After trying lots of ideas, I got my Faemina Baby to work. My original seal was intact, but just was shrunken from its original diameter. My solution was to leave the seal on but add an o-ring to the recess at the top of the original seal. To get the right size, I went to my local hardware store and they let me try all their o-rings to see which one entered the cylinder with enough pressure. One required a huge amount of force for my arm to press the piston into the cylinder, but another one required only a moderate amount of force. I went with the moderate one and it worked and the Baby's arms made it go into the cylinder effortlessly, but with no leaks. I possibly could have gone with the tighter o-ring because the leverage with the arms is much greater than my hand pushing it in. (I just took the piston and cylinder to the store, not the whole machine, so my test just involved pushing the piston with o-ring into the cylinder by hand.)

I took photos of the o-ring package info, the o-ring on the machine, and the first espresso that I made. I didn't even bother with a fine enough grind or heating the portafilter. I just wanted to see if I could avoid leakage.



I originally posted a photo of the o-ring package here. But I now realize that the store gave me the wrong o-ring package. They opened up several for me and put the fitting o-ring into the wrong package. I know this because my package had a cross-section (height) of 1/16". I think the one I have is really 3/32", using a tape measure. Even though it works with no leaks, I would like to see if I can find something even tighter.

I apologize to people who saw the 1/16" size and found that it leaked and did not solve the problem. When I find out the maximum size that fits the cylinder, I'll report back and I hope I don't make any mistakes.

To the best of my knowledge, the o-ring in the above photo actually is this:
Danco #73
2-3/16 in. OD x 2 in. ID x 3/32 in. wall

Nicely done! I will look for one today!

I got some leakage with that O-Ring, so I ordered a slightly thicker one from Amazon.

https://smile.amazon.com/gp/product/B00 ... UTF8&psc=1

We will see how that works.

You probably need the thicker one I saw in the store. If you have a friendly hardware store nearby, you can try what I did, in case your new one doesn't work.

Also, you can try silicone grease or similar on the one you bought and see if it stops the leak.

I didn't really pay attention to that but it was very easy to clean. No real mess at all.

I also was thinking about o-ring sizing. My o-ring's cross section is 1/16 in., which equates to 1.58mm. My estimate of the original seal's diameter shortfall was 1-2mm, so this agrees with my estimate. If I were to try for an additional increase in o-ring pressure, I'd try to get a 2mm cross section (something like 1/12 or 1/13 in., if such a non-metric size existed).

So, it looks like OD and ID of the unstretched o-ring are irrelevant, as long as the ring can stretch onto the piston. The main factor in stopping leaks is the cross section or ring height, as it's called on my package, which creates the new larger seal diameter after the ring is added.

Got these today: https://smile.amazon.com/gp/product/B00 ... UTF8&psc=1

Seem to be working. I have 24 more if anyone needs one!

Glad to hear it's working.

I tried another trick I found on the Internet. I put a round Aeropress paper filter between the tamped coffee and the bottom of the Baby's shower screen. Helps with even water dispersion. Also, the Baby is using the finest grind of any machine I own.

I wanted the Baby to go with my Faemina, but I didn't want to mess with gaskets, etc. so I got a Robot. Still, it's good to see more Baby Faemina's being enjoyed.

What a simple solution! Can't believe I never tried this. Hope I can get my Baby to make espresso soon.