Jackshaft jack shaft gearing

Discussion in 'Transmission / Drivetrain' started by bigcountry2212, Nov 26, 2013.

  1. bigcountry2212

    bigcountry2212 New Member

    hi new here, wondering if any one can help with gearing using a jackshaft. I have A 10 t to a 36 t witch I think is 3.6:1 then a 16 t to a 43 t witch should be like 2:1 witch would be a overall gear ratio of 9:1. I have a 25cc homelite engine rated around 7000 rpms and a 16 inch wheel. I don't have a clutch plan to bump start Wondering if it will start the motor At 9:1 and be able to take off any advice/help.

  2. IbedaYank

    IbedaYank Member

    you need closer to 18-1 that is a low power high rpm motor
  3. 5-7HEAVEN

    5-7HEAVEN Active Member

    Change the 36t to another 43t = 18.49:1, which is perfect for starters.
    43t/10 x 43/10 = 18.49.
  4. bigcountry2212

    bigcountry2212 New Member

    thanks for the help I appreciate it
  5. LR Jerry

    LR Jerry Well-Known Member

    I'm sure living in Virgina you've got some steep hills. A 25 cc engine isn't going to give you much power. So a lot is dependent on your's and the bike's combined weight and what grade hills you encounter as to how much reduction you'll need. If you're a large person you may need much more than 18:1.

    I use 33 cc engine, 18.75:1 gearbox. GB to shiftkit 18-44. SK to rear freewheel 34(34-16). Total reduction range: 45.83:1 to 21.57:1. I weigh 250 lbs and my bike is 87 lbs with 26" wheels. Hills over a 25% grade I have to peddle assist.

    I know you're using 16" wheels but you may need a very high reduction if you're over 170 lbs with such a small engine on steep hills.
  6. bigcountry2212

    bigcountry2212 New Member

    The bike is a 20 inch bmx not sure of the weight. I weigh around 180 and I would need to pull some big hills. Well thanks for your help do you know of a website or place I could by a gearbox or parts to help?
  7. LR Jerry

    LR Jerry Well-Known Member

    Here is a setup you could do with the 25 cc HomeLite engine. Engine to jack shaft 10-44. Jack shaft to shift kit 10-44. Shift kit to freewheel. 22(7 speed 34-13). This should give you enough to pull hills. Get a Sunlite or SunRace 7 speed 34-13 freewheel. On the shimano 7 speed 34-14 the 34, 24, are riveted to the back of the 22 sprocket. The SunLite and SunRace both have all their sprockets directly in contact with the core.

    You're definitely going to need a bike that you can shift gears on with an engine that small on steep hills. Really not sure if you can put a 22 t chain ring on a SBP shiftkit.

    Staton Inc sells good kits and double freewheel shift kits. The Staton shift kit will have the engine drive sprocket and you can also put 3 chain rings on it to drive the rear freewheel.