base for a new build

Moto

Member
Jan 7, 2012
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San Francisco, CA.
I've been collecting parts for this build for a while, and I'm pretty excited to get it going. first got to make it a functional bike though. It's gonna be rear rim brake, front disk. I would ideally use a jack shaft but I am not sure I will go that route because I'm trying to build this on the cheap. will probably use a spring loaded chain tensioner to take the slack out of the drive chain caused by rear suspension. should be very fun to ride! power plant is going to be a 50cc Chinese engine.
 

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Jan 21, 2015
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Portland, Oregon
If you want a cheap jackshaft, get 2 heavy duty 5/8" bearings, a foot of 5/8" keyed shaft, a 5/8" mini hub, and then whatever size sprocket to bolt onto the mini hub, as well as a sprocket that bolts directly onto a 5/8" shaft. Use a bit of steel shapes from the hardware store to mount the bearings. Including the sprockets it should easily cost less than a hundred bucks. If you can't figure out how to assemble it all I will take a picture of one of my bikes and post it for you.
 

crassius

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Sep 30, 2012
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pic doesn't show area that swingarm pivots on, but distance between that pivot and rear axle should remain constant - you might be able to hang a double sprocket on a sealed bearing there with chain dropped from motor to that sprocket, then 2nd chain from that sprocket to rear sprocket

should work and shouldn't be expensive to make
 

Moto

Member
Jan 7, 2012
403
14
18
San Francisco, CA.
the issue is that I would want to keep the pedals functional. I cant see how I would do that without buying a sbp crankset and freewheeling chainring.

edit: Crassius: I see what you mean. Installing a jackshaft that still outputted on the left hand side but lower and closer to the pivot would significantly drop the amount of slack created when the bike's suspension moves.
 
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Jan 17, 2015
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ca.
I've got a frame like that id like use...but seat position is way to high for me, I like to stop sitting down with feet on the ground. I haven't found a way to have a shifter w/o spending at least 100$. And that's with your own Js. But its worth it!!
 

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crassius

Well-Known Member
Sep 30, 2012
4,032
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USA
the issue is that I would want to keep the pedals functional. I cant see how I would do that without buying a sbp crankset and freewheeling chainring.

edit: Crassius: I see what you mean. Installing a jackshaft that still outputted on the left hand side but lower and closer to the pivot would significantly drop the amount of slack created when the bike's suspension moves.
I was thinking NOT closer to pivot, but replacing pivot with a bit longer shaft for the sprocket, that way chain should stay constant length.
 

Moto

Member
Jan 7, 2012
403
14
18
San Francisco, CA.
I was thinking NOT closer to pivot, but replacing pivot with a bit longer shaft for the sprocket, that way chain should stay constant length.
ooh. that makes sense. the pivot doesn't go all the way through though :-(. would be dope asf. I'll see if it is possible. zpt