4-stroke direct drive to ŗear wheel?

Discussion in '4-Stroke Engines' started by taureanirishman, Dec 26, 2014.

  1. taureanirishman

    taureanirishman New Member

    I'm 200# with a steel frame cruiser, I was looking to do a 4-stroke buikd with a 100cc HF motor with no reduction drive, jackshaft, etc...

    I've seen some bikes with this build, but am wondering about clutch longevity.

    My other option is a gt-5 2-stroke. But looking at the extras i woukd need like mikuni carb & upgraded ignition, the price is basically the same as doing a 4-stroke build if there's no gear box.

    Going to utilize a hub mounted sprocket either way. Could I run a 100cc directly to a 44tooth+ sprocket safely?

  2. wheelbender6

    wheelbender6 Well-Known Member

    If you don't want to run a jack shaft for reduction, you could use a belt and sheave.
  3. MotorBicycleRacing

    MotorBicycleRacing Well-Known Member

    Take a straight line from the sprocket on your engine shaft mounted clutch to the sprocket on your rear wheel.
    How much would your motor be hanging out on the right side of your bike?

    Do you know what your gearing ratio is with, say a 10 tooth sprocket to a 44 tooth?

    You would need more like a 100 ++ tooth sprocket.
  4. KCvale

    KCvale Motorized Bicycle Vendor

    Look at a Wizzer, they run just a clutch with a pulley to a giant pulley almost as big as the 26" wheel and even then don't have much low end speed before the clutch slips, but hey if you want ride 50+MPH on a bicycle that'll do it.
  5. MotorBicycleRacing

    MotorBicycleRacing Well-Known Member

    Whizzers do not run one belt from the clutch to the back wheel.

    If you Look at a Whizzer you will see a 2 belt reduction jackshaft.

    The Whizzer rear wheel sheave is not that big at only about 15"
  6. KCvale

    KCvale Motorized Bicycle Vendor

    The point was how big the rear sprocket would have to be to run without a reduction is all.
    We both know this direct drive is folly, just a suggestion of what it would take.
  7. wheelbender6

    wheelbender6 Well-Known Member

  8. SunkyWorks

    SunkyWorks Member

    With a 11t #35 clutch and 20" wheel on a rear rack, IF you could mount a
    80t rear sprocket. This would give 41 mph at 5000 rpm. (Governor removed)
    Rider would need to do some pedaling on start.

    Speed Calculator For Go Karts and Mini Bikes

    80T Drive Sprocket for #35 chain, Manco 9986
    Center hole is 1 3/8" diameter
  9. KCvale

    KCvale Motorized Bicycle Vendor

  10. ronphelps

    ronphelps New Member

    PA190199.jpg PA190200.jpg PA190201.jpg PA190200.jpg PA190199.jpg Hello, I have a beach cruiser bike that I have put a 79cc HF motor on and it works great I love it and get a lot of comments on it. It will go up hills no problem although I do have The pedals I mainly use them for foot support. I recommend using a jackshaft, very easy to install and gets the most of the small engine. I am also 200lbs. The bike will do 30mph easy maybe more but 20 to 25mph is perfect to cruise on. I got a lot of the info to build here on this forum and on youtube. Don't cheat on the build put a jackshaft on. Here is a photo of mine PA190201.jpg Get the Professor to give you the gearing it's easy. good luck
  11. KCvale

    KCvale Motorized Bicycle Vendor

    A gear ratio reducing transfer case is by far the best route.
    This is my HF 79cc with Q-matic on a 29" Macargi.


    Nice quite smooth operation that will work just as well on 100cc.
    Go proven good or go for trying to direct drive it, you have seen the options.