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  • 2-cycle combustion chamber

    Hey all,

    I have a need to make the combustion chamber
    larger (lower comp) on 2-cycle motors.

    I want to increase the head volume without
    affecting the shape of the chamber. The
    chamber is a dome shape and I need to make
    a cutter (for aluminum) that conforms to
    the origional shape of the dome.

    Any sugestions out there for making a cutter
    like this?

    TIA... MD

  • #2
    if all you want to do is lower the compression ratio add a couple of head gaskets...jim
    ...jim

    Comment


    • #3
      Or a piece of annealed copper the appropriate thickness.
      Lin

      Comment


      • #4
        Thicker gasket is not an option. These
        heads have whats called a squish band.
        (Perhaps I should have mentioned that)

        The squish clearance is critical (.025-
        .035") to engine performance.

        So, I need to make a cutter that conforms
        to the inner dome shape (x).

        GDamn it!


        .../--\
        --/ x \--



        [This message has been edited by maddog (edited 12-04-2004).]

        [This message has been edited by maddog (edited 12-04-2004).]

        [This message has been edited by maddog (edited 12-04-2004).]

        [This message has been edited by maddog (edited 12-04-2004).]

        [This message has been edited by maddog (edited 12-04-2004).]

        [This message has been edited by maddog (edited 12-04-2004).]

        [This message has been edited by maddog (edited 12-04-2004).]

        I hope you can get the idea,,, this POS
        MB won't take my crude graphics without
        f--king them all up.

        [This message has been edited by maddog (edited 12-04-2004).]

        Comment


        • #5
          On my old flh panhead I had all them years.

          I put four extra cylinder base gaskets under it to lower the 11.5:1 factory compression. It sounded like popcorn was poppin in them jugs.

          If your block is a one piece, no help.

          David

          Comment


          • #6
            Raising the cylinder is of no use. It would
            change the port timing for one thing. Not to
            mention screwing up the squish clearance.
            (same as thicker head gaskets, no dice!)

            What I need is to make a cutter that has
            the same shape as the combustion chamber
            dome. Has anyone made custom cutters like
            this?

            Thanks...

            Comment


            • #7
              I mounted head on a faceplate and made up a radius turning attachment to re-cut a chamber. may work for your application

              scott
              "Good judgment comes from experience, and often experience comes from bad judgment" R.M.Brown

              My shop tour www.plastikosmd.com

              Comment


              • #8
                I have re-cut 2-cycle heads on the lathe,using an old spark plug hole as a mandrel. grind a a HSS tool to the contour you need and start with light cuts. Make a bondo squeese of the head before you start, so you have a reference to re-cut your squish band. (wax the chamber, cut a section of thin wood,plastic or metal, close to the shape of the chamber,apply bondo to this edge and squeese into the waxed chambr,allow bondo to kick, Instant template.)You can also adjust compression in a 2-cycle by altering the port timing. (raising the exaust port a milileter or two, this will also enhance performance But If it was me I would add a few Copper gaskets first, to make sure you get the desired results,as the squish,in a low compression 2-stroke are not as critical. Are you trying to increase the RPM of your engine? Reducing compression should help. Trying to get it from detinating? retard the ignition timing,it's qucker than milling the head.

                Comment


                • #9
                  Whats the radius of the chamber. And how deep from the flat surface of the head to the top/inside of the dome?

                  Don't know how much material you want to remove but consider sanding it off.

                  You could make a dome out of wood (oak) or hard rubber the same shape as yer head then mount the dome to a shaft that fits your drill press or mill.

                  Clamp the head down, chamber up. Use some powdered abrasive in the chamber and spin the dome shape into the chamber. Would be very slow but doable.

                  Use oil to make a slurry from the abrasive.

                  If you could locate a grinding stone as large as the chamber you could form it to the correct shape then use the drill press/mill to turn it?

                  I have some large grinding cups for concrete that would work, check that avenue.
                  JRouche
                  My old yahoo group. Bridgeport Mill Group

                  https://groups.yahoo.com/neo/groups/...port_mill/info

                  Comment


                  • #10
                    Maddog, do I sense a turbocharger. If so I am planning on putting one on a 2 cyl 2stroke Polaris 700 and we should talk.
                    As far as a cutter that big it would most likely chatter real bad. I would make a template of how you want the radius of the pocket and squish and do it with a normal tool. Or cnc mill the chamber.
                    Stephen

                    Comment


                    • #11
                      Yeah, my cnc mill got ran about five minutes this week. I got the huge indexer on it now. (for my harley wheel) My back is throbbing so it still ain't gonna see no action.

                      Take the digitizing probe, scan into machine. Raise table cut old pattern out. Same pattern just deeper.

                      There you are.

                      What time should I expect you? Are you bringing the beer? Actually the probe is apart, but I do have one.

                      David

                      Comment


                      • #12
                        I have a video tape showing a machinist milling a convex dome using a flycutter on a vertcal milling machine. The head of the mill was set at an angle, and the work was on a rotary table. Maybe this method could be used for a concave area such as your project.
                        THAT OLD GANG 'O MINE

                        Comment


                        • #13
                          <font face="Verdana, Arial" size="2">Originally posted by sdeering:
                          Maddog, do I sense a turbocharger. If so I am planning on putting one on a 2 cyl 2stroke Polaris 700 and we should talk.
                          As far as a cutter that big it would most likely chatter real bad. I would make a template of how you want the radius of the pocket and squish and do it with a normal tool. Or cnc mill the chamber.
                          Stephen
                          </font>
                          I don't have the luxury of CNC. I'm stuck
                          with the old fashon manual lathe/bp.

                          I modified the squish shape on the lathe.
                          Bacically, I took a 1" round bar, turned
                          the end down and cut 14mm sparkplug threads
                          on it. Then I thread it into the head and
                          chuck it up in the lathe.

                          I wish I could draw a picture...

                          I'm going to need a cutter that has the
                          same shape/contour as the combustion
                          chamber so I can make it bigger without
                          changing the basic shape of it.

                          And yes, turbochargers are the ultimate goal
                          (I work on vintage Kawasaki 750 two-strokes)

                          Comment


                          • #14
                            <font face="Verdana, Arial" size="2">Originally posted by shawnspeed:
                            I have re-cut 2-cycle heads on the lathe,using an old spark plug hole as a mandrel. grind a a HSS tool to the contour you need and start with light cuts. Make a bondo squeese of the head before you start, so you have a reference to re-cut your squish band. (wax the chamber, cut a section of thin wood,plastic or metal, close to the shape of the chamber,apply bondo to this edge and squeese into the waxed chambr,allow bondo to kick, Instant template.)You can also adjust compression in a 2-cycle by altering the port timing. (raising the exaust port a milileter or two, this will also enhance performance But If it was me I would add a few Copper gaskets first, to make sure you get the desired results,as the squish,in a low compression 2-stroke are not as critical. Are you trying to increase the RPM of your engine? Reducing compression should help. Trying to get it from detinating? retard the ignition timing,it's qucker than milling the head.</font>

                            Shawn, I'm trying to get rid of a high rpm
                            pre-ignition rattle. The EX port has been
                            raised considerably, I played with the
                            timing with limited success.

                            I think the problem is exagurated by the
                            huge expansion chambers we built. It runs
                            like a scalded dog but that rattle has me
                            bugged. (adding some race fuel eliminates
                            it altogether, but thats not a long term
                            option)


                            Comment


                            • #15
                              Could you put a few washers underneath the spark plug to raise it a bit? probably wont lower your compression anywhere near enough to what you want though.

                              Comment

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