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Firewall pass-thru

Sam_B

Well Known Member
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For getting cables and wire through the firewall, I like the idea of the doubletree ball pass throughs, but they?re a bit spendy. Seeing as how I own a lathe, and a milling machine, I was thinking of making something similar, since I have the stock around, and just have to take the time to cut it. I was thinking of making a tapered collet, a tapered hole for said collet to nest into, and a cap to squeeze the collet into the hole and tighten it to whatever wire/cable/plumbing needs to pass through the firewall. Slather it in the 3M fireproof adhesive before it all goes together to fill in the cracks. So my idea may be well intentioned, but not work in the real world, so I was looking for opinions here.
 
I turned a stainless flange on my lathe, riveted that on the left side of the firewall and passed all three cables thru one hole. Fill the flange with firebarrier. Simple and cheap.
 
Yes machine or fab a bushing.

+1 for Rocket Bob suggestion. Dan H helped me years ago and the little T bushings riveted and sealed with firebarrier are flawless.
 
Get the nice SS passthrough flange that comes in the RV-14 kit. Put a piece of fire sleeve inside the flange and a piece over the top of the flange on the firewall side. Wire runs in the middle of course.

Carl
 
Little T bushings?

+1 for Rocket Bob suggestion. Dan H helped me years ago and the little T bushings riveted and sealed with firebarrier are flawless.

By ?little T bushings? do you mean the ones that come with the Vans kit?
 
One thing to consider before you fill up your pass thru with fire barrier is whether or not you "might" be adding another wire or cable thru that hole in the future. If so, it will be significantly more work to pass it thru if you have it filled with fire barrier caulk. I used short pieces of 4130 steel tubing welded to a flange (similar to what fl-mike posted) I used a short piece of fire sleeve held in place with safety wire around the tubing and then another safety wire at the end of the sleeve wrapped tightly (no gaps) around the cables/wires/ I then used "rescue tape" around the wire and sleeve to prevent any gases to flow thru. In the event of a fire, the rescue tape would be worthless but the fire sleeve and safety wire should work pretty well until that particular area is not my main concern anymore.

I did use fire barrier around my heavy (#2) starter cable pass thru but knew that I would not be adding any more wires there. It is messy stuff.

Keith
 

Yes Brian, that's the stuff.

Sam, I'm guessing you can weld. If so, tubular pass-throughs are easy to make in any diameter, as they are just a tube welded into a base plate.

I've run burn tests on them. When pumped full of Firebarrier 2000, they're as fireproof as anything you can do. Here's one at 2000F, still sealed tight:

2%20Minutes%20Front.jpg


The only one I've seen from Vans was on an RV-14. FWIW, I like the tube a little longer, but that's a nit. I snapped a photo of the RV-14 install because it illustrated a caution. Note the exit angle on the heavy gauge electrical wire as it leaves the fitting, rubbing against the edge of the tube. Don't want it to be like that in service. Also, I'm not real wild about Bowden cables and electrical wires in the same fitting. Bowden cables generally connect to the engine, which moves on the mounts. Hang around this game long enough and you'll see an example of a Bowden cable acting like a saw.

Firewall%20Pass-through.jpg


Did you use the same method for control cables? Throttle, mixture, etc.

Works for everything Tim. Note that Keith's note regarding the difficulty of removing the silicone plug is valid. To remove the plug, just make a half-moon cutter from a length of tubing one size smaller than the pass-through tube, and force it through to cut the sealant perimeter. The firesleeve approach is also accepted in some certified applications, although perhaps not as fire-tough as the solid plug.

Firewall%20Penetrations.jpg
 
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How about using a "conduit bushed nipple" available at hardware stores.
A google search will show pictures.
APLTON_MP_CN-100.jpg
Joe,
I was just looking at those yesterday. I don’t know what I don’t know, yes? I couldn’t find any made of steele. Either by description or magnet. I know my magnet works as now my ATM card doesn’t. Most of the items were listed either as zinc or galvanized. Is it solid zinc, or coated in zinc. Zinc melts around 790’F. So, if solid zinc, it’s not durable enough. Then the galvanized stuff can gas off nasty stuff. So why not avoid that entirely? The zinc part was only $.99, so I may pick one up today and put it through my friends torch to see what happens.

BTW, my Cessna 150 was built with a galvanized firewall and had a sound blanket on the back side/interior of the firewall. Plastic coated with what looked like fiberglass sandwiched between the plastic. Replacement firewalls are stainless steel. But how many 150s have an engine fire? Although, I think I was close. When I added a JPI fuel flow meter... I found the great looking fire sleeved fuel hose was extremely brittle. With very little handling, it leaked 100LL all over. Glad I added a ff transducer, new fuel line and avoided a time bomb.

Edit: stupid me. If it is solid zinc or coated, it doesn’t matter. It’s the zinc which gasses off on galvanized steel which is nasty. So, I’ll avoid either. YMMV. Tim
 
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Thanks

Dan, thanks for answering my question. Thanks to all for posting experiences.

I?m rebuilding an -6A. A solid build but no Bronze Lindy. Flown, but sat in a back corner of a hangar for 15 years. I ran into the ?Layers of an onion? thing. ?While the wings are off and the tail is off and the engine is off, etc. I might as well get that fixed/changed/uncomplicated...?

The de-construction stopped in December. The new Vans -A engine mount and nose gear are on. I have a slick firewall. So this is a timely thread. Going the fiberfrax / SS foil route, as well.

Again,a big thanks to all those who?ve tested & shared knowledge on firewall forward.
 
Many of the home-depot conduit parts are zinc, so no good at all for this application. If you find them in steel, they should work well enough.

I made my own, 4130 tube welded to a base plate. The wires are wrapped with firesleeve tight enough that it is a job to get the sleeve inside the conduit. Then another firesleeve is on the outside of the conduit. a hose clamp holds it on the conduit and a stainless band clamp to the bundle.

FP24112013A0003G.jpg
 
Conduit

Non RV. I made my own same as Colin P but all stainless. Stainless machine screws and stainless all metal nuts to attach to firewall. In my opinion the long portion should be forward of the firewall and at least 1" long.
Several years ago these were available from the same source as the all stainless cabin heat boxes but I haven't seen them for a long time.
 
Thanks

Thanks everyone for their input, I appreciate it. I?ll get to work on fabricating something this weekend
 
Another quick question

Perhaps this is evidence as to how slow I work, but I originally asked the question about 3 months ago and am finally getting to this. Now that I have a better idea where the wires, cables, and hoses will go, do I need to put firesleeve inside the pass through to protect the wires from the stainless pass throughs, or will the fire barrier seal adequately protect the tefzel insulation from the stainless on the ID of the pass through and limit wire to pass thru relative movement (and thus, abrasion of the insulation). Just wondering how big to bore the inside diameter, assuming smallest hole to accommodate the hardware going through it is best.

Comments from the brain trust?

Thanks
 
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