The new flush-mounted gascap will use the bayonet system from a stock Harley tank,
so that if the gascap ever goes missing it can be easily replaced with a stock cap.
In the pics above you can see the donor-tank in the front, the "new" tank in the rear
and the donor gascap (vented ofcourse) of which we will use the internal parts.

 

We used a hole-saw to remove the filler neck from the donor tank,
the neck was cleaned up and shortened in a lathe
.
 
 

We scrounged up a piece of thick steel tubing and a round steel disc, cleaned up the steel
tube in the lathe, machined an edge to center the steel disc, and cut off about an inch.

 
 

Aad welded the disc in the pipe section (damn he's a good welder!), then we machined
a hole in the steel plate and welded in the filler neck from the donor tank. Finally we
cut a new hole in the King Sportster tank, as far forward as possible. Aad has left
for a well deserved holiday on some faraway sunny beach, when he returns we will make
a rib over the full length of the tank, including over the new fuelcap. Then we will make a
drain system so that the rain and spilled fuel can escape from the fuelcap. Finally we will
make a new and extra deep tunnel, new bottom and mount the whole shebang with hidden
rubber mounts. By then the summer will probably be upon us so it will most likely be grey
primer or matt black for me this season, but what the hell; I like grey primer and matt black!

This is what the next steps will look like, the finished tank is on Cadbike #1