Friction to Chain Drive?

Discussion in 'General Questions' started by bilboby, Oct 20, 2011.

  1. bilboby

    bilboby Member

    Having spent last Summer riding around on a Honda GXH 50 friction drive setup offlate i've had to change 3 tyres & inner tubes. Therefore i've decided that for next Summer's MB'riding i wish for replacing the friction drive to that of chain drive using the GXH 50. However, is such a conversion easily possible & if so how as i've thought maybe replacing the friction roller for a small wheel sprocket via the chain fitted around a 44 tooth sprocket as used with HT engine kits. However before i attempt such a mod i thought it best i ask on here if it's possible using the said GXH 50 engine?

    Cheers in advance

  2. 5-7HEAVEN

    5-7HEAVEN Active Member

    A motorized bicycle engine needs low gearing to propel the bike well. A ratio of 18.75:1 is a good all-around number to shoot for. If you replaced the roller with an 11-toothed sprocket and installed a 44-toothed wheel sprocket, your ratio would be 4:1. You would burn your clutch and your bike would not be moving.

    Before BMP company went under, they offered two excellent drive systems, the belted version and the chained one. Using two sets of gears and a jackshaft system, BMP was able to get the gear ratio to around 18:1. JMO, it would've been an excellent upgrade from a friction drive.

    I dabbled with friction driven motorized bikes for years. Like you, I ruined many tires. Now I use a shift kit which connects my Tanaka 47R engine to my 8-speed rear cassette. It is the greatest system, because extremely low gear is available for standing starts, and high gear is there for highway speeds.
  3. Happy Valley

    Happy Valley Active Member

    To convert what you have will depend on either how handy you are or the machine shops at your disposal and your budget. You will need to fabricate a primary and secondary gear reduction to get the final gearing right, something that might look like this:

    Other options might be to fore go the FD channel and use a reduction gearbox off the motor in either a rackmount or an in-frame. If you have a Staton FD then you can look at his gear and chain drive solutions.

    As to FD burning through tires, what you report sounds excessive. I haven't experienced that and get several thousand miles or more from a tire using the Mitsu 43 and Robin 35 engines. Perhaps the Honda 50 has enough additional torque to be problematic, though I do know of at least two people who own them and seem to be satisfied with what they have. Excessive tire wear sometimes can be traced to alignment issues, quick throttle starts, roller down pressure, tire inflation and sometimes just soft tire composition.

  4. since you already have that engine it has a 78 millimeter clutch drop 350 dollars on the golden eagle mount kit and be done with it