Damaged rear mech

Rob Morley said:

Tom Crispin said:

In the longer term I am having maintenence issues with the Beinn 26s.
The chains appear to have stretched, and in gear 1 one of the jockey
wheels traps the chain between it and the large sprocket, making a
funny sound. The mech does have a tensioning screw, but this often
slips. Indeed, on the damaged mech the tensioning screw is
completely missing. Will I be able to resolve this issue by removing
a link from each of the bikes' chains?

That doesn't do quite the same thing - the B-tension screw adjusts the
angle of the parallelogram, chain length affects the attitude of the
cage. They're interrelated but different.

They both affect clearance between jockey wheel and sprocket when in bottom
gear. Scewing in the screw, or removing a link, will increase clearance.

(I've been there and done that a few times).

Quoted message said:

Quoted message said:

Is chain wear likely to be the cause?

If the B-tension screw is slipping then thread-lock compound should
fix it - Loctite 242 or equivalent (medium strength undoable). Chain
length should normally be adjusted so that you can just run big-big -
shorter can result in a nasty crunch and longer just leaves
unnecessary slack on small-small. It's possible that the chains were
originally a bit long, but wear shouldn't have that much effect.

Although it was after more than 2000 Km's worth of wear, I've had it happen
with bikes of mine when I've had to use a chain that was longer than ideal
for the bottom gear as I was exceeding the mech's capacity.

I wouldn't be surprised if the chain was originally longer than necessary.

~PB

I have taken this off one of my pool bikes, an Islabike Beinn 26.
www.johnballcycling.org.uk/photos/misc/rearmech

I do not know exactly how it came to get into this state. Possibly
the hanger bent when the bike was in a high gear after the bike was
previously dropped, and when the child riding changed into a low gear
the jockey wheel casing went into the spokes causing the damage.

As far as I can tell, the only damaged parts are the hanger - I keep a
stock of spares - and the outer jockey wheel casing. I am able to buy
a replacement without buying a whole new rear mech? If so, from
where?

In the longer term I am having maintenence issues with the Beinn 26s.
The chains appear to have stretched, and in gear 1 one of the jockey
wheels traps the chain between it and the large sprocket, making a
funny sound. The mech does have a tensioning screw, but this often
slips. Indeed, on the damaged mech the tensioning screw is completely
missing. Will I be able to resolve this issue by removing a link from
each of the bikes' chains? Is chain wear likely to be the cause? Each
bike has done about 2000Km in their lifetimes.

Thanks for your help.

"Tom Crispin" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

I have taken this off one of my pool bikes, an Islabike Beinn 26.
www.johnballcycling.org.uk/photos/misc/rearmech

I do not know exactly how it came to get into this state. Possibly
the hanger bent when the bike was in a high gear after the bike was
previously dropped, and when the child riding changed into a low gear
the jockey wheel casing went into the spokes causing the damage.

As far as I can tell, the only damaged parts are the hanger - I keep a
stock of spares - and the outer jockey wheel casing. I am able to buy
a replacement without buying a whole new rear mech? If so, from
where?

In the longer term I am having maintenence issues with the Beinn 26s.
The chains appear to have stretched, and in gear 1 one of the jockey
wheels traps the chain between it and the large sprocket, making a
funny sound. The mech does have a tensioning screw, but this often
slips. Indeed, on the damaged mech the tensioning screw is completely
missing. Will I be able to resolve this issue by removing a link from
each of the bikes' chains? Is chain wear likely to be the cause? Each
bike has done about 2000Km in their lifetimes.

Thanks for your help.

Only Campagnolo do spares down to component level.

I've twice put Chorus mechs into my rear spokes. This was due to there not
being enough chain to cope with the rear mech being accidentally put into
the large sprocket whilst the chain was on the large chainring. The largest
diameter that a chain has to cope with is not root diameter of the tooth, it
is the tip diameter plus the diameter of the chain's barrels. Add a couple
of links to cope with this.

--
David Lloyd
Time flys when you're having fun.
Your luggage flys only after you've left Terminal 5.

Tom Crispin said:

In the longer term I am having maintenence issues with the Beinn 26s.
The chains appear to have stretched, and in gear 1 one of the jockey
wheels traps the chain between it and the large sprocket, making a funny
sound. The mech does have a tensioning screw, but this often slips.
Indeed, on the damaged mech the tensioning screw is completely missing.
Will I be able to resolve this issue by removing a link from each of the
bikes' chains?

That doesn't do quite the same thing - the B-tension screw adjusts the
angle of the parallelogram, chain length affects the attitude of the
cage. They're interrelated but different.

Quoted message said:

Is chain wear likely to be the cause?

If the B-tension screw is slipping then thread-lock compound should fix
it - Loctite 242 or equivalent (medium strength undoable). Chain length
should normally be adjusted so that you can just run big-big - shorter
can result in a nasty crunch and longer just leaves unnecessary slack on
small-small. It's possible that the chains were originally a bit long,
but wear shouldn't have that much effect.

Pete Biggs said:

Rob Morley wrote:

Quoted message said:

Quoted message said:

That doesn't do quite the same thing - the B-tension screw adjusts the
angle of the parallelogram, chain length affects the attitude of the
cage. They're interrelated but different.

They both affect clearance between jockey wheel and sprocket when in
bottom gear. Scewing in the screw, or removing a link, will increase
clearance.

Shortening the chain increases A-tension, which can have the same effect
as reducing B-tension (and thus sprocket clearance).