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Oscar rebuild and modification

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  • #31
    Re: Oscar rebuild and modification

    Nice solution, too.

    Yes, same experience here, just a small flush and you get 94-95°C shots. A little more and you can drop the temp to 92-93, then 90-91 etc.

    This second Oscar Ive restored I let the OPV (opening around 10 bar) right there where the neplax valve is (in fact, this is the old neplax valve Simonelli used). So a little bit of hot water is tossed out, but Ive measured the group using a Scace and seems to be stable. Maybe this can help specially very slow ristrettos shots, where the HX tends to overheat with a slower flow (OPV before HX or no OPV).

    I have to make some videos before I sell it...

    Márcio.

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    • #32
      Re: Oscar rebuild and modification

      Thanks Kevin and Marcio,
      Wha pressure do you have your boilers set to? Marcio I think I remember you said yours ranges between 1.4 and 1.2, is that right? What about you Kevin?
      Id love to get hold of a scace to check the temp, but Im not sure anyone would lend me one!

      Comment


      • #33
        Re: Oscar rebuild and modification

        Ok - what the heck.
        My wife bought me a Pullman barista tamper for Christmas (score!), pulled 1 shot with it Christmas day and it was ok, similar to my video with the VST. Since then though, totally different story.
        Yesterday and today my pours have been super super thin, watery and gross - similar to before doing the mods. Same beans, same machine, same grinder, same dose and grind setting, only change was the new tamper. Tried slight changes in dose and grind to see if that made a difference, only difference was how long it took for the watery grossness to come out. Tried adjusting flush amount to alter the temp of the water coming through... again, no improvement.
        What on earth could be causing this?
        Ive had it for trying today - Ill come back tomorrow and take a vid and post if its still happening.
        Grrrrr!

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        • #34
          Re: Oscar rebuild and modification

          Heres a video taken this afternoon after a few bum shots. I seriously dont know whats going on. Ive done the 5c test and thats fine, I seriously dont think Im doing anything differently to what I was doing 2 days ago - except using the new Pullman tamper. I even tried the old stock plastic crappy thing I was using before and it made little difference.
          Take a look and give me your thoughts - Im using the 18g VST as in the video above.
          http://youtu.be/Lz6DfTUIn9Q

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          • #35
            Re: Oscar rebuild and modification

            Originally posted by 39323E362023313632203F362A530 link=1320798434/33#33 date=1324975864
            Heres a video taken this afternoon after a few bum shots. I seriously dont know whats going on. Ive done the 5c test and thats fine, I seriously dont think Im doing anything differently to what I was doing 2 days ago - except using the new Pullman tamper. I even tried the old stock plastic crappy thing I was using before and it made little difference.
            Take a look and give me your thoughts - Im using the 18g VST as in the video above.
            http://youtu.be/Lz6DfTUIn9Q
            Looks like youve got channelling and not fine enough grind to me, You say you havent changed the beans, grind settings, or any other things? how odd

            Have you tried tightening up the grind a bit?

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            • #36
              Re: Oscar rebuild and modification

              Yeah if I tighten up the grind a bit it does the same thing, just a bit slower...

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              • #37
                Re: Oscar rebuild and modification

                wow thats chanelling alright! Ive seen that before with my el-cheapo grinder - thermoblock combo.

                I doubt your grinder is the issue, but you never know - can you borrow one, or take yours to a shop and try it on their machine?

                What I think _may_ be more likely is the pressure - its possibly too high. I had a quick scan - did you say you moved the OPV from the group to closer to the pump? That would change the pressure at the group from what it used to be, plus all the plumbing changes you may have made. I highly suggest getting hold of Gregs gauge. The OPV could also be fautly, but Im just guessing. Best bet is to measure or were all guessing why!

                HTH

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                • #38
                  Re: Oscar rebuild and modification

                  Originally posted by 2328242C3A392B2C283A252C30490 link=1320798434/33#33 date=1324975864
                  Heres a video taken this afternoon after a few bum shots. I seriously dont know whats going on. Ive done the 5c test and thats fine, I seriously dont think Im doing anything differently to what I was doing 2 days ago - except using the new Pullman tamper. I even tried the old stock plastic crappy thing I was using before and it made little difference.
                  Take a look and give me your thoughts - Im using the 18g VST as in the video above.
                  http://youtu.be/Lz6DfTUIn9Q
                  Hmmm James - you have mega channelling Id say. Can you see holes in the puck?

                  I dont know the exact OPV youve fitted, but I doubt it has altered pressure - it looks like one of those that you have to screw to adjust. I cant see that style of OPV working its way tighter..

                  Given that there is nothing much to adjust in an Oscar, and with the mods youve made there still isnt much to adjust - Id suggest the same as the others - grind, distribution or dose.

                  Maybe the humidity has shifted a tad and youve got a bit of clumping now? My personal attack would be to manually distribute using a fine steel thing - like a fat needle or something, level, tamp and try. You definitely have channelling around the edge at the start (and then all over). Even if Oscar was way over/under pressure - it shouldnt channel like that. Assuming the extraction is even but fast then the usual grind adjustment should fix it..

                  The next thing Id check is the dose. I ended up using a volumetric dose in Oscar and Ive just weighed the shot glass full of beans - 19.16g my scales tell me. But since you had excellent results with 18g, I dont know if updosing will fix it..

                  Then Id sort the pressure and temperature. If you were in Adelaide Id come round with the gauges

                  Just so you dont feel so alone/frustrated - I had a very similar experience on Christmas day. Shots went to /dev/hell. It turned out to be distribution. Just distribution. No other changes other than the needle trick. I put it down to having the windows open in the kitchen (while obscenely large quantities of Turkey cooked). As soon as I did the manual distribution thing, all shots were good. I havent done the manual distribution for quite a while and I did waste a fair bit of coffee trying to sort it out - the manual/needle thing is this: http://www.home-barista.com/weiss-di...que-steps.html.

                  Let us know!! My Oscar is currently in bits having surgery!!

                  /Kevin

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                  • #39
                    Re: Oscar rebuild and modification

                    Originally posted by 7170773A0 link=1320798434/37#37 date=1325055319
                    I dont know the exact OPV youve fitted, but I doubt it has altered pressure
                    The pressure at the OPV will be the same, but the pressure at the group will be different if the OPV has moved substantially.

                    Originally posted by 7170773A0 link=1320798434/37#37 date=1325055319
                    Shots went to /dev/hell
                    a fellow nix-user eh? Greets!

                    Comment


                    • #40
                      Re: Oscar rebuild and modification

                      Originally posted by 222A22252F294B0 link=1320798434/38#38 date=1325116016
                      The pressure at the OPV will be the same, but the pressure at the group will be different if the OPV has moved substantially.
                      No - what I meant was that since it was OK on day n, then the chances of it having changed pressure on day n+1 is basically nil. While there is a small chance vibrations might change the setting, the reality is that Oscar is unlikely to do so to any great extent..

                      Originally posted by 222A22252F294B0 link=1320798434/38#38 date=1325116016
                      a fellow nix-user eh? Greets!
                      Since 1979, Im afraid... with a punch-tape dump of an RK-05 disk from one Dennis Richie..

                      /Kevin

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                      • #41
                        Re: Oscar rebuild and modification

                        Originally posted by 6766612C0 link=1320798434/39#39 date=1325121264
                        No - what I meant was that since it was OK on day n, then the chances of it having changed pressure on day n+1 is basically nil.
                        agreed
                        While there is a small chance vibrations might change the setting, the reality is that Oscar is unlikely to do so to any great extent..
                        agreed again, but when I say "if the OPV has moved" I mean its location has been moved. Moving the location of the OPV in the plumbing system will change the pressure at the end, even if the OPV setting is still the same - is that what you thought I meant you said I thunk?

                        Originally posted by 6766612C0 link=1320798434/39#39 date=1325121264
                        with a punch-tape dump of an RK-05 disk from one Dennis Richie..
                        Were not worthy 8-) Still have it? It was so much more fun when you had to get manual patches on disk to recompile your kernel just to install and get to the command line... And that was only about 96 when I started...

                        Comment


                        • #42
                          Re: Oscar rebuild and modification

                          Originally posted by 303830373D3B590 link=1320798434/40#40 date=1325127897
                          agreed again, but when I say "if the OPV has moved" I mean its location has been moved.  Moving the location of the OPV in the plumbing system will change the pressure at the end, even if the OPV setting is still the same - is that what you thought I meant you said I thunk? 
                          The standard Oscar doesnt actually have an OPV - in the sense of something that pegs out the pressure at about 9bar. The OPV in the standard Oscar is there to prevent the HX loop busting - it opens at 16bar or so. What James has done is to sensibly add an OPV (as we would know it) essentially on the pump outlet. My point was that it worked fine then it didnt - and I dont think the OPV is a factor in that. The "new" OPV hasnt been moved between the two experiments..

                          Likewise the temperature - the standard Oscar runs quite hot and needs bulk flushing to get back to sane grouphead temperatures.. People (including NS) have determined that a 3.2mm and 3mm restriction on the inlet/outlet points of the thermosyphon loop give about the right steady state. My experience also backs that up. If we assume the boiler is running at about the right pressure (there is no gauge, so I have no idea what actual pressure is in there in mine...) - then the temperature of the group and the brew water should remain within sensible bounds.

                          So it isnt likely to be the temperature either

                          Which only leaves - the grind/dose/distribution/tamp.

                          Having said that - and trying to help debug things remotely aint easy or even necessarily helpful - actually measuring some things would definitively eliminate issues!

                          Originally posted by 303830373D3B590 link=1320798434/40#40 date=1325127897
                          Still have it? It was so much more fun when you had to get manual patches on disk to recompile your kernel just to install and get to the command line... And that was only about 96 when I started...
                          Have a souvenir piece : Dont have an ASR-33 teletype to read it on, or a PDP-11 to run it on though! Dennis was a really nice guy and we all owe a huge debt to him and Ken..

                          /Kevin

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                          • #43
                            Re: Oscar rebuild and modification

                            Hi, there!

                            About the bad shot, I would bet in the grind... Im just testing Oscar again, as I finally got a new boiler pressure gauge and installed it.

                            I dont distribute/level, just grind the coffee using the Vario Home bin and pour it over the basket using the OE rim. In general I get very nice shots. I remember getting bad shots like that with bad grinder or beans.

                            BTW, the boiler pressure is around 1.2-1.3. Im using a PID controller, so I let the SV at 121°C. If I set to 122°C the pressure goes to 1.3 bar and the recovery time is shorter, but the flush get longer if the machine is idle.

                            One interesting experiment today - I turn the controller off by entering its setup menu right before the shot and I get around 4°C temperature drop using a Scace. Please note that my OPV is after the HX. So, a simple switch to turn the heat element off (or some kind of relay during the shot) could help with the temperature during very slow ristrettos. Or, if anyone care to experiment, it can give a different temp profile to taste! YMMV considering OPV placement.

                            Márcio.

                            Comment


                            • #44
                              Re: Oscar rebuild and modification

                              Thanks for all the thoughts and advice, I ran out of coffee so havent had a change to try again.
                              I did, on my last few grams, try my Nemox Lux which I retrieved from a mate for the test. It did the same thing - started extracting around the edge of the basket during pre-infusion then dumped thin blonde water into the cup at a rapid rate.
                              I have read on HB about someone with channelling issues on thier Electra A3, and when he installed a 0.6mm jet (I think in the group where the brew water exits for extraction) to get his free flow to 90ml in 10 seconds. Is the group head flow supposed to be around that? I think my flow is much higher, so Im toying with adding a little jet resrictor somewhere on the cold side to get it down to that. Anyone have thoughts/ experience with that?

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                              • #45
                                Re: Oscar rebuild and modification

                                Well James - I keep coming back to the fact it worked fine one day and then fell off  :-[  Plus I got very decent shots out of mine!

                                So Im still thinking it is a grind/distribution/tamp issue.  Particularly since you get the nice start around the edge and then it all turns to crap.. 

                                You have the system set to give 9 bar (or so).  The maximum pressure youll get is the pressure set by the OPV.  The flow will be determined by the grind/distibution/tamp.  Too hard/fine and youll get stuff all flow (but at 9 bar!) and too coarse youll get a gusher (at less than 9 bar!).

                                You seem to have the in-between - a good start and then a gusher, which seems to (logically, to me anyway  :-?) point to everything being OK and then some failure of the puck.  Now, it could also be because the water distribution isnt working right and you have a jet being forced into the centre of the puck, but I dont think so.  The NS distribution disks seem a bit better than that.

                                Still putting my quids on the table on the G/D/T solution!!

                                Happy new year!

                                /Kevin

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