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Oscar rebuild and modification

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  • #61
    Re: Oscar rebuild and modification

    Thanks KJM,

    Ive been trying with a VST 18g and a Gaggia 18g basket (which looks very similar to a Synesso ridgeless).

    Just thought Id post an update on the mods. I finally got a pressure gauge courtesy of iaindb (thanks again) which I unblocked from the scale inhibiting it, which I successfully installed and now it works a treat!

    I installed it on the fitting with the pressure stat and boiler safety valve. I needed a 1/8 female to 3/8 male to fit to the pressure gauge, then a 1/8 female to male elbow join to get it onto the t-join with houses the pstat and safety valve. Then carefully cut a hole in the plastic body of the Oscar and had to put a little screw through the back of the body into the side of the pressure gauge housing to hold it stable.

    Having a working pressure gauge is great! Ive set the pstat to run between 1.05 and 1.2 bar, for the moment it seems to work well but will continue to tinker.









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    • #62
      Re: Oscar rebuild and modification

      Lovely work there. The gauge even looks like it should be there..

      Maybe I will whack one in before I sell him :

      Excellent!

      /Kevin

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      • #63
        Re: Oscar rebuild and modification

        Ive heard the polished finish on the VST baskets make it very susceptible to side wall channeling since they have a much smoother finish than other baskets. Have you checked if this still occurs using other baskets?

        http://coffeesnobs.com.au/YaBB.pl?num=1329877036/2

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        • #64
          Re: Oscar rebuild and modification

          THanks mompt. Yeah I seems to get similar behavior from my Synesso basket, but the polished walls on the VST definitely contribute I think - Ill keep playing. I have noticed though that the behavior seems to have gotten a bit better with changing the valve Im using as an OPV for a different one. im going to see if I can get hold of a proper OPV to see if that helps.

          Thanks KJM - Yeah it might increase resale value - Im not too sure!

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          • #65
            Re: Oscar rebuild and modification

            i want one on mine now lol

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            • #66
              Re: Oscar rebuild and modification

              So I want to play around with the size of the thermosyphon restrictors in my group as I have a feeling the water coming out of the group head was still a bit hot with a rising profile. The manufacturers solution for the Musica was to install thermosyphon restrictors in the inlet and outlet of the group - 3.2mm in the group inlet and 3.0 in the group outlet.

              I dont have a scace (obviously) to test temperature at the puck, nor do I even have a multimeter to do a bead probe test. I know that would be helpful (although not perfect), but wifey wont let me get one yet (I want the CS datalogger for roasting as well).

              Marcio said that with 2.5mm restrictors in both inlet and outlet, he got around 90-91, dropping to 89 at 30 seconds. Then after boring them out to 3.2 and 3.0, he got 94/95 with no flush, around 92 with a 3 second flush, and only a slight drop in temperature after 40 seconds (all tested with a scace - see http://www.home-barista.com/espresso-machines/nuova-simonelli-oscar-rebuild-t13832-20.html)
              I installed 3.2 and 3.0 restrictors, but I feel like mine is still not perfect
              (NB this is all with the disclaimer that Im sure my technique plays a factor, and Im trying to minimise its negative effect!)

              So... any ideas on the theory behind the inlet at 3.2 and the outlet at 3.0?
              Why not both the same size?
              What effect does a slightly larger inlet have?
              What effect would a larger outlet have?

              I know that the best people to answer my questions will probably be site sponsors who have done such modifications to imported and hot running machines in their bench tests to get them to a good, predictable and repeatable temperature profile. I also understand that in order to do this, these site sponsors would have spent big money on measurement equipment, spent lots of time on research, and a generally vast experience with coffee and machines. I know that thats why we pay service fees to such site sponsors to make use of their expertise for the betterment of our machines and coffee experience.

              Given all that - I understand Im trying to side-step such service fees in the hope I can play around myself, and get some advice, possibly even from the site sponsors, so I can get my machine running predictably. Therefore I am totally ok if some of the site sponsors reply to my question with "The conclusive answers to your questions are how I get paid, so sorry but I cant tell you"

              Just thought Id ask.

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              • #67
                Re: Oscar rebuild and modification

                hehe! Didnt I just read recently that Atillio used to do this without a scace? So it is possible, if you know what youre doing

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                • #68
                  Re: Oscar rebuild and modification

                  Originally posted by 676F67606A6C0E0 link=1320798434/66#66 date=1332204065
                  hehe! Didnt I just read recently that Atillio used to do this without a scace? So it is possible, if you know what youre doing
                  yep I read that too...
                  2 problems though for me:
                  1) Im not Atillio
                  2) I dont know what Im doing!

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                  • #69
                    Re: Oscar rebuild and modification

                    Just an update for those looking at doing the same sorts of mods.This is what Ive found with the Oscar

                    Pressure
                    Dialling in the pressure to to the right level is very important I found! I was reading on HB that too low pressure increased the liklihood of channelling, and thats what was happening!
                    After dialling in the OPV to 8.5 - 9 bar using Gregs gauge, the channelling has reduced dramatically. Definitely get a gauge and set it properly.

                    Dose
                    The Oscar doesnt like a high dose, or will increase the chances of channelling. In doing the 5c test to find the right dose level, you only want the slightest indentation on the puck, any more than this is too much - even more slight than most people get when doing this test. Even a 10c test and getting a normal to slight indentation is better. This further reduced my channelling.

                    Restrictors
                    After playing around with different sized restricters, I came back to the 3.2 and 3.0. If I had a scace (or imitation scace) I might have been able to get a better idea, but in my case 3.2 and 3.0 restrictors combined with 1.15 at the top cycle of the boiler pressure was the sweet spot. This seemed to produce the most stable temp profile - at least to my unscientific tests. That is, this seemed to produce little to no flash boiling (unless sitting idle for 2 hours or so) and the best tasting coffee.

                    In the end, I dont think the design of the HX is quite as good or the group head as forgiving and holds thermal stability as much as the more expensive HX machines (eg Giotto or VBM). While the Oscar can be tweaked and improved to produce much much better shots than stock with the mods Ive done, (and much much better shots than, for example, a Silvia) doing these mods wont quite give you a half-price Giotto!

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                    • #70
                      Really nice work here. Am just starting down this path with an old Oscar. Who is the Simonelli parts distributor in Australia? A few Google searches have born no fruit for me.

                      Thanks in advance.

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