[ARC5] R23 repair, dynamotor mounts, questions...

[Kenneth G. Gordon]

On 23 Dec 2015 at 20:28, Brian wrote:

> Hello Ken et al,
> 
> Not all dyno shocks simply unscrewed. I have met some where there were nuts
> under the chassis and some where, once the shock absorber was screwed into
> either the nut or the threaded bush rivetted to the chassis, they were pinned or
> otherwise maimed to prevent easy removal.

Yes. But even pinned, it is possible to remove most of those by simply using 
a channel-lock plier to force them past the pin. Most pins I have (so far) run 
into are aluminum. Many that I have run across are "locked" with either some 
sort of black paint-like substance, or even some form of "glyptal".

> Even if you do find shock absorbers, the rubber in them is now probably over 70
> years of age, and very likely perished or glutenised.

Agreed. I have found very few of those which are still good. Even so, since I 
use those mounts to hold a dynamotor base to the receiver, they suffice...

> After stripping out the
> remnant goo, I have fitted a modern silastic grommet over the centre pin and
> glued the outer of the grommet to the threaded outer shell. But you need to set
> all four of them all up to the same height.

Ah! Good idea! I had not thought of that. Thank you.

> Yes, on the three bottoming studs. You may want to consider adding a 
> grounding strap under two of these bottoming studs; the other end of the 
> grounding straps fit under two of the snap slides holding the dyno to the 
> shock absorber - this was a late WWII mod to reduce noise from the dyno 
> getting into the antenna circuit.

Yes. Exactly. I have mentioned that in the past.

> Add some Noalox between the bottoming 
> stud, the grounding strap and the cleaned chassis before final fastening. 
> The OEM grounding straps I have encountered were plated copper about 0.010" to
> 0.015" thick, usually fastened to the rear deck of the chassis with steel PK
> screws - naturally, a corrosion attractant.

Indeed!

> I suppose toward the end of WWII,
> the life expectancy of a combat plane and crew was known to be about three
> weeks; so, corrosion resistance was not an important design consideration.

Yes.

I am certain that the original ARC folks would be very, very surprised to find 
their receivers (and transmitters) still being used 70+ years after they were 
first built.

Ken W7EKB