loose hub adapter

Z

Zeeb

Member
hi everyone, i'm new to the topic of motorized bike building, here goes my first post.
i'm building a motorized bike for the gf, and seem to have acquired a hub adapter that is too large for the hub.
see attached picture; adapter diameter is 1 3/16", but hub is 1 1/16" dia.

ideas on how to make it fit? ive tried wrapping tape around hub, but adapter always ends up off center, causing sprocket up-down wobble. a piece of hose, inner dia 1" outer dia 1.25" also did not work as a spacer. adapter would not squish over it as id hoped.

thanks!
 

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if you can't get an adapter that fits, you need metal in there that is same thickness on both sides - I'd try sawing off a piece of old handlebar, split it down the middle to make 2 "C" sections, hammer it a bit as needed to fit tight on hub, then clamp with one piece under each side of clamp
 
looking thru a bunch o' shims I've made, I see some that might have once been an old steering tube - very hard steel and a bit thinner than handlebar steel - might be just right
 
Thank you for the idea Crassius! I have some old pipe that might do the trick.

off topic, but is there a story behind your user name?
 
update; the "c section" spacers worked, the sprocket and adapter are mounted. however, the sprocket has some slight up-down wobble when rotating (total runout is less than 1/16"). Is it possible to get a cheap imported sprocket to rotate perfectly true? I know the up down wobble can cause chain issues.
 
Instead of using two C sections, you can try a beer can, or thin copper /sheet metal to wrap fully around the hub so you have no high spots.

If you slightly enlarge the holes on the sprocket, snug it down, but don't fully tighten it, put it on the bike without the chain, then rig up a feeler gauge with a ziptie or just hold something against the teeth as you spin it, the use a piece of wood over the teeth and a hammer on the high spots to tap it around, you should be able to get it pretty round.

Pretty much every sprocket has a low and high spot, but you want to get it as even as possible, especially if you're not running a chain tensioner.

All this is just a fix for your main problem, and should really be solved by getting the correct adapter.
 
if spacers are equal in thickness, there shouldn't be much alignment difficulty - in cases where they are really thick, you can file equal amounts straight up and down to get sprocket holes to line up with adapter
 
Thanks for the input. The challenge i face is the fact my rear wheel hub is so small, about 7/8" diameter. I was unable to find a hub adapter that small, hence why im using shims to make one work.
 
Yes, I considered the rag joint, but have heard about tendencies toward broken spokes. I'm sure there are plenty of success stories surrounding rag joints, but didn't want to risk it.
Due to risk of adapter slipping, I put a nut/bolt through each of 9 holes in the sprocket, to transfer force to the spokes. This way, with engine torque distributed between hub adapter and spokes, my hope is that none of the components will be stressed to the point of failure.
 
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