Holding my breath up here Doug. Good news indeed! Are these 'o' rings the same spec as those that you suggest I use?

Do I understand that you used 2 side by side or that you used one in the upper race and one in the lower?

Simon

Now I go to the big book and figure out which O-ring is needed for the piston in question. The eureka moment is that the o ring will work, one per piston race, with a little shimming. I like off the shelf parts, as well as working espresso machines.
I have run the o ring question as replacements for u cups by my most trusted leverhead and he sees no reason why it won't be a reasonable fix. The concern is wear and he suggests giving the cylinder a nice dressing with fine emory cloth or wet and dry sandpaper to make sure it is nice and smooth and to use plenty of Dow 111, which is generally good advice no matter what seal you are using. My test machine is down at present since I took the sight glass apart to clean the gunk out of it and found I have a leaking connection fitting, but the group seems just fine so far.
So, the priciple seems sound, at least it works in practice. Seems to me that the CMC is getting incrementially closer to function, and this o ring solution may just get a lot of old levers back into service at a reasonable cost.

Doug

That means really fine wet/dry paper. 1000grit or finer used wet with water. Be careful not to polish too long in one place as you want a cylinder not a wavy tube. Your local body shop has these papers. A pound of fresh coffee will get you a friend. The papers are about $1 a sheet but you would have to buy a package at a high price.
I have used a brake hone in a low RPM electric drill motor and wrapped the paper around each stone to assure the bore is parallel.
4 ought steel wool (0000) will work but it does leave a bunch of fines in the bore. And there is oil in the stuff to prevent rusting.
Cheers
Richard
PS apply the Dow 111 with a finger tip and wipe the bore afterward lightly with a paper towel leaving a thin film. Coat the rings with Dow just enough to shine them. If a bit of Dow comes out with your first shots, that is fine. Just ridding itself of the excess.

Ok... Now I will get these parts and give it a shot. (that must be THE oldest pun 'round here - sorry)

As a reference for tooling other than machinists, one might find a local jewelers supply. You might find some usable kit. Wool wheels and polishing compound for starters.

So... after a couple of exchanges with Doug from orphanespresso, I had several O rings and a couple of U gaskets in hand and went to work. He also supplied instructions and some very nice 3M adhesive silicone (?).

First I slipped on the U gaskets...
They were tight in the cylinder and did not turn on the piston but after applying Dow 111 the cylinder fit seemed a bit loose. In operation the U cups leaked downwards at 0.2 Bar and by the time the boiler element cut out at 1.25 Bar I had a cup of water out the bottom, 2 - 3 drops out the top. Top stable at 1 drop per motor cycle - bottom did not seal itself after ten cycles so I presumed to quit and try O ring W/ Tape packing.

After some testing I put the lower ring (which went on to EXACT match of outer diameter to the U cup without packing) with 1 wrap of tape with zero stretch and replaced O ring. The upper O ring which seems to bear less load I put the tape on with some 'strech' to reduce the sectional area.

This combination holds easily to 1.25 bar (has bounced to 1.4bar) W/ no seepage.

Success on the gaskets! Thank you Doug!

The motor seems happier now that it used to - but that could be the residue of the Dow 111. The Crema is (after adding thickness to the lower gasket) slightly better that it used to be - but this machine has never supplied much. I should be looking to other ways to improve that I guess, but the nature of this mechanism does not allow for adjusting the 'pull'. I will need to consider this further.

So for anyone interested... I attach a link to a video clip of the little motor that could, kinda...

http://www.youtube.com/watch?v=B-JWq5vfLsc

I rather hate the idea of closing her up again, I have grown fond of the brass uppers and piston rod!

Simon!!!! Yesssss!!!!! Very good news indeed, and am glad you got the Dow 111 instead of the olive oil idea, even extra virgin! I am so pleased that the o-rings are doing the job, and you have seen the logic to it all. Too bad about the u cups but it is tricky to fit those exactly, particularly that double sided w cup, but a very nice chapter to the saga of the CMC machine. Now to get that crema, join the club with dialing in the grind and tamp until it gets better and better, hopefully. Can't judge the performance by those first shots, but just to see it working is a real joy. Congratulations!
Doug

I have been following this thread today with interest. I just returned from my parents' house, and in the basement is the same machine, owned for years by my late uncle. He was always the renaissance man of the family. My dad has been trying to get it back to life, and I could not understand the workings of the machine. Big honking boiler, no pump. My uncle had it plumbed, but has since been cinched shut. Does this CMC machine need to be plumbed? Manual boiler fill? Is it an HX machine? Any input or parts availability in the Toronto area appreciated.