Firewall Forward

October 20, 2012

Electrical Parts on the Firewall - 8.0 Hours

Now that the battery box is finished, I've been studying and working on more items that go on the firewall. The plans and documents from Vans lay this out for you quite nicely. So next, I'm installing a Master Solenoid Relay, and the Starter Relay, and planning for some other items as well.

The Relays go to the right side of the firewall centerline, just below the battery box. I can see that it's a convenient place for these items, located near the battery. This will keep wiring runs to a minimum. Once again, you locate a couple of existing rivets that need to be drilled out and enlarged to #12 for bolts and nutplates. You start by fabricating a doubler that goes inside the firewall. Once all the drilling, dimpling or countersinking, priming, painting, and riveting is done, here's the Starter Relay Solenoid, loosely bolted in place. The two red arrows to the upper left show where the Master Relay will go. As the plans indicated, the flange on the Master Relay was overlapping the Starter Relay's flange, and I had to grind a little bit of the corner away. The red arrow to the right shows where the fuel line comes out of the firewall, leading from the fuel pump inside the cabin. I removed the AN fitting I had here, since I ordered a replacement fitting made of steel instead of aluminum. The hole way over to the right, just under the firewall recess opening, is where a 2" hole will be made for the cabin heater valve box. I have ordered a Stainless Steel unit, since the only one Vans offers is made of aluminum.

Another consideration that I seldom see mentioned is the riveting along the bottom of the firewall. Once the motor mount is bolted on, these rivets will be very hard to reach for squeezing or bucking, because the motor mount tubing is in the way. So it's best to do it now. If you look at the bottom cowl, it opens away from the firewall in the middle for room for the exhaust pipes to exit. As seen below, between the red arrows, these middle rivets do not hold any hinges or anything related to the cowling. So you can go ahead and squeeze them in place now. I could have done this months ago, had I realized this. There are six rivets on each side of center that you can put in now. The center hole was enlarged way back when building the fuselage. I can't remember why, at this point, but there must be a reason. It was in the plans. I'm sure it will come to light shortly. Along this same line of reasoning, I will also be fabricating the hinge pieces that go in on the right and left of these rivets, for the cowling. I'll be cutting, drilling, countersinking, and riveting them in as well, before putting the motor mount back on.

But back to the relays. Here is the Master Relay installed, after trimming a bit of the ear of the flange off. The two relays are connected by this solid copper bar that you get from Vans. It's much better than trying to fabricate and run a piece of wire between the two. It's actually 2 pieces of the copper bar, stacked together. I trimmed them and deburred them carefully, drilled the holes to match, and then put some heat shrink tubing over most of the bar to minimize the exposure of bare electricals. It looks nicer, too! I have to warn you, wear leather gloves when deburring copper. It gets very HOT very fast!

Here's the doubler for the relays, on the inside of the firewall:

And finally, once the relays are in place, you can go ahead and install the battery box. Nice!

The bolts are only in part way for now, since they will have to come off when the firewall recess gets riveted in place. Which, incidentally, I've been wondering about. When's the best time to do that? It's not clear, at least not in my mind or anything I've read. If I don't learn any big reasons why not to, I'll probably do it after I get the rest of these items mounted on the firewall.

To the upper left, you can see the reservoir for the brake fluid. I installed this quite a long time ago.

It looks great to see these items in place! My heater box should be showing up, so it's next on my list.

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