[R-390] Gear lube suggestions

[Roger Ruszkowski]

-----Original Message-----
From: Charles P. Steinmetz <charles_steinmetz at lavabit.com>
To: 390 list <r-390 at mailman.qth.net>
Sent: Mon, Jul 15, 2013 8:12 pm
Subject: Re: [R-390] Y2K Manual Question


Don wrote:

>MIL-L-7870 is a general purpose, stable at low temp., instrument oil with
>anti-oxidation properties.  That part number is superseded by part number
>MIL-PRF-7870.  7870[D] seems to be the last available revision and Royco
>lists that oil as commercial part 363.  Anyone disagree with my conclusion
>that 7870 is the proper citation?

Good detective work!

>He likes dry, I like a little Mobile-1

I have used both light oil and dry graphite with good success (when I 
use graphite, I apply it dry, not in a solvent carrier -- I found 
that the graphite left after the solvent evaporated did not lubricate 
nearly as well as graphite applied dry).  The primary application for 
graphite is in very dusty locations (sandstorms, etc.), where the 
dust can get caught in oil to form an abrasive paste.  This may be 
why your friend doesn't use oil.  If so, he should consider keeping 
the radio room cleaner (if dust getting caught in the oil is really a 
problem for him) or using graphite.  You can get by with an 
unlubricated gear train, but it is not the preferred solution.  (I 
have only once or twice seen a 390/390A used by a ham or SWL where 
dust in the oil was a problem, out of several hundred units.)

When using oil, the lubricity demands are not high -- the tuning 
mechanism is very lightly loaded -- so you don't need extreme 
pressure or high-speed additives.  The most important criterion is 
that it be non-gumming over long periods of time and at somewhat 
elevated temperature.  Second is some corrosion inhibitor, given the 
different metals used in the gear train.  I'm sure there are many 
oils that fit this description.  I've been using and recommending 
Mobil 1 for 390/390A gear trains (and many other uses) since the 
mid-'70s and it is well-proven.

I have generally avoided grease of any sort, because until very 
recently there weren't any that were as gum-resistant as a fine light 
synthetic oil.  There are some specialized greases available today 
that meet the requirement (e.g., some of the DuPont Krytox products), 
although the ones that do are quite expensive and I see no benefit 
generally to grease over light oil.

Best regards,

Charles


Amen,

Good stuff Charles

Roger

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