According to the small scale the Technic Engine Cylinder (2850) and it's half stud Crankshafts (2853, 2854) were no option. In the end I came up with this concept using a Bar 4L Lightsaber Blade (30374) and two Tiles, Modified 1 x 1 with Clip (2555).
As usual I made a short video to show you the sweet engine sound.
Additionally I provide you something new. My first try in a LEGO® -style building instruction. I will try to develop my own style in the future and hopefully have some time to create some other instructions, too.
I recommend to use the old Technic, Axle 2 (3704) instead of the Technic, Axle 2 Notched (32062) to guarantee a smooth run.
With best regards,