Matt's RV-7 Project

The plans have you pass the engine control cables through the firewall using plastic snap bushings, but I since I wanted something a lot more chafe- and fire-resistant I decided to use metal "eyeball" swivel fittings. These come in two basic varieties – one where the halves of the ball are retained only by a twist-on locking ring, and one where there are six screws holding everything in place. I've seen instances where the no-screw variety has come apart unexpectedly, so I decided to go with the seven-hole eyeballs despite the fact that they are a little more work to install.

Also, after the big deal I made about aluminum versus steel on the firewall, I was happy to see that the seven-hole eyeballs are available in steel as well as aluminum. However, after further investigation it became obvious that the steel flavor can only be enlarged up to 0.26" because of they way they're built (look at the photo on Van's website and you'll see why). The engine control cables are more like 3/8", so the steel eyeballs are out. Oh well, maybe since the aluminum balls are solid chunks of metal, not hollow, it'll take them longer to melt…

Anyway, I received three of the seven-hole eyeballs in my latest Aircraft Spruce order, so I decided to try installing one tonight. First you use a punch to mark the hole locations using the handy template they send you. I put my shop light on the other side of the firewall to help me line up the center pilot hole.

After drilling the screw holes, I used a Greenlee knockout punch to make the 1 1/8" center hole.

Those punches are expensive (on the order of fifty bucks per size) but they make pretty nice holes that need minimal deburring.

Here's the finished product. Four of the screws hold the ball retainer ring to the firewall, and the other two screws keep the nut ring on the back in place.

Viewed from the cabin side of the firewall, you can see the nut ring. Simple as can be.

I'm pretty happy with these fittings – I think they should work just fine. It should be easy later on to adjust them without needing to find somebody to help me put a wrench on both sides of the firewall. It's like two more minutes per eyeball to install, but the payoff in terms of secure attachment and ease of adjustment seems worth it to me.

I mounted my firewall ground block on the upper part of the firewall, pretty much directly above the battery box, with enough room below it to replace the battery without hassle. You can see that the brass bolt B&C sent with the ground block kit is absurdly long. Next time I order another batch of electro-goodies I'll have to remember to ask them to throw in a shorter bolt for my firewall.

Here's the cabin side of the ground block, where you can see there are a lot more grounding tabs. I sprung for the biggest size (48 terminals) because I'm not sure how many ground points I'll need and I didn't want to run out. You can also see that I added an extra bolt (left side) to support the thing, because it seemed like it needed more attachment strength over there.

Here's a nutplate I installed that will eventually hold a clamp for the breather tube. It's right next to the heater valve I installed last night.

I drilled a pilot hole for the throttle cable, in the location specified in the plans – low and approximately in the middle of the firewall.

The mixture and prop cables come through higher up, on the left side of the airplane. The mixture cable hole was fine, but I couldn't put the hole for the prop cable in the spot spelled out in the plans because my parking brake valve is right there. In order to make it work I had to move the hole 1 3/4" to the left side of the airplane. This is probably a blessing in disguise, since apparently the stock position requires the prop control cable to have a pretty tight bend, which will be somewhat relieved by moving the hole further outboard. The only downside is that I'll probably have to use a cable with an unknown amount of extra length on it.

Looking from the inside, you can see that the prop and mixture cables will clear the parking brake on either side, whereas the plans position would have put the prop cable right underneath where I'd previously decided to put the parking brake valve. I suppose if I were smarter I would have done a better job of reading ahead when I installed the brakes, but oh well.

I drilled the bolt holes for the transducer manifold, but I can't attach it permanently until I get the subpanel ribs riveted on. That will in turn have to wait until I get a little further down the road, avionics-wise.

Not shown are a couple other locations where I drilled holes that will eventually allow various things to be bolted to the firewall. I think I'm nearly done with the firewall stuff that needs to get done before the engine arrives, with the exception of expanding the control cable holes up to full size and riveting on the firewall recess for good.