Schwinn Chopper/3 speed hub/ powered thru the gears

Discussion in '4-Stroke Engines' started by rredrockk, Oct 24, 2008.

  1. rredrockk

    rredrockk New Member

    Hello 4-stroke garage....

    So I have two Schwinn choppers to build with HondaGHX 50. One of the choppers is a rare adult size which fits my 6'2'' frame. the other will be for the girlfriend.

    I was all set to change out the three speed hubs because I was having trouble with the 56 tooth attaching with enough clearence to get by the wide 4 inch wheel. I then read and began to study! I wrote back and forth to their tech-Jim and he said they had nothing for the 4 stroke yet but that he was in fact working in his mind to build a shifting chopper - 4 stroke.

    Now the choppers bottom bracket is way forward so he came up with and idler wheel below the jack-shaft. the idler wheel would have three gears on it.

    here is what he writes:
    Yes there would be 3 gears on the idler. This was my vision and it should line up OK. On the idler hub you have the normal BMX type freewheel driven from your cranks. On the outside of what would be the right spoke flange would be one of the fixed sprockets. Then on the inner side of the right spoke flange would be the other fixed sprocket so there would be no sprocket on the left spoke flange. The left spoke flange would actually need to be machined off so you could get the inner sprocket on. I have not played with the gearing required to do this so I don't know what size sprockets would be needed. I would think it should be similar to our current system so you would want a 44t fixed driven by the jackshaft and a 36t to drive the rear wheel.


    I returned with

    the idea of skipping either the idler wheel or the jack-shaft by keeping one of the gears on the gear box side of the motor and running a chain (415) from the gear box to this gear.

    There is a freewheel in the skyhawk so this wheel can be fixed.
    Now I will need help with this math but it seems like because I am going to be able to shift down that I don't need the stock 56 tooth ratio to the skyhawk gearbox. Schwinn 3 speeds shift 1/3 easier , then one to one, then 1/3 harder. So I thought I might try a 44 tooth or 48. Hopefully some of you mathmaticians can help me here.

    Then thru to the other side I would run one fixed 20 tooth back to the bike freewheel which is 20 tooth. And I would run one Bmx freewheel forward...possibly a 17 tooth because adding any pedal power will be hard to do with easy gears and such a strong motor.

    This Idler wheel would be mounted in a homemade bracket that sits right behind the seat tube and in front of the fender. Up enough for all gears to clear. The tension in the gear box would have to come from moving the motor forward or backward. (special mount)....

    the tension in the fixed gear going to the back hub on the pedal side would come from the chopper's horizontal dropouts. With a possible idler tensioner on the front chain going to the crank... these seems to run ok a little loose anyway.

    OK another math question...
    It seems to me that I would not have to run all the gear ratio from the gear-box on the one side .... (gear box ratio) that in fact I could run some on both sides there-by running smaller gears and making everything look a little tighter...

    Can anyone give me insight as to the sizes of these two gears that would equal the ratio that is needed with this skyhawk?

    On-ward thru the fog!:cool:

  2. InfoCentral

    InfoCentral Member

    Good find. Keep us posted. I was looking at the new mopeds for sale and notice they are all 2 speeds. I wonder how hard that would be to port over to a bicycle frame?
  3. piecepatrol99

    piecepatrol99 Member

    How did you make out with Jims design?

    I'm currently working on making my flip flop fix a 3 speed on the free wheel side. I've located a 3 speed free wheel and shifter on ebay. I already have an old derailer to experiment with in the parts bin.
    Gears will shift like on a 10 speed, but here are some of the possibe obstacles I foresee...

    The 3 speed shifters I've found are all for triple chainrings or internal hubs. The shifters have a different cable pull length than a rear derailer. I'm thinking if I can't set it up so its only hard shifting into 1st and rely on the adjust stop screw to keep from shifting past third, I'll have to disassemble the free wheel to add spacers between the cogs.


    I came back to edit this post as I realized I missed a few details...

    I'm using a 49cc chinese motor with a boost bottle and jackshaft kit. The free wheel side of the fix rim currently has an 18T cog. The three speed free wheel I've ordered is 16, 19, 22T.
    I'm hoping the cable pull distance for a front shifter is close enough to what a rear derailer needs that I can avoid disassembly of the FW or building a cable pull adapter.

    If this works on the fix, I'll apply the same modification to my stingray.
    Last edited: Oct 15, 2014
  4. KCvale

    KCvale Motorized Bicycle Vendor

    You do realize this topic is from 2008 correct?

    3-speed hubs jackshafted from a 4-stroke are awesome!
    Perhaps start yourself a New Topic for you new build?
    Just a tip not diss ;-}
  5. piecepatrol99

    piecepatrol99 Member

    Was hoping someone was still interested in chatting the subject up...

    Any way, I got it running with some 'cousin cob job' magic. One last part to swap for longevity and added gearing and I'll be a hill climbing speed freak!

    Thanks for the reply.
  6. piecepatrol99

    piecepatrol99 Member

    I checked out your link. Nice job chasing that water truck. Smooth shifts and plenty of power.

    A quick question to pick your brain...
    Ever heard of a motorized bicycle with a jackshaft kit capable of being bump started?
  7. KCvale

    KCvale Motorized Bicycle Vendor

    Thanks piecepatrol, the shifters really are fun to ride.

    Sure you could bump start a jackshafted bike if you put a fixie sprocket single speed back wheel on it, that of course would be foolish because the whole point of using a jackshaft is to use bike gears.

    2-stroke engines are started with the pedals because all shifting back wheels freewheel.
    piecepatrol99 likes this.
  8. piecepatrol99

    piecepatrol99 Member

    Sure you could bump start a jackshafted bike if you put a fixie sprocket single speed back wheel on it, that of course would be foolish because the whole point of using a jackshaft is to use bike gears.

    2-stroke engines are started with the pedals because all shifting back wheels freewheel.[/QUOTE]

    I believe I've found the answer to having the best of both worlds...

    Here's where my progress stands right now.
    I ordered and received a 3 speed freehub from ebay.
    I've ordered and I'm waiting for a pair of rapid fire shifters, also from ebay.
    I've built up my front freewheel so I have a dedicated chainring for the jackshaft output and a 30 and 40T CR for a high/low range to drive the rear wheel. I also modified a front derailuer to fit between the the paths of the chain on the JS output.
    Dropped off my flip flop fix rear wheel to have the single speed FW swapped for the 3 speed freehub.
    While using the single speed FW, the rear derailuer only served as a chain tensioner. I didn't suceed in permanantly mounting a vertical DO mounted rear D in a horizontal DO, but I did have a D that had the wafer style nut which makes it easier to just hang the rear D when servicing the back wheel.
    When I get the wheel back from the bike shop, I'm going to install the direct drive sprocket to the left side. I've already tried using the fix cog (when mounted on the right side) to bump start the motor. It worked until the cog unscrewed and pushed the lockring off.
    Because my single speed FW will only work with 1/8" chain, that's what I've been using. Sadly 1/8" chain was not meant to shift. Links have gotten stuck causing it to skip over the single speed FW. One front FW has broken and a second has jammed.
    I'll be running DD on the left side until I can replace the front FW on the pedal crank.

    All of the parts I've mentioned so far are standard bicycle and motorized bicycle parts...

    I found a JS mounted FW on the staton site. When I have all the parts in, I'm going to change the frozen front FW and add an FW to the left side of the JS.

    This is what I'm aiming for...

    To start the motor, pedal to get the bike rolling and let the clutch out.
    The DDS on the left side of the rear wheel will engage the added FW, turn the JS which will turn the 17T connected to the motors 10T. Motor will fire.
    Once the motor is running, 10T drives 17T, turning the shaft and the 9T on the right side (that's the purpose of the FW on the left side).
    9T is driving a 44T CR. 30 and 40T CR's will drive the 16, 19, 22T cogs on the new 3 speed freehub.

    The one thing I need to figure out is the T number on the CR's, cogs and sprockets so the rotational speed of the left side never catches up with the output on the right. The FW on the left side of the JS will keep the bike from trying to take off at low speed with the equivelant gear ratio of 5th gear. The gear ratio on the right side will allow the motor to spin the JS faster than the rear wheel is turning the left FW.
    I just need to figure out the gear ratios/tooth numbers to make sure that either the left side never catches the right or it at leasts tops out @40mph. I don't go past 35 so 40 will be plenty for me.

    I believe it was Star Trek 3 that. Scottie said " The more piping you add to the plumbing, the easier it is to back it up."
    I think I just proved him wrong...
    The convienence of bump start. The. Hill climb ability and top end of shifting.

    IMG_20141026_183059.jpg IMG_20141026_194219.jpg
    IMG_20141026_183059.jpg IMG_20141026_194219.jpg

    That's the site for the jackshaft with freewheels. If the link doesn't take you to the page, go to and type FWADP in the search.
    Last edited: Oct 28, 2014
  9. KCvale

    KCvale Motorized Bicycle Vendor

    That is some build you have going there Peace...
    Impractical and over complicated but clever ;-}

    Here are some things to consider moving forward:

    By keeping the direct drive you loose one of the best parts of shift kit riding, the drag free idle coast.
    That, along with having to maintain a completely unneeded secondary drive is a heavy price to pay 100% of the time for a marginally easier way to start the thing.

    You might want to give your handlebars some more thought as well.
    It looks like you love complicated so your handlebars will be interesting with all the cable controls it needs.

    I am a very safety orientated guy and just behind having front and rear brakes, handlebar layout and a helmet tie for second most important.
    Note that odds of needing a helmet decrease with ease of machine operation.

    For a bicycle, motorized or not, all controls should be placed where you never need to look down or remove a hand from the handlebar grip.

    For a 2-stroke shifter my rule is simple.
    Rotary shifter for rear gears and clutch lever on the left, brake lever (dual pull for 2 brakes) and throttle on the right.


    Everything can be operated without your palms ever leaving the grip or even looking down.
    Your handlebars are your connection to the machine, I try to make all of mine easy to operate and comfortable, hence the BMX foam grips.

    Just tips and I look forward to seeing how it turns out.
  10. piecepatrol99

    piecepatrol99 Member

    I'm looking forward to finishing ;-)

    As for your safety concerns, I guess you can say I was taught by the worst of teachers.
    I have 2 older brothers. When I was about five years old, they were asked by our parents to build be a bike with the spare parts they had the basement cluttered with. I had just out grown my first bicycle. Mom and Da tried to kill two birds with one stone. Get me riding (which I was begging to do) and get the basement cleaned up by the persons that made the mess.
    My brothers oblidged and rebuilt an Apollo 5 speed for me. But they neglected to tell me they traded the top tube shifter out for other parts. Once the bike was assembled it was given to me - without Mom and Dad present...
    I looked at the shifters on the stem and thought "wow! They suped it up! I've got a 10 speed!"
    I went flying down the block, worked my way through the gear with the right shifter. It wasn't until I grabbed the left shifter to use high gear that I fount out it was connected to the front brake.
    That was the last bike I let any one touch!

    As you know the clutch is the left hand.
    The other controls on the left are the shifter for the front deraileur and my turn signal control. I only have to use my thumb to actuate either.
    The shifter is currently an SIS. But the D is adjusted so my eyes never have to leave the road ahead. The D will only move as far as needed to shift from high to low and vise versa.
    On the right side of the bar is the throttle with kill switch, my dual brake lever (with home made cable splitted and a rapid fire thumb shift lever. I can just hit the button and the read D will only shift one of the three gears at a time.
    Again, both hands on the bar and eyes on the road.

    I understand completely your points on extra wieght and increased drag.
    I counter, I'm not 15 any more. Just getting the motor started with the shift kit, I'm ready to go back home.
    For right now I'm removing the jackshaft due to my spare front freewheel jamming. While not stranded, I couldn't use the motor without keeping cadence. An added benefit I didn't fathom when first dreaming the concept is "if one drive line fails, disconnect it". I'll still be able to start the motor with iether of the two and the only way I'll be stuck is for a critical part to fail. IE: the front FW.
    If I had the JS FW when the FW jammed, I could have simply removed the right JS chain and been on my way again under motor power. Stuck in the one ratio available with Direct Drive, but on my way none the less ;

    I'm still trying to figure out what T numbered sprocket to use on the left side of the rear wheel though...
    If I use a S large enough that its only good for starting the motor and high speed use, when I shift on the right side the wheel speed will eventually catch the motor RPM and limiting low RPM use. That I believe would be building a motorized circle made of chains. Also known as a chain saw. Not a pretty thought on a bicycle.

    This is the only paradox I face. I don't mind staying under 35pmh. I've done 72 on a 20" 10 speed when I was 15. I've seen speeds in excess of 160mph on sevveral occasions. The last time I believe I broke 220mph on my motorcycle. Those events we're more than 20+ years ago...
    God protects babies and fools. I'm too old not to know better...

    I'd like the ease of bump start combined with the hill climbing ability of gears. But I'm also looking to stay in one piece and keep the skin I've regrown... ;-)

    The only other thing I can think of (other than pull start) is to add an electric starter and really make people scratch their heads...
  11. KCvale

    KCvale Motorized Bicycle Vendor

    Hehe, I know the feeling, we build a couple 2-stroke shifters every month and though they usually start right up, it does get exhausting if they don't.

    Yep, that is going to be an obstacle and I have no solutions to offer.

    Actually that is not as hard as it sounds.
    You tie the electric motor to the JS to start the 2-stroke.
    Still hard and heavier than your solution but they add virtually no resistance when not in use.

    Good luck with it Peace.
    Last edited: Oct 30, 2014
  12. piecepatrol99

    piecepatrol99 Member

    I think I'll stick with the FW on the JS with a third S. The weight an electric start would add I believe would out weigh the drag created by the extra chain and sprockets.

    I also have to point out part of the reason I'm attempting this is a stepping stone to an electric drive system that doesn't need to be charged. Though its not an origonal idea (as I had hoped), the main obstacle is the expense of a quality motor. Adding the JS w/FW to start the motor is so I will still be here to build the electric kit.

    View attachment 54638


    This is the kit/part I found on the site. I'll be using the JS motor mount I already have from SBP.

    As for the electric kit, I found a vid on youtube (posted 2009) of a gent in Europe that added an alt to his electric powered bike.
    The one thing I have over him is a circuit (not a solar panel) that will charge a battery with no external input. I can't wait til I have the resources to build that one!

    Attached Files: