Years ago a machinists’ magazine performed scientific comparisons of commercial penetrants advertised to be useful in obtaining release between “stuck” mechanical items. Included was a test of a “home remedy” of 50% acetone and 50% automatic transmission fluid. FWIW, PB Blaster released better than WD-40, but that’s not saying much. The hands down winner ? …. the 50-50 mixture of acetone and transmission fluid. I’ve made this up with synthetic auto transmission fluid, in one instance, and non-synthetic auto transmission fluid in another. I did not perform a scientific torque release test, but suspect that using the synthetic fluid may work the best because it should have smaller molecules. Please note that whether you use the synthetic or non-synthetic auto transmission fluid in the mixture, either will separate from the acetone unless you shake it up and apply it quickly thereafter.
Of course, if there is actual corrosion causing the issue with the slugs, that’s a different issue probably not solvable with a penetrant. Good luck & 73, Bill W5WHB ++++++++++++++++ Bill Blodgett Arlington, Texas > On Oct 26, 2025, at 9:33 AM, Mack McCormick <[email protected]> wrote: > > I'm repairing/aligning a R-391 for a friend. Every single RF deck slug > tuning screw is solidly stuck. I think it is a galvanic response between > the brass and steel. > > Does anyone have tips to free the slugs? They won't budge using a moderate > amount of force. I've used PB Blaster and heat to no avail. > > I've repaired at least one hundred 389/390/390a/391 over the years but this > is the first one I've encountered with every slug stuck. > > Thanks in advance for any ideas. > > 73, > > Mack > W4AX > https://www.qrz.com/db/w4ax > ______________________________________________________________ > R-390 mailing list > Home: http://mailman.qth.net/mailman/listinfo/r-390 > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:[email protected] > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html ______________________________________________________________ R-390 mailing list Home: http://mailman.qth.net/mailman/listinfo/r-390 Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
