Crazy idea for gear reduction

Discussion in 'General Questions' started by mslipac, Jan 3, 2008.

  1. mslipac

    mslipac Guest

    can someone measure the shaft size on the pedal's shaft on left side?
    If we could use the left facing shaft on the motor link up by chain straight down to pedals shaft ( remove the pedals ) and that could potentionaly give us ie 10 18 21 speed gearing that is allredy on the bike...I imagine you have to be careful on shifting while the engine is under power... could this work guys???


  2. mslipac

    mslipac Guest

    This would have to involve the reversal of the pedal axle to the left side and rear wheel gears to face to the left and somehow lock the coasting mech so it's solid both directions

    attached diagram :) dont mind the art skills

    What I am trying to do is use 4.0 OHV Honda engine to power this setup max rpm 3400 rpm with 2000 RPM clutch

    Attached Files:

    Last edited by a moderator: Jan 4, 2008
  3. Alaskavan

    Alaskavan Guest

    For clarity, we're not talking about a motor assisted bike here. The result would (I believe) be illegal on the roads of any state. You are basically talking about using the bottom bracket as a jack shaft. Using the bikes gearing: It would only be using the multiple gears on the rear wheel, so we're talking about 5 - 10 gears, not 10 to 21. Much of that gearing would not result in an increase in speed. It could be used for ultra low end. But there are limits to how much you might want to gear down. For top end there are limits dictated by aerodynamics. There are places on the web where this can be easily researched. I haven't tried using the bike gears myself, but I've heard rumors that motors eat derailers.
    For moving the power along the left side of the bike, southpaw hubs and freewheels exist, and could be used.
  4. Dockspa1

    Dockspa1 Guest

    You can do a search here and you will find a lot of threads on this subject. I think it has been cancelled do to what Van has stated. Too much torque.
  5. mickey

    mickey Guest

    Ghost0 was doing that last year on his off-road project bike. He hasn't updated lately *cough* and I wish he would. That was a cool looking bike.
  6. kerf

    kerf Guest

    I believe what you're talking about can and has been done. Check the Staton website and check the two wheel chain drive section under Giant Stiletto.
    On this bike they use a jack shaft and freewheel sprockets to run the engine power to the dérailleur. The freewheels allow you to run the engine and the petals independent of each other.
    Last edited by a moderator: Dec 16, 2015
  7. mslipac

    mslipac Guest

    the problem I am runing in to that the setup that I am after is low reving engine 4 stroke OHV ( low nosie level ) 4 hp + so I can cruise at 2500 rpm or so....the setup does not have built in gear reduction so I have to figure out how to do the setup that somewhat looks clean and for using pedals long as they work ( dont have to work well to use 100% of time they will leave you moped I had was considered motor asist bicycle...didnt have to register it or nothing just give'er :)

    Engine I am after
    Model: GX120UTTX6
    Engine Type: Air Cooled, 4-Stroke, Overhead Valve (OHV)
    Cylinder Sleeve Type: Cast Iron
    Bore x Stroke (mm): 60 x 42
    Displacement (cm³): 118
    Crankshaft: Horizontal - 5/8" Dia. 18 UNF
    Compression: 8.5 : 1
    Maximum Power Output: 4 HP @ 3600 rpm (2.9 Kw)
    Maximum Torque: 7.4 Nm @ 2500 rpm (0.75 Kgm)
    Ignition System: Transistorised
    Starting System: Recoil
    Air Cleaner Type: Dual Element
    Oil Alert: Yes
    Fuel Tank Capacity (l - g): 2.5 - 0.66
    Engine Oil Capacity (l - g): 0.6 - 0.16
    Dimensions (L x W x H): 30.5 x 34.1 x 31.8
    Dry Weight (lbs - kg): 28.7 - 13
    I would relocate the tank to the rear rack and custom muffler and air cleaner

    I saw the post of exactly what I was thinking of has been done...that's what I am after...anyone feel free to throw their 2c in to this project
    Last edited by a moderator: Dec 18, 2015
  8. fetor56

    fetor56 Guest

  9. mslipac

    mslipac Guest

    yeah I know :shock: the store I deal with has these units for $128 CDN surplus equipment...have not been used picked out my clutch $40
    need some chain and hardware

  10. trustclive

    trustclive Guest

    Gear reduction

    I found that the best way to do this was to build a frame from scratch and use a jack shaft.
    I have used a shimano 8 speed hub which has no problem with the power, as for speed I have got up to 80kmh. cruse around town at your requested 2500rpm no problem. Shifting with this set up is great and smooth, I dont think that the derailar set up would cut it.

    I made my own jack shaft using a cassette hub. This way you can play around with ratios that suit your needs.
    You end up with a fixed sprocket to the motor and rear wheel. and the freewhell off the casstte to the pedels
    workes well and really needs a pull start motor.

    I have attached some pics


    Attached Files:

  11. mslipac

    mslipac Guest


    That is somewhat complicated for me...i dont have acess to a welder 24/7
    ...what is the speed you are traveling when the clutch engages? can you take off from dead stop?
  12. mickey

    mickey Guest

    You're an artist Clive. That looks factory fresh.
  13. Jim H

    Jim H Guest

  14. trustclive

    trustclive Guest

    Take off

    Yes the bike can take off from dead stop, it is also great for hills.