If there is a single F2 connector on the back side then the bulb will only light when powered. That could be connected to the NO or NC contact on the pressurestat to show you heater is ON or when heater is OFF when unit is at set pressure or NOT at set pressure.

Hmm, that makes sense. I'll take a look this weekend and see if I can figure out how to connect it. I know the pStat was replaced a year or so before the machine went out of service, so perhaps when they installed the new one, they just didn't bother to connect to the indicator light.

So I'm at the point where I will be re-installing piston seals. The configuration one sees in most of the exploded diagrams from online retailers (there are still a handful who sell some of the parts for this) use a standard u-cup for the top seal, and then an o-ring with a hard teflon seal in the lower position, with the middle space blank. The bottom seal looks like this:


It's completely rigid, and if you look at it from the side it has a flare at the bottom.

But HBer kitt rebuilt one of these a few years back, and used what I see as a more conventional setup (my piston type is the one on the right):

Having a u-cup in the middle slot makes much more sense to me than leaving it blank. One thing that is concerning to me is that this particular machine was taken out of service because water kept getting above the seals at the top of the group, and the local water was highly corrosive. There are other posts about M20Ls having an issue with water getting above the seals:

Frequent piston seal replacement

All of which makes me wonder if the seal failure on my machine was not entirely due to the corrosive water, but also in an inherent structural issue with the seal configuration - or that the u cup seals one commonly finds for this model, are in reality a poor fit.

I'm inclined to try the configuration that Kitt used, and am very interested to hear other people's thoughts on this.

Well, Kitt's piston is for an M15, and slightly different than mine. The middle slot has a larger OD than the top or bottom ones. So putting a standard Cimbali u-cup there would not work, as it wouldn't fit in the bore. So I will probably look for a different u-cup that would have the same finished OD upon install as the top and bottom ones, if such a seal exists. It's not an insignificant difference, and I may try using an o-ring if I can't find an appropriate u-cup seal.

grog wrote:It's not an insignificant difference, and I may try using an o-ring if I can't find an appropriate u-cup seal.
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I'm not feeling the o-ring as the solution here, with all respect. In the boutique espresso industry, I'm wagering $1 USD on the proposition there is a u-cup out there. Most likely it will be for a La Spaziale. Ha. Just kidding on the LaSp notion, but who knew that that element is exactly what makes a Club 110V?

I'd take my inside bore gauge to get the ID of the grouphead, then mic the piston O.D., and this distance I'm calling "X".



I will help look - I owe you for the find on the Club 110V heating element.

Yeah, the o-ring might be useless...but certainly there isn't a u-cup that will fill that entire middle void. I have a couple of u cup seals on the way from McMaster, just to see if they work out.

It doesn't appear that any of the people who have posted about this 'water getting past the seals after a few months' issue have been active on HB for a few years. Would love to find out what seals they used, was their water a factor, etc.

First group is back together (although not bolted on to the bore in this photo). My compression jig worked a treat, although it's slower going than I thought to get the springs compressed.

The seal failure issue comes up on multiple threads (including Kaffee Netz, which has multiple restoration threads for this machine). I'm sure Rich is correct that this is much less a corrosive water issue and more about the seals failing eventually due to heat. What is odd to me, is that this doesn't seem to be an issue with other commercial levers - even though silicone seals are a much more recent arrival to the lever group world. I wonder if the Cimbali seals in particular are made from a lower quality material than as is supplied with most lever groups?

I have some of Paul's silicone seals on the way, but they have a smaller ID than the stock Cimbali seals. I'll give it a go at shimming with PTFE tape and see where that gets me. I have silicone o-rings and EPDM u-cups that fit the middle 'slot' perfectly, both ID and OD. My harebrained idea is that the silicone o-rings will keep the u-cup in place, instead of allowing it to move up and down in that large middle slot. My effort is to emulate the older style piston, which had the more standard 3 seal setup.

What I'll probably do is set up one group with a Cafelat (shimmed) seal on top, empty middle slot as per spec, and the spec bottom stiff seal. Then the other group I'll use the standard EPDM Cimbali seal on top, the middle slot will have my wacky stack of a thin EPDM U-cup with three thin silicone o-rings under that, and then the spec stiff seal at the bottom. Will add photos when everything is installed on the pistons. I'll use each group such that the number of shots on them is equal, and see what holds up better after a few months. The good news is that changing seals on this is pretty straightforward, since you can pull the whole assembly out from the top without having to tension/de-tension the spring. You just remove the bolts holding the aluminum spring surround and it all pulls right out.

After being out of town for most of July, I finally had some time to work on this again. I have Cafelat silicone seals, but they have a 2.5mm smaller ID than the OEM Cimbali seals. So I found some high temp PTFE tape and shimmed the piston with that. Then I went ahead with my wacky middle stack of 3 silicone o-rings and one Buna u-cup on top of that:



The Cafelat seals flare out quite a bit more than the Cimbali ones, despite being massively easier to install due to being much softer. Luckily TSE in Austria, which has quite a few obscure parts for this machine, also has a tool to facilitate inserting the piston into the bore without damaging the seals:

I suspect the middle stack will not really be necessary and the real issue will be if the tape shim is adequate, as the Cafelat seals aren't going to fail due to heat. But the middle stack also seems unlikely to do any harm, so I'll give it a go. In the above photos I've not yet placed the stiff bottom seal, as I need to put the piston,
springs, and surround in my compression jig in order to get the lever attached to the piston rod.

At this point I just need to get the second group back together, plumb it in and start pressure testing.

Got the second group together and back in the bore. Compressing these double spring groups is tedious but I prefer to do this the safe way.