Seat Sling Bolts

[wmfife]

Has anyone ever had to replace the bolts in the seat sling frame on a '41? The originals on mine had been removed and no one caught the fact that short wood screws (!) had been substituted. They didn't even engage the threads.

The problem I'm having is the fact that while AN3 bolts are 10-32 these nuts (the ones welded into the frame) are not. They are 10- something just don't know what. I have tried cutting and re-threading AN3 bolts to 10-26, 10-27 and 10-28 to no avail, even going to two metric threads 1.0 and 0.9mm. Nothing.

U.S threads were standardized in 1947 but these were manufactured sometime before April 1941. The closest so far are the 10-28 leading me to think these nuts are somewhere between 10-29 and 10-31 best guess.

Any ideas? I'm ready to drill these out and use longer bolts and elastic stop nuts. Didn't want to permanently alter an antique but I have to secure the sling some way that's legal.

[Hank Jarrett]

Re: Seat Sling Bolts

If you are talking bolts that hold the wood strip across the front of the seat to the airframe , mine are standard AN-3 bolts and the threads are fine. I can't see where anyone has ever removed or modified the "nuts" in the past. Maybe someone has welded new nuts on yours in the past. Metric maybe, or Whitworth? People do crazy things when they have a box of nuts and bolts in hand and don't want to go get the right parts. Some past owner could have had a Triumph or MG and didn't even realize he had the wrong bag of bolts.

Hank

[wmfife]

Re: Seat Sling Bolts

Hi, Hank.

Yes that's the part- the u-channel frame the sling bar attaches to.

The same info was posted by Tom Baker on another thread so looks like I am outvoted already. Just wondering if when the designation of these bolts changed post-W.W. II is it possible they went to standard '49 UTS/ISO threads from something else? Thinking something like if your '41 still has the original bolts then yes, they would of course fit but have you tried exchanging them for a new set to see? That is the only positive proof I can see that there wasn't any change.

I know from a recent post here that the ones used on the '40 model (from the sling diagram on the '40 SB on lowering the seat) were given as AN970-3 while the equivalent ones sold by AS today are listed as AN3-14A. '40 as I understand was the last year of using separate nuts (loose, applied by hand not attached to the frame; the Bulletin specifies "elastic stop nuts") here so possibly bolts of a different length were used. Or not - all I know is when I put these in I get less than 2 turns before they jam.

Somehow I don't think 74-year-old elastic stop nuts would give that much resistance. (Or maybe I'm really getting that old...?)

Or could it just be the elastic has so hardened over the years with NO bolts in place it's now necessary to use a wrench to force these through?

[3Dreaming]

Re: Seat Sling Bolts

The only thing I have seen is AN3 bolts for both pre and post war airplanes. I don't ever recall seeing them welded in place, but rather a special nut that was crimped into the hole in the channel. I have seen when the special nut was gone and a regular nut was use in its place, but that is kind of a PIA.

[Hank Jarrett]

Re: Seat Sling Bolts

I can check next time out, but I know I had a couple of bad bolts and just went to the bin and got a replacement AN-3s. Tom is right that the nuts were not actually welded in, but trapped by some kind of crimp. Same on the 45 and 41.

Hank

[wmfife]

Re: Seat Sling Bolts

That means they can be removed. We shall see. New nuts and bolts are on the way.

One thing I did discover after taking impressions of the threads using a highly-guarded top secret technique (known only to kids who like tootsie-roll pops and makers of bird toys) and compared them using a jeweler's loupe was that they are not all the same. The ones on the passenger side appear to be consistent with the AN bolts while at least one on the pilot's side (the ones I tried first) are noticeably larger. The threads don't line up with the ones on the bolt.

So Hank maybe your Triumph theory is the best one. Because if the elastic material was causing the problem the paper sucker stick would not have turned all the way through and come out the other side - yet they did for all four.

So looks good now for locating the replaced nuts, un-crimping the channel and removing them. Man. And I could have done all this long ago instead of wasting precious $$ on dies. Live and learn as usual.
Stay tuned. In a few days we should know how this turns out. Thanks to all for the insight.

[astjp2]

Re: Seat Sling Bolts

You could put in 10/32 steel marson rivnuts as a substitution of hardware which is a minor alteration and only needs a log book entry. Takes about 10 seconds to install one if you are really taking your time. Tim

[wmfife]

Re: Seat Sling Bolts

...Just a quick comment regarding Aircraft Spruce- parts were ordered at beginning of day Monday and arrived on Wed. If you ask me that's pretty good turnaround time.

On my way to the airport to install them. Thanks to all for the timely input.