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  #11  
Old 09-26-2022, 06:55 AM
Freemasm Freemasm is offline
 
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Location: Orlando
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Quote:
Originally Posted by PilotjohnS View Post
If the jam nut is loose,I think it could cause the threads inside the clevis to wear. This could lead to a sloppy fit between the clevis and the cable. If it gets really bad, then the cable and clevis could slip a few threads.

I would check the cable and clevis threads for excessive wear. If any is found, then it might be prudent to replace both. JMHO
...and then some. If the jam nut is loose, you can easily get a reversing load on the threads; never a good idea. They will wear and fret away or even fail from fatigue. In quick summary, their purpose is two fold.
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  #12  
Old 09-26-2022, 01:55 PM
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sahrens sahrens is offline
 
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Location: Battle Ground WA
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Default Ground

Could this be a chaffed wire grounding somewhere? The trim motors are reversible based on grounding through the trim switch. Perhaps it’s a loose connection or a frayed wire. That’s where I’d start searching; maybe start where the wire passes through the elevator to the horizontal and into the fuselage.
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Last edited by sahrens : 09-26-2022 at 04:17 PM.
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  #13  
Old 09-26-2022, 03:07 PM
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Roadjunkie1 Roadjunkie1 is offline
 
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Location: Erie, Colorado
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Default SB 06-9-20

While you are under there.....actually has to do with checking your log books: make sure SB 06-9-20 was complied with. That has to do with WD 415 which is the welded fitting your cable passes through visible through the hole in the elevator. There is a better designed WD 415-1 that has welds on both sides of that nut the cable fitting passes through. When I was replacing mine, the welded nut on the original WD 415 actually snapped off Pretty happy I replaced THAT!
Van sells the new -1 for just over $8. Worth it. Hopefully the previous owner replaced it. It is a little bit of a PITA to replace the thing.....
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  #14  
Old 09-26-2022, 03:38 PM
Everwild Everwild is offline
 
Join Date: Feb 2020
Location: Maumee
Posts: 114
Default Video that explains it

Very informative video on the subject of rod end bearings as they apply to aircraft.

The answers related to reversing loads and wear on threads are correct. Most installations wont let the rod end unscrew by design.

https://www.youtube.com/watch?v=foyZLBneV08
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  #15  
Old 09-27-2022, 12:17 AM
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ronrapp ronrapp is offline
 
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Location: North Tustin, CA
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Quote:
Originally Posted by Freemasm View Post
If the jam nut is loose, you can easily get a reversing load on the threads; never a good idea. They will wear and fret away or even fail from fatigue. In quick summary, their purpose is two fold.
That does not sound good. I do not have the construction documents for the airplane; is there a place where I could find a torque value for the jam nut? Do people put torque seal on this nut?

Thanks for the info!

--Ron
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  #16  
Old 09-27-2022, 12:19 AM
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ronrapp ronrapp is offline
 
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Quote:
Originally Posted by sahrens View Post
Could this be a chaffed wire grounding somewhere? The trim motors are reversible based on grounding through the trim switch. Perhaps itís a loose connection or a frayed wire. Thatís where Iíd start searching; maybe start where the wire passes through the elevator to the horizontal and into the fuselage.
I suppose anything is possible. I'll as much of the wiring as I can get access to and see if anything stands out as worn, chafing, etc.

The behavior of the motor is interesting. Once it starts to trim nose up -- and it's always been nose UP -- it just keeps running until I disconnect the autopilot.

--Ron
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  #17  
Old 09-27-2022, 12:21 AM
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ronrapp ronrapp is offline
 
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Quote:
Originally Posted by Roadjunkie1 View Post
While you are under there.....actually has to do with checking your log books: make sure SB 06-9-20 was complied with.
Thanks for the information! There is nothing in the logbooks about this SB having been completed on the airplane (first flight in '97), so I probably have the single sided weld. For $8 it's hard to go wrong.

--Ron
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  #18  
Old 09-27-2022, 12:30 AM
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ronrapp ronrapp is offline
 
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Quote:
Originally Posted by Everwild View Post
Very informative video on the subject of rod end bearings as they apply to aircraft.

The answers related to reversing loads and wear on threads are correct. Most installations wont let the rod end unscrew by design.

https://www.youtube.com/watch?v=foyZLBneV08
Thanks, David. I learned quite a bit about rod end bearings from that vid. It certainly clarified the role of the jam nut. What I'm still not 100% sure of is how to ensure the jam nut is tight enough. At the very least, it's something I'll be checking closely in my preflight inspections.

--Ron
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  #19  
Old 09-27-2022, 08:29 AM
lr172 lr172 is offline
 
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Location: Schaumburg, IL
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Quote:
Originally Posted by ronrapp View Post
Thanks, David. I learned quite a bit about rod end bearings from that vid. It certainly clarified the role of the jam nut. What I'm still not 100% sure of is how to ensure the jam nut is tight enough. At the very least, it's something I'll be checking closely in my preflight inspections.

--Ron
one wrench on the flat area of the clevice and the other on the jam nut.
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  #20  
Old 09-27-2022, 11:03 AM
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RV7A Flyer RV7A Flyer is offline
 
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Location: US
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Quote:
Originally Posted by ronrapp View Post
I suppose anything is possible. I'll as much of the wiring as I can get access to and see if anything stands out as worn, chafing, etc.

The behavior of the motor is interesting. Once it starts to trim nose up -- and it's always been nose UP -- it just keeps running until I disconnect the autopilot.

--Ron
Does it *ever* run away when the autopilot is NOT on?
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