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Old January 9th 17, 03:30 PM posted to rec.bicycles.tech
AMuzi
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Posts: 13,447
Default Need advice on bottom bracket repair

On 1/9/2017 2:12 AM, Jeff Liebermann wrote:
On Mon, 09 Jan 2017 12:48:48 +0700, John B.
wrote:

On Sun, 08 Jan 2017 20:41:16 -0800, Jeff Liebermann
wrote:

On Mon, 09 Jan 2017 08:34:44 +0700, John B.
wrote:

There is a recipe for "home made penetrating fluid" I found on the web
- equal measures of kerosene, ATF, mineral spirits, and acetone - that
worked really well the time or two I tried it. The problem with it is
I cold never find a bottle to store it in that the acetone didn't
evaporate :-(

I'm surprised that this concoction works. There are quite a few
claims that ATF+acetone works best, but I don't see how. None of the
comments I read talked about using it with aluminum, or an aluminum
and steel combination. If the idea is to attack the oxides, which
requires an acid, none of the mentioned ingredients will do anything
useful, except lubricating the parts of the threads that are already
broken loose.

I'm not sure what the kerosene and mineral spirits actually add to the
concoction as neither have much lubricity and are both of a higher
viscosity than acetone so I suspect that the 50% ATF and 50% acetone
mix that I've also seen recommended probably works as well.

Seems like a popular concoction:
http://www.instructables.com/id/Home-made-penetrating-oil/
https://www.youtube.com/watch?v=CESDxCloCoQ
https://www.youtube.com/watch?v=K5X0EMlIVx4
https://www.youtube.com/watch?v=c0kIPEzeTQ8
https://www.youtube.com/watch?v=2WuVBFTzoKc
The last video claims that acetone breaks down rust (at 1:32), which
it doesn't.

What the ATF brings to the table is a detergent, a rust inhibitor,
anti-foaming agent, an anti-oxidant, and some kind of lubricant, none
of which seem useful for breaking loose rust or aluminum oxide.


Forget the detergent, the anti-foaming, the anti-oxidant and
concentrate on the lubricant. If you mix acetone with ATF you get a
lubricant that initially has a viscosity of approximately 1/2 - 1/3
that of water (water centipose = 0.89,. acetone = 0.31) so it flows
into some pretty small cracks. Then the acetone evaporates leaving at
least some oil in the joint.


Good point.
https://en.wikipedia.org/wiki/Viscosity#Viscosity_of_selected_substances
The only other solvent on the list that might work is methanol at
0.54. Looks like acetone might be the best choice as a thinner.

Low viscosity silicon oil (0.65):
http://www.clearcoproducts.com/pure-silicone-super-low-viscosity.html
http://www.clearcoproducts.com/pdf/volatile/NP-PSF-0_65cSt.pdf
Might work instead of the ATF+acetone mix, but also might be
expensive.

And the crux of the argument - it works.


I want to know why it works at least twice as good as the others on
the list.

As for aluminum and steel joints. Yes iron and aluminum in the
presence of an electrolyte results in some pretty spectacular
corrosion but even a little insulation prevents that. Grease in the
threads for example.


On the bottom bracket in question, corrosion has already set in and
it's too late for preventive measures.

A favored insulation for sail boats where one has
a considerable amount of stainless in contact with aluminum spars is
lanolin for some reason.


PTFE tape is my favorite. Close to lanolin is white lithium grease,
which is essentially a soap.
https://en.wikipedia.org/wiki/Lithium_soap

I wanted to read the original Machinists Workshop Magazine article,
but couldn't find any back issues or copies online. This was the
earliest reference I could find:
http://forums.sohc4.net/index.php?topic=20131.0


Try
http://www.practicalmachinist.com/vb...ng-oil-196347/
which describes the torque loads using different penetrating oils.
From the Machinist Workshop Magazine, April 2007, issue.


Thanks, but that is roughly the same as what I found in numerous other
references to the article. I was looking for a copy of the original
article.

Or the magazine at http://www.machinistsworkshop.net/
But they don't seem to allow searching back issues.


Yep, that's the problem. Usually, when there's something mentioned
that often, someone scans the original article and posts it. Not this
time.



Nothing wrong with white lithium grease, lanolin, teflon
tape or Gene's favorite linseed oil.

Where steel threads to aluminum, assuming moisture or just
humidity, a molybdenum-rich paste is the go-to prep. Note
molybdenum paste is not much of a lubricant but it is a
great anticorrosive barrier.

--
Andrew Muzi
www.yellowjersey.org/
Open every day since 1 April, 1971


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