Originally Posted by wes
you will relize that if the sproket is moving upand down it is also moving side to side causing the chain to tighten and then loosen.
The two are not related. "Up and down" due to off center sprocket is rare. Most common cause of tight/loose chain is uneven chain wear (they don't actually stretch).
"Side to side" is caused by uneven tightening of rag joint and is most common cause of chain coming off along with uneven alignment of sprockets. This and the occasional "click" problem can also be minimized by filing teeth. "Click" tends to disappear on it's own as teeth wear.