Small Weed Whacker or 7.0HP Lawn Mower?

Discussion in 'Introduce Yourself' started by Bryc3, Aug 31, 2010.

  1. Bryc3

    Bryc3 New Member

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    I've been browsing these forums for a couple days. My friend got a Flying Horse kit on his bike and, needless to say, I loved riding around on it. I'm in high school in an engineering charter school and I would greatly prefer to build my own. I've been looking and I decided that it wouldn't be very difficult at all.

    Right now I have a 7.0HP lawn mower and a smaller weed whacker. I'm definitely a larger guy (~220lbs) and I was thinking that I should go for the lawn mower engine. Does anyone have any objections or any tips?

    If I use the lawn mower, I'd use bevel gears to transfer the power 'horizontally'. This combined with the lawn mower's throttle seems like it would make a good candidate.

    My main concern is that the lawn mower is overpowered and the weed whacker is underpowered.
     
  2. Bryc3

    Bryc3 New Member

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    Apparently, the weed whacker motor is 30CC or so.
     
  3. Kevlarr

    Kevlarr New Member

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    Well you could go for the middle of the road and use a Harbor Freight motor,

    2-1/2 HP Horizontal OHV Gas Engine

    Being that you're an engineering student you could build your own gearbox and drive system.

    Come up with a lefthand pullstart and a righthand drive system that would do away with a jackshaft for a shift kit. :D
     
  4. Bryc3

    Bryc3 New Member

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    The reason I was choosing these two is because we're going to be throwing them out. I was hoping to make some use of one or the other.
     
  5. wheelbender6

    wheelbender6 Active Member

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    Welcome to the forum. The weedeater motor can work if you don't mind pedaling along with the motor. If you don't like to pedal, I guess you have to use the mower motor.
    However, the weedeater motor would probably be street legal, if you plan to ride on campus.
     
  6. Bryc3

    Bryc3 New Member

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    I think I decided to mount the lawn mower engine onto a push trailer. Is this recommended? I would greatly prefer it than to have a large 4 stroke engine hacked together between my crotch.
     
  7. Nougat

    Nougat New Member

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    I was figuring you'd mount it as a rack mount, over the rear tire.

    I don't know that anyone's done a vertical shaft engine with a bevel gear to horizontal, so you're breaking some new ground with that. Can't wait to see how it works out.
     
  8. Chalo

    Chalo New Member

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    A seven horsepower gas engine is not overpowered in any meaningful sense of the word. But it could be excessive in all the other things that go along with it-- size, noise, vibration, weight distribution, etc. It also might move the speed of your bike into a range where either you or the bike do not operate safely.

    It seems to me like a better engineering exercise to make effective use of the limited power of the smaller motor. If you have the motor drive through the bike's gears, you can do a lot with a small amount of power-- which is what bikes are for, anyway. You could end up with a bike that's road-legal in your area, and more fun to ride too, because of its light weight and small displacement.

    You'd need to carefully match the motor's output speed to the bike's drive chain speed for a range of real world conditions, which is a more complex and satisfying problem to solve than just changing the orientation of the output shaft.

    Chalo
     
  9. professor

    professor New Member

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    There is another thing to watch out for with a vertical mower engine- mfgs put a light flywheel on most engines because the blade becomes the flywheel.
    Remove the blade and you may not even be able to start the engine. It will rip the rope right out of your hands as it backfires. You need a heavy flywheel engine or a horisontal engine.
    Take the blade off and see if you can get it running before you do anything.
     

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