[R-390] R-390A gear train cleaning

[Ken Harpur]

Hi Bob,

I've just finished my first gear rain re-build a couple of days ago. I took the plunge and disassembled it, soaked everything in mineral turpentine for a few days, removed the stubborn grease with WD-40, a tooth brush and lots of paper towels and with the excellent reassembly pictorial on the web  http://militaryradio.com/r390a-rfdeck-geartrain.html
  put it all back together.

My gear train is very well worn and although it is much better than it was...some gears show signs of very heavy use and after breaking the first two circlips for the split gears regardless of how careful I was, I didn't risk pulling apart the others. So on my deck I have three split gears that badly need to be lapped with a stone as Roger suggested as they feel very gritty when the gears are rubbed together as opposed to the nice smooth feel they are supposed to be.

Loading up the split gears can be a challenge on some gears...but with patience and perseverance success awaits. Also, be aware that there are some very thin washers that go either side of the gear that drives the khz readout bezel. On my one there were two at the back and two on the front. 

I decided to pull apart the differential assembly...cleaned it with WD-40 and reassembled. I found the way to load the split gears on it was to rest one gear on the gear it mates to, then load the remaining half of the gear and using my fingers as a clamp wiggle the gears slightly until they come together. 

I created extra work for myself though because I removed the geneva drive and the gear on the bandswitch...it took me a long time to get that set up again and for the other 390A radios I have I think I'm going to leave the geneva drive alone.

I learned a lot by doing mine. When I find a source of suitable circlips I will be getting back into it to smooth up the gears that are catching. The point is...a newbie can do it! As long as you take your time, work in a logical fashion and keep referring to the pictorial.
I suppose it depends on what you're comfortable with. There was so much caked-on grease on my one that I felt disassembly was the best option.

Good luck with it.

Regards,
Ken