What did you use to lube? And did you lube the seals or also the cylinder, the piston rod and seal and the lever pins? Did you make sure the seals went in smoothly without tearing the edges?

The only other thing I can think of is your spring may be weak and this may show up because the seals are now tighter. A replacement spring is inexpensive. What year is your MCAL? I replaced the old spring, piston and piston rod with the newer versions even though I had a 1989 MCAL. Those changes completely revitalized the machine.

Hmmm...this is an interesting and timely thread! I recently put in new MCAL seals for a friend. The tank was really encrusted with a ton of scale, so I descaled it before changing the seals. It took about 3 boiler fulls of solution to get all the scale out, and when I replaced the seals, lubed up with Dow 111 for all moving parts plus the group cylinder, the pull now has a squeegee-like squeak to it...not the smooth glide it had before.

Stefano said to sand the cylinder but the owner of the mill is OK with the squeak. However, from the sounds of this thread, it doesn't seem that sanding is going to do anything.

I'll be interested in seeing how this thread develops!

One of the problems with the MCAL is that the upper piston seal is in a dry environment. On many other machines there is water and/or water vapour on both sides of the piston. Lately I have been following a different technique for lubrication with the MCAL. After removing the piston assembly and cleaning everything, I try to put a thin film of silicone 111 over the cylinder wall. Then I insert the piston so that just the first seal is in the bore. I generously lubricate the metal between the two seals, and then carefully insert the piston farther so that the second seal enters the bore. I wipe off any silicone 111 that is outside the bore before installing the two securing screws and tightening it down. With plenty of silicone 111 between the seals it stays there for a while and lubricates both the upper and lower one. Water high in chloride, as has been discussed before in HB, can cause pitting on the dry side of the piston because any water that gets there evaporates leaving chloride behind.

A little excess silicone 111 on the top (dry) side is harmless. The same cannot be said for the bottom side, because it can cause problems with the dispersion screen.

^ ^ ^

That's probably the answer. Once again Robert comes through.

Also, generous amounts of Silicone 111 on the UPPER side of the MCAL piston results in more of it being on the cylinder walls at all times, that also provides more protection from pitting and corrosion. I think one should be very "stingy" with the lubricant on the walls before inserting the piston, but generous with it between the two seals, and also some excess above the top seal is good. It is okay to push any excess silicone grease back into the bore just before putting the piston completely in the bore. I did that the last time I did this.

Viscosity of polymers is due to long chains becoming entangled and to inter molecular attraction. The inter molecular attractions are lower in "silicones" than in most other polymers so more of their viscosity is due to chain entanglement. This results in the viscosity of these polymers decreasing much slower with increasing temperature than most other similar materials. That fact and their low toxicity are the reasons they make good lubricants for espresso machines. Also, these materials tend not to cause most O rings and seals to swell much by absorbing lubricant because of insolubility and because of the high molecular weight of "silicones" that are used as greases. (I hate to sound so professorial, but this information may be useful to some.)