[ScalaFan]

Might not rubber belts have been possible instead of chains? Rubber was available 18th Century - maybe not in industrial quantities but still. In fact, latex was was available to the Mayans and Aztecs according to https://en.wikipedia.org/wiki/Natural_rubber#History

[smogcutter]

AFAIK you'd need vulcanization to make rubber belts practical, so wouldn't have been available much earlier than chains and sprockets.