[R-390] Friction in KC Change Chain

[KA9EGW]

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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