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Firewall-forward thoughts while working on fuselage?

Draker

Well Known Member
Two somewhat-related questions for all-knowing VAF!

1. Reading some past threads, it seems there is some wisdom to having the engine mount available and test fit well before starting FWF, in order to double check the location and fit of components you plan to attach to the engine side of the firewall (e.g. the brake fluid reservoir), and in general to start planning the firewall-forward side. I'm going nose-dragger but have still not finalized my engine choice. Between the IO-360-M1B (180hp) and IO-360-A1B6 (200hp), is the engine mount the same? If so, I don't see why I wouldn't want to order it early, before whatever kit it actually comes with.

2. For fuel injected engine, the fuel line passes through the firewall on the lower center-right area, with a metal doubler on the engine side. In some threads, builders using Van's documented location for this hole have reported interference between the doubler and the starter contactor, and also clearance issues with the engine mount. Is there a consensus on the best location for this pass-through hole? Without the mount and starter hardware, I have little confidence I'm drilling in the right spot. Should I just hold off and not pass the fuel line through the firewall until much later in the build?
 
While I'm not building one of the side-by-side models, I know that some of the drawings are available on the $10 thumb drive plans. Look for the OP drawings. They cover at least some aspects of what you need.

There's this to be said for settling on an engine: it lets you get the finish kit and the FWF kit, if there is one for your plane.

Dave
 
wait

Someone advised me to wait to drill holes in the firewall until the engine was mounted, that way I could see the conflicts. I decided not to wait and regretted it.

If you can, wait.
 
Ryan,

I?ve already drilled my firewall for the fuel line for a fuel injected engine and I put on the starter contactor. There was an issue that I worked through where I had to make an adjustment. I shifted things around slightly and at at this point I think it worked out. Only time will tell for sure though.

Ray
 
This is a no brainer

With the engine mounted, you will see many conflicts in wires , hose, cable and scat potential routing. Stainless patches are not good for your ego or resale. Yes, some holes will be impossible to drill with mount in place so take it off to drill.
 
I, too drilled all the holes in firewall before engine mount was installed. And yes, my fuel line (injected) is very close to the starter contacter. It will work, but that?s one I would do differently.

Also drilled the hole for manifold pressure (per plans). Regret that one as well, since the MP line will wont need to penetrate the firewall.

The hole for air filter bypass (alt air) is so close to part of the engine mount, I would hold off on that too.

Everything else seems to be pretty good.
 
Thanks for sharing. It seems so far the consensus leans toward "waiting" to drill major firewall pass-throughs. I confirmed the answer to my first question directly with Vans. If I wanted to buy the engine mount early, the part number for the -7A is WD-739-PC and it's the same for both the IO-360 180hp and 200hp engines.
 
Thanks for sharing. It seems so far the consensus leans toward "waiting" to drill major firewall pass-throughs. I confirmed the answer to my first question directly with Vans. If I wanted to buy the engine mount early, the part number for the -7A is WD-739-PC and it's the same for both the IO-360 180hp and 200hp engines.

The only downside to that is the mount is not a small part, shipping it would be pricey.
 
The mount is not the whole story !

Trust me Ryan, beyond the mount is FI vs Carb, Mag vs EI vs Pmag vs Efii,etc. Cold sump vs Lyc, cooler on baffle vs. firwall, on and on. If you dont have your engine, you will have some hindsight regrets.
 
Vans had the motor mounts on backorder until recently. They shipped mine separately from my finishing kit with the front gear leg. Shipping weight 44 lbs. They paid the freight in this case but you can figure it out if your interested.
 
Use the advanced search function and use my user name (N941WR). Some time back I posted all the firewall penetrations called out in the plans.

Some are best done early but don't show up in the plans until after the engine is hung
 
Even if I was very confident I knew where to drill the holes without the final engine on I would only drill them as max #30 pilot holes. If when the engine is on they are indeed in the right place enlarge. If not it's only a #4 rivet to fill the hole rather than a patch. I still have holes to drill to locate some pass throughs and FW parts. The only holes I drilled before the engine was on was the holes to attach the engine mount itself. All my stainless holes start as #40 the pilot hole is the hardest to get through after that step drill and or final drill size easily enlarges the pilot when your certain. The side benefit is that you can use cleccos to easily hold components on to confirm any interferences. But lots of my stuff is non-standard/oddball FWF, (standard aviation) but so far off the Vans reservation no idea anymore what a standard Vans plans build is like following their instructions.
 
Ryan, prior planning always helps. But those plans can change, and often do. Especially locations for accessories. Think about what you want--check the plans, and pics of others with similar equipment. Think some more, measure about 3 times. Prior planning certainly will save you a bunch of potential headaches later.

Tom
 
Indeed! After drawing these items onto the firewall with a sharpie, it's obvious that there will be a conflict between the fuel line doubler and the starter solenoid's bracket:

IMG_1995-L.jpg


I'll either move the fuel line hole down a hair or grind off the corner of the doubler. It doesn't look like this will make any difference whatsoever because there's a flexible hose on the engine side.

This exercise has convinced me not to drill anything until I at least have all the things that attach to the firewall in my possession. I'll also be sketching out Vans entire plan onto the firewall as a way to familiarize myself with what's on this side earlier and plan ahead.

And, related to planning ahead: Not sure how I'm going to dimple the new hole that's needed for nutplate that the starter solenoid's bolt goes through. The firewall is already riveted to the vertical stiffener angle. I may just have to end up countersinking through the thin firewall.
 
There are a couple options for dimpling those types of holes. One is to countersink a metal block, place the block on the back side and use a rivet and rivet gun to do the work. Another is a kit you can purchase with small dies and a nail that you pull with a hand squeezer rivet gun.

For what its worth, I did not rivet the backing plate for the master and starter relays. The bolts hold it in place just fine.

My fuel line is much lower than the plans; maybe 3 inches above the lower side of the FW.
 
Ray, I'm not too worried about dimpling through only the firewall--I do have tools for that. What I'm puzzled about is dimpling the firewall where there is already an aluminum stiffener behind it. Normally I'd countersink the stiffener, and then dimple the sheet, but in this case, the stiffener has long ago been riveted to the sheet!
 
Ray, I'm not too worried about dimpling through only the firewall--I do have tools for that. What I'm puzzled about is dimpling the firewall where there is already an aluminum stiffener behind it. Normally I'd countersink the stiffener, and then dimple the sheet, but in this case, the stiffener has long ago been riveted to the sheet!

If you re-use an existing rivet hole, that should be covered. I don't recall having to install/countersink any other holes in the FW where a stiffener backed the hole.
 
Watching thread with interest as I'm just starting the fuselage slow build and working on the firewall. Seems like a lot other steps could/should be done while it's easy to work on the SS including:
1.) Fuel line doubler for the I/O 360, others say no and wait... seems like that should be a very well known placement? (DWG OP32)
2.) Dimple upper holes now for the F-1107 L&R, why not?
3.) Battery mount holes, why rivet to only drill out later? Order battery box now or wait?
4.) Master relay and starter solenoid, drill now? and fab doubler? Seems like I should order these now?
5.) Holes for brake reservoir?

Thoughts on these?
 
Battery box

The only thing i did on my firewall during initial build was add the Vans battery box for the odyssey battery and drill the holes for the relays. I figure everything else can wait until i have the engine mounted. I will let you know how it turned out in a few years.
 
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