[R-390] Friction in KC Change Chain
nryan at mchsi.com
nryan at mchsi.com
Sun Feb 27 13:22:22 EST 2011
Hi, Curt,
Will this link help?
http://r-390.com/cosmos.htm
73 de Norman, KG4SWM
----- Original Message -----
From: Curt Nixon <cptcurt at flash.net>
To: KA9EGW <ka9egw at britewerkz.com>
Cc: 'Drew P.' <drewrailleur807 at yahoo.com>, r-390 at mailman.qth.net, captcurt at flash.net
Sent: Sun, 27 Feb 2011 11:54:38 -0600 (CST)
Subject: Re: [R-390] Friction in KC Change Chain
Searching the DBase it looks like a two part article in Issues 30 and 31
but only #30 is listed as an available back issue.
I would have thought there was a military manual or section on it also
but haven't seen reference to that. As a newbie it is hard to get arms
around the sheer mamount of documentation available for these radios.
Thanks,
Curt
KU8L
KA9EGW wrote:
> Wasn't there an article over 2 issues of Electric Radio telling how to D&R
> the PTO and reet the cam stack and all?
> 73, Brian KA9EGW
>
> -----Original Message-----
> From: r-390-bounces at mailman.qth.net [mailto:r-390-bounces at mailman.qth.net]
> On Behalf Of Curt Nixon
> Sent: Sunday, February 27, 2011 9:56 AM
> To: Drew P.
> Cc: r-390 at mailman.qth.net
> Subject: Re: [R-390] Friction in KC Change Chain
>
> Thanks Drew:
>
> The seal O-ring is EXACTLY what it feels like. I mentioned that to another
> tech off list and said it was smooth but felt like an shaft sealed with an
> O-ring. I have dry nitrogen here purge with but being there is no valve, it
> must have been assembled in a nitrogen chamber which I DON'T have :).
> knowing what is involved to get that O-ring removed, I might just leave it
> in there and live with the friction at this point. I can always pick up
> another PTO assembly and do the disection on it instead of this original
> one.
>
> I looked and searched a lot but never saw any type of drawing or internals
> information on the non-cosmos PTO.
>
> BTW, sorry for the messed up subject line..it was late. I attached the rest
> of my original post here so it would show up with the good information you
> offered.
>
> I re-looked at the stack follower and believe they are both riding on the
> stack. It must have been a light reflection making it look otherwise.
>
> The metal roller does not rotate..the stack edge is simply greased. It sure
> would seem that they would have made that a roller and not a slider. Can
> you confirm this one way or the other. Also, is there a reference somewhere
> on the internals and assembly, etc of the Collins PTO..I have had no success
> finding anything.
>
> I did find the reference to removing the dessicant bags. Wonder if its
> worth adding one of the current generation no-plastic dessicant containers?
>
>
>
>
> Drew P. wrote:
>
>> Curt Nixon wrote:
>>
>> "I am hunting down all sources of friction in the KC change chain and
>> decided to pull and inspect the PTO. It is smooth but stiffer than I
>> would expect with ball bearings. So it is apart and looks to be in
>> clean condition..pix on my blog site."
>>
>> On both Cosmos and non-Cosmos design PTO's, there is a small o-ring in a
>>
> groove in the bore in the housing through which the lead screw shaft passes.
> The function of that o-ring is to provide a seal to prevent the pressurized
> nitrogen from escaping. The small o-ring is in addition to the larger one
> around the outside of the housing between it and the can.
>
>> Removal of the shaft o-ring will quite noticeably reduce PTO shaft drag.
>>
> The o-ring would not be needed by most of us as the nitrogen leaked out long
> ago. To remove the o-ring will require disassembly of the PTO and removal
> of the tank coil, slug, and lead screw. Once these parts are removed, the
> o-ring may be removed with a sharp hooked tool such as an appropriate dental
> pick. I have also found that the anti-backlash nut on the slug can be set
> somewhat looser and this will reduce drag further and make tuning smoother
> as well. If too loose, there will be annoying backlash.
>
>> It has been recommended to remove the dessicant packs inside the can as
>>
> these have been known to disintegrate, filling the PTO mechanism with an
> apparently corrosive grit, as mentioned in forum postings past.
>
>> Drew
>>
>>
>>
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>>
>
> Collins PTO in R390A ser 3981
>
> I am hunting down all sources of friction in the KC change chain and decided
> to pull and inspect the PTO. It is smooth but stiffer than I would expect
> with ball bearings. So it is apart and looks to be in clean condition..pix
> on my blog site.
>
> One thing I noticed is the stack follower rollers....the fiber side rolles
> fine. The opposite side, the steel roller, does not roll at all. It is
> greased lightly and the grease is still soft, but it looks like that roller
> should spin freely. Is this correct?
>
> Also, as the followers ride along the travel length of the stack shims, it
> would seem that both rollers should ride on the shims--in this case, the
> fiber side roller is not in contact with the stack. The spring is in place
> and the arms for the followers are free.
>
> There was no rebuild sticker or data on the PTO. the original Collins
> security sticker over the cover seam was intact..so I am the first to be
> inside since new I suspect.
>
> PTO Pics at http://curtsworkshop.blogspot.com/
>
> Thanks
>
> Curt
> __________________________
>
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