On 15 Apr 2004 10:40:08 -0700, [email hidden] (Mr Pook) may
have said:So my question is: would a soft aluminium sump-plug
washer of correct size also circumvent the problem,
acting as a sacrificial face, on which this fretting
damage could occur?
No. You need to either distribute the load across a more
durable and rigid interface, or lock the shaft against
motion. The soft aluminum washer would, in my experience,
have the opposite effect, likely making the problem worse.
It would be more effective to substitute a machined,
hardened washer with a slightly concave contact face which
would increase the steel/aluminum contact patch, in my
opinion...and such a washer would probably be thick enough
that it would hazardously reduce the dept of the threaded
stub's penetration into the crank eye, so it would still
need a pedal shaft mod before it would be workable.
Jobst's split conical collar is a better fix for the same
amount of work.
On the other hand, in my collection of cobbled-together bits
and bikes, there's a unit with an old set of Deore LX cranks
that I obtained gratis because the threads in the left crank
were wallowed and torn out. I drilled and tapped the eye for
a bushing, and loctited a right-hand-thread pedal in there.
It's been working acceptably for quite a while, but this is
not a solution I'd apply on a bike that was going to see
heavy use.
I will note that an inexpensive (in mass production) better
design for the pedal mounting method would not be difficult
to implement at the component manufacturing level, but
there are two big problems with trying to introduce any
such change..
First, the existing design has incredible marketplace
inertia, as it has literally been in use for a century and
has become regarded as a truly standardized part of bike
design with just one change in that time; an increase in the
threaded stub's diameter for the three-piece cranks. As a
result, any attempt to introduce a new design would have to
be embraced by both the crank makers and the multitude of
specialty pedal manufacturers before it would have a chance
of becoming popular.
Second, the failures, though hardly unusual, are not so
common that they constitute a major source of ire for the
buying public. It is difficult to get people excited about a
product that solves a problem that they never have had
themselves. This factor is also a big part of the reason
that the disc brake wheel ejection issue doesn't get more
attention; until it happens to enough people (or exactly the
right single individual), it's obscured by a "not my
problem" field.
I will also note that the inclusion of a suitable steel
bushing in the end of the crank could essentially eliminate
the problem you're addressing, but this adds both cost and
weight to an item whose buyers are typically sensitive to at
least one of those factors. (And yes, there are some cranks
with this feature in my experience, but they're not top-of-the-
line gear.)
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