I'm also wondering, based on drgary's comment, if you somehow changed your piston depth. The two nuts on the top of the shaft control how low your piston is allowed to drop. If it is a different depth than it used to be, this may cause your Cremina to act differently

Since you'll have the piston removed from the group, that's the time to make sure it's fully tightened onto the piston rod. If you discover it's not fully tightened you may not need to change the seals.

These are great points about piston depth. If the piston depth has changed even slightly, this could cause the change in flow. I don't think it's the nut on the top of the piston, since this has always been fully tightened, but I never checked to see if the piston was fully tightened onto the rod, I just assumed it was and didn't' give a second thought.

If it weren't for the useful advice of this community, I have no idea what stupid things I would be attempting (like when I idiotically stripped off some of the chrome plating by submerging the group in hot citric acid to descale)

I recently pressure tested a rebuilt Europiccola with the piston in but no lever arm or pins attached. Considering it was somewhere into the double digits of levers I've rebuilt, it was pretty idiotic. To Gary's point, these mistakes are how we all learn.

I had similar issues, when I used too much grease to lubricate the head/piston seals, and the extra stuff blocked a part of the shower screen. Worth to check that too, it can be the cause of the uneven dispersion.

grog wrote:I recently pressure tested a rebuilt Europiccola with the piston in but no lever arm or pins attached. Considering it was somewhere into the double digits of levers I've rebuilt, it was pretty idiotic. To Gary's point, these mistakes are how we all learn.

drgary wrote:That's idiotic the second time you do it. How do you think I learned??? Same thing about tightening the piston onto the rod.

True, I should think of mistakes as learning opportunities rather than beat myself up for them

Katoci wrote:I had similar issues, when I used too much grease to lubricate the head/piston seals, and the extra stuff blocked a part of the shower screen. Worth to check that too, it can be the cause of the uneven dispersion.

I do tend to be heavy handed with the Dow 111, due to a somewhat irrational fear of under lubricating. Having only worked on one lever machine, it is hard to know how much is enough until you've done it a few times, and to add to that, my under-lubrication fear was exacerbated after reading about how critical lubricating the pins/roller on the lever yoke is for preventing wear in the slot...

UPDATE: I removed, disassembled, cleaned and rebuilt the group over the weekend. I didn't have as much time as I anticipated for changing one variable at a time, so I did everything at once. The shotgun approach is probably not useful for future troubleshooters, but just didn't have the time to try each recommendation and then test, so I did everything at once.

1) I replaced the Orphan Espresso seals with the Olympia factory seals (with only enough Dow 111 to just skim coat the seals). I also vigorously cleaned the dispersion screen. The piston seal change is the biggest geometrical change to the entire system, since the factor seals are shorter than the Orphan Espresso seals and leave a noticeable gap in the seal groove. When I have time, I may swap back to the Orphan Espresso seals to see how big a difference the geometry change makes. I didn't notice any difference in the feel of the lever between the two piston seal versions.

2) I twisted the piston rod and piston together as tightly as possible by hand, I didn't detect any significant movement of the threads, but it's certainly as tight as I can get it now so I have confidence that the piston is at the correct depth.

3) I very lightly sanded the piston bore and bottom of the piston with wetted 600 grit sandpaper. This made the surfaces shinier, but didn't noticeably change the fit of the piston in the bore.

4) I readjusted the boiler p-stat and verified the pressure range with two different gauges, and I am confident that the boiler cycles between 11-14 psi. I noticed an occasional arc inside the microswitch in the p-stat, so I'm wondering if this part may be failing/failed. The arc doesn't occur often enough to record it, but it concerns me. I've left the case off the machine to observe more closely, and I may replace the p-stat if it continues. I also noticed slightly blackened and brittle terminal insulation on the on/off switch (the hot wire from the terminal block to the switch). I replaced this with a new wire and a new terminal. Time to research electrical stuff.

The results...well, the piercing spray from the dispersion screen is gone. No more obvious channeling!!! The pulls are still a spongy, and volume of a full lever pull is decreased by 5-10 ml. There still seems to be some air that is difficult to remove from the chamber so I have been incorporating a half pump (fellini move?) and pre-infusing longer than I did before (waiting for droplets all over the screen, rather than following a predetermined 10 second countdown), which helps. The espresso is drinkable if maybe a bit over extracted due to longer pre-infusion, but works fine for wife's milk drink. I think I can make adjustments to grind and dose to work this out though to make good straight shots again. There seems to be a lot of information on the site about short pulls and half pump methods, so time to read up on this technique.

Oh, and for the puckology experts, the pucks look nice again albeit a little ragged probably due to the half pump method at the start of the pull.

Thanks for all the help troubleshooting, I think I am back on the right track now.