Chain jam

<snippage of chainsuck incident>

Chainwatcher. Available at all finer bicycle outlets.

D'ohBoy

Peter Cole said:

Last Sunday my daughter's chain fell off to the inside of the granny
ring (MTB) and wedged itself (well, with some help on her part) in the
gap between the ring and the BB. I had a heck of a time getting it out.
If there was a little less space it couldn't have become trapped, a
little more, ditto. I just know it'll happen again. Any ideas for
prevention? (typical square-end BB).

You can buy little widgets that attach to the seat tube just above the
BB, and prevent the chain from dropping off the small ring. Here's
one:

http://www.gvtc.com/~ngear/whatis.html

Other than that, make sure everything is adjusted correctly, and teach
your daughter about the "bad" gear combinations to avoid.

Josh

It's a little gritty and greasy*, but tasty nonetheless.

Bill "slow morning" S.

*or waxy

Sorni said:

It's a little gritty and greasy*, but tasty nonetheless.

Bill "slow morning" S.

*or waxy

But at least most of them are entirely free of trans fats and tropical
oils.

--
Typoes are a feature, not a bug.
Some gardening required to reply via email.
Words processed in a facility that contains nuts.

Peter Cole said:

Last Sunday my daughter's chain fell off to the inside of the
granny ring (MTB) and wedged itself (well, with some help on
her part) in the gap between the ring and the BB. I had a heck
of a time getting it out. If there was a little less space it
couldn't have become trapped, a little more, ditto. I just
know it'll happen again. Any ideas for prevention? (typical
square-end BB).

I got sucked in by your subject line. I was hoping for a
recipe.

John

Josh Hassol said:

Peter Cole said:

Last Sunday my daughter's chain fell off to the inside of the granny
ring (MTB) and wedged itself (well, with some help on her part) in the
gap between the ring and the BB. I had a heck of a time getting it out.
If there was a little less space it couldn't have become trapped, a
little more, ditto. I just know it'll happen again. Any ideas for
prevention? (typical square-end BB).

You can buy little widgets that attach to the seat tube just above the
BB, and prevent the chain from dropping off the small ring. Here's
one:

http://www.gvtc.com/~ngear/whatis.html

Other than that, make sure everything is adjusted correctly, and teach
your daughter about the "bad" gear combinations to avoid.

Doesn't look like that one will fit, unfortunately. I guess I'll try to
dial it in & hope for the best, thanks.

Peter Cole said:

Last Sunday my daughter's chain fell off to the inside of the granny
ring (MTB) and wedged itself (well, with some help on her part) in the
gap between the ring and the BB. I had a heck of a time getting it out.
If there was a little less space it couldn't have become trapped, a
little more, ditto. I just know it'll happen again. Any ideas for
prevention? (typical square-end BB).

Shorter BB? Next time, if you're not on the road, instead of forcing
it out - take off the driveside crank.

-nate

"Peter Cole" wrote: Doesn't look like that one will fit, unfortunately. I
guess I'll try to dial it in & hope for the best, thanks.
^^^^^^^^^^^^^^^
How about making something out of a piece of hardwood--hold it with a hose
clamp?

Peter Cole said:

Last Sunday my daughter's chain fell off to the inside of the granny
ring (MTB) and wedged itself (well, with some help on her part) in the
gap between the ring and the BB. I had a heck of a time getting it out.
If there was a little less space it couldn't have become trapped, a
little more, ditto. I just know it'll happen again. Any ideas for
prevention? (typical square-end BB).

There's a relatively inexpensive little widget that typically looks
like a plastic shark fin; it attaches to the seat tube and keeps the
chain from dropping into the gap. It doesn't always do the whole job
(I've seen a chain get stuck between a fat downtube and the inner
sprocket, for one thing) but it's usually pretty effective.
--
Typoes are a feature, not a bug.
Some gardening required to reply via email.
Words processed in a facility that contains nuts.

Llatikcuf said:

Peter Cole said:

Last Sunday my daughter's chain fell off to the inside of the granny
ring (MTB) and wedged itself (well, with some help on her part) in the
gap between the ring and the BB. I had a heck of a time getting it out.
If there was a little less space it couldn't have become trapped, a
little more, ditto. I just know it'll happen again. Any ideas for
prevention? (typical square-end BB).

Shorter BB? Next time, if you're not on the road, instead of forcing
it out - take off the driveside crank.

Either a slightly shorter or longer BB would prevent the problem, the
chain got jammed through basically an interference fit. I think I'll
just put a thin shim on the axle flats to space the right crank out a
couple of mm.

Unfortunately, this type of thing is most likely to happen (as it did)
bouncing over rough terrain and shifting under load, just the way things
are in the woods. My real concern isn't so much frame damage (in this
case the jam was between ring & BB flange anyway) as a several mile hike
out. All MTB bikes seem to occasionally drop chains in these conditions,
this is the first time I've had one jam like this.

Peter Cole said:

Llatikcuf said:

Peter Cole said:

Last Sunday my daughter's chain fell off to the inside of the granny
ring (MTB) and wedged itself (well, with some help on her part) in the
gap between the ring and the BB. I had a heck of a time getting it out.
If there was a little less space it couldn't have become trapped, a
little more, ditto. I just know it'll happen again. Any ideas for
prevention? (typical square-end BB).

Shorter BB? Next time, if you're not on the road, instead of forcing
it out - take off the driveside crank.

Either a slightly shorter or longer BB would prevent the problem, the
chain got jammed through basically an interference fit. I think I'll
just put a thin shim on the axle flats to space the right crank out a
couple of mm.

A shim on a "typical square-end BB"? How should this be possible? The
crank has to be as thight as possible on the BB axle.

If mounting a chain guide is not possible, you can try to adjust the
lower limit stop, so the derailer cage does not move so far - just
enough to get the chain to the smallest ring, not more.

Quoted message said:

All MTB bikes seem to occasionally drop chains in these conditions,
this is the first time I've had one jam like this.

This is the reason, why things like "N-Gear" where invented ;-)

--
http://arnowelzel.de
EMail: [email hidden]
de.rec.fahrrad-FAQ: http://drffaq.freezope.org

Arno Welzel said:

Peter Cole said:

Llatikcuf said:

Peter Cole wrote:
> Last Sunday my daughter's chain fell off to the inside of the granny
> ring (MTB) and wedged itself (well, with some help on her part) in the
> gap between the ring and the BB. I had a heck of a time getting it out.
> If there was a little less space it couldn't have become trapped, a
> little more, ditto. I just know it'll happen again. Any ideas for
> prevention? (typical square-end BB).

Shorter BB? Next time, if you're not on the road, instead of forcing
it out - take off the driveside crank.

Either a slightly shorter or longer BB would prevent the problem, the
chain got jammed through basically an interference fit. I think I'll
just put a thin shim on the axle flats to space the right crank out a
couple of mm.

A shim on a "typical square-end BB"? How should this be possible? The
crank has to be as thight as possible on the BB axle.

If you cut a strip of thin aluminum (I've used beverage can or roof
flashing material) and cover 2 adjacent sides of the square spindle end,
you can then make it as tight as you want. If done carefully, this will
just slightly reduce the insertion depth, but won't change the interface
otherwise. This technique won't fix deformed bores, but it's useful to
move the crank out a little.

Quoted message said:

If mounting a chain guide is not possible, you can try to adjust the
lower limit stop, so the derailer cage does not move so far - just
enough to get the chain to the smallest ring, not more.

Of course, that is the way the derailer should be (and is on this bike)
adjusted, which is why I wrote the below:

Quoted message said:

Quoted message said:

All MTB bikes seem to occasionally drop chains in these conditions,
this is the first time I've had one jam like this.

Quoted message said:

This is the reason, why things like "N-Gear" where invented ;-)

There is no room to mount that device on this bike. Other similar
devices have received pretty bad reviews on MTBR.com.

I'm not so much trying to avoid chain drop, since it happens
infrequently and is otherwise harmless, but trying to prevent it jamming
once it drops.

Peter Cole said:

Arno Welzel said:

A shim on a "typical square-end BB"? How should this be possible? The
crank has to be as thight as possible on the BB axle.

If you cut a strip of thin aluminum (I've used beverage can or roof
flashing material) and cover 2 adjacent sides of the square spindle end,
you can then make it as tight as you want. If done carefully, this will

Ah - ok, now i got the idea.

But if the chain can get trapped between the crank and the BB, the gap
must be fairly wide. Maybe a BB with a shorter axle is the better way,
since the crank can still move inwards a little after a while.

On my commuter i use a crank, which is "officially" designed for a 113mm
BB squared axle. After i had other problems with the front derailer
there (chain scratching on the cage under load etc.) i mounted the
shortest axle, which i was able to get. It works fine and there is no
danger of anything getting trapped between the BB and the crank and the
tendency of the chain to scratch the front derailer cage under load is
also much lower than before.

--
http://arnowelzel.de
EMail: [email hidden]
de.rec.fahrrad-FAQ: http://drffaq.freezope.org