When I started with the CMA group, I heard somewhere that every six months, the piston seals should be changed. How often would you suggest they be changed?

One of my groups seemed to work well, but I took out the piston/spring assembly and learned that I had the seals oriented exactly in reverse of correct. There was some moisture about the brew chamber, but relatively little. I replaced the seals in correct orientation. It worked well but there were occasional knocks during late phases of extraction from that group which suggested to me that a seal was allowing intermittent pressure release.Now that group has failed, obviously a piston seal has slipped and the lever will not move smoothly. Should I expect that new seals will resolve the problem or should I also change out the seals between the group brass chrome lined insert as well?

Any comments would be appreciated, including observations about seal failures/clues/replacement periodicity related to other lever groups. Thanks!

Chert wrote:When I started with the CMA group, I heard somewhere that every six months, the piston seals should be changed. How often would you suggest they be changed?

About 3-6 months, depends on your usage.

Chert wrote:One of my groups seemed to work well, but I took out the piston/spring assembly and learned that I had the seals oriented exactly in reverse of correct. There was some moisture about the brew chamber, but relatively little.

Brew chamber = spring chamber? then the spring, if not made of stainless, might got rust. it's better to change the spring as the part is available widely.

Chert wrote:I replaced the seals in correct orientation. It worked well but there were occasional knocks during late phases of extraction from that group which suggested to me that a seal was allowing intermittent pressure release.Now that group has failed, obviously a piston seal has slipped and the lever will not move smoothly. Should I expect that new seals will resolve the problem or should I also change out the seals between the group brass chrome lined insert as well?

I think the seals are dead. Changing the new seals with correct orientation and right amount of lube will make it good for work again, given that the inside chamber is still in good shape. It is also a good idea to lube the seal when you notice the lever doesn't move back smoothly.

I ordered a new set of seals and stopped using that group. I removed the piston and the seals were still well seated; the lower one looked a bit flat. I replaced the seals, relubed, replaced the piston. When the machine came to pressure water welled up within the group and the piston did not move smoothly. So I powered off, removed the piston, removed the group and took out the sleeve. All the seals appear in good shape, in proper position, and lubed. I am stymied.

Is this the v down up down correct orientation of the seals?

Leaks out the top can only be the upper piston gasket or the top o ring in the sleeve. The knocking may be spring knock usually remedied by some lube on the ends of the spring (dow 111) or possibly some alignment issue with the bearings on the top or something in the upper assembly to make to rod be a bit crooked.

That makes sense. I went back and looked again at the dismantled group. The sleeve and bell look good. The upper piston seal was rolled a bit in position, maybe it shifted when I first replaced it and that's why the leak. I'll put it together again but if it fails, I've got the sleeve and bell gaskets on order.

Just an update: I put it back together. Lever action is not as smooth as the other group, which is completely smooth. I think the knuckle is worn somehow so that there is some play with the lever in the up position. Hopefully when I test it and run it again in a few weeks it won't leak this time.

I couldn't wait, and necessity was the mother of persistence since the chrome peacock's plastic piston broke making espresso at home impossible without the CMA beast. (Decent shots today from the good group) There was repeat failure of the stiff group. I removed the piston and examined the inner sleeve - nice and smooth. I can easily slide the group without play as I remove it. But using the lever there is resistance and the piston actually catches on something on the way down. (Boy did that ruin the shot, but no leaks; seals are good.) I have spare parts which I haven't used because of some corrosion. Here is a picture of a knuckle and upper group assembly which only has minimal play (eliminated with the rear bumper in place).



Here is the defective group with a bottle cap and a small pair of scissors in the space where the rear bumper fits. With the bumper in place and the group in the bell, there is app 2 mm play with the lever in the up position.



So I will change out that knuckle and possibly the upper assembly and see if the problem is solved.

(Please excuse the lousy photographic effort; I do have plans to show eventually the completed beast in full with good lighting etc.)

Thanks to Orphan Espresso for the suggestions posted above.

It worked! I changed the knuckle out and they are both now smooth.