Hi, If you haven't found the metal wheel yet, it should be in the room where you start this level, you just have to slowly move your cursor around and you should spot it, you Do Not have to raise the Cart. This is for Level Four, if you are past that level, then the next metal wheel you are looking for is:
I
f are you are standing by a miner's cart? If so, you have to click on it and choose "Action", he will get on the cart and it will crash, after the cut scene, look at the cart and you should see a metal wheel.
I hope this helps, if not, I can send you the Walkthrough.