it is possible to create a piston that constantly extends and retrakts.
To construct it you need a Stiky piston a slime block and a redstone block.
Place the slime block infront of it and the redstone block diagonaly above the piton atached to the slime block. than update the piston tith a Block update.
it is possible to togellsuch behavior with a redstone signal.
it is not therystable because a new block update will destroy it.
the redstoneblock also creates a 0-tick pulse every time it is pushed.
it works in all directions eceptdownwards.
this behavior can also sustain itself after reopening the world.
This is known as quasi-connectivity, and your build is a way to make a clock out of it
See MC-108