Lou Holtman said:Snoopy *is n said:On Sun, 08 May 2005 09:51:59 +0200, Lou Holtman
<[email hidden]> wrote:
When I take hold of the pulley and lift it upwards holding the pulley
teeth in opposing fingers the pulley bearing has a natural tendancy to
'fall out' (remain on the table surface).
I should add here that a 'natural tendency to fall out' does not mean
it is so loose that the pulley bearing 'just falls out'. I mean that
if I pick up the guide pulley as described and shake it up and down
that eventually the pulley bearing will fall out, without me having to
touch it directly.
Quoted message said:Quoted message said:
This is not surprising. I observe a clearance between the outer
circumference of the pulley bearing and the steel lined 'hole' in the
centre of the upper guide pulley. The clearance between the outer
circumference of the pulley bearing and the inner circumference of the
upper guide pulley is what gives me about 1mm of 'back and forth'
movement.
That is way too much. In front of me lies a upper pulley of my spare
(brand new) Veloce rear derailleur. The outer diameter of the bolt
measures 4.95 mm and the inner diameter of the inner bushing measures 5
mm, leaving a 0.05 mm radial play.
My measurement may be a bit out, as I was using a rather blunt
instrument - a 300mm ruler! I grabbed the pulley bearing from both
exposed ends, between thumb and forefinger, then grabbed opposite side
teeth on the guide pulley and pulled in opposing radial directions
with both hands. I thought I could see a maximum radial gap,
comparable to around 1mm, opening up on one side between the outer
circumference of the pulley bearing and the inner circumference of the
guide pulley. However, I don't know if in 'normal operations' you
would open up a gap like that.
Nevertheless I accept my upper guide pulley could easily be worn. It
certainly doesn't have any pulley seals on it, unlike the upper guide
pulley in the drawing, which probably doesn't help long term wear.
Quoted message said:Quoted message said:
Normally the upper guide pulley is held inside the derailleur cage.
It is a tight fit and no side to side movement is possible.
The above is a wrong observation of mine - see below.
Quoted message said:
That is not true (in my case). The inner bushing (pulley bushing in your
drawing) is a little bit wider than de outer bushing and/or the plastic
pulley so when the bolt is tightened body cage plates are not squeezed
against the pulley leaving some side to side movement.
Ooops, on closer inspection you are quite correct!
Yes the pulley bushing in the lower (tension) pulley, when placed flat
on the table, *is* flush with the upper surface of the tension pulley
BUT.
OTOH when I do the same thing with the upper (guide) pulley, the
pulley bushing sticks out a bit. Not much, only 1mm or so (my trusty
ruler comes in useful again!), which is why I hadn't noticed it
before. Thanks very much for pointing that out.
Comparing the lower (tension) pulley bushing and the upper(guide)
pulley bushing side by side, they seem to be the same length. The
only way I can reconcile that fact with your observation repeated
below
Quoted message said:
The inner bushing (pulley bushing in your
drawing) is a little bit wider than the outer bushing
Is that the upper (guide) pulley bushing is narrower (by 1mm) than the
lower (tension) pulley bushing. I never knew that before, and sure
enough on close comparative inspection it does appear to be true!
On the subject of lateral pulley movement, I make another observation.
I take my lower (tension) pulley assembly and grasp it with one hands
thumb and forefinger pressing opposing pulley caps together. I now
take my other hand and hold the teeth of the lower (tension) pulley
between my thumb and opposing finger. By doing this, I can get the
tension pulley to wobble in my hand away from its normal plane of
rotation quite easily. I can get at least 1-2mm of 'wobble' by doing
this. This is of the same order as the 1mm of lateral movement
available in the upper guide pulley (because the upper guide pulley is
1mm narrower than the pulley bearing it contains).
I don't believe the available tension pulley movement I observe is
because the tension pulley is worn. If you look at the fit between
the tension pulley cap and the cylindrical plastic recession in the
lower (tension) pulley it is *not* a tight fit. There is 'wobble
room' designed into it. Why is that wobble room not sufficient to use
as the 'lateral float' in the upper guide pulley?
Quoted message said:
Quoted message said:
That is why I say the upper guide pulley is *designed* to
go back and forth.
It is not, because it has no purpose
What about smoother engagement of the chain and tooth as a purpose?
Quoted message said:
Quoted message said:My first observation is that I cannot see that it is *possible*, using
the design in the picture and as described, to eliminate back and
forth movement.
Take one apart. You see.
If your above measurement of a mere 0.05mm is typical, then yes I
agree with you. But perhaps Shimano and Veloce have different design
philosophies?
Quoted message said:
Quoted message said:
I will add another separate observation here. If I
1/take the upper guide wheel assembly AND
2/hold it in one hand between my thumb and opposing finger (one each
on opposing pulley caps) THEN
3/I am able to move the upper guide wheel by turning it slightly about
the 'up down' axis (**).
I can't.
If you have measured a clearance of even 0.05mm, as described above,
you must be able to do what I describe, because it is this clearance
that enables it to be done! I don't accept that you can't do what I
describe.
I do accept that any movement you do get may be so small that it is
effectively insignificant.
In my case 1mm of back and forth movement over a pulley width of 7mm
gives a 'maximum wobble angle' of artan(1/7)= 8 degrees which was
quite noticable.
In your case with only 0.05mm over a pulley width of 7mm, I calculate
a 'maximum wobble angle' of artan(0.05/7)= not quite 0.5 degrees. Not
very much, but nevertheless still discernable to a trained eye. The
movement has to be there if your clearance measurements are correct,
and with wear it will become more and more obvious.
Quoted message said:
Quoted message said:
[(**) Before you think I am doing something bizarre here, I am using
the Right Hand rule to describe the twisting motion I am performing.
Point your thumb in the direction of the up-down axis. The way your
fingers wrap around the axis is the direction of movement.]
How old are your pulleys?
Quoted message said:
IIRC I bought the derailleur late last century and don't recall
replacing any pulley bearings on it since new. They have now done
around 25,000km.
It is primarily a road bike, but I do take it on dirt tracks and ride
it in the rain. I clean up and relubricate the chain and sprockets a
couple of times a year: Normally just before winter and just after
winter. Compared to other road bikes out there, my bike gets a hard
life but I do try to look after it.
All the gears still work fine, but I use friction gear shifting on
that bike. It has no provision for indexed gear shifting.
Quoted message said:Quoted message said:
I have never heard of having an upper guide pulley that has a worn out
internal bearing.
I did. I know of someone who's pulley developed so much wobble that he
was not able to adjust his rear derailleur correctly. He replaced the
jockey wheel and after that everything was fine.
Any idea how many kilometres were ridden on that bike before the
derailleur deteriorated like that?
SNOOPY
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