Re: Chain Slip Problem cont'd....

Mark Taylor said:

Ok.. so I have checked for shark tooth on the chain wheels... nothing
there... I have removed the crank to check it's fitting... Nothing
obvious...

I have test rode the bike again whilst looking at the crank (not to be
advised..!) and have noticed some sideward motion to the front chain wheel
which seems to be throwing the chain off to the right under pressure (i.e.
when I'm pushing hard and the bike is in top gear putting the maximun force
throught he drive train.
This seems to be a sudden problem which started yesterday... I'm wondering
if i have had a sudden failure of something like the bottom bracket? (what
would this feel like as i've never had this happen before..?)

Some of the teeth on the front ring seem to be different shapes, but I know
this can be a design to help the chain move smoothly between them on gear
change....

Hope you can help me with this really annoying problem..!!

Mark Taylor

I've had this recently, the chainring bolts are loose or have fallen off.

Look at the right side of the biggest chainring and you'll see 4 or 5
allen key bolts these attach the middle ring to the largest ring. If
you're lucky you'll be able to tighten them using an allen key, if
you're unlucky you'll need a (v) wide flat headed screwdriver round the
back and an allen key at the front, and if you're really unlucky you'll
need to buy one of the special tools for holding the back of the nut.
There's similar bolts holding the smallest chainring to the middle one,
but they're harder to get to.

And then just check them occasionally.

If, like me, you've lost one then they're easy enough to get hold of,
they come in packs of 5 and cost about a tenner or so.

HTH,

Adam

Ok.. thanks for the idea but...... I've checked the chainrings and....
they're one unit - not bolted together.... bummer....

Any other ideas please???????

(AAAARRRRGGGGHHHH!!!!)

Mark

"Adam H" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

I've had this recently, the chainring bolts are loose or have fallen off.

Look at the right side of the biggest chainring and you'll see 4 or 5
allen key bolts these attach the middle ring to the largest ring. If
you're lucky you'll be able to tighten them using an allen key, if you're
unlucky you'll need a (v) wide flat headed screwdriver round the back and
an allen key at the front, and if you're really unlucky you'll need to buy
one of the special tools for holding the back of the nut. There's similar
bolts holding the smallest chainring to the middle one, but they're harder
to get to.

And then just check them occasionally.

If, like me, you've lost one then they're easy enough to get hold of, they
come in packs of 5 and cost about a tenner or so.

HTH,

Adam

in message <[email hidden]>, Mark Taylor

(') said:

Ok.. so I have checked for shark tooth on the chain wheels... nothing
there... I have removed the crank to check it's fitting... Nothing
obvious...

I have test rode the bike again whilst looking at the crank (not to be
advised..!) and have noticed some sideward motion to the front chain
wheel which seems to be throwing the chain off to the right under
pressure (i.e. when I'm pushing hard and the bike is in top gear
putting the maximun force throught he drive train.
This seems to be a sudden problem which started yesterday... I'm
wondering if i have had a sudden failure of something like the bottom
bracket? (what would this feel like as i've never had this happen
before..?)

If it was a sudden failure of the bottom bracket it would not cause
movement of the chainwheel, it would cause horrible grunchy noises. The
one thing that /would/ cause the chainwheel to move which might happen
suddenly would be a cracked frame. Sorry to say this, because it's bad
news - but that's what you should look for.

Chainwheels do frequently 'move' a little under load. Various things may
be flexing: the chainset, the BB axle itself, the frame. But only the
frame is likely to change 'suddenly' in a way which could induce that
sort of flexing.

--
[email hidden] (Simon Brooke) http://www.jasmine.org.uk/~simon/
"This young man has not the faintest idea how socialists think and does
not begin to understand the mentality of the party he has been elected
to lead. He is quite simply a liberal"
-- Ken Coates MEP (Lab) of Tony Blair

Simon Brooke said:

If it was a sudden failure of the bottom bracket it would not cause
movement of the chainwheel, it would cause horrible grunchy noises. The
one thing that /would/ cause the chainwheel to move which might happen
suddenly would be a cracked frame. Sorry to say this, because it's bad
news - but that's what you should look for.

Chainwheels do frequently 'move' a little under load. Various things may
be flexing: the chainset, the BB axle itself, the frame. But only the
frame is likely to change 'suddenly' in a way which could induce that
sort of flexing.

If it's cracked enough to show movement at the chainwheel, I'd be
expecting an accompanying noise, no?

Checked the frame - no crack (Yay!!!)

Test riding it tonight also made the chain slip off the chainwheel to the
right (making it fall off the sprocket out to the pedal) This is corrected
by shifting down to the middle gear and back up again....

Any other ideas...?????

Mark

"Simon Brooke" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

in message <[email hidden]>, Mark Taylor

(') said:

Ok.. so I have checked for shark tooth on the chain wheels... nothing
there... I have removed the crank to check it's fitting... Nothing
obvious...

I have test rode the bike again whilst looking at the crank (not to be
advised..!) and have noticed some sideward motion to the front chain
wheel which seems to be throwing the chain off to the right under
pressure (i.e. when I'm pushing hard and the bike is in top gear
putting the maximun force throught he drive train.
This seems to be a sudden problem which started yesterday... I'm
wondering if i have had a sudden failure of something like the bottom
bracket? (what would this feel like as i've never had this happen
before..?)

If it was a sudden failure of the bottom bracket it would not cause
movement of the chainwheel, it would cause horrible grunchy noises. The
one thing that /would/ cause the chainwheel to move which might happen
suddenly would be a cracked frame. Sorry to say this, because it's bad
news - but that's what you should look for.

Chainwheels do frequently 'move' a little under load. Various things may
be flexing: the chainset, the BB axle itself, the frame. But only the
frame is likely to change 'suddenly' in a way which could induce that
sort of flexing.

--
[email hidden] (Simon Brooke) http://www.jasmine.org.uk/~simon/
"This young man has not the faintest idea how socialists think and does
not begin to understand the mentality of the party he has been elected
to lead. He is quite simply a liberal"
-- Ken Coates MEP (Lab) of Tony Blair

Mark Taylor said:

Checked the frame - no crack (Yay!!!)

Test riding it tonight also made the chain slip off the chainwheel to the
right (making it fall off the sprocket out to the pedal) This is corrected
by shifting down to the middle gear and back up again....

Any other ideas...?????

Take the chain off the front chainrings so you can rotate the pedals
freely. Spin it, and look for a kink in the ring or a tooth which sticks
out sideways. Look at it end on and use the derailleur as a sight. It
should go round without moving from side to side at all.

--

JimP

" " - John Cage

in message <[email hidden]>, Tim Binns

(') said:

Simon Brooke said:

If it was a sudden failure of the bottom bracket it would not cause
movement of the chainwheel, it would cause horrible grunchy noises. The
one thing that /would/ cause the chainwheel to move which might happen
suddenly would be a cracked frame. Sorry to say this, because it's bad
news - but that's what you should look for.

Chainwheels do frequently 'move' a little under load. Various things
may be flexing: the chainset, the BB axle itself, the frame. But only
the frame is likely to change 'suddenly' in a way which could induce
that sort of flexing.

If it's cracked enough to show movement at the chainwheel, I'd be
expecting an accompanying noise, no?

Not in my (limited) experience. I've never cracked a frame personally,
but I have examined frames other people have cracked, and they weren't
noisy.

--
[email hidden] (Simon Brooke) http://www.jasmine.org.uk/~simon/

:: Wisdom is better than weapons of war ::
:: Ecclesiastes 9:18 ::

Ok... Will try in the morning - you can only look at a sprocket for so
long.....!

Thanks guys!!

Mark

"Jim Price" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

Mark Taylor said:

Checked the frame - no crack (Yay!!!)

Test riding it tonight also made the chain slip off the chainwheel to the
right (making it fall off the sprocket out to the pedal) This is
corrected by shifting down to the middle gear and back up again....

Any other ideas...?????

Take the chain off the front chainrings so you can rotate the pedals
freely. Spin it, and look for a kink in the ring or a tooth which sticks
out sideways. Look at it end on and use the derailleur as a sight. It
should go round without moving from side to side at all.

--

JimP

" " - John Cage

in message <[email hidden]>, Mark Taylor

(') said:

Checked the frame - no crack (Yay!!!)

Test riding it tonight also made the chain slip off the chainwheel to
the right (making it fall off the sprocket out to the pedal) This is
corrected by shifting down to the middle gear and back up again....

Any other ideas...?????

This is probably Shimano kit, which doesn't let you trim the front mech.
You could try changing the front shifter for a SRAM (if mountain bike)
or Campag (if road bike) one so that you /can/ trim the front mech.

I still don't like the idea that this has 'suddenly' started happening.
That suggests that something has failed in a nasty sort of way. Things
which happen because of wear tend to develop gradually.

--
[email hidden] (Simon Brooke) http://www.jasmine.org.uk/~simon/
-----BEGIN GEEK CODE BLOCK-----
Version: 3.1
GP/CS s++: a++ C+++ ULBVCS*++++$ L+++ P--- E+>++ W+++ N++ K w--(---)
M- !d- PS++ PE-- Y+ PGP !t 5? X+ !R b++ !DI D G- e++ h*(-) r++ y+++
------END GEEK CODE BLOCK------

It might be that this problem has been developing slowly now I come to think
about it - I did a 37km ride on Sunday which was the first real opportunity
to get the bike in a fast gear for a long time -

Thanks for the advice , I'll take a closer look during this week.

Mark

"Simon Brooke" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

in message <[email hidden]>, Mark Taylor

(') said:

Checked the frame - no crack (Yay!!!)

Test riding it tonight also made the chain slip off the chainwheel to
the right (making it fall off the sprocket out to the pedal) This is
corrected by shifting down to the middle gear and back up again....

Any other ideas...?????

This is probably Shimano kit, which doesn't let you trim the front mech.
You could try changing the front shifter for a SRAM (if mountain bike)
or Campag (if road bike) one so that you /can/ trim the front mech.

I still don't like the idea that this has 'suddenly' started happening.
That suggests that something has failed in a nasty sort of way. Things
which happen because of wear tend to develop gradually.

--
[email hidden] (Simon Brooke) http://www.jasmine.org.uk/~simon/
-----BEGIN GEEK CODE BLOCK-----
Version: 3.1
GP/CS s++: a++ C+++ ULBVCS*++++$ L+++ P--- E+>++ W+++ N++ K w--(---)
M- !d- PS++ PE-- Y+ PGP !t 5? X+ !R b++ !DI D G- e++ h*(-) r++ y+++
------END GEEK CODE BLOCK------

"Mark Taylor" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

Ok.. so I have checked for shark tooth on the chain wheels... nothing
there... I have removed the crank to check it's fitting... Nothing
obvious...

I have test rode the bike again whilst looking at the crank (not to be
advised..!) and have noticed some sideward motion to the front chain wheel
which seems to be throwing the chain off to the right under pressure (i.e.
when I'm pushing hard and the bike is in top gear putting the maximun
force throught he drive train.
This seems to be a sudden problem which started yesterday... I'm wondering
if i have had a sudden failure of something like the bottom bracket? (what
would this feel like as i've never had this happen before..?)

Some of the teeth on the front ring seem to be different shapes, but I
know this can be a design to help the chain move smoothly between them on
gear change....

Hope you can help me with this really annoying problem..!!

Mark Taylor

Original Post....
Can anyone help me solve a really frustrating problem please?
I have a problem whereby when I am in top gear (largest front, smallest
rear ring) and peddle hard, the chain seems to slip off the chain ring. It
sometimes happens if I'm in middle front and smallest rear as well (though
I know that this will place strain on the chain and was only tried to see
if the chain jumped in other gears) If I peddle with a little less force,
things are ok. I have SPD pedals so do
put a lot of force throught the drive train to get up difficult hills (Its
a mountain bike by the way...).
I've checked the front changer and it is aligned parallel to the chain
wheels and have checked the bottom bracket for play. There is VERY little
play in the bottom bracket and I think that this is necessary for the
bearings to move freely, certainly not enough to make the chain rings move
out of alignment.

Can anyone help? The bike is a Giant XTC 840 cross country.

Thanks, Mark

Bent axle or chainrings causing by bashing it/falling off?

Test by holding a bit of stick or a ruler against the frame so it nearly
touches the ring.
Turn pedals backwards and the gap should stay the same.

Paul.