I had a wind-up caterpillar tractor, with a sheetmetal shell. It was hefty, powerful, had a two-speed shift, and ran quite a while on a good winding. It would pull a little trailer full of stuff like toy building blocks up a fairly steep slope. It lasted for quite a few years, until some "governing" mechanism gave out so that the spring would unwind too fast, without much power. I don't know that you can get a windup toy anywhere near that good anywhere now.