[R-390] Lubing the R-390A

[Tisha Hayes]

I love Mobil 1 synthetic oil and as I have to buy three gallons every six
months for my car I always end up with extra in the container. It does a
fine job of general lubrication in almost every boat-anchor I own but I use
a synthetic tungsten disulphide grease for certain parts of the '390 or the
SP-600.

I got myself in trouble at one time by lubing up a SP-600 liberally with
Mobil 1 and the magical friction driven dial drive became "too slippery" and
spinning the dial only resulted in an occasional jump on the tuning disk. It
became a major undertaking to restore the slight drag necessary for the
Hammarlund SP-600 to it's silky smooth operation. (hint, polishing those
brass friction wheels and the edge of the tuning dial just made things all
the worse).

Even on the R-390 there are places where an excellent grease is a better
choice, those tiny little rollers on the RF tuning deck. The challenge was
finding a very high quality grease that would not separate out into it's
constituent components (oils that run, greases that harden). My quest led me
to a specialized tungsten disulphide grease sold only in five pound
containers. The breakdown temperature on where the grease separates is
somewhere around 320 C, the coefficient of friction is incredibly low at
0.015 (teflon-teflon surfaces are around 0.04, steel-graphite 0.09, even
sapphire is 0.2) and it has an extraordinary high pressure rating (where you
end up compressing the grease film away and end up metal on metal).

On a side project that took me into the tungsten disulphide grease was while
trying to find a good grease for the bolt roller on an M1A rifle. For anyone
who ever owned an M1A or was issued an M14 rifle you will recall the nasty
task of packing the bolt roller with the specialized little grease cup or
your thumb. I digress...

It takes an incredibly small amount of this grease in very specific
locations to do it's job. I do not lather it on but when I disassemble any
radio gear-train or drive I use a small syringe to put a microscopic dot of
this grease onto gear shafts (I still have this obsession about using metal
polish on gears to make things nice and shiny, it is sort of like cleaning
my kitchen sink). It is more like a watchmaking operation. The one downside
of this grease is it is darned near impossible to de-grease your thumb when
finger packing a roller bearing.
http://www.lowerfriction.com/pdfs/hightempgrease_bro.pdf

With a five pound tub of grease I have enough to restore radios for the next
700 years so I use it on door hinges, farm equipment, rack rails and the
occasional squeaky fan bearing. On the R-390A I was able to take the tuning
smoothness down to a lightly placed index finger on the knob to move across
the dial. Spinning fast I just hear the click, click, click as the stops
wind down. I spent the most amount of time dealing with the slight binding
of the tuning slug racks in the RF deck where the rack sides touch the RF
deck frame (magic grease applied with a Q-tip worked there too).

Tisha Hayes