So way back when, I laid out and pilot drilled the bracket that hangs under the panel where the engine control cables mount. This morning I botched that part; Because it's not a vernier, the throttle cable housing is smaller and it goes in a 1/2" hole while the mixture and prop need 3/4" holes.

I discovered this prior to drilling, but when I drilled, I stupidly drilled them backward so that teh throttle hole was on the far right.

Since I was going to have to redo this anyway, I strategized about possibly moving the oil cooler butterfly cabe to a different location so the sub panel isn't so crowded I had in mind to recess it under the panel just left of the sub panel and I messed around with this for, no joke, 3 hours. Ultimately, I decided that I wasn't comfortable with something like that tucked away where I might not notice it and made a duplicate out of some scrap.

The prop knob is dead center with throttle and mixture spaced 2 - 7/16". The little knobs for alt air and oil cooler are outboard as much as I could get them and up from the big knobs about 3/8".

Once that was sorted out, I laid out and drilled the firewall holes for the 3 big cables to pass through. Last week I had determined that the solution I've seen others use where the cables go through the angled part of the firewall recess seemed like would work for me as well.

Over the last few days I had reviewed a lot of build logs as well as some phone start Darwin Barrie and Stephan Christopher were kind enough to send me. I also got an idea of how I'll be running oil cooler and sensor lines and don't see any catastrophic conflicts so I had made the decision to do the same thing.

But first, in all that research, I came across the Vans print re oil lines and engine plumbing. That lead to the discovery that per print, there are 3 additional nutplates on the firewall that I had missed prior to hanging the engine. The two upper ones are easy get to any time prior to installing the upper skin, but the lower one is a real bear with the engine in the way. It's for an adel clamp that holds the breather tube so it's not like it's going to be on and off a bunch. Based on that, I skipped the nutplate and am just going with a screw and lock nut. The back side of it is behind the rudder pedals, so it will take 2 people to remove it again, but I can't imagine I'm ever going to run into a situation where that will be a problem in this case.

With that dealt with, I set in to drill the holes for the firewall ball grommets. I went with the aluminum ones from Spruce simply because I knew I was going to have limited access and I didn't want to have to deal with cover plates and pop rivets and whatnot with the steel ones. Yes, I know that aluminum melts faster than steel in a fire, but these are quite beefy and I'll pack the back side with fire seal so i the event of an engine fire, by the time these burn through I'm pretty sure the cowling wold also be gone and they will be the least of my worries.

The holes are on a vertical line 1" from the right side of the recess, and spaced about 1-5/8" on center. This is pretty tight spacing, but the firewall is stainless steel so it's pretty tough stuff and there's nothing structural about that recess so I'm okay with it. If it turns out that it needs stiffening up I can add a doubler on the aft side later.

Cutting those holes was a huge hassle. First, I had to pull remote comm 2 to get access to drill these from the back side. I have a good quality uni-bit that goes up to an inch, but these holes need to be about 1.08 or so. I screwed around with files and so forth for a while before I remembered I had a metric uni-bit left over from when I put a roof rack on my jeep so I dug it out and took some measurements. Turns out 28mm is just about perfect for these. Problem solved.

But on to the next issue! You can order the ball grommets with different size holes for the cables. I had measured the cables at .268" so I ordered grommets size .260" on the theory that .270" would be to loose and wouldn't offer any kind of clamping action. The instructions that come with the grommets say that they should be .002 - .005 smaller that the cable, and I was concerned that this would squeeze hard enough to deform the cable. Drat.

Fortunately, the math works out for a 17/64" drill bit to yield the right size hole and I happened to have one on hand. I clamped everything in my drill press vise and reamed the holes out on two of the balls. Why only two? Because for whatever reason, the prop cable I ordered from Vans doesn't have rubber sheathing? So the cable for that one is only .25" Bother. I think that I can make this work though by just adding a single layer wrap of silicone tape around the cable where the ball clamps down. As I said previously, I'm going to fill these with Red RTV from the back side so it will be plenty fire proof.

All that monkey motion took all day without much to show for it, but I'm glad it's done.

WARNING!!! this is a note from the future. with the firewall penetrations per this entry, Vans 58" prop cable was about 1/2" to short by the time it got the governor. I ended up relocating the firewall passthrough for that cable to a point above the recess. Check out the entry from 4-22-23 for details