Initial Prep (Debur, Trim, Drill, and Cut)
10/12/22 – 3.0h
10/13/22 – 1.6h
10/14/22 – 0.8h
The final parts to prepare for the fuel tanks are the Tank Attach Brackets and the top and bottom shims for the tank attach brackets. I also needed to re-do the left and right T-00005B vent line clips from an earlier step. The Vent Line Clips have a pilot hole to final-drill 7/16” holes for the snap bushings that hold the vent line next to the fuel cap flange at the top of the tank. The final hole leaves very little margin on the sides of the clips, and my first attempt got a little off center resulting in a very thin wall on one side of the clip. I also did a poor job trimming and filing the clips, so I decided to try again. The clips came out much better the second time around!

The top and bottom tank attach bracket shims get cleco'd to the brackets and then trimmed flush with the inboard bracket ends. I had to look at the drawing in the plans a couple of times to make sure I was aligning the top shim properly with the bracket. After I had the shim cleco'd in place, I compared it to the completed tank drawing on the first page of the plans for a different perspective, to ensure I had it right. The actual trimming and filing was relatively straight-forward, but I was careful to mark each shim left or right and top/bottom to get them back into the same place later. Dimpling will also take some extra care since the shims are dimpled opposite of each other.
[Band Saw, Dremel with Metal Cutting Disk, Large Flat File, Small Modelling File, Hole and Edge Deburring Tools]

Final Prep (Dimple, Countersink, and Shape)
10/13/22 – 0.8h
Both the top and bottom shims (left and right) need several holes dimpled. I started with the #19 holes on the part of the upper shim that does not contact the tank attach bracket, which is the forward edge of the shim. I dimpled those holes with a #8 Screws dimple die. All of the #40 holes in the top and bottom shim get dimpled as well. I used a reduced diameter 3/32” dimple die to provide some clearance from the larger dimples I just finished, and to dimple the two outboard holes in each of the upper and lower shims. Those holes are very close to each other and the edge of the part, and the reduced diameter die minimizes the chance of damaging the nearby dimples.

The holes on the tank attach bracket flanges are countersunk to accept the skin and shim dimples. I set the countersink cage .007” deeper than flush, which works well for me on countersinks like this. Most of the holes are pretty easy to get to, but the holes at the ends of the brackets don't leave much to square up the countersink cage, so those take a little longer to ensure the countersinks are aligned properly.
[22” C-Frame, #40 Reduced Diameter Dimple Die, #8 Screw Dimple Die, #40 Countersink Cutter, Microstop Countersink Cage]

Prime
10/14/22 – 0.6h
Priming goes very quickly on this step because you only prime parts that are outside the tank. In this case it is the inboard 1/3 of the tank attach brackets and the upper and lower shims. I scuffed the areas to be primed on each part as well as the area on the tank attach brackets that will be inside the tank where the inboard ribs contact the tank attach brackets. I am concerned about the final assembly of the inboard ribs (forward and aft) to the tank attach brackets because of the notches at the top and bottom of each rib. Each notch will need a blob of sealant to prevent fuel from leaking through in addition to the standard sealant treatment on the flanges and rivets. The good news is those areas are accessible from the outside after the tank is assembled, so it will be easy to fix if there is a leak there. Still, I'd rather not chase down and repair leaks when the tanks are finished!
[Grey Scotchbrite Pads, Bon-Ami Cleanser, Dupli-Color Degreaser, Dupli-Color Automotive Self Etching Primer (Green – Rattle Can)]

Assemble
10/16/22 – 3.2h
10/17/22 – 1.1h
10/18/22 – 2.8h
10/19/22 – 1.4h
10/20/22 – 1.8h
This step is completed with some minor assembly including attaching flanges, bearings, shims, and nutplates to the tank attach brackets and inboard ribs. The parts for the tank attach brackets are outside the fuel tank, so no sealant is required to attach the flange bearings, top and bottom shims, and assorted nutplates. Similarly, the K1000-08D nutplates on the aft inboard ribs don't need sealant since they will be covered and sealed later by the fuel sender unit. Access to all of the items on the tank attach brackets and the nutplates on the rib is good for the pneumatic squeezer 3” yoke. The 3” yoke doesn't provide access to all of the rivets for the nutplates on the inboard aft ribs, so I experimented with back-riveting using the 22” C-Frame. This technique will be used to set the very large 3/16” rivets to plug the tooling holes in the inboard and outboard ribs. I was really happy with the ease of back-riveting with the C-Frame and the results. This is definitely a good option for riveting in the future!

The moment I'd been fretting about since before I purchased my first kt finally arrived - assembly with tank sealant. I decided to start with an “easy” step to chalk up an early success with this new-to-me product and process. Each of the inboard and outboard ribs have tooling holes that need to be filled with 3/16” rivets and leak-proofed with sealant. The rivets don't attach parts together, so the process is to apply sealant and drive the rivet in the holes in the ribs.

While I had hoped for an early success, the reality was a dismal failure. The sealant mixing and application went very well. I used a digital kitchen scale to measure out 10g of sealant (white) and 1g of catalyst (black) on an aluminum plate protected with masking tape. I mixed the sealant with a popsicle stick, and used the stick to apply the sealant to the area for the rivet. I found with a little care, some good disposable gloves, and protective paper on the work bench; the sealant was reasonably easy to work with and clean up at the end of the session. The sealant is roughly the consistency of butterscotch ice-cream topping, and is extremely sticky. A plan to contain and control the mess is definitely a good idea before mixing the first batch. I also learned that 70% alcohol wipes are very effective at cleaning sealant off tools and parts before the sealant sets up.

The 3/16” rivets are too large for a standard light-duty pneumatic squeezer to set. The Van's tank assembly video recommends using a C-Frame and rivet gun on the floor to set the large rivets. I set up my C-Frame with a 3/16” cupped set and installed the flat set on the rivet gun to back-rivet. Given the large rivet size, I upped the rivet gun pressure to 60 PSI. I also used small levels to ensure I held the part square in the C-Frame during the riveting process. Unfortunately, my very best effort wasn't good enough to drive the rivet correctly. I tried 3 rivets, and all three ended up tipped and off-center. That may be OK as long as they will stay in place and seal the hole, but they are not pretty. Ultimately, I decided to drill out the rivets. My analysis is the AN470AD6-5 rivets are too long, and it might be worth spending some time with a rivet cutter to shorten them a bit. A shorter rivet also takes less sealant after it is set to encapsulate it. I didn't have access to a rivet cutter, so I needed another option to set the rivets at their original length.

I enlisted the help and advice of a fellow builder friend to try again with the 3/16” rivets. We managed to drill out the bad rivets successfully, and straightened the rib webs where the tilted rivets had twisted them a bit. We used a hand squeezer this time to allow us to set the rivets slowly with as much control as possible. Fortunately, this method worked, and we ended with relatively straight squeezes for each rivet. The rivets are not fully set, since that amount of squeezing would probably tempt fate and end up with badly tilted rivets. Instead, per the plans, we squeezed the rivets enough for them to swell inside the holes and hold firm. After encapsulating the rivet shop heads in sealant, they should be pretty effective fuel tank plugs.

The fuel strainer flanges and anti-rotation plates on the aft inboard ribs use AN470AD4-5 rivets. I am much better equipped to set the 1/8” rivets than the 3/16” rivets used to plug the tooling holes. Getting back to a manageable rivet size and familiar rivet setting process allowed me to clearly see the additional complexity of the tank sealant, and highlighted poor riveting practices that I mostly got away with on dry rivets.

The first thing I did was make plugs for each of the flanges with paper towels to keep sealant from getting inside the threaded area of the flange. The plugs worked great - I simply threaded them into the flange before starting, and threaded them the rest of the way through when I was finished. No mess there at all! I then mixed up another 10g+1g batch for the 4 strainer flanges and 2 anti-rotation plates, and prepared them the same way the Van's tank assembly video does with the fuel filler flange. I put down a medium-thick layer of sealant around the entire contact area, and then used a craft stick to thin and bevel the layer of sealant. A couple of clecos secured the flanges in place, and I could see a reasonable amount of sealant squeeze-out around the edge of the flange and in the rivet holes. I used the rivet squeezer to set each of the rivets with mostly good results. There were a couple of rivets that didn't get set squarely, so I drilled those out and tried again.

I was surprised at how much stray sealant ended up on the part and tools. Even a minor touch of wet sealant on your gloves will end up absolutely covering everything else you touch. There isn't much you can do about it other than clean as much as you can when you're done – the alcohol wipes are great!
[Pneumatic squeezer, 3” Squeezer Yoke, 1/8” Cupped Squeezer Set, 3/16” Flat squeezer Set, 22” C-Frame, Flat Rivet Set, 3x Rivet Gun, Hand Squeezer, Digital Scale, Mixing Sticks, Dupli-Color Degreaser, 70% Alcohol Wipes, Acetone, Shop Rags]