UPDATE:
I removed the p-stat, and it appeared visually free of scale, but all the nooks and crannies were not completely visible so I descaled it anyways. I reinstalled it and the boiler still cycles at the original range, peaking at around 0.9 bar. Of course, this is with an uncalibrated gauge, so I'm not sure how much I trust the outputs.

I took a short video of the water dispersion at the "as found" boiler pressure, and then after lowering the boiler pressure by about a third (peaking at around 0.6 bar). The flow seems more vigorous at a higher pressure (makes sense) and more flow out the sides of the dispersion screen where it clamps onto the cylinder, but shots pulled at high and low pressures are about the same in the pull feeling, puck disruption and taste, so it doesn't seem like boiler pressure is the root cause here. I'll revisit this after I get a new pressure gauge to check boiler pressure.

Boiler at 0.9 bar: Boiler at 0.6 bar: I did notice that there is an high velocity spurt from a spot on the screen toward the back of the group. So there could be an initial, violent spray of water coming out of the group disrupting the coffee bed. I tried to capture this with a screenshot of the video frame, but it's not super clear.



From reading up on forum topics about dents in pucks, spongy pulls, etc., I found there are some things to try based on various theories on what's happening inside the group when the piston is raised, but none seem to offer a 100% guaranteed solution, with varying degrees of success reported.

Dispersion screen: My dispersion screen is not pristine by any means, but none of the holes are blocked and it snaps tightly into place. There is a very minor deflection in the screen that has been there I first purchased the machine. This may result in less than perfect flow dispersion, but it was working fine until this week, so I doubt the screen is a cause. Also, I am pretty sure these cannot be purchased anymore so not sure if anything could be done.

Tamp harder: I've attempted many iterations of grind and tamp since this issue began with the same result, so I don't think tamping is an impactful variable for my specific issue.

Piston orientation: One of Doug Garrott's posts in another topic mentioned that over time the piston can develop an orientation due to routine wear in a constant position. This seems simple enough to test. Tonight I will rotate the piston 180 degrees and see if there is any change.

Orphan Espresso vs Olympia piston seals: In another thread, some folks had success changing to the Olympia OEM seals as opposed to the Orphan Espresso replacement seals. I have been using the Orphan Espresso piston seals without issue until this week, so I am skeptical this will make a difference, but I have a set of new Olympia OEM seals, so this will be the second thing I try.

Honing the piston bore: I've read a couple forum topics that honing the piston bore with high grit wet sand paper or a brake cylinder hone might help. I have some reservations about physically removing even a minute amount metal from the cylinder, since this is not a reversible fix, so I'll only consider this once all other options are exhausted. But maybe it's worth a shot.

I'm still stumped, so any other suggestions are highly welcome and thanks in advance!

Hello,

It seems you're battling two issues. I know how frustrating it can be - I was the OP of the dented puck thread (survived to tell the tale!).

For spongy pull, it isn't so much of an issue, as long as it isn't excessive. Sponginess is caused by residual air, and residual air is always going to be in the equation for a lever. It's not related to mechanical failure so don't worry.

For the dented puck, unfortunately that's partially due to the way how Cremina is designed. There's only one water inlet (similar to my Aurora), instead of 2-3 inlet like on a Pavoni or other group lever. So any imperfection (dispersion screen, seals, piston alignment, excessive water flow/pressure etc) is likely to show up as a piercing jet onto the puck. For some reason, the two seals (OEM rubber & OE Viton) can perform differently for different machine. I am a big fan of OE's work, but my dented puck issue was resolved completely when I reverted back to the original seal, and the issue was 100% replicable at least for my machine that time. My only explanation is there are manufacturing tolerances for the group heads. There're some recent comments how there're variance even among the big $$$$ Londinium lever groups that cause some piston to slip more than the other!

Anyhow, I digressed a bit. Your dented puck look different to mine so I am not entirely sure you have the same issue. Mine had a single dent on puck whereas yours look like the entire puck is disturbed, and the screen touching the puck. Am I interpreting that correctly or it's the way the picture was taken?

It's been frustrating for sure! I have finally improved my technique to a point where I was consistently getting drinkable (decent to excellent) shots, and then this.

Anyhow, I digressed a bit. Your dented puck look different to mine so I am not entirely sure you have the same issue. Mine had a single dent on puck whereas yours look like the entire puck is disturbed. Am I interpreting that correctly or it's the way the picture was taken?

I didn't think to start taking pictures of the spent pucks until after I initiated this forum topic. The appearance of the puck damage varies, sometimes a crater, sometimes a big crack, sometimes just a very uneven surface of the coffee bed. The picture I posted is one of the more extreme cases but the damage always originates in the same general location.

The reason I can tell the damage originates in the same location is that a large foamy droplet almost always appears on the same spot on the bottomless portafilter (0.5 cm from the edge of the basket at 12 o'clock on the group head) as soon as the water flows into the group.

So any imperfection (dispersion screen, seals, piston alignment, excessive water flow/pressure etc) is likely to show up as a piercing jet onto the puck. For some reason, the two seals (OEM rubber & OE Viton) can perform differently for different machine

Tonight I'm going to try changing the orientation of the piston by 180 degrees, and if that fails I'll try installing the Olympia OEM seals. Fingers crossed that I'll eventually arrive at the right combination of the variables to make this issue go away.

thesharpener wrote:It's been frustrating for sure! I have finally improved my technique to a point where I was consistently getting drinkable (decent to excellent) shots, and then this.

Tonight I'm going to try changing the orientation of the piston by 180 degrees, and if that fails I'll try installing the Olympia OEM seals. Fingers crossed that I'll eventually arrive at the right combination of the variables to make this issue go away.

I dose around 17.5 to 18.0g depending on my mood in the morning, I've become less picky about the .5 g variance. I never see anything but the same looking puck; but I am dosing very close to the basket spec (18 g). I think you might be seeing those puck differences because of greater headspace gap between the top of the puck and dispersion screen. That space will allow more turbulence with the incoming steam/water.

Secondly, through my Naked pressure gauge, I've found some sponge in my lever came from remaining espresso. Now I hold the lever down until there isn't hardly anything left dripping. Even with nothing dripping I still get a small "psst!") from pressure being released.

While there is a quote about the relevance of looking pucks in the quotable section of this website, I think we established there are no gastroenterologists here, or they chose not to respond.

jwCrema wrote: While there is a quote about the relevance of looking pucks in the quotable section of this website, I think we established there are no gastroenterologists here, or they chose not to respond.

I understand the irrelevance of puckology especially from the perspective of a pump machine with 3 way valve. But what I have also been finding is, on a lever, they can be really hintful in certain ways (after the puck is mostly dried).

For example:
(i) How intact the puck surface is relates to the gentleness of water flow/shower screen function - I don't want to see divots/dents for sure. Bottomless can usually tell you that, but if you don't have one, the puck surface is a good correlation.

(ii) The bottom of a knocked-out puck with dark colored spots indicates dead spots or area with low flow - indicates you need to buckle up your distribution technique/WDT (flat-out dead spot can be visible with bottomless, but some deadspots are more subtle and can only be seen on the bottom of puck).

(iii) The graininess/texture of a puck's top is trying to tell you something about your grinder -big conical tends to have a grainy puck top, flat grinder less so. If the puck is unusually grainy, that might indicate if you're using too coarse of a grind (wrong basket for the dose) or potential grinder alignment issue.

But of course, as the caveat goes, taste is everything.

samuellaw178 wrote:I understand the irrelevance of puckology especially from the perspective of a pump machine with 3 way valve. But what I have also been finding is, on a lever, they can be really hintful in certain ways (after the puck is mostly dried).

But of course, as the caveat goes, taste is everything.

Leaving the allusion to the medical profession alone for a second, you make the case for the need for puckology as a field of expertise in our pursuit of a better cup. And I agree with you. You're further ahead in this than I am. My Cremina's pucks are regular, consistent, pull with expected pressure and taste fantastic.

Here's to hoping the OP solves his problem!

As a novice, I don't know enough to be able to judge the merits of puckology, I'm sure there are arguments for and against. For the most part, I follow my tongue. However, I do know that in this specific case, the puck damage was a symptom of an undetermined issue (along with spongy pulls and terrible tasting espresso).

Before servicing piston seals, pucks were solid and dry. After servicing seals, pucks were damaged and wet. And this happened to correspond to the espresso taste suddenly changing from decent to awful. The puck damage always being in the same location led me to carefully observe the flow from the dispersion screen, which shows a violent spray from a single part of the screen as soon as the lever is raised high enough to allow water into the group.

Spray from dispersion screen slo-mo: What's causing the violent spray? I still have no clue. I am going to make a video (hopefully without destroying my iPhone) of water entering the group with the dispersion screen off, to see if that helps me understand the spray pattern and what can be done.

I agree with your point on puckology. The puck and your video shows us that something has changed and isn't right, causing intense and uneven flow through the shower screen. Is your piston tightened all the way onto the piston rod? In other words, when you lift the lever, is it fully clearing the intake port?

UPDATE: Last night I rotated the piston 180 degrees and this resulted in a minor improvement in espresso taste, and the flow pattern from the bottomless portafilter was slightly improved...and the pucks aren't as damaged.

Based on this, it's clear to me that my piston seal servicing had the unintended consequence of changing the orientation of surfaces inside the group just enough to adversely impact the flow through the dispersion screen. If there were only a little window on the group head to see what was happening inside

Tonight I am going to experiment with different piston seals, and see if this results in any improvement.

I agree with your point on puckology. The puck and your video shows us that something has changed and isn't right, causing intense and uneven flow through the shower screen. Is your piston tightened all the way onto the piston rod? In other words, when you lift the lever, is it fully clearing the intake port?

Good thought - I will take a peek inside tonight with the dispersion screen off while I try different piston seals.

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,