chain falls outside w/o shifting

Quoted message said:

New bike, full Dura Ace, 500 miles on it, compact crank (Truvativ
Rouleur CarbonCrank 50/36T, 23-11 cassette, Ksyrium SL wheels)
Going downhill I was passing a guy at a hairpin turn, and I when wanted
to re-gain speed by pressing semi hard on the crank (50-11) the chain
fell off outside. This was the 2nd time it happenned, in the same
cirumstances. No shifting was involved. Shifting and the drivetrain
overall are flawless otherwise. What is it? Does the crank bend when I
press hard on it?
Also, when back pedalling there is a hesitation in the chain. I
could've backpadaled half rev before the turn before the chain fell of.

1- Even if you can exert enough force on the pedal to significantly
flex a carbon crank (doubtful), flexing the crank won't cause the chain
to jump off.
2- I don't understand why you'd feel any need to backpedal *but* since
when you do you notice a "hesitation" I'd start by checking the chain
link by link to find the sticky one.
3- From your description I'd say you have a very nice bike. Didn't the
LBS you bought it from offer you a free initial tuneup? Even if they
didn't, take it back to them. I'd be surprised if a few free
adjustments didn't solve your problem.

Regards,
Bob Hunt

P.S.- You may want to repost this to rec.bicycles.tech

Bob said:

Quoted message said:

New bike, full Dura Ace, 500 miles on it, compact crank (Truvativ
Rouleur CarbonCrank 50/36T, 23-11 cassette, Ksyrium SL wheels)
Going downhill I was passing a guy at a hairpin turn, and I when wanted
to re-gain speed by pressing semi hard on the crank (50-11) the chain
fell off outside. This was the 2nd time it happenned, in the same
cirumstances. No shifting was involved. Shifting and the drivetrain
overall are flawless otherwise. What is it? Does the crank bend when I
press hard on it?
Also, when back pedalling there is a hesitation in the chain. I
could've backpadaled half rev before the turn before the chain fell of.

1- Even if you can exert enough force on the pedal to significantly
flex a carbon crank (doubtful), flexing the crank won't cause the chain
to jump off.
2- I don't understand why you'd feel any need to backpedal *but* since
when you do you notice a "hesitation" I'd start by checking the chain
link by link to find the sticky one.
3- From your description I'd say you have a very nice bike. Didn't the
LBS you bought it from offer you a free initial tuneup? Even if they
didn't, take it back to them. I'd be surprised if a few free
adjustments didn't solve your problem.

Regards,
Bob Hunt

P.S.- You may want to repost this to rec.bicycles.tech

thanks, Bob!
I moved at the same time as I bought the bike, and the LBS is now 40
miles away. Not that far, but I thought I can figure out this out by
myself (after all, I did figure out how to adjust stretched cables! 🙂 )

Quoted message said:

thanks, Bob!
I moved at the same time as I bought the bike, and the LBS is now 40
miles away. Not that far, but I thought I can figure out this out by
myself (after all, I did figure out how to adjust stretched cables! 🙂 )

You adjusted the limit screws when you tightened the barrel adjusters,
right?

Regards,
Bob Hunt

In article <[email hidden]>,

Quoted post said:

thanks, Bob!
I moved at the same time as I bought the bike, and the LBS is now 40
miles away. Not that far, but I thought I can figure out this out by
myself (after all, I did figure out how to adjust stretched cables! 🙂 )

You might also double check your chain for a stiff or bent link.

--
*Help Animals, the Earth and Your Health! *
*Find out how:* www.VeganStarterPack.com <http://www.veganstarterpack.com/>

Quoted message said:

Also, when back pedalling there is a hesitation in the chain. I
could've backpadaled half rev before the turn before the chain fell of.

Backpedaling with a bad chainline will tend to drop the chain. How bad
it is depends on the crankset and the shaping of its chainrings. You
can test this by wheeling the bike backward with the chain in various
positions on the rear cogset.

actually, no, I only tightened the barrel adjusters.

Bob said:

Quoted message said:

thanks, Bob!
I moved at the same time as I bought the bike, and the LBS is now 40
miles away. Not that far, but I thought I can figure out this out by
myself (after all, I did figure out how to adjust stretched cables! 🙂 )

You adjusted the limit screws when you tightened the barrel adjusters,
right?

Regards,
Bob Hunt

Quoted message said:

actually, no, I only tightened the barrel adjusters.

Then you should check the limit screws after you find the stiff link in
the chain. Alternatively, you could just shlep your bike that 40 miles
back to the LBS you bought it from to let them go through all the
driveline adjustments and check to make sure your wheels are still
true. Part of selling high end road bikes is (or at least should be)
making sure the customer gets his fair value for his money. Adjusting
cable tension and limit screws and trueing wheels within about 90 days
of the purchase seems pretty much standard at the shops I patronize.

Regards,
Bob Hunt

Quoted message said:

actually, no, I only tightened the barrel adjusters.

Then you should check the limit screws after you find the stiff link in
the chain. Alternatively, you could just shlep your bike that 40 miles
back to the LBS you bought it from to let them go through all the
driveline adjustments and check to make sure your wheels are still
true. Part of selling high end road bikes is (or at least should be)
making sure the customer gets his fair value for his money. Adjusting
cable tension and limit screws and trueing wheels within about 90 days
of the purchase seems pretty much standard at the shops I patronize.

Regards,
Bob Hunt

Quoted message said:

actually, no, I only tightened the barrel adjusters.

Then you should check the limit screws after you find the stiff link in
the chain. Alternatively, you could just shlep your bike that 40 miles
back to the LBS you bought it from to let them go through all the
driveline adjustments and check to make sure your wheels are still
true. Part of selling high end road bikes is (or at least should be)
making sure the customer gets his fair value for his money. Adjusting
cable tension and limit screws and trueing wheels within about 90 days
of the purchase seems pretty much standard at the shops I patronize.

Regards,
Bob Hunt

Quoted message said:

actually, no, I only tightened the barrel adjusters.

Then you should check the limit screws after you find the stiff link in
the chain. Alternatively, you could just shlep your bike that 40 miles
back to the LBS you bought it from to let them go through all the
driveline adjustments and check to make sure your wheels are still
true. Part of selling high end road bikes is (or at least should be)
making sure the customer gets his fair value for his money. Adjusting
cable tension and limit screws and trueing wheels within about 90 days
of the purchase seems pretty much standard at the shops I patronize.

Regards,
Bob Hunt

amakyonin said:

Quoted message said:

Also, when back pedalling there is a hesitation in the chain. I
could've backpadaled half rev before the turn before the chain fell of.

Backpedaling with a bad chainline will tend to drop the chain. How bad
it is depends on the crankset and the shaping of its chainrings. You
can test this by wheeling the bike backward with the chain in various
positions on the rear cogset.

If I read his post correctly he was in the big ring in front and small
cog in back. If his chainline is bad there he'd have other problems.
There's no harm in checking it though.

Regards,
Bob Hunt

amakyonin said:

Quoted message said:

Also, when back pedalling there is a hesitation in the chain. I
could've backpadaled half rev before the turn before the chain fell of.

Backpedaling with a bad chainline will tend to drop the chain. How bad
it is depends on the crankset and the shaping of its chainrings. You
can test this by wheeling the bike backward with the chain in various
positions on the rear cogset.

If I read his post correctly he was in the big ring in front and small
cog in back. If his chainline is bad there he'd have other problems.
There's no harm in checking it though.

Regards,
Bob Hunt

In article <[email hidden]>,

Bob said:

Adjusting
cable tension and limit screws and trueing wheels within about 90 days
of the purchase seems pretty much standard at the shops I patronize.

Mine too. A checkup/tuning within a certain time limit is de rigeur for
a good LBS.

--
*Help Animals, the Earth and Your Health! *
*Find out how:* www.VeganStarterPack.com <http://www.veganstarterpack.com/>

In article <[email hidden]>,

Bob said:

Adjusting
cable tension and limit screws and trueing wheels within about 90 days
of the purchase seems pretty much standard at the shops I patronize.

Mine too. A checkup/tuning within a certain time limit is de rigeur for
a good LBS.

--
*Help Animals, the Earth and Your Health! *
*Find out how:* www.VeganStarterPack.com <http://www.veganstarterpack.com/>

Bob said:

If I read his post correctly he was in the big ring in front and small
cog in back. If his chainline is bad there he'd have other problems.
There's no harm in checking it though.

I meant "bad" with respect to backpedaling. Even with a chainline that
is acceptable for normal pedaling with the chain under tension on the
top, there is less margin for chain offset before it unmeshes from a
chainwheel when backpedaling.

Just a follow-up on this. At an LBS (not the one that sold the bike) I
was told that I indeed am capable of flexing the carbon fiber crank and
cause the chain to fall outside. I was advised to pedal more smoothly.
I was suggested to swich the carbon fiber crank to a Dura Ace aluminum.
I may do that, but not immediately.

Sounds like the right experiment to do.

I did a thorough cleaning of the drivetrain on the weekend, and the
hesitation of the chain when backpedalling is gone. Perhaps the sticky
chain was the reason.

Michael Warner said:

Quoted message said:

New bike, full Dura Ace, 500 miles on it, compact crank (Truvativ
Rouleur CarbonCrank 50/36T, 23-11 cassette, Ksyrium SL wheels)
Going downhill I was passing a guy at a hairpin turn, and I when wanted
to re-gain speed by pressing semi hard on the crank (50-11) the chain
fell off outside. This was the 2nd time it happenned, in the same
cirumstances. No shifting was involved. Shifting and the drivetrain
overall are flawless otherwise. What is it? Does the crank bend when I
press hard on it?

Have you tried replicating this by back-pedalling and coasting, then
standing and pushing hard suddenly, either on the road or a trainer? You or
someone else should be able to watch and see what's happening.

--
Home page: http://members.westnet.com.au/mvw

Quoted message said:

New bike, full Dura Ace, 500 miles on it, compact crank (Truvativ
Rouleur CarbonCrank 50/36T, 23-11 cassette, Ksyrium SL wheels)
Going downhill I was passing a guy at a hairpin turn, and I when wanted
to re-gain speed by pressing semi hard on the crank (50-11) the chain
fell off outside. This was the 2nd time it happenned,

This is also the second report of chains being dropped off of Dura-Ace
drivetrains. I don't know whether the previous thread resolved the
problem or not.

First be sure that everything is adjusted properly. In particular, make
sure the chainring-to-derailleur clearance is not too wide (the narrower
the better, as long as no collisions occur). Maybe your dealer should do
that, to keep the warrantee valid.

Quoted message said:

Also, when back pedalling there is a hesitation in the chain. I could've
backpadaled half rev before the turn before the chain fell of.

Derailleur-equipped bikes are not made to backpedal. Don't do it. There
is no problem indicated by poor backpedaling, except that the chainline
is not perfect, and that will always happen with a derailleur.

--

David L. Johnson

__o | Deserves death! I daresay he does. Many that live deserve
_`\(,_ | death. And some that die deserve life. Can you give it to
(_)/ (_) | them? Then do not be too eager to deal out death in judgement.
-- J. R. R. Tolkein