Similar here. I was like 10-11yo and another kid brought over a little 50cc bike. We weren't even doing anything "stupid" with it, and somehow I had a burn on my calf about the size of my palm that took a relatively long time to heal. The skin there was a different color for years afterward.

And, that was so long ago, and I've interacted with bike so little since then, I still couldn't tell you which bits get hot, just that some do so be careful.