From: firstname.lastname@example.org (Jobst Brandt)
Subject: Re: a new use for liquid nitrogen?
Date: 9 Jan 1998 01:46:04 GMT
John DeGrace writes:
> I am restoring a 50 year-old Phillips bike. The crank arms are
> attached by cotter pins that I don't think have been removed since
> the bike was assembled, and that don't seem to want to be extracted
> by the conventional approach (hammering them out against a notched
> support-board, and this after attempted loosening with penetrating
The problem is often that the cotters yielded in use and this makes
them bulge into the major diameter bore in the crank. To test for
this, look at the position of the cranks to one another. If the left
crank is ahead of the 180 degree point with respect to the right one
(in the direction of rotation) then you have mushed cotters.
The solution for this is to place the cranks horizontally with the
left crank rearward. Standing on the two pedals, lunge onto them as
though you were trying to bend the cranks back into plane. There
should be some change in the alignment by this. This is the first
step that must be done otherwise the bores of the cotters do not align
with driving them out.
Next, support the back face of the horizontal crank on a solid anvil
of some sort, (not wood) and use a one pound hammer on a large drift
pin to drive the cotter out. If the threaded end of the cotter (the
one you are pounding on) protrudes more than 1/4 inch, hack saw it off
or it will buckle. Once the cotter has been driven out until its head
is flush, use a smaller drift pin to push it the rest of the way out.
> The suggestion has been given that a means of loosening the pins might be to
> pour some liquid nitrogen on them and then tap them out immediately - the
> theory being that the pin would shrink differentially and loosen. I have
> access to the liquid, but: Has anyone ever tried this?
Probably, but it doesn't work because you must plastically deform
steel to get it out (if it hasn't responded to initial attempts).
There is no easy way and that is why we don't use them anymore.
Besides, a strong rider can smush most cotters on the first hard
spring. I found that only the French "Acier Dupratnik" cotters held
up to climbing steep grades. I made a fixture to machine their side
cuts to be at a low angle so that the narrow part of the wedge face
was not so narrow and that they were identical.
Jobst Brandt <email@example.com>