This is one of those things where I wish I was better at fabrication. There is an awful lot of room for variation in the way you tackle this. I'm pretty happy with how it came out, but I'm also pretty sure if I did it again I'd do a better job. Functionally I think it will be great. I'd have been a bit happier if it looked as nice as some of the jobs I've seen.
First I had to fit the flange/plate that bolts to the carb. I had to do a lot of filing around the drain plug and accelerator pump housing to get it to fit right.
All the black marks are alignment lines. Basically the carb doesn't sit centered and is slightly offset to the pilot's side, so the intake has to be angled back to the center to mate with the intake snout. I spent a lot of time lining everything up with alignment lines and putting the cowl off and on over and over until I got it as straight as I could. I then match drilled it to lock that in.
Below is a shot when match drilling the upper plate to the carb attach plate.
Once I had that done I felt comfortable trimming the filter. The plans call for cutting the filter first, but without having the plate in place and everything tightly held down I couldn't tell where to put it to trim it.
What I did was go ahead and mount the filter holders, then bolted everything up to the carb, and clamping the fiberglass box to the flange with cleco clamps. That held the filter in place so I could see where to cut it and ensured everything was aligned properly.
Here's the trimming. I did most of the trimming with my band saw and cleaned it up with a rotary cutter on the dremel and some metal shears.
I gooped up the carb with vaseline and filled the void with high temp black RTV. Forgot to take a picture, but after about 3 days of setting up it popped right off and is a great fit.
Here's a shot of what I said about lining up the snout with the intake. Takes a lot of fussing to get it all where you want.
This also told me how far the upper plate needed to be bent upward to align with the top of the intake. That in turn allowed me to establish the lower limit with the fiberglass. Basically it's just a lot of putting things on and taking them back off and measuring/marking until it looks good.
Once I had the filter right and had figured out where everything was going, it was time to match drill the fiberglass box to the flange. I totally forgot that these were supposed to be an3 470 rivets instead of the -4s, so I drilled everything to #30. Didn't realize my mistake until I started riveting. Doesn't matter, but it's way stronger than it needs to be.
Here it is mostly assembled. The angled pipe just above the forward part of the airbox is the carb heat fitting from Van's. I bolted it on loosely so I could try various options to make sure it would align with the carb heat door, which was the next fabrication task.
I established the door shape with some really light scrap I had (.020). I worked with that and some masking tape until I had all the angles and sizes established, then used it as a template to make the door out of the real material. It's a fairly snug fit.
You can only move the door so far back due to the filter flange and the bend in the upper plate, and you can only go so far forward because you have to leave room for the hinges.
Getting ready to drill and rivet the forward upper plate to the airbox. I left this till later to make sure I had a good fit with the door and so I could fine tune any height adjustment needed.
I did the foam insert in the intake snout twice. The first time when I carved out the hole it was just a lousy fit, so I dug it all out, sanded it clean, and started over.
This is the second effort. I tried to do a better job of fitting the foam precisely to the snout before I glued it in with the Bondo.
The oval dent on top is from where it fit into the snout, so it's a pretty good fit at this stage.
This is the forward side after it's been bonded in. When cutting it out I used a spare hacksaw blade and left plenty of room around the edges. I then slowly snuck up on the proper shape by just sanding the foam away.
I don't have a picture, but what I did was use spray adhesive to bond some 80 grit sandpaper to some scrap 1/2 round wood trim I had from working around the house. It worked perfectly, and was a nice straight and stiff reference which was good for sneaking up on the fit I wanted.
This is the inside after bonding. I just used Bondo as Van's suggested. Worked very well. Sets up really really fast. You have maybe 5 minutes working time max.
This is the inside after cutting the hole and glassing it. I used 4 plies of 9 oz. cloth. I tried to use the ballon idea, but the epoxy was so slippery it just slid right out. I ended up standing it up on end (on the back edge) and just pressed it out to the edges.
I had a good coating of epoxy on the foam to start, so it stuck pretty well once it started to set up. I just used West Systems epoxy with the slow hardener. Worked fine.
I found a shot of what it looked like before I glassed it but after all the final shaping and sanding. Pretty happy with how it came out.
