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 sickbikeparts.com! 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:
Bruce,
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.
Thanks,
Jim
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!
Bruce
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 sickbikeparts.com! 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:
Bruce,
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.
Thanks,
Jim
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!
Bruce