[trevtherevs]

My mate has dropped off a TF petrol cap he had been polishing. He started this about 6 months ago and has now forgotten how it goes together. I can sort of get how it goes together, except for the ring in picture 2. Any help would be
help would be greatfully received. I know he did have the lock out of the unit, but can't see if that matters at all. The thin ring has got me beat and can't see anything to give me a clue as to where it should go.

 

[trevtherevs]

Having come back to this again I'm wondering if this thin ring sits in side as in pics 3 and 4 then the lock centrepiece pushes inside of this. It does seem incredibly tight when I tried.

 

[roobs]

I suspect the black ring would go underneath to secure the lock into the unit. So, lock through the middle, the small black ring must clip over the rear of the lock to hold in place in the main cap then large black ring behind the silver ring, screwed in place with the alan nuts? That's my guess.

 

[roobs]

There is no visible seal around the locking centre from the outside

 

[trevtherevs]

Right, finally the solution. When the lock unit is out of the centre portion, the centre unit splits into blue cover and top and bottom black unit. The thin ring fits between the two halves of the black centrepiece. In turn, this all easily snaps back into the polished ring. I did remember when doing my engineering apprenticeship, the solution is always to crank up the swearing, which always helps.