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understanding the rear sprocket



 
 
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  #21  
Old April 10th 15, 03:10 AM posted to rec.bicycles.tech
Emanuel Berg
external usenet poster
 
Posts: 318
Default understanding the rear sprocket

James writes:

I must have done something wrong reassembling the
sprocket because tho the break and everything seems
to work at first glance I have now detected an
unexpected behavior which isn't always but often
enough and that is when I pedal sometimes there is
no resistance for perhaps a quarter (plus) of the
full circle before normal resistance kicks in and
there is forward force. So there is an unpleasant
"leap", like falling through a trap door. Do you
recognize this problem? Is it indeed related to
the sprocket?


Was there a ratchet mechanism that allowed the
sprocket to free wheel? Did you grease the ratchet?
Sometimes grease or heavy oil can prevent the pawls
in a free wheel from engaging.


I don't know what a "ratchet mechanism" is - do you
see in in these pictures?

http://user.it.uu.se/~embe8573/bike/sprocket/

But yes! I did put grease on the ball-bearings and
a thin (but still) layer on everything else.

So probably that is it! Should I disassemble it and
wipe it dry or will it start working automatically
in time?

--
underground experts united
http://user.it.uu.se/~embe8573
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  #22  
Old April 10th 15, 03:20 AM posted to rec.bicycles.tech
James[_8_]
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Posts: 6,153
Default understanding the rear sprocket

On 10/04/15 12:10, Emanuel Berg wrote:
James writes:

I must have done something wrong reassembling the
sprocket because tho the break and everything seems
to work at first glance I have now detected an
unexpected behavior which isn't always but often
enough and that is when I pedal sometimes there is
no resistance for perhaps a quarter (plus) of the
full circle before normal resistance kicks in and
there is forward force. So there is an unpleasant
"leap", like falling through a trap door. Do you
recognize this problem? Is it indeed related to
the sprocket?


Was there a ratchet mechanism that allowed the
sprocket to free wheel? Did you grease the ratchet?
Sometimes grease or heavy oil can prevent the pawls
in a free wheel from engaging.


I don't know what a "ratchet mechanism" is - do you
see in in these pictures?

http://user.it.uu.se/~embe8573/bike/sprocket/

But yes! I did put grease on the ball-bearings and
a thin (but still) layer on everything else.

So probably that is it! Should I disassemble it and
wipe it dry or will it start working automatically
in time?


Ah, I see. Couldn't remember what you had.

It could be that the clutch mechanism is worn or not moving freely, or
the spring is weak. Mr Muzi would know best what to do.

http://www.troubleshooters.com/bicyc...d_overhaul.htm

"If the clutch were to lose its friction, the clutch body would simply
rotate with the sprocket, and no screwing in would occur, and therefore
either propelling would never occur, or would occur slowly and only with
a great deal of pedal spinning. I had that happen once, and the problem
was fixed by replacing the clutch assembly."

--
JS
  #23  
Old April 10th 15, 03:42 AM posted to rec.bicycles.tech
Frank Krygowski[_4_]
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Posts: 10,538
Default understanding the rear sprocket

On 4/9/2015 10:10 PM, Emanuel Berg wrote:
James writes:

Was there a ratchet mechanism that allowed the
sprocket to free wheel? Did you grease the ratchet?
Sometimes grease or heavy oil can prevent the pawls
in a free wheel from engaging.


I don't know what a "ratchet mechanism" is - do you
see in in these pictures?

http://user.it.uu.se/~embe8573/bike/sprocket/

But yes! I did put grease on the ball-bearings and
a thin (but still) layer on everything else.

So probably that is it! Should I disassemble it and
wipe it dry or will it start working automatically
in time?


Have you looked at these sites?
http://sheldonbrown.com/coaster-brakes.html

http://www.parktool.com/blog/repair-...edal-brake-hub

It's been years since I overhauled a coaster brake, but I don't remember
pawls or ratchet mechanisms. I remember coarse square threads that
moved an internal component side to side, causing it to either engage
the brake surfaces or drive the hub forward.

Sheldon's site mentions the "retarder spring" as being a source of
irregular action. I can't identify that in your photos, but perhaps you
can.

OTOH, I suppose yours may be very different...


--
- Frank Krygowski
  #24  
Old April 10th 15, 01:00 PM posted to rec.bicycles.tech
AMuzi
external usenet poster
 
Posts: 13,447
Default understanding the rear sprocket

On 4/9/2015 7:22 PM, Emanuel Berg wrote:
I must have done something wrong reassembling the
sprocket because tho the break and everything seems to
work at first glance I have now detected an unexpected
behavior which isn't always but often enough and that
is when I pedal sometimes there is no resistance for
perhaps a quarter (plus) of the full circle before
normal resistance kicks in and there is forward force.

So there is an unpleasant "leap", like falling through
a trap door.

Do you recognize this problem? Is it indeed related to
the sprocket?


The clutch is not grabbing the hubshell.

Did you set the bearing to a trace of play at the rim?

Are the driver threads lubricated and clean where they
engage the clutch carrier?

When it was open, did you notice significant wear or glaze
on the clutch and mating surface in the hubshell?

--
Andrew Muzi
www.yellowjersey.org/
Open every day since 1 April, 1971


  #25  
Old April 11th 15, 12:53 AM posted to rec.bicycles.tech
Emanuel Berg
external usenet poster
 
Posts: 318
Default understanding the rear sprocket

AMuzi writes:

I must have done something wrong reassembling the
sprocket because tho the break and everything seems
to work at first glance I have now detected an
unexpected behavior which isn't always but often
enough and that is when I pedal sometimes there is
no resistance for perhaps a quarter (plus) of the
full circle before normal resistance kicks in and
there is forward force. ...


The clutch is not grabbing the hubshell.


Yes, that sounds exactly right!

But: I don't remember any clutch. The "hubshell" - is
that the outer, rim shell or the little bronze (?)
shell inside the sprocket? - i.e., the forth piece on
this picture, in comic book reading order:

http://user.it.uu.se/~embe8573/bike/...et/parts-2.jpg

Did you set the bearing to a trace of play at
the rim?


I remember three bearings: one on the outside which is
big, one small on the inside of the chainwheel but
still visible, at the edge, and one in the "inner
shell" that wasn't exactly a bearing but it looked
somewhat like that.

If we are at the rim one right now I don't remember
doing anything in particular to that one save for
putting some fat on the balls. I don't remember seeing
different traces but if they are there let me
disassemble it again and see if I can detect them.

Are the driver threads lubricated and clean where
they engage the clutch carrier?


Everything was very dirty with mud and God knows what
but now it is clean. The bearings are lubricated but
everything else I just put on a thin layer because
I didn't know what was the right thing to do.

From your post I've been able to conclude that:

The bearing should be at a trace of play at the rim.

The driver threads engage the clutch carrier.

The clutch should grab the hubshell on the
mating surface.

If you can help me identify those parts and properties
I think that'd be a good start! (Boy, this is exiting
by the way!)

When it was open, did you notice significant wear or
glaze on the clutch and mating surface in
the hubshell?


No, everything looked good, so I think disfunction is
on the account of the mechanic

--
underground experts united
http://user.it.uu.se/~embe8573
  #26  
Old April 11th 15, 12:05 PM posted to rec.bicycles.tech
[email protected]
external usenet poster
 
Posts: 6,374
Default understanding the rear sprocket

On Friday, April 10, 2015 at 8:00:46 AM UTC-4, AMuzi wrote:
On 4/9/2015 7:22 PM, Emanuel Berg wrote:
I must have done something wrong reassembling the
sprocket because tho the break and everything seems to
work at first glance I have now detected an unexpected
behavior which isn't always but often enough and that
is when I pedal sometimes there is no resistance for
perhaps a quarter (plus) of the full circle before
normal resistance kicks in and there is forward force.

So there is an unpleasant "leap", like falling through
a trap door.

Do you recognize this problem? Is it indeed related to
the sprocket?


The clutch is not grabbing the hubshell.

Did you set the bearing to a trace of play at the rim?

Are the driver threads lubricated and clean where they
engage the clutch carrier?

When it was open, did you notice significant wear or glaze
on the clutch and mating surface in the hubshell?

--
Andrew Muzi
www.yellowjersey.org/
Open every day since 1 April, 1971


an elegant post of beauty and grace on a subject worth considering
 




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