Every exterior hole on the fuel tank gets dimpled except for the line where the rear baffle will be riveted. According to Van's, the plans have you machine countersink these holes instead because this location has historically been prone to builders having trouble getting a good seal with the fuel tank sealant when installing the dimpled baffle. Leaving the inside of the skin and the baffle itself flat supposedly makes it easier to ensure that the sealant creates a continuous bead on the inside of the skin and effectively prevents fuel leaks.
Some builders have dimpled this area anyway and have said they got good results, but I'm not one to take chances when it comes to something like this. The rear baffle is the final piece that goes on and immediately cuts off access to most of the inside of the tank, so I want to get it right the first time and not have to open the tank up somewhere down the line to fix an easily preventable leak. That said, machine countersinking the skin is a very time-consuming and tedious task. It took me a couple of sessions to muscle through it.
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| Not quite there... |
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| Perfect. These are actually some of the most perfect machine countersinks I've done to date. |
With that finally done, I took apart the left fuel tank and then repeated the entire process for the right tank. I only have the one cradle, so I'll have to work on each tank one at a time from now on.
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| Skin test fitted... |
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| ...everything match drilled... |
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| ...and into the cradle she goes. |
