There you go... If you're going to sieze something, sieze the stock engine, not a crazy expensive kit. I've never siezed an engine, and probably won't for a long time, because I learned how everything works before I dove into aftermarket parts. If you play it safe, you won't sieze. Start high with the jets, work down one by one. If you stay too rich the whole time and test for air leaks, how the hell will you melt the piston?
I'm tired of people complaining because they didn't spend enough time getting familiar with their engine before they decided to throw a kit on it. If they F up, it's not my fault. Don't complainn because you didn't know what upjet meant and stuck with your 52 bing jet and your 12mm carb on your 80cc kit.
People throw money at their bikes. Parts DO NOT make the bike faster. Your most expensive build could get you to a whopping 5mph. The tuning will make your bike go faster. a 50cc engine can go 50mph, so why would you buy an 80cc kit if your goal is 45mph? You shouldn't!
Hell, if the stock cylinder is shot, you can get a whole new top end for $25 in the buy/sell forum. I've never seen a kit for that cheap.