Eyeball firewall carrythrough

[Flying Scotsman]

Got the "eyeball" firewall passthroughs for the control cables, from Van's. They're okay, but I recall that a friend had some that were solid, while these have hollow "balls".

Anyone have a source for the solid ones (assuming I remembered this correctly)?

TIA!

Steve

[marchudson]

Steve

Are these what you are looking for?
http://www.aircraftspruce.com/catalo.../eyeballfw.php

[DanH]

The all-steel ball swivel is fine. Aluminum firewall fittings melt.

There is a fast, cheap, and reliable alternative:



Each takes about 15 minutes to fabricate. The base plate is 2"x2" and the straight tube is 1-1/2" long. Material thickness is in the 0.030" to 0.040" range. TIG or gas weld. Pick tube diameter as desired. You can "point" the tube or use elbows if you wish, or (not shown) gang them as multiple tubes on one base plate (throttle, mixture, prop). Stainless rivets fasten the base to the firewall. After inserting your cable, wire bundle, or whatever, pump the tube full of an intumescent caulk like 3M FireBarrier 2000.

The tube pass-through concept has been around for years. The intumescent caulk comes directly from the construction industry. It is used in exactly this manner to fire seal where pipe and wire is passed through slabs and walls. When heated it swells and thus seals even if the wire or cable burns away. For our purpose it is completely vapor tight.

[RWoodard]

I used a bunch of the ball pass-throughs on my Midget Mustang. The steel balls were hollowed out behind the ball and the aluminum version was solid. As I understand it, steel is preferred for firewall penetrations so I used the steel as much as possible.

The benefit to the aluminum version is that you can drill it out (within reason) to the size you need.

The picture of the steel version shown in ACS makes it look like the hollowed version will look different when installed in your firewall. In reality, they're showing the backside of the fixture.



The only difference in appearance is that the aluminum version is more silver in color without the gold tint of the steel version. Even here, the difference isn't quite as stark as the ACS photos might suggest. Here's a shot of the aluminum version.



This version only requires a single hole, but is all aluminum so it probably won't provide the same level of fire protection. it's definitely easiest to work with.



Here's a shot of a bunch of pass-throughs on my Midget Mustang. The lower 3 are steel and the top one is aluminum.



Financially, all these buggers are a little pricey. This was one of those shocker items that I purchased towards the end of my project after I thought i was through spending bigger chunks of money. I think I ended up with 8 pass-throughs.

All FWIW because I'm certainly no expert on much of anything!

[Flying Scotsman]

Thanks, guys, for all the info. I just couldn't tell from the pics on ACS that it was the Al ones that are solid (should have guessed that, I suppose).

Yeah, I'm a bit surprised by the price on these little doodads. Sigh.

Steve

[SmittysRV]

I'm glad this thread was started. I'm at that stage of running wires through the firewall. I've already done one set, as shown in the picture below. The instructions just call for the regular black plastic fitting inside the hole with proseal added later to seal the hole.

I really don't want to take this dude apart and redo it with and eyeball. But I am intrigued by the eyeball concept. Is the trip necessary to use the eyeballs instead?

PS: the relays aren't really crooked, the camera and the camera man are ....

[Ironflight]

Hi Smitty,

If it were me, I'd at least put stainless steel firewall shields over the grommets, along with some serious fire resistant goop. I'd have to go back and look at Van's instructions, but I think that is how they recommend you cover the plastic grommets - otherwise, you really don't have a "firewall" anymore. Eyeballs are nice, but there are less expensive pass-throughs that will give you good protection as well.

That's what I'd point out if I was doing a TC visit.

[SmittysRV]

Thanks Paul.

I think that's a good idea. Here's what I've found so far. Aircraft Spruce has these firewall shields:

http://aircraftspruce.com/catalog/ap...allshields.php

Which can be sealed with 3M Fire Barrier 2000:

http://www.aircraftspruce.com/catalo...l2000caulk.php

[DanH]

Originally Posted by SmittysRV

Aircraft Spruce has these firewall shields.....
.....Which can be sealed with 3M Fire Barrier 2000...

Depends on how you seal them.

When subjected directly to flame, 3M FB 2000 behaves like this:

(1) at about 600F the intumescent calcium carbonate component causes the sealant to swell.

(2) Further exposure to flame causes the polysiloxane binder to burn away.....

(3) ....leaving only a fragile powder char.

When applied to a 2000F metal surface (dull red) not subjected to direct flame, it tends to merely peel and fall off.

So, to make it work as desired you need to (1) ensure some thickness, and (2) trap it or wedge it or otherwise give it some mechanical reason to stay in place. Merely daubing it on the exposed surface is useless (that goes for orange "high temp" silicone too). It must be under the shield in some reasonable quantity, or inside a tube, or at least tucked up in a corner. "Inside a passageway" is the engineered method. The goal is an outer char (the powder) over an intact, swelled section of sealant.

[Ironflight]

Smitty, those are the shields I was talking about, and Dan's advice is right on - use lots of the sealant, under the shield - essentially backfill the grommets and make sure that the shield "cavity" is full of stuff. you can also use pass-throughs that have a tube mounted to a plate - the tube provides some space for lots of sealant. they might look old-fashioned (they are), but they work!

Paul