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Uncooperative Firewall Recess

BoilermakerRV

Well Known Member
I'm trying to assemble my firewall for match drilling. I'm having a heck of a time getting the pre-punched holes in the F-601K-1 recess to line up with the pre-punched holes on the F-601A-1 firewall. It seems that the upper most, 1/8" holes on the side flanges aren't far enough apart. However, this distance is set by the factory and I'm unsure how to get everything fitting well together.

Picture1.jpg


I thought about cutting a slot in the upper corners to increase the flexibility of the part enough to line everything up. Anyone else dealt with this issue?

Thanks!
 
I just removed my flat piece and installed a recess piece I got from Van's as part of the engine conversion on my 7A. On mine the thing clecoed up with only a little fussing around. I just riveted it in place yesterday without any issues, other than those holes in the corners that need to be sealed up.

I did use some Fireblock Sealant between the recess and the firewall to help keep the fumes etc. out of the cabin.

You might experiment with some sort of pressure on the insides of the recess to see if you can get the movement you need with out too much distortion of the part. Careful use of a small hydraulic jack comes to mind...
 
The following is from my log entry on this subject:

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Today I finished fitting and drilling the firewall recess to the firewall. I had to do quite a bit of "massaging" of the recess with a hammer and blocks to get it to fit the firewall.

I have a sheet from Van's separate from the plans and instruction manual stating that the recess can either be riveted to the front of the firewall, or on the rear between the firewall and stiffener angles. I'd like to do the latter, to provide a smoother surface on the forward side. The instruction manual suggests not installing the recess until later to provide access for installing the rudder pedal brace, but I don't see how to get the recess between the stiffeners and firewall after the stiffeners are installed. I'll have to do some research to figure this out.

While I had the firewall parts on the bench, I went ahead and deburred all the holes, and deburred the edges of the firewall and recess. Deburring the stainless steel is much slower and tedious than aluminum!.


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IIRC, the "massaging" I had to do involved moving the bend radius a bit to get the rivet holes to line up. If you look at the picture closely you can see a little bulge on the left side where the raised part transitions to the angle, but it isn't bad. My log indicates it took me 4 hours to get this thing to fit...

FP07042013A0004S.jpg
 
Firewall Forward Plans

You may want to check the firewall forward plans, particularly the battery box and oil line plans, as several of the rivet holes become bolt and screw holes. And I wouldn't rivet on that recess untill almost all of your other firewall penetrations are done.
 
Miles and John are right on.

You can "fit" it, using the BMF hammer and blocks but don't rivet until the last possible minute. That hole is gold while putting in cockpit and firewall penetrating systems.

And yes the tailcone needed very similar persuasion. :)
 
From the picture it looks like the recess is backwards.the flange on the firewall faces forward and the recess is indented into the cockpit. It gives the oil filter room. Flip the part 180 and install it on the opposite side and it will probably fit better.
 
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Same thing.

I am not installing it any time soon, but I just don't see a way to force these holes without cutting a slot in the flange so it is more flexible.

Will see once I get there, but one option I am thinking about is to put these two rivets under the flange (so they will attach firewall to the stiffeners, but not to the recess). This part is not structural, and it has enough rivets that it is not going to go anywhere. Also, it is very rigid in these areas, too, so I don't think it will flex much without these two.
 

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No slot

I would not cut a slot anywhere on this part. This is sealed to prevent gasses from leaking in. Normally, the sealant is between the flanges and does not span a gap. If you cut a slot, now the sealant has to span that gap; not good.

I would make sure it is being installed on the correct side of the firewall, and then enlarge a hole/ re-drill a rivet hole to make it fit; there are enough rivets to make it more than adequate if one or two holes are not completely right. JMHO
 
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