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DT125R FORUM

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Best piston

Scheduled Pinned Locked Moved Top End
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  • CalumC Calum

    @irongamer727 That new Forged Vertex one I've just got is going to slap like a BIATCH!

    Massive piston to wall clearances.

    It's hard to tell from the finish how decent a piston is, to really appreciate it you have to understand the properties of the alloy they used. This gets above my comprehension level and I leave that to the professionals.

    But in my book, "Tuning For Speed", Irwin explains what type of alloy is best used for each application. And more interestingly, the best places to get such metals. Namely Birmingham England (about 40 minutes drive from me), whilst referencing the company. Bare in mind this chap is from Australia, so the fact he's referencing something from across the globe is pretty impressive.

    Alas, our manufacturing has since long gone. But a good book never the less.

    Irongamer727I Offline
    Irongamer727I Offline
    Irongamer727
    wrote on last edited by
    #16

    @calum why would you want big clearances? I measured the bore and the piston and the diameter was nearly the same. To tight is not good of course but I can't imagine why a performance engine would want big clearances.

    CalumC 1 Reply Last reply
    0
    • Irongamer727I Irongamer727

      @calum why would you want big clearances? I measured the bore and the piston and the diameter was nearly the same. To tight is not good of course but I can't imagine why a performance engine would want big clearances.

      CalumC Offline
      CalumC Offline
      Calum
      wrote on last edited by
      #17

      @irongamer727 It's the thermal co-efficients of forged components which is why there are big piston to wall clearances. Forged components will expand much greater than weaker cast components. Which means the gap will close and it will be fine, but this makes it absolutely paramount that you wait for the engine to get up to operating temperature.

      Same thing as my Starlet.

      Always Originate, Never Pirate!

      Irongamer727I 1 Reply Last reply
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      • CalumC Calum

        @irongamer727 It's the thermal co-efficients of forged components which is why there are big piston to wall clearances. Forged components will expand much greater than weaker cast components. Which means the gap will close and it will be fine, but this makes it absolutely paramount that you wait for the engine to get up to operating temperature.

        Same thing as my Starlet.

        Irongamer727I Offline
        Irongamer727I Offline
        Irongamer727
        wrote on last edited by
        #18

        @calum oh now that you say it I remember.
        I mean I would not be surprised if my previous piston has expanded a bit too much in the cylinder.

        As you can see on the link there is like a mirror finish in the exhaust and inlet side. I don't have a clue where the ticking/rattling sound came from though.

        CalumC 1 Reply Last reply
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        • Glynn123G Offline
          Glynn123G Offline
          Glynn123
          wrote on last edited by
          #19

          My wossner was absolutely silent when I first rebuild the Dt, had a barrel bored to match the piston at the recommended tolerances from wossner. Hundred miles on it started getting rattley, it's now pretty piston slappy at the top end but checked 1000 miles on when headgasket went and piston and ring tolerances were perfect haha, makes great power and starts good so I'm not worried, never heard a good running two stroke any better really, it's when they're silent you need to worry haha.

          1 Reply Last reply
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          • CalumC Calum

            @irongamer727 That new Forged Vertex one I've just got is going to slap like a BIATCH!

            Massive piston to wall clearances.

            It's hard to tell from the finish how decent a piston is, to really appreciate it you have to understand the properties of the alloy they used. This gets above my comprehension level and I leave that to the professionals.

            But in my book, "Tuning For Speed", Irwin explains what type of alloy is best used for each application. And more interestingly, the best places to get such metals. Namely Birmingham England (about 40 minutes drive from me), whilst referencing the company. Bare in mind this chap is from Australia, so the fact he's referencing something from across the globe is pretty impressive.

            Alas, our manufacturing has since long gone. But a good book never the less.

            declanD Offline
            declanD Offline
            declan
            wrote on last edited by
            #20

            @calum only 21 mins from me 😀

            1 Reply Last reply
            0
            • Irongamer727I Irongamer727

              @calum oh now that you say it I remember.
              I mean I would not be surprised if my previous piston has expanded a bit too much in the cylinder.

              As you can see on the link there is like a mirror finish in the exhaust and inlet side. I don't have a clue where the ticking/rattling sound came from though.

              CalumC Offline
              CalumC Offline
              Calum
              wrote on last edited by
              #21

              @irongamer727 Sounds more like glazed bore which is due to incorrect run in procedure.

              I've switched from Wossner now, after PJME have advised they've started manufacturing their stuff in China.

              Now China has some of the worlds foremost engineering plants in the world. It's their QC that lets them down.

              I've now switched.

              Always Originate, Never Pirate!

              Irongamer727I 1 Reply Last reply
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              • CalumC Calum

                @irongamer727 Sounds more like glazed bore which is due to incorrect run in procedure.

                I've switched from Wossner now, after PJME have advised they've started manufacturing their stuff in China.

                Now China has some of the worlds foremost engineering plants in the world. It's their QC that lets them down.

                I've now switched.

                Irongamer727I Offline
                Irongamer727I Offline
                Irongamer727
                wrote on last edited by
                #22

                @calum have a look at the link😛

                1 Reply Last reply
                0
                • CalumC Offline
                  CalumC Offline
                  Calum
                  wrote on last edited by
                  #23

                  Definiteoy got a fueling issue there.

                  Always Originate, Never Pirate!

                  Irongamer727I 1 Reply Last reply
                  0
                  • CalumC Calum

                    Definiteoy got a fueling issue there.

                    Irongamer727I Offline
                    Irongamer727I Offline
                    Irongamer727
                    wrote on last edited by
                    #24

                    @calum is that cylinder scrap? The piston was 58.4 mm. So I guess it is soon no point boring that cylinder? Not that I will use it again.

                    CalumC 1 Reply Last reply
                    0
                    • Irongamer727I Irongamer727

                      @calum is that cylinder scrap? The piston was 58.4 mm. So I guess it is soon no point boring that cylinder? Not that I will use it again.

                      CalumC Offline
                      CalumC Offline
                      Calum
                      wrote on last edited by
                      #25

                      @irongamer727 You can go overbore. Really need to modify the valve when you do. And you can have a new liner put in.

                      Always Originate, Never Pirate!

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