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Firewall penetrations

nohoflyer

nohoflyer

Well Known Member
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I’m building a 7A with an IO-360-M1B. Anyone have a good builders log with firewall penetrations. I keep reading that there are “best practices” to minimize problems. I’d love to see some pics. All I have are a few sites but everyone’s airplane is a little different.

So far this is mine but I’m not too far and can still make adjustments….
 

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nohoflyer said:
I’m building a 7A with an IO-360-M1B. Anyone have a good builders log with firewall penetrations. I keep reading that there are “best practices” to minimize problems. I’d love to see some pics. All I have are a few sites but everyone’s airplane is a little different.

So far this is mine but I’m not too far and can still make adjustments….
Click to expand...

I think this is the classic DanH stuff. Start around post #38.
 
nohoflyer said:
I’m building a 7A with an IO-360-M1B. Anyone have a good builders log with firewall penetrations. I keep reading that there are “best practices” to minimize problems. I’d love to see some pics. All I have are a few sites but everyone’s airplane is a little different.

So far this is mine but I’m not too far and can still make adjustments….
Click to expand...
I used Dan H's stainless overlay with the intumescent material underneath and also purchased from Dan the all-stainless wire pass-thru's shown on the photo. For the modern -7A the plans don't cover everything as far as firewall penetrations and item placement goes. I was trying to be cognizant of the gear tower location and size and so I moved things around a bit. I moved the contacts towards the outside for better access. I had the advantage of having my engine on-site so as to verify locations. I have to say that so far - with the engine hung - all is working out well. If you want any further pictures with the engine installed just PM me. Here is what the FW looked like with Dan's kit and as many components as I had before I installed the motor mount. Of course YMMV.....
5726E90C-5263-442E-A6C6-A4733B40BE9B_1_105_c.jpeg
 
Dan H. sells a nice stainless pass thru and can custom make whatever you need. In the past I’ve just made them. 4130 steel plate .070” thick with a 1” long 4130 steel tube 1/2” dia welded in. I mount the flange on the cabin side of the firewall with Stainless hardware and let the tube protrude forward. Firebarrier 2000 seals the plate to the firewall. Short lengths of firesleeve get the ends sealed. You can buy a dip, but I thin some red RTV with mek and use that. Firesleeve gets clamped to the tube, pumped full of Firebarrier 2000 then clamped to the control cable. For small wires and push/pull control cables I use bulkhead fittings, wires get heat shrink where they pass thru the fittings.

Don Broussard
RV9 Rebuild in Progress (home stretch)
57 Pacer
 

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And has anyone used pop-rivets on the firewall port-cover? You know the concave piece you fit in the middle at the end.
 
nohoflyer said:
And has anyone used pop-rivets on the firewall port-cover? You know the concave piece you fit in the middle at the end.
Click to expand...
Plans call for solid rivets there so that woud be the way to go, there aren't too many and a second person could help with bucking.
 
nohoflyer said:
I’m building a 7A with an IO-360-M1B. Anyone have a good builders log with firewall penetrations. I keep reading that there are “best practices” to minimize problems. I’d love to see some pics. All I have are a few sites but everyone’s airplane is a little different.

So far this is mine but I’m not too far and can still make adjustments….
Click to expand...
I'm getting ready to cut mine soon( same set up as yours). I'm using the Avery penetration kits and currently plan to position them near the upper engine mount area, taking care not to interfere with firewall support angles, etc. Then, wire routings in the enge compartment can generally follow the engine mount to the firewall. I'm hoping I can get all wires through two penetrations. We'll see. I Just ordered a 1-1/8" greenlee knockout punch. These punches make holes in stainless much easier than anything else I've tried.
 
PaulvS said:
Plans call for solid rivets there so that woud be the way to go, there aren't too many and a second person could help with bucking.
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Honestly if someone doesn’t have experience with bucking steel rivets, I’d strongly consider using some #6 stainless hardware instead. There is a much smaller chance of damaging the underlying material than bucking Monel or similar. Just a thought for the OP’s consideration.
 
nohoflyer said:
How to best layout for an M1B and 7A combo
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You're worrying too much. Hang the engine and do the rest later.

Do not use proseal in the lap seams around the center recess

I do have fireproof tubular penetrations, but they are mild steel, not stainless. Just paint them before installation.
 
Yea well with lack of instructions and a bunch of different techniques I worry. Plus I’d like to close up the center recess after most of the penetrations since finishing the holes is so easy with that thing in the O-F-F position.
 
There are variants of “Stainless Steel Cable Glands” out there that appear to have some tolerance to higher temps. Anyone have thoughts on using them here?
 
Tall_Order said:
There are variants of “Stainless Steel Cable Glands” out there that appear to have some tolerance to higher temps. Anyone have thoughts on using them here?
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Cable glands typically have rubber bushings that squish down to form the strain relief . I wouldn’t think you would want that? Maybe Dan has tested some.
 
nohoflyer said:
Yea well with lack of instructions and a bunch of different techniques I worry. Plus I’d like to close up the center recess after most of the penetrations since finishing the holes is so easy with that thing in the O-F-F position.
Click to expand...

Tubular penetration fittings with base plates are fastened from the front.

If ugly holes are a problem consider purchasing a RotaCut set. For the larger holes, use something like a Greenlee punch.

JonJay said:
Cable glands typically have rubber bushings that squish down to form the strain relief . I wouldn’t think you would want that? Maybe Dan has tested some.
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If you can get them with silicone insets they would probably be ok. The inserts would need to be sized correctly so they would tighten on the cable or wire...and a 1/4 " OD bare control cable has a threaded end just under 1/2" D.
 
nohoflyer said:
How to best layout for an M1B and 7A combo
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I have a M1B, 7A, Elastomeric.
There were a few things I would do differently. Most of the plan penetrations were pretty close. Here's a few that filled the cuss jar.
-Fuel line is crazy close to the output side of the starter relay. Yes, it's only hot during start, but all it takes is one zap. I would relocate the relays a little starboard with a doubler.
-Battery box. OMG! Cut the front off. Install two hinges to hold it on but add a 1/4" of depth. Much easier to R&R the battery and the extra depth comes in handy if a battery is slightly different or swells. I use a section of baffle to take up space and protect the firewall from a short. It's a "T" shaped piece that lives between the battery and firewall. No way for a wire to touch. Also, add nutplates to the firewall. Crazy to have that box, or anything else, mounted with bolts and nuts. Unless you like crawling around under the panel.
-Throttle cable hole could move a little starboard. It goes through the lower corner of the recess.
-Prop governor cable was a bear. Sort of my fault though. I have the RV10 oil cooler with a 4" scat plenum. It hogs up a lot of real estate. Cables had to route around the parts. I wouldn't trade it though. I can manage oil temp easy from stone cold to 200 just by adjusting the butterfly control.
Pressure transducer manifold is fine but works better with a 1/8" shim. Kavlico sensors clear mounted from the side. More clearance in front.
-Dan's insulation works. I used 1/8" Fiberfrax and 0.005" Titanium foil. A few wide stainless pop rivets hold open areas. Cut away so the engine mount is flush to the firewall.
-DoubleTee eyeball pass thrus are great. Expensive but hold cables any orientation.
-Bowden cables, I used the steel AN fitting trick. Heat, Alt Air, Oil Cooler
Probably others. Shoot me a PM if you need more.
 
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