There is a document in the archives that outlines exactly how to assemble the gear train.
https://www.r-390a.net/R-390A-Gear-Rebuild.pdf 73, Barry - N4BUQ > Like an idiot I removed the RF deck and the gears for cleaning/clamp > replacement > and now cannot get this back together working correctly! I tried to write this > so it makes sense, probably will not. I do not know the formal name of each > gear and the part numbers I refer to are from the r390a-063-2010-7004 pdf of > NAVSHIPS Technical Manual. > The problem gear I am talking about is the one shown in Step 2 of Chapter 10 > (part #79/66 in the manual). It has a shaft with THREE gears on it (small > pinion gear (#79); large brass gear with 4 hole cut-outs and another smallish > gear (#66). Step 2 of Chapter 10 says “Insert it with the pinion meshing with > the Geneva Drive gear”. So its shaft inserts into bushing M in the frame and > the pinion (#79) meshes with the Geneva Drive gear. The problem is the next > step; the large brass gear on this same gear assembly is I THINK supposed to > mesh with “small gear” of the large 4 hole cut-outs brass gear assembly #42 > (#42 is on the same shaft as gear assembly #63/64/65 that attaches to a > different gear with three screws). > When the pinion gear of #79/66 meshes with the Geneva Drive gear, the large > gear > on this assembly can BARELY reach “small gear” of #42; it almost completely > falls out of its bushing. It is as thought #42 should “go back” more, but it > can not. Am I missing something, is the large gear on #66 NOT supposed to mesh > with the rear gear of #42? > > From: Jacques Fortin <[email protected]> > Date: Thursday, June 18, 2026 at 10:40 AM > To: 'R390A' <[email protected]> > Cc: [email protected] <[email protected]> > Subject: RE: [R-390] Removing Megacycle Change shaft > > Hello Paul, > I also have a spare of the right size clamp (13/32" hole - 0.406 in from the > spec sheet) but sending it to the US became a big problem since... you know > what. > I also searched for a commercial source for these clamps (or any valid > replacement) yesterday and failed to find anything suitable. > The clamps used in the R-390 and R-390A were also used in some other Collins > products of the same era, but they are not of "standard" dimensions, compared > to the commercially available ones I have seen. > There is four different size clamps in the R-390A. Not very hard to machine > with > the right equipment. > One of this forum members already made one from "scratch", it was one for the > knobs if I remember well. > Having one that breaks is unlikely, except if someone greatly over-torqued the > screw: the clamp broke instead of the screw...oh my. > Your set was "overhauled" by a US Army depot, right? > I will tend to inspect EVERYTHING within. And I really mean EVERYTHING. > Canadian Army was not better: the worst case I run across was a substitution > of > the racks tuning slugs with some other of different origin, meaning different > relative permeability, which rendered the set impossible to align properly. > The whole radio was probably "junked" (sent to the surplus disposal), for that > very reason. > And yes, it is the 1st contract Collins that figures in the Gianni Becattini > book. > > Paul, You mentioned that the R-390A is a "beast" compared to your Hammarlund > radios. > Your are lucky that it is not a R-390, which is a "beast and a half" ! > > 73, Jacques, VE2JFE in Montreal > > I have panel off and waiting for a gear clamp off a MC shaft assembly I just > got > on eBay. > Going forward, is there a COMMERCIAL source who sells clamps that would work > as > gear clamps, (Bristol or hex or slotted) for other clamps that might break? > Thanks for the help. I might need help with aligning this thing to read > correct > frequency when I am done, lots of gears! But I will read the literature and > hope I get it. At least now that this is apart I can clean off the gears/gear > teeth with isopropanol and “re-lube”. I assume just put light oil on the > shafts > themselves, not the teeth on the gears? > > Paul > > ______________________________________________________________ > 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
