Technical petrol cap

[YorkshireFettler]

First Post...
Classic 500R, 1974. Recently acquired and now in full rebuild mode.
How do i get the petrol cap off?!
It's a plastic cap with central vent.
It doesn't push down - to release any 'bayonet'.
I have applied a LOT of rotational effort but am scared of breaking something (my wrist perhaps). I don't want to use any torque assistance unless i know it should just turn and release.
ANY ideas/experience please let me know.
tks

 

[fiat500]

Hi Fettler, if it's the standard tank under the bonnet, the full width of the space, it should unscrew. without pressing down. You're not likely to break the tank neck but fuel caps are readily available new. Go for it and get some images up please.

 

[Pazzo500]

The cap can be very hard to remove if it was previously tightened down a lot and has been sitting for awhile. I've definitely had to use two hands and all of my strength to remove it several times. Like fiat500 said, it's just a simple threaded cap, no tabs or anything.