bypassing the pedal crank

Discussion in 'Frame Mounted Engines' started by jaguar, Nov 28, 2010.

  1. jaguar

    jaguar Well-Known Member

    Here's my drawing of what a bike would look like if the shifter kit bypassed the pedal crank altogether. Of course a pull start would be necessary. And foot pegs would have to be welded to the frame.

    Has anyone done this?

    Attached Files:

  2. 5-7HEAVEN

    5-7HEAVEN Guest

    No pedals?

    So the pullstart would be on the opposite side, right? You'd still need the jackshaft to swing the sprocket to the right.

    Seems do-able...Ifff the HT engine had enough torque for a standing start, and the clutch was strong enough.

    Of course, you'd have to rack up a decent gear ratio combination, using a rear cassette with 38 teeth in first gear.

    Engine has a built-in 4.1:1 ratio.....
    10t engine sprocket/17t on jackshaft = 1.7:1.....
    9t on jackshaft/38t on cassette = 4.222:1.....29.43:1 in first gear...
    9t to 26t = 2.9:1.....20.21:1 in second gear.....
    9t to 23t = 2.56:1.....17.77:1 in third gear.....
    9t to 20t = 2.22:1.....15.47:1 in fourth gear.....

    The gearing combinations seem to work out. Unsure if any alignment or chain-jumping issues would arise. I guess you could add side flanges to the 9-tooth sprocket, or add two "sandwiching" sprockets as "jump stops". :idea:

    Here's what I'd do, if I wanted no pedals: :idea:

    Install pullstart.
    Install complete SBP shift kit with cheaper freewheel mechanism(HD freewheel not needed).
    Remove pedals and install foot pegs.

    Then if the need arises, it's a simple matter of reinstalling the pedals.
    Last edited by a moderator: Nov 28, 2010
  3. jaguar

    jaguar Well-Known Member

    So you're saying that at the pedal crank the sprockets used (with the shifter kit) gear it down even more? I was not aware of that. Then at the jackshaft the first sprocket would need to be much larger than the second sprocket.
  4. 5-7HEAVEN

    5-7HEAVEN Guest

    At the jackshaft, the sprocket that links to the engine sprocket would be 17t. On the bikechain side, the jackshaft sprocket would be smallest, like 9t.

    All sprockets are available at SBP.

    Yes, your intended 9t/38t combination is 4.22:1...Factor the complete 1st gear ratio to be 4.1:1(engine), 1.7:1(17t jackshaft/10t engine sprocket), 4.22:1(9t jackshaft/38t rear cassette) = 4.1 x 1.7 x 4.22 = 29.41:1

    SBP combination of 4.1 x 1.7 x 4.89(9t jackshaft/44t chainring) x 1.27 (30t chainring/38t rear cassette.)....Factor the complete 1st gear ratio to be 4.1 x 1.7 x 4.89 x 1.27 =43.16:1...

    EXCELLENT gearing for first gear from a standing start!

    Besides, 2nd-3rd-4th-5th-6th-7th-8th- gears would be 29.65:1.....26.24.....22.49.....19.31.....17.04.....14.77.....12.5.....

    FWIW, a HT engine with 48t rear sprocket-44t rear sprocket-40t sprocket-36t sprocket-30t sprocket.....would be 19.68.....18.04.....16.4.....14.76.....12.3.....

    Sooo, using your setup, the last four gears will be ineffective. With SBP setup, you MIGHT be able to make use of ALL eight speeds.

    Besides, it's a great ratio for pedalling...if you choose to.:detective:
    Last edited by a moderator: Nov 28, 2010
  5. jaguar

    jaguar Well-Known Member

    frame clearance

    So far so good except that the lower chain would probably touch the frame when the chain runs on the rear gears at one of the three highest (smallest) gears. You'd have to cut and weld to have that part of the frame out of the way. :annoyed:
  6. 5-7HEAVEN

    5-7HEAVEN Guest

    It would seem that the lower gears would shift the bike chain closer to the chainstay(frame). Since the jackshaft sprocket would be so high, only the intersecting part of the chain and frame would be affected. A very short section of chain.

    Maybe install a plastic chain protector tube like recumbent bikes.....

    or install the SBP shift kit.:idea:
    Last edited by a moderator: Nov 28, 2010
  7. jaguar

    jaguar Well-Known Member

    I was just thinking of a way to make my own shift kit to avoid the extra expense of buying one. The hardest part is making the jackshaft. I think sprockets bolted to a wheel hub would do.
  8. 5-7HEAVEN

    5-7HEAVEN Guest

    There is no extra expense of buying SBP components. You can buy the complete engineered kit, or piecemeal. Everything fits. No headaches, no fuss, excellent support staff, reasonable prices, very quick shipping.
  9. wbuttry

    wbuttry Member

    you remove the pedals then it becomes a scotter and licences and insurance to make street legal be careful people dont use bad judgement or we all coould loose our rideing privilages:sweatdrop: