I am confused because when I picture using the exhaust pipe adapter, the gas cap will no longer fit because the top portion of the filler neck that the cap screws onto is gone. What am I missing?
I think the idea is to use the adapter to join the top and bottom of the filler neck after it has been shortened and so avoid having to weld them together. That way you are still able to use the cap.
So the diameter of the adapter is so close to diameter of the filler tube that they are a tight enough fit for epoxy?
@Todd M - the OD of the adapter is close to the ID of the filler tube. It acts as an internal "sleeve" that joins the removed section. I could have done it with a piece of 2" OD metal tube.
At the bottom of the filler neck where it joins the tank there is a lip that will stop the tube from falling into the tank. If you have access to a TIG welder just cut off the center section of filler neck and rejoin the pieces. One note, if you have a cap with a logo you'll want to put it on and position the two pieces before welding. That would bother me having a nice cap that is not positioned right.