Matt,
Maybe I'm misunderstanding here, but if it is indeed the sneeze (pull shot.. remove PF.. ah choo!) then there is an easy, easy remedy for that. Take your time removing the PF - I do this all the time. You will hear and see vapour easing out as you slowly "unwind" the PF. As you get closer to the end (of pulling it out/end of handle it just about facing you), try to wiggle it up and down a bit.

-phillip

Hi Phillip,

That technique worked pretty well with the old o-ring. Now there's simply too much pressure. It escapes, but for some reason it wants to come out right where my index finger grips the handle. I've tried a few different ways of doing it, but no luck escaping the scald and the sneeze. I think I may put the old o-ring back into the group. I did notice that the new one had a slightly different shape so perhaps that's the issue. Thanks.

Matt

To help with the sneeze (and volume), I've done two things:

1) Release half way and wiggle - then remove. You can usually tell just by the sound if it is going to explode or not.

and just recently...

2) I put the group together as normal on a recent rebuild, then removed the two nuts on the piston rod. Pushed up on the shower screen until touching the piston, and then tightened those two nuts.

I actually did #2 b/c I was suddenly getting soupy pucks. I'm a "no headroom" kind of guy, and my pucks were always dry - then one day soup city. Checked to see it the piston head was starting to unscrew, which it wasn't and started to play around. The result was pleasing, and put more volume in the cup.

KnowGood - are you referring to the lock nuts on the top of the piston shaft? The one is a cap nut and under it is the lock nut?

I have wondered about those while breaking mine down. I always guessed that it was to limit the depth that the piston / shower screen can travel at the end of the stroke. I chalked it up to the Italians not wanting that last bit of blonde that sometimes comes at the end of the shot.

It never occurred to me that it might limit the pressure in the head to avoid the sneeze. Hmmm....

thanks everyone for the responses. today I pulled my first double, steamed the milk, then my second and got no sneezes - now I need to figure out how to do two lattes

MattJ wrote:KnowGood - are you referring to the lock nuts on the top of the piston shaft? The one is a cap nut and under it is the lock nut?

It never occurred to me that it might limit the pressure in the head to avoid the sneeze. Hmmm....

Yep, those two nuts, and it never occurred to me either until I got those soupy pucks. Everything seems kosher since I tweaked it.

I started looking a little harder at those two lock nuts on the top of the group head that are threaded on to the post that connects to the piston.

It seems to me that the function of those two nuts is to set the most bottom position of the piston so as to guarantee too much pressure isn't continually put on the screen. I put my finger inside the screen and felt when the piston bottomed onto the screen. You can feel when the piston is putting pressure onto the screen and then lock the nuts down an eighth of a turn or so higher on the post.

My machine is now functioning about the same as before the rebuild. I guess it takes a hundred shots or so to gunk it up enough to make it feel the same

I comfort myself with the lack of volume in saying that I'm pulling "ristrettos" although I've found that the best shots I pull put a lot of pressure on the seals. I'm getting a small leak out of the steam handle (which I didn't rebuild) and between the group and the tank. I'm going to tighten those screws on the group head a bit and see if that fixes it considering there's a new o-ring there.

Damn...yet another variable on the LP? Locknuts on the grouphead, really?

well, it's two nuts to "lock" against each other to set the depth of the piston

I had seen a few reputable tutorials about rebuilding that mention these nuts, but none of them triggered a logical explanation or understanding of why they exist. My theory is they limit the amount of manual pressure you exert on the shower screen with the piston via the lever. Probably to avoid the possibility that you could pop the screen out and damage it, the piston, or the o-ring.

The other day, I changed the piston on my 1999 Europiccola from the original plastic to brass. When I reassembled the group head, I pushed the lever all the way down and screwed the top nuts tight. The result was that the shower head and gasket were depressed sufficiently to make it impossible to insert the portafilter. So I removed the nuts, raised the handle slightly so that it no longer touched the shower screen, screwed the nuts down tight, and all is now well.