Derailler Problem.

Neil Smith said the following on 27/11/2006 16:23:

Quoted message said:

Dear All,
I fitted a new chain - the same length as the old - now the
upper pulley wheel bumps and sometimes jams against the rear cogs, usual the
lower middle. When the chain is on the the largest front and rear cogs it
seems tight. Should I add an extra link?

It sounds as if the old chain is shorter than the new because of lack of
wear. Did you actually count links, or measure? Mind you, it would
have to be very badly worn for there to be that much difference. A
better way of checking the chain length is to wrap it around the largest
cog and the largest chainring (not through the derailleur), pull it
tight then add a link.
http://sheldonbrown.com/derailer-adjustment.html#chain explains it much
better!

If that fails, then the B-adjustment screw needs adjusting.

I have to ask - why did you replace the chain? Was it worn? If it was
worn enough to need replacing, it's almost certain that the cassette and
chainrings will need replacing as well.

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

Neil Smith said:

Dear All,
I fitted a new chain - the same length as the old -
now the upper pulley wheel bumps and sometimes jams against the rear
cogs, usual the lower middle. When the chain is on the the largest
front and rear cogs it seems tight. Should I add an extra link?

No, that will /decrease/ clearance between upper pulley wheel and cassette,
and the chain doesn't need to be longer if it's long enough for the largest
combination. Doesn't matter that it's tight because it's not a combo that
you should normally use.

I can't think what could be causing the problem if it was OK with the
previous chain, but anyway try the B-tension screw....
www.sheldonbrown.com/derailer-adjustment.html

~PB

Paul Boyd said:

Neil Smith said the following on 27/11/2006 16:23:

Quoted message said:

Dear All,
I fitted a new chain - the same length as the old -
now the upper pulley wheel bumps and sometimes jams against the rear
cogs, usual the lower middle. When the chain is on the the largest
front and rear cogs it seems tight. Should I add an extra link?

It sounds as if the old chain is shorter than the new because of lack
of wear.

An unlikley way round, isn't it? Old chain isn't much worn so replace it
with one that's more worn?

Quoted message said:

Did you actually count links, or measure?

Or lay the new chain besides the old one?

Quoted message said:

Mind you, it
would have to be very badly worn for there to be that much
difference.

Sometimes there's just enough difference the other way round. A new chain
(or removing one link from old chain) cures rubbing between upper jockey
wheel and cassette.

Quoted message said:

A better way of checking the chain length is to wrap it
around the largest cog and the largest chainring (not through the
derailleur), pull it tight then add a link.
http://sheldonbrown.com/derailer-adjustment.html#chain explains it
much better!

If that fails, then the B-adjustment screw needs adjusting.

I have to ask - why did you replace the chain? Was it worn? If it
was worn enough to need replacing, it's almost certain that the
cassette and chainrings will need replacing as well.

Not true. They won't necessarily need replacing if the chain is replaced
early enough. Cassettes often last for two, three or four chains like this,
large chainrings practically forever.

www.sheldonbrown.com/chains.html explains it much better :-)

~PB

Response to Pete Biggs:

Quoted message said:

Quoted message said:

Did you actually count links, or measure?

Or lay the new chain besides the old one?

When I last replaced the chain on the bent I counted links & tied the
old & new chains together with a bit of string every n links, where n is
the highest number at which I could be confident I hadn't lost count.

--
Mark, UK
"Defoe says that there were a hundred thousand country fellows in his
time ready to fight to the death against popery, without knowing whether
popery was a man or a horse."

Pete Biggs said the following on 28/11/2006 01:15:

Quoted message said:

An unlikley way round, isn't it? Old chain isn't much worn so replace it
with one that's more worn?

Er, yes. I meant to say "new chain".

Quoted message said:

Or lay the new chain besides the old one?

That's really what I meant by 'measure'. I didn't think anyone would
actually think I meant get out a tape measure in this context.

Quoted message said:

Not true. They won't necessarily need replacing if the chain is replaced
early enough.

I suspect that in this instance the chain was replaced because it was
badly worn rather than as a pre-emptive measure.

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

Paul Boyd wrote on 27/11/2006 16:35 +0100:

Quoted message said:

It sounds as if the old chain is shorter than the new because of lack of
wear. Did you actually count links, or measure?

If the old chain was that worn that it made a difference it would have
fallen apart because the pins would have had to have worn through the
bushes. Chain lengths can only be set to +/- one link length. An
extremely worn chain might be an extra 1/4th of an inch longer - i.e.
much less than one link length.

--
Tony

"Anyone who conducts an argument by appealing to authority is not using
his intelligence; he is just using his memory."
- Leonardo da Vinci

Tony Raven said:

If the old chain was that worn that it made a difference it would have
fallen apart because the pins would have had to have worn through the
bushes. Chain lengths can only be set to +/- one link length. An
extremely worn chain might be an extra 1/4th of an inch longer - i.e.
much less than one link length.

A moderately worn chain can make the difference when the chain was on the
brink of being too long for bottom gear in the first place. Sometimes the
chain has to be longer than ideal when using a wider range than the mech was
designed for.

~PB

I tracked the problem down to a masterbolt in the chain that had worked
lose. Ah! Shimano.
Thanks for your help
"Neil Smith" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

Dear All,
I fitted a new chain - the same length as the old - now the
upper pulley wheel bumps and sometimes jams against the rear cogs, usual
the lower middle. When the chain is on the the largest front and rear cogs
it seems tight. Should I add an extra link?
Thanks
Neil