Asked if I could do something to save this Fuel Tap from an early 60s machine for a friend. I first tried to obtain the part as a spare from the manufacturers (Karcoma). They still produce them for various motorcycles etc . No parts available even though the design is pretty well unchanged.
The original little screw on Filter Cup is plastic with a coin slot and hex end to undo it. A mistake in design really, as they are likely to be over tightened, I suppose as there are no spare parts, they can sell more for replacement (up to £35.00 each) -
The cup is the 3rd fuel filtration process which will also separate and retain any water (small quantity) and has a small cylindrical filter which fits onto small spigots both in the cup and the Tap body, so I had to measure carefully to ensure it is not crushed when the Cup is screwed on, but that the seal doesn't leak.
I settled for Brass to make it, which allowed me to do all the work and produce and insert the small internal spigot, then Hard solder it in the exact position.
I also had to I.D. the thread form (metric 18 x 1mm) and cut it on the old Myford (imperial). After reading up on it, I had to do this by manual turning, as you can't disengage the 'Leadscrew' drive, or it will be misaligned!. All went well-
Fortunately, there were only 4 full threads and it was the first time for me producing them.
To finish it off, I produced a new sealing washer from reinforced Viton rubber of the correct thickness.
To reduce the over tightening factor, I added a 'reeded' finger grip area on it, rather than a screwdriver slot etc. All finished ready for years of use-