Home Forums 2-Cycle Racing Square Piston 2-Stroke

This topic contains 9 replies, has 6 voices, and was last updated by  mike clements 5 years, 9 months ago.

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  • #5076

    mike clements

    You will need to go to our facebook page for the pictures, http://www.facebook.com/clementsracingproducts Thought you guys might enjoy seeing photos of my square piston creation.  This little engine was never intended to be a race engine.  This was an engineering exercise for myself, I just wanted to see if I could do it and make it run.  As you can see by the photos it is a piston port engine, rectangular piston, rectangular bore and employs the use of a scotch yoke crankshaft.  You will notice where the carburetor is on one end of the engine and the spark plug is located on the other end, also the little shiny silver exhaust port on the one side of the engine.  Opposite of the exhaust port is the PTO end of the crankshaft.  For my purposes I bolted on a home built billet flywheel with rare earth magnets installed and I used a 3hp Briggs & Stratton ignition coil for spark.  I had the block, cylinder and piston all hard anodized and ran 10 oz. of 2-stroke oil per gallon in my fuel.  Next I used 2 large ‘C’ clamps to clamp the engine to a work bench, attached a fuel line, wrapped a rope around the flywheel and gave it a yank, it ran at a low rpm for about 20 seconds when I shut it off, that’s the only noise it’s ever made.  BTW, if you’re wondering what I used to make square piston rings, I cut up some used Mazda apex seals and installed them in the piston.  I hope you enjoy my warped innovation.

  • #5102

    Brian Thomas

    McCulloch built a square piston motor, just to see if it could be done.

  • #5164


    I remember (I think) Honda had a bike engine with an oval shaped piston. Had 2 rods/piston if I remember correctly. That was quite a few years back tho.

  • #5187

    mike clements

    Alan, I read about that Honda engine also. It was an experiment to see if they could flow the same amount of air with a V Twin as they do with a V-4.   So, they used 2 BIG oval shaped pistons with 2 rods per piston and 8 valves over each piston.  I could see where the thing would Fly if they ever got the rings to seal.

    The Scotch Yoke type crank I used is the main draw back to making HP with this little motor.

  • #5258

    Jim Russell, Jr

    Honda has built experimental engines with square and rectangle pistons. The Oval piston engine was a production engine in a motorcycle. Anyone could purchase one with enough $$$ as it was a race homologation special. It was a V-4 engine designed within the rules that did not allow 8 cylinder engines.

  • #5261

    mike clements

    James, I couldn’t remember if it was 4 or 8. But I did remember it was intended to make 1 cylinder move as much air as 2 cylinders. I did not know it ever made it to production for public consumption. I would love to see whatever they used for piston rings though.

  • #5384

    Jim Russell, Jr

    Soichiro Honda first created a piston ring company. Then developed into motorcycles, cars, and all sorts of combustion engines.

    He focused on R&D so lots of radical ideas were implemented and tested in real world settings.

    Did a little research. First Honda using oval pistons was 1979 NR500 GP motorcycle. Production for public sale was 1992 with 90 degree V-4 750cc for a paltry $50k. <!–nextpage–>

  • #6120

    Walt Gifford

    Looks like a good torpedo motor.

    FAA certified jet engine and aircraft technician,
    Nicholson Speedway class champion 2001,
    Yamaha KT100 Service Center,
    41 years karting experience

  • #10589

    Colm O’Higgins

    Weird history, but valid.

  • #10591

    mike clements

    The weak link in my square engine is no doubt that scotch yoke crank unit. I just don’t see how I can ever make any rpm with it.

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