What not to do with a Lever Espresso Machine

Luckily, I figured out what I did wrong

Robert McKeon Aloe
4 min readFeb 5, 2021

Two years ago, an odd thing started happening with my espresso machine. The area above the piston head, where the spring is located, filled with water. I ended up pulling out the spring, cleaning it, and fixing the seals. However, I didn’t know how I got into that situation before, but I do now.

My Kim Express. Images by author

It all started because I was experimenting with pre-infusion. Typically, you pull the down all the way to let water in. I thought the pressure during pre-infusion might be too much. Typically, it is around 2 bars, but I haven’t measured on my machine. So I actually don’t know.

The water comes in from three holes on the side. Only a small change will cause water to come in.

I wanted to test reducing the pressure. So after a few trials, I decided to let the lever rise just enough to stop water from flowing into the chamber but without putting pressure on the puck. This modification didn’t seem to affect the final extraction, and I found other ways to get around issues.

Until the steam came out…

A few shots later, as I was pulling the shot, steam started coming out of the top pin where the lever arm connects to the piston shaft. I knew this could not be good.

See the water on the pin. Water should not be here.

So I pulled out the piston, and it was a quarter filled with water.

The spring has a little bit of rust on there as well as some dirt that won’t come off without harsher chemicals.

I was worried the O-rings were broken, but luckily, I didn’t find any issues. The piston was covered in grease and coffee residue.

I let it dry off, and put the machine back together. My next shot was just fine.

My theory is that when I let the lever back down, the water entry point was sitting on an O-ring cause some water to accumulate. This continued to accumulate until it pushed through the top. Or at least I think that’s what happened.

The moral of the story: a lever machine is not supposed to do anything fancy in pre-infusion. The piston needs to sit above or below the shower entry holes, but not on top otherwise, the o-rings will fail to function because they aren’t made to handle sustained pressure from the side.



Robert McKeon Aloe

I’m in love with my Wife, my Kids, Espresso, Data Science, tomatoes, cooking, engineering, talking, family, Paris, and Italy, not necessarily in that order.