Sorry to hear that...
Sorry to hear about your ordeal John-Forrest.
Glad that you were not badly hurt when the engine failed. Smart move on wearing the helmet! :helmet:
Have you contacted the vendor about this? Any reply?
You mentioned something in another thread about your "mechanic" telling you that the engines you received did not have the centrifugal clutches that they were supposed to have. Perhaps the same person could look the seized engine over and give some insight on why the engine seized?
If it makes you feel any better - I came very close to seizing my first PK80 HT engine from zoombicycles. The day when I installed the engine we had a few drinks with friends. My buddy wanted a ride. I figured the more it would get ridden the faster it would break in, so why not. Buddy took off around the block. Since the engine was not broken in it did not have much power. To "compensate" for this my buddy rode it WOT the whole ride. When he got back the engine was making a "scraping" noise and died on its own shortly after he came to a stop. It was smoking hot. I was furious and blamed him for almost killing it. The next day i realized it was not really his fault, nor the engines - see, the only gas we could source before the ride was some "chainsaw gas" from a neighbor that said there was "more then enough oil in it". Well, it turns out that "more then enough oil" was in fact something around 32 to 1, when the engine called for 16 to 1 for break in... The insufficient oil ratio along with the WOT ride caused the engine to overheat, the cylinder got tight and a piece of casting flash from around the exhaust port broke off and got stuck between the cylinder and the piston (that was the scraping noise....). Fortunately apart from a mark on the piston no damage was done, the rings and cylinder were not damaged and the engine is still running strong.
Makes me wonder - what gas/oil ratio were you running when the engine seized on you?