frame mounted 2stroke w/jackshaft that can be bump started.

Discussion in 'General Questions' started by piecepatrol99, Oct 26, 2014.

  1. piecepatrol99

    piecepatrol99 Member

    IMG_20141022_180921.jpg FB_IMG_1413255836696.jpg FB_IMG_1413255836696.jpg IMG_20140722_140834.jpg

    Has any one ever tried building a motorized bicycle with a jackshaft for shifting gears and still be able to bump start like a direct drive install?

    I started out with a 26" wheel and a 7 speed hub. A frame mounted 49cc china girl backed up by a JS kit to connect my geared driveline.
    The fork broke and it was stripped down to stock and exchanged for another bike.
    Sadly the cruiser was no longer available in store and I bought the only bike available that the motor would filt in W/O having to buy more parts. A 700c flip flop fix.

    Unfortuantely my 7 speed hub is too wide for the new bike. It works with the origonal wheel, but with out a first gear its a bit more work to get started. I've built up the chainring to atleast have a high/low gearing. But the seperation of the ratios is limited by the space in have on the front freewheel and clearance to the chainstay. 30 and 40T CR's make my high/low for now. Any smaller and I have no top end. Any bigger and I can't get the motor started. And I can't increase the gap in CR tooth number, that's limited by front deraileur travel.

    In my search for inexpensive parts to better my build, I came across a freewheel cog that is mountable to a 5/8" keyed JS. The same as my JS currently in use.
    I also have the 50T direct drive sprocket that came with the motor kit...

    I'm thinking:
    Motor output to 17T Sprocket on JS input.
    9T JS output runs to 48T CR input.
    30 or 40T CR output drives the 18T freewheel (currently on the back wheel. I have a 3 speed freehub waiting for a trip to the bike shop to have it installed).
    Direct drive sprocket on the left side of the wheel will then turn the (smallest T number freewheel I can find) on the left side of the JS, next to the 17T connected directly to the motor.

    I believe this design will work.
    But contingent on the output of the motor 'spinning' faster than the 'returning RPM' from the left side of the back wheel.

    Any thought, opinions, suggestions, ideas and information is greatly appreciated.

    I do know this: you can use 1/8 chain on dual chainrings and cassettes...but
    You can't shift with 1/8 chain.
    Even just on the from derailuer, it shifts just like 3/32, but after a limited number of shifts, the links sieze and start skipping on the rear cog.
    This skipping has already taken out my front freewheel.

    I was shifting with 1/8 chain because the 3/32 doesn't fit the 1/8 rear cog. It skipped no matter how I fiddled with it.

    My to do list is short. Front and rear deraileurs are installed. Front is connected and functional. Rear is waiting for shift lever I ordered and a trip to the bike shop to have the cog swapped for the freehub. Then change the chain to 3/32....

    And I'll be back on the road again, hopefully with the third freewheel for bump starting the motor ;-)

  2. fattirejack

    fattirejack Member

    I am looking for freewheel sprocket for 5/8 js,any info would be appreciated.
  3. piecepatrol99

    piecepatrol99 Member

    fattirejack likes this.
  4. fattirejack

    fattirejack Member

    I have been searching the Stanton site and couldn't find this. Thank you, not exactly what I was looking for, but it's a place to start. thank you again
    piecepatrol99 likes this.
  5. piecepatrol99

    piecepatrol99 Member

    I think I typed 3 speed freewheel in my search on ebay and the jack shaft mountable freewheel came up in the results list.

    I have the three speed freehub for the right side of my flip flop fix wheel. Just need to make the time to get to the bike shop to get the single speed swapped out for the three.
    I never had to remove a freehub before so I don't have a chainwhip or like tool as yet...

    I'm thinking if I get a big enough sprocket for the left side of the wheel to give it a ratio that tops out at 5 to 10mph, I should be able to use the left sprocket to "bump" start the motor and the gears on the right side will get me up to 35mph.
    With the jack shaft spinning faster than the left sprocket can keep up, that's where the freewheel comes into play to keep the two sides of my drive line from fighting each other and jamming.
    I know I've seen a cog as small as 14T for a hub mounted freewheel. I'm hoping to find a 12T cog that mounts to the 5/8" 3/16" keyed jackshaft.

    Then I'll have the best of both worlds...
    Gears for get up n go, hill climbing and top end. And the ability to only have to pedal to get the rolling vs risking a coronary to start the motor by foot ;-)


    Happy hunting :) Hope you get rolling soon.
  6. piecepatrol99

    piecepatrol99 Member


    Looks like Staton has what I'm looking for and more unfortunately. I guess I'm going to have to call them to find out if they'll sell just the parts I'm looking for rather than buying the kit. I don't need all the parts of the kit.
    I do how ever need a longer shaft than what I have or their kit comes with.
  7. fattirejack

    fattirejack Member

    OMB warehouse has 5/8 jackshafts up to 14",price is a lot cheaper than Stanton. On the Stanton site search "FWADP" you can build your own kit with only the parts you need. Good Luck with your build
    Last edited: Oct 26, 2014