La Cimbali M20 Eleva rebuild - Page 7

#61: Post by **Jake_G** » August 26th, 2018, 12:08 am

Whoo hoo!

Nice work. Can't wait to see how it performs.

Cheers!

- Jake

August 26th, 2018, 1:23 pm

First shot attempt was a gusher. This guy requires a much finer grind than my small home levers.

But it passed the pressure test. All the new gaskets are holding. The boiler comes to temp very quickly, perhaps 15 minutes or even less. Getting the massive groups up to temp takes a bit longer of course.

I did a tightness check with it at temp and will do so again once it cools down. One of the steam arms has a slow leak so I'll deal with that next, but that's an easy, quick job.

August 28th, 2018, 9:45 am

This morning, I finally got the grind dialed in. The mouthfeel on the shots from this machine is very different from anything I've experienced on any of my home levers. It's somehow thicker and softer at the same time. It's weird, but plush is the word that comes to mind.

I was working with one coffee I know well (Lusso's Gran Miscela Carmo) and a Kenyan from Olympia that I know less well. It has proven difficult to pull as espresso across all of my machines. I'm down to the last 18-20 g and this shot on the M20 was easily the best I've pulled. The flavor separation is what I would expect from a spring lever, but more pronounced.

I had thought my basket prep game was getting pretty solid, but working with 58mm baskets is a bit different than 49mm. It will be fun to further refine those skills and establish a new work flow.

Thanks to all who leant their expertise and patience on the various issues I can into on this rebuild. All that's left now is to put all the panels back on!

#64: Post by **drgary** » August 28th, 2018, 4:45 pm

Congratulations, Greg! Your experience with this commercial lever reminds me of a post Doug Garrott made long ago, when I was first blown away by my first shots on a Conti Prestina commercial lever.

orphanespresso wrote:Gary....over on the restoration thread I actually did laugh out loud when you began to experience some espresso from your new commercial group for the first time...HA! I seem to recall a conversation with you before you bought it (for the sum of 300 bucks or so) warning you that once you tried a commercial lever that it would ruin you for the smaller home machines....and now even your sweet wife is clearing counter space!!

So yeah I can now say I TOLD YOU SO!!

But to the point, you are going to be able to see some design quirks on the Prestina that are not shared on other commercial groups...but a lot of this may have to do with Conti-specific concepts....short(ish) lever plus strong spring using the linkages for force multiplication and piston centering...that odd choke down at the end of the piston effectively reducing the piston bore then expanding the diameter again in the filter basket....I am sure you will come up with a few more concepts unique to the Prestina...but to comment on your question..yes. I do think that by and large all commercial lever groups/machines produce a very similar shot as far as consistency and quality.

They all have some little or large design idea that sets them apart...some of these ideas are in the user preference area and some are obviously patent avoiders, but the espresso turns out to be very similar since the groups are by and large the same. I like Faema groups becauase they can be so readily updosed and have a very simple seal and piston alignment system (also they look like I expect a group to look). Even more beautiful are the Conti Empress groups or the Aurora groups in a more modern era. The Gaggia Italy groups are so machine age that they break your heart but always worry me due to the gearing on the lever and rod...the rod can be replaced but not the lever. The wide format machines are real barista friendly with a great workspace (Bosco, Gaggia both spain and Italy, Faema multi groups) which is wide and roomy. Thermosiphons, direct bolt on dippers, HX setups etc....all produce by and large a very similar shot as far as the quality that you are now experiencing, though on each and every machine one has to learn what the machine likes to do and what it simply will not do (La San Marco is very dose specific, but comes with 6 different basket sizes to very dose).

August 31st, 2018, 5:20 pm

Love that quote, Gary.

I decided to leave the machine on overnight for the first time, to see the difference in the shots with the groups fully temp stabilized. It gets to full boiler pressure amazingly quickly, and so far I had just been firing it up and doing a couple of group flushes to get things moving. None of the shots had showed poorly due to low temps. A couple of observations: the boiler fill level was higher this morning than last night, so at some point the float sank enough that the solenoid kicked on. At least I know it's all working properly. Also, the shots were, unsurprisingly, definitely warmer but still not 'too hot'. As many others have attested, the thermal stability of these massive old lever groups is really something to behold. It's nice that all of the seals are available in teflon now, so you get a heat break between the group and the boiler as an added bonus (this machine is a simple dipper).

I'm currently pulling a natural Ethiopian from Sweet Bloom, and it's fantastic. Blends on the M20 have been tasty, but nothing transformative. But SOs have been quite eye-opening on the larger group.

So far I'm not noticing much difference between my two groups, if any. One has the stock setup with an OEM La Cimbali seal on top, the middle blank, and the rigid 'seal' on the bottom of the piston. The other is pictured earlier in the thread and has a Cafelat silicon seal on top, a McMaster Carr-sourced Buna u-cup in the middle supported by a silicon o-ring stack, and the OEM rigid seal on the bottom. It may be that the key difference is seal longevity with the silicon setup.

I am also using a hodgepodge of IMS baskets of various sizes in terms of gram capacity, although I'm using an 18g dose in everything. Certainly I'll need to settle on one basket to do comparisons between the two groups.

I've been following the Londinium piston mod thread over in the Levers forum, and between that and Dominico's classic thread from a couple years back about pressure profiling on spring levers, I'll be removing the inner spring on the stock setup group as another comparison between setups.

September 9th, 2018, 11:52 am

I've settled on the '14g' IMS basket as the clear favorite. An 18g dose fits easily. This is the basket where the lever catches the soonest - around 9:30. It has a good flow rate with a traditional espresso blend (currently running Red Bird's standard espresso, an extremely forgiving coffee) as well as SOs. I don't get channeling with this basket either, while the larger baskets (18g and 21g) are more prone to channeling and spritzers. Head space is a clear factor with this machine.

I'll be sourcing some of Espresso Parts' 14g HQ baskets so I have more consistency. The crazy 21g triple basket definitely needs to come out of rotation.

January 18th, 2019, 10:04 am

A quick update - I pulled each lever assembly to check how the two seal configurations were doing. The stock setup looked pristine, but the one with the Cafelat seal was a failure. Extractions are fine on both groups, but my effort to get the Cafelat seal to work via shimming under it with Teflon tape didn't work. Water has clearly been getting above the seal, as evidenced by a bit of rust starting to form on the spring. I'll disassemble that, clean it up with Evapo-Rust (bearing in mind Dr. Pavlis' advice that rust is auto-catalytic and therefore must be completely removed) and reassemble with the stock Cimbali top seal.

#68: Post by **OldNuc** » January 19th, 2019, 9:20 am

Teflon tape is not going to work in that application. You have to find a seal with an inside diameter a bit less than the groove diameter of the piston and with a sealing lip diameter when mounted on the piston that is equal to or very slightly greater than the cylinder bore diameter or it will bypass liquid at low pressures. EPDM and Buna-N are at the limit of there service life temperature range in these machines so have spares on hand as failure rate can be quite high depending on the actual fit.

January 19th, 2019, 1:16 pm

The irony is that I was hoping to get the silicone seal to work so as to avoid the seal failure of the OEM top seal and attendant rust. The OEM seal looked fine and the spring was perfect, while my experimental side had rust.

The Cafelat seal was in perfect condition - I knew going in the ID was not appropriate for the piston and just tried to make it work. To Rich's point, even the high temp Teflon tape I used wasn't up the the task. Shimming not an option in this situation.

May 29th, 2019, 3:44 pm

Pulled the groups for a checkup, and the right hand one (that has always had the stock seal setup with OEM top seal) is leaking steam now. The spring has a tiny bit of rust at the top.

I've got it soaking in EvapoRust and will get it all cleaned up. This is a ridiculous failure rate - basically you would be replacing that top seal at least twice a year, perhaps more. Plus there is the associated PITA of cleaning up the spring each time since the only way you know it's time for a new top seal is finding rust on the spring.

I've found a place in NJ that makes silicone u-cup seals to custom specs. Unfortunately I can't use Paul's excellent silicone seals (which fit Bosco, Londinium, et al) as the ID on my machine's piston is 3mm narrower. The custom seals aren't cheap - $20 per seal - but if I only have to replace them every few years instead of every few months, they will be more cost effective in the long run. Will report back on how successful that is, since they could be a useful supplier for other seals on out of production, vintage machines.