Vintage Tibaldi 20-L - Piston needs new cork

In a previous post I said I bought this vintage pen. I have to remove the piston assembly to see if and how I can replace the cork seal or maybe use an o-ring.
In my opinion the piston mechanism is inserted like the Parker Vacumatic button filler. The blind cap screws on to a protruding threaded bit that, I can see, is threaded inside the barrel. How to remove this though is a mistery. Shall I put the barrel in the ultrasonic cleaner and see what happens after a few cicles? Shall I find a tool similar to that of the Vacumatic to try and unscrew the end bit? The pen is clean, I have removed the screwed in section, I can see the piston going up and down but water/smoke comes out at the back. Definitely a new seal is needed. Other suggestions? Thank you. Marco

Do you have a way to precisely measure the blind cap thread diameter? If so, you could see if one of the vacumatic filler tools might work (https://www.etsy.com/listing/7796499...BoCA0IQAvD_BwE).

The references I found on this pen model say that the pen is a button filler. Found a picture on the internet and indeed it has a button filler system. Mine has a piston. Which is which ?
I tried the Parker Vacumatic tool I have and it is too small. I measured the diameter of the screw and will have to look for a nut of that size. In the meantime I've given the barrell about 6 rounds in the ultrasonic cleaner, the piston system doesn't budge.
I wrote present day Tibaldi asking for info, no reply.

Good news at last! I removed the piston assembly.
A bit of heat from a hair dryer and a plier helped me unscrew the assembly and here you can see how it is made:

Attachment 63942

The knob had been already 'mishandled' prior to me working on it.

I am thinking of using an o-ring where the groove is highlighted as I don't think I can find the whole 'groovy' bit anymore.

I have cleaned the grooves of the piston assembly screw and will use silicon grease to reassemble it and the section hoping the o-ring does its job.

This is what the, disassembled, pen looks like:

Attachment 63943

The flashed photo doesn't do it justice but it is, I believe, green and striated silver.

The pen is all plastic, IMO.

Ciao - Marco

The o-rings I have found in a shop are too thick. Where do you suggest I look for them online in UK ?

Could be wrong, but I expect there never has been an O ring in the groove....
I think the part with the groove is the piston seal itself.
Does the part fit with a slight radial pretension in there barrel bore?
Francis

Hi Fountainbel, I agree with you. But the piece with the groove has hardened and it is not air tight anymore. I thought of using an o-ring just to get it air tight again. Water exists from the blind cap and also smoke, which I blew into the barrel :-)
Marco

The set of silicone o-rings I have ordered has arrived.
The o-rings have Internal Diameter = 6 mm and Cross Section = 1 mm
The piston head has a diameter of 8+ mm.
I
assumed that if I got a smaller o-ring by putting it in the groove it would stretch and possibly reduce the Cross Section a bit more.
The grove on the head is smaller than 1 mm as this o-ring sticks out a bit.

I mounted the o-ring, spread some silicon grease on it and inserted it into the barrell, it goes up and down very smoothly.
I sucked in some water and then some ink and the barrell fills as emptying it the liquid comes out, something that didn't happen before.

Unfortunately it writes while the feed is wet, after filling the pen, but then it dries out.
I had pushed water through the section and it flowed perfectly so can't think of where the blockage is.

Something else to investigate now.
Have a nice week end
Marco

Marco did an excellent job with the piston seal. I've just had the pen to re-install the nib and feed, it's a celluloid section, much less forgiving than hard rubber sections. Pen now writes very well, and as previously stated, the photos do not do justice to the Arco like material.
et

Thank you eckiethump, the pen indeed writes very well. You have done a marvelous job. Which other, I guess Italian, pens have this type of pattern that you call Arco ? THank you
Marco

Arco is most often associated with Omas vintage pens.
et