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Thread: AD 57-22-01 for fire hazard periodic inspection

  1. #1
    Todd's Avatar
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    Default Firewall-to-boot cowl fasteners

    I am about to fasten my new boot cowls to my new SS firewall (1959 PA-22/20), and am doing a bit of head scratching. The original / existing fasteners in my old firewall assembly were 4-40 countersunk machine screws. Another old Pacer nearby has 6-32 truss head machine screws. The truss heads sort of get absorbed into the cowl chafe seal. Looking at these 50 year old examples that have been re-worked countless times makes it hard to determine the original, or best method.

    Any advice?

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    Administrator Steve Pierce's Avatar
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    Most that I have seen are 4-40 countersunk screws and small Tinnerman nuts. I have seen them riveted.

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    Todd's Avatar
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    Quote Originally Posted by Steve Pierce View Post
    Most that I have seen are 4-40 countersunk screws and small Tinnerman nuts. I have seen them riveted.
    Glad to know mine uses the same size fasteners as the original. Rivets are tempting, but I'd hate to have to drill them out someday.

    Are the parts put together dry or is it wise to use a sealant between the parts?

    Thanks!

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    Administrator Steve Pierce's Avatar
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    Do you have the kit that overlaps the seam and does away with the firewall inspection AD. If you don't have to inspect I seal with PRC.

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    I've seen it referred to as Piper kit P/N 754237, and sold by Univair, but I'm not sure what it looks like. I'm using a new Cub Doctor s.s. firewall, not sure if it needs that kit or not. Thanks for bringing it to my attention.
    Last edited by Todd; 07-05-2010 at 09:12 PM.

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    Administrator Steve Pierce's Avatar
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    It is a "U" channel that goes over the lip of the firewall and boot cowl to eliminate oil etc. from getting through.

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    After Piper made this a change and began installing them on airplanes they were building, they used the 4-40 machine thread and the "speed nuts" when they did it. There was a Service Letter (No. 177) issued stressing compliance with a sealing the firewall inspection dated Aug 10, 1951. Subsequently, there was another issued September 2,1952 pointing out that oil was migrating between the firewall "lip" and the boot cowl and soaking the insulation there, getting in where they overlap (S.L. 194). Apparently, not everybody in the Field was getting the idea...

    Eventually, AD 57-22-01 was issued requiring the inspection, and it offered as terminating action (for the PA-22 Models) the installation of Piper Kit 754237 OR ITS EQUIVALENT. I have never found this kit available by this Piper p/n from Univair (although there may have been enough "interest" that over the years Univair just starting selling the individual "piece/parts" (which they DO have a PMA for) when people called wanting that "kit".

    The kit consisted of a left-hand and right hand "side/lower" moulding and an across-the-top top moulding. As a "kit", it had the 4-40 CS screws, the Tinnermans and a one page "instructions for installation" sheet as a matter of convenience for the installer. That's it. I used to buy these kits from what used to be the only Piper Dealer in New York (and that was many years ago that they closed) and they were dirt cheap. Not to worry...Univair sells the pieces (one each U14972-000, U14972-001 and U14973-000 respectively) although dirt has seemed to have gotten more expensive over the last five decades! Everybody that sells AN hardware sells the screws and nutplates (including Univair, of course!). These piece/parts may also be found listed in the Piper PA-22 Parts Catalog (of which, Piper sells a reprint of [presumably] the last revision as their p/n 22PM). As we all know... Dealers for The New Piper don't have a lot of these p/ns in stock.

    Note that the PA-22s are the only model that this "kit" terminates the 100hr inspection for. These "mouldings" would not fit directly on the PA-20s anyway (...and PA-22s that are "altered" by conventional gear are NOT PA-20s and remain PA-22s, as you no doubt recall). A PA-20 with the [reworked] "mouldings" installed would require an AMOC to terminate the inspection requirements. The fact that "Field Installations" on various and sundry "old airplanes" might be found to have "oversized hardware" shouldn't be overly confusing or perplexing. The original kits that were available -and those later PA-22s that had the mouldings installed from the Factory- had the 4-40 screws and nutplates, and anytime aluminum, and/or steel, and/or terneplate are sandwiched together for eons, you may find "oversized fasterers" that were at some point "replaced". AS always, on a restoration, you should always "start with the smallest screws that are acceptable" when lacing stuff together with screws.

    4-40, it is. *grin*
    Last edited by JohnW; 07-06-2010 at 09:08 AM.

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    Thanks for the Univar numbers John. I am also closeing the boot and this will help.

    Terry

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    I hear that there was a Clipper at the SWPC convention that had the top piece from the PA22 on the bottom of the boot cowl and it worked. You would have to do like JohnW said to get "Terminating Action" from the FAA.

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    Thanks for the details John. I bet a lot of these haven't been re-installed during re-builds, at least mine and the other PA-22 I looked at didn't have any trace of them. I called Univair and got a set on their way. Gee, just when I thought I was done spending money on this project....!

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