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RE: 2 St - Primary Compression Ratio?

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  • Swiss
    Thanks, got in with the Paeroa answer. From: mc-engine@yahoogroups.com [mailto:mc-engine@yahoogroups.com] On Behalf Of Caparo Sent: Wednesday, June 26, 2013
    Message 1 of 24 , Jun 26, 2013
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      Thanks, got in with the Paeroa answer.

       

      From: mc-engine@yahoogroups.com [mailto:mc-engine@yahoogroups.com] On Behalf Of Caparo
      Sent: Wednesday, June 26, 2013 4:03 AM
      To: mc-engine@yahoogroups.com
      Subject: Re: 2 St - Primary Compression Ratio?

       

       

      On Tuesday 25 June 2013 22:57:52 Swiss wrote:

      > Wallace,
      >
      > Tried to register on the Forum but it asks Kiwi questions that I don't know
      > the answer to? Things like City with a soft drink named after it and city
      > that smells of sulfur?
      >
      > Swiss
      >
      >
      Swiss,
      soft drink is paeroa according to Google :-} and yes it is correct.

      --
      TTFN
      Caparo.

    • marshengnz
      Things like City with a soft drink named L&P - Lemon and Paeroa ... Rotorua I even had to do a web search to get the spelling right. We have Jan Theil on the
      Message 2 of 24 , Jun 26, 2013
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        Things like City with a soft drink named

        L&P - Lemon and Paeroa
        > that smells of sulfur?
        Rotorua

        I even had to do a web search to get the spelling right.

        We have Jan Theil on the forum from from Denmark or the Netherlands.

        Cheers Wallace
      • marshengnz
        ... Just been talking about this recently. The flow bench is just a simulation. Think on this. 1 m3 of air weighs 1.2 kg. Now take your intake charge with fuel
        Message 3 of 24 , Jun 26, 2013
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          --- In mc-engine@yahoogroups.com, Ken Augustine <kineticanalysis@...> wrote:
          >
          > I have heard of something similar.  
          >
          > BTW, if you put a complete carb and reed inlet system from a late model 2/S engine on a flow bench then draw with it hard enough to produce the flow that 4/S coefficients dictate to make the power that th test configure is confirmed to make, the reeds hardly open.   Even if you draw on it harder to make say 50% more flow than 4/S coefficients state which might compensate for flow lost out the exhaust port and thus the relatively fuel mileage that 2/S engines yield, the reeds still barely open.   However reeds and cages  always show witness and wear marks which clearly show that the reeds have been contacting their stops at pulsed deflections many times greater than are seen on the steady state flow bench even at flow rates double of what 4/S coefficients indicate.  
          >

          Just been talking about this recently. The flow bench is just a simulation. Think on this.

          1 m3 of air weighs 1.2 kg. Now take your intake charge with fuel and run it at Mach 0.5.

          The reeds hitting the stops now seems possible.

          Cheers Wallace
        • hans_o_man
          Did you measure the squish, means, the clearance between squishband of the head to piston-dome? If you rise it to more than 1,5mm, the engine probably will
          Message 4 of 24 , Jun 26, 2013
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            Did you measure the squish, means, the clearance between squishband of the head to piston-dome? If you rise it to more than 1,5mm, the engine probably will knock.
            Useful literature is Alexander Graham Bells two stroke tuning book.
            You may contact me per email about it...

            Cheers,
            Hans
            --- In mc-engine@yahoogroups.com, Ken Augustine <kineticanalysis@...> wrote:
            >
            > Have you tried using decent gasoline?   Even using 100 low lead avgas can make the difference you need.   Ken A
            >
            >
            >
            >
            > Interesting.  Thanks for this.  Published compression for this engine was 11.4 but it would knock until I lowered to about 10.5.  I'm down to about 9 now and the power feels soft but it still pops.  Interestingly, the new generation engine is published at around 9 also.  Although..... that knock happened in the same exact type of conditions as this pop.  (The pop was also there when it knocked.)
            > >
            > >
            > >
            > >On Mon, Jun 24, 2013 at 11:47 PM, hans_o_man <der_hiha@...> wrote:
            > >
            > >
            > >> 
            > >>Hi there,
            > >>I made following experience: I increased compression ratio on my '86 TY250-Yamaha(trials) by welding and reshaping the combustion chamber to a more "modern" dome-shape. Before cr was around 11:1, now it's about 13:1. That's what modern competition trialsbikes have (so far I could find out..) Now it's popping badly into the exhaust, what makes slow riding with a bit more than idle-gas problematic . I'm still fiddling around with the carb adjustment, but it's difficult to find jets for the 26mm teikei. Possibly I have to change the slide-cut, but for easier bike-handling simplest would be to remount the old low compression head..
            > >>So my 5¢: dont't think about primary compression. I belive you'll find the answer in the secondary ...
            > >>
            > >>Cheers,
            > >>Hans
            > >>
            > >>
            > >
            > >
            > >
            > >
            >
          • Dan McManus
            I have the tuning book. Most of the assemblies have been with a 0.055 squish but it is now up to about .0.082 as I m trying lower compression to see what it
            Message 5 of 24 , Jun 27, 2013
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              I have the tuning book.  Most of the assemblies have been with a 0.055" squish but it is now up to about .0.082 as I'm trying lower compression to see what it does for the popping.  The challenge here is that reducing squish requires removing material in the non squish area to maintain compression.  I don't know how far I can go before hitting the water passage in the head.  I have all ready made it about 0.125" deeper.  Based on all of the input, I have more things to try.  Thanks for everyone's input.
              1. Try best race gas
              2. smaller slide cutaway (I finally found one and have it on order.)
              3. Reduce squish even further - This may require making a head with removable chamber so various chambers shapes/ sizes can be tried easily without cutting into water passage.
              4. Bring primary compression back to OEM spec.  - This is a lot of work and I don't even know if the crank has stuffers.  Most listers do not think this could be the cause.  Plus I ride it every weekend so it means down time.
              5. I would also would like to try a different head pipe but have not found one.  I wonder if there could be a small pocket or protrusion causing some weird aerodynamic/ pressure situation.  (When blocking the air intake in a CA model NT650 exhaust port, the exhaust started to produce a chirping sound like a bird.  The hole had to be plugged down close to the exhaust port to get rid of the chirp.)

              Thanks,


              Dan


              On Wed, Jun 26, 2013 at 10:29 PM, hans_o_man <der_hiha@...> wrote:
               

              Did you measure the squish, means, the clearance between squishband of the head to piston-dome? If you rise it to more than 1,5mm, the engine probably will knock.
              Useful literature is Alexander Graham Bells two stroke tuning book.
              You may contact me per email about it...

              Cheers,
              Hans


              --- In mc-engine@yahoogroups.com, Ken Augustine <kineticanalysis@...> wrote:
              >
              > Have you tried using decent gasoline?   Even using 100 low lead avgas can make the difference you need.   Ken A
              >
              >
              >
              >
              > Interesting.  Thanks for this.  Published compression for this engine was 11.4 but it would knock until I lowered to about 10.5.  I'm down to about 9 now and the power feels soft but it still pops.  Interestingly, the new generation engine is published at around 9 also.  Although..... that knock happened in the same exact type of conditions as this pop.  (The pop was also there when it knocked.)
              > >
              > >
              > >
              > >On Mon, Jun 24, 2013 at 11:47 PM, hans_o_man <der_hiha@...> wrote:
              > >
              > >
              > >> 
              > >>Hi there,
              > >>I made following experience: I increased compression ratio on my '86 TY250-Yamaha(trials) by welding and reshaping the combustion chamber to a more "modern" dome-shape. Before cr was around 11:1, now it's about 13:1. That's what modern competition trialsbikes have (so far I could find out..) Now it's popping badly into the exhaust, what makes slow riding with a bit more than idle-gas problematic . I'm still fiddling around with the carb adjustment, but it's difficult to find jets for the 26mm teikei. Possibly I have to change the slide-cut, but for easier bike-handling simplest would be to remount the old low compression head..
              > >>So my 5¢: dont't think about primary compression. I belive you'll find the answer in the secondary ...
              > >>
              > >>Cheers,
              > >>Hans
              > >>
              > >>
              > >
              > >
              > >
              > >
              >


            • Duane Forth
              On Thu, Jun 27, 2013 at 8:31 AM, Dan McManus wrote: The challenge here is that reducing ... Just spit-balling here... could the piston
              Message 6 of 24 , Jun 27, 2013
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                On Thu, Jun 27, 2013 at 8:31 AM, Dan McManus <dan.mcmanus5@...> wrote:
                The challenge here is that reducing
                > squish requires removing material in the non squish area to maintain
                > compression. I don't know how far I can go before hitting the water passage
                > in the head.

                Just spit-balling here... could the piston crown be dished a bit to
                reduce compression if you tighten the squish up some more?
              • hans_o_man
                ... Keep us informed. I m very interested... :-) ... Smaller cutaway makes mixture rich. I feel, you d need a bigger cutaway. (but it s only a feeling ..) ...
                Message 7 of 24 , Jun 27, 2013
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                  > on all of the input, I have more things to try. Thanks for everyone's
                  > input.
                  Keep us informed. I'm very interested... :-)
                  > 2. smaller slide cutaway (I finally found one and have it on order.)

                  Smaller cutaway makes mixture rich. I feel, you'd need a bigger cutaway. (but it's only a feeling ..)

                  > this could be the cause. Plus I ride it every weekend so it means down
                  > time.
                  Get a spare engine. Best for systematic adjustments/tuning.

                  Cheers and success,
                  Hans
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