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Thread: Mounting firewall

  1. #1
    Marty57's Avatar
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    Mounting firewall

    Hi all,
    I'm getting ready to fabricate and attach the firewall to my 2+2. I have a couple questions. The engine mounting plates welded to each corner have a bushing welded to the cluster and to the plate front and back. Like many things less than clear in the plans, the busing was not shown flush to the surface. So, I welded the bushing around to the plate; leaving the bushing protruding out from the plate. I of course realized after all the welding, that the plate needs to be flat and true to the bushing to mount the firewall. I don't want to grind the bushing flush with the plate; it will basically remove all of the weld between the bushing and the plate. Suggestions on solving this problem? I can grind the bushing down some; should I then make a large washer that will fit over the bushing and sit flat against the plate? I attached a couple pictures of how it sits now.

    I also need to fabricate my firewall. I can use a PA-12 or PA-14 firewall or fabricate my own. Can I make a wood form and hammer the flange over the form to create the flange if using SS? I'm not against buying a firewall; just haven't found a good source at a reasonable price for the firewall. Thanks for your help.

    Marty

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    N367PS
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  2. #2
    skywagon8a's Avatar
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    The ss will not extrude over your mold as will aluminum. That is why the flange is generally formed in the aluminum wrap around. It would generally require a very powerful press to shape a flange in ss. Piper used a stove pipe crimping tool to form the flange in the aluminum.
    A tool like this works very well.
    N1PA

  3. #3
    Steve Pierce's Avatar
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    You can cut your own out of stainless, galvanized or titanium. You can form an aluminum flange with a shrinker to rivet to the firewall to fasten the boot cowl to. You can buy the flange from Clyde Smith for $60 last I checked. It is worth $60 of my time to buy them from Clyde.
    Steve Pierce

    Everybody is ignorant, only on different subjects.
    Will Rogers

  4. #4

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    Are you fabricating your own engine mount? Will this be a swing out mount?
    On my project I deliberately have the bushings in the fuselage extend through the firewall and the mount's bushings are machined so they fit over the extended fuselage bush.
    I have hinges on one side and extended bushings on the other. This way when the mount get swung into place it gets supported onto the bush and the fastener slides through easily. As such any side loads are not carried by the fasteners.

    The stainless sheet is simply fitted as needed against the fuselage and clamped in place by the mount. There are secondary fasteners that hold it when the mount is off.
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  5. #5
    Gordon Misch's Avatar
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    I used an Atlee Dodge boot cowl with integral s/s firewall. The firewall is fastened to the boot cowl with formed aluminum angle. It might be that Atlee's would sell the parts individually. Might be worth a call?
    Gordon

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  6. #6

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    Last edited by stewartb; 06-08-2018 at 12:26 PM.
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  7. #7
    flybynite's Avatar
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    Check with Jay at Javron about a -12 firewall. I know he has the digital file to have one cut with a waterjet or laser.

    I talked to Clyde about a flange a few years back. He usually brings some panels, cowl pieces and various items to OSH to sell in the fly mart. You might reach out to him. The flange is tough to ship by itself.

    He starts out with a 8' long aluminum angle that he bends and then shrinks/stretches it to shape.

  8. #8
    Marty57's Avatar
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    Great info here, thanks so much. The picture sequence is great. I did check with Clyde Smith but after about three months, he is still having a difficult time locating the SS for firewalls and no specific date when he will have that solved. Shipping from PA to CA is pretty high so I'm going to fabricate one my self. I have the mounting hardware for the cowl to firewall from Jay so that's here and ready to go. I think it's time to get a shrinker/stretcher, that will come in handy on other parts up front. What about bead rolling the fire wall; necessary for rigidity? May need to buy a few new tools ........ What rivets are used for the flange to firewall; steel or aluminum? Any concerns with dissimilar metal corrosion between the flange and the SS firewall?
    Thanks,
    Marty
    N367PS
    Psalm 36:7 "High and low among men find refuge in the shadow of His wing"
    www.marty2plus2.com

  9. #9
    Steve Pierce's Avatar
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    He has shipped me the flange not riveted together in two pieces. I use soft AN455-3A rivets since the flange is 3003 aluminum. Never had any dissimilar metal corrosion issues or really seen any on the original aluminum to Galveston boot cowls on Piper's.
    Steve Pierce

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    Will Rogers

  10. #10
    www.SkupTech.com mike mcs repair's Avatar
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    Atlee WILL sell just a -12 firewall, which has the flange formed into it... you may want the stainless bottom/belly piece too...

  11. #11

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    I've had good luck twice with Clyde's fire wall and flanges, I'd go that way again if need be. Note that his flange mounts opposite of the original piper angle and you'll need to cut 3/4" off the cowl mounting channels to make original cowlings fit. . I'm with Steve, he shipped me the flange, in one hoop piece without a crazy shipping fee. I also picked one of them up from him at Oshkosh already riveted
    to a very nice firewall.

    Doug
    Staying alive in an airplane has a lot more to do with mastering ourselves than mastering the aircraft.

  12. #12
    Hardtailjohn's Avatar
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    I've built about a half dozen firewalls out of stainless for Stinsons with a fluting pliers. It's easy, just takes time. I can usually crank one out in half a day.
    Grind the weld flat and flush on the fuselage...don't waste your time trying to make things to fit them.
    JH
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