Sven Posted July 10, 2011 Report Posted July 10, 2011 We purchased our D model three years ago and this is our third annual. As we are pulling the belly panels off this year we came to a conclusion based on a building suspicion. Our belly has 5-6 different screws and the pattern makes no sense. What we suspect is that since 1963 various mechanics have replaced old or broken Tinnerman clips with sonething they had on hand. Sometimes it's a #8 and sometimes a #10. Some are machined and some are sheet metal Several of these clips (and screws) need replacing. I have the hardware and maintenance manuals but cannot find any mention of the clips and screws. So my question is this, are all the screws on the belly supposed to be roughly the same? Obviously, there a couple of places where anchor nuts & machined screws are used. But the rest should all be the same, right? I'm guessing that sheet metal #8's are the correct answer. Thanks for the help. -Sven
Piloto Posted July 10, 2011 Report Posted July 10, 2011 You are correct on your asumption. The reason for the different sizes is wear. As the screws get screw in many times during 40 years some of the holes in the structure get bigger and the mechanic goes for the next size screw. This is very comon in old planes. You can standarize by using the same size tinermann nuts. But even tinermann nuts holes get bigger with time. Typically a mechanic will be putting back one of these panels just to find out that the last screw is not tightening. Instead of removing the hole panel and replacing the nut he will just use a bigger screw. José
carusoam Posted July 10, 2011 Report Posted July 10, 2011 Sven, From my 65C experience, There were two size machine screws used. Dozens of the larger size and about eight of the smaller size. The parts manual can tell exactly what size they are supposed to be. What the manual does not say is where they each go. Since they are so close in size, it is easy to jam the larger fastener in the smaller threaded hole. I believe the smaller fasteners were used in the center area of the panels in a circular pattern, the larger ones were along the outer edges. Compare the threaded hole hardware and see if there is a discernible difference. These devices are riveted in place. if they get ruined / stripped, they can be replaced. As for the tinnermans, purchase new ones with matching screws. Spruce has the parts. The matching screws are blunt. There is no need for the sharp point. New tinnermans have all the proper spring loading that you probably can't find left in the old hardware. I think it takes four or five annuals to finally rid the plane of old mismatched hardware. Keep up the effort it is worth it. Purchase extra hardware in advance so you have it at annual time..... The only tinnermans I could not find were the tiny ones used on the engine baffling/doghouse. Best regards, -a-
Sven Posted July 10, 2011 Author Report Posted July 10, 2011 Thanks for the reply. Any idea what the screws are supposed to be? I'm guessing #8 blunt end sheet metal.
carusoam Posted July 10, 2011 Report Posted July 10, 2011 Sven, My 65 parts manual for the C, D, E... indicates screw AN530 8R8....as required. Blunts probably did not exist at press time! Website. Www.usmilitaryfasteners.com has pictures.... 8Z-3 is what they called the tinnermans "speed nut" AN507 8R8 and 6R7 I believe would be the two sizes of machine screws indicated. Again, this was from the 65 parts catalog. Best regards, -a-
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