Keep losing chain

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

Quoted message said:

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/

PhilD said:

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.

Quoted message said:

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 [email hidden] http://www.dundee.ac.uk/~pjclinch/

"PhilD" <[email hidden]> a écrit:

Quoted message said:

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.

Quoted message said:

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

PhilD said:

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

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

Jon

Peter Clinch said:

PhilD said:

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.

Quoted message said:

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

--
<><

In article <[email hidden]>, Jonathan Schneider
[email hidden] says...

Quoted message said:

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?

PhilD said:

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 [email hidden] http://www.dundee.ac.uk/~pjclinch/

In article <[email hidden]>, Peter Clinch
[email hidden] says...

Quoted message said:

PhilD said:

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. :-)

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

Quoted message said:

Or the big adjustable one. :-)

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

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

Paul Boyd said:

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

Quoted message said:

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

In article <[email hidden]>, Paul Boyd
usenet.is.worse@plusnet says...

Quoted message said:

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

Quoted message said:

Or the big adjustable one. :-)

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

No. :-)

In article <[email hidden]>, M-gineering
[email hidden] says...

Quoted message said:

Paul Boyd said:

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

Quoted message said:

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.
:-)