William,
When I bought my S4 (1987 in Hong Kong), one of the previous owners had removed the filler, bogged up the hole and used a VW filler neck and cap inside the boot. Fortunately, when I picked all of the bog out of the hole, the hole, and profile where intact and did not require repairing.
I purchased a new filler neck, seal and locking cap for the restoration. I can tell you now, that they seal very well. The first couple of tankfuls, after the car was back on the road, the cap was difficult to open due to a vacuum in the tank. The fuel tank was also oilcanning due to this vacuum.
On investigation, I found that the breather hole, as shown in Brian's post was only drilled on one side. There is a annular void moulded into the cap with holes drilled in each side, 180 degrees apart, or there should be. I had to disassemble the cap to drill the extra hole. This after speaking to the manufacturer.
Possibly worthwhile giving the hole a suck, just to be sure that all is in order.
Cheers,
Colin.
William2 wrote:I have just bought a new locking fuel filler cap to fit to my S4 Elan and would like to find out whether it is necessary to drill a small hole somewhere in the cap to act as a tank breather or not?