Bent piston -- can it be fixed? - Page 4

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beer&mathematics (original poster)

#31: Post by beer&mathematics (original poster) »

Really appreciate the advise y'all!

I took the group off and the pipe seems perfectly fine. I put it in some citric acid since I have some other parts in there now. I'll look for any cracks but it looks ok.

Here's a side-by-side of the old piston vs the new piston. Old is on the left and the new is on the right.




I don't have any precise measuring tools so I can't be sure but they seem pretty close to my eyes. There's a small difference in the new piston. It has some machining, visible in the second photo, which I'm not sure what they could be for. The old rod doesn't have (need?) them.

So to recap, the dipper tube looks ok. The dow111 was ok as it wasn't globbed up or anything. Seals came out looking good. Also, before I removed the group I did fill up the tank and brought it up to pressure with the fork flipped and it still wasn't enough. With a mirror showing me the group and the screen off, I tried a few pulls with the machine at pressure (it is over 1.2 bar, since I usually run it at 1 bar and put it up to make sure this wasn't an issue) but I could see that the small amount of water that made it through was from the hole that is likely only partially exposed by the seal.

The issue I think is simple. The piston needs to move up ever so slightly. I doubt I can do anything about it tho :x
LMWDP #431

miab

#32: Post by miab »

There is always something you can do. Don't give up.

Is the piston taller or does the bottom gasket sit at a different height from the bottom then the old one? Do the shafts have the hole at precisely the same height from the bottom? All measurements from a common plane at the bottom.

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peacecup

#33: Post by peacecup »

Just to be sure, before you start cutting or drilling:

1. Was there plenty of steam when the machine was up to pressure? (in case somehow the pstat isn't working)
2. Just to be sure the dipper tube is not blocked, if you attach the group with the piston not installed, then fill the boiler and heat the water, the water should begin to flow freely from the grouphead as the boiler starts to fill. OR:
3. Or I guess you can just try running water into the dipper tube from the facet to see if it flows freely.
4. I don't know how the rod is attached to the piston, but if you can remove them you might be able to switch them.
5.Before doing any changes, maybe a techinical question to the seller of piston, to see if they will send you a replacement?
LMWDP #049
Hand-ground, hand-pulled: "hands down.."

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beer&mathematics (original poster)

#34: Post by beer&mathematics (original poster) »

Hey Joseph, I so appreciate the encouragement:) I'll need to invest in some calipers to measure precisely if I can't get this fixed since that seems like the next logical step.

Jack, I can definitely rule out adequate pressure (steam wand lets out crazy strong steam, also I have it set pretty high since the pressure release valve whistles a bit before the element shuts off) and I can rule out the dipper tube (came out of citric bath looking shiny and brand new; also blew air with sides plugged to check in there were micro cracks and there weren't).

Also, I flipped the piston 180 degrees with the side with the grooves facing forward. Maybe they have some effect with the travel of the lever or rolling pin.

Okay, did a quick test and brought it up to pressure after re installing the group with the 180 flip. Still with the shower screen off, there is a bit more water/steam that will shoot out of the group. Progress? I'll have to wait a couple hours to use the kitchen but we'll be able test if I can coffee with it. Stay tuned!
LMWDP #431

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peacecup

#35: Post by peacecup »

On my machines the lever yoke has the piston rod home off center. You want it the opposite of how it looks in this picture, that is, with the hole offset on the upside. This will give the piston 1-2 mm more travel, and hopefully allow the inlet port to open fully

LMWDP #049
Hand-ground, hand-pulled: "hands down.."

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beer&mathematics (original poster)

#36: Post by beer&mathematics (original poster) »

Success! This story will have a happy ending. Thanks to all who helped out!

In the end, I believe it comes down to two factors: 1) the lever fork needs to be oriented correctly (as Jack has shown in the diagram, also see picture included below); 2) the new Ponte Vecchio Piston needs to have the flat side facing forwards (see second picture below; it's subtle for visible)




I didn't dial in the coffee perfectly, but after a 10 second pre-infusion I let go of the lever and held my breath.....was the lever going to catch? ....yes! The spring started to do it's thing! With 2 pulls, I got 20 g of coffee in about 45 seconds. Again, not dialed in (it's a very light roast Peru from Sey) but that's espresso!

Again, can't thank this community enough!
LMWDP #431

miab

#37: Post by miab »

Glad you got it sorted. That rollers diameter matters too. If you ever have to replace it, make sure you get the appropriate one. If you want to experiment get the smallest one where piston just touches shower screen. All the best.