I managed to get my piston off this morning and the screen was black with goo. Also, the head of the piston was covered in goop as well. This is odd, since I cleaned it 5 months ago (maybe I should be cleaning it every month?).
There is also goop IN the skirts of the seals. I think I may want to get it out of there for the reasons in this thread. Any ideas? I'm afraid i'll break them if I try to take them out. Any ideas?

samuellaw178 wrote:That's more like it. Sealing the dispersion screen's gaps with teflon tape. Is there any other food-safe filling material that I could use for that? Solder? The gap is created by cut-out metal so I am sure I cant close the gap enough just by bending it. My gut tells me that everything on this machine is stock though, so is the dispersion screen. Possible

Well done Sam. That last video shows a big improvement in flow. Your shorter piston seals and the teflon tape really cut down the sideways flow giving you a substantial flow through the screen.

BTW, the gaps are so wide because the sides are spread out. If you could push the sides back to their original positions the gaps would narrow. But it's not just the gaps; the sides also leak because they are pushed out and are not flush against the sides of the cylinder. Hopefully your fix will last a while. For a longer term solution you could try food safe silicon mold material to build a more substantial edge all around the perimeter of the screen. Or for a permanent solution you could pay the big bucks for a new screen.

bostonbuzz wrote:<image><image>I managed to get my piston off this morning and the screen was black with goo. Also, the head of the piston was covered in goop as well. This is odd, since I cleaned it 5 months ago (maybe I should be cleaning it every month?).
There is also goop IN the skirts of the seals. I think I may want to get it out of there for the reasons in this thread. Any ideas? I'm afraid i'll break them if I try to take them out. Any ideas?

John,
I think it's recommended to take off the piston for lubrication every 3 months. In my case, I used a flat screwdriver to carefully pry out part of the seal. Then, stretch the seal over the rim to get it out. Just be careful not to scratch the piston.

espressoperson wrote:Well done Sam. That last video shows a big improvement in flow. Your shorter piston seals and the teflon tape really cut down the sideways flow giving you a substantial flow through the screen.

BTW, the gaps are so wide because the sides are spread out. If you could push the sides back to their original positions the gaps would narrow. But it's not just the gaps; the sides also leak because they are pushed out and are not flush against the sides of the cylinder. Hopefully your fix will last a while. For a longer term solution you could try food safe silicon mold material to build a more substantial edge all around the perimeter of the screen. Or for a permanent solution you could pay the big bucks for a new screen.

Thanks! Personally, I think my dispersion screen is meant to have that curve so that it can snap into the group which has a lip sticking out. Does yours have that as well?


Honestly, I can't figure out how to narrow the gap. Even if I push the sides closer to each other, there would still be a hole at the base which allows the water to jet out. A new screen is definitely out of my reach now. The screen for La Pavoni, Faema, Olympia Club and even the new Olympia Cremina all cost around $15 max. But it's just that this cremina 67 screen that has a price tag of $70 due to its rarity.

Thanks! Personally, I think my dispersion screen is meant to have that curve so that it can snap into the group which has a lip sticking out. Does yours have that as well

Oooh! Mine is to polite to give me any lip. You may be right that you have an older model screen that is meant to be that way. Or maybe you have a Pavoni lip and screen.

Howdy folks, I have photo proof!!!!! I watched the dispersion screen as I lifted the lever closely and look what I found. Once any water passes the dispersion screen a jet is made in the far side. Even when the lever is lifted almost all the way, the jet just grows stronger. I can't tell if it's there when the lever is totally lifted, however. I cleaned everything thoroughly as well.

Curiously, the first time I flushed, this did not happen! My routine is to flush once before pulling to heat the group, and i get some dripping as I lift the lever up if I don't flush first. My dispersion screen is flat, I can post a photo of it as well.

Can anyone help? If it's the gaskets again, can anyone point me to where I can get the shorter ones?

John,
That's some serious water shooting! That's even more vigorous than mine was. I think it could be the seals as it was on mine. But I am not even sure if it's just the seals. What was your pressurestat setting? Also, have you cleaned the rest of the group? I asked OE about the OEM seals - you gotta get the group rebuild set, which costs $60+ Unfortunately, the piston seals are not sold by itself. So, it's not going to be a cheap fix if the piston seals are the cause.

OK, all this got my interest up so this video is of a freshly rebuilt Cremina group, using the OE piston seals.

http://www.youtube.com/watch?v=EXOX-6lgCTM

That's a nice even flow, Doug. I am not sure what happened but I swear the problem is gone when I switched the seal back. After you put in the seal, does it have a gap there between the gasket and rim or does it fit tightly? My water flow doesn't show that shooting but when I brew with it, it has the divot, which is perplexing.

Also, I felt weird for having a oddball dispersion screen myself. All the Creminas I saw have a very nice screen and not hammered and pointy like mine does. Have you ever seen a screen like that before when doing refurb? The machine, when it came, was with the portafilter, single and double baskets, manual, knockbox, metal scoop, tamper, and basically all the stuff you get originally from Olympia. And they all looked shiny and pretty much used very little. So I am not really willing to believe that this machine has been tampered with before.

There is a small gap...if there was no gap the seal edge would get pinched between the cylinder and piston. The size of the gap does not matter, IMO. You see, there are quite a number of things going on here, particularly with no coffee in the pf to impede the flow. Without coffee the cylinder isn't even completely filling and you are just jetting superheated water out of the boiler, so there this whole thing is prone to chasing artifacts. I do think you may be misinterpreting the function of the holes in the piston edge and the kinetics of the water flow on piston travel...look back at Timo's or Mogogear's posts about how the water flows on the lever stroke, I recall them as very informative...some of the Greybeards now seemingly having moved on from the habit of HB posting.
I believe your results, but you also have a severely damaged screen which is curved (the original is by the way flat), and as you said, possibly other factors going on as well, so it is hard to figure this out since one cannot see what is going on inside the cylinder. If changing the seals cured your issue then it seems that on your machine, for whatever reason, your problem is solved.
I think it would be perfectly fine if everyone suddenly "needed" to change to the OEM seals, since they do not last as long as the OE seal, are harder to install, and result in a very stiff lever action....we have often lamented that the OE seal is "too good" and does not need to be changed as often as the OEM so this could be good for us and Olympia as well.

This is frustrating, especially considering how simple the cremina is. It's making more sense to me how the seal/piston is deflecting the water straight down and perhaps a shorter seal could solve this problem. However, EVERYONE should be having this problem, and they aren't. So what's the deal?

3 other options I just thought of:
1) lift the lever quickly to get the piston past the intake valve
-but this is universally shunned for good reasons I think.
2) lower my pressure setting
-I'm fairly certain that it's fine though, I had checked it a while back.
3) Put some secondary screen in like someone already mentioned.
-but this is treating the symptoms, and i want to fix the problem!

Someone will chime in...

O, and thanks Doug/barb for that video, you're awesome!