Reviving this long-dormant thread with an update:

While my GS/3 was down awaiting a new logic board (see Another La Marzocco GS/3 Malfunction), I took the opportunity to open the group to see if verdigris had accumulated during the year since I last cleaned it out (see post earlier in this thread). The answer is yes.

Although the TL30 tube was in better shape than last time, the underside of the group cap was in quite bad shape. The condition of both parts pretty-much parallels that of shadowfax (see his posts here, here, and here. Could be more than coincidence. We both have "fire sale" machines (though mine was probably delivered at the tail end of that fiasco), we both started out using cation softeners, and we both switched to Claris Everpure systems. I'm not sure if the softeners really had anything to do with it, but we used the same ones nonetheless.

Here's what the group looked like when I popped the cap this time:



Not too bad, really, the curved portion of the TL30 looks much better than it did a year ago. The buildup on the tube and nut is considerably reduced, as is the amount of debris inside the group chamber. However, there was a thin layer of buildup along the tube leading back to the 3-way valve:



The deposits were quite thin and quite hard. It appeared that there wasn't enough buildup for bits to flake off, as they had a year earlier. A soak in distilled vinegar removed all of the deposits:



Oddly, the vinegar soak removed the copper patina, which came off when I lightly wiped the tube down with a paper towel. Also, the shiny areas evident on the tube after I cleaned the tube last year are completely gone. I thought they looked like some sort of plating, but maybe not. Anyway, it's just down to the bare copper now.

The group cap was another story. As you can see from the photos in my previous post, last year the underside of the group cap looked pretty good -- the chrome plating was intact, and I was able to wipe the verdigris away with a cloth. This year, the underside of the cap looked awful:



Not only is the chrome plating in bad shape, there's quite a buildup of "puke-colored" verdigris. This is the stuff shadowfax was worried about, and I don't blame him (yuk!) Incidentally, you can see in this photo that the paper gasket was destroyed when I removed the cap. It was really baked on and brittle. Of course, I had a spare gasket on hand for reassembly.

After soaking the group cap in vinegar for an hour or so, here's what the solution looked like:



I was able to wipe away most of the remaining verdigris on the cap with a paper towel. I was surprised and somewhat dismayed that a lot of the chrome plating came with it, too. Evidently, the plating was just hanging on by a thread, so to speak. Here's what the cap looked like after the soak and wipe-down with paper towels:



I figured it wasn't a good idea to leave the cap like that, and decided to follow shadowfax's lead and remove the rest of the plating down to the bare brass. Here's what the cap looked like after a light rub with a Scothbrite pad:



I thought it was best to remove all traces of the plating, so I used some fine sandpaper to get rid of those last couple of dark spots. Here's the final result:



We'll see how the cap fares when next I open the group. I'm betting it'll look a lot like shadowfax's group cap.

Here's the group after cleaning and reassembly:



If you look carefully, you can see a bit of the copper nut is missing. It splintered off when I tightened the nut with a wrench. I think the awkward angle of the wrench was responsible for that -- LM probably uses a special thin, bent wrench for that job. You can see the chipped area better in this close-up:



Just to be safe, I removed the TL30 and filed down the sharp edges of the cut, making sure no loose bits of metal could flake off. I think the tube is OK. Unfortunately, the nut can't be fixed without replacing the entire TL30. I'm going to ask LM if they have a plated version of the tube. If so, I'll replace it. Otherwise, I think the nut will hold up OK. I'm also going to ask if I should replace the group cap or live with the bare brass.

Comments welcome.

I recommend using a nylon brush to get the deposits off, personally. I find that the patina that develops, which gets removed when you do an acid soak, is key to reducing the formation of deposits... the oxidized metal seems less prone to the buildup. I use a wire brush for the stubbornest pieces, but I avoid using it any more than necessary, because it scrapes off the patina as well.

Clearly you had to acid soak this round on account of the nastiness on your group cap. I stick by my initial thought that it's best to sand it down to the bare brass. Now that you've done that, I recommend avoiding acid exposure and using a brush/rag/scotch-brite to remove any new deposits you find till a full patina can develop. You should have minimal problems after that I think.

Luckily, my $700 Silvia has none of these problems.

Luckily, neither does my GS/3.

LM probably uses a special thin, bent wrench for that job.

Or one of these: http://www.graytools.com/catalogue/crowfoot%20wrenches.pdf . I believe the size is 14 mm but espresso machines seem to fluctuate between english and metric sizes or somewhere in between.

How does the other side (the outside) of the group cap look?

godlyone wrote:How does the other side (the outside) of the group cap look?

Just fine. Why do you ask?

I could probably find the answer to my OT question somewhere in this tread but is the dispension block one solid piece or is it actually two pieces screwed together, please?

I believe on the GS3 and all newer La Marzocco machines the dispersion "block" is machined out of the single solid piece, rather than being affixed to the group/boiler with screws. Older Marzoccos did have a detachable dispersion block, from what I have seen.

Thanks