Originally Posted by
lopek77
Stiff link would be my first quess without knowing how often is happening and so on....
A stiff link might be the problem if the bike has a spring chain tension arm (like a derailleur).
OTOH, it couldn't be a problem with a typical SS or IGH set up, because there's no slack to allow the chain to climb off the sprocket, and even the stiffest of links would be pulled out.
Depending on the nature of the popping, either the chain is tight, and becomes over tight as the high spots or eccentric sprockets are opposite. Or the chain is materially too loose, and partly disengages trying to fall off (this problem is most common on kids bikes, where wheels aren't tight enough).
So check tension/slack as follows, hold your finger
under the middle of lower loop and pedal until you find the tightest spot. At this place the lower loop should sag about 1/8-1/4". Test by pushing the chain up and down. Note even tight chains can be pushed up and down, you're looking to do it with slack, not by pushing against the tension.