[R-390] R-390 (Non-A) RF Gears Cleaning

[Jim Whartenby]

AlexI haven't cleaned an R-390/URR but I have done the deed on several R-390A/URR receivers with the modules powered by the geartrain still in place.  It is interesting that none of the R-390/URR receivers that I have seem to have as great a buildup of grease and grime as the later series of receivers have had.  
My method uses several spray bottles salvaged from home spray cleaners each of which is filled with WD-40 used as a solvent, diluted Krud Kutter 50/50 with water as a detergent, water as a rinse and alcohol as a final water release agent.  I use an acid brush on a wood dowel to extend it's reach to scrub deep into the geartrain using each of the above sprays in succession.
The thought was that no one cleaner would be sufficient to easily remove all of the grease and grime.  Krud Kutter does not seem to attack aluminum, unlike some strong cleaners.  Simple Green also may not attack aluminum but I have no first hand knowledge.
I just cycle through the above spray bottles outside on a nice day until the geartrain moves freely.  The process does not take long.  One R-390A was so gummed up that the kc and mc knobs were frozen in place.  It did not take long to dissolve the gum and free up the stuck geartrain.  
Once all is clean and shiny and after the final alcohol rinse, I let the radio set outside to air out to be sure all of the water has evaporated.  I only lube the gear pivot points but not the gears themselves.  This is what the clock collectors recommend since lubed gears attract dust and crud which will only cause the gear teeth to gum up again and wear prematurely.  My lube of choice is Tuff Oil but any decent synthetic oil will do.  I use a sharpened wooden stick, like a six or so inch Q-tip, to get into the gearworks to reach the various pivot points with a tiny drop of lube.
The final trick is to recenter the bushing on the front panel where the kc and mc shafts protrude.  You should be amazed at how easily the frequency knobs now turn.  Don't forget to lube all of the guide rollers found in the RF and IF modules.Regards,Jim
Logic: Method used to arrive at the wrong conclusion, with confidence.  Murphy 

    On Wednesday, February 11, 2026 at 12:01:36 PM CST, Alex Hopper <ahopper0216 at gmail.com> wrote:   

 Hi All,

I have done quite a bit of reading on the best ways to clean the RF deck
gear train on the R-390.  Seems that most people recommend a thorough flush
of WD-40.

Does anyone have personal experience with this?  I am tempted to try it,
however I am NOT interested in removing my RF Module.  Is this something I
can carefully do with the RF module still intact?  I would use a long
'staw' aimed down carefully into the gears.

-Alex
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