Have done a forum search and not found much info on this. Some of you may have seen the Cimbali M20 two group that was being offered for free on another board. I drove up to Vancouver a few weeks ago and picked it up from its generous prior owner. He had this in a commercial setting for about ten years, and has had it in his home for several more years. He was running it off of well water at his home, which was extremely corrosive and pretty much destroyed the springs and bearings. It appears possibly the seals failed and allowed water up past the piston bore and into the top of the group. All of the carbon steel components on the group are toast. Everything that is bronze or stainless is fine - just some scale and such that will clean up. Luckily the interior of the boiler doesn't look too bad (it's a stainless boiler) and the element tests fine.

Has anyone worked on this group and have disassembly tips? I'm thinking I'll need to build a tool with wood plates and threaded rod to compress the spring for re-assembly, but I know with some groups you can screw the piston off of the piston rod for the disassembly portion of the process.

Edit: turns out you can remove the screws that hold the spring surround casting to the big bronze piston bore section, and 'walk' the whole assembly up and out just by working the lever up and down.

Here be the group:

I'm making progress cleaning up the groups and pistons on the Cimbali M20. I decided to focus on this first, as there are some unobtanium parts and I didn't see the point of continuing if I determine that parts of the group are toast yet not replaceable.

Here's how the pistons looked upon first pulling them from the group:








And here is how they look after an overnight soak in Joe Glo, followed by about 8 hours in citric right off the boil:








Clearly there is some material still to be removed from the piston rods, and some material loss as well. I'm deciding if I focus my efforts on cleaning that up further or on removing the piston head from the rod with an eye to having new rods machined.

The bronze group castings are cleaning up well after the same routine I used on the pistons. I have to say that a Dremel with the plastic (or is it rubber?) wheel attachment is amazing for cleaning off rust and scale.





Still some work to do in terms of removing stubborn scale but getting close. The final frontier is the aluminum spring surrounds that go on top of the big bronze castings. The bottoms of those where they were in direct contact with the bronze got mega hammered. Lots of stubborn scale and pitting, and some surface rust that cleans off easily. They are ugly but I think still viable for use, especially since the most unsightly parts won't be visible when the case is all back on the machine post-group reinstall. Getting the bearing pins out is proving to be a major PITA. WD40 and patience...

Nice work. Could you post a photo of the Dremel wheel you're using?

Sure thing. It's this one. Really amazingly effective:

https://www.amazon.com/Dremel-EZ472SA-1 ... BWCQ1K2MMQ

This afternoon, I discovered that a good old hammer is quite effective at removing stubborn mineral deposits. Just wrapped the rods in a shop rag, smacked the piston rods a few times and most of it fell away. There is some pitting on the rods to be sure, but I think they are still useable.

Dropped off the parts depicted in above posts at abrasive blasting shop. They recommended glass bead blasting.

One challenge is that the Cimbali piston design is such that there are two parts of the piston that move independently of each other, but can't be separated. Others have posited that the design is so that the piston self-centers in the bore. In any event, the guys at the shop pointed out that abrasive media would get into that gap and be nearly impossible to get out. Clearly you don't want abrasive media in a ball joint.

So I have a couple of options. I can get serious about removing the rod from the piston (hit it with the torch), and get just the rod blasted. But the guys at the shop felt I had gotten 95% of the buildup off already, and suggested using a bench grinder at a slow speed. I hadn't considered that at all since it seemed too easy to inadvertently remove more material instead of mineral buildup, but I may try.

Use Evaporust if it is marked as being OK for contact with brass.

I had soaked them overnight in naval jelly back when I was still working on getting the springs off. Do you think Evaporust is better in this situation than PB Blaster?

I measured the rod with calipers along its length and it's consistent within .1 mm. So no real need to take the risk of bench grinding. I will probably use the bench grinder for final polishing and buffing instead of removing material.

I've got the pistons down to bare metal. Just waiting on a very incommunicative machine shop to finish up the bead blasting on the other group components and I'll reassemble the groups.

Still quite a bit of work to do on this though. I need to clean up the boiler. It's stainless but full of a black residue (doesn't appear to be scale). I have realized that I should check through all the components (solenoid, magnetic float, etc) that also could have been impacted by whatever corrosive well water this was running on. There are a couple of plumbing issues to be addressed, including re-soldering. And I have to plumb it in.

I had an electrician take a look, and it had already been converted to run on 220v single phase (the tag indicated 3 phase and it had a 4 wire cord with no plug). So this runs on two hots with a ground and no neutral. They are hard wiring it in on its own circuit.

Erm...perhaps there is a bit of scale in there: