DIY-Olympia Cremina piston rod seal "tool" and Fix

[mogogear]

Ok, this is not fancy but they are available just about everywhere. You can come up with your own interpretation very easily. I had been thinking about this when I saw Bob Craig's post and went "AHAA!"

If tape was too flimsy and prone to it's own difficulties, why not something like a big, really good straw- that could be warmed up just a little with hot water first. Then screwed over the threads of the top of the piston shaft.

So I went to a 7-11 and so forth and found the straws too small. Then I found one of those cheap water "bottles" with the ribbed straws that have a cheap cap on the end. Sorry, I didn't take a picture of the bottle but the straw works perfectly. You can cut it down as desired and then lightly lubed. It is long enough to feed up through the seal with no damage. It screws right onto the threads and right up to the very slight shoulder after the threads that transitions to the final O.D. of the piston shaft.


So take a look and I think the rest is self explanatory:



Here it is screwed into place. The O.D. of the straw is just lightly less than that of the rod, but matches up nicely to the transition area. They should be easy to source.




Now a sufficient piston seal installer is the next challenge!

Is there a small engine piston ring compressor tool that is cheap and available? Those of you that have put pistons in engine block cylinders know what I mean...... a small bore 2 stroke piston tool?

[espressme]

Hi Greg,
With your expertise in the camp stove field perhaps this would appeal.
Why not use the thin sheet metal from a "Oly" can. Overlap the seam and put a screw type hose clamp around it with the mechanism over the overlap. Shrink the end of the assembly to the inner diameter of the cylinder. Make sure the can is well de-burred and lubricated! The metal only makes a smoother transition along the inside of the hose clamp. A sheet of cheap "shim brass" or stainless steel would work as well. For the Enrico I used just the can material and a rubber band to reload the piston. I used a "tin can" on my " '49 Crosley Hotshot."
That is all the commercial shrinkers are. They have a thicker stronger metal because the iron piston rings are harder to compress. Also, the rings themselves are taking out the unevenness of the overlap from the thicker metal.
my 1¢
richard

[wmfamily]

Google for small engine ring compressor. There are several to pop up but the problem is that most will be too large.

What's the diameter of the piston?

John

[mogogear]

Yep Richard,
That was the way I was thinking too- and of course use of an Olympia beer can would be appropriate



Pardon my C.A.D ( camera assisted drawing) attempt. A little emory cloth on the top and bottom edges and fold the edge as show, there will be no sharp vertical edge for the seal to be against. Insert in to the cylinder bore and with a little lube should slide right in.

[Fullsack]

A woman from Oakland, who rebuilt a Cremina, was at my house last weekend. She said, she put the seal and clip on the piston rod first, inserted it into the group and still had enough room to insert the clip compression tool to do its job. A neat trick, if you have the dexterity.

[TUS172]

Mo,
I noted that in your picture the piston rod threads came into a short bevel that transitioned to the full thickness of the rod. My '86 has no such bevel just a 90 degree shoulder that is treacherous to the seal. I was thinking that the next time I have to pull it I would just take it to the shop and bevel a nice shoulder with perhaps a bit more length and less angle after a 'stop' for the nut. Then perhaps the need for jumping through any hoops would be avoided.

[mogogear]

FYI-

While at Home Espresso Repair last week -Will confirmed to me that he had used a fine stone grinder to bevel the shoulder area on the piston rod. He said he has done this for years to keep from damaging the seals. His recommendation "seals" the deal in my humble mind. A easy modification.

Upon checking my two rods on the Cremina girls- one was done and one was not. Bench Grinder ( fine wheel ) and emory cloth made twins of them in no time.

[TUS172]

Well that confirms it... The next time I pull the group head it will be a done deal. Thanks for the update Greg.

[bobcraige]

Actually, this is currently done on new Cremina's at the factory. It needs to be done on a lathe and not free hand as many piston shafts have been ruined this way.

[timo888]

Is this clever device designed to protect the ring comprised of three pieces (a rubber ring, a metal washer, and a circlip) that fits into a cutout at the top of the group bell?

Is that ring meant to prevent rubbing of the shaft against the group? Or is it meant to augment the seal formed by the piston rings?

Regards
Timo

[roadman]

Here's a solution that works well for the 90° shoulder type piston rod. Cut the tip off an unused tube of caulk so that the o.d. of the plastic tip matches that of the piston rod's shoulder. With a small amount of lube on the seal and plastic cone, the seal slips on easily, no muss, no fuss.
Jon

[mogogear]

Roadman -good find- There are many such items that can ease the shoulder of the piston rod pas the seal and prevent damage- that was a good eye on your part. Looks more elegant than my segmented snake.......... and Tim, yes sir- the tube on mine slides up through the installed circlip washer and seal.

[TUS172]

Hey Roadman,
Thank you, it is simple, effective and most of all cost effective (cheap)!

[timo888]

Mighty Casey® U-Seal Tool

I looked around the house for something to help install a u-type piston seal. Don't know how this will work yet-- it is made from a piece of a wiffle-ball bat.

[Fullsack]

The brass washer with the 4 holes that goes between the clip and the piston rod seal was corroded and in pieces inside the '86 Cremina grouphead. I haven't been able to find a replacement washer. Can anyone think of a downside to operating the Cremina without this washer?

[bobcraige]

The brass washer with the 4 holes that goes between the clip and the piston rod seal was corroded and in pieces inside the '86 Cremina grouphead. I haven't been able to find a replacement washer. Can anyone think of a downside to operating the Cremina without this washer?

Yes!

[timo888]

The brass washer with the 4 holes that goes between the clip and the piston rod seal was corroded and in pieces inside the '86 Cremina grouphead. I haven't been able to find a replacement washer. Can anyone think of a downside to operating the Cremina without this washer?

Does this part (brass washer) appear on the Cremina 67 parts diagram at the Olympia website? All I see are two parts #42 and #43, a non-descript "ring" and 20mm circlip, respectively.

On the other hand, on the diagram that accompanied the complete machine gasket set that I ordered last year, there appear three parts, #12, #13, and #14, respectively, the circlip, what looks to be a metal washer, and the rubber ring. However, no metal washer was included in the set I was sent.

I don't know what to conclude from these discrepancies -- hopefully that the metal washer is not critical.

Regards
Timo

[mogogear]

A standard brass washer of equal thickness would be easy to drill 4 quarter placed holes in if one is not. The holes allow pressure to distribute under the fullness of the underside of the v-seal. Over time with I suspect pressure can be directed solely at the edges of the lip of the seal and not keep pressure on the outer shoulder of the seal . It immolates the same action from the 4 holes around the top and bottom of the piston faces. Keeps good equal distribution of force in play.

I have great respect for seemingly minute design details in this machine - I would make sure they are in your washer. Let me know if you need the hole size since my machines are apart.

[Fullsack]

Just used the Roadman, (it's so brillant, it deserves a name), to install the piston. The process was seamless, no seal damage. This was the only part of working on a Cremina I use to dread. Thanks Roadman.


The Roadman

[Fullsack]

The replacement black circlip I used when I rebuilt the group last month, (the one that came with the complete seal and gasket kit), was already rusted when I took apart the group today. I don't know if the black clip rusts and the original chrome one doesn't or maybe it should have been installed with the smooth surface facing the 4 holed washer, (the rust was between the clip and the brass washer). Regardless, I put the original chrome one back, smooth surface facing the washer this time.