Mike, it pulls drinks just fine so doesn't really need a new piston. But you can look up my other thread on Londinium seal replacement a few months ago. It has relevant information and a lot of users who have had the machine a lot longer than I were chiming in on niggling problems some folks were having. I did have a couple instances of seal slip, just a touch, and then it went away and has not come back; not too worried about it, but its always at the back of my mind. Also, the catch point when I pull the lever is about normal, far as I can tell, with other Londinium I owners.... roughly 10:30 ish. But that doesn't leave very much headroom; I have zero problems pulling a tasty single; but if I want a double, I usually just turn on the Strega instead because it has so much more volume. By the time the Londinium's lever goes to the top, the amount of liquid in the cup is a bit on the sparse side for a double, and I'm never sure if the pressure gradient favored a good pull or not. So, Paul Pratt was kind enough to show some pics of a prototype piston he had made, and its not a difficult thing to do to make a piston out of brass; and I actually have a hunk of brass lying around here that I was going to use to make a Pavoni cylinder, but that project fell through because there isn't enough interest, so its going to go into a piston instead
If I didn't do ridiculously time wasting, semi useless projects like this, what else would I find to spend the time on??
notes on new piston; the lands (grooves for the seals) will be tighter, and not quite as deep as original, to hold the seals better and hopefully provide a touch more outward pressure. First ring will have holes into the chamber on the perimeter to puff out the seal under pressure. That's the easy part. The new piston will have to be 2 part, to afford a little movement so the shaft can rock a touch. Probably the shaft is metric, meaning I have to order a metric tap to duplicate
I already made one mistake, I didn't measure the height of the piston when its mounted tight on the shaft.... need this measurement so the new piston is same height relative to the water inlets and chamber.