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What causes cotterred cranks to wobble?



 
 
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  #1  
Old January 31st 04, 07:04 PM
Sofa
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Default What causes cotterred cranks to wobble?


Hello, I have a spare uni that has cotterred cranks.

I have the cranks on the hub, and the cotter pins and nuts tightened to
what seems 'good'

However, if I put the wheel on the ground, and reef up and down on the
cranks, they change positions (no longer 12 and 6, or 3 and 9, more
like 11 through 1 to 5 through 7)

The cranks don't go beyond 'too crazy' but are able to change enough to
be not good for riding.

How do you get a cottered set of cranks to 'stay put' ?


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  #2  
Old January 31st 04, 07:15 PM
evilewan
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Default What causes cotterred cranks to wobble?


the problem with cotter cranks is that they dont actualy "fit" on the
axle it seems that they always have about 0.5 mm gap,
and the cotter pin does its half assed job of squishing itself to make
them snug.

i suppose you could cover them in locktite or something to make them a
tight fit on the axle. perhaps even a bit of colke can would make them a
tight fit.

or you could try the traditional way, just weld the little *******s onto
the axle.

or carry a little hammer and a spanner in your pocket everywhere you
go......

p.s. you are whacking them on with a hammer aren't you?


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  #3  
Old January 31st 04, 07:29 PM
Max_Dingemans
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Default What causes cotterred cranks to wobble?


According to a bike shop mechanic from the late 70's, the trick is to
have two hammers of equal weight, one to hit the cotter in, one on the
bottom to absorb the blow. and then just small the cotter in as much as
you can. only THEN do you tighten the nut to keep the pin in.


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  #4  
Old January 31st 04, 07:37 PM
Sofa
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Default What causes cotterred cranks to wobble?


Here's what I did:

I pounded the crank on until it was flush with the spindle.

Then I pounded the cotter pin in until I could fit a nut on it to
tighten. Apparently this was not the best method.


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  #5  
Old January 31st 04, 07:46 PM
john_childs
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Default What causes cotterred cranks to wobble?


Cotters are such a pain.

Sheldon Brown has some good info on how to install and remove cotter
pins.
'Cottered Cranks' (http://www.sheldonbrown.com/cotters.html)
'Tool Tips for Cottered Cranks'
(http://www.sheldonbrown.com/tooltips/cotters.html)


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  #6  
Old January 31st 04, 07:50 PM
Sofa
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Default What causes cotterred cranks to wobble?


Thanks for the link John,

Cotters are indeed a pain, but as it is a unicycle that was donated to
our club, I am trying to make due. Although at our last meet, the
newbies couldn't even ride it as it was fine at the beginning of the
meet but within 10 mins was messed up.


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  #7  
Old January 31st 04, 10:24 PM
forget_your_life
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Default What causes cotterred cranks to wobble?


i have cottered cranx on my UW.make sure you have the right sized
pin.there are about 4 differant sizes and use a cotter pin press if you
can.Var makes one.


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  #8  
Old February 1st 04, 05:15 AM
HandyAndy
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Default What causes cotterred cranks to wobble?


evilewan wrote:
*
or you could try the traditional way, just weld the little *******s
onto the axle.
p.s. you are whacking them on with a hammer aren't you? *



thats what i would do if you dont intend on bending cranks any time soon


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  #9  
Old February 1st 04, 06:25 AM
cyberbellum
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Default What causes cotterred cranks to wobble?


forget_your_life wrote:
*i have cottered cranx on my UW.make sure you have the right sized
pin.there are about 4 differant sizes and use a cotter pin press if
you can.Var makes one. *


You don't need to use a press on a unicycle. If you hammer a cotter in
on a bike then you wind up ruining the bottom bracket bearings.
Unicycles spindles are fixed to the wheel so you're pretty much ok.

Sounds like the cotter faces are rockered. The cotter is only
contacting the spindle in the middle of it's flat. That happens if you
do anything other than just pedal on them - they're not capable of
taking jumps. Even strong hopping is probably too much.

The fix is easy. Drive the cotters out and file the flats flat again.
Set the crank on a block of wood or other solid object to hammer so that
the force of the blow doesn't ruin anything. (DON'T just turn the
unicycle upsidedown and set it on it's seat, then you've got a similar
situation to the bike crankset and you'll ruin the bearings.)

Then when you put the cotters in, jiggle everything around until until
the cotter flat is exactly on the spindle flat. (The threads should
already be sticking out the other side. If not then you've got the wrong
size pins.) Then tap those puppies home. If you mushroom the top
you've hit them just a little bit too hard.

The crank is now completely on; that nut is there only to keep the pins
from coming out again. It doesn't have enough pull to seat the cotters
by itself. You can carry a wrench with you if you like, but if the
cranks come loose on a ride you're better off with a rock.

Good luck.


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  #10  
Old February 1st 04, 08:44 AM
forget_your_life
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Default What causes cotterred cranks to wobble?


CYBERBELLUM

Why are you quoting me? did you think i saying everyone with cotter pin
crank should stick their uni in a vise? -oh no no noh-

'look at what Sheldon says the 1st option should be'
(http://www.sheldonbrown.com/cotters.html)

the cotter pin press is a dying tool but nontheless a real one...


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