| Home > TECH TIPS > Olympia Cremina 2002 Piston Overview
|The Cremina Model 2002 from Olympia-Express incorporated numerous changes from the original format of the machine....many good additions: larger boiler, redesigned pstat, the addition of a manometer, power switch on the frame with fancy pilot light on the front panel, a very nice lever yoke design using cap bolts instead of pins and clips, and most importantly a lot of changes to the group for better performance....largely an attempt to avoid overheating issues as on the older machines. These changes included the addition of a thick Gortex based thermal break at the group to boiler junction and high tech plastic insulation at the siphon tube connection. The redesign of the piston is one of the more significant and problematic of the changes in the machine as they went from a solid one piece piston body using rubber u cup seals to a multi piece piston body and very rigid Trelleborg seals made of Turcon (a relative of teflon). This piston is a chicken and egg concept since to install the rigid Turcon seals the piston has to be a stacked sandwich affair (the seals do not stretch)....the piston is screwed together with a cap bolt through the end of the lower piston face into the rod.
The use of this type of piston/seal assembly is very maintenance friendly as this makes it very simple to change the seals, but the idea of using these seals is that they are rated for extremely high temperature and pressure and in theory would last forever....or at a minimum a very long time in comparison to an EPDM or Viton rubber seal. The rod seal was of the same design and material composition.
This is a view of the multi part piston with seals removed and when assembled the piston appears as such:
Now, we can only speculate (Olympia Express is not big on sending out tech bulletins) but something went wrong with the Turcon seal design after the introduction of this system. Most reports indicate a problem with the rod seal developing a leak as the first indication of failure of these seals. From observation, the seals a quite rigid and prone to marking and it is evident when handling them that if they suffer some blunt force or wear trauma that they get out of shape and do not come back.....very unforgiving I suppose would be the description. But what happened was that Olympia stopped selling replacement seals and when asked for seals they requested that the owner send in the group for "factory installation of new seals" as the only option. This "factory installation" included a $250 "machining charge".
If you examine the piston body it is composed of a brass discs and a central piston like machined disc which holds another high tech plastic spacer ring and when sent to the factory the owner received a completely different piston with no plastic spacer and two standard rubber u cup seals. They basically installed a standard Cremina brass piston (the 2002 piston is about 1mm larger diameter than the older model piston) which has 4 holes on the rim upper and lower to act as u cup expander ports. Again, this is the Model 67 piston format.
We and other tech joints would not touch a model 2002 since there was something very mysterioso going on with it and those Trelleborg seals were, as with many Olympia parts, proprietary, or at least very difficult to find or purchase.....and the fact that it was known that these seals had failed to live up to their potential made it a dicey proposition to take in a machine for repair.
So, we received a "please fix my Cremina" request and what arrives but a Model 2002 and after a lot of self doubt it turns out that the piston can be rebuilt and successfully sealed using some fairly standard EPDM rubber seals that we had all along....a very thin u cup for the rod seal....fits perfectly but is a little tricky to install and two piston u cups that slide right on and work great. WHO KNEW!!!!
We are still in the dark as to why Olympia Express insisted on the remanufacturing of the piston but the stacked piston body makes it very easy to install the seals and as far as we can tell the blow out holes in the piston top and bottom are not critical to performance (La Pavoni does not use these holes on their lever machines) and if needed they could be drilled quite simply.
So there you have it....what seemed complicated turned out to be quite simple...time will tell how this seal solution holds up, but whatever the case as far as longevity, the immediate solution is in hand and we are happy to have brought a little light on the subject.
2002 GROUP/PISTON SEAL REPLACEMENT TIPS
There are two areas of concern when installing the piston seals on the 2002 Cremina...the rod seal and the piston seals. The rod seal is quite thin and can be easily damaged during installation...this is the main concern.
We tried 3 or 4 methods of installing the seals on the 2002 piston and found that the following method works the best:
- Loosen the small set screw (hex head) on the back of the left side of the lever yoke (it is a very small set screw)...remove the top cap nut and jam washer from the rod.
- Remove the rear lever bolt using 5mm allen hex wrench
- Remove the front lever bolt pin using 5mm hex wrench
- Pay VERY close attention, when you remove the yoke - there are Delrin spacer washers on the rear pin, and small brass bearings on each side of the front pin & they must be reinstalled (after cleaning & lubing) when you put the yoke back together.
- Drive the piston downwards using wooden mallet...this will pop off the dispersion screen and group portafilter gasket....you may need to come up with a wooden dowel to finish driving out the piston .
- Continue driving the piston downwards (this is all taking place with the group still bolted on the machine) until it protrudes from the bottom of the bell.....the 2002 and 2008 groups are machined with very close tolerances and all of these procedures will feel VERY tight.
- When you have the piston out, unscrew the allen head screw on the face of the piston by holding the piston rod still with a screwdriver through the lever pin hole and turning the bolt on the face of the piston with an allen wrench.
- Remove the clip which holds the rod seal in place and take out the washer and old seal.
- Clean all the parts.
- Remove the group from the machine - you will reassemble with the group OFF the machine. The group to boiler seal is reusable.
- Now that you have the group broken down, inspect the cylinder for any scale or crud lines that have formed around the cylinder....wipe/hone the cylinder clean with 400 grit wet/dry abrasive paper.
- To assemble....believe me, we have a big supply of seals and went through at least 5 rod seals before we got it right........with the piston all broken down and only a naked piston rod, lube and slide the rod seal in the proper orientation onto the rod...carefully working it past the machined indentation at the lever pin hole until it is BELOW the pin hole.
- Insert the rod, containing the seal, into the group until the seal seats in the socket at the top of the group....you may have to coax it with a probe. Slide the rod seal washer over the rod and into the rod seal sump at the top of the group. Install the clip. This is tricky since the rod is in the way, but it is the safest way to install the rod seal.
- Push the piston rod back down so you can install the piston and seals on the end of the rod.
- Install the top piston plate and o ring (your old one should still be good).
- Install the piston seals on the center section of the piston
- Work the center section of the piston (with seals installed) on to the end of the piston rod.....work the lip of the top seal into the cylinder with some sort of blunt probe as you push the piston body in to the cylinder....you are more or less shoehorning the top seal into the cylinder as you push....by the way, all of this is being done with the group removed from the machine at this point.
- Once the top seal has been shoehorned in to the cylinder the rest will just POP in
- Install the lower plate of the piston and finger tighten the hex screw on the face of the piston.
- I did not mention lubrication...silly me.....be sure to lubricate the cylinder walls and the rod and the spacer ring and all the seals with Dow 111....THAT would have been a mistake to leave out of this....
- Install the lever yoke with pin/bolts in the reverse of removing them.
- Once you have the pin/bolts in place then return to the piston face and REALLY tighten the allen hex bolt on the face....do not use threadlock, just hammer that bolt down. Do not use a hammer....I was speaking metaphorically.
- Once the piston is tight and the group is all lubed up, put the clean dispersion screen in place and follow with the portafilter gasket.......this can get a bit tricky as well, due to the tolerances, but you will be able to get about 2/3 of the gasket easily in the track but the last 1/3 will give you trouble and you have to take a thin screwdriver and push inwards against the outer edge of the gasket, using the group bell as a fulcrum, at the same time pushing downward with a screwdriver or other blunt force instrument, on the face of the gasket and it will eventually work in to the slot. Seat the gasket with the portafilter.
- Of course, I probably left out a few dozen details such as turn off the machine and drain the water and things that you should think of yourself, but the main thing is to PUT THE ROD WASHER ON THE NAKED ROD TO INSTALL AND THEN FOLLOW WITH THE PISTON WITH THE ROD SEAL IN PLACE!!!! Otherwise you will likely screw it up. Plan on being a little frustrated on this job since the tolerances are really close and there is very little room for error,
- GOOD LUCK!!!!!