Let's build a V twin engine

Discussion in 'Board Trackers and Vintage Motorized Bicycles' started by RocketJ, May 16, 2019.

  1. RocketJ

    RocketJ Active Member

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    Gents, It's time to discuss the elephant in the room: v twins!

    For years, this forum has been asking about the ability to use a v twin in a frame and this summer I plan on making that a reality. Several months ago I saw a v twin air compressor pump and wondered if it was possible to convert one into a v twin engine. After much research I've discovered that it is infact possible, albeit with some modification. I've already taken the liberty of fitting an exhaust system, carburetor, and spark plugs to the compressor, but the only obstacle right now is the ignition system. Unfortunately the pump has a very awkward 1" diameter crank shaft, which doesn't exactly allow conventional flywheels from being mounted. So these are the options:

    1. create an extended crankshaft out the back of the pump and mount a flywheel to it
    2. mount the flywheel somewhere else (this will have a gearbox)
    3. Use an alternative ignition system such as a alternator
    4. use an alternative fuel such as diesel
    5. convert the existing flywheel into a magneto
    6. Create or find a gear driven magneto like a bosch

    I really would like to get this project off the ground so that the community could use this information for their own builds. If you have any suggestions as to how to get past this problem let me know.

    pic of the pump in question: https://imgur.com/a/ZQo9S51
     
    fasteddy likes this.
  2. MotoMagz

    MotoMagz Well-Known Member

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    Here is a great build...to look at
     
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  3. RocketJ

    RocketJ Active Member

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    update: 5/20/19

    ok, so here's the current plan. Adding a flywheel would be too difficult without proper machining tools. Instead i'm thinking of going with plan B: alternative fuel. There's an engine design called the brayton cycle, which uses compression from one cylinder to charge the second piston. This method could be used to ignite diesel. Diesel needs a compression ratio of 13:1 to properly ignite. the compressor has a calculated compression of 8:1, not nearly enough for ignition, but with the assistance of extra compression via the charge piston, it might just work. Youtuber "John Lucas" has built one of these before and it seems to work quite well on diesel.

    Here's a link to the engine build and a diagram of the brayton cycle:



    https://upload.wikimedia.org/wikipe.../428px-Scuderi_Split_Cycle_Engine_-_Cycle.gif
     
    fasteddy likes this.
  4. curtisfox

    curtisfox Well-Known Member

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    Think a chain drive a mag. like the old motorcycles..............Curt
     
  5. RocketJ

    RocketJ Active Member

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    Where can i mount a sprocket to a chain driven mag? The only geared mag i can think of are the old boschs. A bit out of my price range
     
  6. curtisfox

    curtisfox Well-Known Member

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    Not sure about the sprocket, but maybe to the flywheel somewhere? My thought would be a weed eater flywheel and set up chain driven. Or even a China girl engine ignition setup, or something like it...........Curt
     
  7. RocketJ

    RocketJ Active Member

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    It could work IF i can find a way to bore the flywheel out to a 1" diameter
     
  8. curtisfox

    curtisfox Well-Known Member

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    ?? what flywheel, you have to keep the compressor flywheel for balance of it. Mount a plate on the end were the compressor one bolts on, sprocket to it. ............Curt
     
  9. RocketJ

    RocketJ Active Member

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    oh right, that could work.
     
  10. RocketJ

    RocketJ Active Member

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    I'm guessing I didn't get enough sleep last night because i'm drawing a blank on how to go about this. so what I think you're saying is to: bolt a 2 stroke flywheel onto the existing flywheel and then building a mount to have the magneto near that flywheel?
     
    #10 RocketJ, May 22, 2019
    Last edited: May 22, 2019
  11. curtisfox

    curtisfox Well-Known Member

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    My thought would be to use a small #25 chain and sprockets and mount the weed eater flywheel and mag off to the side. Or regular chain, be much easier to mount just a sprocket to the compressor flywheel..............Curt
     
  12. RocketJ

    RocketJ Active Member

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    oooh, I see. That might do the trick. I'll draw up some sketches and see what works best.
     
    Tom from Rubicon likes this.

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