I was riding my Schwinn clairmont 7 speed cruiser with 80 cc engine today when the engine seized as I was riding. I was hitting about 29 mph when I heard a snap crackle pop noise that followed by the engine bogging down real fast. I also noticed after I heard the noise I heard what sounded like something metal bouncing around the engine. I was able to pedal the bike home about a mile where I took off the clutch cover to see if anything was wrong. Everything looked normal and the clutch was working as usual only now when you engage the clutch the engine will no longer crank over. It does freewheel but not crank over with the clutch engaged, Locked is what it is. I took off the spark plug to look inside and the piston is at the bottom position with no hope of turning. I am looking for any input on this situation,