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A new look at Opposed Twin I.C. Engine

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  • A new look at Opposed Twin I.C. Engine

    A few years ago, I built my version of an opposed twin i.c. engine. It ran very well, and I was very pleased with it. There was always a problem with the configuration of this engine, because the sparkplugs were at the very bottom of the horizontal cylinders, and if you happened to flood it while starting it, you could crank all day and it wouldn't clear itself. However, it did run, and I made some good videos of it running. The crankshaft was riding on bronze bushings, and the crank wasn't "dead nuts" straight. I was using my standard 1975 Chrysler ignition points, and a cam running on the crankshaft. As time went by, with more and more hours running time accumulated on the engine, the bronze crankshaft bushings began to wear, cause by the crank that wasn't truly perfect. It wasn't a wet sump engine, so that didn't really matter a lot ---BUT--as it wore, the ignition cam, attached to the crankshaft began to move around with the sloppy crankshaft. Finally, the ignition cam on the less than perfect crankshaft was moving around enough to seriously affect the timing and spark of this engine. This took me the longest time to figure out what was going on, and when I did figure out what was happening the engine went "Up on the shelf". I promised myself at that time that eventually I would redesign this engine, using ball bearings on the crankshaft, a crankshaft that was truly straight, and a configuration which put the sparkplugs at the top of the horizonal cylinders. I would be able to re-use the cylinders, cylinder heads, overhead valve mechanisms and valves and cams, while making a new central crankcase and fan assembly. This is early days yet, and I still have some unanswered questions about the T head engine I have currently been building, but I think this will be the direction I move in next.
    Brian Rupnow
    Design engineer
    Barrie, Ontario, Canada

  • #2
    I do believe I see where the spark plug extension is needed.

    Comment


    • #3
      Could the spark plugs come in on top between the pushrods?
      Kansas City area

      Comment


      • #4
        Toolguy---This second set of heads are already made, and if possible I would like to salvage them. There is a possibility that I will have to design and build a third set of heads, but if I can make a pair of sparkplug extensions work, it would certainly be a lot less work for me. Back a year or two ago, when I was trying to set up a governor on that twin, I designed and built a set of heads that moved the sparkplugs up to the center of the heads. The heads were great, but the sparkplugs were so short that sparks were jumping over to the rocker arm towers.

        Brian Rupnow
        Design engineer
        Barrie, Ontario, Canada

        Comment


        • #5
          Originally posted by brian Rupnow View Post
          The heads were great, but the sparkplugs were so short that sparks were jumping over to the rocker arm towers.
          Perhaps you could get a glass tube and slip that over the plug and lead?

          Comment


          • #6
            Could you use a different taller spark plug rather than the baby CM6 ?
            Larry - west coast of Canada

            Comment


            • #7
              Perhaps take some layout ideas from the opposed aircraft engines, and, Volkswagon.
              The aircraft flat opposed engines have dual ignition and they fit 2 spark plugs in the head.
              the aircraft has the head/cylinder as 1-piece, when a mechanic says 'cylinder' than means head & all.
              Here is some easy to find pics of a typical Continental O-200 acft cylinder.
              Maybe take some layout ideas from this

              ​​​​​​https://www.ebay.com/itm/14414481420...RoC6L8QAvD_BwE

              Comment


              • #8
                Here is a link to Ageless engines, they have plans for radial engine.
                Notice the inclined valves make more room between them

                ​​​​​​https://www.agelessengines.com/9cyppic.htm

                Comment


                • #9
                  Can you just flip the entire block 180 deg, so the push rods are on the bottom, and the spark plus are on top? May need to make some elbows for the intake and exhaust.
                  When I get Time... I'll...

                  Comment


                  • #10
                    Just spitballing, but it seems that the intake and exhaust ports are at the top of the head while the actual valves are near the bottom. So there must be internal passageways on both sides. You could move those ports to the two sides, putting them closer to the valves and that would leave much more space at the top for the spark plug.



                    Originally posted by brian Rupnow View Post
                    A few years ago, I built my version of an opposed twin i.c. engine. It ran very well, and I was very pleased with it. There was always a problem with the configuration of this engine, because the sparkplugs were at the very bottom of the horizontal cylinders, and if you happened to flood it while starting it, you could crank all day and it wouldn't clear itself. However, it did run, and I made some good videos of it running. The crankshaft was riding on bronze bushings, and the crank wasn't "dead nuts" straight. I was using my standard 1975 Chrysler ignition points, and a cam running on the crankshaft. As time went by, with more and more hours running time accumulated on the engine, the bronze crankshaft bushings began to wear, cause by the crank that wasn't truly perfect. It wasn't a wet sump engine, so that didn't really matter a lot ---BUT--as it wore, the ignition cam, attached to the crankshaft began to move around with the sloppy crankshaft. Finally, the ignition cam on the less than perfect crankshaft was moving around enough to seriously affect the timing and spark of this engine. This took me the longest time to figure out what was going on, and when I did figure out what was happening the engine went "Up on the shelf". I promised myself at that time that eventually I would redesign this engine, using ball bearings on the crankshaft, a crankshaft that was truly straight, and a configuration which put the sparkplugs at the top of the horizonal cylinders. I would be able to re-use the cylinders, cylinder heads, overhead valve mechanisms and valves and cams, while making a new central crankcase and fan assembly. This is early days yet, and I still have some unanswered questions about the T head engine I have currently been building, but I think this will be the direction I move in next.
                    Paul A.
                    SE Texas

                    And if you look REAL close at an analog signal,
                    You will find that it has discrete steps.

                    Comment


                    • #11
                      I think some folks are missing the point that Brian wants to use the heads in post number 4 that he already has. The heads in post number 1 are also ready to use but there are issues there that make starting a flooded engine difficult.
                      The heads in post #4 work great, the issues is ignition energy is finding it more easy to jump to the rockers than jump the spark plug's gap due to the close proximity between the top of the plug and the rockers.

                      Much easier to remedy this issue that to design and build new heads.

                      Brian, I'm a not sure which Rimfire plug you have in those heads now but looking at their website I see plugs with a longer insulator. Is this an option or is the increased length not adequate? Would a short silcone sleeve be an option?
                      Home, down in the valley behind the Red Angus
                      Bad Decisions Make Good Stories​

                      Location: British Columbia

                      Comment


                      • #12
                        How about making new rockers and supports? Could make U shaped rockers and offset pivots away from the plug

                        Comment

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