Read the above post, save it and print it then paste it to your workbench.
Thanks Tom, and wouldn't it be nice if the poor excuse for an Instruction Manual in the kits did too? ;-}
I try to pound that same message home every time I see one of these chain topics here.
Other than a solid motor mount THE most important part of these builds is the chain drive, and you simply can't fudge either and expect it to work under load for long.
I have 2 simple drive tests I always do.
1. I hold the bicycle top bar with one hand, then try to rock the motor back and forth as hard as I can with the other hand.
If it moves at all it fails, period.
If I can wiggle it with my 50+ year old arm strength then even a bone stock 48cc is going to lean left and throw off the chain alignment.
2. I put the rear wheel in a front fork (upside down bike) and give it a spin.
If the wheel isn't even true it has to be made true because if the whole wheel wobbles any sprocket mounted to it will too.
I am lucky enough to have a close fellow bike builder friend that helps me double team installing these rag joint sprockets to a wheel in 20 minutes or so... we have it down to a science actually heheheh ;-}
It sucks having to do one on your own, I know, but with help you can breeze through the several steps of checking and tightening everything for a good solid and true sprocket mount.
Once you have your sprocket mounted you can easily judge how much vertical up and down wobble it has from the sprocket not being centered on the hub (every other step of checking as you tighten), and also see the side to side horizontal wobble if the rag joint bolts are not all torqued down correctly.
There is almost always a bit of wobble even with direct hub mounted sprockets one way or the other, and a little (1/16") is acceptable, it is the big wobbles that will screw you up, especially if you have more than one or two.
"My chain gets tight, then it gets loose when I roll it..."
Well, the sprocket isn't centered (vertical wobble) ;-}
One thing you should ALWAYS do BEFORE you mount the rag sprocket is
check the the level of the rag sprocket itself on a true flat hard surface, lay it cupped side with the teeth down, bowl side up, and see if it rocks in any direction.
If you can make it wobble on a table it's going to horizontal wobble the chain no matter how you adjust the rag joint bolts, it's a bent gear!
Again, for me 1/16th" is acceptable, and I have had luck putting an 1/8th", maybe even a 1/4" wobble sprocket on a concrete floor with a chunk of wood on top and giving it a couple of blows with my 4 pound short handle sledge hammer to true it up, if it is much more than that you better make sure every other aliment is perfect is all the more I can suggest.
Well, that and when you roll it around looking for final alignment you oil the chain at the rag sprocket as you go ;-}