0TreeLemur Posted October 3 Report Posted October 3 An A&P did some work on my Mooney today. He and I put the lower cowl on and he left for the day. While installing the upper cowl I encountered a problem. The upper cowl on my '83 J has a bunch of quarter-turn fasteners and three machine screws on each side. Two machine screws go into the stanchion around the propeller flange, and one on the forward corners. The screw on the right forward corner started normally but after a few turns started to get real tight... Those are stainless steel screws and it felt like it might be starting to spall. So I backed it out. It was tough to turn and definitely felt like it was spalling. The threads were definitely messed up. Looking in there, the threads on the inside nut plate are not perfectly aligned with the hole in the nut plate. The threads on the left front nutplate are centered. On the right hand side it seems that the nut is too high. Looking in there I could see a many threads in the bottom of the hole and none in the top. Question: are those nut plates with captured floating nuts? Why is it suddenly out of alignment, and how can I center it? Any ideas on how to fix this? One Idea I have is to run a tap in there and see if that centers it. Thought I would ask the collective about this idea before trying it. Thanks, Fred
Slick Nick Posted October 3 Report Posted October 3 Just drill out the rivets and put some new nut plates in.
0TreeLemur Posted October 3 Author Report Posted October 3 2 hours ago, Slick Nick said: Just drill out the rivets and put some new nut plates in. Does not answer my questions at all. 1
N201MKTurbo Posted October 3 Report Posted October 3 There are floating and fixed nut plates. Just look at them and you can tell. You can also chase the threads with a tap.
Slick Nick Posted October 3 Report Posted October 3 10 hours ago, 0TreeLemur said: Does not answer my questions at all. Q: "How can I fix this?" A: Install new nut plates. Not sure how that didn't answer your question? Most nut plates are squished at the end so they will retain the fastener. Tapping it out removes that, which is why it's best to replace them. Not sure if the cowl ones are like that, but replacing it would be the easiest and most professional solution.
N201MKTurbo Posted October 3 Report Posted October 3 16 minutes ago, Slick Nick said: Q: "How can I fix this?" A: Install new nut plates. Not sure how that didn't answer your question? Most nut plates are squished at the end so they will retain the fastener. Tapping it out removes that, which is why it's best to replace them. Not sure if the cowl ones are like that, but replacing it would be the easiest and most professional solution. If you replace them, you will traumatize the fiberglass and paint. Chasing the threads will get it working without screwing up the appearance of the cowl. 2
0TreeLemur Posted October 4 Author Report Posted October 4 14 hours ago, N201MKTurbo said: Chasing the threads will get it working. To answer my own question it is not a floating nut plate so alignment was not the issue. Running a tap in did clear the way. It seems odd to me that suddenly it developed a problem. I can't imagine what caused it to change. I suspect that nut plate is going to need replacing sooner rather than later by an A&P with the experience and tools, which I am not. 2
jetdriven Posted October 4 Report Posted October 4 Stainless screws tend to gall and seize up in the nut plate and then break off and then you have one heck of a problem. We just started using more and more cad plates steel fasteners, which don’t do this nearly as often. Spinner screws in M20Js are another notable example. 1
Yetti Posted October 7 Report Posted October 7 On 10/3/2025 at 11:52 PM, 0TreeLemur said: To answer my own question it is not a floating nut plate so alignment was not the issue. Running a tap in did clear the way. It seems odd to me that suddenly it developed a problem. I can't imagine what caused it to change. I suspect that nut plate is going to need replacing sooner rather than later by an A&P with the experience and tools, which I am not. yep stainless and nut plates don't play so well together. Toss the screw.
Slick Nick Posted October 8 Report Posted October 8 A little bit of anti sieze on stainless fasteners seems to help immensely. 1
N201MKTurbo Posted October 8 Report Posted October 8 28 minutes ago, Slick Nick said: A little bit of anti sieze on stainless fasteners seems to help immensely. I don’t even do that, I just put them in a Dixie cup and spray them with LPS before I screw them in. They never stick. 1
Z W Posted October 8 Report Posted October 8 I do the same but with Corrosion-X on most fasteners before they get re-installed somewhere exposed to the environment. Seems to give you a few more years before anything rusts or seizes in place. 1
PT20J Posted October 8 Report Posted October 8 Galling is microwelding caused by pressure and friction heating. Lube and not turning fasteners at high speed with a power driver will prevent it. 2
MikeOH Posted October 9 Report Posted October 9 I have SS machine screws into plain steel nut plates in six places on my cowl. I NEVER use a power screwdriver either to remove or replace them; I go slow and have not had any problems (knock on wood). My guess is that sometimes these get cross threaded just a little and then the nut plate is prone to gall due to the increased friction from the damaged threads. That's why I'm very careful when installing; any sign of resistance I back the screw out and check threads, put on a spot of oil and try again. 2
0TreeLemur Posted October 12 Author Report Posted October 12 On 10/8/2025 at 8:30 PM, MikeOH said: I NEVER use a power screwdriver Ditto. Installing screws by hand so you can feel what is happening is the ONLY way on an airplane. When it starts to feel "odd" you can back it out and investigate further. That's how I spotted the problem in the first place. 3
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