In article >, Jonathan Schneider
says...
> Maybe the derailler's chain tensioner is gunged up and needs cleaning
> and lubing. It certainly afflicts my commuter from time to time.
>
With a hub gear?

[Peter Clinch]

PhilD wrote:

> Thanks (and to others who gave the same suggestion). I will have a
> look at my spanners and see if there's one that will fit the wheel
> nuts!

15mm usually the one, IIRC.

Pete.
--
Peter Clinch Medical Physics IT Officer
Tel 44 1382 660111 ext. 33637 Univ. of Dundee, Ninewells Hospital
Fax 44 1382 640177 Dundee DD1 9SY Scotland UK
net http://www.dundee.ac.uk/~pjclinch/

[Rob Morley]

In article >, Peter Clinch
says...
> PhilD wrote:
>
> > Thanks (and to others who gave the same suggestion). I will have a
> > look at my spanners and see if there's one that will fit the wheel
> > nuts!
>
> 15mm usually the one, IIRC.
>
Or the big adjustable one. :-)

[Paul Boyd]

Rob Morley said the following on 21/11/2007 13:03:

> Or the big adjustable one. :-)

What, the one with the big, serrated curved jaws?

--
Paul Boyd
http://www.paul-boyd.co.uk/

[M-gineering]

Paul Boyd wrote:
> Rob Morley said the following on 21/11/2007 13:03:
>
>> Or the big adjustable one. :-)
>
> What, the one with the big, serrated curved jaws?
>
nope, the one with the wooden handle and the lump of iron at one end

--
/Marten

info(apestaartje)m-gineering(punt)nl

[Rob Morley]

In article >, Paul Boyd
usenet.is.worse@plusnet says...
> Rob Morley said the following on 21/11/2007 13:03:
>
> > Or the big adjustable one. :-)
>
> What, the one with the big, serrated curved jaws?
>
No. :-)

[Rob Morley]

In article >, M-gineering
says...
> Paul Boyd wrote:
> > Rob Morley said the following on 21/11/2007 13:03:
> >
> >> Or the big adjustable one. :-)
> >
> > What, the one with the big, serrated curved jaws?
> >
> nope, the one with the wooden handle and the lump of iron at one end
>
That's just for removing cranks when the extractor thread is knackered.
:-)