LS.,
Iam taking this to a new thread since I don't want to polute the below mentioned thread with my blabla.
Conti Prestina ARRIVED!!

drgary wrote:TY, I installed a new spring when doing my original restoration and the shots please my palate more than any of my other machines, so I wonder if the piston seals are in good shape or whether there is wear inside the cylinder. If your new spring doesn't give you satisfactory pressure, have you thought of adding a booster spring that would sit inside it? Double springs are a common practice.

Gary, I had the boilerplate and the boiler sandblasted...they're like new now. All the gaskets, seals etc have been replaced by new OEM parts. I also replaced the spring with a new OEM part. Considering that espresso quality is determined by temperature and pressure (on the machine side) I have quantified these parameters in various parts of the process. Puck temperature, boiler pressure, boiler temperature, spring pressure. I compared the results side-by-side with my Aurora brugnetti. The latter has a preinfusion (line) pressure of 3.5 bar and spring pressure of 10 bar.

Temperature-wise there are no problems with the Conti. Temperature in the puck shooting up to 95 C. See some pics below.

I see a problem with the spring pressure. I have a great coffee and the Aurora brugnetti (10 bars) performs accordingly. However, the Conti produces a dull and flat shot with thin crema. I am thinking that 5 bar spring pressure is not enough.
The reason why I am confused is that my earlier Conti produced great shots at 5 bars. I addition, most Conti users have their machine at 5 bar and nobody is complaining (in contrary). What is happening here?? Is it possible that the 3-piece group should be equipped with a stronger spring? Seems also strange to me, while I received the machine with a 5 bar spring...
Anyways, next week I will tackle this issue with Ismael. We will give the machine a stronger spring and I subsequently pray to the espresso gods.

Some pics for fun.
Cheers, TY

TY,

First, here are some thoughts about your dissatisfaction with the Prestina's current spring: I've not had the pleasure to experience a Brugnetti Aurora in a very long time, so it's hard to make a direct comparison. I certainly have machines that can pull shots at 9 bar, including very simple ones like that Cafelat Robot and the Flair Signature PRO. I don't have a way rigged up to test spring pressure with my Conti Prestina. As you probably know mine has the same three-piece group that yours does. I am able to make wonderful shots on the Robot and Flair using the suggestion below from Paul Pratt. Sometimes I will use 5 - 6 bar, as suggested by Andrew at Flair.

In his Cafelat Robot user manual, Paul writes: " Ignore the magic 9 bar, that figure originally referred to the pump output pressure of a Faema E61 machine, when in actual fact the pressure at the group will be lower, maybe even 1-2 bar lower. Traditional lever machines (as measured by us) typically extract at 6-7 bars...."

At the time I completed my Prestina restoration, I had my own Elektra Microcasa a Leva. Shots from the Prestina were similar to the Elektra, where I had installed a current version spring. The Prestina's shots were larger but also layered, like the Elektra. They produce ample crema. I have been able to updose or nearly choke the machine and produce very rich shots. Jim Schulman visited my home the year after I'd completed the restoration. He tried the Prestina, and his comment was, "it's a gentle machine." I think he was indicating that there are different styles of commercial levers. He did not say, "the spring is too weak," which Jim would not hesitate to do.

I trust that you are pulling shots you like with the Aurora. Have you experimented with a full range of dose and grind to get shots you like on the Prestina without trying to duplicate what you're getting with the Aurora? The styles may be different. Have you ever tried a well-functioning Elektra Microcasa to see if you like its style of espresso?

Back to your proposed project of adding a booster spring: This certainly can be done. Some years ago Marcio Carneiro started a project where a number of us experimented with double and even triple springs with the Elektra Microcasa a Leva. These were all able to produce much higher pressures. It can be done. You may not need to go all the way to 9 bar, but I expect that this is achievable. In the end, I preferred the Elektra with its standard spring. I've boosted the spring on my rare Lady Duchessa, which truly has a tiny original spring that cannot produce crema. Now it pulls like an Elektra in the rare times that I use it.

I look forward to reading your explorations here. Thanks for starting this as its own thread.

Hi Gary,
Many thanks for responding here. Iam a believer of "the truth is in the cup"...I look and taste the result. When I have the impression that the result is sub-optimal I start trouble-shooting. Iam giving this prestina more play-time than any other machine I've worked on. Reason: Iam in love with this machine. I can give a number of reasons why this machine is absolute class. Most likely you have seen Thomas' resurrection of the Aurora Brugnetti. Well, the Conti prestina would definitely an option for a resurrection 2.0.

Anyways, Iam not saying that every Conti prestina requires a springboost, Iam just saying that my own analysis points at the direction of a springboost for my own particular machine (for reasons I do not understand at present). I have also noticed that the shot-volume of the Conti prestina is pretty high. I did not measure it, but my best guess would be 60 mL...(as compared to my Aurora at "only" 40 mL).
Next week we will do more experimentation. I want to boost the pressure at least to 8 bar.
Keep you posted!!
Cheers, TY

turboyeast wrote:I have also noticed that the shot-volume of the Conti prestina is pretty high. I did not measure it, but my best guess would be 60 mL...(as compared to my Aurora at "only" 40 mL).

Could this be it? I always stop the shot at an intended weight or where it starts to blond. That's also how Jim Schulman used my machine. He got a shot started. When it reached the point he wanted he pulled back on the lever to stop flow and removed the cup, letting the remainder of the shot flow into the tray. I may do that or I may pull the cup sideways at that point.

During espresso reviews for Home-Barista, my cup is sitting on a scale, and when it reaches the intended weight, I pull the cup sideways.

Paolo,

Thanks for your experienced comparison. That's very helpful. It'll be interesting to read about TY's result if he gets a 9 bar spring.

LS.,
Thanks for all the interesting feedback.
I take it that everybody out there watched the Netherlands win the Eurovision Songfestival? I hope the lyrics of Duncan Laurence don't apply to my machine..."loving you was always a losing game"....

Anyways, I fired up the Aurora and the Conti this morning...
The Aurora produces (indeed) approx 40 grams shots and the Conti approx 60 grams shots. I have a very good Yirgacheffe bean which was roasted two days ago. The Aurora produced a killer shot...in this respect I totally agree with Paolo that this machine can set the benchmark in terms of shotquality.
Comparing side-by-side with the Aurora (both 18 grams in the basket), the result with the Conti was not superbad. However, thin crema with a more pronounced acidious taste. Iam putting my money on a springpressure boost and this puppy will sing...theory now.
My fellow Dutchman Ismael has a more powerfull spring for the Conti and we do the experiments accordingly. In these experiments we will also consider a more appropriate brewratio.
To be continued.
Cheers, TY

A small video to illustrate the shot. Also note the birds on the background...

TY, with the same coffee on the Conti, can you pull the shot at 40 gm or even less? See how the taste changes if you aren't overextracting.

We are definitely moving in the right direction Gary. The taste of the shots now approaches the Aurora. Crema is still a bit thinnish but we are definitely in the sweet spot. I still believe that we can crank up the extraction efficiency with more pressure. I will provide an update.
Thanks for all the help till now, greatly appreciated.
Attached some pics of a 18 gr-total 40 gr extraction in a small cup and large cup.
Cheers, TY

What's it like at 18 gm/36 gm? Awhile back I was trying to figure out one of my lever machines, and another member suggested I tune my shots to the group.