Jackshaft Better than Jackshafting?

Discussion in 'Transmission / Drivetrain' started by Nanonevol, Dec 17, 2015.

  1. Nanonevol

    Nanonevol Member

    Imagining a design for transmission from a left side output motor (China Girls, etc) to a freewheeling sprocket on the left side of the bottom bracket. This would require a bottom bracket with basically two axles - sprockets on both sides connected and freewheeling on a central pedal crank axle. Someone would have to create this of course as it is not available anywhere. Simpler than jack-shafting to the right side though with less friction and fewer parts to keep tuned and adjusted. I wonder if it could be made with any off the shelf parts or would require some real innovation and a machine shop.
    Would then have all the advantages of a jack-shaft. I'd like to see a heavier - than - bicycle sprockets and chain on the right side as well to a sturdy rear hub with internal gears. Anyone?

  2. troyg

    troyg Member

    I believe that's called a freewheel kit, that you can get premade at sick-bike-parts all day long.
  3. jaguar

    jaguar Well-Known Member

    for the same amount of trouble you can have a bike that goes 48mph maximum and yet still take off good from a start.
    That is possible by utilizing my recommendations for these engines. I know because my 55cc Grubee did that.
    Shift kits add complexity and rob 8 % of engine power. The people that race these engines don't use shift kits.
    Ronen likes this.
  4. KCvale

    KCvale Motorized Bicycle Vendor

    Or you could just kiss 2-stroke hassles good-bye and use a 4-stoke/transfer case combo that drops the output right above the freewheel pedal chain rings to use the pedal side gears.


    That's a 53cc 4-stroke with a 7-speed that does over 45mph too, and it's a pull start, automatic clutch, regular gas burning breeze to ride.

    In short there are systems available, I know, I develop them ;-}
    yoyofred and boneswood like this.
  5. Nanonevol

    Nanonevol Member

    Well that's cool - but the complexity is still there it's just built into the motor (and is surely reflected in the price). And sure, I could improve my 2 stroke and get more power but that's not the point. I want to shift gears. Nobody wants to take on putting a sprocket on the left?
  6. Timbone

    Timbone Active Member

    Two gears on the 66cc two stroke would be very sweet. Dollar for dollar, jackshaft is the way to go. I can envision a simple two speed gear box with two axles and a simple dog clutch deciding which of the two ratios (high or low). The devil is in the details. You'd have to have a really good, foolproof mechanism for the clutch (and engagement would have to be perfect every time) because diddlng with the tranny on the side of the road would be an enormous pain.
    Christopher Kelly likes this.
  7. Fabian

    Fabian Well-Known Member

    The police would throw you in jail for that setup in Australia, and then give you water boarding torture, and throw you in a cell with a person of the same gender, who takes fancy to a person of the same gender.
    Murkle, yoyofred, james65 and 2 others like this.
  8. KCvale

    KCvale Motorized Bicycle Vendor

    Actually the 4-stroke engine has no internal gearing or clutch at all, that's why they require an output reduction and cent. clutch.
    A simple belt reduction, the gearing shifting gearing is done at the back wheel for there no simpler way.

    But you have a 2-stroke with an internal gear reduction and manual clutch.
    You can just mount two different size sprockets on the back wheel and make a derailleur to change between the two.
  9. Pablo

    Pablo Motored Bikes Sponsor

    Why not do both? Improve engine power and jackshaft? Sure of course some power is consumed in the drive chain, but racing isn't the street. The racing so far is just a flat track affair, where the person with the biggest and smartest gonads going into corners wins. Some hills, much tighter corners, and people with the skills and engines to use gears, the outcome will be different.
  10. butre

    butre Well-Known Member

    for general rideability and longevity nothing beats a shift kit, but bicycle gears are clunky and inefficient. a CVT would be more ideal on the racetrack.
  11. KCvale

    KCvale Motorized Bicycle Vendor

    I like an internal 3-speed hub.
  12. Ronen

    Ronen New Member

    Did you use Centrifugal clutch or regular? is there a way to start from zero with regular clutch (i have 80cc 2 stroke chinese) or make an upgrade besides cent?
  13. KCvale

    KCvale Motorized Bicycle Vendor

    (sigh) I told you this in your other topic about' not wanting to pedal'.
    Your 2-stroke engine has no way to start it on the engine.
    If you want to use a centrifugal clutch so it will stand still at idle and go when you give it gas, you need another way to start it.
  14. Ronen

    Ronen New Member

    Yes but the most ipmortant to me is to be able start from zero after its running and to not pedal every time I stop.
    why Its impossible to slowly give gas and in the same time release the clutch like in motorcycle?
    Is there regular clutch I can put that will not get destroyed when doing this?
  15. Nanonevol

    Nanonevol Member

    Relax Dude, that's not me - I only have to hear it once.
  16. Nanonevol

    Nanonevol Member

    Are you suggesting doing this on the left side of the wheel? Interesting. I wonder if a derailleur could be reversed like that. But I like internal gears too. Any way to put that on the left side??
  17. KCvale

    KCvale Motorized Bicycle Vendor

    You can, it is called 'feathering' the clutch.
    You give it near full throttle and let the clutch out gradually.

    Depending how small your rear sprocket is (for speed) it may take awhile until you are moving fast enough for your engine to stay above stall speed.

    That is the bane of wanting to go real fast with a fixed gear ratio, you loose your low end 'get going' power.
    To do it, you have to slip the crutch which eats up the clutch pads.

    Nano, sorry bud, my mistake, it just sounded so familiar I made the cardinal mistake of assuming he was the same guy.
    As you know now, you just can't have it all with a stock 2-stroke.
  18. KCvale

    KCvale Motorized Bicycle Vendor

    No, you would have to make something 'mirrored' to that, and it would have to be real close step, a couple teeth or so, so it could climb back uo to the bigger sprocket.

    Again, just design a mirror mechanical design and you are set as nothing for a bicycle is designed for left side operation, hence why we have jackshaft systems to just put the drive on the right side.
  19. HeadSmess

    HeadSmess Well-Known Member

    snif sniff. woe is me. i bought a bicycle with an engine. sniff. i thought it was like a motorbike and it didnt need to be pedalled, ever.

    oh woe, oh lament! why didnt i just buy a motorcycle if i didnt want to pedal a BLEEDING BICYCLE!?!?!?

    seriously, is it me or is the world getting stupider?

    Timbone likes this.
  20. butre

    butre Well-Known Member

    your legs make way more torque than any bicycle engine can. something on the order of 75 ft-lbs average. I don't have to pedal if I don't want to, but it helps a huge amount with off the line acceleration and hill climbing.

    if you never want to pedal again, get a 60 tooth sprocket. then again, you could pedal faster than a stock motor with a 60 tooth will take you