Corbin, 

The bottle cap is a shitty design. Besides the cap cracking, the threads can also crack. With a carbureted engine, when that happens it introduces low pressure into your header tank and winds up having an engine that doesn't want to run too well and it first starts acting up at about three or four hundred feet after takeoff. Then you have to Mayday and see if you can limp around the pattern. If you're lucky you will have a passenger along who will later praise your excellent skills and nerves of steel. 

I don't know what happens with a fuel injection engine but if it was me, I wouldn't want to investigate too far. There are a lot of different ways the guys have done fuel caps, not just the one that I use, but mine is pretty simple and you can get parts at any hardware store. There are more elegant methods out there, such as with the Vai-Ez guys may use.

Take care.

Sam 

On Mon, Mar 15, 2021, 2:17 PM Corbin via groups.io <c_geiser=icloud.com@groups.io> wrote:

I haven't made Sam's modification using the PVC fitting yet so I am curious if anyone knows the source of this fuel cap that I have.  My A&P found a crack in it during my conditional this week (ready to fly now).

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Corbin 
N33QR