Bricklink has piece 3651 as Axle and Pin Connector, while piece 3652 is Engine Piston Square 2x2. You could attach them to each other to form a piston. Service pack 5260, Connecting Rods and Stop ...
I recently got interested in LEGO Technic again. The last set I own is maybe 15 years old, so my knowledge is a little bit outdated. Back then some of the Technic sets had action figures included, ...