Another shear screw

rocclobster

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Joined
Sep 12, 2010
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18
I've broken 2 shear screws in my RV-10's roll servo over 4 years and 450ish hours. The original broke a couple years ago and it was chalked up to a weak batch of pins. The second one was one of the newer screws that is supposed to have better fatigue resistance. It broke a couple days ago on a perfectly calm, no turbulence day while doing a practice IFR approach. When the next one breaks I do not have any empty threaded holes in the hub. What is the solution when this happens? With red loctite it is going to be very difficult to remove the threaded stubs. Is field replacement of the hub an option? Can I purchase one and have it in my parts bin?
 
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jakej

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Oct 10, 2007
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Adelaide, Australia
Shear pins can fail anytime after an ‘event/s, sometimes people can inadvertently grab the stick for support when sudden turbulence happens, it may not break then but latter due the cycle of stress - not saying this happened in your case but it can.
HUB for servo - Reach out to Dynon, they will sell you one ( same suggestion applies for those who have already broken 1 or 2 shear screws).
 

rocclobster

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Sep 12, 2010
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Thanks and you are correct. I got a reply from Dynon Service and the disk (I called it hub in my OP) is not field replaceable. It would be extremely difficult to remove the remnants of the shear screws from the disk so a return to Dynon would be required.
 

Followthemark

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May 13, 2020
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I had the same issue, three shear screws all broken, two from before my time as owner of my plane. With the holidays right around the corner, I decided to try and remove the remaining portion of the screws. I figured if I was unsuccessful, I’d simply send the servo back to Dynon for repair. I spent considerable time drilling out the screws, being careful to stay centered. I then went to an auto parts store and purchased a screw extractor. The kit included several sizes of drill bit and extractors. The smallest was just right. All three screws came out with a little bit of finesse. Once I had the extractor, it took less than 10 minutes to remove all 3 screws.
 

rocclobster

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Sep 12, 2010
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Thanks, that's good to know. I was mostly concerned about them being held in with red loctite. Usually anything installed with that is very difficult to remove without heat. In this case maybe the screws are so small there's not much for the loctite to hold onto.
 

Followthemark

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May 13, 2020
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Per installation instructions for the shear screw, only the lower half of the screw should have medium Locktite. I didn’t find removing the shear screw with the extraction tool any problem. Since you must remove the servo anyway if you’re sending it out to Dynon for repair, trying the extraction tool can save you a lot of time waiting for the return. Dynon quotes 10 days plus shipping time, although the support tech felt the time would likely be a few days.
 

rocclobster

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Sep 12, 2010
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Thanks, I'm aware of the instructions and followed them closely. Red loctite is included with the shear screw replacement kit from Dynon.
 
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