FWF wiring org, part 3

Yeah, I’m getting behind on build log posts yet again. Haven’t had any real extended work sessions, but I’ve been chipping away.

Last week, after getting my new crimpers, I got the connector done for the MAP sensor – which gave me the opportunity to fire up the panel and see an actual functioning engine readout. It’s not much, but it’s something!

Beyond that, I’ve been a little hung up on some parts on order, and I kept forgetting to place those orders, which didn’t help. But now  I have some terminals coming from Stein, plus an order with Van’s for the standoff pieces I’ll use for routing wiring near the sump. Not sure how long it might be before I get the Van’s order, though – I’ve heard they’re running behind on shipments, and they had messaging on their site to that effect as well.

I did get the CHT sensors installed; these are pretty easy. There are threaded holes in the cylinders to accept fittings, to which the actual sensors mount bayonet-style. I had to go in and clean up these holes, thanks to mud dauber activity…which in turn required removing the exhaust, as well as the #2 intake tube.

Then there was the matter of the EGT sensors. To mount these, I need to drill a hole in each exhaust pipe. Which means I have to decide where to drill that hole. After a fair bit of research, I ended up going with a position about 2” from the exhaust flange. Then I had to ensure that the probes – which project out a few inches – wouldn’t interfere with the spark plugs or the lower cowl. So I got to hang the cowl again briefly just to check clearances, which turned out to be fine.

So finally after a lot of thinking I took the drill to my expensive exhaust. In the end it was undramatic, but it’s always fun going with these sort-of irreversible actions. So now I have the EGT sensors mounted all around:

Finally, I did some other prep work for that upcoming sump routing. I decided it would be a good idea to put the prop governor oil line back in place, since it’s a potential conflict for the wires I’ll be running. When I removed that before, it was a real pain to snake it out around everything. I was smarter this time, and just went ahead and removed the exhaust and intake pipes on that side of the engine, which made things go a lot better. I’ll have to remove the line again at some point when I’m finalizing the baffles, but such is life.

Now I’ve just got to figure out what I can work on while waiting for those standoffs to come in. I suppose one thing to be thinking about is the lower spark plug wires – those will have relatively long runs from the mag pad on the back of the engine. Plus there are some other terminations I can still work on in the meantime.

Posted in Electrical, Firewall Forward | Hours Logged: 3

FWF wiring org, part 2

So as I’d hoped, I was able to start getting into some of the satisfying wiring stuff – routing wires to their final locations, trimming and terminating them, and lacing up bundles. It wasn’t all fun and games, though – as seems to be inevitable at this point, I had instances where I needed materials, or discovered a misstep from earlier. Nothing awful, just minor annoyances.

The first question was a classic one: where to start. It seemed to make sense to work from the firewall out, picking off branches as I got to them and working on the branches. Accordingly, the first thing I came to were the wires for the battery bus and contactors. On Tuesday I was able to get the four battery bus circuits taken care of, along with the switched ground wire to the E-bus relay. That was when I hit a misstep – I need a +12V source for the other side of the relay coil. Looking at my schematics, my intent was just to jump a small wire from the hot relay input. It’s an easy enough fix – cut the terminal and crimp on a new one, with a 22AWG wire tucked in alongside the 10AWG supply – but I don’t have the right terminal to redo that relay connection. First item on the order list right there.

OK, well at least I can pull the switched wires for the contactors while I’m in the neighborhood, right? They’re close enough that they might as well just get bundled along with some of the battery bus stuff. Except…I don’t have the right ring terminals for this. The ones I have are too small for the contractor studs. Yet another item on the shopping list.

But those were easy to tuck out of the way so I could move on. Next step before starting any more lacing was to splice in the +5V and ground wires for the hall sensor – which will also get wired alongside the other battery stuff. Getting those window splices done was a little fun, since I was working really close to the firewall fitting. Once they were done, I went ahead and laced the battery bus/contactor/hall sensor branch, then started working my way down the line.

The next junction was for the manifold pressure sensor. I was hoping to go ahead and get the termination done here, but the connector for this sensor is odd. After some research I determined it was a Weather Pack connector, and while I could probably do OK crimping the pins with what I had on hand, I decided to go ahead and order a specific crimping tool. At least Amazon had that for delivery tomorrow, is it skipped right past the running shopping list.

To make a long story short, I ended up adding the +5v and ground branches for both the MAP sensor and the fuel flow (well, fuel flow only gets ground, it runs off +12V). Those are all the branches I need on the right side of the engine, so I was able to lace things all the way up to where two branches split off – one for the fuel flow sensor and top mount coil pack, and another for the main ammeter shunt.

Before I really go any further, I want to get the CHT and EGT sensors installed so I can properly handle the wiring routing for those. So I put a top to lacing for the night, but did decide to go ahead and secure what I had laced to the engine mount tubes. A couple adel clamp pairs took care of this, and as of now the harness is looking pretty nice for the first couple feet:

Tomorrow I figure I’ll see about getting the MAP termination done, and maybe get those CHT/EGT probes mounted. The only thing that might delay me here are the various crimp terminals I need to order – I doubt I’ll get those this week, so it might be next week before I can sit back and feel like the FWF wiring is largely done.

That reminds me, I also want to order some standoff pieces from Van’s for routing wires along the sides of the engine forward – like the alternator/starter cables. The shopping list grows again…

Posted in Electrical, Firewall Forward | Hours Logged: 3.5

Organizing FWF wiring stuff

So, the first order of business after the last work session was to fix that battery bus feed cable. It occurred to me that I didn’t need to completely re-make the cable; there was enough slack that just clipping off one terminal and crimping on a new one was perfectly fine. I did check for the proper orientation of the sensor about 47 times before I crimped on the new terminal, though.

That also led me to think about connectors; my intent has been to put in a three-pin Deutsch connector for the hall sensor, but if I do that I think I want to mount the connector to an engine mount tube, instead of having it hang around in midair. So I ended up ordering some little pads for that purpose, which should be here tomorrow.

From there, it was on to the sort of vague task of how to best organize the wiring runs, and how to actually work things into nice bundles. I decided a good way to make practical progress here was to start picking off the various wire groups, running them to somewhere near their sensor, and let that sort of flesh out the layout. To do that properly, I decided it was time to cut the hole in the right rear baffle where the coil pack and fuel flow sensor wires will go through.

After some thought, I decided the best way to do this was to drill two adjacent 3/4” holes and then open that up to a nice oval shape. That cutout is large enough to allow the coil pack plug to pass through, but will still be covered up by the grommet I bought. Then I laid out the screw holes for the grommet, drilled them, and installed nutplates. I got a picture of the hole itself, but I don’t have the right screws to actually install the grommet…plus that would have been purely for the photo op.

Next, I needed to figure out where to mount the manifold pressure sensor, along with the vacuum block that came with the CPI2 ignition. I ended up mounting those sort of back-to-back, since they’re connected together with a vacuum hose. I didn’t get a good photo of this, but if you look carefully in the following photo, you might see the gold-anodized vacuum block hiding back there.

With those items mounted, I could finally pull wires around. That still didn’t give me a great look at what the routing would look like, so I decided to use some temporary zip-ties to better mock up the harness run, along with where stuff would branch off. The result still doesn’t look super organized, but hey – it’s still a work in progress:

Of course, about the time I was taking this photo, I realized I forgot to include the CHT and EGT sensor wires in the bundles. Those should be fairly straightforward, though.

You might also notice the two stray wires at the bottom of the photo. These are the 5V and ground for the various sensors; they’ll need to serve three and four sensors, respectively, so I’ve got some window-splicing work to do. The general idea will be to pull them along the temporary bundles I have in place, figure out where to put the splices, and then I should be in a pretty good place to maybe start lacing some things up here and doing some terminations.

Electrical stuff is fun. Really.

Posted in Electrical, Firewall Forward | Hours Logged: 4

Power distribution panel

Well, that was quite a productive day…seems like as of late, even when I work on stuff on the weekends, I can only squeeze out a few hours. Today I managed to get in basically a full day’s work, and ended up with a nice payoff.

I’ve been sort of wracking my brain over today’s assembly for some time. I knew I needed to mount a few fuse holders, plus the E-bus relay, on the firewall, and I was pretty sure I wanted to mount these items to a panel, and then mount the panel to the firewall, rather than just direct-mounting everything. The main reason for this is to have only four new holes in the firewall instead of ten. A side benefit is that if stuff needs to be modified down the road, it’ll be possible to modify or replace the panel, instead of turning the firewall inset Swiss cheese.

About a week ago I made a cardboard mockup just to test the layout of everything, and ensure that it’d all fit where I wanted it. Today I actually got to work on building the panel. It’s fairly straightforward – just a rectangular piece of sheet, to which I added 1/4” flanged top and bottom for some stiffness. It mounts to the firewall at the four corners; the top two screws go through one off the angles, while the bottom two are just through the stainless.

Actually building this was more involved – I worked out an order of operations for things to go relatively smoothly, cutting the panel piece, laying out the flange bends, then the attach screw holes, then transferring those holes to the firewall. That part required some creativity, because things were tight in a few places thanks to the engine mount tubes.

I didn’t bend the flanges until I’d laid out the attach holes for all the components, and drilled the rivet holes for the nutplates. Only then did I bend the flanges in my little sheetmetal brake, followed by riveting a bunch of nutplates, mounting the parts, and doing the most fun part – building out the various wires. I did what I could with the panel on the bench, before mounting it in the airplane and working on integrating it with the battery/contactors/etc.

Here’s the final product mounted on the firewall. From left to right, we have:

  • An ANL fuse holder for the main bus feed. This will protect all the circuits downstream of the battery and alternators.
  • The battery bus – just a small fuse block with a few always-hot circuits
  • The battery bus then feeds a relay, which can be activated by a switch in the cockpit. This provides a way to power essential equipment in the event of a master contractor failure
  • Another ANL fuse holder for the alternate feed

Obviously we’re still missing some things here, like the alternator feeds, and the cables from the fuse holders feeding across to the firewall penetration and into the cabin. This long runs will come later.

Here’s a slightly wider shot, showing how the panel sits above the contactors:

Finally, a closer look at the contactors, where I also fabricate a few of these cable/wire runs today. Visible here is the cable from the battery to the master contactor, a smaller tap from the hot side of the contractor to the battery bus, the big jumper from the master to starter contractor, and the tap from the hot side of the starter contractor up to the power distribution panel:

Of course, as I type this, I realize I made at least one mistake. I have a Hall sensor that I want run the battery bus tap through, so I can see how much current it’s drawing at any time. This will work in concert with a shunt on the main bus feed; the two together will give me a full picture of current flow.

Problem is…those terminals on the battery bus feed are too big go go through the Hall sensor. I needed to feed that cable through the sensor before terminating both ends. So I guess I’ll be prefabricating that cable at some point. Maybe tomorrow, assuming I have enough of the big terminals…

Posted in Electrical, Firewall Forward | Hours Logged: 9

Control cable mockup

So today had a bit of an absurd theme going on. My intent going in was to install the engine control cables temporarily so I could have then in place around the engine as I worked through routing the assorted wires and stuff. What I wanted to do was to actually rig the cables to the throttle quadrant, with the hopes that I might not have to remove it later on. For various reasons, that didn’t happen.

Farce #1 came after I retrieved the throttle quadrant and cleaned it off. The next thing I needed was the cable anchor bracket, which, well, anchors the ends of the cables. I spent a full hour looking for that thing, doing the circuit around the shop (shelves? nope. big work table? nope other tables? nope. in the fuselage? nope) and gradually moving more and more stuff around, until…I found it sitting IN PLAIN SIGHT in the fuselage.

sigh

Well, at least I found it…I was getting to the point of considering just fabricating a new one, glad I didn’t have to do that. This, however, led directly into farce #2. The control cables attach to the quadrant levers with clevises and pins. I just had to find those clevises, because surely they came with the kit, right? Well, I dug through all the hardware bags I had and found nothing like that. Then I did my usual next step when I’m looking for hardware – I pulled out the kit pick lists and went through those. Sometimes this helps me know the bag number and maybe figure out where that bag might be stashed.

Well, long story short, I didn’t find any of the proper clevises in any of the pick lists. Apparently they’re not included with the kit after all, and I need to figure out the right parts and make yet another Aircraft Spruce order.

sigh again

I almost gave up on the whole thing right there, but after sitting (and yes, stewing) a bit, I realized that I was overly focused on rigging the cables to the levers. While it’d be nice to get that done, it wasn’t necessary. Just having them mounted to the cable anchor would be enough to see what the routing would look like. Any adjustments at the anchor to fit up with the levers wouldn’t make any real difference in the routing.

So I went ahead and installed the cables that way, knowing the entire time that I’d definitely be removing them again. That’s OK, it’s not like there’s anything else on the plane that hasn’t been installed repeatedly…

So here we are with the cable routing. Center cable is for the prop governor, and routes over to behind the engine. The other two are throttle and mixture, and they go under the sump to the injector servo. The eyeball fittings ensure that everything is locked down just as it would be for the real installation:

And just for fun, we can look at the cables routing through the fuselage from the firewall to the gear tower. It’s going to be a little snug in here once the scat tubing for the cabin air vent is installed:

Not pictured here: I also went back to planning the main power distribution stuff. As part of this, I modified the cable between the master and started contactors; I’d fabricated that some time ago, but I didn’t care for the routing, especially how it would interact with the other stuff I’m planning. I’m actually still thinking of replacing that cable with a copper bus bar. That would be a much more compact option, but the potential problem is that given the way the contactors are mounted, it might make maintenance difficult. The flexible cable is much easier to install here than a rigid bus bar would be. If I do the bus bar, the end result will probably be that one of the contactors will have to be removed in order to free up the bar. Which isn’t really that bad, I suppose…if I need to remove the bar, chances are it’s because I’m replacing a contactor. Anyway, more food for thought…

Posted in Firewall Forward | Hours Logged: 3

Exhaust hangers

So I started today with the intent of getting some of the main power distribution stuff done, starting with one of the main ground cables. But I pretty quickly devolved into my usual state of overthinking; in this case it was due to the proximity of the ground cable routing and the exhaust. I was considering a different approach to the ground cable, but I kind of needed to know what the exhaust setup was going to look like, particularly the hangers that support the pipes near the firewall.

This is, in fact, something that Van’s recommends when working on the FWF area – to start by getting the exhaust in place, since it’s an object with a pretty fixed position, and the heat it radiates is important to consider.

So I changed gears to the exhaust. I’ve had the upper pipes in place for a while, but not the tailpipes. I did fit them some time ago and briefly tinker with the heat muss and hangers hardware, but nothing major. So today I remounted the tailpipes and started really thinking about how to arrange things.

The hangers are sort of a point of contention among builder. Specifically, there’s the question of whether they should be braced to the engine mount, or the engine itself. An important point here is that the engine mounts are nowhere near solid, so the engine is going to move relative to the mount, whether it’s shaking during startup/shutdown, or sagging under G-load. This all makes sense to me, so I was leaning towards bracing the tailpipes to the engine.

Thing is, it’s not quite that easy. First off, the hangers provided by Vetterman – which are two stainless tubes joined by a piece of high-temp hose to give some flex – are too short to reach the engine sump (the usual attach point). That’s not an automatic show-stopper, though getting past it would require me to acquire or fabricate longer tube pieces.

The real problem emerged when I temporarily put the heat muff in place. There’s really no flexibility as to where to put this, and since the hanger mounts must be behind it, the muff really restricts where the hangers can go. It’s just not possible to route a hanger from the tailpipe mount to the engine sump without it occupying the same space that the scat tubing to/from the muff will go.

So in the end, I tied the exhaust to the engine mount instead. Doing it this way means that the hangers go up, forward, and outboard to the mount, which keeps the right-hand one clear of the heat muff.

The real fun was getting through the spatial reasoning needed to put all this together, At first I thought I was going to have to tweak the bend on the tailpipe attach tabs, but it turned out that it was possible to rotate them to a position where everything worked. I had similar fun getting the forward end of the hangers to properly mate with the adel clamps on the engine mount tubes.

This is all just a temporary setup for now, but seeing how particular the arrangement of everything is, I’m definitely going to be making some match marks between the stainless tubes and the flex hose pieces, to ensure I can easily put this stuff back like it belongs.

Also, it’s worth noting in the picture below that the hangers will have hose clamps when assembled for real; obviously, without that these wouldn’t exactly be functional… I may also add a bit of a flare to the ends of the tube pieces just to help with security.

Posted in Uncategorized

CPI vacuum plumbing

Main thrust of the last couple of work sessions was to get that vacuum line for the CPI routed, with the general idea of wrapping up wiring-related stuff in behind the firewall. But before I got to the vacuum line, there was some more lacing to do. I’d briefly considered leaving the wiring run through the forward baggage compartment unlaced, since it’ll eventually be covered by some sort of plastic piece, but it was just too unruly for me.

Good thing I enjoy lacing so much, because it was kind of a pain in this awkward spot. Still rewarding to see things looking so tidy, though:

For the vacuum line itself, I dug out a bulkhead fitting I bought a while back for this specific purpose. After some careful consideration of the surrounding structure, I laid out the firewall hole just below the wiring fitting, drilled the hole, and installed the bulkhead fitting. I also laid out and drilled a larger hole through the forward gear tower wall, and installed a snap bushing for the vacuum line to pass through.

To route the line itself, I dug out some velcro cable ties I had lying around, and just used those to secure the vacuum line alongside the wiring harness. That should keep things tidy, but in a non-permanent way, and won’t leave any sharp zip-tie edges waiting to bite me in the future.

Finally, there was dealing with the line termination at the CPI ECU. Since I have the dual-ECU unit, I also have two vacuum ports, and so a tee fitting is needed. The fitting provided by SDS was kind of bulky, so I ended up positioning it outside the wiring harness, a couple inches away from the ECU, and routing the two stub lines above and below the harness:

In other news, I’ve been doing some thinking regarding FWF wiring routing. Way back when, I’d mocked up putting the amp shunt and main ANL fuse holder on an engine mount tube using Adel clamps. Since then, I’ve decided to add a second ANL fuse for the battery bus feed, plus I still have to mount a current sensor for that bus feed, the battery bus fuse block itself, and the E-bus alt feed relay. I haven’t fully fleshed this idea out yet, but I think I’m going to fab up a mount plate for all that stuff and mount it to the firewall with standoffs, kind of like how I did the battery box mount. Still got to think that one through some more, though, especially what the wire routing will look like.

Posted in Electrical | Hours Logged: 2

Finishing some harnesses

Today’s job was to get the inside harnesses done. To review, I was waiting on being able to route the coil pack and crank sensor harnesses from the engine bay back tp the CPI ECU. I pulled those through a few weeks ago, but had started working on other FWF stuff before deciding that it made more sense to finish the harnesses inside; that way I’d know exactly how much slack I had to work with to route stuff around the engine.

So I started out today by finishing cleaning up all the avionics I removed a while back, and reinstalling it all. Technically I only needed the ECU, but I kinda figured I’d do a better job with everything in place, so I just went all the way. Then I dug out the CPI manual and installed the various pins into the appropriate plugs.

That just left the part of the job that I (unironically) really enjoy: lacing up the harnesses. This is one of those things that you’d think would be tedious, but I just get sort of Zen about it, plus it’s satisfying to watch unorganized forests of wire turn into nice tidy harnesses. Now this entire area near to top of the right gear tower is done:

Well…mostly. It’s not technically electrical, but I do need to route an engine vacuum line to the ECU as well. I have a bulkhead fitting to install in the firewall, and I’ll need to also add a hole through the gear tower for that line. I imagine I’ll route it alongside the harness here, but not quite sure how. Lacing probably isn’t a good idea, as it’d probably kink the vacuum line and cause a problem. I might just break down here and use zip ties, even though they’re not my favorite thing. Gotta think about that one some more.

Posted in Electrical | Hours Logged: 2.5

Firewall passthroughs and baffle bracing…again

Nice to have a Friday off where I can get in some good work. Yeah, the theme is identical to last time, I didn’t feel like trying to come up with a more clever title.

First up was moving forward with that baffle brace. I made some measurements and marks on my cardboard template for some stuff I wanted to tweak, then laid out and made the first bend. The final piece will have two bends, but I decided I didn’t need that complexity for the template. A better idea was to just keep trimming it until it touched the baffle at the desired spot – mostly I just wanted a basic template for bending the metal later.

When I was satisfied with that, I started laying things out on the actual material. As before, I started with the two bolt holes, since they’re by far the most critical dimension. Then it was just a lot of measuring and drawing and so on, followed by a lot of work with the band saw/Dremel/files/etc.

Bending was even more fun. I should have been smarter about this; instead of camping the piece to a table with lumber, I clamped it straight in the vise. This was good in terms of holding the piece securely while I beat on it with a hammer, but it left some marks from the jaws that I’ll need to clean up. And of course the bending required some trial and error, with repeated fits on the engine until I was satisfied.

For the final act, I laid out and cut a couple lightening holes. This still will need to have the screw holes drilled in assembly with the baffle, but for now it sits in place nicely:

With that buttoned up, I turned my attention back to the firewall passthroughs. I popped into the local hardware store last week and bought some longer stainless screws, which I judged to be perfectly fine for this non-structural use. After drilling and preparing the screw holes in the firewall, attaching the passthrough just required coating the backside with fire stop sealant before actually putting the screws in. Getting the nuts on these screws wasn’t much fun, but I got it done. I did both the right- and left-side passthroughs, even though for the moment I’ll mostly be working with the right-side one.

Next up I got to fish all the harness wires through the fitting – very carefully, so as to not disturb the tape flags on each wire. I’d really rather not have to trace a circuit to figure out what a wire was if I lost a flag. I also went ahead and put the outer firesleeve stub in place.

The final bit of work for the day was to fish the CPI2 ignition harness wires through the fitting. Since these are pre-terminated on the firewall side, it’s necessary to fish them back into the cabin, and thence into the area of the avionics shelf. This was also a slightly tense moment, as I got to find out if the harness lengths I estimated when ordering the system were going to work. The good news is that everything reaches, though there’s a lot less slack than I might have expected.

As usual for wiring in progress, it looks messy now, but soon the routing and tidying will begin:

Next, I think I need to finish cleaning the avionics shelf and get it reinstalled in the fuse. That’s so I can finish terminated the CPI2 harness, then work on lacing that part of the harness up to the firewall. Then I’ll know exactly how much slack I have up front to start routing wires around to sensors and so forth.

Posted in Electrical, Firewall Forward | Hours Logged: 4

Firewall passthroughs, baffle bracing

So…what I’ve really been wanting to work on has been the firewall passthroughs for electrical stuff. Specifically, I wanted to get the fitting installed on the right side of the firewall so I could pull the wiring bundle through and start working on routing the ignition wiring back into the cabin.

When I looked at the fittings I bought, and read the instructions, I saw they specified #6 stainless screws for attachment, or stainless pop rivets. Given how tight things are inside the cabin where these fittings would attach, I really wanted to go the rivet route, and so I spent way too much time trying to find any 9/64” stainless pop rivets, to no avail. I also considered sizing up to 5/32” – a much more common size – but all the rivets I could find had too much grip length.

So I resigned myself to the screws. Before ordering from Spruce, I worked up a few other parts I needed, in a vain attempt to save on shipping. Critically, when it came time to place the order, I wasn’t sure the right screw length. But I thought to myself, “these are only going through two thin pieces of stainless, the shortest length is probably right.”

You can probably guess where this is headed. I got the attach holes for the fitting drilled into the firewall, grabbed one of my new screws, and…oh my, that’s way too short. The screws aren’t even long enough to get full engagement from a lock nut with no material in between, much less my two pieces of stainless and a washer.

Welp, time to move on to something else until I can grit my teeth and either order from Spruce again or just buy some hardware screws locally. Fortunately, I had another task I’d been thinking on – how to brace the baffles at the back of the engine. I’ve mentioned this a bit before – the baffle kit comes with a brace that attaches to the case bolts and holds the baffles in place, but I can’t use that because my ignition coil pack will be mounted there.

I’d ginned up a few possible ideas, none of which I liked much, but then a couple weeks ago I saw a photo with a brilliant solution. Instead of bracing from the front, using the case bolts, this person was bracing from the rear, using the top two bolts on the accessory case. The brace itself looked relatively simple to fabricate, and I’ve got some scrap .063 stock lying around that would be perfect for this.

The main challenge for fabricating and fitting this would be the work space – on the back of the engine, near the engine mount, and up at about my shoulder level with the plane on the gear. Visible here – with that annoying mount in the foreground – are the two bolts that will anchor the brace:

The first fun part if figuring out the spacing of those bolt holes, since obviously the brace has to be drilled to match them. Trying to measure this with all the stuff around was going to be a real pain, but after some more thinking, I came up with an idea: a simple shop-made measuring tool. I cut a couple strips of scrap, drilled 1/4” holes in one end of each, and a 1/8” hole in the other end. A cleco through the smaller hole acted as a pivot, and a third 1/8” hole in one piece anchored a final piece of stock. That final piece made a sort of “A” shape, allowing the tongs to be fixed in a relative position.

Then I just bolted the ends to the case, clamped my crossbar in place, and I had a template for those two holes:

Easy to measure this over on the bench, and…very nice of Lycoming to make the bolt hole spacing exactly three inches:

Using that measurement, I started working on a cardboard template. First step was to just locate the bolt holes and lay out the surrounding shape to clear the accessory case, then I did a trial fit to make sure that my bolt hole spacing and the surrounding shape would work out. Seems good to me:

That was the end of the night’s work. Next will be the more-fun task of roughly locating the two bends I’ll need to get this piece touching the baffle, and then will come the real fun of starting to replicate this thing in aluminum and getting it to fit right.

Posted in Firewall Forward | Hours Logged: 1.5