Yes - I removed the stock cap first - ha, ha
The cap is in the collar already. I've removed 2 of the little bolts and put the brass things in place. As I try to simply screw the collar into the thread on the tank I get a fraction of a turn, not even a quarter, and that's it ! Feels like the thread is just wrong.
As soon as I felt the obvious resistance I went cautious - not only so I didn't bust the collar but more importantly, if I did crack the whole thing, I was worried about fragments dropping in the tank. Perhaps another nights sleep, a drink and a little grease might help.
