I agree with Pe. A damaged front bearing would certainly cause the overheating symptoms you describe. A technique I recently learned for removing sleeves is to carefully heat the cylinder ( from the outside) with a propane torch of the type used for soldering copper plumbing pipes. The cylinder being an aluminum alloy will expand more than the steel sleeve allowing the sleeve to loosen so it can easily be pulled out. Don't use any presses, pullers, or heavy mechanical force or you could ruin the engine. Add a little heat, try the sleeve, and repeat until it loosens.

Amazing how a bad bearing won't show up until a combination of time and high rpm have worked on it. I recently went through a similar scenario with a 35cc.