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Check Your Autopilot Servo Arm Screws!

arm screw loose

I just started my condition inspection friday and sure enough the screw that holds the arm was loose almost to the point of falling out.

I chose to use lock tight and i will recheck after 10 hours of flight

ken in maine
 
Steve Sampson said:
Did TT ever come out with a statement as to their view or a fix?
Click to expand...

Lucas from TruTrak advised Cleve Thompson (see Post #75) that TT would issue a statement when they had a "solution".

That was 5 weeks ago and not a word from them since....neither here nor on their website.

They're probably scratching their heads about how to address the problem without it costing them a lot of money by way of a major recall.
 
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loose screw

As i posted the other day i found the loose screw on the elevator servo i just check the right wing servo and that screw was tight and now signs of being loose

ken in maine
 
Checked the pitch servo.

I checked my pitch servo screw. It was not loose, but I have not flown yet. Still have to check the aileron servo.

It is a bit scary though, just the screw with some lock-tite (if there is any!) and nothing else that one can actually see, holding that screw in.

Regards, Tonny.
 
Pilottonny said:
It is a bit scary though, just the screw with some lock-tite (if there is any!) and nothing else that one can actually see, holding that screw in.
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That's all that holds your baffling together or your valve covers on.....a bunch of blind screws.;) Let's wait to see what TT has to say. I'm not saying there isn't a problem to be addressed but there are thousands of units flying. In the mean time, a little Locktite and the proper torque will probably be all that's needed.

BTW, if you check the torque on the screw and you move the screw from where it was, you quite possibly broke the Locktite bond and you may actually ASSIST the screw in vibrating out. If you check the screw, remove it all the way and re-apply Locktite before re-installing.
 
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Lycoming recommends...

f1rocket said:
That's all that holds your baffling together or your valve covers on.....a bunch of blind screws.;) ......
Click to expand...

...that lock washers should be used at these locations....

A STD-1925 - 1/4-20 x 5/8 long, pan head, self locking according to my parts manual....:)
This is the O-360 valve cover screw, and in this case, has an attached lock washer.

Perhaps you need to check your engine hardware?
 
Prooving a negative....the screw is not loose?

Clearly there is a temptation to unscrew the screw to see if its tight. Are there folk out there with a loose screw who can honestly say they never touched it?

If it is clearly loose there is a problem, but if the only loose screws are ones that someone has messed with then its the problem only of trying to proove its not loose.
 
f1rocket said:
That's all that holds your baffling together or your valve covers on.....a bunch of blind screws.;) Let's wait to see what TT has to say. I'm not saying there isn't a problem to be addressed but there are thousands of units flying. In the mean time, a little Locktite and the proper torque will probably be all that's needed.

BTW, if you check the torque on the screw and you move the screw from where it was, you quite possibly broke the Locktite bond and you may actually ASSIST the screw in vibrating out. If you check the screw, remove it all the way and re-apply Locktite before re-installing.
Click to expand...


This is exactly the message I have been providing to all the phone calls I have received. If you "check" the screw, you need to remove it and reapply the thread locker, because you just broke the bond. We have a solution in the works, it's just not available quite yet. It will be easy to retrofit any existing servo and all new servos will implement it. We will also offer it free of charge to anyone who wants to retrofit their servos. Once we have the parts on hand, I will make a separate post. Thanks for you patience!
 
TrutrakTech said:
This is exactly the message I have been providing to all the phone calls I have received. If you "check" the screw, you need to remove it and reapply the thread locker, because you just broke the bond. We have a solution in the works, it's just not available quite yet. It will be easy to retrofit any existing servo and all new servos will implement it. We will also offer it free of charge to anyone who wants to retrofit their servos. Once we have the parts on hand, I will make a separate post. Thanks for you patience!
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Lucas,
is there a preferred loctite grade that should be used? How tight must the screw be?
 
rv72004 said:
Lucas,
is there a preferred loctite grade that should be used? How tight must the screw be?
Click to expand...

Lucas told me today to use a medium grade locktite, blue is what I used. Just torque the screw to specs for a #8.

I checked mine today and it was kinda loose. I removed the screw, cleaned it up, oiled the rod end bearings, and reinstalled and retorqued the screw. I'm sure I'm gonna need 4-6 hours of flight testing to make sure it is good. ;)
 
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loose screw

I did not loosen the screw it became loose there is a problem and i'm glad they will have a fix for it they(TT) is a great CO. when you can see the screw backed out with out touching it you know there is a problem the loctight is a short term fix

for now we must do what we need to to be safe

this forum is a great place to post this stuff

Duog i thing in some degree you save lives

ken in maine
 
4kilo said:
The screw which holds the arm on a TruTrak autopilot servo is a #8 panhead stainless 1/4 inch long, with a nylon washer between the screw head and the servo arm.

Pat
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Is this a good idea guys? Having a nylon washer in a place where a good torque setting is needed? The nylon washer would deform after awhile and be more susceptible to heat. Would a metal washer be a better choice?
 
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Geico266 said:
Lucas told me today to use a medium grade locktite, blue is what I used. Just torque the screw to specs for a #8.

I checked mine today and it was kinda loose. I removed the screw, cleaned it up, oiled the rod end bearings, and reinstalled and retorqued the screw. I'm sure I'm gonna need 4-6 hours of flight testing to make sure it is good. ;)
Click to expand...


Thanks for the info, but isnt blue the light duty ,easily removable loctite?
 
Geico266 said:
Is this a good idea guys? Having a nylon washer in a place where a good torque setting is needed? The nylon washer would deform after awhile and be more susceptible to heat. Would a metal washer be a better choice?
Click to expand...

My guess is that the Nylon washer assures the over torque shear screw will do it's job and allow the arm to move free of the servo should some electronic fault happen and make the servo go TU.
 
John, the point to understand about TT's stepper motor servos is that there is no direct connection. It is only a magnetic field you are breaking if you want to do one thing and the motor another. It wont get worse than when you ask the pitch servo to hold an altitude with the trim well off where it should be. Nothing needs to shear, just the magnetic field.

Is the screw doing anything other than holding the arm back? I had assumed but dont know since there is no reason to undo it, and every reason not to, that its a splined shaft.
 
It is not a splined shaft. It is designed so the arm swivels on the servo saft if a shear pin (another off center brass screw on the shaft) is sheared. There are two screws, One with the nylon washer to hold the arm on the shaft and a second shear screw to handle the torque on the arm. Actually on mine there are three shear screws, one metal and two nylon ones. If I recall, initially there were three nylon ones and the changed one to metal (brass) after i bought it.
 
Actually, thinking about the shear screws on the arm. If they put a head on those screws and also locktit'd them, the shear screws could act as redundant attachements as well to keep the arm from falling off if the main screw backs out. Detection of a loose main screw would still be my inspection.
 
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