I think I may have tamed my 1984 La Pavoni Professional and the classic group overheating issues. I modified the group from a steam heated group to water heated group for temperature stability. While it's not exactly the same as 1st generation and Millenium models it is similar and gives similar heat stability with a little practice.
NOTICE: HERE IS THE FINAL MOD POSTING. MUCH IMPROVED OVER THE ORIGINAL DESIGN. GREAT TEMP CONTROL.Heat control of 1984 La Pavoni Professional
READ THE REST OF THE THREAD IF YOU ARE INTERESTED THOUGH.
These things heat the group using group metal to boiler metal conduction, but even more so with the steam heating of the group. I've used the classic 2mm Teflon heat break for the group to boiler connection, but that didn't do enough. I've tried using wine corks around the dipper tube to block air from the group, but they get wet, swell and end up popping out when I lift the lever. I've used corks with extra holes and grooves cut, but eventually it swells and pops out again.
Now that I have to use this machine as my current daily driver, pulling 5-8 back to back shots every morning, I wanted a solution to the overheating. I was dipping the group into a cup of cold water, pulling the cool water into the group while raising the lever, doing the dance to keep the group heating under control.
Finally, I decided to give the cork another shot, but this time with some kind of plastic instead. Luckily a bottle cap had a ridge inside that perfectly fit the group opening to the boiler. I cut the cap down to leave that ridge and a flange around it fitting nicely to the back of the group opening. Drilling a hole in the center of the cap, enlarging the hole with a screwdriver until I had a tight fit with the dipper tube. Then I drilled 2 tiny holes on opposite ends of the cap to allow for some airflow and condensed steam drainage. Fit the dipper tube through the opening, position the tiny holes vertically, screw in the dipper tube to the group.
Put it back together with the Teflon heat break in place and started the heatup. It took a bit longer to heatup, required a few more pumps of the group to get up to full heat, but it got there. The second day of use it started boiling shots out of the PF, and an inspection of my "fix" showed it had popped loose.
Next mod was to wrap some uncoated copper wire around the dipper tube, firmly against the bottle cap. This seems to keep the cap in place for over 1 week without issue. Once I get the group up to heat, I'm able to pull up to 8 shots without any need to cool the group. After a shot is pulled and decompressed I unlock the PF, give it a brief flash of steam & water to flush the group screen, reload the PF, lift lever until steam comes out of the group, lock in the PF and pull the shot. Repeat, repeat, repeat, but not one shot boils out of the PF!
The narrow part of the group just above the flare tops out at around 103c, usually around 101.5-103c. The shots themselves come out quite a bit cooler per the infrared thermometer that I aim at the PF with about 93c being my top range there. I might want to open up the holes a little to have more heat, but at this point I'm also very happy and don't see too much need for it. I'll probably make another cap adapter so I can swap between the 2 and see if my shots come out warmer and improved.
Here are the pics:
Teflon heat break, trimmed bottle cap, copper wire keeper.
View of the bottle cap inside and 2 vertical holes.
Bottle cap removed from dipper tube.