The other day the portafilter of my MCaL popped off mid-brewing, and of course broke the cup. The shower screen came off with it, so I used this opportunity to clean things up and replace the gasket (I had a spare, and it's been at least 2 years since I replaced the last one). Then I brewed another shot and it happened again. Another broken cup. I tried to tighten it stronger the next time, and kept my eye on the portafilter handle while brewing. It still started sliding out so I had to tighten it back. What's going on? I can't find other reports of this issue...

Thanks!

I have had this problem more than once. The first time it happened the cup was broken, and there was coffee and grounds everywhere. The second time it happened I was making a cappuccino and the special stainless pitcher I always use for that purpose got knocked to the floor, with grounds and espresso everywhere.

The problem seems to be from a too slippery seal. The top of the portafilter is narrow, and this may contribute to the problem too. I tried to wash the seal with alcohol the last time I had the thing disassembled, perhaps that helped a little. I also tried to wipe off the top of the portafilter's ridge with alcohol to get rid of any oils. This did not seem to help much, but you could try and see if you should be able to get better results than I did.

Does it still happen to you occasionally, or has either of these remedies solved the problem?

Come to think about it, in both cases it happened to me the the shot took longer than normal because the coffee was ground too fine. It's still a bit odd, because I had shots that took even longer for the same reason, but the portafilter stayed connected (perhaps I should mention that the shots I normally pull take around 25-30 seconds, so the coffee isn't ground too fine).

It has not happened for a while, but I never trust it with my favourite cups. Then I watch it to be sure the portafilter is not turning! I often wipe the top ridge of the portafilter with a paper towel after each use. Perhaps a different type of polymer for the seal would be the best solution?

I am not sure what polymer is used on the stock sealing ring.

This problem keeps happening and is extremely annoying, not to mention dangerous. Any suggestions how to prevent it? Do I need to take the machine to service, or is it something that can be fixed by the user?

Thanks!

One thing I have done that definitely helps, and that is to rub the top of the filter basket with a piece of paper towelling before loading it. The problem seems to stem mostly from the fact that the O ring is slippery and so is the top of the filter basket. I have also found that if I lay a sheet of very fine sand paper on a table and slide the top surface of the filter basket over the fine sand paper it seems to rough up the surface so that it is less slippery. When you service the group also try to avoid getting lubricant on the O ring surface. In fact, I have examined the surface of the top of MCAL filter baskets with a metallurgical microscope before and after sliding them over a sheet of fine sand paper, and the microscopic appearance is very different. Note that the problem is a slipper filter basket, not portafilter!

The O-ring is completely new, so I'd be surprised if it needs to be cleaned already. I haven't cleaned the previous one for years and had no issue (until I eventually did). I thought about roughening up the surface, but it wasn't needed with the previous one, so what's the difference that requires it now? I think it must be some other malfunction. Did I mention the shower-screen pops out too? Maybe that has something to do with it.

The new O ring may contain oily residues that would be slippery. Chemical impurities in monomers end up being "pushed out" during polymerisation so that some new polymeric materials may have a residue on the surface. (A company for which I once consulted had an extreme problem with this, the monomer supplier sold them monomer with substantial concentrations of saturated high molecular weight hydrocarbons that ended up making their product come out as an oily mess!) I would thus expect NEW polymeric products to be more slippery than older ones. I am not sure what polymer they use for these O rings. Most likely impurities would either dissolve in hydrocarbon solvents or 190 proof ethanol. (Everclear at rum shops.) In recent years Coleman fuel has become a very good solvent for things like this because it seems to have little high molecular weight impurities. It is similar to lighter fluid, in fact. If you should have some Coleman fuel or lighter fluid, you might, outside, put a little bit in a ramekin or other small bowl, and immerse the ring in it for a few seconds, and then be sure to wipe it immediately with a paper towel. (Remember this stuff has high vapour pressure, and sparks can ignite it. It is a bad idea to use indoors.) You might do the same thing with 190 proof alcohol. Do not use gasoline because it contains some nasty compounds like toluene and even some benzene. Do not let it stand in the hydrocarbon or alcohol for long, as the solvent molecules will begin to migrate into the polymer, just a few seconds for a rinse.