Andy Dingley writes:
>>> I use copper grease. My reasoning is not for the contact areas, but to reduce electrolytic
>>> corrosion in any areas where the contact isn't perfect. Large areas of steel/aluminium interface
>>> with a narrow gap and plenty of water aren't ideal.
>> Could you explain why you believe this has any advantage
> It avoids the formation of electrolytic corrosion cells. Mainly by simply filling up the gap and
> excluding moisture.
How is this grease able to do this more so than other greases, is the question. To what "gap" are
you referring anyway. There is no gap in a press fit.
>> and how this grease remains in the interface?
> Because I put it there, and there's nothing to move it away. I'm talking about ancient old sheds
> of bikes here, where the tapers are less pristine than your boxfresh Campag might be. They're not
> going to have an accurate mating surface over the whole taper.
You better believe that there is contact over the mating surfaces, considering the elastic nature of
the metals and the softness of aluminum. Proof of this contact is that the surfaces run "dry" on any
crank after use and the lack of grease in this interface. After use a crank spindle has rouge on its
surface that bears witness to high pressure fretting.
>> What is it in "copper grease" that makes this occur?
> Depends on your brand. Obviously Duralac (a chromate loaded varnish) is the proper stuff to use
> for a steel/aluminium fit like this, but that's messy. The main function of copper grease is
> twofold; it's a stable grease that doesn't migrate, and it's conveniently to hand at all times.
> The other functions, like heat resistance, are a little superfluos here, but not detrimental.
> Assuming any cathodic protection would depend on the alloys you have around, and that's always
> complex on bikes with their unobtainium waterbottle cages.
That is a nice compendium of buzz-words but you might show some reason for anyone to believe in
these superior qualities of your choice of grease. I see no evidence that any of this has an effect
on the spindle and crank. Do you have any comparative tests to see whether your grease is better
than any other or no grease at all, as is often advised? Credibility is hard to come by, especially
if you make claims and then dodge and weave when asked about them.
Jobst Brandt
[email protected] Palo Alto CA
