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Trapdoors and Fuel tank sealing – Part 1

This afternoon I got back into the shed and finished making the trapdoors. I trimmed the hinge pieces on the band saw and rounded all the edges with my Scotchbrite wheel.

Trapdoor hinges trimmed

I then marked the centre line and rivet hole locations and drilled the hinges. I then used the lower hinge to match drill the trapdoors.

Trapdoors drilled

I then dimpled the trapdoor and countersunk the hinge to provide a flush face between the trapdoor in the rib. After riveting the trapdoor to the lower hinge, I used a Cleco clamp to bend the triangular tab up so it would act as a stop for the trapdoor. I then bent the hinge pivot rod at each end using some pliers, to hold the pin into position.

Trapdoor stop

Next, I clamped the trapdoor into position (allowing for a small gap between the bottom of the trapdoor and the skin for the bead of sealant) and match drilled the rib to the upper hinge.

Trapdoor drill to rib

I then riveted the trapdoors into position and checked to make sure they swung freely. All good!

Trapdoors riveted

The next stage was starting work on sealing the fuel tanks. I knew this part was going to be messy and a little tricky, so I tried to prepare things and have stuff laid out in advance. One idea suggested to me by a builder near Lethbridge, Victoria (I’ve forgotten your name – sorry!) was to use disposable syringes for the tank sealant instead of trying to spread this stuff around with pop sticks. After ringing around a few places, I found the local Vet was the best place to get extra large syringes that was big enough for my purposes. Thanks to Pinjarra Vets for selling these to me!


As the weather was hot I decided to only make small batches of sealant as I didn’t know how short my working time was going to be. Ideally, you mix this stuff at cooler temperatures and is usually gives 45 – 90 mins of working time. I decided to play is safe and make up a batch of 50g sealant/5g accelerator, which was a bit over half a syringe. I later found that this was enough for about 9 stiffeners so I had to make 2 batches. I did find however that the sealant was starting to set towards the end of the batch so I think making small batches was a good idea.

I have a new appreciation of working with tank sealant. Imagine a hybrid between Superglue and melted Mozarella cheese. This stuff is horrible to work with but I reckon it would have been a lot worse if I didnt have the syringes. Application was pretty easy and the sealant didn’t drip everywhere. The mess came from twirling the rivets in sealant before placing them. This put sealant on your fingers which meant everything you touched then got sealant on it too, including the skin, the desk, the rivet gun, the air line, my nose, my forehead, my ear, my cheeks, my new T-shirt … uh ho. (I forgot to change into a shed shirt … oops).

I had to drill about 8 rivets out in total. This was complicated by the sealant which made the rivets a tad stubborn to get out (not to mention spreading sealent onto the hammer, drill and punches). Some of these rivets I drilled out because I didn’t like how I had set them. However, there were a few around the fuel cap flange I had to drill out because they were the incorrect length. The plans call for -4 length rivets but I discovered the deluxe fuel caps required different length rivets around the flange as the flange thickness varies in the middle (its thicker). I didn’t pick this up because I was too busy trying to work fast before the sealant set. I also discovered I had forgotten to rivet the vent line clip on (like most builders). I ended up fixing all this up and getting all the stiffeners, fuel cap and tank drain riveted on and cleaned up on the left tank skin. I wouldn’t even attempt to try and do both tanks at the same time. One by one is the way to go. Here is a shot of the where I got up to today.

Left tank stiffeners on

I was wearing rubber gloves throughout and went through about 8 pairs during this build session. I also went through about 500mL of Acetone and about a dozen sheets of lint-free paper towel. Next phase will be putting the ribs on.

Build time 4 hours.

About gstrack

Husband and father of 2. Control & Instrumentation Engineer. Flying nut. Gadget geek.


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