Please critique my HF 79cc 7 speed idea...

Discussion in 'Rack Mounted Engines' started by macarollo, May 17, 2009.

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  1. macarollo

    macarollo Guest

    I just sold my 196cc push trailer and now I am itching to build something new... Take a look at my picture and tell me what you think. I do not own this bike, but saw it at walmart today and thought it would be nice to have full suspension.

    The idea would be to use a jackshaft and connect the chain to the bikes gears/derailer so it can shift as well. I would have to remove the chain going to the pedals since I cannot have two chains going at once.

    I would turn/move the derailer forward (counterclockwise).

    One concern I have is that not enough chain would be in contact with the bike gears because of how the engine drive chain is positioned. This might cause jumping of the gears.

    It is not drawn exactly to scale and most likely the jackshaft and engine would be closer to the seat than pictured.

    Any thoughts?

    Attached Files:

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    Last edited by a moderator: May 17, 2009

  2. Rgvkid

    Rgvkid Member

    There was a guy who built a side mounted honda GX50 next to his peddles on the Ecomodder website forum. He had to remove his peddles but he sure did haul *** while shifting gears. Let me see if i can find it. The problems i can think of are the peddle chain if you want to keep the peddles and the chain size might would be a little weak for the power of 2.5 motor. Won't know until you try though.
  3. kerf

    kerf Guest

    IMO, if you're going to lose the pedals, save both time and money and pickup a used Honda.
  4. bluegoatwoods

    bluegoatwoods Well-Known Member

    kerf is probably right on that one. But on the other hand, half the fun is in building something new that's all your own, right?

    So....How about a very solidly mounted idler sprocket (or even pulley) that will give you more tooth coverage? It would have to be tough. But if you could manage that it would remove the only source of trouble that's obvious at a quick glance.
  5. macarollo

    macarollo Guest

    I assume you mean a used honda motorcycle or dirtbike. If that is the case I already have a motorcycle.

    I think I build the entire thing for under $300, including the bicycle.
  6. kerf

    kerf Guest

    Don't mean to throw cold water on your plan, just an observation. In order to do this you'll need about 18 -20 / 1 reduction, so some serious jack shafting is in order. I have been thinking about a plan to jack shaft my Staton chain drive into a Sick Bike Parts chain ring freewheel that directs the engine power through the pedals. The freewheel allows you to use the engine or pedals independently of each other and have full shifting on the dérailleur.

    This can be done but it ain't gonna be easy or cheap. Right now my Staton is setup with a two speed on the chain drive giving me 18/1 for cruising and 23/1 for hills. Don't know if I'll fool with it or not.
    Last edited by a moderator: Dec 16, 2015
  7. macarollo

    macarollo Guest

    after a little more thinking I came up with a new idea. I would buy a front freewheel so I could pedal and use the engine. I would use a chain running to a jackshaft then to the front freewheel sprocket.

    Then I would have the standard chain running from a second freewheel sprocket to the rear derailer.

    Attached Files:

  8. HoughMade

    HoughMade Guest

    Won't need 18 or 20 to 1 (that is the reduction for engines with a higher rpm range), but a nice 7 to 9 to 1 would be good. And you're right, the front freewheel will be a good idea.
  9. DetonatorTuning

    DetonatorTuning Active Member

    if you use a 5:1 scooter tranny at the engine you will automatically have the drive on the right side of the bike.

    from there you could go directly to the front freewheel. the bike gears would give you enough added reduction.

    OR, you could put a jackshaft (like the second drawing) to keep the chain loops shorter, which is a good idea.

    the fly in the ointment will be getting a spring loaded tensioner in the lower loop going to the freewheel, since the chain slack will alter each time the suspension moves.

  10. Mountainman

    Mountainman Active Member

    looks like a problem -- as seen in your plans anyway

    one would wish to have at least twice that much chain into the cluster sproket

    some slight re-planning -- you should be up and running

  11. macarollo

    macarollo Guest

    Do you see my jackshaft? I am a little confused as to what the problem is that you see?
  12. Mountainman

    Mountainman Active Member

    maybe I am missing something

    looks like your drive chain from motor goes to cluster ??

    if so it is not catching enough teeth so as to drive without skipping

  13. macarollo

    macarollo Guest

    Look at the second picture I posted.
  14. Mountainman

    Mountainman Active Member

    told the story

    second picture explained it all

    nice -- with a lot of power going on there ------ sweet

    looking forward to seeing it come along

  15. loquin

    loquin Active Member

    Just be sure to put a chain guard over that drive sprocket from the motor to the chainring. Otherwise, with a break, you could really cut up your back.
  16. Gen3Benz

    Gen3Benz Member

    Nice...I like the JS placement on the 2nd idea.
    The 2.5 seems to fit in the frame of my schwinn, but this idea seem pretty sound.
  17. s_beaudry

    s_beaudry Member


    Please keep up with this post and keep us updated.

    This seems like it could be a very inexpensive, very reliable, and very powerful system when it gets up and running.

    I really like the idea of rack mounting that engine, and running it via jackshaft to the front sprocket.
  18. Gen3Benz

    Gen3Benz Member

    Any updates?
  19. pdxrhett

    pdxrhett Member

    you could even run a chain to the front cluster, and have a freewheel up there (take a look @ thescooterguy's setup, it is almost the same as what you are trying to do, except its a rack mount in the front.
  20. macarollo

    macarollo Guest

    I have been too busy to do anything with my idea.