It's not as crazy as it seems at first glance. Too small a front sprocket combined with an o-ring chain is at least part of the problem. I would buy a new 15 tooth front sprocket and a new sprocket retainer plate. Try that and see what happens. It is known by over 100 years of experience that too small a sprocket causes too much chain angularity. Chain angularity causes "pumping" of the sprocket on the shaft (jerking backwards and forwards). If you need more final drive reduction, go to a larger rear sprocket. The countershaft is made of very hard steel. The sprocket is made of softer steel, and so is the sprocket lock.

It appears that the sprocket and retainer is not a perfect match for the output shaft? It also appears that the engaging teeth on the sprocket are riding to far over the retaining ring groove on the sprocket.

I would try one or two washers between the retaining clip and the sprocket to locate the sprocket further inward and fully engaged on the output shaft.

Was this problem present with the non o-ring chain? Is the o-ring chain wider than standard? Might the added width of the chain be causing outward force on the sprocket?

Yes, o-ring chain is wider than non o-ring chain. And yes, he needs a new sprocket and sprocket retainer. And, if he wants to use that o-ring chain, he needs to switch to at least a 15 tooth front sprocket, to get a little more clearance in there.

it's a alimement issue...
has nothing to do with sprocket size of chain type...
being a chinese bike the misalinement could well be
built into the frame or swing arm.. It can happen I had to cut the frame
in 2 on the boys pit bike weld it back to geather to get the wheels alined.....

yer need to check the alinement in three directions
across the bike & length wise & horizontal alinement...

to me it looks as if the chain is pulling the sprocket to the left
check wheel /sprocket alinemant & sprocket centres , sprocket face alinement...

Remember a mm at one end can be 5 or 10 mm at the other..
so spend the time and get it right close enough is NOT close enough...

put the bike up so the rear wheel is off the ground remove the retainer on the front sprocket
turn the wheel by hand and watch if the sprocket trys to walk off the shaft or moves towards
the motor.. while doing this have the chain all but tight so it wants to pull to one side or the other
as it turns...

my bike runs a 12 tooth with a 520 O ring chain... theres no issues because it's alined unlike
yours..




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I think Pete's idea on checking chain alignment is a good, practical way to do it. I know you had a bike shop do the alignment for you, but check it the way Pete suggested anyway. It is possible that the power plant is slightly out of line with the centerline of the frame. You may have to shim the motor mounts a little to get it right. But we won't know until you do what Pete suggested. Also check the swing arm cross bolt, at the front of the swing arm, and that none of the power plant (motor) mounts are loose.

just another thought...
when riding the sprocket drives the wheel so spining the wheel
you now have the wheel driving the sprocket than could change
things... So t might be best to use the motor to turn it the same
as when yer riding it..
then see if the sprocket walks off the shaft...



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