The GY6 was a Honda engine... very simple... very reliable... It was sooo good that everybody copied it... Honda discontinued the GY6 for a better design....
Now, there are lots of variants of the GY6... as long as the basic design is there, they call it a GY6.... All GY6 look the same but differ in some parts like displacement, bolts, gaskets, bearings, etc. There's also this Honda Cub engine that everybody copied, but that's another story...
The Honda GY6...