They work like a gear-puller. The outer shell fastens into the crank arm
and then you tighten the center bolt. As you do, the center bolt pushes
on the axle while the outer shell pulls on the crank arm, separating
the two.
I would stick with the Park Tool extractors. It is critical that the
extractor threads fit tightly in the crank, especially with aluminum
cranks, or else you might pull the extractor out of the crank,
destroying the threads in the crank in the process. The Park Tool
extractors have very high quality threads. For Unicycles, I prefer the
CWP-6 (requires a wrench) over the CCP-2(square-taper) or CCP-4(ISIS)
because I don't need to pull the pedals first. An extractor for ISIS or
Shimano splined cranks has a larger "tip" where it contacts the axle; it
is important to use the right tip for the type cranks you have. The
small tip will go into and destroy the threads on an ISIS axle; the
large tip will hang up on the crank arm of a square-taper crank and
probably result in the destruction of the extractor threads in the
crank arm. KH/Onza cranks have left-hand threads and can't be pulled
with a standard extractor, Campy used to make a left-handed extractor
if you can find one.
Proper use of the extractor is very important. Pull the crank bolts and
carefully thread the extractor into the crank. If there is any doubt
that you might be cross-threading it, stop. Be sure that you thread it
all the way in; a common mistake is to not fully retract the center
drive bolt before you start and have the drive bolt contact the axle on
the way in. You mistake the feeling of "tight" that comes from the drive
bolt blocking the extractor from going in further for "in all the way".
After you thread the extractor in, be sure you can spin the center
drive bolt freely with your hands to verify that it isn't yet touching
the axle and that this wasn't the case. Then you tighten the drive
bolt on the extractor until the crank arm releases. If a tapered
(square or ISIS) crank has been on for a long-long time, it may be
difficult to release. A few quick hops with the bolt out should help
loosen it to the point where the extractor will work.
If for some reason you cross-thread the extractor into the crank, or
the extractor pulls out of the crank arm (damaging the threads) before
the crank pulls off the axle, I'd stop and seek professional help. All
is not necessarily lost, but it is best to seek help before doing more
damage.
--
adelman
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