[R-390] Friction in KC Change Chain

[Curt Nixon]

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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