65MooneyPilot Posted June 20, 2023 Report Share Posted June 20, 2023 I have a question about step 14 where it says to remove AN7H-17A and run a magnet inside the tube. The parts manual in figure 2 index 2 says that bolt is an AN7H-16A. Somehow it has turned into a -17A bolt. Also is the nut/ thread for that bolt inside the tube? If so, is it possible the thread is corroded and has this been a problem during this inspection? Thanks Quote Link to comment Share on other sites More sharing options...
Sabremech Posted June 21, 2023 Report Share Posted June 21, 2023 21 hours ago, 65MooneyPilot said: I have a question about step 14 where it says to remove AN7H-17A and run a magnet inside the tube. The parts manual in figure 2 index 2 says that bolt is an AN7H-16A. Somehow it has turned into a -17A bolt. Also is the nut/ thread for that bolt inside the tube? If so, is it possible the thread is corroded and has this been a problem during this inspection? Thanks Good morning, I can’t explain the discrepancy with the bolt P/N without some research into the documentation including service bulletins which could have changed the P/N from what’s shown in the IPC. As for the threads, they are a threaded insert that is welded into the tubing. The point of the magnet being inserted through the opening and past the threads is to see if there is corrosion inside the tubing. From the ones I’ve done, you will pull out light fuzz on the magnet. If you pull out heavy chunks or more than light fuzz, you have a problem with the tubing. I’ve gone so far as to borescope the tubing through both bolt holes to see if there’s heavy pitting which would also be bad. As for the threads, if the bolt torques to spec, the threads are good as you typically won’t see them corroded due to anti seize being applied to the threads of the bolt before installation. Hope this answers your questions. David 1 Quote Link to comment Share on other sites More sharing options...
65MooneyPilot Posted June 23, 2023 Author Report Share Posted June 23, 2023 Thank you for answering my question. I knew it was technical and only a fellow mechanic that has done the inspection could answer it. I am still waiting for the bolts to be delivered before I start. Quote Link to comment Share on other sites More sharing options...
A64Pilot Posted June 26, 2023 Report Share Posted June 26, 2023 (edited) You may consider getting an ultrasonic thickness gauge, or borrow one, anyone that works on fabric covered airplanes ought to have one, they are a very easy non intrusive way to measure the thickness of a tube, any internal corrosion of course reduces the thickness. The are used to determine extent of internal corrosion Good ones can accurately measure to .001mm or less. I believe that’s to .000039 inches Edited June 26, 2023 by A64Pilot Quote Link to comment Share on other sites More sharing options...
65MooneyPilot Posted June 28, 2023 Author Report Share Posted June 28, 2023 I removed the bolt on the right side and found out it was in fact a -17A bolt with two light washers installed. I used a bore scope to look up inside and it still has most of the zinc chromate primer in it. I ordered the -17A bolts and they should be here this week. Quote Link to comment Share on other sites More sharing options...
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