unique jackshafted bmx/dual suspension drive idea

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irishpowerjunkie

irishpowerjunkie

Member
Jan 24, 2012
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letterkenny, ireland
anyone here ever try putting 2 freewheels on right side of a wheel with 2 chains, 1 to engine, 1 to pedals, for drive setup, comtemplating doing it on a rack mount with jackshaft to right side with 2 bmx freewheels to totally eliminate drivechain drag, i read somewhere that a bottom bracket cup from 3 piece cranks is exactly same as freewheel thread on back wheel, i have plenty bikes to scavenge for bits, just no rack mount kit or engine, dont want to waste effort to end up failing.

also how hard is it to make a dax friction drive kit a rack mount jackshaft kit?
what do i need other than drive cogs and chain, i know i would immediatly void warranty, not worried about that unless there is another kit out there already like that that i cant find, have tried every sponsor.
 
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cannonball2

cannonball2

Well-Known Member
Oct 28, 2010
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Colonial Coast USA.
The Dax FD would be quite easy to convert to jackshaft/chain drive if the dimensions allow everything to align properly. Sick Bike Parts has a threaded FW adapter that fits a 5/8 shaft, I know you guys on the other side of the pond are metric and the counterpart is 15mm. Daxes might be 15mm not sure. Anyway using the adapter would get you a second freewheel in place pretty easily for the drive side. You will have to work around any bearing differences. The 5/8x1 3/8 bearing will fit in the 15mm bearings place but will be slightly loose on the hole.Down side is no engine braking. If hills factor in get some good brakes, you will be using them a lot! http://www.sickbikeparts.com/catalog/product_info.php?cPath=21&products_id=139
 
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irishpowerjunkie

irishpowerjunkie

Member
Jan 24, 2012
143
21
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letterkenny, ireland
cannonball i was thinking it would be easy conversion. the placement of the freewheel i was thinking have it right on the wheel not in jackshaft, eliminate as much drag as possible as soon as possible, so i would not be looking for a fw adaptor although i knew about sbp one. the dual freewheel thing was so i have in effect two drive trains with possiblity to freewheel down inclines and hills without annoying parasitic drag from a clutch. you wouldn't happen to know what largest size freewheel tooth count is available that would take a normal 9 hole back sprocket i think i seen it done that way before?
 
cannonball2

cannonball2

Well-Known Member
Oct 28, 2010
3,682
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Colonial Coast USA.
I just checked and an 18t bolts on, I have done that before and it works fine. You will need to find a sprocket with a larger hole to center on the FW( or make it that way or make a spacer). Seems like most are coming with smaller center holes these days.
 
Davezilla

Davezilla

New Member
Mar 15, 2014
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San Antonio Texas
You could also try using one way bearings to eliminate the parasitic drag if no freewheels are available for your size requirements... These things come in all sizes and configurations so if you got some welding and fab skills, this shouldn't be too hard to come up with a working setup... http://www.vxb.com/page/bearings/CTGY/One-Way-Bearings Just find one that meets your inside and outside diameter needs as well as one that has a fairly high torque rating for the front sprocket since pedaling can produce some pretty good amounts of torque... like a Lot more torque than the engine can produce. For the drive side tho you just need one that can hold about 10 to 15 ft/lb of torque, basically your engine's torque x 4 is what's coming off the output sprocket of a typical China Girl engine since the clutch is reduced 4:1... you'll need to know the friction drive engine's torque output and multiply by the gear ratio to get the right torque rating for the output shaft bearing if a one way is used here.
 
irishpowerjunkie

irishpowerjunkie

Member
Jan 24, 2012
143
21
18
letterkenny, ireland
thanks cb2, i think i while just file/grind out hole on sprocket to fit if its doesn't out of the box.

dave, i think that for the basic tools i have trying to use a one way bearing would be too much work than just going thread on freewheel with sprocket bolted to it.
 
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