New To Engines, and Bikes -- Planning a Build

Discussion in 'DIY Home Built Motorized Bicycle (non kit)' started by Vanderbleek, Apr 22, 2011.

  1. Vanderbleek

    Vanderbleek New Member

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    Hello everyone,

    A friend recently showed me some "Derringer" bikes -- and from the sounds of it, a moped/motorized bike is what I need.

    Currently my vehicle (a 1988 Cadillac) gets around 15MPG. As a college student, driving around the campus end of town gets costly, fast. Because of that, I've been looking into alternative means, but I can't warrant purchasing a motorcycle/scooter/new car. Enter the moped.

    First, a note: I like building things myself. I'm an engineering student, and I enjoy planning, building, and troubleshooting. I have hardly any experience with gasoline engines, but I do know a bit about gears from working on robotics. I have seen the kits for $150 or so, but I don't want a 2 stroke, and I don't think they'd have enough torque for me -- I live in "Hill Country", Tennessee and so it needs to have fairly high torque.

    What I'm looking for is:
    4 Stroke Engine (I don't want to mess with adding oil to gas)
    Relatively high torque
    Cruising speed of 25-30mph
    Ability to carry about 240lbs total (me, bike, engine, and backpack)
    Cheapest I can get it -- this is a basic mode of transport around town, and more importantly something I can learn engine maintenance/tuning on.

    What I've seen is the Harbor Freight 2.5HP 79cc 4 stroke -- this seems to be what I'm looking for. Cheap, about the power I need, and did I mention cheap? I wouldn't feel bad about tinkering with it, since I screw it up, a new one wouldn't break the bank.

    To achieve a gear ration of 12:1 (Which should give me the speed I want, and the hill climb ability I need) I could run a 10T off the engine to a jackshaft with a 60T, then another 10T off the jackshaft to a 60T on the wheel, correct? The easiest way to do this would be to remove the pedals, I think, and replace them with a jackshaft, however that seems to be frowned upon. Another location could be chosen, I suppose.

    I'm currently following leads on different bicycles, so unfortunately I don't have one to start with. I don't really want to pay more than $30 for one. I'm going to try to mount the engine inside the frame, for weight distribution, plus I want to add a rack and some saddle bags to the rear.

    Lastly I have a question: does the HF 2.5 have a dynamo to power a headlamp off of? Mostly so other vehicles could see me, it can get a little foggy where I am.

    Essentially, what I'm looking for is any suggestions/modifications to this plan, and, if everything looks to be in order, I would appreciate some suppliers/specific parts to consider.

    I've been looking at the various threads involving the HF 2.5, about removing the oil sensor, and tuning it up -- lots of excellent information, and I have a pretty good idea what I have to do to get this bike built and working.

    Eventually I'd like it to look like a Cafe bike, but form is more important than function, to start with.

    --Vanderbleek
     
  2. cannonball2

    cannonball2 Well-Known Member

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    Your math is wrong. To get a 12:1 it would be like a 10 to a 20t turning a 10 to a 60t, ie a 1:2x1:6=12:1
     
  3. Vanderbleek

    Vanderbleek New Member

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    That makes things even more affordable. I'm now thinking 10t to 36t, 10t to 36t. This will give me a larger ratio than twelve, but will cut down on the size/cost of the sprockets.

    I also realized I probably need some kind of clutch, to allow me to actually stop...any suggestions?
     
  4. cannonball2

    cannonball2 Well-Known Member

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    Max Torque is about as good as you can do for the money.
     
  5. Vanderbleek

    Vanderbleek New Member

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    Ok, so:

    Thanks cannonball, the Max Torque clutch seems like exactly what I need, for the clutch at least. Ideally my jackshaft would look something like

    affordablegokarts: Jackshaft Assembly for 79cc HF Engine

    I'm hesitant to order that one, though, since I still haven't found the bike and am not quite sure how the engine is going to be mounted. It can't be too hard to fabricate though right -- just a steel plate with holes drilled in it? Then I attach a shaft with spacers to get the sprockets to line up right, and off I go.

    School's getting out, and people are going to be leaving campus, so hopefully I can snag a bike in the next week or two, and get to building.
     

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